Heater pattern for in situ thermal processing of a subsurface hydrocarbon containing formation

A system for in-situ production of hydrocarbon fluids from a subsurface hydrocarbon-containing formation, the system comprising:

• a heater cell divided into nested inner 210 and outer 214 zones such that an enclosed area ratio between respective areas enclosed by substantially-convex polygon-shaped perimeters 208, 204 of the outer 214 and inner 210 zones is between two and seven, heaters being located at all polygon vertices of inner and outer zone perimeters 204, 208, inner zone 226 and outer zone heaters 228 being respectively distributed around inner 298 and outer 296 zone centroids such that a heater spatial density in inner 210 zone significantly exceeds that of outer 214 zone, each heater cell further comprising inner-zone 224I production well(s) and outer-zone 224O production well(s) respectively located in the inner 210 and outer 214 zones.

A system for in-situ production of hydrocarbon fluids from a subsurface hydrocarbon-containing formation, the system comprising:

• a heater cell divided into nested inner 210 and outer 214 zones such that an enclosed area ratio between respective areas enclosed by substantially-convex polygon-shaped perimeters 208, 204 of the outer 214 and inner 210 zones is between two and seven, inner zone 226 and outer zone heaters 228 being respectively distributed around inner 298 and outer 296 zone centroids of each heater cell such that, for each heater cell, (i) an average distance to a nearest heater within the outer zone significantly exceeds that of the inner zone;
• (ii) an average distance to a nearest heater on the inner zone perimeter 204 is at most substantially equal to that within inner zone 210;
• and (iii) an average distance to a nearest heater on the outer zone perimeter 208 is equal to at most about twice that on the inner zone perimeter 204, each heater cell further comprising inner-zone 224I production well(s) and outer-zone 224O production well(s) respectively located in the inner 210 and outer 214 zones.

A system for in-situ production of hydrocarbon fluids from a subsurface hydrocarbon-containing formation, the system comprising:

• a heater cell divided into nested inner 210 and outer 214 zones such that an enclosed area ratio between respective areas enclosed by substantially-convex polygon-shaped perimeters 208, 204 of the outer 214 and inner 210 zones is between two and seven, heaters being located at all polygon vertices of inner and outer zone perimeters 204, 208, inner zone 226 and outer zone heaters 228 being respectively distributed around inner 298 and outer 296 zone centroids such that an average heater spacing in outer zone 214 significantly exceeds that of inner zone 210, a significant majority of the inner zone heaters 226 being located away from the outer zone perimeter 208.

A system for in-situ production of hydrocarbon fluids from a subsurface hydrocarbon-containing formation, the system comprising:

• a heater cell divided into nested inner 210 and outer 214 zones such that an enclosed area ratio between respective areas enclosed by substantially-convex polygon-shaped perimeters 208, 204 of the outer 214 and inner 210 zones is between two and seven, heaters being located at all polygon vertices of inner and outer zone perimeters 204, 208, inner zone 226 and outer zone heaters 228 being respectively distributed around inner 298 and outer 296 zone centroids such that a heater spatial density in inner 210 zone significantly exceeds that of outer 214 zone, a significant majority of the inner zone heaters 226 being located away from the outer zone perimeter 208.

A system for in-situ production of hydrocarbon fluids from a subsurface hydrocarbon-containing formation, the system comprising:

• a heater cell divided into nested inner 210 and outer 214 zones such that an enclosed area ratio between respective areas enclosed by substantially-convex polygon-shaped perimeters 208, 204 of the outer 214 and inner 210 zones is between two and seven, inner zone 226 and outer zone heaters 228 being respectively distributed around inner 298 and outer 296 zone centroids of each heater cell such that, for each heater cell, (i) an average distance to a nearest heater within the outer zone significantly exceeds that of the inner zone;
• (ii) an average distance to a nearest heater on the inner zone perimeter 204 is at most substantially equal to that within inner zone 210;
• and (iii) an average distance to a nearest heater on the outer zone perimeter 208 is equal to at most about twice that on the inner zone perimeter 204, a significant majority of the inner zone heaters 226 being located away from the outer zone perimeter 208.

The system of any preceding claim wherein the area ratio is at least three.

A system for in-situ production of hydrocarbon fluids from a subsurface hydrocarbon-containing formation, the system comprising:

• a heater cell divided into nested inner 210 and outer 214 zones such that an enclosed area ratio between respective areas enclosed by substantially-convex polygon-shaped perimeters 208, 204 of the outer 214 and inner 210 zones is between two and seven, heaters being located at all polygon vertices of inner and outer zone perimeters 204, 208, inner zone 226 and outer zone heaters 228 being respectively distributed around inner 298 and outer 296 zone centroids such that an average heater spacing in outer zone 214 significantly exceeds that of inner zone 210, a majority of the heaters in the inner zone 210 being electric 242 heaters and a majority of the heaters in the outer zone 214 being non-electric heaters or combustion-based heaters or advection-based heaters.

A system for in-situ production of hydrocarbon fluids from a subsurface hydrocarbon-containing formation, the system comprising:

• a heater cell divided into nested inner 210 and outer 214 zones such that an enclosed area ratio between respective areas enclosed by substantially-convex polygon-shaped perimeters 208, 204 of the outer 214 and inner 210 zones is between two and seven, heaters being located at all polygon vertices of inner and outer zone perimeters 204, 208, inner zone 226 and outer zone heaters 228 being respectively distributed around inner 298 and outer 296 zone centroids such that an average heater spacing in outer zone 214 significantly exceeds that of inner zone 210, a majority of the heaters in the inner zone 210 being electric 242 heaters and a majority of the heaters in the outer zone 214 being molten-salt heaters.

A system for in-situ production of hydrocarbon fluids from a subsurface hydrocarbon-containing formation, the system comprising:

• a heater cell divided into nested inner 210 and outer 214 zones such that an enclosed area ratio between respective areas enclosed by substantially-convex polygon-shaped perimeters 208, 204 of the outer 214 and inner 210 zones is between two and seven, heaters being located at all polygon vertices of inner and outer zone perimeters 204, 208, inner zone 226 and outer zone heaters 228 being respectively distributed around inner 298 and outer 296 zone centroids such that a heater spatial density in inner 210 zone significantly exceeds that of outer 214 zone, a majority of the heaters in the inner zone 210 being electrical 242 heaters and a majority of the heaters in the outer zone 214 being non-electric heaters or combustion-based heaters or advection-based heaters.

A system for in-situ production of hydrocarbon fluids from a subsurface hydrocarbon-containing formation, the system comprising:

• a heater cell divided into nested inner 210 and outer 214 zones such that an enclosed area ratio between respective areas enclosed by substantially-convex polygon-shaped perimeters 208, 204 of the outer 214 and inner 210 zones is between two and seven, heaters being located at all polygon vertices of inner and outer zone perimeters 204, 208, inner zone 226 and outer zone heaters 228 being respectively distributed around inner 298 and outer 296 zone centroids such that a heater spatial density in inner 210 zone significantly exceeds that of outer 214 zone, a majority of the heaters in the inner zone 210 being electrical 242 heaters and a majority of the heaters in the outer zone 214 being molten-salt heaters.

A system for in-situ production of hydrocarbon fluids from a subsurface hydrocarbon-containing formation, the system comprising:

• a heater cell divided into nested inner 210 and outer 214 zones such that an enclosed area ratio between respective areas enclosed by substantially-convex polygon-shaped perimeters 208, 204 of the outer 214 and inner 210 zones is between two and seven, inner zone 226 and outer zone heaters 228 being respectively distributed around inner 298 and outer 296 zone centroids such that (i) an average distance to a nearest heater within the outer zone significantly exceeds that of the inner zone;
• (ii) an average distance to a nearest heater on the inner zone perimeter 204 is substantially equal to that within inner zone 210;
• and (iii) an average distance to a nearest heater on the outer zone perimeter 208 is equal to at most about twice that on the inner zone perimeter 204, a majority of the heaters in the inner zone 210 being electrical 242 heaters and a majority of the heaters in the outer zone 214 being non-electric heaters or combustion-based heaters or advection-based heaters.

A system for in-situ production of hydrocarbon fluids from a subsurface hydrocarbon-containing formation, the system comprising:

• a heater cell divided into nested inner 210 and outer 214 zones such that an enclosed area ratio between respective areas enclosed by substantially-convex polygon-shaped perimeters 208, 204 of the outer 214 and inner 210 zones is between two and seven, inner zone 226 and outer zone heaters 228 being respectively distributed around inner 298 and outer 296 zone centroids such that (i) an average distance to a nearest heater within the outer zone significantly exceeds that of the inner zone;
• (ii) an average distance to a nearest heater on the inner zone perimeter 204 is substantially equal to that within inner zone 210;
• and (iii) an average distance to a nearest heater on the outer zone perimeter 208 is equal to at most about twice that on the inner zone perimeter 204, a majority of the heaters in the inner zone 210 being electrical 242 heaters and a majority of the heaters in the outer zone 214 being molten 244 salt heaters.

A system for in-situ production of hydrocarbon fluids from a subsurface hydrocarbon-containing formation, the system comprising:

• a heater cell divided into nested inner 210 and outer 214 zones such that an enclosed area ratio between respective areas enclosed by substantially-convex polygon-shaped perimeters 208, 204 of the outer 214 and inner 210 zones is between two and seven, heaters being located at all polygon vertices of inner and outer zone perimeters 204, 208, inner zone 226 and outer zone heaters 228 being respectively distributed around inner 298 and outer 296 zone centroids such that an average heater spacing in outer zone 214 significantly exceeds that of inner zone 210, the system further comprising control apparatus configured to regulate heater operation times so that, on average, heaters in outer zone 214 operate above a one-half maximum power level for at least twice as long as the heaters in inner zone 210.

A system for in-situ production of hydrocarbon fluids from a subsurface hydrocarbon-containing formation, the system comprising:

• a heater cell divided into nested inner 210 and outer 214 zones such that an enclosed area ratio between respective areas enclosed by substantially-convex polygon-shaped perimeters 208, 204 of the outer 214 and inner 210 zones is between two and seven, heaters being located at all polygon vertices of inner and outer zone perimeters 204, 208, inner zone 226 and outer zone heaters 228 being respectively distributed around inner 298 and outer 296 zone centroids such that a heater spatial density in inner 210 zone significantly exceeds that of outer 214 zone, the system further comprising control apparatus configured to regulate heater operation times so that, on average, heaters in outer zone 214 operate above a one-half maximum power level for at least twice as long as the heaters in inner zone 210.

A system for in-situ production of hydrocarbon fluids from a subsurface hydrocarbon-containing formation, the system comprising:

• a heater cell divided into nested inner 210 and outer 214 zones such that an enclosed area ratio between respective areas enclosed by substantially-convex polygon-shaped perimeters 208, 204 of the outer 214 and inner 210 zones is between two and seven, inner zone 226 and outer zone heaters 228 being respectively distributed around inner 298 and outer 296 zone centroids such that (i) an average distance to a nearest heater within the outer zone significantly exceeds that of the inner zone;
• (ii) an average distance to a nearest heater on the inner zone perimeter 204 is substantially equal to that within inner zone 210;
• and (iii) an average distance to a nearest heater on the outer zone perimeter 208 is equal to at most about twice that on the inner zone perimeter 204, the system further comprising control apparatus configured to regulate heater operation times so that, on average, heaters in outer zone 214 operate above a one-half maximum power level for at least twice as long as the heaters in inner zone 210.

