CN115434671A - Coal seam pressure relief and permeability increasing method and system - Google Patents
Coal seam pressure relief and permeability increasing method and system Download PDFInfo
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- 239000003245 coal Substances 0.000 title claims abstract description 226
- 230000035699 permeability Effects 0.000 title claims abstract description 50
- 238000000034 method Methods 0.000 title claims abstract description 34
- 230000001965 increasing effect Effects 0.000 title description 40
- 239000007789 gas Substances 0.000 claims abstract description 85
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 claims abstract description 66
- 239000007788 liquid Substances 0.000 claims abstract description 64
- 238000002347 injection Methods 0.000 claims abstract description 54
- 239000007924 injection Substances 0.000 claims abstract description 54
- 238000000605 extraction Methods 0.000 claims abstract description 34
- 229910002092 carbon dioxide Inorganic materials 0.000 claims abstract description 33
- 239000001569 carbon dioxide Substances 0.000 claims abstract description 33
- MGWGWNFMUOTEHG-UHFFFAOYSA-N 4-(3,5-dimethylphenyl)-1,3-thiazol-2-amine Chemical compound CC1=CC(C)=CC(C=2N=C(N)SC=2)=C1 MGWGWNFMUOTEHG-UHFFFAOYSA-N 0.000 claims abstract description 27
- JCXJVPUVTGWSNB-UHFFFAOYSA-N nitrogen dioxide Inorganic materials O=[N]=O JCXJVPUVTGWSNB-UHFFFAOYSA-N 0.000 claims abstract description 27
- 239000011435 rock Substances 0.000 claims abstract description 18
- 238000005553 drilling Methods 0.000 claims abstract description 15
- 238000005336 cracking Methods 0.000 claims description 44
- 230000006872 improvement Effects 0.000 claims description 13
- 230000015572 biosynthetic process Effects 0.000 claims description 5
- 230000000694 effects Effects 0.000 description 22
- 230000035882 stress Effects 0.000 description 9
- 230000008646 thermal stress Effects 0.000 description 6
- 238000010438 heat treatment Methods 0.000 description 4
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 4
- 238000005065 mining Methods 0.000 description 4
- 239000000243 solution Substances 0.000 description 4
- 238000001179 sorption measurement Methods 0.000 description 4
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 2
- 229910052799 carbon Inorganic materials 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 238000012544 monitoring process Methods 0.000 description 2
- 239000011148 porous material Substances 0.000 description 2
- 150000003254 radicals Chemical class 0.000 description 2
- 238000004064 recycling Methods 0.000 description 2
- 239000007921 spray Substances 0.000 description 2
- 235000019738 Limestone Nutrition 0.000 description 1
- 230000002745 absorbent Effects 0.000 description 1
- 239000002250 absorbent Substances 0.000 description 1
- 230000036760 body temperature Effects 0.000 description 1
- 239000003990 capacitor Substances 0.000 description 1
- 238000009795 derivation Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 239000000284 extract Substances 0.000 description 1
- 239000005431 greenhouse gas Substances 0.000 description 1
- 230000001939 inductive effect Effects 0.000 description 1
- 239000006028 limestone Substances 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 239000011241 protective layer Substances 0.000 description 1
- 238000011084 recovery Methods 0.000 description 1
- 238000001028 reflection method Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 238000002336 sorption--desorption measurement Methods 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
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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
- E21B43/006—Production of coal-bed methane
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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
- E21B43/25—Methods for stimulating production
- E21B43/26—Methods for stimulating production by forming crevices or fractures
- E21B43/2605—Methods for stimulating production by forming crevices or fractures using gas or liquefied gas
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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
- E21B47/00—Survey of boreholes or wells
- E21B47/06—Measuring temperature or pressure
-
- 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
- E21B47/06—Measuring temperature or pressure
- E21B47/07—Temperature
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Abstract
The invention discloses a method and a system for pressure relief and permeability increase of a coal seam, wherein the method comprises the following steps: drilling a pressure relief hole into the coal seam from a rock stratum at the top plate of the coal seam, and placing at least a first microwave device in the pressure relief hole; a microwave fracturing hole, an injection drill hole and a coal bed gas extraction hole are formed in a coal bed, at least a second microwave device is placed in the microwave fracturing hole, and at least a liquid fracturing device is placed in the injection drill hole; opening a first microwave device in the coal seam for microwave fracturing, closing the first microwave device after working for a specified time, repeating the operation for a plurality of times at equal time intervals, and crushing a hard rock stratum above the coal seam; opening a second microwave device in the coal seam for microwave fracturing, and then injecting liquid carbon dioxide or liquid nitrogen dioxide into the injection drill hole by using a liquid fracturing device for fracturing; and repeating the steps for multiple times, and separating the coal bed gas and the carbon dioxide at the coal bed gas extraction hole to obtain the coal bed gas.
