CN116641685A - Underground coal bed gas extraction method for closed goaf - Google Patents
Underground coal bed gas extraction method for closed goaf Download PDFInfo
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- CN116641685A CN116641685A CN202310510524.4A CN202310510524A CN116641685A CN 116641685 A CN116641685 A CN 116641685A CN 202310510524 A CN202310510524 A CN 202310510524A CN 116641685 A CN116641685 A CN 116641685A
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- 239000003245 coal Substances 0.000 title claims abstract description 123
- 238000000605 extraction Methods 0.000 title claims abstract description 72
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims abstract description 74
- 238000000034 method Methods 0.000 claims abstract description 57
- 238000005553 drilling Methods 0.000 claims abstract description 35
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 25
- 238000007789 sealing Methods 0.000 claims abstract description 24
- 238000005065 mining Methods 0.000 claims abstract description 23
- 238000004364 calculation method Methods 0.000 claims abstract description 14
- 238000004088 simulation Methods 0.000 claims abstract description 6
- 238000012937 correction Methods 0.000 claims abstract description 4
- 239000011241 protective layer Substances 0.000 claims abstract description 4
- 239000011435 rock Substances 0.000 claims description 42
- 239000000523 sample Substances 0.000 claims description 40
- 230000010354 integration Effects 0.000 claims description 18
- 238000012360 testing method Methods 0.000 claims description 12
- 238000009933 burial Methods 0.000 claims description 11
- 238000005086 pumping Methods 0.000 claims description 11
- 230000003287 optical effect Effects 0.000 claims description 10
- 230000008859 change Effects 0.000 claims description 9
- 238000011161 development Methods 0.000 claims description 9
- 238000004519 manufacturing process Methods 0.000 claims description 8
- 239000010410 layer Substances 0.000 claims description 7
- 238000004458 analytical method Methods 0.000 claims description 6
- 238000009826 distribution Methods 0.000 claims description 6
- 238000005259 measurement Methods 0.000 claims description 6
- 230000007246 mechanism Effects 0.000 claims description 6
- SLXKOJJOQWFEFD-UHFFFAOYSA-N 6-aminohexanoic acid Chemical compound NCCCCCC(O)=O SLXKOJJOQWFEFD-UHFFFAOYSA-N 0.000 claims description 3
- 230000015572 biosynthetic process Effects 0.000 claims description 3
- 239000000084 colloidal system Substances 0.000 claims description 3
- 238000005520 cutting process Methods 0.000 claims description 3
- 238000010586 diagram Methods 0.000 claims description 3
- 238000005755 formation reaction Methods 0.000 claims description 3
- 238000011835 investigation Methods 0.000 claims description 3
- 238000004806 packaging method and process Methods 0.000 claims description 3
- 238000012545 processing Methods 0.000 claims description 3
- 239000000565 sealant Substances 0.000 claims description 3
- 238000003860 storage Methods 0.000 claims 1
- 210000004027 cell Anatomy 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 1
- 210000005056 cell body Anatomy 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 238000005457 optimization Methods 0.000 description 1
- 230000002265 prevention Effects 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
Classifications
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- 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
-
- 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
- E21B17/00—Drilling rods or pipes; Flexible drill strings; Kellies; Drill collars; Sucker rods; Cables; Casings; Tubings
-
- 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
- E21B47/00—Survey of boreholes or wells
-
- 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
- E21B49/00—Testing the nature of borehole walls; Formation testing; Methods or apparatus for obtaining samples of soil or well fluids, specially adapted to earth drilling or wells
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21F—SAFETY DEVICES, TRANSPORT, FILLING-UP, RESCUE, VENTILATION, OR DRAINING IN OR OF MINES OR TUNNELS
- E21F7/00—Methods or devices for drawing- off gases with or without subsequent use of the gas for any purpose
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- Life Sciences & Earth Sciences (AREA)
- Geology (AREA)
- Physics & Mathematics (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Geochemistry & Mineralogy (AREA)
- Environmental & Geological Engineering (AREA)
- Fluid Mechanics (AREA)
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- Investigation Of Foundation Soil And Reinforcement Of Foundation Soil By Compacting Or Drainage (AREA)
Abstract
The invention provides a closed goaf coal bed methane underground extraction method, and belongs to the technical field of coal bed methane exploitation. The method comprises the following steps: s1, reservoir space boundary calculation: judging the goaf pressure relief influence range indirectly through a ground geophysical prospecting method and by utilizing a method combining three-subzone coal mining water guide fracture zone height theory and a protective layer mining theory with numerical simulation correction, and determining the goaf reservoir space boundary; s2, underground extraction directional long drilling arrangement of coal bed gas in a closed goaf; s3, sealing underground extraction hole sealing and extraction of coal bed gas in the goaf. According to the method, the pressure relief range of the goaf can be effectively identified through reservoir space boundary calculation, the directional long drilling arrangement and the downhole extraction hole sealing of the goaf coal bed gas are realized, the goaf coal bed gas extraction efficiency is improved, and the resource utilization rate is further improved.