A system for in-situ production of hydrocarbon fluids from a subsurface hydrocarbon-containing formation, the system comprising:

• a heater cell divided into N nested zones (N≧2), N being an integer having a value of at least two, the heater cell being divided such that, for each neighboring zone pair NZP of the N−1 neighboring zone pairs defined by the N nested zones, an enclosed area ratio between respective areas enclosed by perimeters of the more outer zone and the more inner zone is between two and seven, heaters being arranged in the heater cell such that for each neighboring zone pair NZP of the N−1 neighboring zone pairs, a heater spacing ratio between an average heater spacing of the more outer zone of the neighboring zone pair NZP and that of the more inner zone of the neighboring zone pair NZP significantly exceeds unity and is about equal to a square root of the enclosed area ratio.

A system for in-situ production of hydrocarbon fluids from a subsurface hydrocarbon-containing formation, the system comprising:

• a heater cell divided into N nested zones (N≧2), N being an integer having a value of at least two, the heater cell being divided such that, for each neighboring zone pair NZP of the N−1 neighboring zone pairs defined by the N nested zones, a zone area ratio between respective areas of the more outer zone and the more inner zone of the neighboring zone pair NZP is between two and seven, heaters being arranged in the heater cell such that for each neighboring zone pair NZP of the N−1 neighboring zone pairs, a heater spatial density of the more inner zone of the neighboring zone pair NZP is about equal to a product of the zone area ratio and heater spatial density of the more outer zone of the zone pair NZP.

The system of preceding claim wherein heaters are distributed around of the inner zone 210.

The system of any preceding claim wherein for each zone of the N−1 zone pairs, the heaters are respectively distributed around a respective centroid thereof.

The system of any preceding claim wherein for each zone of a majority of zones of the N−1 zone pairs, the heaters are respectively distributed around a respective centroid thereof.

The system of any preceding claim wherein N has a value of two.

The system of any preceding claim wherein N has a value of three.

The system of any preceding claim wherein at least one production well is respectively located within each of the N zones.

The system of any preceding claim wherein for each zone of a majority of the N zones, at least one production well is respectively located therein.

The system of any preceding claim further comprising control apparatus configured to regulate heater operation times so that for each neighboring zone pair NZP, an average production well operation time in the more outer zone of the zone pair operate is at least twice that of the more inner zone of the zone pair.

The system of any preceding claim wherein for each neighboring zone pair NZP the respective area ratio is at most six.

The system of any preceding claim wherein for each of the zones, production wells are respectively located on substantially on opposite sides of the zone.

The system of any preceding claim wherein a centroid 296 of an innermost zone 210 is located in a central portion of the region enclosed by a perimeter 208 of the neighboring zone 214 of the innermost zone.

The system of any preceding claim wherein for each neighboring zone pair NZP of the N−1, a centroid of the more inner zone is located within a central portion of the region enclosed by a perimeter of the more out zone of the neighboring zone pair NZP

A system for in-situ production of hydrocarbon fluids from a subsurface hydrocarbon-containing formation, the system comprising:

• heaters arranged in a target portion of the formation, the target portion being divided into nested inner 210 and outer 214 zones heaters so that inner zone 226 and outer zone heaters 228 are respectively distributed around inner 298 and outer 296 zone centroids, a majority of the heaters in the inner zone 210 being electrical 242 heaters and a majority of the heaters in the outer zone 214 being non-electric heaters or combustion-based heaters or advection-based heaters.

A system for in-situ production of hydrocarbon fluids from a subsurface hydrocarbon-containing formation, the system comprising:

• heaters arranged in a target portion of the formation, the target portion being divided into nested inner 210 and outer 214 zones heaters so that inner zone 226 and outer zone heaters 228 are respectively distributed around inner 298 and outer 296 zone centroids, a majority of the heaters in the inner zone 210 being electrical 242 heaters and a majority of the heaters in the outer zone 214 being non-electric heaters or combustion-based heaters or advection-based heaters.

The system of any previous claim wherein at least two-thirds of the heaters in the inner zone 210 are electrical 242 heaters and at least two-thirds of the heaters in the outer zone 214 are non-electric heaters or combustion-based heaters or advection-based heaters.

The system of any preceding claim wherein inner 210 and outer 214 zones respective have polygon-shaped perimeters 208, 204 such that heaters are located at all polygon vertices of inner and outer zone perimeters 204, 208.

The system of any preceding claim wherein the inner zone 210 is substantially-convex.

The system of any preceding claim wherein an average heater spacing in the outer zone 214 significantly exceeds that of the inner zone 210.

The system of any preceding claim wherein an average heater spacing in the outer zone 214 is about twice that of the inner zone 210.

The system of any preceding claim wherein a spacing ratio between an average heater spacing of the outer zone and that of the inner zone is about equal to a square root of the area ratio between respective areas enclosed by the inner zone and outer zone perimeters 204, 208.

The system of any preceding claim wherein a heater spatial density in inner 210 zone significantly exceeds that of the outer 214 zone.

The system of any preceding claim wherein a heater spatial density in the inner 210 zone is at least twice that of the outer 214 zone.

The system of any preceding claim wherein a heater spatial density in inner 210 zone is at least about three times that of the outer 214 zone.

The system of any preceding claim wherein a heater density ratio between a heater spatial densities in inner 210 that of outer 214 zones is substantially equal to a zone area ratio between an area of outer 214 zone and that of inner 210 zone.

The system of any preceding claim wherein an average distance to a nearest heater within the outer zone significantly exceeds that of the inner zone.

The system of any preceding claim wherein an average distance to a nearest heater within the outer zone is between two and three times that of the inner zone.

The system of any preceding claim wherein an average distance to a nearest heater on a perimeter 204 of the inner zone 204 is at most substantially equal to that within inner zone 210.

The system of any preceding claim further comprising at least one inner zone production well 224I within inner zone 210 and at least one outer zone production well 224 within outer zone 214.

The system of any preceding claim wherein a majority of the outer zone heaters are arranged on a perimeter 208 of the outer zone.

The system of any preceding claim wherein heaters are located at all polygon vertices of inner and outer zone perimeters 204, 208,

The system of any preceding claim wherein heaters are located at all vertices of the OZS additional zone perimeter 202.

The system of any preceding claim wherein an average distance to a nearest heater within the outer zone is equal to between about two and about three times that of the inner zone.

The system of any preceding claim wherein average distance to a nearest heater within the outer zone is equal to between two and three times that of the inner zone.

The system of any preceding claim wherein for each of the zone pairs, a heater spacing of the more outer zone is at least about twice that of the more inner zone.

The system of any preceding claim wherein for each of the zone pairs, the area ratio between respective more outer and more inner zones is about four, and a heater spacing of the more outer zone is about twice that of the more inner zone.

The system of any preceding claim wherein for each of the zone pairs, ratio between a heater spacing of the more outer zone and that of the more inner zone is substantially equal to square root of the area ratio between the more outer and the more inner zones of the zone pair.

The system of any preceding claim wherein for each of the zone pairs, the area ratio between respective areas enclosed by perimeters of the more outer zone and the more inner zone is at most six.

The system of any preceding claim wherein for each of the zone pairs, the area ratio between respective areas enclosed by perimeters of the more outer zone and the more inner zone is at most five.

The system of any preceding claim wherein for each of the zone pairs, the area ratio between respective areas enclosed by perimeters of the more outer zone and the more inner zone is at least 2.5.

The system of preceding claim wherein a significant majority of the inner zone heaters 226 are located away from outer zone perimeter 208.

The system of any preceding claim wherein a significant majority of the outer zone heaters 226 are located away from a perimeter 202 of outer-zone-surrounding (OZS) additional 218 zone.

The system of any preceding claim wherein for each of the zone pairs, a heater spatial density of the more inner zone is equal to at least about twice that of the more outer zone.

The system of any preceding claim wherein for each of the zone pairs, a heater spatial density of the more inner zone is equal to at most about six times that of the more outer zone.

The system of any preceding claim wherein for each of the zone pairs, a centroid of the more inner zone is located in a central portion of the region enclosed by a perimeter of the more outer zone.

The system of any preceding claim wherein for each of the zone pairs, an average distance to a nearest heater in the more outer zone is between about two and about three times that of the less outer zone.

The system of any of preceding claim wherein for each of the zone pairs, an average distance to a nearest heater in the more outer zone is between two and three times that of the less outer zone.

The system of any preceding claim wherein a centroid 298 of inner zone 210 is located in a central portion of the region enclosed by a perimeter 208 of the outer zone 214.

The system of any preceding claim wherein the heater cell includes at least one inner zone production well 224I located within the inner zone 210.

The system of any preceding claim wherein the heater cell includes at least one outer zone production well 224O located within the outer zone 214.

The system of any preceding claim wherein the heater cell includes first and second outer zone production wells 224O located within and on substantially on opposite sides of the outer zone 214.

The system of any preceding claim wherein a production well spatial density in the inner zone 210 at least exceeds that of the outer zone 124.

The system of any preceding claim wherein an average heater spacing in outer 214 zone is at least about twice that of inner 210 zone.

The system of any preceding claim wherein the area ratio between respective areas enclosed by inner zone and outer zone perimeters 204, 208 is about four, and an average heater spacing in outer 214 zone is about twice that of inner 210 zone.

The system of any preceding claim wherein a spacing ratio between an average heater spacing of the outer zone and that of the inner zone is about equal to a square root of the area ratio between respective areas enclosed by the inner zone and outer zone perimeters 204, 208.

The system of any preceding claim wherein a spacing ratio between an average heater spacing of the outer zone and that of the inner zone is about equal to a square root of the area ratio between respective areas enclosed by inner zone and outer zone perimeters 204, 208.

The system of any preceding claim wherein a heater spatial density in inner 210 zone is at least about twice that of outer 214 zone.

The system of any preceding claim wherein a heater spatial density in inner 210 zone is at least twice that of outer 214 zone.

The system of any preceding claim wherein a heater spatial density in inner 210 zone is at least about three times that of the outer 214 zone.

The system of any preceding claim wherein a heater density ratio between a heater spatial densities in inner 210 that of outer 214 zones is substantially equal to a zone area ratio between an area of outer 214 zone and that of inner 210 zone.

The system of any preceding claim wherein an enclosed area ratio between an area enclosed by a perimeter 208 of outer zone 214 to that enclosed by a perimeter 204 of inner zone 210 is at most six.

The system of any preceding claim wherein an enclosed area ratio between an area enclosed by a perimeter 208 of outer zone 214 to that enclosed by a perimeter 204 of inner zone 210 is at most five.

The system of any preceding claim wherein an enclosed area ratio between an area enclosed by a perimeter 208 of outer zone 214 to that enclosed by a perimeter 204 of inner zone 210 is at least 2.5

The system of any preceding claim wherein an average distance to a nearest heater in the outer zone 214 is between about two and about three times that of the inner zone 210.

The system of any preceding claim wherein an average distance to a nearest heater in the outer zone 214 is between two and three times that of the inner zone 210.

The system of any preceding claim wherein an average distance to a nearest heater on the inner zone perimeter 204 is substantially equal to that within inner zone 210.

The system of any preceding claim wherein along the perimeter 208 of outer zone 214, an average distance to a nearest heater is at most four times that along the perimeter 204 of inner zone 210.

