A method of fracturing and connecting mining of coal seam wells based on supercritical water injection pyrolysis and gasification

Abstract

The invention provides a coal seam group well fracturing connection mining method based on supercritical water injection pyrolysis gasification, belonging to the coal seam group well fracturing connection mining technology field; the technical problem to be solved is: to provide an improvement of the coal seam group well fracturing connection mining method based on supercritical water injection pyrolysis gasification; the technical scheme adopted to solve the technical problem is: to investigate the geological conditions of typical coal-bearing gas occurrence mining areas, to establish a reservoir geometry model based on geological drilling data, to obtain the lithology characteristics, physical and mechanical properties, and permeability parameters of rocks in different layers of the coal-bearing reservoir and the coal-rock interface area under ultra-high temperature and complex stress conditions, and to establish a coal-bearing reservoir geometry model; to select the lower group coal with low layer position and thick thickness in the coal-bearing reservoir as the target gasification mining coal seam, to design the mining area range, to analyze the lithology characteristics of the coal seam gasification zone according to the rock layer control key layer theory method, and to determine the layer distribution of the overburden key layer; the invention is applied to coal seam mining.

Description

Technical Field

[0001] The invention provides a coal seam group well fracturing and connecting mining method based on supercritical water injection pyrolysis and gasification, belonging to the technical field of coal seam group well fracturing and connecting mining. Background Art

[0002] The mining of coal resources buried deep in the ground is difficult. It is necessary to overcome the difficulties of traditional mining technology and solve the problems of high ground stress, high gas pressure, high ground temperature and strong disturbance encountered in the mining process. The current underground coal gasification mining method is to inject gasifiers into underground coal seams through injection channels, so that a series of physical and chemical reactions occur between coal and gasifiers in the in-situ coal seams to generate hydrogen, carbon monoxide, methane and other combustible gases. This is a chemical coal mining method. Underground coal gasification realizes the clean and closed development of coal underground, and there is no solid waste emission in the production process. This method is a clean energy development method that integrates the three major processes of well construction, coal mining and gasification. It has technical advantages such as good safety, low investment, high efficiency and less pollution. At this stage, it is preferentially applicable to the development and utilization of deep coal seams, unmineable coal seams and uneconomical coal resources.

[0003] However, traditional underground coal combustion gasification is to control the combustion of coal in situ. A large number of field practices have proved that the process causes the collapse of the roof and floor surrounding rocks and easily leads to leakage of generated gas. Problems such as loss of control of the fire surface, ground collapse, water gushing into the gasification chamber and escape of generated gas often occur. As a result, the large-scale application prospects of underground coal combustion gasification technology are still unclear and it has not yet entered the stage of practical promotion. Therefore, it is urgent to develop a mining model for the clean and efficient utilization of deep coal resources to achieve efficient and stable gasification mining of coal seams. Summary of the invention

[0004] In order to overcome the deficiencies in the prior art, the present invention aims to solve the technical problem of providing an improved method for fracturing and connecting coal seam wells based on supercritical water injection pyrolysis and gasification.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a coal seam group well fracturing and connection mining method based on supercritical water injection pyrolysis and gasification, comprising the following mining steps:

[0006] Step S1: Investigate the geological conditions of typical coal-measure gas deposits with a burial depth greater than 1500m, establish a reservoir geometry model based on geological drilling data and geomechanics theory, obtain the lithology, physical and mechanical properties, and permeability parameters of rocks at different layers of the coal-measure reservoir and the interface of the coal-rock layer under ultra-high temperature and complex stress conditions, and establish a coal-measure reservoir geometry model;

[0007] Step S2: Based on the coal-bearing reservoir geometric model, the lower coal group with low layer position and thick thickness in the coal-bearing reservoir is selected as the target gasification mining coal seam, the mining area is designed, and the lithological characteristics of the coal seam gasification zone are analyzed according to the rock stratum control key layer theory method to determine the stratigraphic distribution of the overburden key layer;