Description
Technical Field
The invention relates to the technical field of coalbed methane exploitation, in particular to a closed goaf coalbed methane underground extraction method.
Background
With the optimization of energy structure and the adjustment of coal industry structure, a large batch of backward productivity coal mines are closed and withdrawn in China. The shut-down mine and the production mine leave a large number of old goafs in which a large amount of valuable coalbed methane resources are accumulated. From the aspects of coal mine gas disaster prevention and control and coal bed gas resource development and utilization, coal bed gas resource development of a closed goaf of a closed/abandoned/produced mine is more and more valued and supported by national level policies, and is a hotspot and an important point of future industrial development, but the research on the pressure relief influence range of the goaf, the arrangement of extraction drilling holes, the hole sealing process and the like in the current stage is insufficient, and the extraction and utilization of the coal bed gas resource of the goaf are not sufficiently supported.
Disclosure of Invention
In order to overcome the defects, the invention provides a closed goaf coal bed methane underground extraction method, which aims to solve the problems in the background technology.
The embodiment of the invention provides a closed goaf coal bed methane underground extraction method, which comprises the following steps:
s1, reservoir space boundary calculation: judging the goaf pressure relief influence range indirectly through a ground geophysical prospecting method and by utilizing a method combining three-subzone coal mining water guide fracture zone height theory and a protective layer mining theory with numerical simulation correction, and determining the goaf reservoir space boundary;
s2, directional long drilling arrangement for underground extraction of coal bed gas in a closed goaf: extracting coal bed gas underground by utilizing a large-diameter directional long drilling hole, enabling a drilling track to avoid the pressure relief influence range of a goaf through reservoir space boundary calculation, arranging the drilling track in a rock stratum with a certain distance above a roadway, and then downwards pricking to a rock-covering fracture zone;
s3, sealing underground extraction hole sealing and extraction of coal bed gas in a closed goaf: and determining the distance between the lower extraction pipe in the drill hole, the depth of the two-plug one-injection-belt pressure sealing hole, the vertical height of the sealing hole section and the extraction negative pressure parameters according to the extraction characteristics of the coalbed methane in the sealed goaf, and extracting the coalbed methane.
In a specific embodiment, the reservoir space boundary calculation in S1 further includes: geological investigation is carried out on the whole coal rock stratum in the goaf before mining, a full-rock core is drilled, and a full-rock histogram is drawn; and performing physical and mechanical property test on the all-rock core to obtain stress-strain curves and basic physical and mechanical parameters of each rock stratum, wherein the physical and mechanical property test comprises the following steps: density, modulus of elasticity, poisson's ratio, internal friction angle, cohesion, uniaxial compressive strength, triaxial peak strength.
In a specific embodiment, the ground geophysical prospecting method specifically completes the identification of the goaf reservoir space boundary by simulating the principle of searching and prospecting by utilizing the difference of physical characteristics of the geological body in the geophysical prospecting method.
