CN114810028A - Underground in-situ pyrolysis mining process for huge thick coal seam - Google Patents
Underground in-situ pyrolysis mining process for huge thick coal seam Download PDFInfo
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Abstract
The invention discloses an underground in-situ pyrolysis mining process for a huge thick coal seam, which comprises the following specific steps of: step one, geological evaluation is carried out on a target coal mining area: determining whether the coal seam of the block is suitable for mining by adopting an underground in-situ pyrolysis process through evaluation, evaluating that the huge thick coal seam of the block is suitable for pyrolysis development, and entering the next step; step two, building a pyrolysis unit; step three, draining and mining coal bed water; and step four, pyrolyzing the coal bed. The invention solves the problems of low recovery rate, poor mining benefit, high coal spontaneous combustion and gas outburst risk, water permeability and surface subsidence existing in the mining of the huge thick coal bed by a well mining method, and particularly can solve the problems of safe, efficient and high recovery rate of the huge thick coal bed with a single-layer thickness of more than 30 meters.
Description
Technical Field
The invention relates to the technical field of pyrolysis mining of a huge thick coal seam, in particular to an underground in-situ pyrolysis mining process of the huge thick coal seam.
Background
The mining of the existing thick coal seam can mine some coal seams with the thickness of about forty meters by a method of combining layering with large mining height top caving coal, but the requirement is that a water system at the upper part of the coal seam does not develop and has a good water-resisting layer, and meanwhile, enough coal pillar support needs to be reserved to reduce or delay top plate collapse, the coal seam with the occurrence condition is rare, the phenomenon of surface collapse is serious when the mined coal seam is thicker, and for the mining of the thick coal seam with the possibility of spontaneous combustion, not only the mined coal is easy to spontaneously combust when being stacked on the ground surface, but also the coal is easy to combust in the stratum because water and air enter the coal seam due to the top plate collapse, so that the mining of the existing huge thick coal seam (the single layer is more than 30 meters), the problems of low recovery ratio, high mining cost, great influence on environment and ecology and the like exist, and the large-scale economic, high-efficiency and environment-friendly mining cannot be carried out.
Australian invention patent publication No. AU2019438341B2 provides A method for the radial rendering of open end slurry recovery circuit, refining of arrangement of L-shaped main domains (6,13) or a U-shaped main domains (11) and radial rendering. Branch domains (4,9,10) or a shaped B expression of the L-shaped main domains (6,13) or the U-shaped main domains (11) to a direction dependent or object oriented with the main domains (6,11,13) or the A method and a translation of the radial rendering (11) and the arrangement of the radial modified main domains (6,11,13) or the A method and a translation of the radial modified main domains (1, 13), 9,10) is expressed in a required manner, the length of the branched expression and control of the moved control system, and the length of the n expression (6,11,13) the new to the induced third end slurry modified complex in the case of the cassette at the length of the branched expression and control of the moved control system.
The invention discloses a process for mining ultra-thick coal seam in ascending layer by layer in Chinese patent with publication number CN103726846A, which comprises the steps of dividing the thick coal seam reasonably, mining and filling the lower layer working face, analyzing the filling effect and roof migration, and mining each layer upwards step by step until the filling mining of all layers is completed.
The mining methods are all in the field of underground mining, are physical mining modes of coal, have certain choice to reservoir characteristics and geological conditions of the coal seam, require the coal seam to have the condition that can form the regenerated coal body, the coal seam is difficult to be spontaneous combustion, the gas content is not large, require the construction machinery to be able to deal with complicated caving and complicated engineering construction requirement, etc. at present, the mining of the thick coal seam mainly has the following restrictions in several respects, one is that the recovery rate of coal mining in the mining process is lower, including the loss of layering and coal caving and the loss of the coal pillar of the sector; the problems of safety and environmental protection in the mining process include gas control and coal spontaneous combustion; the problems of water permeation and water pollution caused by stratum collapse are also needed to be solved; thirdly, the mining economy problem, because of the restriction of the above problems, the mining work of the thick coal seam in some areas is difficult to develop.