[0008] Step S3: Based on the mining area, the spacing of the surface wells is designed. Each well is drilled vertically into the coal seam with a depth of 1500m or more, and the bottom of the well is drilled to the bottom rock layer of the target gasification mining coal seam;

[0009] Step S4: selecting appropriate fracturing media according to the physical and mechanical properties of the coal-rock mass at the coal-rock interface area, and performing repeated fracturing along the coal-rock interface area of ​​the coal-rock layer to achieve interconnection between wells and provide a channel for underground pyrolysis of the coal seam;

[0010] Step S5: injecting supercritical water with a temperature greater than 600°C into the interface area, allowing it to flow along the interface area and preheat the coal body, and then injecting oxygen to cause an oxidation-reduction reaction in the coal seam to produce a mixed gas mainly composed of hydrogen and carbon dioxide, thereby completing the pre-gasification work;

[0011] Step S6: continue to inject supercritical water into the coal seam, gradually gasify it from bottom to top along the height direction of the coal seam, and realize upward gasification and control of hydrogen;

[0012] Step S7: during the gasification process, a filling slurry is synchronously injected into the gasification chamber, so that the water in the slurry self-generates supercritical water at high temperature to participate in the reduction reaction;

[0013] Step S8: The gas produced by gasification is discharged from the production well and separated on the ground to obtain hydrogen, and the separated carbon dioxide is stored deep underground;

[0014] Step S9: real-time monitoring and collection of gasification cavity temperature and pressure distribution data, as well as rock mass change data of key layers of roof surrounding rock;

[0015] Step S10: Based on the monitoring data, a gasification chamber temperature field evolution model is established, a gasification method is designed, and an intelligent linkage control model is established to realize automatic selection of injection well and production well interval rotation, automatic selection of supercritical water and oxygen injection intervals and ratios, and uniform expansion of the reaction zone.

[0016] The geological conditions of typical coal-measure gas deposits investigated in step S1 specifically include: fault distribution characteristics, aquifer level, aquifer water pressure, coal seam level, and coal seam thickness;

[0017] The lithological characteristics and physical and mechanical properties of different reservoir layers and coal-rock interface zones obtained in step S1 specifically include: mineral composition, porosity, elastic modulus, Poisson's ratio, uniaxial compressive strength, triaxial compressive strength, cohesion, internal friction angle, fracture characteristics, and heat transfer characteristics;

[0018] In the process of establishing the coal-bearing reservoir geometric model in step S1, the model lithology parameters are adjusted and the model is verified and corrected by comparing the measured data of borehole water pressure of aquifers in different layers with the numerical simulation data.

[0019] The key overburden layers determined in step S2 specifically include: a key layer with the lowest permeability that functions as a water barrier and a gas barrier, and a key layer with the highest mechanical strength that functions as a rock layer control.

[0020] The fracturing medium selected in step S4 includes gas or fluid fracturing medium, specifically supercritical carbon dioxide, water or nitrogen foam.

[0021] The specific process of injecting oxygen in step S5 to cause the coal seam to undergo oxidation-reduction reaction is as follows:

[0022] When injecting oxygen, the injection is controlled according to the temperature change of the reaction chamber. When the temperature of the reaction chamber is lower than the reduction reaction threshold, oxygen is injected. When the temperature of the reaction chamber is lower than the reduction reaction threshold, the injection of oxygen is stopped.

[0023] Oxygen reacts with coal to produce carbon dioxide. This reaction is an exothermic reaction. The accumulation of heat generated by the reaction will cause the coal temperature to reach the critical threshold of the reduction reaction. At this time, supercritical water reacts with the coal to produce carbon dioxide and hydrogen.

[0024] The specific methods for deep underground storage of carbon dioxide in step S8 include coal seam storage, ultrabasic rock storage, and aquifer storage. Ultrabasic rock storage specifically involves injecting carbon dioxide into deep ultrabasic rock formations to cause a chemical reaction between carbon dioxide and ultrabasic rocks to achieve solidification and storage.