The system of any preceding claim wherein along the perimeter 208 of outer zone 214, an average distance to a nearest heater is at most three times that along the perimeter 204 of inner zone 210.

The system of any preceding claim wherein along the perimeter 208 of outer zone 214, an average distance to a nearest heater is at most about twice that along the perimeter 204 of inner zone 210.

The system of any preceding claim wherein among outer-perimeter heaters located on the perimeter 208 of outer zone 214, an average distance to a nearest heater significantly exceeds that among inner-perimeter heaters located on the perimeter 204 of inner zone 210.

The system of any preceding claim wherein among outer-perimeter heaters located on the perimeter 208 of outer zone 214, an average distance to a second nearest heater significantly exceeds that among inner-perimeter heaters located on the perimeter 204 of inner zone 210.

The system of any preceding claim wherein the system includes a plurality of the heater cells, first 608 and second 602 of the heater cells having substantially the same area and sharing at least one common heater-cell-perimeter heater.

The system of any of preceding claim wherein the system includes a plurality of the heater cells, at least one of which is substantially surrounded by a plurality of neighboring heater cells.

The system of any of preceding claim wherein a given heater cell 608 of the heater cells is substantially surrounded by a plurality of neighboring heater cells and the given heater cell 608 shares a common heater-cell-perimeter heater with each of the neighboring heater cells.

The system of any preceding claim wherein inner zone heaters 226 are distributed substantially uniformly throughout inner zone 210.

The system of any preceding claim wherein the heater cell is arranged so that within the outer zone 214, heaters are predominantly located on the outer zone perimeter 208.

The system of any preceding claim wherein at least one of the inner and outer perimeters is shaped like a regular hexagon, like a lozenge, or like a rectangle.

The system of any preceding claim wherein the inner 204 and outer 208 perimeters are like-shaped.

The system of any preceding claim wherein within the inner 210 and/or outer 214 zones, a majority of heaters are disposed on a triangular grid, hexagonal or rectangular grid.

The system of any preceding claim wherein a total number of inner zone heaters exceeds that of the outer zone.

The system of any preceding claim wherein a total number of inner zone heaters exceeds that of the outer zone by at least 50%.

The system of any preceding claim wherein at least five inner zone heaters are dispersed throughout the inner zone.

The system of any preceding claim wherein at least five or at least seven or at least ten outer zone heaters are located around a perimeter 208 of outer zone.

The system of any preceding claim wherein at least one-third of at least one-half of inner zone heaters 226 are not located on inner zone perimeter 204.

The system of any preceding claim wherein each of the inner zone and outer zone perimeters 204,208 has an aspect ratio equal to most 2.5.

The system of any preceding claim wherein each of the inner zone and outer zone perimeters 204,208 has an aspect ratio equal to least 10.

The system of any preceding claim wherein each of the inner zone and outer zone perimeters 204,208 has an aspect ratio equal to least 10.

The system of any preceding claim wherein each of the inner zone and outer zone perimeters 204,208 is shaped like a rectangular.

The system of any preceding claim wherein at least five heaters are distributed about the perimeter 204 of inner zone 210.

The system of any preceding claim wherein at least seven heaters are distributed about the perimeter 204 of inner zone 210.

The system of any preceding claim wherein at least nine heaters are distributed about the perimeter 204 of inner zone 210.

The system of any preceding claim wherein at least five heaters are distributed about the perimeter 208 of outer zone 214.

The system of any preceding claim wherein at least seven heaters are distributed about the perimeter 204 of inner zone 210.

The system of any preceding claim wherein at least nine heaters are distributed about the perimeter 208 of outer zone 214.

The system of any preceding claim wherein at least ten heaters are distributed throughout inner zone 214.

The system of any preceding claim wherein a majority of the heaters in inner zone 210 are electrical 242 heaters and a majority of the heaters in outer zone 214 are molten 244 salt heaters.

The system of any previous claim wherein at least two-thirds or at least three-quarters of inner-zone heaters are electrical 242 heaters and at least two-thirds of outer-zone heaters are molten salt heaters.

The system of any preceding claim wherein the system further includes control apparatus configured to regulate heater operation times so that, on average, heaters in outer zone 214 operate above a one-half maximum power level for at least twice as long as the heaters in inner zone 210.

The system of any preceding claim wherein the system includes control apparatus configured to regulate heater operation times so that, on average, outer zone heaters operate above a one-half maximum power level for at least twice as long as the inner zone heaters.

The system of any of preceding claim wherein an average inner-zone heater spacing is at most 20 meters.

The system of any of preceding claim wherein an average inner-zone heater spacing is at most 10 meters.

The system of any of preceding claim wherein an average inner-zone heater spacing is at most 5 meters.

The system of any of preceding claim wherein an area of the inner zone is at most one square kilometer.

The system of any of preceding claim wherein an area of the inner zone is at most 500 square meters.

The system of any preceding claim wherein the heaters are configured to induce pyrolysis throughout substantial entireties of both the inner 210 and outer 214 zones.

The system of any preceding claim wherein the heaters are configured to heat respective substantial entirety of the inner and outer regions to substantially the same uniform temperature.

The system of any preceding claim wherein, among the inner zone heaters and/or outer zone heaters and/or inner perimeter heaters and/or outer perimeter heaters, a ratio between a standard deviation of the spacing and an average spacing is at most 0.2.

The system of any preceding claim wherein all heaters have substantially the same maximum power level and/or substantially the same diameter.

The system of any preceding claim wherein a ratio between the area of the inner 210 zone and a square of an average distance to a nearest heater within the inner 210 zone is at least 80.

The system of any preceding claim wherein a ratio between the area of the inner 210 zone and a square of an average distance to a nearest heater within the inner 210 zone is at least 60.

The system of any preceding claim wherein a ratio between the area of the inner 210 zone and a square of an average distance to a nearest heater within the inner 210 zone is at least 70.

The system of any preceding claim wherein a ratio between the area of the inner 210 zone and a square of an average distance to a nearest heater within the inner 210 zone is at least 80.

The system of any preceding claim wherein a ratio between the area of the inner 210 zone and a square of an average distance to a nearest heater within the inner 210 zone is at least 90.

The system of any preceding claim wherein a ratio between the area of the inner 210 zone and a square of an average distance to a nearest heater within the inner 210 zone is at least 100.

The system of any preceding claim wherein along a perimeter 208 of outer zone 214, an average distance to a nearest heater is at most 10% of a length of the outer zone perimeter 208.

The system of any preceding claim wherein along a perimeter 208 of outer zone 214, an average distance to a nearest heater is at most 7.6% of a length of the outer zone perimeter 208.

The system of any preceding claim wherein along a perimeter 208 of outer zone 214, an average distance to a nearest heater is at most 5% of a length of the outer zone perimeter 208.

The system of any preceding claim wherein along a perimeter 208 of outer zone 214, an average distance to a nearest heater is at most 4% of a length of the outer zone perimeter 208.

The system of any preceding claim wherein along a perimeter 208 of outer zone 214, an average distance to a nearest heater is at most 3% of a length of the outer zone perimeter 208.

The system of any preceding claim wherein along a perimeter 204 of inner zone 210, an average distance to a nearest heater is at most 10% of a length of the outer zone perimeter 208.

The system of any preceding claim wherein along a perimeter 204 of inner zone 210, an average distance to a nearest heater is at most 7.6% of a length of the outer zone perimeter 208.

The system of any preceding claim wherein along a perimeter 204 of inner zone 210, an average distance to a nearest heater is at most 5% of a length of the outer zone perimeter 208.

The system of any preceding claim wherein along a perimeter 204 of inner zone 210, an average distance to a nearest heater is at most 4% of a length of the outer zone perimeter 208.

The system of any preceding claim wherein along a perimeter 204 of inner zone 210, an average distance to a nearest heater is at most 3% of a length of the outer zone perimeter 208.

The system of any preceding claim wherein within the inner zone 210, an average distance to a nearest heater is at most one-eighth of a square root of an area of the inner zone 210.

The system of any preceding claim wherein within the inner zone 210, an average distance to a nearest heater is at most one-tenth of a square root of an area of the inner zone 210.

The system of any preceding claim wherein within the inner zone 210, an average distance to a nearest heater is at most one-twelfth of a square root of an area of the inner zone 210.

The system of any preceding claim wherein within the inner zone 210, at most 30% of the inner zone is displaced from a nearest heater by length threshold equal to at most one quarter of a square root of the inner zone 210.

The system of any preceding claim wherein within the inner zone 210, at most 20% of the inner zone is displaced from a nearest heater by length threshold equal to at most one quarter of a square root of the inner zone 210.

The system of any preceding claim wherein within the inner zone 210, at most 10% of the inner zone is displaced from a nearest heater by length threshold equal to at most one quarter of a square root of the inner zone 210.

The system of any preceding claim wherein the length threshold equals at most one fifth of a square root of the inner zone.

The system of any preceding claim wherein an aspect ratio of the inner 210 and/or outer 214 zone is at most four.

The system of any preceding claim wherein an aspect ratio of the inner 210 and/or outer 214 zone is at most three.

The system of any preceding claim wherein an aspect ratio of the inner 210 and/or outer 214 zone is at most 2.5.

The system of any preceding claim wherein among the inner 210 and outer 214 zones, a ratio between a greater aspect ratio and a lesser aspect ratio is at most 1.5.

The system of any preceding claim wherein an isoperimetric quotient of perimeters 204, 208 of the inner 210 and/or outer 214 zone is at least 0.4.

The system of any preceding claim wherein an isoperimetric quotient of perimeters 204, 208 of the inner 210 and/or outer 214 zone is at least 0.5.

The system of any preceding claim wherein an isoperimetric quotient of perimeters 204, 208 of the inner 210 and/or outer 214 zone is at least 0.6.

The system of any preceding claim wherein a perimeter 204 of inner zone 210 has a convex shape tolerance value of at most 1.2.

The system of any preceding claim wherein a perimeter 204 of inner zone 210 has a convex shape tolerance value of at most 1.1.

The system of any preceding claim wherein a perimeter 204 of inner zone 210 has a convex shape tolerance value of at most 1.05.

The system of any preceding claim wherein a perimeter 208 of outer zone 214 has a convex shape tolerance value of at most 1.2.

The system of any preceding claim wherein a perimeter 208 of outer zone 214 has a convex shape tolerance value of at most 1.1.

The system of any preceding claim wherein a perimeter 208 of outer zone 214 has a convex shape tolerance value of at most 1.05.

The system of any preceding claim wherein a perimeter 202 of OCS additional zone 218 has a convex shape tolerance value of at most 1.2.

The system of any preceding claim wherein a perimeter 202 of OCS additional zone 218 has a convex shape tolerance value of at most 1.1.

The system of any preceding claim wherein a perimeter 202 of OCS additional zone 218 has a convex shape tolerance value of at most 1.05.

The system of any preceding claim wherein a perimeter of 204 of inner zone 210 is convex.

The system of any preceding claim wherein a perimeter of 208 of outer zone 214 is convex.

The system of any preceding claim wherein a perimeter of 202 of OCS additional zone 218 is convex.

The system of any preceding claim wherein heaters are arranged within inner 210 zone so that inner zone heaters are present on every 72 degree sector thereof for any reference ray orientation.

The system of any preceding claim wherein heaters are arranged within inner 210 zone so that inner zone heaters 226 are present on every 60 degree sector thereof for any reference ray orientation.