Description
Technical Field
The invention relates to the technical field of coal bed gas extraction, in particular to a method and a system for releasing pressure and increasing permeability of a coal bed.
Background
In recent years, with the advance of the policy of double carbon in China, how to reduce the emission of carbon dioxide becomes an important problem gradually. However, china has abundant coal bed gas, and the utilization of the coal bed gas can greatly relieve the pressure of carbon emission. And the coal bed gas development is also of great significance for relieving the current situation of oil and gas resource shortage in China, lightening the disaster degree of mines, reducing the emission of greenhouse gases and the like. How to extract coal bed gas from coal beds and improve the yield of the coal bed gas becomes important to research. However, the traditional coal bed gas mining method often causes pollution to the coal bed. Thus, microwave fracturing is becoming a new method for increasing the yield of coal bed gas. However, compared with the traditional coal bed gas mining methods such as hydraulic fracturing, the microwave fracturing still has low efficiency. Therefore, how to improve the yield of the coal bed gas in an efficient and environment-friendly way becomes an important problem.
Disclosure of Invention
In order to solve the problems and requirements, the scheme provides a coal seam pressure relief and permeability increasing method and a permeability increasing system, and the technical purpose can be achieved due to the adoption of the following technical characteristics, and other technical effects are brought.
The invention aims to provide a coal seam pressure relief and permeability improvement method, which comprises the following steps:
s10: drilling a pressure relief hole from a rock stratum at the top plate of the coal seam into the coal seam, and placing at least a first microwave device in the pressure relief hole;
s20: a microwave fracturing hole, an injection drill hole and a coal bed gas extraction hole are formed in a coal bed, at least a second microwave device is placed in the microwave fracturing hole, and at least a liquid fracturing device is placed in the injection drill hole;
s30: opening a first microwave device in the coal seam for microwave fracturing, closing the first microwave device after working for a specified time, repeating the operation for a plurality of times at equal time intervals, and crushing a hard rock stratum above the coal seam so as to realize effective pressure relief;
s40: opening a second microwave device in the coal seam for microwave fracturing, and then injecting liquid carbon dioxide or liquid nitrogen dioxide into the injection drill hole by using a liquid fracturing device for fracturing;
s50: and repeating the step S40 for many times, and separating the coal bed gas from the carbon dioxide or the nitrogen dioxide at the coal bed gas extraction hole to obtain the coal bed gas.
In the technical scheme, the method utilizes the microwave to relieve the pressure of the external load of the coal bed, so that when the coal bed is used for extracting the coal bed gas, the effective stress is reduced, the original fractures are gradually increased, the air permeability of the coal bed is increased, and the cracking effect of the microwave and the liquid carbon dioxide or the liquid nitrogen dioxide is greatly increased. Simultaneously, when reutilizing the microwave and sending and splitting, the microwave can heat the coal seam, under microwave heating, the crack of coal seam can crescent, then liquid carbon dioxide or liquid nitrogen dioxide pour into rapidly for the coal seam cools off fast, and under this kind of expend with heat and contract with cold's effect, thermal stress makes and appears many cracks in the coal seam, and the absorptive coal bed gas of coal seam discharges gradually, and the permeability greatly increased of coal seam has effectually increased the output of coal bed gas. Therefore, under the superposition effect of pressure relief and temperature difference of the coal bed, the cracks in the coal bed are greatly expanded, the air permeability of the coal bed is increased, the yield of the coal bed gas is greatly improved, and the permeability increasing method is environment-friendly and has low cost.
In addition, the coal seam pressure relief and permeability increasing method provided by the invention can also have the following technical characteristics:
in one example of the present invention, the microwave-induced cracking holes and the injection-drilled holes are alternately arranged in sequence along an extending direction and a depth direction of the return air drift and/or the transport drift, wherein the microwave-induced cracking holes and the injection-drilled holes along the extending direction form a cracking hole group.
In one example of the invention, the coal bed gas extraction holes are arranged at intervals along the extending direction of the return air drift and/or the transport drift and are positioned between two adjacent fracturing hole groups in the depth direction.
In one example of the invention, the microwave fracturing holes and the injection drill holes adjacent to each other in the extending direction in each fracturing group and the microwave fracturing holes and the injection drill holes in the adjacent fracturing groups corresponding to the microwave fracturing holes and the injection drill holes in the depth direction form a fracturing unit, and the coal bed gas extraction holes are located at the center of the fracturing unit, wherein the microwave fracturing holes and the injection drill holes are arranged in the adjacent fracturing groups and at positions corresponding to each other in the depth direction.
