CA2441640A1 - Method for enhancing methane production from coal seams by inducing matrix shrinkage and placement of a propped fracture treatment - Google Patents
Method for enhancing methane production from coal seams by inducing matrix shrinkage and placement of a propped fracture treatment Download PDFInfo
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- CA2441640A1 CA2441640A1 CA 2441640 CA2441640A CA2441640A1 CA 2441640 A1 CA2441640 A1 CA 2441640A1 CA 2441640 CA2441640 CA 2441640 CA 2441640 A CA2441640 A CA 2441640A CA 2441640 A1 CA2441640 A1 CA 2441640A1
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- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 title claims abstract description 80
- 239000003245 coal Substances 0.000 title claims abstract description 68
- 206010017076 Fracture Diseases 0.000 title claims abstract description 62
- 208000010392 Bone Fractures Diseases 0.000 title claims abstract description 40
- 238000000034 method Methods 0.000 title claims abstract description 36
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 19
- 239000011159 matrix material Substances 0.000 title claims abstract description 18
- 238000011282 treatment Methods 0.000 title claims abstract description 12
- 230000001939 inductive effect Effects 0.000 title claims description 5
- 230000002708 enhancing effect Effects 0.000 title description 5
- 239000007789 gas Substances 0.000 claims description 31
- 230000000638 stimulation Effects 0.000 claims description 5
- 238000011065 in-situ storage Methods 0.000 claims description 3
- 238000003825 pressing Methods 0.000 claims description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims 2
- 229910052757 nitrogen Inorganic materials 0.000 claims 1
- 230000035699 permeability Effects 0.000 abstract description 12
- 238000002347 injection Methods 0.000 abstract description 11
- 239000007924 injection Substances 0.000 abstract description 11
- 230000008569 process Effects 0.000 abstract description 7
- 230000000694 effects Effects 0.000 abstract description 5
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 abstract description 5
- 238000006073 displacement reaction Methods 0.000 abstract description 4
- 230000001419 dependent effect Effects 0.000 abstract description 3
- 230000001965 increasing effect Effects 0.000 abstract description 3
- 239000012530 fluid Substances 0.000 description 8
- 230000004936 stimulating effect Effects 0.000 description 8
- 239000000126 substance Substances 0.000 description 7
- 230000015572 biosynthetic process Effects 0.000 description 5
- 238000005755 formation reaction Methods 0.000 description 5
- 239000011800 void material Substances 0.000 description 5
- 238000011084 recovery Methods 0.000 description 4
- 208000002565 Open Fractures Diseases 0.000 description 3
- 238000011161 development Methods 0.000 description 3
- 230000037361 pathway Effects 0.000 description 3
- 230000008901 benefit Effects 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- 238000000605 extraction Methods 0.000 description 2
- 230000014759 maintenance of location Effects 0.000 description 2
- 241000332699 Moneses Species 0.000 description 1
- 239000011260 aqueous acid Substances 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 230000000593 degrading effect Effects 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000003795 desorption Methods 0.000 description 1
- 230000003467 diminishing effect Effects 0.000 description 1
- 239000006260 foam Substances 0.000 description 1
- 230000000977 initiatory effect Effects 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 125000002320 montanoyl group Chemical group O=C([*])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])[H] 0.000 description 1
- 239000003345 natural gas Substances 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 230000008092 positive effect Effects 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 230000001902 propagating effect Effects 0.000 description 1
- 239000003507 refrigerant Substances 0.000 description 1
- 239000002002 slurry Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- 230000003068 static effect Effects 0.000 description 1
Classifications
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/006—Production of coal-bed methane
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/16—Enhanced recovery methods for obtaining hydrocarbons
- E21B43/166—Injecting a gaseous medium; Injecting a gaseous medium and a liquid medium
- E21B43/168—Injecting a gaseous medium
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/25—Methods for stimulating production
- E21B43/26—Methods for stimulating production by forming crevices or fractures
- E21B43/267—Methods for stimulating production by forming crevices or fractures reinforcing fractures by propping
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- Engineering & Computer Science (AREA)
- Geology (AREA)
- Life Sciences & Earth Sciences (AREA)
- Mining & Mineral Resources (AREA)
- Physics & Mathematics (AREA)
- Environmental & Geological Engineering (AREA)
- Fluid Mechanics (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Geochemistry & Mineralogy (AREA)
- Chemical Kinetics & Catalysis (AREA)
- General Chemical & Material Sciences (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Chemical & Material Sciences (AREA)
- Solid Fuels And Fuel-Associated Substances (AREA)
Abstract
Production of methane from coal seams is primarily dependent on the permeability of the coal. The present invention uses a three-step process to stimulate a coalbed methane well, wherein step one comprises injection of a predetermined gas into a well bore intersecting a coal seam, step two comprises a shut-in period and step three comprises the placement of propped fracture treatment. In step one, the injection of the predetermined gas physically opens pre-existing paths of weakness in the coal. As the predetermined gas travels along these planes of weakness, it preferentially adsorbs onto the coal and displaces the methane. This displacement process induces shrinkage of the coal matrix which further increases the size of the intervening existing fractures. The second step, or shut-in period, allows time for this gas exchange process to substantially complete, thereby maximizing the effect of matrix shrinkage and enhancement of the intervening fractures. The third step comprises placement of a propped fracture treatment into this enhanced fracture system. Propping of the enhanced fractures ensures that they remain open, even as removal of water and methane work to close the fractures by increasing effective stress within the coals. The result is a stimulated coal seam which maintains enhanced permeability during production operations.