[0025] The rock mass change data of the key layers of the roof surrounding rock monitored and collected in step S9 are specifically the deformation of the key layers of water blocking and gas isolating and the key layers of rock stratum control during the gasification process and the range of the plastic failure zone of the surrounding rock.

[0026] The specific method for establishing the gasification cavity temperature field evolution model in step S10 is:

[0027] By obtaining the spatial distribution of coal-bearing reservoirs at different levels and the deformation characteristics of overlying rocks at different coal seam gasification stages, integrating the migration and dynamic change laws of temperature field, seepage field, and fracture field in coal-bearing reservoirs between different vertical layers and different horizontal factors, the development, update, evolution, and iteration laws of the temperature field of the gasification cavity throughout its life cycle are analyzed, and a multi-mechanism collaborative evolution mechanism is constructed, ultimately forming a dynamic evolution model of the temperature field in the gasification process of the gasification cavity throughout its life cycle.

[0028] The beneficial effects of the present invention over the prior art are as follows: the present invention provides a method for fracturing and connecting coal seam wells based on supercritical water injection pyrolysis gasification. The supercritical water used in the method has extremely strong mass transfer, heat transfer and dissolution properties, and can be used as an excellent reaction medium. It can achieve efficient and clean gasification of various biomass, coal, petroleum coke and organic waste solids and liquids. Deep coal seams are generally dense and have poor permeability, which can easily form a supercritical reaction pyrolysis environment for coal. Therefore, the present invention adopts the method of arranging wells on the ground, and implements the method along the interface area between the coal seam and the bottom rock layer. The fracturing realizes interconnection of the well groups, and then supercritical water is injected into the interface area, and oxygen is injected to cause oxidation-reduction reaction in the coal seam, and then supercritical water is continuously injected into the coal seam, and gasification is gradually carried out from bottom to top along the height direction of the coal seam, so as to realize upward gasification hydrogen production, generate hydrogen, carbon dioxide and other gases, and at the same time, synchronous grouting filling, deep underground storage of carbon dioxide and monitoring and control of the gasification cavity are implemented by the injection well, so as to realize intelligent control and mining of the well group in the gasification area; the present invention is of great significance for realizing large-scale industrial development of deep coal resources by in-situ supercritical water gasification. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The present invention will be further described below in conjunction with the accompanying drawings:

[0030] Figure 1 is a flow chart of the steps of the mining method of the present invention;

[0031] Figure 2 This is a rendering of the geological state of a borehole in a mining area in an embodiment of the present invention;

[0032] Figure 3 for Figure 2 Reservoir geometry model diagram;

[0033] Figure 4 This is a layout and orientation effect diagram of the surface injection and production well group in the present invention;

[0034] Figure 5 This is a schematic diagram of the effect of the interface zone fracturing connection in an embodiment of the present invention;

[0035] Figure 6 This is a schematic diagram of the effect of injecting supercritical water gasification gas production in an embodiment of the present invention;

[0036] Figure 7A schematic diagram of the effect of synchronous filling in an embodiment of the present invention;

[0037] Figure 8 This is a schematic diagram of the effect of deep underground storage of carbon dioxide in an embodiment of the present invention;

[0038] Fig. 9 This is a circuit structure diagram of placing sensors in a group of wells according to an embodiment of the present invention.

[0039] The meanings of the serial numbers in the figure are: 1-target coal seam; 2-main key layer; 3-sub-key layer; 4-water-blocking and gas-isolating key layer; 5-injection well; 6-production well 1; 7-production well 2; 8-production well 3; 9-production well 4; 10-bottom rock layer; 11-gasification cavity; 12-proppant; 13-interface zone; 14-ultra-high temperature zone; 15-high temperature zone; 16-filling slurry; 17-carbon dioxide deep storage; 18-high-efficiency gasification intelligent system; 19-controller; 20-control valve; 21-temperature sensor; 22-pressure sensor. DETAILED DESCRIPTION