In one example of the present invention, in two adjacent fracture inducing hole groups, the distance between the microwave fracturing hole or the injection drill hole and the adjacent injection drill hole or the microwave fracturing hole in the depth direction and the extension direction is 4m to 6m.
In an example of the present invention, in the step S30, the method further includes:
and when the first microwave device is used for fracturing, monitoring the pressure at the pressure relief hole in real time, and when the pressure value of the coal bed reaches 80% of the original pressure, stopping fracturing by the first microwave device.
In one example of the present invention, the liquid gas comprises: liquid carbon dioxide and liquid nitrogen dioxide.
Another objective of the present invention is to provide a coal seam pressure relief and permeability increasing system, which includes:
the pressure relief hole is formed in a hard rock stratum at the top plate of the coal seam;
the microwave induced cracking holes, the injection drill holes and the coal bed gas extraction holes are arranged in a coal bed, the microwave induced cracking holes and the injection drill holes are sequentially and alternately arranged at intervals along the extending direction of a return air drift and/or a transportation drift to form induced cracking hole groups, the induced cracking hole groups comprise a plurality of induced cracking hole groups, the induced cracking hole groups are arranged at intervals along the depth direction of the return air drift and/or the transportation drift, and the coal bed gas extraction holes are arranged at intervals along the extending direction and are positioned between two adjacent induced cracking hole groups;
the pressure relief and permeability increasing devices are respectively arranged in the pressure relief holes, the microwave fracturing holes and the injection drill holes and comprise: an outer tube, a spray tube and a microwave device;
the spray pipe extends through the outer pipe and is configured to input liquid carbon dioxide or liquid nitrogen dioxide;
and the microwave device is arranged on the outer wall of the outer pipe and is configured to microwave-induced crack the coal bed.
In one example of the present invention, the method further comprises: a one-way valve is arranged on the upper end of the valve body,
the one-way valve is disposed on the spout and configured such that liquid carbon dioxide or liquid nitrogen dioxide can only flow from the proximal end toward the distal end of the spout.
In one example of the present invention, the method further comprises: a temperature sensor and a pressure sensor, wherein the temperature sensor and the pressure sensor are arranged on the base plate,
the temperature sensor is arranged on the outer pipe and configured to monitor temperature information of a coal seam;
the pressure sensor is arranged on the outer pipe and configured to monitor pressure information of a coal seam.
The following description of the preferred embodiments for carrying out the present invention will be made in detail with reference to the accompanying drawings so that the features and advantages of the present invention can be easily understood.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings of the embodiments of the present invention will be briefly described below. Wherein the drawings are only for purposes of illustrating some embodiments of the invention and are not to be construed as limiting the invention to all embodiments thereof.
FIG. 1 is a top plan view of a coal seam according to an embodiment of the present invention;
FIG. 2 isbase:Sub>A sectional view taken along line A-A of FIG. 1;
FIG. 3 is a sectional view taken along line B-B of FIG. 1;
FIG. 4 is a schematic structural diagram of a pressure relief anti-reflection device according to an embodiment of the invention;
fig. 5 is a flow chart of a pressure relief anti-reflection method according to an embodiment of the invention.
List of reference numbers:
a gob 100;
a geological formation 110;
a rock formation 111;
a coal seam 112;
a return airway 120;
a haulage gate 130;
a pressure relief vent 140;
microwave-induced cracking holes 150;
an injection bore 160;
coal bed gas extraction holes 170;
a set of fracturing holes 180;
a fracturing unit 190;
an extension direction Y;
a depth direction S;
a thickness direction H;
a pressure relief and permeability improvement device 200;
an outer tube 210;
a nozzle 220;
a check valve 221;
a proximal end portion 220A;
a distal portion 220B;
a microwave device 230;
a temperature sensor 240;
a pressure sensor 250.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings of specific embodiments of the present invention. Like reference numerals in the drawings denote like parts. It should be noted that the described embodiments are only some embodiments of the invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the described embodiments of the invention without any inventive step, are within the scope of protection of the invention.
Unless defined otherwise, technical or scientific terms used herein shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention belongs. The use of "first," "second," and similar terms in the description and claims of the present application do not denote any order, quantity, or importance, but rather the terms are used to distinguish one element from another. Also, the use of the terms "a" or "an" and the like do not necessarily denote a limitation of quantity. The word "comprising" or "comprises", and the like, means that the element or item listed before the word covers the element or item listed after the word and its equivalents, but does not exclude other elements or items. The terms "connected" or "coupled" and the like are not restricted to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "upper", "lower", "left", "right", and the like are used only to indicate relative positional relationships, and when the absolute position of the object being described is changed, the relative positional relationships may also be changed accordingly.