Description
Baclc~round of the Invention 1~
1. Field of the Invention This invention relates to the stimulation of coal seams for methane recovery.
Coal seam Qas production is primarily dependent on the permeability of the coal seam.
Coal seam 20 reservoirs are fractured reservoirs wherein the fractures intervene between essentially impermeable blocks of coal matrix. As the fractures are the only effective pathways for movement of methane through a reservoir to a well-bore for recovery, the size, intensity and connectedness of the fractures determine the permeability and, hence, producibility of the reservoir. No known method exists for artificially creating fracturing within a coal seam on a reservoir wide scale, so techniques and methods for stimulating coal seam permeability are limited to enhancing the near well bore environment with the goal of effectively connecting the well bore to the existing natural fracture system.
S
Underground coal seams contain large amounts of natural gas, a significant amount of which is methane. The methane exists in a sorbed state in the coal and several techniques exist for increasing permeability near the wellbore and, hence, methane production.
Several challenges exist in creating an open pathway from the coals natural fracture system to the wellbore for the recovery of methane. Firstly, coals are known to possess stress dependent permeability, meaning that the application of additional effective stress upon a coal causes deformation which often closes the fracture system, thus degrading permeability and methane production. A critical challenge in stimulating coalbed methane wells is to design a completion technique that allows the fracture system to maintain an open posture throughout production, thereby minimizing the effect of stress dependence on permeability.
Secondly, the nature of prior art fracture treatment on coals also serves to damage and degrade coal permeability in some regions of the reservoir while simultaneously enhancing it in others. The intent of the prior art is that the enhanced regions of permeability outweigh the damaged areas, with a net positive effect to the near well-bore environment. In a prior art fracture treatment, proppant is entrained within a foam or water-based slurry into newly created and/or existing fractures within the coal seam. As these fractures are opened, stress is redistributed and other fractures which may be surrounding the opened fracture become pressed shut. This effect degrades the reservoir by diminishing the amount of reservoir effectively connected to the hydraulic fracture treatment. The object of the present invention minimizes this degradation by shrinking the coal matrix prior to the introduction of the propped fracture.
Prior art discloses three main techniques for stimulating coalbed methane wells. All of these techniques disclose injection of a treatment comprising various gases, fluids and/or proppants into the coal seam to fracture the coal.
The first technique is a chemical bath stimulation in which the coals are subjected to various aqueous-borne chemicals to either increase cleat or fracture development within the coals or to change a chemical characteristic of the coals. U.S patent 5,249,627 discloses a method for stimulating methane production from coal seams by treating the coals with various chemicals to improve the removal of water. No disclosures for either gas injection or proppant placement are made. U.S patent 5,470,823 discloses a method for stimulating methane production from coal seams by treating the coals with an aqueous acid solution. No disclosures for either gas injection or proppant placement are made. U.S patent 5,669,444 discloses a method for stimulating methane production from coal seams by treating the coals with various aqueous chemicals to increase fracture development. No disclosures for either gas injection or proppant placement are made.
U.S patents 5,669,444 and 5,964,290 disclose methods for stimulating methane production from coal seams by treating the coals with various aqueous chemicals to increase fracture development. No disclosures for either gas injection or proppant placement are made. None of these disclosed techniques follow the chemical treatments with a proppant.