Disclosure of Invention
Aiming at the technical defects, the invention aims to provide an underground in-situ pyrolysis mining process for a huge thick coal seam, which solves the problems of low recovery rate, poor mining benefit, high risk of spontaneous combustion and gas outburst of coal, water permeability and surface subsidence existing in the mining of the huge thick coal seam by a well mining method, and particularly can solve the problems of safe, efficient and high recovery rate of coal under the condition of the huge thick coal seam with the thickness of more than 30 meters.
In order to solve the technical problems, the invention adopts the following technical scheme:
the invention provides an underground in-situ pyrolysis mining process for a huge thick coal seam, which comprises the following specific steps of:
step one, geological evaluation is carried out on a target coal mining area: determining whether the coal seam of the block is suitable for mining by adopting an underground in-situ pyrolysis process through evaluation, evaluating that the huge thick coal seam of the block is suitable for pyrolysis development, and entering the next step;
step two, pyrolysis unit construction: the method comprises the following steps that coal bed pyrolysis heat input and product output channels are constructed in a ground drilling mode, well patterns are deployed in a reverse five-point method, injection wells and production wells penetrate through a coal bed at a vertical angle or a nearly vertical angle, when one well serves as an injection well, the surrounding adjacent well serves as a production well, the group of wells form a pyrolysis unit, two adjacent pyrolysis units share the adjacent well, and pyrolysis exploitation of a block is achieved through orderly starting and running of the pyrolysis units; the coal bed pyrolysis exploitation is realized by arranging a heat carrier injection well and a coal gas and coal tar production well in the coal bed, bringing heat required by low-temperature pyrolysis of the coal bed into the coal bed by a heat carrier, and carrying out pyrolysis reaction on the coal bed to form low-temperature pyrolysis coal gas and coal tar and output the low-temperature pyrolysis coal gas and coal tar from the production well in a gaseous state.
Step three, draining and mining coal bed water: coal seams contain different amounts of moisture, particularly huge and thick coal seams are generally low-metamorphic coal with high moisture content, and free moisture in the coal seams must be discharged before pyrolysis is carried out effectively. The method comprises the following steps of adopting an overall drainage working process, namely starting drainage operation after completion of all well groups in a block, wherein drainage is carried out by adopting equipment used for current oil field mechanical oil extraction, in the drainage process, if a coal bed contains coal bed gas, the coal bed gas is recycled at the same time, in the drainage process of the block, the water content of the coal bed at a higher part is quickly reduced, when the water level in the well is lower than the bottom of the coal bed, the drainage work of the well is considered to be finished, other wells with water levels not reduced to the bottom of the coal bed continue to drain water, and when the drainage work of most wells is finished, some wells are properly reserved at the lower part of the block coal bed structure to continue to serve as drainage wells, so that the water level in a block production well is always lower than the bottom of the coal bed;
step four, coal bed pyrolysis: firstly, removing drainage equipment, installing pyrolysis supporting facilities for a well group, comprising installation of a heat insulation pipe for injecting a heat carrier and producing a pyrolysis gaseous product, installation of a bottom hole thermodetector and a special well mouth, installation and debugging of a ground heat carrier heater, a heat carrier pressurizing pump and a produced product treatment system, and construction of a related pipe network, a storage tank and supporting facilities, wherein when a pyrolysis unit starts a pyrolysis process, pressurized heat carrier gas is injected into a coal bed through an injection well after being heated by the ground heater, the injection amount of the heat carrier gas can be determined according to the thickness and the permeability of the coal bed, a higher injection rate is adopted when the coal bed is thick and the permeability of the coal bed is higher, otherwise, a lower injection rate is adopted, the injection rate is continuously adjusted along with the pyrolysis process, is smaller at the beginning, and is gradually increased along with the gradual formation of a pyrolysis channel and the continuous expansion of a pyrolysis surface, then when the yield of the pyrolysis product is reduced, the injection rate is reduced until the pyrolysis is finished, generally, the injection amount of the heat carrier in the pyrolysis process is adjusted according to 50-150 cubic meters (volume under a standard state) per hour of the thickness of each meter of the coal bed, when the heat carrier gas is injected from the injection well, a well head valve of the production well is in a closed state, the pressure of the well head of the injection well is continuously increased along with the continuous injection of the heat carrier gas, the pressure of the well head of the production well is also increased, when the pressure of the well head of the injection well is increased to 65-75% of the formation pressure, the valves of the wells with less pressure increase in the production well are sequentially opened to start production, along with the production, the yield of the wells is gradually increased, the well head pressure is also gradually increased, the well head temperature of the production well product is detected, and the opening amount of the production valve of the production well is dynamically adjusted by monitoring the production pressure, the yield and the temperature of the well head, the production parameters of each well are balanced, the high pyrolysis rate and the utilization rate of the coal bed are finally realized, when the coal bed parameters are different greatly, the condition of unbalanced pyrolysis reaction of the coal bed can occur, at the moment, the matching relation between the production wells and the injection wells in the area and related production parameters need to be adjusted, and when the quantity of the injected gas in the area is basically the same as that of the produced gas and the components are consistent, the pyrolysis exploitation of the coal in the area is completed.