The system of any preceding claim wherein heaters are arranged within inner 210 zone so that inner zone heaters 226 are present on every 45 degree sector thereof for any reference ray orientation.

The system of any preceding claim wherein heaters are arranged within outer 214 zone so that outer zone heaters 228 are present on every 72 degree sector thereof for any reference ray orientation.

The system of any preceding claim wherein heaters are arranged within outer 214 zone so that outer zone heaters 228 are present on every 60 degree sector thereof for any reference ray orientation.

The system of any preceding claim wherein heaters are arranged within outer 214 zone so that outer zone heaters 228 are present on every 45 degree sector thereof for any reference ray orientation.

The system of any preceding claim wherein heaters are arranged within OCS additional zone 218 so that heaters are present on every 72 degree sector thereof for any reference ray orientation.

A system for in-situ production of hydrocarbon fluids from a subsurface hydrocarbon-containing formation, the system comprising:

• a heater cell divided into nested inner 210 and outer 214 zones such that an area ratio between respective areas enclosed by substantially-convex polygon-shaped perimeters 208, 204 of the outer 214 and inner 210 zones is between two and seven, heaters being located at all polygon vertices of inner and outer zone perimeters 204, 208, inner zone 226 and outer zone heaters 228 being respectively distributed around inner 298 and outer 296 zone centroids such that an average heater spacing in outer zone 214 significantly exceeds that of inner zone 210, the system further comprising control apparatus configured to regulate heater operation times so that, on average, heaters in outer zone 214 operate above a one-half maximum power level for at least twice as long as the heaters in inner zone 210.

A system for in-situ production of hydrocarbon fluids from a subsurface hydrocarbon-containing formation, the system comprising:

• a heater cell divided into nested inner 210 and outer 214 zones such that an area ratio between respective areas enclosed by substantially-convex polygon-shaped perimeters 208, 204 of the outer 214 and inner 210 zones is between two and seven, heaters being located at all polygon vertices of inner and outer zone perimeters 204, 208, inner zone 226 and outer zone heaters 228 being respectively distributed around inner 298 and outer 296 zone centroids such that a heater spatial density in inner 210 zone significantly exceeds that of outer 214 zone, the system further comprising control apparatus configured to regulate heater operation times so that, on average, heaters in outer zone 214 operate above a one-half maximum power level for at least twice as long as the heaters in inner zone 210.

A system for in-situ production of hydrocarbon fluids from a subsurface hydrocarbon-containing formation, the system comprising:

• a heater cell divided into nested inner 210 and outer 214 zones such that an area ratio between respective areas enclosed by substantially-convex polygon-shaped perimeters 208, 204 of the outer 214 and inner 210 zones is between two and seven, inner zone 226 and outer zone heaters 228 being respectively distributed around inner 298 and outer 296 zone centroids such that (i) an average distance to a nearest heater within the outer zone significantly exceeds that of the inner zone;
• (ii) an average distance to a nearest heater on the inner zone perimeter 204 is substantially equal to that within inner zone 210;
• and (iii) an average distance to a nearest heater on the outer zone perimeter 208 is equal to at most about twice that on the inner zone perimeter 204, the system further comprising control apparatus configured to regulate heater operation times so that, on average, heaters in outer zone 214 operate above a one-half maximum power level for at least twice as long as the heaters in inner zone 210.

A system for in-situ production of hydrocarbon fluids from a subsurface formation, the system comprising:

• molten salt heaters and electrical heaters arranged within a target portion of the sub-surface formation.

The system of any previous claim wherein, within the target formation, a first heater that is a molten salt heater is located at most 50 meters from a second heater that is an electrical heater.

The system of any previous claim wherein, within the target formation, a first heater that is a molten salt heater is located at most 20 meters from a second heater that is an electrical heater.

The system of any previous claim wherein, within the target formation, a first heater that is a molten salt heater is located at most 10 meters from a second heater that is an electrical heater.

The system of any previous claim wherein, within the target formation, a first heater that is a molten salt heater is located at most 5 meters from a second heater that is an electrical heater.

The system of any previous claim wherein, within the target formation, the average separation distance between neighboring molten salt heaters significantly exceeds the average separation distance between neighboring electrical heaters.

The system of any previous claim wherein, within the target formation, the average separation distance between neighboring molten salt heaters is about twice the average separation distance between neighboring electrical heaters.

The system of any previous claim wherein, within the target portion, the average heater separation distance for electrical:molten-salt neighboring heater pairs significantly exceeds the average separation distance for all-electrical neighboring heater pairs.

The system of any previous claim wherein, within the target portion, the average heater separation distance for electrical:molten-salt neighboring heater pairs is about twice the average separation distance for all-electrical neighboring heater pairs.

The system of any previous claim wherein within the target portion, an average heater separation distance for all-molten-salt neighboring heater pairs is substantially equal to the average separation distance for electrical:molten-salt neighboring heater pairs neighboring heater pairs.

A system for in-situ production of hydrocarbon fluids from a subsurface formation, the system comprising:

• (i) electrical heaters and (ii) non-electric heaters or combustion-based heaters or advection-based heaters or non-electric heaters other than molten salt heaters or advection-based heaters other than molten-salt heaters arranged within a target portion of the sub-surface formation.

The system of any previous claim wherein, within the target formation, a first heater that is a non-electric heaters or combustion-based heaters or advection-based heaters or non-electric heaters other than molten salt heaters or advection-based heaters other than molten-salt heaters is located at most 50 meters from a second heater that is an electrical heater.

The system of any previous claim wherein, within the target formation, a first heater that is a non-electric heaters or combustion-based heaters or advection-based heaters or non-electric heaters other than molten salt heaters or advection-based heaters other than molten-salt heaters is located at most 20 meters from a second heater that is an electrical heater.

The system of any previous claim wherein, within the target formation, a first heater that is a non-electric heaters or combustion-based heaters or advection-based heaters or non-electric heaters other than molten salt heaters or advection-based heaters other than molten-salt heaters is located at most 10 meters from a second heater that is an electrical heater.

The system of any previous claim wherein, within the target formation, a first heater that is a non-electric heaters or combustion-based heaters or advection-based heaters or non-electric heaters other than molten salt heaters or advection-based heaters other than molten-salt heaters is located at most 5 meters from a second heater that is an electrical heater.

The system of any previous claim wherein, within the target formation, the average separation distance between neighboring molten salt heaters significantly exceeds the average separation distance between neighboring electrical heaters.

The system of any previous claim wherein, within the target formation, the average separation distance between neighboring non-electric heaters or combustion-based heaters or advection-based heaters or non-electric heaters other than molten salt heaters or advection-based heaters other than molten-salt heaters is about twice the average separation distance between neighboring electrical heaters.

The system of any previous claim wherein, within the target portion, the average heater separation distance for electrical:molten-salt neighboring heater pairs significantly exceeds the average separation distance for all-electrical neighboring heater pairs.

The system of any previous claim wherein, within the target portion, the average heater separation distance for electrical:molten-salt neighboring heater pairs is about twice the average separation distance for all-electrical neighboring heater pairs.

The system of any previous claim wherein within the target portion, an average heater separation distance for all-molten-salt neighboring heater pairs is substantially equal to the average separation distance for electrical:molten-salt neighboring heater pairs neighboring heater pairs.

A system for in-situ production of hydrocarbon fluids from a subsurface formation, the system comprising:

• molten salt heaters and electrical heaters arranged within a target portion of the sub-surface formation.

The system of any previous claim wherein, within the target formation, a first heater that is a molten salt heater is located at most 50 meters from a second heater that is an electrical heater.

The system of any previous claim wherein, within the target formation, a first heater that is a molten salt heater is located at most 20 meters from a second heater that is an electrical heater.

The system of any previous claim wherein, within the target formation, a first heater that is a molten salt heater is located at most 10 meters from a second heater that is an electrical heater.

The system of any previous claim wherein, within the target formation, a first heater that is a molten salt heater is located at most 5 meters from a second heater that is an electrical heater.

The system of any previous claim wherein, within the target formation, the average separation distance between neighboring molten salt heaters significantly exceeds the average separation distance between neighboring electrical heaters.

The system of any previous claim wherein, within the target formation, the average separation distance between neighboring molten salt heaters is about twice the average separation distance between neighboring electrical heaters.

• 218×8 The system of any previous claim wherein, within the target portion, the average heater separation distance for electrical:molten-salt neighboring heater pairs significantly exceeds the average separation distance for all-electrical neighboring heater pairs.

The system of any previous claim wherein, within the target portion, the average heater separation distance for electrical:molten-salt neighboring heater pairs is about twice the average separation distance for all-electrical neighboring heater pairs.

The system of any previous claim wherein within the target portion, an average heater separation distance for all-molten-salt neighboring heater pairs is substantially equal to the average separation distance for electrical:molten-salt neighboring heater pairs neighboring heater pairs.

A system for in-situ production of hydrocarbon fluids from a subsurface hydrocarbon-containing formation, the system comprising:

• heaters arranged in a target portion of the formation, the target portion being divided into nested inner 210 and outer 214 zones heaters so that inner zone 226 and outer zone heaters 228 are respectively distributed around inner 298 and outer 296 zone centroids, a majority of the heaters in the inner zone 210 being electrical 242 heaters and a majority of the heaters in the outer zone 214 being molten 244 salt heaters.

A system for in-situ production of hydrocarbon fluids from a subsurface hydrocarbon-containing formation, the system comprising:

• heaters arranged in a target portion of the formation, the target portion being divided into nested inner 210 and outer 214 zones heaters so that inner zone 226 and outer zone heaters 228 are respectively distributed around inner 298 and outer 296 zone centroids, a majority of the heaters in the inner zone 210 being electrical 242 heaters and a majority of the heaters in the outer zone 214 being non-electric heaters or combustion-based heaters or advection-based heaters.

The system of any preceding claim wherein inner 210 and outer 214 zones respective have polygon-shaped perimeters 208, 204 such that heaters are located at all polygon vertices of inner and outer zone perimeters 204, 208.

The system of any preceding claim wherein the inner zone 210 is substantially-convex.

The system of any preceding claim wherein the outer zone 214 is substantially-convex.

The system of any preceding claim wherein a heater density ratio between a heater spatial densities in inner 210 that of outer 214 zones is substantially equal to a zone area ratio between an area of outer 214 zone and that of inner 210 zone.

The system of any preceding claim wherein an average distance to a nearest heater within the outer zone significantly exceeds that of the inner zone.

The system of any preceding claim wherein an average distance to a nearest heater within the outer zone is between two and three times that of the inner zone.

The system of any preceding claim wherein an average distance to a nearest heater on a perimeter 204 of the inner zone 204 is at most substantially equal to that within inner zone 210.

The system of any preceding claim wherein an average distance to a nearest heater on the outer zone perimeter 208 is equal to at most about twice that on the inner zone perimeter 204.

The system of any preceding claim further comprising at least one inner zone production well 224I within inner zone 210 and at least one outer zone production well 224 within outer zone 214.

The system of any of preceding claim wherein a majority of the outer zone heaters are arranged on a perimeter 208 of the outer zone.

The system of any preceding claim wherein the inner zone 210 is substantially-convex.

The system of any preceding claim wherein the outer zone 214 is substantially-convex.

The system of any of preceding claim wherein an isoperimetric quotient of perimeters 204, 208 of the inner 210 and/or outer 214 zone is at least 0.4.