[0040] The present invention provides a method for fracturing and connecting coal seam wells based on supercritical water injection pyrolysis and gasification. The method can effectively improve the connectivity rate and heat exchange area of ​​the gasification cavity in deep coal seam gasification mining, thereby achieving rapid and large-scale production of hydrogen from deep coal seams and deep underground storage of carbon dioxide to meet the requirements of commercial development; Figure 1 As shown, the mining method provided by the present invention involves gasification mining of deep low-permeability coal-bearing reservoirs, and the mining means include: based on the establishment of a geomechanical model, the selection of gasified coal seam positions, the arrangement of surface injection and production well groups, and the use of a group of wells to carry out coal-rock interface zone fracturing, interface zone pre-gasification, coal seam upward regulation gasification, synchronous grouting and filling, deep storage of carbon dioxide, gasification cavity monitoring and regulation, and the construction of an efficient gasification intelligent system, etc., to produce hydrogen from deep coal seams on a large scale and realize deep storage of carbon dioxide.

[0041] Furthermore, the present invention is centered on the construction of channels by fracturing and connecting wells, and the production of hydrogen by pyrolysis and gasification of supercritical water, and mainly includes the following steps:

[0042] Fracturing at the interface area of ​​the coal-rock layer; arranging a group of wells on the ground to the bottom plate of the target coal seam, and carrying out fracturing along the interface area between the coal seam and the bottom plate rock layer to achieve interconnection between the supercritical water (energy) injection well and multiple gas production wells.

[0043] Gasification of the interface area: Supercritical water (>600℃) is injected into the interface area connected by the fracturing, so that it flows along the interface area and preheats the coal body. Then oxygen is injected to cause the coal seam to undergo an oxidation reaction (exothermic) and the temperature reaches 900℃, which promotes the reduction reaction of the coal seam and produces gases such as hydrogen, carbon monoxide, and carbon dioxide.

[0044] Ascending coal seam gasification and hydrogen production; coal seam gasification and pyrolysis in the interface area will cause the upper coal seam to be depressurized and ruptured, resulting in an increase in the number of pores and cracks in the coal body and an increase in the area of ​​the gasification channel. At this time, supercritical water is continuously injected into the coal seam, and gasification is gradually carried out from bottom to top along the height direction of the coal seam, thus realizing upward gasification and hydrogen production;

[0045] Synchronous grouting filling: during the gasification process, high-water filling slurry is injected into the gasification cavity simultaneously. The water in the slurry generates supercritical water at high temperature and participates in the reduction reaction. At the same time, the dehydrated solid filling material supports the coal skeleton in the reaction area to prevent the roof surrounding rock from collapsing.

[0046] The carbon dioxide is stored deep underground; the gas produced by gasification is discharged from the production well and separated on the ground to obtain hydrogen, and the separated carbon dioxide is stored deep underground.

[0047] Monitoring and control of gasification chamber: Monitoring technology is used to monitor the temperature and pressure distribution of the gasification chamber and the deformation of the key layers of the roof surrounding rock in real time. Based on the monitoring data, injection wells and production wells are selected in rotation, and the injection interval and ratio of supercritical water and oxygen are selected, thereby regulating the uniform expansion of the reaction zone and realizing intelligent control and exploitation of the gasification zone group of wells.

[0048] Furthermore, the purpose of the present invention is to overcome the many shortcomings of the existing gasification process, such as the collapse of the roof and floor surrounding rocks, which easily leads to the leakage of the generated gas, the frequent occurrence of problems such as loss of control of the ignition surface, ground collapse, water gushing from the gasification chamber and the escape of the generated gas, thereby providing a high gasification rate, high efficiency and high intelligence method for controlling the gasification and hydrogen production by supercritical water injection in deep coal-bearing reservoirs.