Preferably, in the first step, the process is preferentially applied to a thick coal seam with a single-layer thickness of more than 20 meters, the evaluation requires that the coal seam has a complete and compact top-bottom interlayer, the coal seam is not directly communicated with a water system, the distance between the coal seam and the water system is generally required to be more than 50 meters, the water in the water system is ensured not to obviously invade when the coal seam is pyrolyzed, meanwhile, the dip angle, the trend and the fault condition of the coal seam are accurately known through exploration, the permeability and the coal bed gas project test are carried out on the coal seam, and the physicochemical analysis is carried out on a coal sample to serve as the basis of well arrangement and engineering design.
Preferably, in the second step, the well spacing between the injection well and the production well is not more than one hundred meters, the specific well spacing is mainly determined by the thickness of the coal seam and the permeability of the coal seam, a small well spacing is adopted when the coal seam is thicker or the permeability of the coal seam is lower, and a larger well spacing is adopted otherwise.
Preferably, the underground in-situ pyrolysis mining process for the huge coal seam according to claim 1, wherein in the second step, the production casing of the injection well and the production well are made of temperature-resistant and corrosion-resistant steel, and are provided with thermal expansion compensation short joints.
Preferably, in the second step, in order to ensure pyrolysis yield and coal seam utilization rate, the roles of the injection well and the production well in the production process can be interchanged.
Preferably, in the second step, according to the geological condition of the coal seam, the well pattern scheme can also be a four-point method scheme or an anti-nine-point method scheme, so that the well pattern can be set to facilitate uniform and controllable pyrolysis.
Preferably, in the third step, if the coal seam is relatively dense, the coal seam is firstly subjected to fracturing reformation to ensure the communication requirement between the wells in the well group, and then drainage operation is performed to discharge fracturing fluid and coal seam free water.
Preferably, in the fourth step, in order to ensure the heating intensity, a heater is arranged in the injection well shaft to be used as a main heater or an auxiliary heater.
Preferably, in the fourth step, the temperature of the heat carrier gas at the bottom of the injection well is not lower than 600 ℃, and the heat carrier gas can be any one of natural gas, carbon dioxide and nitrogen or a mixture of natural gas, carbon dioxide and nitrogen, and can also be coal bed pyrolysis gas produced in a block.