The system of any preceding claim wherein an isoperimetric quotient of perimeters 204, 208 of the inner 210 and/or outer 214 zone is at least 0.5.

The system of any preceding claim wherein an isoperimetric quotient of perimeters 204, 208 of the inner 210 and/or outer 214 zone is at least 0.6.

The system of any preceding claim wherein a perimeter 204 of inner zone 210 has a convex shape tolerance value of at most 1.2.

The system of any preceding claim wherein a perimeter 204 of inner zone 210 has a convex shape tolerance value of at most 1.1.

The system of any preceding claim wherein a perimeter 204 of inner zone 210 has a convex shape tolerance value of at most 1.05.

The system of any preceding claim wherein for each perimeter 204, 208 of the inner 210 and outer 214 zone, an aspect ratio is less than 2.5.

The system of any preceding claim wherein for each perimeter 204, 208 of the inner 210 and outer 214 zone, an aspect ratio is less than 2.5.

The system of any preceding claim wherein at least 25 heaters are arranged within the target region.

The system of any preceding claim wherein at least 50 heaters are arranged within the target region.

The system of any preceding claim wherein at least 100 heaters are arranged within the target region.

The system of any preceding claim wherein a substantially majority the heaters within the target region are electrical or molten-salt heaters.

The system of any preceding claim wherein at least 20% of the heaters within the target region are electrical heaters.

The system of any preceding claim wherein the target region has a length and a width of at most 500 meters.

The system of any preceding claim wherein the target region has a length and a width of at most 250 meters.

The system of any preceding claim wherein the target region has a length and a width of at most 100 meters.

The system of any preceding claim wherein the target region has a length and a width of at most 50 meters.

The system of any preceding claim wherein the hydrocarbon-containing bearing formation is a coal formation.

The system of any preceding claim wherein the hydrocarbon-containing bearing formation is an oil shale formation.

The system of any preceding claim wherein the hydrocarbon-containing bearing formation is a heavy oil formation.

The system of any preceding claim wherein the hydrocarbon-containing bearing formation is a tar sands formation.

The system of any preceding claim wherein the heaters are horizontally-oriented and a distance between heaters is measured in a vertical plane.

The system of any preceding claim wherein the heaters are vertically-oriented and a distance between heaters is measured in a horizontal plane.

The system of any preceding claim wherein the heaters are slanted and a distance between heaters is measured in a slanted plane.

The system of any preceding claim wherein an about-tolerance-parameter is at most 0.2.

The system of any preceding claim wherein an about-tolerance-parameter is at most 0.15.

The system of any preceding claim wherein an about-tolerance-parameter is at most 0.1.

The system of any preceding claim wherein an about-tolerance-parameter is at most 0.05.

Use of the system of any preceding claim for in-situ production of hydrocarbon fluids from a subsurface hydrocarbon-containing formation.

A method of in-situ production of hydrocarbon fluids in a subsurface hydrocarbon-containing formation, the method comprising:

• for a plurality of subsurface heaters that are arranged within N nested zones of the subsurface formation, N being an integer having a value of at least two, for each neighboring zone pair NZP of the N−1 neighboring zone pairs defined by the N nested zones an area ratio between respective areas enclosed by perimeters of the more outer zone and the more inner zone of the neighboring zone pair NZP is between two and seven, operating the heaters to produce hydrocarbon fluids in situ such that a time ratio between a half-maximum sustained-production-time and a half-maximum rise-time is at least four thirds.

The method of any preceding claim wherein at least 5% of the thermal energy required for hydrocarbon fluid production in the outer zone is supplied by outward flow of thermal energy from the inner zone to the outer zone.

The method of any preceding claim wherein at least 10% of the thermal energy required for hydrocarbon fluid production in the outer zone is supplied by outward flow of thermal energy from the inner zone to the outer zone.

The method of any preceding method claim wherein for each location of a plurality of locations 1098 substantially on opposite sides of the outer zone 214, at least some of the thermal required for hydrocarbon fluid production at the location is supplied by outward flow of thermal energy from the inner zone to the outer zone.

The method of any preceding method claim wherein for each location of a plurality of locations 1098 distributed around the outer zone 214, at least some of the thermal required for hydrocarbon fluid production at the location is supplied by outward flow of thermal energy from the inner zone to the outer zone.

The method of any preceding method claim wherein at least a majority of the outer zone heaters outside of the most inner zone 210 commence operation when at most a minority of hydrocarbon fluids of the most inner zone 210 have been produced.

The method of any of preceding claim wherein substantially all of the heaters are pre-deployed or pre-drilled heaters.

The method of any preceding method claim wherein the time ratio is at least 1.5.

The method of any preceding method claim wherein the time ratio is at least two.

A method for in-situ production of hydrocarbon fluids from a subsurface hydrocarbon-containing formation, the method comprising:

• producing hydrocarbon fluids by operating heaters of a heater cell divided into N nested zones (N≧2) where N is an integer having a value of at least two, the heater cell being divided such that for each neighboring zone pair NZP of the N−1 neighboring zone pairs defined by the N nested zones, a respective enclosed area ratio between respective areas enclosed by perimeters of the more outer zone of the neighboring zone pair NZP and the more inner zone of the neighboring zone pair NZP is between two and seven, Zonei representing the ith most inner zone where i is a positive integer having a value equal to at most N, a rate of production of the hydrocarbon fluids being characterized by a sequence of N zone-specific production peaks {Peak1, . . . PeakN}, the ith peak Peaki representing a time of a production peak in the ith zone Zonei, wherein for each i between 1 and N, a time ratio between a time required to ramp up to the (i+1)th peak Peaki+1 and ith peak Peaki is substantially equal to the zone area ratio between the area of the (i+1)th zone Zonei+1 and ith zone Zonei.

A method for in-situ production of hydrocarbon fluids from a subsurface hydrocarbon-containing formation, the method comprising:

• producing hydrocarbon fluids by operating heaters of a heater cell divided into N nested zones (N≧2) where N is an integer having a value of at least two, the heater cell being divided such that for each neighboring zone pair NZP of the N−1 neighboring zone pairs defined by the N nested zones, a respective zone area ratio between respective areas enclosed by perimeters of the more outer zone of the neighboring zone pair NZP and the more inner zone of the neighboring zone pair NZP is between two and seven, Zonei representing the ith most inner zone where i is a positive integer having a value equal to at most N, a rate of production of the hydrocarbon fluids being characterized by a sequence of N zone-specific production peaks {Peak1, . . . PeakN}, the ith peak Peaki representing a time of a production peak in the ith zone Zonei, wherein for each i between 1 and N, a time ratio between a time required to ramp up to the (i+1)th peak Peaki+1 and ith peak Peaki is substantially equal to a reciprocal of a heater density ratio between a heater density zone area ratio between a heater special density of the (i+1)th zone Zonei+1 and that of the ith zone Zonei.

The method of any preceding claim wherein for each neighboring zone pair NZP of the N−1 neighboring zone pairs defined by the N nested zones a heater spatial density of the more inner zone of the neighboring zone pair NZP significantly exceeds that of the more outer zone of the zone pair NZP.

The method of any preceding claim wherein each of the N zones has a respective substantially-convex polygon-shaped perimeter and heaters are located at every vertex thereof.

The method of any preceding claim wherein heaters are located in each of the N zones and respectively distributed around a respective centroid thereof.

The method of any of preceding claim wherein a value of N is two.

The method of any preceding claim wherein a value of N is three.

The method of any preceding claim wherein a value of N is four.

A method of in-situ production of hydrocarbon fluids from a subsurface hydrocarbon-containing formation, the method comprising:

• a. providing a heater cell divided into nested inner 210 and outer 214 zones such that an area ratio between respective areas enclosed by substantially-convex polygon-shaped perimeters 208, 204 of the outer 214 and inner 210 zones is between two and seven, heaters being located at all polygon vertices of inner and outer zone perimeters 204, 208, inner zone 226 and outer zone heaters 228 being respectively distributed around inner 298 and outer 296 zone centroids such that an average heater spacing in outer zone 214 significantly exceeds that of inner zone 210, each heater cell further comprising inner-zone 224I production well(s) and outer-zone 224O production well(s) respectively located in the inner 210 and outer 214 zones;
• and
• b. operating the heaters and the production wells to produce hydrocarbon fluids.

The method of any of preceding claim wherein an average heater spacing in outer 214 zone is at least about twice that of inner 210 zone.

The method of any preceding claim wherein the area ratio between respective areas enclosed by inner zone and outer zone perimeters 204, 208 is about four, and an average heater spacing in outer 214 zone is about twice that of inner 210 zone.

The method of any of preceding claim wherein a heater spatial density in inner 210 zone is at least about twice that of outer 214 zone.

The method of any of preceding claim wherein a heater spatial density in inner 210 zone is at least twice that of outer 214 zone.

The method of any of preceding claim wherein a heater spatial density in inner 210 zone is at least about three times that of the outer 214 zone.

The method of any preceding claim wherein a minimum value of X % is at least 15%.

The method of any preceding claim wherein a minimum value of X % is at least 25%.

The method of any preceding claim wherein the heater power level operation(s) is carried out at a time when a minority of hydrocarbon fluids have been produced within the outer zone 214.

The method of any preceding claim wherein the inner zone heater power reduction operation is carried out for at least one-third of the inner-zone heaters.

The method of any of preceding claim wherein a rate of inner zone hydrocarbon fluid production is monitored and the predicting or detecting is carried out according to the results of the monitoring.

The method of any of preceding claim wherein the fluid flow operation(s) is carried out in response to a predicting or detecting that an inner zone production rate 354 drops to a level that is Y % below an inner zone production rate peak 310 level, wherein Y % is at least 5% and at most 95%.

The method of any of preceding claim wherein the fluid flow operation(s) is carried out at a time when a minority of hydrocarbon fluids have been produced within the outer zone 214.

The method of any preceding claim wherein the fluid flow operation(s) is carried out at a time when within a majority of outer zone production wells 2260, flow of production fluids is substantially unrestricted.

A method of in-situ production of hydrocarbon fluids in a subsurface hydrocarbon-containing formation, the method comprising:

• for a plurality of subsurface heaters arranged in convex, nested inner 210 and outer 214 zones of the subsurface formation, an area enclosed by a perimeter 208 of the outer zone 214 being three to seven times that enclosed a perimeter 204 of the inner zone 210, an average heater spacing in the inner zone being significantly less than that of the outer zone, employing both inner-zone and outer-zone heaters to heat the subsurface formation and produce hydrocarbon fluids in-situ such that an average above-half-maximum-power operation time of outer-zone heaters significantly exceeds that of inner-zone heaters.

A method of in-situ production of hydrocarbon fluids in a subsurface hydrocarbon-containing formation, the method comprising:

• for a plurality of subsurface heaters arranged in convex, nested inner 210 and outer 214 zones of the subsurface formation, an area enclosed by a perimeter 208 of the outer zone 214 being three to seven times that enclosed a perimeter 204 of the inner zone 210, an average heater spacing in the inner zone being significantly less than that of the outer zone, employing both inner-zone and outer-zone heaters to heat the subsurface formation and produce hydrocarbon fluids in-situ such that an average operation time of outer-zone heaters exceeds that of inner-zone heaters by a factor of two.