The second type of stimulation is a one-stage completion technique relying on artificially initiating a fracture and/or propagating an existing fracture through the coals through the application of high pressure injection of gas and/or water based fracturing fluids.
Hydraulically fracturing coals is difficult given the plastic behavior of many coals, which tend to fracture at a greater treating pressure than the surrounding strata.
In a one-stage completion, the completion process is one continuous application of pressured fluid, with or without proppant, and the well is placed on production thereafter.
No attempts are made to induce shrinkage in the coal. U.S. patent 3,384,416 discloses a method where a refrigerant fluid containing a proppant is injected into a coal seam to create fracturing. The inducement of matrix shrinkage prior to proppant placement is undisclosed. U.S. Patent 6,412,559 B1 discloses method for recovering methane and/or sequestering fluids in coals whereby a gas more strongly adsorbing than methane with or without a proppant is injected into a coal seam, shut in for a period of time from hours to days and released. The inducement of matrix shrinkage prior to proppant placement is undisclosed.
The third type of completion is a cycled gas completion, in which gases are repeatedly injected and allowed to flow back, with the intention of causing in-situ failure of the coals and thereby inducing fracturing. U.S. patent 5,014,788 discloses a method for injecting a gas into a coal seam which is intended to swell the coals and increase stress within the coal. A rapid depressurization of the coals caused by suddenly releasing the pressurized gas to surface shrinks the coal, removing the induced stress, and mechanically failing the S coal. This process is designed to be repeated as many times as necessary. No disclosure is made for following this process with a propped fracture treatment. U.S.
patent 5,417,286 discloses a method for stimulating methane production from carbonaceous subterranean formations be injecting a first fluid to sorb into the formation and subsequently injecting a chemically different second fluid to part the formation and relieving the pressure to produce shear failure within the formation. No claims are made regarding the use of a proppant. U.S. patent 5,566,755 discloses a method for recovering methane from solid carbonaceous subterranean formations through the repeated injection and extraction of an oxygen depleted gas. No claims regarding subsequent placement of a proppant are made. U.S. Patent 6,412,559 B1 discloses method for recovering methane and/or sequestering fluids in coals whereby a gas more strongly adsorbing than methane and a proppant are simultaneously injected into a coal seam, shut in for a period of time from hours to days and released. U.S. Patent 6,450,256 discloses an enhanced coalbed gas production system whereby gases are injected into a coal seam and released. The injection of the gas increases methane production displacing water within the cleat system, by affecting the gas saturation within the coal and by reducing the partial pressure between the coal and the cleat system. No disclosure of introducing a proppant after release of the injected gas is made. U.S. Patent 6,571,874 B1 discloses method for extraction of in-situ methane from coals whereby gases are injected into a coal seam, shut in for a period of time from days to weeks and released. The process is repeated many times with the purpose of creating a propped fracture utilizing fines sourced from the coals themselves. This prior art method contains serious drawbacks. Firstly, fines control is considered a major problem in coalbed methane production, as the fines are known to migrate and plug open fractures, rather than maintain open fractures. As well, the low compressive strength of coal makes it a very poor candidate for a proppant, as the fines would be easily crushed into a damaging powder which would cause plugging.
This prior art method does not utilize an introduced proppant after release of the injected gas.
None of the prior art inventions utilize matrix shrinkage in coal and all fail to take into account the benefits of inducing matrix shrinkage first, followed by the placement of a propped fracture.
1. Field of the Invention This invention relates to the stimulation of coal seams for methane recovery.
Coal seam Qas production is primarily dependent on the permeability of the coal seam.
Coal seam 20 reservoirs are fractured reservoirs wherein the fractures intervene between essentially impermeable blocks of coal matrix. As the fractures are the only effective pathways for movement of methane through a reservoir to a well-bore for recovery, the size, intensity and connectedness of the fractures determine the permeability and, hence, producibility of the reservoir. No known method exists for artificially creating fracturing within a coal seam on a reservoir wide scale, so techniques and methods for stimulating coal seam permeability are limited to enhancing the near well bore environment with the goal of effectively connecting the well bore to the existing natural fracture system.
S
Underground coal seams contain large amounts of natural gas, a significant amount of which is methane. The methane exists in a sorbed state in the coal and several techniques exist for increasing permeability near the wellbore and, hence, methane production.