[0049] The high-efficiency pyrolysis gasification method of deep coal seam group wells by fracturing and connecting and injecting supercritical water takes the low-permeability coal-bearing reservoir with vertical superposition as the object, establishes a reservoir geomechanical model, obtains the reservoir lithology, arranges group wells on the ground, implements fracturing along the interface area between the coal seam and the bottom rock layer to achieve mutual connection of the group wells, then injects supercritical water (>600℃) into the interface area, and injects oxygen to make the coal seam undergo oxidation-reduction reaction, and then continues to inject supercritical water into the coal seam, gradually gasifies from bottom to top along the height direction of the coal seam, realizes upward gasification hydrogen production, and produces hydrogen, carbon dioxide and other gases. At the same time, the injection well implements synchronous grouting and filling, deep storage of carbon dioxide and monitoring and control of the gasification cavity, establishes a temperature field evolution model of the gasification zone, designs a dynamic and efficient gas injection method, and establishes an intelligent linkage control model to realize intelligent control and mining of group wells in the gasification zone.

[0050] The specific steps are as follows:

[0051] (1) Establishment of geomechanical model: Investigate the geological conditions of typical coal-bearing gas deposits with a burial depth greater than 1500m. Based on geological drilling data and applying geomechanics theory, establish a reservoir geometry model to obtain the lithological characteristics, physical and mechanical properties, and permeability parameters of rocks at different levels of the coal-bearing reservoir and at the coal-rock interface under ultra-high temperature and complex stress conditions.

[0052] (2) Selection of gasification coal seam stratigraphic positions: Based on the reservoir geometry model, the lower coal group (one or several layers) with lower stratigraphic positions and thicker thickness in the coal-bearing reservoir is selected as the target gasification mining coal seam. The mining area is designed, and the lithological characteristics of the coal seam gasification zone are analyzed according to the theoretical method of rock stratum control key layers to determine the stratigraphic distribution of the overburden key layers.

[0053] (3) Surface injection and production well group layout: Based on the scope of the mining area, the layout spacing of the surface well group is reasonably designed. Each well adopts a vertical well form to enter the coal seam with a depth of more than 1500m, and the bottom of the well is drilled to the bottom rock layer of the target coal seam.

[0054] (4) Fracturing at the coal-rock interface: Based on the physical and mechanical properties of the coal-rock interface measured in the laboratory, a suitable fracturing medium is selected, and repeated fracturing is carried out along the coal-rock interface to achieve interconnection between wells and provide a channel for underground pyrolysis of the coal seam.

[0055] (5) Pre-gasification of the interface zone: Supercritical water (>600°C) is injected into the interface zone to make it flow along the interface zone and preheat the coal body. Oxygen is then injected to cause oxidation-reduction reaction in the coal seam to produce a mixed gas mainly composed of hydrogen and carbon dioxide.

[0056] (6) Upward gasification control of coal seams: Gasification of coal seams in the interface zone will cause pressure relief and rupture of the upper coal seams, resulting in an increase in the number of pores and cracks in the coal body and an increase in the area of ​​the gasification channel. At this time, supercritical water is continuously injected into the coal seams, and gasification is gradually carried out from bottom to top along the height direction of the coal seams, thus realizing upward gasification and hydrogen control.

[0057] (7) Synchronous grouting filling: During the gasification process, high-water filling slurry is injected into the gasification cavity. The water in the slurry generates supercritical water at high temperature and participates in the reduction reaction. At the same time, the dehydrated solid filling material supports the coal skeleton in the reaction area to prevent the collapse of the roof surrounding rock.

[0058] (8) Deep underground storage of carbon dioxide: The gas produced by gasification is discharged from the production well and separated on the ground to obtain hydrogen. The separated carbon dioxide is then stored deep underground.

[0059] (9) Gasification chamber monitoring and control: Monitoring technology is used to monitor the temperature and pressure distribution of the gasification chamber and the changes in the key layers of the roof surrounding rock in real time.

[0060] (10) Construction of an efficient gasification intelligent system: Based on the monitoring data, a gasification chamber temperature field evolution model is established, and a dynamic efficient gasification method is designed. An intelligent linkage control model is established to construct an efficient gasification intelligent system to achieve intelligent interval rotation selection of injection wells and production wells, as well as the injection interval and ratio of supercritical water and oxygen, thereby regulating the uniform expansion of the reaction zone and realizing intelligent control and exploitation of a group of wells in the gasification zone.