The invention has the beneficial effects that:
the method can realize the development and utilization of the huge thick coal seam which is difficult to mine or cannot be mined by the current underground technology: the pyrolysis process is adopted to mine the huge coal seam, the thicker the coal seam is, the more beneficial the economical efficiency of the process is, the gas in the coal seam is also mined out as high-quality resources, the effective development and utilization of the huge resources can relieve the stock pressure of the coal resources;
secondly, the development requirement of low-carbon clean mining of coal is met: the low metamorphic coal has the advantages of large chemical activity, high volatile content and high tar content, and high-quality mixed gas and tar products are obtained through pyrolysis, so that the problems of transportation, storage and use of the low metamorphic coal after being mined out of the ground are solved, and in the pyrolysis mining process of a coal bed, because the coal is only separated out of light components and coal tar after being pyrolyzed, the basic form framework of the coal bed still exists, only the porosity is increased, and the water permeability and the surface subsidence and a series of problems caused by the water permeability and the surface subsidence are avoided;
thirdly, the resource utilization rate is high: after the huge thick coal seam is thermally untied and mined, the original coal seam basically exists in situ in the form of semicoke, the coal seam can be further exploited by well engineering or further underground chemical synthesis, if further exploited by well engineering, the problems of spontaneous combustion and gas outburst are avoided because light components of the coal seam are extracted, the strength of the coal is increased, the exploitation of the coal is facilitated, the value of the produced product is obviously improved, and if further coal seam chemical processing or synthesis is performed, the strength and the porosity of the coal seam are obviously increased, the properties of the coal are more stable and consistent, and the related reactions are facilitated.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a well pattern layout of an underground in-situ pyrolysis mining process for a huge coal seam provided by an embodiment of the invention;
FIG. 2 is a schematic representation of drainage and production of a coal seam;
FIG. 3 is a flow chart of underground in-situ coal mining.
Description of reference numerals: 1. a coal pyrolysis mining area; 2. a production well; 3. an injection well; 4. a drainage well; 5. the earth surface; 6. an earth formation; 7. a coal seam; 8. pyrolysis gas, coal tar; 9. and (4) coal bed water.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.
the method comprises the following steps: and carrying out geological evaluation on the target coal mining area. Whether the coal seam of the block is suitable for mining by adopting an underground in-situ pyrolysis process is determined through evaluation, under the general condition, the process is preferentially applied to a thick coal seam with the thickness of more than 20 meters in a single layer, a complete and compact top-bottom plate interlayer is required to be arranged on the coal seam, the coal seam is not directly communicated with a water system, the distance between the coal seam and the water system is generally required to be more than 50 meters, the water of the water system is ensured not to be obviously invaded when the coal seam is pyrolyzed, meanwhile, the inclination angle, the trend and the fault condition of the coal seam are accurately known through exploration, the permeability, the coal bed gas and other projects of the coal seam are tested, the coal sample is subjected to physical and chemical analysis, and if the block is evaluated to be suitable for pyrolysis development, the next step is carried out.
Step two: and (5) building a pyrolysis unit. The pyrolysis mining of the coal bed is realized by arranging a heat carrier injection well and a coal gas and coal tar production well in the coal bed, the heat carrier carries in heat required by low-temperature pyrolysis of the coal bed, the coal bed carries out pyrolysis reaction to form low-temperature pyrolysis coal gas and coal tar, the coal gas is produced by the production well in a gaseous state, a well pattern can be arranged in a reverse five-point method, as shown in figure 1, the injection well and the production well penetrate through the coal bed at a vertical or nearly vertical angle, when one of the wells is used as the injection well, the peripheral adjacent well is used as the production well, the group of wells form a pyrolysis unit, two adjacent pyrolysis units share the adjacent well, the pyrolysis mining of a block is realized by orderly starting and operating a plurality of pyrolysis units, the well distance between the injection well and the production well is generally not more than one hundred meters and is mainly determined by the thickness of the coal bed and the permeability of the coal bed, and the thicker well distance is adopted when the permeability or the coal bed permeability is lower, otherwise, a larger well spacing is adopted, in order to ensure the pyrolysis yield and the coal seam utilization rate, the roles of an injection well and a production well can be interchanged in the production process, according to the coal seam geological condition, the well pattern scheme can also be a four-point method, an anti-seven-point method, an anti-nine-point method and the like, as long as the well pattern can be arranged to facilitate the uniform and controllable pyrolysis, during the well arrangement engineering design, the well pattern can be designed into a directional well or a straight well, the injection well and the production well are made of temperature-resistant and corrosion-resistant steel, a thermal expansion compensation short joint is arranged, and the next step is carried out after well completion.