Several challenges exist in creating an open pathway from the coals natural fracture system to the wellbore for the recovery of methane. Firstly, coals are known to possess stress dependent permeability, meaning that the application of additional effective stress upon a coal causes deformation which often closes the fracture system, thus degrading permeability and methane production. A critical challenge in stimulating coalbed methane wells is to design a completion technique that allows the fracture system to maintain an open posture throughout production, thereby minimizing the effect of stress dependence on permeability.
Secondly, the nature of prior art fracture treatment on coals also serves to damage and degrade coal permeability in some regions of the reservoir while simultaneously enhancing it in others. The intent of the prior art is that the enhanced regions of permeability outweigh the damaged areas, with a net positive effect to the near well-bore environment. In a prior art fracture treatment, proppant is entrained within a foam or water-based slurry into newly created and/or existing fractures within the coal seam. As these fractures are opened, stress is redistributed and other fractures which may be surrounding the opened fracture become pressed shut. This effect degrades the reservoir by diminishing the amount of reservoir effectively connected to the hydraulic fracture treatment. The object of the present invention minimizes this degradation by shrinking the coal matrix prior to the introduction of the propped fracture.
Prior art discloses three main techniques for stimulating coalbed methane wells. All of these techniques disclose injection of a treatment comprising various gases, fluids and/or proppants into the coal seam to fracture the coal.
The first technique is a chemical bath stimulation in which the coals are subjected to various aqueous-borne chemicals to either increase cleat or fracture development within the coals or to change a chemical characteristic of the coals. U.S patent 5,249,627 discloses a method for stimulating methane production from coal seams by treating the coals with various chemicals to improve the removal of water. No disclosures for either gas injection or proppant placement are made. U.S patent 5,470,823 discloses a method for stimulating methane production from coal seams by treating the coals with an aqueous acid solution. No disclosures for either gas injection or proppant placement are made. U.S patent 5,669,444 discloses a method for stimulating methane production from coal seams by treating the coals with various aqueous chemicals to increase fracture development. No disclosures for either gas injection or proppant placement are made.
U.S patents 5,669,444 and 5,964,290 disclose methods for stimulating methane production from coal seams by treating the coals with various aqueous chemicals to increase fracture development. No disclosures for either gas injection or proppant placement are made. None of these disclosed techniques follow the chemical treatments with a proppant.
The second type of stimulation is a one-stage completion technique relying on artificially initiating a fracture and/or propagating an existing fracture through the coals through the application of high pressure injection of gas and/or water based fracturing fluids.
Hydraulically fracturing coals is difficult given the plastic behavior of many coals, which tend to fracture at a greater treating pressure than the surrounding strata.
In a one-stage completion, the completion process is one continuous application of pressured fluid, with or without proppant, and the well is placed on production thereafter.
No attempts are made to induce shrinkage in the coal. U.S. patent 3,384,416 discloses a method where a refrigerant fluid containing a proppant is injected into a coal seam to create fracturing. The inducement of matrix shrinkage prior to proppant placement is undisclosed. U.S. Patent 6,412,559 B1 discloses method for recovering methane and/or sequestering fluids in coals whereby a gas more strongly adsorbing than methane with or without a proppant is injected into a coal seam, shut in for a period of time from hours to days and released. The inducement of matrix shrinkage prior to proppant placement is undisclosed.
The third type of completion is a cycled gas completion, in which gases are repeatedly injected and allowed to flow back, with the intention of causing in-situ failure of the coals and thereby inducing fracturing. U.S. patent 5,014,788 discloses a method for injecting a gas into a coal seam which is intended to swell the coals and increase stress within the coal. A rapid depressurization of the coals caused by suddenly releasing the pressurized gas to surface shrinks the coal, removing the induced stress, and mechanically failing the S coal. This process is designed to be repeated as many times as necessary. No disclosure is made for following this process with a propped fracture treatment. U.S.