[0061] Preferably, the geomechanical model establishment comprises the following steps:

[0062] The lithological characteristics and physical and mechanical properties of different reservoir layers and coal-rock interface areas include mineral composition, porosity, elastic modulus, Poisson's ratio, uniaxial compressive strength, triaxial compressive strength, cohesion, internal friction angle, fracture characteristics, and heat transfer characteristics.

[0063] Ultra-high temperature and complex stress conditions refer to the coupling effects of high-ultra-high temperature intermittent cyclic thermal loads, wet-hot pore fluid pressure wetting, and mining-filling cycle loading and unloading.

[0064] Preferably, during the process of establishing the geomechanical model, the model lithology parameters are corrected by comparing the measured data of the borehole water pressure of aquifers at different levels with the numerical simulation data, and the model is reasonably verified and corrected.

[0065] Preferably, the gasification coal seam layer selection includes the following steps:

[0066] The key layers of coal seam overburden include the key layers with the lowest permeability that play the role of water isolation and gas barrier, and the key layers with the highest mechanical strength that play the role of rock layer control.

[0067] Preferably, the coal-rock interface zone fracturing comprises the following steps:

[0068] Gas or fluid fracturing media, mainly supercritical carbon dioxide, water, and nitrogen foam.

[0069] Microseismic monitoring technology is used to monitor the acoustic emission signal characteristics generated by the rupture and expansion of interface cracks. A distributed optical fiber monitoring system is set up in parallel to monitor the fluid, crack initiation point, and microseismic events in the well, calculate the direction and shape of the interface cracks, and determine the rupture position of the interface cracks in the well in real time, thereby realizing visual monitoring of downhole hydraulic fractures.

[0070] Preferably, the pre-gasification of the interface zone comprises the following steps:

[0071] Supercritical water (>600°C) is injected into the interface zone, either through a single well or through a group of wells simultaneously.

[0072] Oxidation and reduction reactions can occur simultaneously or sequentially, depending on the pressure and temperature conditions of the two reactions.

[0073] Oxygen reacts with coal to produce an oxidation reaction. , the reaction is exothermic, the heat accumulation generated by the reaction will make the coal temperature reach the critical threshold of the reduction reaction, at this time, the supercritical water and the coal undergo a reduction reaction, the reaction formula is In addition, there are many intermediate reactions in the process, including ,as well as .

[0074] The injection of oxygen can be controlled according to the temperature change of the reaction chamber. When the temperature of the reaction chamber is lower than the reduction reaction threshold, oxygen is injected, and when the temperature of the reaction chamber is lower than the reduction reaction threshold, the injection of oxygen is stopped.

[0075] Preferably, the upward regulation of coal seam gasification includes the following steps:

[0076] Regulation is mainly based on regulation theory, which specifically refers to establishing a mathematical model of porous media evolution and multi-component multiphase fluid diffusion migration and heat exchange based on fracturing and chemical action, and providing a numerical simulation solution algorithm. Numerical means are used to simulate the unsteady evolution of coal seam stress field, seepage field, temperature field, and concentration field during gasification, and to deeply study the non-uniform expansion law of the gasification zone and its influencing factors, and to establish a multi-component multiphase fluid regulation theory during the evolution of the gasification zone under the coupling of thermal-hydraulic-mechanical-chemical multi-fields.

[0077] Preferably, the synchronous grouting filling comprises the following steps:

[0078] Indoor experimental methods are used to determine the liquid-solid two-phase flow migration and filling characteristics of the ultra-high water filling material in the pyrolysis residual coal skeleton, as well as the long-term mechanical and deformation characteristics of the roof rock mass-coal skeleton-filling body combination under complex thermal-hydraulic-mechanical-chemical coupling.