A method of in-situ production of hydrocarbon fluids in a subsurface hydrocarbon-containing formation, the method comprising:

• for a plurality of subsurface heaters arranged in convex, nested inner 210 and outer 214 zones of the subsurface formation, an area enclosed by a perimeter 208 of the outer zone 214 being three to seven times that enclosed a perimeter 204 of the inner zone 210, an average heater spacing in the inner zone being significantly less than that of the outer zone, employing both inner-zone and outer-zone heaters to heat the subsurface formation and produce hydrocarbon fluids in-situ such that an average operation time of outer-zone production wells significantly exceeds that of inner-zone production wells.

A method of in-situ production of hydrocarbon fluids in a subsurface hydrocarbon-containing formation, the method comprising:

• for a plurality of subsurface heaters arranged in convex, nested inner 210 and outer 214 zones of the subsurface formation, an area enclosed by a perimeter 208 of the outer zone 214 being three to seven times that enclosed a perimeter 204 of the inner zone 210, an average heater spacing in the inner zone being significantly less than that of the outer zone, employing both inner-zone and outer-zone heaters to heat the subsurface formation and produce hydrocarbon fluids in-situ such that an average operation time of outer-zone production wells exceeds that of inner-zone production wells by about a factor of two.

The method of any preceding claim, carried out to produce a substantial majority of both inner-zone and outer-zone hydrocarbon fluids.

The method of any preceding claim wherein outer zone heaters are distributed around a perimeter 208 of outer zone 214.

The method of any preceding claim wherein outer zone heaters are predominantly outer zone perimeter heaters.

The method of any preceding claim wherein a majority of inner-zone heaters are electrical heaters and a majority of outer-zone heaters are non-electric heaters or combustion-based heaters or advection-based heaters or non-electric heaters other than molten salt heaters or advection-based heaters other than molten-salt heaters.

The method of any preceding claim wherein a majority of the inner zone heaters 226 are located away from the outer zone perimeter 208.

The method of any preceding claim wherein a significant majority of the inner zone heaters 226 are located away from the outer zone perimeter 208.

A method of in-situ production of hydrocarbon fluids in a subsurface hydrocarbon-containing formation, the method comprising:

• a. during an earlier stage of production, producing hydrocarbon fluids primarily in a first portion of the target region that is heated primarily by thermal energy of electrical heaters;
• and
• b. during a later stage of production, producing hydrocarbon fluid primarily in a second portion of the target region that is heated primarily by thermal energy of molten salt heaters, wherein at least some of the thermal energy required for hydrocarbon fluid production in the second portion of the target region is supplied by outward migration of thermal energy from the first portion to the second portion of the target region.

The method of any preceding claim wherein at least some of the thermal energy required for operating the molten salt heaters is supplied by combustion of hydrocarbon fluids produced during the first phase.

The method of any preceding claim wherein a majority of the thermal energy required for operating the molten salt heaters is supplied by combustion of hydrocarbon fluids produced during the first phase.

The method of any of claims preceding claim wherein a size of the second portion exceeds that of the first portion.

The method of any preceding claim wherein for the combination of the first and second portion, a ratio between a half-maximum sustained-production-time and a half-maximum rise-time is at least four thirds.

The method of any of preceding claim wherein at least a majority of the heaters within the second portion commence operation when at most a minority of hydrocarbon fluids have been produced from the first portion.

The method of any preceding claim wherein at least 5% of the thermal energy required for hydrocarbon fluid production in the second portion of the target region is supplied by flow of thermal energy from the first portion to the second portion of the target region.

A method of operating pluralities of (i) a first type of heater being non-electric heaters or combustion-based heaters or advection-based heaters or non-electric heaters other than molten salt heaters or advection-based heaters other than molten-salt heaters and (ii) a second type of heater being electrical heaters, the first and second types of heaters being co-located within a target portion of the subsurface formation comprising operating the heaters of the first type, on average, a significantly longer amount of time than, or at least twice as much time as, the heaters of the second type.

A method of operating pluralities of (i) a first type of heater being non-electric heaters or combustion-based heaters or advection-based heaters or non-electric heaters other than molten salt heaters or advection-based heaters other than molten-salt heaters and (ii) a second type of heater being electrical heaters, the first and second types of heaters being co-located within a target portion of the subsurface formation comprising operating the heaters of the first type, on average, a significantly longer amount of time than, or at least twice as much time as, the heaters of the second type.

A method of operating pluralities of molten salt and electrical heaters co-located within a target portion of the subsurface formation comprising operating the molten salt heaters, on average, at least twice as much time as the electrical heaters.

A method of constructing a system for in-situ production of hydrocarbon fluids from a subsurface hydrocarbon-containing formation comprising:

• deploying primarily electrical heaters within regions of the formation where a heater density is relatively high;
• and
• deploying primarily molten salt heaters, within regions of the formation where a heater density is relatively low.

The method of any preceding method claim wherein the area ratio for each of the zone pairs is at least three.

The method of any preceding method claim wherein each of the N zones has a respective substantially-convex polygon-shaped perimeter and heaters are located at every vertex thereof.

The method of any preceding method claim wherein heaters are located in each of the N zones and respectively distributed around a respective centroid thereof.

The method of any preceding method claim wherein at least one production well is situated in the innermost zone 210.

The method of any preceding method claim wherein at least one production well is situated in at least one of the N zones outside of the innermost zone 210.

The method of any of preceding method claim wherein at least one production well is situated in each of the N zones 210.

The method of any of preceding method claim wherein for each zone pair of a majority of the N−1 neighboring zone pairs NZP, the area ratio is at least three.

The method of any preceding method claim wherein for each zone pair the N−1 neighboring zone pairs NZP, the area ratio is at least three.

The method of preceding claim wherein heaters are distributed around of the inner zone 210.

The method of any preceding method claim wherein for each zone of the N−1 zone pairs, the heaters are respectively distributed around a respective centroid thereof.

The method of any preceding method claim wherein for each zone of a majority of zones of the N−1 zone pairs, the heaters are respectively distributed around a respective centroid thereof.

The method of any of preceding method claim wherein at least the inner zone is substantially-convex.

The method of any preceding method claim wherein each of the N zones is substantially-convex.

The method of any preceding method claim wherein N has a value of two.

The method of any preceding method claim wherein N has a value of three.

The method of any preceding method claim wherein N has a value of four.

The method of any preceding method claim wherein for each of the zones, the polygon-shaped perimeter is regular-hexagonal in shape.

The method of any preceding method claim wherein at least one production well is respectively located within each of the N zones.

The method of any preceding method claim wherein for each zone of a majority of the N zones, at least one production well is respectively located therein.

The method of any preceding method claim further comprising control apparatus configured to regulate heater operation times so that for each neighboring zone pair NZP, an average production well operation time in the more outer zone of the zone pair operate is at least twice that of the more inner zone of the zone pair.

The method of any preceding method claim wherein for each neighboring zone pair NZP the respective area ratio is at most six.

The method of any preceding method claim wherein for each of the zones, production wells are respectively located on substantially on opposite sides of the zone.

The method of any preceding method claim wherein a centroid 296 of an innermost zone 210 is located in a central portion of the region enclosed by a perimeter 208 of the neighboring zone 214 of the innermost zone.

The method of any preceding method claim wherein for each neighboring zone pair NZP of the N−1, a centroid of the more inner zone is located within a central portion of the region enclosed by a perimeter of the more out zone of the neighboring zone pair NZP.

The method of preceding method claim wherein at least a majority of the heaters in the inner zone 210 are electrical 242 heaters and at least a majority of the heaters in the outer zone 214 are molten 244 salt heaters.

The method of preceding method claim wherein at least two-thirds of the heaters in the inner zone 210 are electrical 242 heaters and at least two-thirds of the heaters in the outer zone 214 are molten 244 salt heaters.

The method of any preceding method claim inner 210 and outer 214 zones respective have polygon-shaped perimeters 208, 204 such that heaters are located at all polygon vertices of inner and outer zone perimeters 204, 208.

The method of any preceding method claim wherein the inner zone 210 is substantially-convex.

The method of any preceding method claim wherein the outer zone 214 is substantially-convex.

The method of any preceding method claim wherein an average heater spacing in the outer zone 214 significantly exceeds that of the inner zone 210.

The method of any preceding method claim wherein an average heater spacing in the outer zone 214 is about twice that of the inner zone 210.

The method of any preceding method claim wherein a spacing ratio between an average heater spacing of the outer zone and that of the inner zone is about equal to a square root of the area ratio between respective areas enclosed by the inner zone and outer zone perimeters 204, 208.

The method of any preceding method claim wherein a heater spatial density in inner 210 zone significantly exceeds that of the outer 214 zone.

The method of any preceding method claim wherein a heater spatial density in the inner 210 zone is at least twice that of the outer 214 zone.

The method of any preceding method claim wherein a heater spatial density in inner 210 zone is at least about three times that of the outer 214 zone.

The method of any preceding method claim wherein a heater density ratio between a heater spatial densities in inner 210 that of outer 214 zones is substantially equal to a zone area ratio between an area of outer 214 zone and that of inner 210 zone.

The method of any preceding method claim wherein an average distance to a nearest heater within the outer zone significantly exceeds that of the inner zone.

The method of any preceding method claim wherein an average distance to a nearest heater within the outer zone is between two and three times that of the inner zone.

The method of any preceding method claim wherein an average distance to a nearest heater on a perimeter 204 of the inner zone 204 is at most substantially equal to that within inner zone 210.

The method of any preceding method claim wherein an average distance to a nearest heater on the outer zone perimeter 208 is equal to at most about twice that on the inner zone perimeter 204.

The method of any preceding method claim further comprising at least one inner zone production well 224I within inner zone 210 and at least one outer zone production well 224 within outer zone 214.

The method of any preceding method claim wherein a majority of the outer zone heaters are arranged on a perimeter 208 of the outer zone.

The method of any preceding method claim wherein heaters are located at all polygon vertices of inner and outer zone perimeters 204, 208,

The method of any preceding method claim wherein heaters are located at all vertices of the OZS additional zone perimeter 202.

The method of any preceding method claim wherein an average distance to a nearest heater within the outer zone is equal to between about two and about three times that of the inner zone.

The method of any preceding method claim wherein average distance to a nearest heater within the outer zone is equal to between two and three times that of the inner zone.

The method of any preceding method claim wherein for each of the zone pairs, a heater spacing of the more outer zone is at least about twice that of the more inner zone.

The method of any preceding method claim wherein for each of the zone pairs, the area ratio between respective more outer and more inner zones is about four, and a heater spacing of the more outer zone is about twice that of the more inner zone.

The method of any preceding method claim wherein for each of the zone pairs, ratio between a heater spacing of the more outer zone and that of the more inner zone is substantially equal to square root of the area ratio between the more outer and the more inner zones of the zone pair.

The method of any preceding method claim wherein for each of the zone pairs, the area ratio between respective areas enclosed by perimeters of the more outer zone and the more inner zone is at most six.

The method of any preceding method claim wherein for each of the zone pairs, the area ratio between respective areas enclosed by perimeters of the more outer zone and the more inner zone is at most five.

The method of any preceding method claim wherein for each of the zone pairs, the area ratio between respective areas enclosed by perimeters of the more outer zone and the more inner zone is at least 2.5.

The method of any preceding method claim wherein a significant majority of the inner zone heaters 226 are located away from outer zone perimeter 208.

The method of any preceding claim wherein a significant majority of the outer zone heaters 226 are located away from a perimeter 202 of outer-zone-surrounding (OZS) additional 218 zone.

