Oil and gas well stimulation

Apparatus for stimulating a well that has a casing which can withstand a rock fracturing detonation, and which has a pay zone with rock formation exposed through the casing to permit fluid access to said rock formation, comprising:

• a source of a fracturing fluid,
• means to transfer said fracturing fluid from said source into said well to a level above said pay zone,
• means for rendering the portion of said well including said fracturing fluid gas tight, and
• means for applying a shock wave to said fracturing fluid, which has a rise time faster than the time required for sound to traverse one half of the periphery of the well opening in said rock at said pay zone, and which when applied to said rock by said fluid has an amplitude which will fracture said rock but which is less than the amplitude required to crush said rock, whereby said rock formation at said predetermined depth is fractured and fluid is forced into the fractures.

Apparatus for stimulating a well that has a pay zone at a predetermined depth that has exposed rock comprising:

• means for applying a stress wave to the rock at said pay zone with an amplitude sufficient to cause fractures in said rock without crushing same, and having a rise time faster than the time required for sound to traverse one half of the perimeter of said rock at said pay zone, including
• a source of a fracturing fluid,
• means for transferring fracturing fluid from said source into said well to fill said well to a level above said pay zone,
• means for sealing the portion of said well including said fluid and pay zone, and
• means for applying a detonation to said fracturing fluid which produces a stress wave therein which when applied thereby to said rock at said pay zone will provide said indicated stress wave.

A method of fracturing the rock formation at a predetermined depth in a well, comprising:

• establishing an elongated chamber in said well of material which can withstand a detonation which can fracture rock, and which has an upper portion which is gas tight and a lower portion extending beyond said predetermined depth and having openings at said predetermined depth to permit fluid outflow to said rock formation;
• filling said lower portion of said chamber with fracturing fluid above the level of said predetermined depth until said upper portion has been reached;
• filling the upper portion of said chamber with a predetermined pressure of a gas, which when detonated creates a shock wave in said fracturing fluid having a rise time which is less than the time required for sound to traverse one half of the periphery of the well opening in said rock, at said pay zone and which has an amplitude which will fracture said rock but which is less than the amplitude required to crush that rock, and;
• detonating said detonatable gas to produce said shock wave which fractures said rock formation at said predetermined depth and forces said fracturing fluid through said open region of said lower chamber portion into the fractures in said rock formation.

A well stimulation method for use in a hydrocarbon well that extends into a pay zone that lies at least several hundred feet below the surface of the earth, and wherein the well has a casing which can withstand a detonation which can fracture rock, said casing having openings for the outflow of fluid to the rock formation at said pay zone, comprising:

• pumping a fracturing fluid down into said well to a level substantially above said pay zone to fill at least a lower portion of said well with a column of said fluid;
• covering the top of said well to render the upper portion of said well above said fluid level gas tight;
• filling said upper portion of said well with a detonatable gas at a pressure which when detonated generates a shock wave in said fracturing fluid having a rise time which is less than the time required for sound to traverse one half of the periphery of the rock around the opening in said well at said pay zone, which has an amplitude which can fracture rock but is less than the amplitude required to crush said rock, and
• detonating said gas to cause the creation of multiple fractures in said rock at said pay zone and to create a high pressure reservoir of gaseous combustion products that pump at least some of said fracturing fluid through said well casing into the rock fractures around said pay zone.

Apparatus for stimulating a well that has a casing which can withstand a rock fracturing detonation and which has openings therein to permit fluid access to the rock formation at a pay zone comprising:

• a source of fracturing fluid;
• means to fill said well with said fracturing fluid from said source, to a level above said pay zone but leaving unfilled a substantial region of said well above the level of said fluid;
• means for rendering the portion of said well above the level of said fracturing fluid gas tight,
• a source of a detonable gas, which, under a predetermined pressure, when detonated produces a shock wave in said fracturing fluid having an amplitude which has a rise time faster than the time required for sound to traverse one half of the perimeter of the rock at said pay zone, an amplitude which is sufficient to fracture rock but is less than is required to crush rock;
• means for filling said substantial region of said well with said gas under said predetermined pressure;
• and
• means for detonating said gas whereby a multiplicity of radial fractures are established in said rock formation at said pay zone.

Apparatus for stimulating a well that has a pay zone at a predetermined depth comprising:

• means for applying a stress wave to the rock at said pay zone with an amplitude sufficient to cause fractures in said rock without crushing same, and having a rise time sufficiently rapid to avoid stress and pressure relief by any of said fractures, including
• pipe means for establishing an enclosed chamber within said well which extends from the top of said well below said predetermined depth, which has openings to said pay zone, and which can withstand a detonation which will fracture rock;
• a source of a fracturing fluid;
• means for filling said chamber in said pipe means with said fracturing fluid to a level above said pay zone but leaving a substantial unfilled region of said well above the level of said fluid,
• a source of a detonatable gas which when a predetermined quantity under a predetermined pressure is detonated produces a shock wave in said fracturing fluid which has a rise time faster than the time required for sound to traverse through one half of the perimeter of the rock formation at the pay zone, which has an amplitude which can fracture rock but is less than that required to crush rock;
• means for filling the substantial unfilled region of said well with said predetermined quantity at said predetermined pressure of said gas from said source, and
• means for detonating said gas.