In a specific embodiment, the coal mining water diversion fracture zone height theory comprises a water diversion fracture zone height prediction method, and the water diversion fracture zone height prediction method specifically comprises the following steps:
s101, calculating the movement deformation of the horizontal rock formations with different burial depths of the overburden by using a probability integration method on the basis of the estimated parameter analysis of the probability integration method of the overburden;
s102, representing the development degree of the crack in the normal direction of the rock layer surface in the overburden by using the stratum surface stretching rate epsilon S, so as to measure the capability of the stratum crack to pass through water or gas;
s103, drawing a layer stretching rate distribution diagram of the horizontal rock stratum at different burial depths on the basis of the calculation of the moving deformation of the overlying strata;
s104, determining the critical surface stretching rate epsilon' S of water diversion of different lithology rock strata on the basis of analysis of the actual measurement value of the development height of the water diversion fracture zone of the overburden rock;
s105, judging the stratum stretching rate distribution map of the horizontal strata of different burial depths of the target mine by using the stratum water-guiding critical stratum stretching rate epsilon' S, and obtaining the predicted value of the coal mining overburden water-guiding fracture zone height under the water body.
In a specific embodiment, the function of the overburden probability integration parameter with respect to the depth of burial z in S101 includes a dip coefficient q (z), an inflection point offset S (z), and a dominant influence radius R (z), and the specific formula is as follows:
wherein: n is n q As the dip coefficient influence coefficient, the dip coefficient is related to the lithology of the overburden; n is n r The method is mainly used for influencing radius influence coefficients, and is related to lithology of overburden rock; n is n s The inflection point offset distance influence coefficient is related to the lithology of the overburden rock; z is the depth of the rock stratum and m; h 0 The depth of the coal bed is m; q 0 Is the sinking coefficient of the earth surface; s is S 0 The inflection point offset distance at the ground surface is m; r is R 0 Is the ground surfaceMainly affecting the radius, m.
In a specific embodiment, the overburden probability integration prediction parameters are in accordance with earth surface movement deformation probability integration parameters: coefficient q of subsidence at earth's surface 0 Inflection point offset S at the earth' S surface 0 And the major influence radius R at the earth's surface 0 And the probability integration method parameters of the earth surface movement deformation are calculated according to the actual measurement data of the earth surface movement observation station and the curve fitting method.
In a specific embodiment, before the arrangement of the underground extraction directional long drilling holes of the coalbed methane in the sealed goaf in the step S2, the method for simulating the extraction directional long drilling holes of the extraction drill further comprises the following steps:
s201, coal body collection: collecting coal bodies of typical geological units underground, conveying the coal bodies to the ground, then carrying out wax sealing, and packaging;
s202, preparing a coal sample: processing and cutting the collected coal body into a cubic coal body sample with the thickness of 300mm multiplied by 300mm, uniformly smearing the surface of the coal body sample with sealant, and curing the colloid with the thickness of more than 1mm;
s203, fixing and stress pressurization of a coal body sample: putting a coal body sample into a true triaxial pressure test device, and applying different stresses in all directions by adjusting three vertical pressurizing mechanisms;
s204, after the stress applied on the coal body sample is constant, an electric drill is used for forming an observation hole at a corresponding position on the side surface of the pressure box, which is designed in advance, and a gas extraction drill hole is formed on the coal body sample, a probe and a probe of an optical drilling deformation observation device are inserted into the sample hole, the aperture change condition is automatically observed, and an aperture change curve is drawn;
s205, observing the evolution condition of the coal body cracks around the drill hole by a microscope and a camera while the optical drilling deformation observation device automatically observes the aperture change, and analyzing the evolution rule of the coal body cracks around the drill hole.
In a specific embodiment, the true triaxial pressure test device comprises a pressure box for placing a coal body sample, three vertical pressurizing mechanisms and an observation hole, wherein the pressure box comprises a box body, a pressurizing plate and an optical drilling deformation observation device, the optical drilling deformation observation device comprises a probe, a probe and an aperture measuring instrument, and the coal body crack evolution observation device comprises a microscope, a camera and a three-dimensional moving microscopic observation frame.
In a specific embodiment, the sealing and extraction of the underground coal bed methane extraction hole of the sealed goaf in the step S3 further comprises the following steps:
s301, constructing a ground coal bed gas pre-pumping well above a goaf roadway, wherein the coal bed gas pre-pumping well is a directional inclined vertical well, a target spot falls on a stoping line of a coal mine planning underground mining working face, and a production sleeve of the coal bed gas pre-pumping well is not cut off after the underground mining working face is stoped to the stoping line;
s302, hermetically connecting a reserved extraction pipeline of the coal face with a production sleeve of a coalbed methane pre-extraction well;
s303, changing the ground extraction equipment of the coal bed gas pre-extraction well into a vacuum pump for extracting the coal bed gas in the goaf under negative pressure.
