US 4,282,587 AGranted

Method for monitoring the recovery of minerals from shallow geological formations

OwnerDaniel Silvermaninventor

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Abstract

In the process of recovering minerals, such as hydrocarbons from shallow tar sands, and the like, one method is to create a shallow horizontal fracture within the tar sand. The size and shape of the perimeter is determined, and one or more secondary boreholes are drilled to the formation inside of the perimeter of the fracture. Pressurized air is injected into the fracture and the hydrocarbons are ignited. After a selected period of burning is carried out, the radius to the burn front, surrounding the recovery area, from which the hydrocarbons have been removed, is determined by placing a source of seismic waves at a selected point over the fracture, and a long array of seismic sensors colinear with the source. The source is energized for different conditions of pressurization in the formation and fracture. The reflected seismic waves are converted to electrical signals, which are compared for all sensors. By comparison of the character and/or energy of the reflections, the geometry of the burn zone can be determined.

In a mineral recovery operation including a shallow substantially horizontal geological formation containing said minerals a first borehole drilled to said formation, a substantially horizontal fracture in said formation resulting from the prior application of pressurized fracture fluid to said formation through said first borehole, a second borehole drilled to said formation at a selected radius from said first borehole less than the radius of the outer perimeter of said fracture, said mineral adapted to be removed from said formation by flowing a selected recovery fluid downwardly through said first borehole, outwardly through said fracture to said second borehole and upwardly to the surface;

where said minerals are recovered;
the method of mapping at a plurality of points at different radii, the shape and size of the zone in said formation, surrounding said first borehole, from which said mineral has been removed after said recovery fluid has been flowing for a first selected time interval T1, comprising the steps of;
(a) providing a first source of seismic waves at or near the surface at at least one point above said fracture;
(b) positioning at or near the surface of the earth a plurality of seismic sensors, such as geophones, at selected known positions, said sensors adapted to receive the upward reflection of downwardly directed seismic waves generated by said source, and to convert them to electrical signals;
(c) pressurizing said previously prepared fracture with a selected pressurizing fluid to a condition P, where the overburden is lifted and the roof of said fracture is out of contact with the base of said fracture, and at least a thin layer of said pressurizing fluid fills said fracture and said cavity;
(d) operating said first source and receiving said seismic waves reflected from the roof of said fracture and said zone and recording a first electrical signal from each of said sensors;
and
(e) comparing said first electrical signal from at least two of said sensors.

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Abstract

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