Step three: and (5) draining and mining coal bed water. The coal beds contain different amounts of water, particularly huge thick coal beds are generally low metamorphic coal and have larger water content, in order to effectively implement coal bed pyrolysis, free water in the coal beds is discharged before pyrolysis, an overall drainage work flow is adopted, namely, all well groups in a block begin drainage operation after well completion, drainage is carried out by adopting equipment used by the conventional oil field mechanical oil extraction, in the drainage process, if the coal beds contain coal bed gas, the coal bed gas is mined and recovered at the same time, in the block drainage process, the water in the coal bed at a higher part drops faster, when the water level in the well is lower than the bottom of the coal bed, the drainage work of the well is considered to be finished, other wells producing water continue to drain, when the drainage work of most wells is finished, some wells are properly reserved at the lower part of the block coal bed structure to continue to serve as drainage wells, and the water level in the block production wells is ensured to be always lower than the bottom of the coal bed, and (3) the well group which completes the drainage requirement enters a pyrolysis operation link, if the coal bed is compact, the coal bed is firstly required to be fractured and reformed, the communication requirement between the wells in the well group is ensured, then drainage operation is carried out, fracturing fluid and coal bed free water are discharged, and after the coal bed drainage operation is completed, the next coal bed pyrolysis operation link is entered, as shown in fig. 2.
Step four: and (4) pyrolyzing the coal bed. Firstly, each well group of the demolished drainage equipment is provided with a pyrolysis supporting facility, which comprises a heat insulation pipe for injecting a heat carrier and producing a pyrolysis gaseous product, a well bottom thermodetector and a special well mouth, a ground heat carrier heater, a heat carrier pressurizing pump, a produced product processing system and the construction of a related pipe network, a storage tank and a supporting facility, when a pyrolysis unit starts a pyrolysis process, pressurized heat carrier gas is heated by a ground heater and then injected into a coal bed by an injection well, in order to ensure the heating intensity, a heater can be arranged in the shaft of the injection well to be used as a main heater or an auxiliary heater, the temperature of the heat carrier at the well bottom of the injection well is required to be not lower than 600 ℃, the heat carrier gas can be natural gas, carbon dioxide, nitrogen and the like, or a mixture thereof, or can be coal bed pyrolysis gas produced in a block, the injection amount of the heat carrier gas can be determined according to the thickness and the permeability of the coal bed, a higher injection rate is adopted when the coal bed is thick and the permeability of the coal bed is high, otherwise a lower injection rate is adopted, the injection rate is continuously adjusted along with the pyrolysis process, the injection rate is smaller at the beginning, the injection rate is gradually increased along with the gradual formation of a pyrolysis channel and the continuous expansion of a pyrolysis surface, then when the yield of pyrolysis products is reduced, the injection rate is reduced until the pyrolysis is finished, generally, the injection amount of the heat carrier is adjusted according to 50-150 cubic meters (under a standard state) per hour per meter of the thickness of the coal bed in the pyrolysis process, when the heat carrier gas is injected from an injection well, a wellhead valve of a production well is in a closed state, along with the continuous injection of the heat carrier gas, the wellhead pressure of the injection well is continuously increased, the wellhead pressure of the production well is also increased, but the wellhead pressure of each production well is not necessarily the same, when the pressure of the wellhead of the injection well rises to about seventy percent of the formation pressure, the valves of the wells with less pressure rise in the production well are sequentially opened to start production, along with the production, the yield of the wells is gradually increased, the pressure of the wellhead also gradually rises, meanwhile, the temperature of the wellhead of the products of the production well is detected, the opening amount of the valves of the wellhead of the production well is dynamically adjusted by monitoring the production pressure, the yield and the temperature of the wellhead to achieve more balanced production parameters of each wellhead, finally, higher pyrolysis rate and utilization rate of the coal bed are achieved, when the parameters of the coal bed are different greatly, the condition of unbalanced pyrolysis reaction of the coal bed can occur, at the moment, the matching relation between the production well and the injection well in an area and related production parameters need to be adjusted, when the amount of the gas injected into the area is basically the same as the amount of the produced gas and the components are consistent, the pyrolysis production of the coal in the area is finished, the underground in-situ pyrolysis mining process of the huge thick coal seam is shown in figure 3.