In a specific embodiment, the diameter of a first open hole in the coal bed methane pre-pumping well is 440-445mm, the diameter of a sleeve is 376-378mm, the diameter of a second open hole is 311-313mm, the diameter of a sleeve is 244-245mm, the diameter of a third open hole is 214-216mm, and the diameter of a sleeve is 138-140mm.
Compared with the prior art, the invention has the beneficial effects that:
the invention provides a goaf extraction technical method for solving the underground extraction problem of the coal bed gas of a closed goaf, wherein the goaf coal bed gas is subjected to underground extraction directional long drilling arrangement and the goaf coal bed gas is subjected to underground extraction hole sealing and extraction by calculating the boundary of a reservoir space, so that the pressure relief range of the goaf can be effectively identified, the goaf coal bed gas efficiency of the directional drilling extraction goaf is improved, and the resource utilization rate is further improved.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed in the embodiments will be briefly described below, it being understood that the following drawings only illustrate some examples of the present invention and therefore should not be considered as limiting the scope, and other related drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a flow chart provided by an embodiment of the present invention;
fig. 2 is a schematic drawing of goaf extraction according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be described below with reference to the accompanying drawings in the embodiments of the present invention.
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, based on the embodiments of the invention, which are apparent to those of ordinary skill in the art without inventive faculty, are intended to be within the scope of the invention.
Referring to fig. 1-2, the invention provides a method for extracting coalbed methane in a closed goaf underground, which comprises the following steps:
s1, reservoir space boundary calculation: judging the goaf pressure relief influence range indirectly through a ground geophysical prospecting method and by utilizing a method combining three-subzone coal mining water guide fracture zone height theory and a protective layer mining theory with numerical simulation correction, and determining the goaf reservoir space boundary;
s2, directional long drilling arrangement for underground extraction of coal bed gas in a closed goaf: extracting coal bed gas underground by utilizing a large-diameter directional long drilling hole, enabling a drilling track to avoid the pressure relief influence range of a goaf through reservoir space boundary calculation, arranging the drilling track in a rock stratum with a certain distance above a roadway, and then downwards pricking to a rock-covering fracture zone;
s3, sealing underground extraction hole sealing and extraction of coal bed gas in a closed goaf: and determining the distance between the lower extraction pipe in the drill hole, the depth of the two-plug one-injection-belt pressure sealing hole, the vertical height of the sealing hole section and the extraction negative pressure parameters according to the extraction characteristics of the coalbed methane in the sealed goaf, and extracting the coalbed methane.
Specifically, the reservoir space boundary calculation in S1 further includes: geological investigation is carried out on the whole coal rock stratum in the goaf before mining, a full-rock core is drilled, and a full-rock histogram is drawn; and performing physical and mechanical property test on the all-rock core to obtain stress-strain curves and basic physical and mechanical parameters of each rock stratum, wherein the physical and mechanical property test comprises the following steps: density, modulus of elasticity, poisson's ratio, internal friction angle, cohesion, uniaxial compressive strength, triaxial peak strength.
When the method is specifically arranged, the ground geophysical prospecting method specifically realizes the identification of the space boundary of the goaf reservoir by simulating the principle of searching and prospecting by utilizing the difference of physical characteristics of the geological body in the geophysical prospecting method.
The coal mining water diversion fracture zone height theory comprises a water diversion fracture zone height prediction method, and the water diversion fracture zone height prediction method specifically comprises the following steps of:
s101, calculating the movement deformation of the horizontal rock formations with different burial depths of the overburden by using a probability integration method on the basis of the estimated parameter analysis of the probability integration method of the overburden;
s102, representing the development degree of the crack in the normal direction of the rock layer surface in the overburden by using the stratum surface stretching rate epsilon S, so as to measure the capability of the stratum crack to pass through water or gas;
s103, drawing a layer stretching rate distribution diagram of the horizontal rock stratum at different burial depths on the basis of the calculation of the moving deformation of the overlying strata;
s104, determining the critical surface stretching rate epsilon' S of water diversion of different lithology rock strata on the basis of analysis of the actual measurement value of the development height of the water diversion fracture zone of the overburden rock;
s105, judging the stratum stretching rate distribution map of the horizontal strata of different burial depths of the target mine by using the stratum water-guiding critical stratum stretching rate epsilon' S, and obtaining the predicted value of the coal mining overburden water-guiding fracture zone height under the water body.