patent 5,417,286 discloses a method for stimulating methane production from carbonaceous subterranean formations be injecting a first fluid to sorb into the formation and subsequently injecting a chemically different second fluid to part the formation and relieving the pressure to produce shear failure within the formation. No claims are made regarding the use of a proppant. U.S. patent 5,566,755 discloses a method for recovering methane from solid carbonaceous subterranean formations through the repeated injection and extraction of an oxygen depleted gas. No claims regarding subsequent placement of a proppant are made. U.S. Patent 6,412,559 B1 discloses method for recovering methane and/or sequestering fluids in coals whereby a gas more strongly adsorbing than methane and a proppant are simultaneously injected into a coal seam, shut in for a period of time from hours to days and released. U.S. Patent 6,450,256 discloses an enhanced coalbed gas production system whereby gases are injected into a coal seam and released. The injection of the gas increases methane production displacing water within the cleat system, by affecting the gas saturation within the coal and by reducing the partial pressure between the coal and the cleat system. No disclosure of introducing a proppant after release of the injected gas is made. U.S. Patent 6,571,874 B1 discloses method for extraction of in-situ methane from coals whereby gases are injected into a coal seam, shut in for a period of time from days to weeks and released. The process is repeated many times with the purpose of creating a propped fracture utilizing fines sourced from the coals themselves. This prior art method contains serious drawbacks. Firstly, fines control is considered a major problem in coalbed methane production, as the fines are known to migrate and plug open fractures, rather than maintain open fractures. As well, the low compressive strength of coal makes it a very poor candidate for a proppant, as the fines would be easily crushed into a damaging powder which would cause plugging.
This prior art method does not utilize an introduced proppant after release of the injected gas.
None of the prior art inventions utilize matrix shrinkage in coal and all fail to take into account the benefits of inducing matrix shrinkage first, followed by the placement of a propped fracture.
2. Summary of the Invention The realization of this object, including advantageous embodiments and modifications of this invention can be seen from the content of the patent claims that follow this description.
The goal of the present invention is to provide a method to stimulate coalbed methane wells. The invention improves on the previously disclosed techniques as it uses the reaction of the coal to the predetermined gas to induce shrinkage within the coal matrix, thus reducing effective stress and enhancing the fracture void volume. This increased fracture void volume allows placement of proppant within the coals while maintaining open fractures in the regions surrounding the propped fracture, thus allowing the enhanced fracture system to communicate more effectively with both the natural fracture system and the wellbore and aiding methane recovery.
S
The goal of the present invention is to provide a method to stimulate coalbed methane wells. The invention improves on the previously disclosed techniques as it uses the reaction of the coal to the predetermined gas to induce shrinkage within the coal matrix, thus reducing effective stress and enhancing the fracture void volume. This increased fracture void volume allows placement of proppant within the coals while maintaining open fractures in the regions surrounding the propped fracture, thus allowing the enhanced fracture system to communicate more effectively with both the natural fracture system and the wellbore and aiding methane recovery.
S
3. Description of the Preferred Embodiments.
The present invention has the advantage that the pressing of the predetermined gas into the coal seam opens the existing natural fracture system within the coal and causes shrinkage of the coal such that when pressure is removed from the system the volume of the coals is less than the volume originally in place. This shrinkage results in additional fracture void volume and serves to create more and better connected pathways through the coal and lessens effective stress.
The object of the present invention is to stimulate a coalbed methane well by injecting a predetermined gas into a well bore that is open to a coal seam, shutting the well in to induce shrinkage of the coal seam and enhancement of the intervening natural fractures and then placing a propped fracture stimulation into the enhanced intervening fractures to maintain the fractures in an open state.
During the first stage injection of the predetermined gas, the gas travels into the fracture network along the fracture planes where it contacts the coal matrix and begins displacement of the methane contained within the coal matrix. This displacement shrinks the contacted portions of the coal matrix, resulting in an increase in the intervening fracture void volume.
In the second stage, the well is shut in for a period of time to allow the maximum amount of methane displacement to occur. In this manner, the coal is an active participant in the production of induced fractures and planes of weakness, with the interaction between the coal and the predetermined gas creating preferential paths of weakness within the coal.
This differs significantly from most prior art fracture treatments which treat the coal as a static medium and attempt to create new fractures within the coal by exceeding it's parting strength.
A second object of the invention is the maintenance of smaller scale fractures in an open posture surrounding the larger scale induced fractures. The second stage shut in period is critical to this effect as it allows the maximum amount of coal matrix to be bathed in the predetermined gas, thereby maximizing the reservoir volume treated for induced fracturing. Once the shut-in period has ended, matrix shrinkage has produced a similar effect to removal of matrix by creating additional void space in the enhanced fractures within the coal seam. This allows the proppant placed in stage three to occupy the enhanced fractures without producing excessively elevated local effective stress fields and collapsing the smaller scale fractures that occupy the region surrounding the propped fracture. In this fashion the propped fracture system maintains an effectively connected posture with both the reservoir's natural fracture system and the well bore and methane collection is enhanced.