The method of any of any preceding method claim wherein for each of the zone pairs, a heater spatial density of the more inner zone is equal to at least about twice that of the more outer zone.

The method of any preceding method claim wherein for each of the zone pairs, a heater spatial density of the more inner zone is equal to at most about six times that of the more outer zone.

The method of any preceding method claim wherein for each of the zone pairs, a centroid of the more inner zone is located in a central portion of the region enclosed by a perimeter of the more outer zone.

The method of any preceding method claim wherein for each of the zone pairs, an average distance to a nearest heater in the more outer zone is between about two and about three times that of the less outer zone.

The method of any preceding method claim wherein for each of the zone pairs, an average distance to a nearest heater in the more outer zone is between two and three times that of the less outer zone.

The method of any preceding method claim wherein a centroid 298 of inner zone 210 is located in a central portion of the region enclosed by a perimeter 208 of the outer zone 214.

The method of any preceding method claim wherein the heater cell includes at least one inner zone production well 224I located within the inner zone 210.

The method of any preceding method claim wherein the heater cell includes at least one outer zone production well 224O located within the outer zone 214.

The method of any preceding method claim wherein the heater cell includes first and second outer zone production wells 224O located within and on substantially on opposite sides of the outer zone 214.

The method of any preceding method claim wherein a production well spatial density in the inner zone 210 at least exceeds that of the outer zone 124.

The method of any preceding method claim wherein an average heater spacing in outer 214 zone is at least about twice that of inner 210 zone.

The method of any preceding method claim wherein the area ratio between respective areas enclosed by inner zone and outer zone perimeters 204, 208 is about four, and an average heater spacing in outer 214 zone is about twice that of inner 210 zone.

The method of any preceding method claim wherein a spacing ratio between an average heater spacing of the outer zone and that of the inner zone is about equal to a square root of the area ratio between respective areas enclosed by the inner zone and outer zone perimeters 204, 208.

The method of any preceding method claim wherein a spacing ratio between an average heater spacing of the outer zone and that of the inner zone is about equal to a square root of the area ratio between respective areas enclosed by inner zone and outer zone perimeters 204, 208.

The method of any preceding method claim wherein a heater spatial density in inner 210 zone is at least about twice that of outer 214 zone.

The method of any preceding method claim wherein a heater spatial density in inner 210 zone is at least twice that of outer 214 zone.

The method of any preceding method claim wherein a heater spatial density in inner 210 zone is at least about three times that of the outer 214 zone.

The method of any preceding method claim wherein a heater density ratio between a heater spatial densities in inner 210 that of outer 214 zones is substantially equal to a zone area ratio between an area of outer 214 zone and that of inner 210 zone.

The method of any preceding method claim wherein an enclosed area ratio between an area enclosed by a perimeter 208 of outer zone 214 to that enclosed by a perimeter 204 of inner zone 210 is at most six.

The method of any preceding method claim wherein an enclosed area ratio between an area enclosed by a perimeter 208 of outer zone 214 to that enclosed by a perimeter 204 of inner zone 210 is at most five.

The method of any preceding method claim wherein an enclosed area ratio between an area enclosed by a perimeter 208 of outer zone 214 to that enclosed by a perimeter 204 of inner zone 210 is at least 2.5

The method of any preceding method claim wherein an average distance to a nearest heater in the outer zone 214 is between about two and about three times that of the inner zone 210.

The method of any preceding method claim wherein an average distance to a nearest heater in the outer zone 214 is between two and three times that of the inner zone 210.

The method of any preceding method claim wherein an average distance to a nearest heater on the inner zone perimeter 204 is substantially equal to that within inner zone 210.

The method of any preceding method claim wherein along the perimeter 208 of outer zone 214, an average distance to a nearest heater is at most four times that along the perimeter 204 of inner zone 210.

The method of any preceding method claim wherein along the perimeter 208 of outer zone 214, an average distance to a nearest heater is at most three times that along the perimeter 204 of inner zone 210.

The method of any preceding method claim wherein along the perimeter 208 of outer zone 214, an average distance to a nearest heater is at most about twice that along the perimeter 204 of inner zone 210.

The method of any preceding method claim wherein among outer-perimeter heaters located on the perimeter 208 of outer zone 214, an average distance to a nearest heater significantly exceeds that among inner-perimeter heaters located on the perimeter 204 of inner zone 210.

The method of any preceding method claim wherein among outer-perimeter heaters located on the perimeter 208 of outer zone 214, an average distance to a second nearest heater significantly exceeds that among inner-perimeter heaters located on the perimeter 204 of inner zone 210.

The method of any preceding method claim wherein the system includes a plurality of the heater cells, first 608 and second 602 of the heater cells having substantially the same area and sharing at least one common heater-cell-perimeter heater.

The method of any of preceding claim wherein the system includes a plurality of the heater cells, at least one of which is substantially surrounded by a plurality of neighboring heater cells.

The method of any of preceding claim wherein a given heater cell 608 of the heater cells is substantially surrounded by a plurality of neighboring heater cells and the given heater cell 608 shares a common heater-cell-perimeter heater with each of the neighboring heater cells.

The method of any preceding method claim wherein inner zone heaters 226 are distributed substantially uniformly throughout inner zone 210.

The method of any preceding method claim wherein the heater cell is arranged so that within the outer zone 214, heaters are predominantly located on the outer zone perimeter 208.

The method of any preceding method claim wherein at least one of the inner and outer perimeters is shaped like a regular hexagon, like a lozenge, or like a rectangle.

The method of any preceding method claim wherein the inner 204 and outer 208 perimeters are like-shaped.

The method of any preceding method claim wherein within the inner 210 and/or outer 214 zones, a majority of heaters are disposed on a triangular grid, hexagonal or rectangular grid.

The method of any preceding method claim wherein a total number of inner zone heaters exceeds that of the outer zone.

The method of any preceding method claim wherein a total number of inner zone heaters exceeds that of the outer zone by at least 50%.

The method of any preceding method claim wherein at least five inner zone heaters are dispersed throughout the inner zone.

The method of any preceding method claim wherein at least five or at least seven or at least ten outer zone heaters are located around a perimeter 208 of outer zone.

The method of any preceding method claim wherein at least one-third of at least one-half of inner zone heaters 226 are not located on inner zone perimeter 204.

The method of any preceding method claim wherein each of the inner zone and outer zone perimeters 204,208 has an aspect ratio equal to most 2.5.

The method of any preceding method claim wherein each of the inner zone and outer zone perimeters 204,208 has an aspect ratio equal to least 10.

The method of any preceding method claim wherein each of the inner zone and outer zone perimeters 204,208 has an aspect ratio equal to least 10.

The method of any preceding method claim wherein each of the inner zone and outer zone perimeters 204,208 is shaped like a rectangular.

The method of any preceding method claim wherein at least five heaters are distributed about the perimeter 204 of inner zone 210.

The method of any preceding method claim wherein at least seven heaters are distributed about the perimeter 204 of inner zone 210.

The method of any preceding method claim wherein at least nine heaters are distributed about the perimeter 204 of inner zone 210.

The method of any preceding method claim wherein at least five heaters are distributed about the perimeter 208 of outer zone 214.

The method of any preceding method claim wherein at least seven heaters are distributed about the perimeter 204 of inner zone 210.

The method of any preceding method claim wherein at least nine heaters are distributed about the perimeter 208 of outer zone 214.

The method of any preceding method claim wherein at least ten heaters are distributed throughout inner zone 214.

The method of any preceding method claim wherein a majority of the heaters in inner zone 210 are electrical 242 heaters and a majority of the heaters in outer zone 214 are molten 244 salt heaters.

The method of any preceding method claim wherein the system further includes control apparatus configured to regulate heater operation times so that, on average, heaters in outer zone 214 operate above a one-half maximum power level for at least twice as long as the heaters in inner zone 210.

The method of any preceding method claim wherein the system includes control apparatus configured to regulate heater operation times so that, on average, outer zone heaters operate above a one-half maximum power level for at least twice as long as the inner zone heaters.

The method of any of preceding claim wherein an average inner-zone heater spacing is at most 20 meters.

The method of any of preceding claim wherein an average inner-zone heater spacing is at most 10 meters.

The method of any of preceding claim wherein an average inner-zone heater spacing is at most 5 meters.

The method of any of preceding claim wherein an area of the inner zone is at most one square kilometer.

The method of any of preceding claim wherein an area of the inner zone is at most 500 square meters.

The method of any preceding method claim wherein the heaters are configured to induce pyrolysis throughout substantial entireties of both the inner 210 and outer 214 zones.

The method of any preceding method claim wherein the heaters are configured to heat respective substantial entirety of the inner and outer regions to substantially the same uniform temperature.

The method of any preceding method claim wherein, among the inner zone heaters and/or outer zone heaters and/or inner perimeter heaters and/or outer perimeter heaters, a ratio between a standard deviation of the spacing and an average spacing is at most 0.2.

The method of any preceding method claim wherein all heaters have substantially the same maximum power level and/or substantially the same diameter.

The method of any preceding method claim wherein a ratio between the area of the inner 210 zone and a square of an average distance to a nearest heater within the inner 210 zone is at least 80.

The method of any preceding method claim wherein a ratio between the area of the inner 210 zone and a square of an average distance to a nearest heater within the inner 210 zone is at least 60.

The method of any preceding method claim wherein a ratio between the area of the inner 210 zone and a square of an average distance to a nearest heater within the inner 210 zone is at least 70.

The method of any preceding method claim wherein a ratio between the area of the inner 210 zone and a square of an average distance to a nearest heater within the inner 210 zone is at least 80.

The method of any preceding method claim wherein a ratio between the area of the inner 210 zone and a square of an average distance to a nearest heater within the inner 210 zone is at least 90.

The method of any preceding method claim wherein a ratio between the area of the inner 210 zone and a square of an average distance to a nearest heater within the inner 210 zone is at least 100.

The method of any preceding method claim wherein along a perimeter 208 of outer zone 214, an average distance to a nearest heater is at most 10% of a length of the outer zone perimeter 208.

The method of any preceding method claim wherein along a perimeter 208 of outer zone 214, an average distance to a nearest heater is at most 7.6% of a length of the outer zone perimeter 208.

The method of any preceding method claim wherein along a perimeter 208 of outer zone 214, an average distance to a nearest heater is at most 5% of a length of the outer zone perimeter 208.

The method of any preceding method claim wherein along a perimeter 208 of outer zone 214, an average distance to a nearest heater is at most 4% of a length of the outer zone perimeter 208.

The method of any preceding method claim wherein along a perimeter 208 of outer zone 214, an average distance to a nearest heater is at most 3% of a length of the outer zone perimeter 208.

The method of any preceding method claim wherein along a perimeter 204 of inner zone 210, an average distance to a nearest heater is at most 10% of a length of the outer zone perimeter 208.

The method of any preceding method claim wherein along a perimeter 204 of inner zone 210, an average distance to a nearest heater is at most 7.6% of a length of the outer zone perimeter 208.

The method of any preceding method claim wherein along a perimeter 204 of inner zone 210, an average distance to a nearest heater is at most 5% of a length of the outer zone perimeter 208.

The method of any preceding method claim wherein along a perimeter 204 of inner zone 210, an average distance to a nearest heater is at most 4% of a length of the outer zone perimeter 208.

The method of any preceding method claim wherein along a perimeter 204 of inner zone 210, an average distance to a nearest heater is at most 3% of a length of the outer zone perimeter 208.