The application proposes that the underground coal bed pyrolysis mining is adopted, firstly, the underground coal bed pyrolysis mining has the characteristics of safety and environmental protection, all operations and control work are finished on the ground, as raw coal exists in situ in a semicoke form after the coal bed pyrolysis, the problem of surface subsidence is avoided, the phenomena of large-scale pollution of a water system and spontaneous combustion of the coal bed are avoided, the oxidation and carbon oxide gas emission in the mining, storage and transportation processes of the coal are avoided, the mining of solid ores is changed into the mining of gaseous ores, the produced product gas and coal tar have higher comprehensive product value, secondly, the pyrolysis method is used for mining the thick coal bed, the process requirements of coal pillars, partition walls and the like are not required to be reserved, the problems of incomplete stripping, coal abandoning and the like are avoided, the dynamic rate is higher, meanwhile, as the pyrolysis method is used for mining the huge thick coal bed, the construction of a pyrolysis unit is simple, required facilities and equipment are simple, and the production scale adjustment is flexible and convenient, in addition, the value of the produced product is high, so that better benefits can be obtained in a long term, and the method has the obvious advantages that the value of mining by a well method is improved by adopting the thick coal bed mined by a pyrolysis method, so that the process complexity and the cost are reduced because the coal beds are further mined by the well method without the risk of spontaneous combustion, the heat value of the produced product is improved, the application value is improved, and the profit level of the project is improved as a whole.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.
Claims (10)
1. An underground in-situ pyrolysis mining process for a huge thick coal seam is characterized by comprising the following specific steps of:
step one, geological evaluation is carried out on a target coal mining area: determining whether the coal seam of the block is suitable for mining by adopting an underground in-situ pyrolysis process through evaluation, evaluating that the huge thick coal seam of the block is suitable for pyrolysis development, and entering the next step;
step two, pyrolysis unit construction: the method comprises the following steps that coal bed pyrolysis heat input and product output channels are constructed in a ground drilling mode, well patterns are deployed in a reverse five-point method, injection wells and production wells penetrate through a coal bed at a vertical angle or a nearly vertical angle, when one well serves as an injection well, the surrounding adjacent well serves as a production well, the group of wells form a pyrolysis unit, two adjacent pyrolysis units share the adjacent well, and pyrolysis exploitation of a block coal bed is realized through orderly starting and running of a plurality of pyrolysis units;
step three, draining and mining coal bed water: the method comprises the following steps of adopting an overall drainage working process, namely starting drainage operation after completion of all well groups in a block, wherein drainage is carried out by adopting equipment used for current oil field mechanical oil extraction, in the drainage process, if a coal bed contains coal bed gas, the coal bed gas is recycled at the same time, in the drainage process of the block, the water content of the coal bed at a higher part is quickly reduced, when the water level in the well is lower than the bottom of the coal bed, the drainage work of the well is considered to be finished, other wells with water levels not reduced to the bottom of the coal bed continue to drain water, and when the drainage work of most wells is finished, some wells are properly reserved at the lower part of the block coal bed structure to continue to serve as drainage wells, so that the water level in a block production well is always lower than the bottom of the coal bed;
step four, coal bed pyrolysis: firstly, removing drainage equipment, installing pyrolysis supporting facilities for a well group, comprising installation of a heat insulation pipe for injecting a heat carrier and producing a pyrolysis gaseous product, installation of a well bottom temperature measuring instrument and a special well mouth, installation and debugging of a ground heat carrier heater, a heat carrier pressurizing pump and a produced product processing system, and construction of a related pipe network, a storage tank and supporting facilities, wherein when a pyrolysis unit starts a pyrolysis process, pressurized heat carrier gas is injected into a coal bed through an injection well after being heated by the ground heater, the injection amount of the heat carrier gas can be determined according to the thickness and the permeability of the coal bed, a higher injection rate is adopted when the coal bed is thick and the permeability of the coal bed is higher, otherwise, a lower injection rate is adopted, the injection rate is continuously adjusted along with the pyrolysis process, is smaller in the beginning, and is gradually increased along with the gradual formation of a pyrolysis channel and the continuous expansion of a pyrolysis surface, then when the yield of the pyrolysis product is reduced, the injection rate is reduced until the pyrolysis is finished, generally, the injection amount of the heat carrier in the pyrolysis process is adjusted according to 50-150 cubic meters (volume under a standard state) per hour of the thickness of each meter of the coal bed, when the heat carrier gas is injected from the injection well, a wellhead valve of the production well is in a closed state, the wellhead pressure of the injection well is continuously increased along with the continuous injection of the heat carrier gas, the wellhead pressure of the production well is also increased, when the wellhead pressure of the injection well is increased to 65-75% of the formation pressure, the valves of the wells with less pressure increase in the production well are sequentially opened to start production, along with the production, the yield of the wells is gradually increased, the wellhead pressure is also gradually increased, meanwhile, the wellhead temperature of the production well product is detected, and the wellhead production valve opening amount of the production well is dynamically adjusted by monitoring the wellhead production pressure, yield and temperature, the production parameters of the wells are balanced, the high pyrolysis rate and the utilization rate of the coal bed are finally realized, when the coal bed parameters are different greatly, the unbalanced condition of the pyrolysis reaction of the coal bed can occur, at the moment, the matching relation between the production wells and the injection wells in the area and related production parameters need to be adjusted, so that coal resources in the area can be fully pyrolyzed and developed, and when the quantity of injected gas and the quantity of produced gas in the area are basically the same and the components are consistent, the pyrolysis exploitation of the coal in the area is completed.