In some specific embodiments, the function of the overburden probability integration parameters with respect to the borehole depth z in S101 includes a dip coefficient q (z), an inflection point offset S (z), and a dominant impact radius R (z), and the specific formulas are as follows:
wherein: n is n q As the dip coefficient influence coefficient, the dip coefficient is related to the lithology of the overburden; n is n r The method is mainly used for influencing radius influence coefficients, and is related to lithology of overburden rock; n is n s The inflection point offset distance influence coefficient is related to the lithology of the overburden rock; z is the depth of the rock stratum and m; h 0 The depth of the coal bed is m; q 0 Is the sinking coefficient of the earth surface; s is S 0 The inflection point offset distance at the ground surface is m; r is R 0 The radius, m, is primarily affected at the surface.
In other embodiments, the overburden probability integration prediction parameters are in accordance with earth surface movement deformation probability integration parameters: coefficient q of subsidence at earth's surface 0 Inflection point offset S at the earth' S surface 0 And the major influence radius R at the earth's surface 0 And the probability integration method parameters of the earth surface movement deformation are calculated according to the actual measurement data of the earth surface movement observation station and the curve fitting method.
In the invention, the method for simulating the directional long drilling holes of the extraction drill is characterized in that the method also comprises the following steps before the arrangement of the directional long drilling holes of the extraction drill of the coal bed methane underground in the sealed goaf in the S2:
s201, coal body collection: collecting coal bodies of typical geological units underground, conveying the coal bodies to the ground, then carrying out wax sealing, and packaging;
s202, preparing a coal sample: processing and cutting the collected coal body into a cubic coal body sample with the thickness of 300mm multiplied by 300mm, uniformly smearing the surface of the coal body sample with sealant, and curing the colloid with the thickness of more than 1mm;
s203, fixing and stress pressurization of a coal body sample: putting a coal body sample into a true triaxial pressure test device, and applying different stresses in all directions by adjusting three vertical pressurizing mechanisms;
s204, after the stress applied on the coal body sample is constant, an electric drill is used for forming an observation hole at a corresponding position on the side surface of the pressure box, which is designed in advance, and a gas extraction drill hole is formed on the coal body sample, a probe and a probe of an optical drilling deformation observation device are inserted into the sample hole, the aperture change condition is automatically observed, and an aperture change curve is drawn;
s205, observing the evolution condition of the coal body cracks around the drill hole by a microscope and a camera while the optical drilling deformation observation device automatically observes the aperture change, and analyzing the evolution rule of the coal body cracks around the drill hole.
It will be appreciated that in other embodiments, the true triaxial pressure test apparatus includes a pressure cell for placing a coal body sample, three vertical pressurizing mechanisms, and an observation hole, the pressure cell includes a cell body and a pressurizing plate filled with the coal body sample, the optical drilling deformation observation apparatus includes a probe, and an aperture measuring instrument, and the coal body fracture evolution observation apparatus includes a microscope, a camera, and a three-dimensional moving microscopic observation frame.
In this embodiment, the sealing and extracting the hole in the underground coal bed methane in the sealed goaf in S3 further includes the following steps:
s301, constructing a ground coal bed gas pre-pumping well above a goaf roadway, wherein the coal bed gas pre-pumping well is a directional inclined vertical well, a target spot falls on a stoping line of a coal mine planning underground mining working face, and a production sleeve of the coal bed gas pre-pumping well is not cut off after the underground mining working face is stoped to the stoping line;
s302, hermetically connecting a reserved extraction pipeline of the coal face with a production sleeve of a coalbed methane pre-extraction well;
s303, changing the ground extraction equipment of the coal bed gas pre-extraction well into a vacuum pump for extracting the coal bed gas in the goaf under negative pressure.
Optionally, the diameter of a first open well hole in the coalbed methane pre-pumping well is 440-445mm, the diameter of a pipe sleeve is 376-378mm, the diameter of a second open well hole is 311-313mm, the diameter of a casing pipe is 244-245mm, the diameter of a third open well hole is 214-216mm, and the diameter of the casing pipe is 138-140mm.