It should be noted that, the microwave device in the present technical solution specifically refers to a microwave emitting device. The microwave emitter consists of mainly magnetron, high voltage transformer, high voltage diode and high voltage capacitor. The magnetron is a main device of a microwave transmitting device, belongs to a vacuum device, and is mainly used for generating and transmitting microwave signals in the microwave transmitting device, and a coal bed is heated by using the energy of the microwave signals.
Fig. 3 is a diagram of a geological formation 110, which is a structure that one side of a goaf 100 (for pre-extracting coal bed gas before coal mining (drill hole pre-extraction)) is distributed with a rock stratum 111, a coal bed 112 and a rock stratum 111 from top to bottom;
according to a first aspect of the present invention, as shown in fig. 1 to 5, a method for increasing permeability of a coal seam by pressure relief includes the following steps:
s10: drilling a pressure relief hole 140 from a rock stratum at the top plate of the coal seam into the coal seam, and placing at least a first microwave device in the pressure relief hole 140; that is, as shown in FIG. 3, the pressure relief holes 140 extend from the formation at the roof of the coal seam obliquely downward into the coal seam.
S20: a microwave fracturing hole 150, an injection drill hole 160 and a coal bed gas extraction hole 170 are arranged in a coal bed, at least a second microwave device is placed in the microwave fracturing hole 150, and at least a liquid fracturing device is placed in the injection drill hole 160; the microwave fracturing hole 150, the injection drill hole 160, the coal bed gas extraction hole 170 and the pressure relief hole 140 are all formed along the thickness direction H of the coal bed, wherein the thickness direction H of the coal bed is mutually vertical to the extension direction Y and the depth direction S;
s30: opening a first microwave device in the coal seam for microwave fracturing, closing the first microwave device after working for a specified time, repeating the operation for a plurality of times at equal time intervals, and crushing a hard rock stratum above the coal seam so as to realize effective pressure relief;
s40: opening a second microwave device in the coal seam for microwave fracturing, and then injecting liquid carbon dioxide or liquid nitrogen dioxide into the injection drill hole 160 by using a liquid fracturing device for fracturing;
s50: and repeating the step S40 for multiple times, and separating the coal bed gas from the carbon dioxide or the nitrogen dioxide at the coal bed gas extraction hole 170 to obtain the coal bed gas.
That is, the first microwave device is firstly opened, microwave fracturing is carried out in the pressure relief hole 140 by the first microwave device, and the microwave fracturing is repeated for a plurality of times at equal time intervals to crush the hard rock stratum above the coal seam so as to realize effective pressure relief of the coal seam roof; then opening a second microwave device in the coal seam to perform microwave fracturing, then injecting liquid carbon dioxide or liquid nitrogen dioxide into the injection drill hole 160 by using a liquid fracturing device to perform liquid carbon dioxide or liquid nitrogen dioxide fracturing, repeatedly operating and executing the microwave fracturing of the second microwave device and the liquid carbon dioxide or liquid nitrogen dioxide fracturing for multiple times, so that the permeability of the coal seam is greatly improved, and separating coal seam gas from carbon dioxide at the coal seam gas extraction hole 170; according to the method, the microwave is used for relieving the external load of the coal bed, so that when the coal bed gas is extracted from the coal bed, the effective stress is reduced, the original cracks are gradually increased, the air permeability of the coal bed is increased, and the cracking effect of the microwave and liquid carbon dioxide or liquid nitrogen dioxide is greatly increased. Simultaneously, when reutilizing the microwave and sending and splitting, the microwave can heat the coal seam, under microwave heating, the crack of coal seam can crescent, then liquid carbon dioxide or liquid nitrogen dioxide pour into rapidly for the coal seam cools off fast, and under this kind of expend with heat and contract with cold's effect, thermal stress makes and appears many cracks in the coal seam, and the absorptive coal bed gas of coal seam discharges gradually, and the permeability greatly increased of coal seam has effectually increased the output of coal bed gas. Therefore, under the superposition effect of pressure relief and temperature difference of the coal bed, cracks in the coal bed are greatly expanded, the air permeability of the coal bed is increased, the yield of the coal bed gas is greatly improved, and the permeability increasing method is environment-friendly and low in cost.