The method of any preceding method claim wherein within the inner zone 210, an average distance to a nearest heater is at most one-eighth of a square root of an area of the inner zone 210.

The method of any preceding method claim wherein within the inner zone 210, an average distance to a nearest heater is at most one-tenth of a square root of an area of the inner zone 210.

The method of any preceding method claim wherein within the inner zone 210, an average distance to a nearest heater is at most one-twelfth of a square root of an area of the inner zone 210.

The method of any preceding method claim wherein within the inner zone 210, at most 30% of the inner zone is displaced from a nearest heater by length threshold equal to at most one quarter of a square root of the inner zone 210.

The method of any preceding method claim wherein within the inner zone 210, at most 20% of the inner zone is displaced from a nearest heater by length threshold equal to at most one quarter of a square root of the inner zone 210.

The method of any preceding method claim wherein within the inner zone 210, at most 10% of the inner zone is displaced from a nearest heater by length threshold equal to at most one quarter of a square root of the inner zone 210.

The method of any preceding method claim wherein the length threshold equals at most one fifth of a square root of the inner zone.

The method of any preceding method claim wherein an aspect ratio of the inner 210 and/or outer 214 zone is at most four.

The method of any preceding method claim wherein an aspect ratio of the inner 210 and/or outer 214 zone is at most three.

The method of any preceding method claim wherein an aspect ratio of the inner 210 and/or outer 214 zone is at most 2.5.

The method of any preceding method claim wherein among the inner 210 and outer 214 zones, a ratio between a greater aspect ratio and a lesser aspect ratio is at most 1.5.

The method of any preceding method claim wherein an isoperimetric quotient of perimeters 204, 208 of the inner 210 and/or outer 214 zone is at least 0.4.

The method of any preceding method claim wherein an isoperimetric quotient of perimeters 204, 208 of the inner 210 and/or outer 214 zone is at least 0.5.

The method of any preceding method claim wherein an isoperimetric quotient of perimeters 204, 208 of the inner 210 and/or outer 214 zone is at least 0.6.

The method of any preceding method claim wherein a perimeter 204 of inner zone 210 has a convex shape tolerance value of at most 1.2.

The method of any preceding method claim wherein a perimeter 204 of inner zone 210 has a convex shape tolerance value of at most 1.1.

The method of any preceding method claim wherein a perimeter 204 of inner zone 210 has a convex shape tolerance value of at most 1.05.

The method of any preceding method claim wherein a perimeter 208 of outer zone 214 has a convex shape tolerance value of at most 1.2.

The method of any preceding method claim wherein a perimeter 208 of outer zone 214 has a convex shape tolerance value of at most 1.1.

The method of any preceding method claim wherein a perimeter 208 of outer zone 214 has a convex shape tolerance value of at most 1.05.

The method of any preceding method claim wherein a perimeter 202 of OCS additional zone 218 has a convex shape tolerance value of at most 1.2.

The method of any preceding method claim wherein a perimeter 202 of OCS additional zone 218 has a convex shape tolerance value of at most 1.1.

The method of any preceding method claim wherein a perimeter 202 of OCS additional zone 218 has a convex shape tolerance value of at most 1.05.

The method of any preceding method claim wherein a perimeter of 204 of inner zone 210 is convex.

The method of any preceding method claim wherein a perimeter of 208 of outer zone 214 is convex.

The method of any preceding method claim wherein a perimeter of 202 of OCS additional zone 218 is convex.

The method of any preceding method claim wherein heaters are arranged within inner 210 zone so that inner zone heaters are present on every 72 degree sector thereof for any reference ray orientation.

The method of any preceding method claim wherein heaters are arranged within inner 210 zone so that inner zone heaters 226 are present on every 60 degree sector thereof for any reference ray orientation.

The method of any preceding method claim wherein heaters are arranged within inner 210 zone so that inner zone heaters 226 are present on every 45 degree sector thereof for any reference ray orientation.

The method of any preceding method claim wherein heaters are arranged within outer 214 zone so that outer zone heaters 228 are present on every 72 degree sector thereof for any reference ray orientation.

The method of any preceding method claim wherein heaters are arranged within outer 214 zone so that outer zone heaters 228 are present on every 60 degree sector thereof for any reference ray orientation.

The method of any preceding method claim wherein heaters are arranged within outer 214 zone so that outer zone heaters 228 are present on every 45 degree sector thereof for any reference ray orientation.

The method of any preceding method claim wherein heaters are arranged within OCS additional zone 218 so that heaters are present on every 72 degree sector thereof for any reference ray orientation.

A system for in-situ production of hydrocarbon fluids from a subsurface hydrocarbon-containing formation, the system comprising:

• a heater cell divided into nested inner 210 and outer 214 zones such that an area ratio between respective areas enclosed by substantially-convex polygon-shaped perimeters 208, 204 of the outer 214 and inner 210 zones is between two and seven, heaters being located at all polygon vertices of inner and outer zone perimeters 204, 208, inner zone 226 and outer zone heaters 228 being respectively distributed around inner 298 and outer 296 zone centroids such that an average heater spacing in outer zone 214 significantly exceeds that of inner zone 210, the system further comprising control apparatus configured to regulate heater operation times so that, on average, heaters in outer zone 214 operate above a one-half maximum power level for at least twice as long as the heaters in inner zone 210.

A system for in-situ production of hydrocarbon fluids from a subsurface hydrocarbon-containing formation, the system comprising:

• a heater cell divided into nested inner 210 and outer 214 zones such that an area ratio between respective areas enclosed by substantially-convex polygon-shaped perimeters 208, 204 of the outer 214 and inner 210 zones is between two and seven, heaters being located at all polygon vertices of inner and outer zone perimeters 204, 208, inner zone 226 and outer zone heaters 228 being respectively distributed around inner 298 and outer 296 zone centroids such that a heater spatial density in inner 210 zone significantly exceeds that of outer 214 zone, the system further comprising control apparatus configured to regulate heater operation times so that, on average, heaters in outer zone 214 operate above a one-half maximum power level for at least twice as long as the heaters in inner zone 210.

A system for in-situ production of hydrocarbon fluids from a subsurface hydrocarbon-containing formation, the system comprising:

• a heater cell divided into nested inner 210 and outer 214 zones such that an area ratio between respective areas enclosed by substantially-convex polygon-shaped perimeters 208, 204 of the outer 214 and inner 210 zones is between two and seven, inner zone 226 and outer zone heaters 228 being respectively distributed around inner 298 and outer 296 zone centroids such that (i) an average distance to a nearest heater within the outer zone significantly exceeds that of the inner zone;
• (ii) an average distance to a nearest heater on the inner zone perimeter 204 is substantially equal to that within inner zone 210;
• and (iii) an average distance to a nearest heater on the outer zone perimeter 208 is equal to at most about twice that on the inner zone perimeter 204, the system further comprising control apparatus configured to regulate heater operation times so that, on average, heaters in outer zone 214 operate above a one-half maximum power level for at least twice as long as the heaters in inner zone 210.

A system for in-situ production of hydrocarbon fluids from a subsurface formation, the system comprising:

• molten salt heaters and electrical heaters arranged within a target portion of the sub-surface formation.

The method or system of any previous claim wherein, within the target formation, a first heater that is a molten salt heater is located at most 50 meters from a second heater that is an electrical heater.

The method or system of any previous claim wherein, within the target formation, a first heater that is a molten salt heater is located at most 20 meters from a second heater that is an electrical heater.

The method or system of any previous claim wherein, within the target formation, a first heater that is a molten salt heater is located at most 10 meters from a second heater that is an electrical heater.

The method or system of any previous claim wherein, within the target formation, a first heater that is a molten salt heater is located at most 5 meters from a second heater that is an electrical heater.

The method or system of any previous claim wherein, within the target formation, the average separation distance between neighboring molten salt heaters significantly exceeds the average separation distance between neighboring electrical heaters.

The method or system of any previous claim wherein, within the target formation, the average separation distance between neighboring molten salt heaters is about twice the average separation distance between neighboring electrical heaters.

The method or system of any previous claim wherein, within the target portion, the average heater separation distance for electrical:molten-salt neighboring heater pairs significantly exceeds the average separation distance for all-electrical neighboring heater pairs.

The method or system of any previous claim wherein, within the target portion, the average heater separation distance for electrical:molten-salt neighboring heater pairs is about twice the average separation distance for all-electrical neighboring heater pairs.

The method or system of any previous claim wherein within the target portion, an average heater separation distance for all-molten-salt neighboring heater pairs is substantially equal to the average separation distance for electrical:molten-salt neighboring heater pairs neighboring heater pairs.

A system for in-situ production of hydrocarbon fluids from a subsurface hydrocarbon-containing formation, the system comprising:

• heaters arranged in a target portion of the formation, the target portion being divided into nested inner 210 and outer 214 zones heaters so that inner zone 226 and outer zone heaters 228 are respectively distributed around inner 298 and outer 296 zone centroids, a majority of the heaters in the inner zone 210 being electrical 242 heaters and a majority of the heaters in the outer zone 214 being molten 244 salt heaters.

The method of any preceding method claim wherein at least 25 heaters are arranged within the target region.

The method of any preceding method claim wherein at least 50 heaters are arranged within the target region.

The method of any preceding method claim wherein at least 100 heaters are arranged within the target region.

The method or system of any preceding claim wherein a substantially majority the heaters within the target region are electrical or molten-salt heaters.

The method or system of any preceding claim wherein at least 20% of the heaters within the target region are electrical heaters.

The method or system of any preceding claim wherein the target region has a length and a width of at most 500 meters.

The method or system of any preceding claim wherein the target region has a length and a width of at most 250 meters.

The method or system of any preceding claim wherein the target region has a length and a width of at most 100 meters.

The method or system of any preceding claim wherein the target region has a length and a width of at most 50 meters.

The method or system of any preceding claim wherein the hydrocarbon-containing bearing formation is a coal formation.

The method or system of any preceding claim wherein the hydrocarbon-containing bearing formation is an oil shale formation.

The method or system of any preceding claim wherein the hydrocarbon-containing bearing formation is a heavy oil formation.

The method or system of any preceding claim wherein the hydrocarbon-containing bearing formation is a tar sands formation.

The method or system of any preceding claim wherein the heaters are horizontally-oriented and a distance between heaters is measured in a vertical plane.

The method or system of any preceding claim wherein the heaters are vertically-oriented and a distance between heaters is measured in a horizontal plane.

The method or system of any preceding claim wherein the heaters are slanted and a distance between heaters is measured in a slanted plane.

The method or system of any preceding claim wherein an about-tolerance-parameter is at most 0.2 or at most 0.15 or at most 0.1 or at most 0.05.

The method or system of any preceding claim wherein at least some of the non-electric heaters, or a majority of the non-electric heaters, or a majority of heaters in the outer zone 214 are other than molten salt heaters.

The method or system of any preceding claim wherein at least some of the non-electric heaters, or a majority of the non-electric heaters, or a majority of heaters in the outer zone 214 are combustion-based heaters.

The method or system of any preceding claim wherein at least some of the non-electric heaters, or a majority of the non-electric heaters, or a majority of heaters in the outer zone 214 are advection-based heaters.

The method or system preceding claim wherein at least some of the non-electric heaters, or a majority of the non-electric heaters, or a majority of heaters in the outer zone 214 are advection-based heaters other than molten-salt heaters.