The principle and the advantages of the invention:
according to the method, the pressure relief range of the goaf can be effectively identified through reservoir space boundary calculation, the directional long drilling arrangement and the downhole extraction hole sealing of the goaf coal bed gas are realized, the goaf coal bed gas extraction efficiency is improved, and the resource utilization rate is further improved.
The above description is only an example of the present invention and is not intended to limit the scope of the present invention, and various modifications and variations will be apparent to those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention. It should be noted that: like reference numerals and letters denote like items in the following figures, and thus once an item is defined in one figure, no further definition or explanation thereof is necessary in the following figures.
The foregoing is merely illustrative of the present invention, and the present invention is not limited thereto, and any person skilled in the art will readily recognize that variations or substitutions are within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (10)
1. The underground coal bed methane extraction method in the closed goaf is characterized by comprising the following steps of:
s1, reservoir space boundary calculation: judging the goaf pressure relief influence range indirectly through a ground geophysical prospecting method and by utilizing a method combining three-subzone coal mining water guide fracture zone height theory and a protective layer mining theory with numerical simulation correction, and determining the goaf reservoir space boundary;
s2, directional long drilling arrangement for underground extraction of coal bed gas in a closed goaf: extracting coal bed gas underground by utilizing a large-diameter directional long drilling hole, enabling a drilling track to avoid the pressure relief influence range of a goaf through reservoir space boundary calculation, arranging the drilling track in a rock stratum with a certain distance above a roadway, and then downwards pricking to a rock-covering fracture zone;
s3, sealing underground extraction hole sealing and extraction of coal bed gas in a closed goaf: and determining the distance between the lower extraction pipe in the drill hole, the depth of the two-plug one-injection-belt pressure sealing hole, the vertical height of the sealing hole section and the extraction negative pressure parameters according to the extraction characteristics of the coalbed methane in the sealed goaf, and extracting the coalbed methane.
2. The method for extracting coalbed methane from a closed goaf according to claim 1, wherein the calculating of the reservoir space boundary in S1 further comprises: geological investigation is carried out on the whole coal rock stratum in the goaf before mining, a full-rock core is drilled, and a full-rock histogram is drawn; and performing physical and mechanical property test on the all-rock core to obtain stress-strain curves and basic physical and mechanical parameters of each rock stratum, wherein the physical and mechanical property test comprises the following steps: density, modulus of elasticity, poisson's ratio, internal friction angle, cohesion, uniaxial compressive strength, triaxial peak strength.
3. The underground coal bed methane extraction method of the closed goaf according to claim 1, wherein the ground geophysical prospecting method is specifically used for completing the identification of the space boundary of the storage layer of the goaf by simulating the principle of searching and prospecting by utilizing the difference of physical characteristics of a geological body in a geophysical prospecting method.
4. The method for underground extraction of coal bed gas in a closed goaf according to claim 1, wherein the coal mining water guiding fracture zone height theory comprises a water guiding fracture zone height prediction method, and the water guiding fracture zone height prediction method specifically comprises the following steps:
s101, calculating the movement deformation of the horizontal rock formations with different burial depths of the overburden by using a probability integration method on the basis of the estimated parameter analysis of the probability integration method of the overburden;
s102, representing the development degree of the crack in the normal direction of the rock layer surface in the overburden by using the stratum surface stretching rate epsilon S, so as to measure the capability of the stratum crack to pass through water or gas;
s103, drawing a layer stretching rate distribution diagram of the horizontal rock stratum at different burial depths on the basis of the calculation of the moving deformation of the overlying strata;
s104, determining the critical surface stretching rate epsilon' S of water diversion of different lithology rock strata on the basis of analysis of the actual measurement value of the development height of the water diversion fracture zone of the overburden rock;
s105, judging the stratum stretching rate distribution map of the horizontal strata of different burial depths of the target mine by using the stratum water-guiding critical stratum stretching rate epsilon' S, and obtaining the predicted value of the coal mining overburden water-guiding fracture zone height under the water body.