It should be noted that, because the pressure relief permeability improvement method is mainly applied to the protective layer mining, four zones necessarily exist on the coal seam: stress centralizing belt, initial pressure relief belt, full pressure relief belt and stress recovery belt. The diameter of the drilling hole diameter parameter of the microwave fracturing pressure relief hole 140 is 20mm, the depth of the drilling hole diameter parameter is 25m, the main stress area is the basic top position in the mine pressure, and the drilling hole diameter parameter generally comprises rock stratums such as sandstone, limestone, conglomerate and the like. After the microwave pressure relief device is placed in the deep part of the drill hole, the microwave device is opened, so that the pressure relief of the coal bed in the range of 10-50m at the deep part of the drill hole can be realized, and after the pressure relief of the coal bed in the region is realized, the coal bed gas is very active and is convenient to extract.
In one example of the present invention, the microwave fracturing holes 150 and the injection drilling holes 160 are alternately arranged in sequence along the extending direction Y and the depth direction S of the return airway 120 and/or the transport airway 130, wherein the microwave fracturing holes 150 and the injection drilling holes 160 along the extending direction Y form a fracturing hole group 180;
for example, the first set of cracking holes 180 alternate between injection holes 160 and microwave cracking holes 150 in the extending direction Y of the return air level 120 and/or the transport level 130; the second cracking hole group 180 is formed by alternately forming the microwave cracking holes 150 and the injection drilling holes 160 along the extending direction Y of the return air drift 120 and/or the transportation drift 130; the arrangement mode can enable the fracturing of the coal seam to be more uniform and the fracturing effect to be good.
In an example of the present invention, the coal bed gas extraction holes 170 are arranged at intervals along the extending direction Y of the return air drift 120 and/or the transportation drift 130, and are located between two adjacent fracturing hole groups 180 in the depth direction S;
it is expected that the fracture hole groups 180 are arranged on both sides of the coal bed gas extraction hole 170 in the depth direction S, so that the extraction effect obtained at the position of the coal bed gas extraction hole 170 is the best.
In an example of the present invention, the microwave fracturing holes 150 and the injection boreholes 160 adjacent to each other in the extending direction Y in each fracturing hole group 180 and the microwave fracturing holes 150 and the injection boreholes 160 in the adjacent fracturing hole group 180 corresponding to each other in the depth direction S form a fracturing unit 190, and the coalbed methane extraction holes 170 are located at the center of the fracturing unit 190, wherein the microwave fracturing holes 150 and the injection boreholes 160 are arranged in the adjacent fracturing hole groups 180 and at positions corresponding to each other in the depth direction S;
in other words, in two adjacent cracking groups 180, the microwave cracking holes 150 and the injection drill holes 160 in each cracking group 180, which are adjacent along the extending direction Y of the return air drift 120 and/or the transport drift 130 and correspond in the depth direction S, form a cracking unit 190, and the coal bed gas extraction hole 170 is located at the center of the cracking unit 190;
in brief, the fracturing unit 190 includes two microwave fracturing holes 150 and two injection drill holes 160, and two adjacent holes in the extending direction Y and the depth direction S are different;
the coal bed gas extraction holes 170 are arranged at the central positions of the fracturing units 190, so that the microwave fracturing holes 150 and the injection drill holes 160 in each fracturing unit 190 can be radiated to the coal bed gas extraction holes 170, and the coal bed gas extraction holes 170 are equal to the microwave fracturing holes 150 and the injection drill holes 160 in distance, so that the influence effects are consistent, and the extraction effect can be optimal.
In one example of the present invention, in two adjacent fracture hole groups 180, the distance between the microwave fracture hole 150 or the injection borehole 160 and the adjacent injection borehole 160 or the microwave fracture hole 150 in the depth direction S and the extension direction Y is 4m to 6m.
First, due to liquid CO 2 The cracking range is 4-6m, in which the cracking is due to liquid CO 2 The coal is quickly gasified after being injected into the coal body, absorbs a large amount of heat, so that the temperature of the coal bed is quickly reduced, and the CO in the gas state 2 A large amount of coal bed gas can be injected into pores of the coal body and displaced, so that the yield of the coal bed gas is greatly increased.
And secondly, the influence range of the microwave fracturing for long-time heating is about 5m, and the microwave fracturing utilizes microwaves to heat the coal bed, so that the temperature in the coal bed is increased, thermal stress is generated, the coal bed is cracked, and finally the coal bed methane yield of the coal bed is greatly increased.
Preferably, the distance between the microwave-fractured hole 150 or the injection borehole 160 and the adjacent injection borehole 160 or microwave-fractured hole 150 in the depth direction S and the extension direction Y is 5m.