2. The underground in-situ pyrolysis mining process for the huge thick coal seam according to claim 1, wherein in the step one, the process is preferentially applied to a thick coal seam with a single thickness of more than 20 meters, the evaluation requires that the coal seam has a complete and compact top-bottom interlayer, the coal seam is not directly communicated with a water system, the distance between the coal seam and the water system is generally required to be more than 50 meters, the water system is ensured not to have obvious invasion when the coal seam is pyrolyzed, meanwhile, the dip angle, the trend and the fault condition of the coal seam are accurately known through exploration, and the permeability, the coal seam gas project test and the physicochemical analysis of a coal sample are carried out on the coal seam.
3. The underground in-situ pyrolysis mining process of a huge coal seam according to claim 1, wherein in the second step, the well distance between the injection well and the production well is not more than one hundred meters, the specific well distance is mainly determined by the thickness of the coal seam and the permeability of the coal seam, a small well distance is adopted when the coal seam is thicker or the permeability of the coal seam is lower, and a larger well distance is adopted when the coal seam is thicker or the permeability of the coal seam is lower.
4. The underground in-situ pyrolysis mining process of a huge and thick coal seam according to claim 1, wherein in the second step, the well type can be designed as a directional well or a vertical well.
5. The underground in-situ pyrolysis mining process of the huge coal seam according to claim 1, wherein in the second step, the production casing of the injection well and the production well are made of temperature-resistant and corrosion-resistant steel, and are provided with thermal expansion compensation short joints.
6. The underground in-situ pyrolysis mining process of a huge coal seam according to claim 1, wherein in the second step, in order to ensure pyrolysis yield and coal seam utilization rate, the roles of injection well and production well can be interchanged during the production process.
7. The underground in-situ pyrolysis mining process of the huge thick coal seam according to the claim 1, wherein in the second step, the well pattern scheme can be a four-point scheme, an inverse seven-point scheme or an inverse nine-point scheme according to the geological condition of the coal seam, so that the well pattern can be arranged to facilitate the uniform and controllable implementation of pyrolysis.
8. The underground in-situ pyrolysis mining process of the huge thick coal seam according to claim 1, wherein in the third step, if the coal seam is denser, the coal seam is firstly required to be fractured and reformed, the communication requirement between the wells in the well group is ensured, and then drainage operation is carried out, and fracturing fluid and free water of the coal seam are discharged.
9. The underground in-situ pyrolysis mining process of a huge coal seam according to claim 1, wherein in the fourth step, in order to ensure the heating intensity, a heater is arranged in the well bore of the injection well as a main heater or an auxiliary heater.
10. The underground in-situ pyrolysis mining process of the huge coal seam according to the claim 1, wherein in the fourth step, the temperature of the heat carrier gas at the bottom of the injection well is not lower than 600 ℃, and the heat carrier gas can be any one of natural gas, carbon dioxide and nitrogen or the mixture of natural gas, carbon dioxide and nitrogen, and can also be the coal seam pyrolysis gas produced in the block.
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