Title: Method for enhancing methane production from coal seams by inducing matrix shrinkage and placement of a propped fracture treatment References Cited:
U.S. Patents 6,571,874 B1 6/2003 Lovenich et al.
6,450,256 B2 9/2002 Mones 6,412,559 7/2002 Gunter et al.
6,024,171 2/2000 Montgomery et al.
5,964,290 10/1999 Riese et al.
5,669,444 9/1997 Riese et al.
5,566,755 10/1996 Siedle et al.
S,S01,273 3/1996 Puri 5,470,823 11/1995 Williams et al.
5,417,286 5/199 Palmer et al.
5,249,627 10/1993 Harms et al.
5,014,788 5/1991 Puri et al.
Canadian Patent Applications 60/252,956 11/2000 Gunter et al.
Other References Puri, R., King, G.E., and Palmer, LD., 1991, Damage to coal permeability during hydraulic fracturing, Proceedings of the 1991 Coalbed Methane Symposium, The University of Alabama, Tuscaloosa, May 13 - 16, 1991.
St. George, J.D., and Barakat, M.A., 2001, The change in effective stress associated with shrinkage from gas desorption in coal, International Journal of Coal Geology, 45 (2001) pp. 105 - 113.
The present invention has the advantage that the pressing of the predetermined gas into the coal seam opens the existing natural fracture system within the coal and causes shrinkage of the coal such that when pressure is removed from the system the volume of the coals is less than the volume originally in place. This shrinkage results in additional fracture void volume and serves to create more and better connected pathways through the coal and lessens effective stress.
The object of the present invention is to stimulate a coalbed methane well by injecting a predetermined gas into a well bore that is open to a coal seam, shutting the well in to induce shrinkage of the coal seam and enhancement of the intervening natural fractures and then placing a propped fracture stimulation into the enhanced intervening fractures to maintain the fractures in an open state.
During the first stage injection of the predetermined gas, the gas travels into the fracture network along the fracture planes where it contacts the coal matrix and begins displacement of the methane contained within the coal matrix. This displacement shrinks the contacted portions of the coal matrix, resulting in an increase in the intervening fracture void volume.
In the second stage, the well is shut in for a period of time to allow the maximum amount of methane displacement to occur. In this manner, the coal is an active participant in the production of induced fractures and planes of weakness, with the interaction between the coal and the predetermined gas creating preferential paths of weakness within the coal.
This differs significantly from most prior art fracture treatments which treat the coal as a static medium and attempt to create new fractures within the coal by exceeding it's parting strength.
A second object of the invention is the maintenance of smaller scale fractures in an open posture surrounding the larger scale induced fractures. The second stage shut in period is critical to this effect as it allows the maximum amount of coal matrix to be bathed in the predetermined gas, thereby maximizing the reservoir volume treated for induced fracturing. Once the shut-in period has ended, matrix shrinkage has produced a similar effect to removal of matrix by creating additional void space in the enhanced fractures within the coal seam. This allows the proppant placed in stage three to occupy the enhanced fractures without producing excessively elevated local effective stress fields and collapsing the smaller scale fractures that occupy the region surrounding the propped fracture. In this fashion the propped fracture system maintains an effectively connected posture with both the reservoir's natural fracture system and the well bore and methane collection is enhanced.
Title: Method for enhancing methane production from coal seams by inducing matrix shrinkage and placement of a propped fracture treatment References Cited:
U.S. Patents 6,571,874 B1 6/2003 Lovenich et al.
6,450,256 B2 9/2002 Mones 6,412,559 7/2002 Gunter et al.
6,024,171 2/2000 Montgomery et al.
5,964,290 10/1999 Riese et al.
5,669,444 9/1997 Riese et al.
5,566,755 10/1996 Siedle et al.
S,S01,273 3/1996 Puri 5,470,823 11/1995 Williams et al.
5,417,286 5/199 Palmer et al.
5,249,627 10/1993 Harms et al.
5,014,788 5/1991 Puri et al.
Canadian Patent Applications 60/252,956 11/2000 Gunter et al.