In an example of the present invention, in the step S30, the method further includes:
when the first microwave device performs fracturing, monitoring the pressure at the pressure relief hole 140 in real time, and stopping fracturing when the monitored pressure value of the coal seam reaches 80% of the original pressure;
for example, a temperature sensor 240 and a pressure sensor 250 are installed in the pressure relief hole 140. The pressure sensor 250 is used for detecting the pressure relief effect of the coal seam, and when the pressure relief effect of the coal seam reaches 80% of the original stress, pressure relief is stopped, so that the optimal pressure relief effect can be achieved. Afterwards, reuse microwave device heats the temperature in coal seam, and the liquid carbon dioxide of recycling cools off, through the effect of thermal stress for the coal seam produces a large amount of fissures, makes the gas permeability greatly increased in coal seam.
In one example of the invention, a first microwave device in a coal seam is opened for microwave fracturing, the first microwave device is closed after the operation is carried out for 30 minutes, and the fracturing is repeated for 5 times every 1 hour, so that the hard rock stratum above the coal seam is crushed, and the effective pressure relief is realized.
It should be noted that the specific derivation process regarding permeability is as follows:
(1) The temperature versus permeability equation is:
ΔT＝T-T R (2)
in the formula: c. C 1 Is a pressure constant, 1/MPa; c. C 2 Is a temperature constant, 1/K; t is R Reference temperature, K, for gas adsorption/desorption measurements; p is the pore pressure of the gas, MPa; a and b are adsorption constants in cm 3 (ii)/g, 1/MPa; v is a coal body pair CH 4 The adsorption volume of (a); t is the temperature at work, DEG C; delta T is the increment of the coal body temperature in DEG C.
Thus, it can be concluded that coal pairs CH as the temperature increases 4 The smaller the adsorption volume of (A), and thus the desorbed CH 4 The more and further the higher the coal bed gas production.
(2) Influence of microwaves on the temperature of the coal body:
according to the thermodynamic theory, the increment delta T of the coal temperature per unit volume after the microwave field acts for T time can be expressed as
In the formula: rho is the density of the coal body, g/cm 3 ；c p The specific constant pressure heat capacity of coal, J/(g.K); q is the heat gained by a unit volume of coal after the microwave field has been applied for time t, J.
Simultaneous equations (1), (2) and (3) to obtain
Therefore, it can be concluded that when microwaves are usedWhen the power is increased, the heat Q obtained by the coal body in unit volume after the microwave field acts for t time is reduced, and finally the coal body is enabled to be opposite to CH 4 The adsorption volume V of (a) is reduced, thereby resulting in an increase in permeability in the coal body and then a substantial increase in the production of coal bed gas.
(3) Relationship between permeability and coal seam roof pressure:
wherein Q is gas flow, cm 3 S; pa is atmospheric pressure, 0.1MPa; a is the area of the specimen in cm 2 (ii) a L is the length of the test piece, cm; p is a radical of 1 Is the gas pressure at the gas inlet, MPa; p is a radical of 2 The gas pressure at the gas outlet is MPa; mu is gas viscosity, 10 -3 Pa°s。
Wherein the effective stress p 0 And gas pressure p of gas inlet 1 And gas pressure p at the outlet 2 It is related. For the inlet pressure p of the invention 1 Namely the pressure of the coal bed top plate, the invention controls the gas pressure p of the gas inlet by reducing the pressure of the coal bed top plate 1 And then increasing the permeability of the coal seam.
According to a second aspect of the invention, a coal seam pressure relief and permeability improvement system comprises:
the pressure relief holes 140 are formed in the hard rock stratum at the top plate of the coal seam;
the microwave induced cracking holes 150, the injection drill holes 160 and the coal bed gas extraction holes 170 are arranged in a coal bed, the microwave induced cracking holes 150 and the injection drill holes 160 are sequentially and alternately arranged at intervals along the extending direction Y of the return air drift 120 and/or the transport drift 130 to form induced cracking hole groups 180, the induced cracking hole groups 180 comprise a plurality of induced cracking hole groups 180, the induced cracking hole groups are arranged at intervals along the depth direction S of the return air drift 120 and/or the transport drift 130, and the coal bed gas extraction holes 170 are arranged at intervals along the extending direction Y and are located between two adjacent induced cracking hole groups 180;
the pressure relief and permeability improvement device 200 is respectively disposed in the pressure relief hole 140, the microwave fracturing hole 150, and the injection borehole 160, and includes: outer tube 210, lance 220, and microwave apparatus 230;
the nozzle 220 extends through the outer tube 210 and is configured to input liquid carbon dioxide or liquid nitrogen dioxide;
and a microwave device 230 installed on the outer wall of the outer pipe 210 and configured to microwave-crack the coal seam.