5. The method for extracting coalbed methane from a closed goaf according to claim 4, wherein the function of the overburden probability integration method parameter about the burial depth z in S101 includes a subsidence coefficient q (z), an inflection point offset S (z), and a major influence radius R (z), and the specific formula is as follows:
wherein: n is n q As the dip coefficient influence coefficient, the dip coefficient is related to the lithology of the overburden; n is n r The method is mainly used for influencing radius influence coefficients, and is related to lithology of overburden rock; n is n s The inflection point offset distance influence coefficient is related to the lithology of the overburden rock; z is the depth of the rock stratum and m; h 0 The depth of the coal bed is m; q 0 Is the sinking coefficient of the earth surface; s is S 0 The inflection point offset distance at the ground surface is m; r is R 0 The radius, m, is primarily affected at the surface.
6. The method for extracting coalbed methane from a closed goaf according to claim 5, wherein the estimated parameters of the overburden probability integration method are based on the parameters of the earth surface movement deformation probability integration method: coefficient q of subsidence at earth's surface 0 Inflection point offset S at the earth' S surface 0 And the major influence radius R at the earth's surface 0 And the probability integration method parameters of the earth surface movement deformation are calculated according to the actual measurement data of the earth surface movement observation station and the curve fitting method.
7. The method for downhole extraction of coalbed methane in a closed goaf according to claim 1, wherein the method for downhole extraction of coalbed methane in a closed goaf in S2 further comprises extraction drill directional long-drilling simulation before the arrangement of the downhole extraction directional long-drilling in the coalbed methane in the closed goaf, and the method for extraction drill directional long-drilling simulation comprises the following steps:
s201, coal body collection: collecting coal bodies of typical geological units underground, conveying the coal bodies to the ground, then carrying out wax sealing, and packaging;
s202, preparing a coal sample: processing and cutting the collected coal body into a cubic coal body sample with the thickness of 300mm multiplied by 300mm, uniformly smearing the surface of the coal body sample with sealant, and curing the colloid with the thickness of more than 1mm;
s203, fixing and stress pressurization of a coal body sample: putting a coal body sample into a true triaxial pressure test device, and applying different stresses in all directions by adjusting three vertical pressurizing mechanisms;
s204, after the stress applied on the coal body sample is constant, an electric drill is used for forming an observation hole at a corresponding position on the side surface of the pressure box, which is designed in advance, and a gas extraction drill hole is formed on the coal body sample, a probe and a probe of an optical drilling deformation observation device are inserted into the sample hole, the aperture change condition is automatically observed, and an aperture change curve is drawn;
s205, observing the evolution condition of the coal body cracks around the drill hole by a microscope and a camera while the optical drilling deformation observation device automatically observes the aperture change, and analyzing the evolution rule of the coal body cracks around the drill hole.
8. The method for extracting coalbed methane from a closed goaf underground coal bed methane production system according to claim 7, wherein the true triaxial pressure test device comprises a pressure box for placing a coal body sample, three vertical pressurizing mechanisms and an observation hole, the pressure box comprises a box body and a pressurizing plate filled in the coal body sample, the optical drilling deformation observation device comprises a probe, a probe and an aperture measuring instrument, and the coal body fracture evolution observation device comprises a microscope, a camera and a three-dimensional moving microscopic observation frame.
9. The method for extracting coalbed methane from a closed goaf in the pit as claimed in claim 1, wherein the sealing and extracting the coalbed methane from the closed goaf in the step S3 further comprises the following steps:
s301, constructing a ground coal bed gas pre-pumping well above a goaf roadway, wherein the coal bed gas pre-pumping well is a directional inclined vertical well, a target spot falls on a stoping line of a coal mine planning underground mining working face, and a production sleeve of the coal bed gas pre-pumping well is not cut off after the underground mining working face is stoped to the stoping line;
s302, hermetically connecting a reserved extraction pipeline of the coal face with a production sleeve of a coalbed methane pre-extraction well;
s303, changing the ground extraction equipment of the coal bed gas pre-extraction well into a vacuum pump for extracting the coal bed gas in the goaf under negative pressure.
10. The method for downhole extraction of coalbed methane in a closed goaf according to claim 9, wherein the diameter of a first borehole in the coalbed methane pre-extraction well is 440-445mm, the diameter of a pipe sleeve is 376-378mm, the diameter of a second borehole is 311-313mm, the diameter of a pipe sleeve is 244-245mm, the diameter of a third borehole is 214-216mm, and the diameter of the pipe sleeve is 138-140mm.
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