Other References Puri, R., King, G.E., and Palmer, LD., 1991, Damage to coal permeability during hydraulic fracturing, Proceedings of the 1991 Coalbed Methane Symposium, The University of Alabama, Tuscaloosa, May 13 - 16, 1991.
St. George, J.D., and Barakat, M.A., 2001, The change in effective stress associated with shrinkage from gas desorption in coal, International Journal of Coal Geology, 45 (2001) pp. 105 - 113.
Claims (2)
1. A method for in-situ stimulation of a methane production from a methane-bearing subterranean coal seam, said method comprising:
2. A first step of opening flow paths in a methane-bearing subterranean coal seam by pressing a predetermined gas into a wellbore intersecting said subterranean coal seam;
a second step comprising a shut-in period of pre-determined duration whereby said predetermined gas displaces methane from said subterranean coal seam thereby inducing matrix shrinkage in said subterranean coal seam, resulting in enhanced intervening fractures, and;
a third step comprising pressing of a fracture treatment containing proppant into said enhanced intervening fractures.
2. The method of claim 1 wherein said predetermined gas is comprised substantially of nitrogen.
a second step comprising a shut-in period of pre-determined duration whereby said predetermined gas displaces methane from said subterranean coal seam thereby inducing matrix shrinkage in said subterranean coal seam, resulting in enhanced intervening fractures, and;
a third step comprising pressing of a fracture treatment containing proppant into said enhanced intervening fractures.
2. The method of claim 1 wherein said predetermined gas is comprised substantially of nitrogen.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2441640 CA2441640A1 (en) | 2003-09-19 | 2003-09-19 | Method for enhancing methane production from coal seams by inducing matrix shrinkage and placement of a propped fracture treatment |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2441640 CA2441640A1 (en) | 2003-09-19 | 2003-09-19 | Method for enhancing methane production from coal seams by inducing matrix shrinkage and placement of a propped fracture treatment |
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| Publication Number | Publication Date |
|---|---|
| CA2441640A1 true CA2441640A1 (en) | 2005-03-19 |
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| Application Number | Title | Priority Date | Filing Date |
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| CA 2441640 Abandoned CA2441640A1 (en) | 2003-09-19 | 2003-09-19 | Method for enhancing methane production from coal seams by inducing matrix shrinkage and placement of a propped fracture treatment |
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| CA (1) | CA2441640A1 (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2027362A1 (en) * | 2006-03-03 | 2009-02-25 | Gasfrac Energy Services Inc. | Liquified petroleum gas fracturing system |
| CN101575983B (en) * | 2009-02-27 | 2012-07-04 | 河南省煤层气开发利用有限公司 | Directional fracturing permeability improvement outburst elimination method in coal mine and device thereof. |
| US8276659B2 (en) | 2006-03-03 | 2012-10-02 | Gasfrac Energy Services Inc. | Proppant addition system and method |
| CN115822536A (en) * | 2023-02-08 | 2023-03-21 | 太原理工大学 | Carbon dioxide injection displacement type coalbed methane collecting device and using method thereof |
-
2003
- 2003-09-19 CA CA 2441640 patent/CA2441640A1/en not_active Abandoned
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2027362A1 (en) * | 2006-03-03 | 2009-02-25 | Gasfrac Energy Services Inc. | Liquified petroleum gas fracturing system |
| EP2027362A4 (en) * | 2006-03-03 | 2011-03-30 | Gasfrac Energy Services Inc | Liquified petroleum gas fracturing system |
| US8276659B2 (en) | 2006-03-03 | 2012-10-02 | Gasfrac Energy Services Inc. | Proppant addition system and method |
| US8408289B2 (en) | 2006-03-03 | 2013-04-02 | Gasfrac Energy Services Inc. | Liquified petroleum gas fracturing system |
| AU2007219687B2 (en) * | 2006-03-03 | 2013-05-09 | Gasfrac Energy Services Inc. | Liquified petroleum gas fracturing system |
| CN101575983B (en) * | 2009-02-27 | 2012-07-04 | 河南省煤层气开发利用有限公司 | Directional fracturing permeability improvement outburst elimination method in coal mine and device thereof. |
| CN115822536A (en) * | 2023-02-08 | 2023-03-21 | 太原理工大学 | Carbon dioxide injection displacement type coalbed methane collecting device and using method thereof |
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