That is, the microwave device 230 in the pressure relief and permeability increasing device 200 in the pressure relief hole 140 is opened first, the first microwave device 230 performs microwave fracturing in the pressure relief hole 140, and the microwave fracturing is repeated for multiple times at equal time intervals to crush the hard rock above the coal seam, so as to realize effective pressure relief of the coal seam roof; then opening a microwave device 230 in the pressure relief and permeability increasing device 200 in the coal bed microwave fracturing hole 150 for microwave fracturing, then injecting liquid carbon dioxide or liquid nitrogen dioxide into the injection drill hole 160 by a liquid fracturing device in the pressure relief and permeability increasing device 200 for liquid carbon dioxide or liquid nitrogen dioxide fracturing, repeatedly operating and executing microwave fracturing of the microwave device 230 in the microwave fracturing hole 150 and liquid fracturing of the injection drill hole 160 for multiple times of fracturing, so that the permeability of the coal bed is greatly improved, and separating coal bed gas from carbon dioxide at the coal bed gas extraction hole 170; the system utilizes the microwave to relieve the pressure of the external load of the coal bed, so that when the coal bed extracts the coal bed gas, the effective stress is reduced, the original cracks are gradually increased, the air permeability of the coal bed is increased, and the cracking effect of the microwave and the liquid carbon dioxide or the liquid nitrogen dioxide is greatly increased. Simultaneously, when the microwave of recycling sent and splits, the microwave can heat the coal seam, and under microwave heating, the crack of coal seam can crescent, then liquid carbon dioxide or liquid nitrogen dioxide pour into rapidly for the coal seam cools off fast, and under this kind of expend with heat and contract with cold's effect, thermal stress makes a lot of cracks appear in the coal seam, and the absorbent coal bed gas in coal seam discharges gradually, and the permeability greatly increased in coal seam has effectually increased the output of coal bed gas. Therefore, under the superposition effect of pressure relief and temperature difference of the coal bed, the cracks in the coal bed are greatly expanded, the air permeability of the coal bed is increased, and the yield of the coal bed gas is greatly improved.
In one example of the present invention, the method further comprises: the one-way valve 221 is provided with a check valve,
the one-way valve 221 is disposed on the nozzle 220 and configured to allow liquid carbon dioxide or liquid nitrogen dioxide to flow only from the proximal portion 220A toward the distal portion 220B of the nozzle 220;
the one-way valve 221 may be configured to allow the liquid carbon dioxide or liquid nitrogen dioxide to flow only from the proximal end portion 220A toward the distal end portion 220B of the nozzle 220, thereby preventing backflow of the liquid carbon dioxide or liquid nitrogen dioxide.
In one example of the present invention, the method further comprises: a temperature sensor 240 and a pressure sensor 250,
the temperature sensor 240 is arranged on the outer pipe 210 and configured to monitor temperature information of the coal seam;
the pressure sensor 250 is arranged on the outer pipe 210 and configured to monitor pressure information of a coal seam;
for example, each coal seam pressure relief and permeability enhancement system is equipped with a temperature sensor 240 and a pressure sensor 250. The pressure sensor 250 is used for detecting the pressure relief effect of the coal seam, and when the pressure relief effect of the coal seam reaches 80% of the original stress, pressure relief is stopped, so that the optimal pressure relief effect can be achieved. Afterwards, reuse microwave device 230 heats the temperature in coal seam, and reuse liquid carbon dioxide cools off, through the effect of thermal stress for the coal seam produces a large amount of fissures, makes the gas permeability greatly increased in coal seam.
While exemplary embodiments of a method and system for pressure relief and permeability enhancement of a coal seam according to the present invention have been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes and modifications may be made to the embodiments described above without departing from the spirit of the invention, and that various combinations of features and structures may be made without departing from the scope of the invention as defined in the appended claims.
Claims (10)
1. A coal seam pressure relief and permeability increase method is characterized by comprising the following steps:
s10: drilling pressure relief holes (140) into the coal seam from the rock formation at the top plate of the coal seam, and placing at least a first microwave device in the pressure relief holes (140);
s20: a microwave fracturing hole (150), an injection drilling hole (160) and a coal bed gas extraction hole (170) are formed in a coal bed, at least a second microwave device is placed in the microwave fracturing hole (150), and at least a liquid fracturing device is placed in the injection drilling hole (160);
s30: opening a first microwave device in the coal seam for microwave fracturing, closing the first microwave device after working for a specified time, repeating the operation for multiple times at equal time intervals, and crushing a hard rock stratum above the coal seam so as to realize effective pressure relief;
s40: opening a second microwave device in the coal seam for microwave fracturing, and then injecting liquid carbon dioxide or liquid nitrogen dioxide into the injection drill hole (160) by using a liquid fracturing device for fracturing;
s50: and repeating the step S40 for multiple times, and separating the coal bed gas from the carbon dioxide or the nitrogen dioxide at the coal bed gas extraction hole (170) to obtain the coal bed gas.
2. The coal seam pressure relief and permeability improvement method according to claim 1,
the microwave induced cracking holes (150) and the injection drill holes (160) are alternately arranged along the extending direction (Y) and the depth direction (S) of the return air drift (120) and/or the transport drift (130) in sequence, wherein the microwave induced cracking holes (150) and the injection drill holes (160) along the extending direction (Y) form a cracking hole group (180).
3. The coal seam pressure relief and permeability improvement method according to claim 2,
the coal bed gas extraction holes (170) are arranged at intervals along the extending direction (Y) of the air return drift (120) and/or the transportation drift (130), and are located between two adjacent fracturing hole groups (180) in the depth direction (S).
4. The coal seam pressure relief and permeability improvement method according to claim 3,
the microwave fracturing holes (150) and the injection drill holes (160) which are adjacent to each other in the extending direction (Y) in each fracturing hole group (180) and the microwave fracturing holes (150) and the injection drill holes (160) which are in the adjacent fracturing hole group (180) and correspond to the microwave fracturing holes in the depth direction (S) form a fracturing unit (190), and the coal bed gas extraction holes (170) are located in the center of the fracturing unit (190), wherein the microwave fracturing holes (150) and the injection drill holes (160) are arranged in the adjacent fracturing hole groups (180) and correspond to each other in the depth direction (S).
5. The coal seam pressure relief and permeability improvement method according to claim 4,
in two adjacent cracking hole groups (180), the distance between the microwave cracking hole (150) or the injection drilling hole (160) and the adjacent injection drilling hole (160) or the microwave cracking hole (150) in the depth direction (S) and the extension direction (Y) is 4-6 m.
6. The coal seam pressure relief and permeability improvement method according to claim 1,
in step S30, the method further includes:
when the first microwave device conducts fracturing, the pressure at the pressure relief hole (140) is monitored in real time, and when the monitored pressure value of the coal seam reaches 80% of the original pressure, the first microwave device stops fracturing.
7. The coal seam pressure relief and permeability improvement method according to claim 1,
the aperture parameters of the microwave induced cracking holes (150) are as follows: 20mm in diameter and 25m in depth.
8. A coal seam pressure relief anti-reflection system is characterized by comprising:
the pressure relief hole (140) is formed in a hard rock stratum at the top plate of the coal seam;
the microwave induced cracking holes (150), the injection drill holes (160) and the coal bed gas extraction holes (170) are arranged in a coal bed, the microwave induced cracking holes (150) and the injection drill holes (160) are sequentially and alternately arranged at intervals along the extending direction (Y) of the return air drift (120) and/or the transport drift (130) to form a plurality of induced cracking hole groups (180), the induced cracking hole groups (180) are arranged at intervals along the depth direction (S) of the return air drift (120) and/or the transport drift (130), and the coal bed gas extraction holes (170) are arranged at intervals along the extending direction (Y) and are positioned between two adjacent induced cracking hole groups (180);
the pressure relief and permeability improvement device (200) is respectively arranged in the pressure relief hole (140), the microwave fracturing hole (150) and the injection drilling hole (160), and comprises: an outer tube (210), a nozzle (220) and a microwave device (230);
the nozzle (220) extends through the outer tube (210) and is configured to input liquid carbon dioxide or liquid nitrogen dioxide;
and the microwave device (230) is arranged on the outer wall of the outer pipe (210) and is configured to microwave and crack the coal bed.
9. The coal seam pressure relief and permeability reduction system of claim 8,
further comprising: a one-way valve (221),
the one-way valve (221) is disposed on the spout (220) and configured such that liquid carbon dioxide or liquid nitrogen dioxide can only flow from the proximal end (220A) toward the distal end (220B) of the spout (220).
10. The coal seam pressure relief and permeability improvement method according to claim 8,
further comprising: a temperature sensor (240) and a pressure sensor (250),
the temperature sensor (240) is arranged on the outer pipe (210) and configured to monitor temperature information of a coal seam;
the pressure sensor (250) is disposed on the outer tube (210) and configured to monitor pressure information of a coal seam.
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