[0079] Preferably, deep storage of carbon dioxide comprises the following steps:

[0080] Deep storage of carbon dioxide includes coal seam storage, ultrabasic rock storage, and aquifer storage. Ultrabasic rock storage is to inject carbon dioxide into ultrabasic rock formations buried 4,000 meters deep, so that carbon dioxide and ultrabasic rocks produce chemical reactions to achieve solidification and storage. Coal seam storage and aquifer storage are both physical storage.

[0081] Preferably, the gasification chamber monitoring and regulation includes the following steps:

[0082] The rock mass changes of the key layers of the roof surrounding rock in step S9 refer to the deformation of the "key layers for water blocking and gas isolating" and the "key layers for rock layer control" during the gasification process and the range of the plastic failure zone of the surrounding rock.

[0083] Preferably, the construction of an efficient gasification intelligent system includes the following steps:

[0084] The gasification cavity temperature field evolution model is to obtain the spatial distribution of coal-bearing reservoirs and the deformation characteristics of overburden rocks at different coal seam gasification stages, integrate the migration and dynamic change laws of temperature fields, seepage fields, and fracture fields in coal-bearing reservoirs between different vertical layers and different horizontal factors, analyze the development, update, evolution, and iteration laws of the gasification cavity temperature field throughout the life cycle, construct a multi-mechanism collaborative evolution mechanism, and form a dynamic evolution model of the temperature field during the gasification process of the gasification cavity throughout the life cycle;

[0085] Dynamic and efficient gasification method design refers to the integration of multi-source data such as coal-bearing geology and well group injection and production processes to establish a synchronous digital twin model; based on big data mining technology, the changes in the flow field and temperature field of the gasification cavity at different injection and production stages or life cycles are studied, and the relevant influencing factors and weights with gas production volume and gas production efficiency as the target are determined, and dynamic and efficient gasification methods with different life cycles are designed;

[0086] The establishment of intelligent linkage control model refers to building an intelligent linkage model of well group injection and production and gasification cavity flow field and temperature field based on gasification intelligent monitoring data, proposing deep learning technology, clarifying the intelligent parameter adjustment linkage relationship of well group injection and production system, and establishing an intelligent linkage control model for the entire life cycle;

[0087] The construction of an efficient gasification intelligent system refers to the use of digital twin technology and knowledge generation mechanism to organically integrate gasification mechanism models, empirical knowledge and big data, and establish an efficient gasification smart platform with real-time optimization of gasification schemes, intelligent regulation of gasification systems, intelligent diagnosis of gasification systems, and automatic evaluation of gasification compliance, forming an efficient gasification intelligent system with comprehensive perception, real-time interconnection, analysis and decision-making, autonomous learning, dynamic evolution, and collaborative control throughout its life cycle.

[0088] Further, in the embodiments of the present application, Figure 1 The figure shows a flow chart of the steps of the deep coal seam group well fracturing and connecting supercritical water injection efficient pyrolysis gasification method of the present invention, which includes the following steps: establishment of geomechanical model - selection of gasified coal seam layer - layout of surface injection and production group wells - fracturing of coal-rock interface zone - pre-gasification of interface zone - upward regulation of coal seam gasification - synchronous grouting and filling - deep underground storage of carbon dioxide - monitoring and regulation of gasification cavity - construction of efficient gasification intelligent system.

[0089] According to the following Figure 2-9 The typical coal-measure gas deposit area provided is used as the research object as a specific embodiment to further illustrate the steps of the group well intelligent control mining method of the present invention:

[0090] 1) Select typical coal-measure gas deposits as the research object, such as Figure 2 The following is a geological column diagram of a borehole in a mining area. Multiple coal seams were found in the borehole. Then, the reservoir geometry model was established by applying the geomechanics theory, as shown in Figure 1. Figure 3As shown; obtain drill cores from different layers and process them into standard test specimens indoors to measure the lithological characteristics and physical and mechanical properties under ultra-high temperature and complex stress conditions, including: mineral composition, porosity, elastic modulus, Poisson's ratio, uniaxial and triaxial compressive strength, cohesion, internal friction angle, and permeability.

[0091] 2) Select the lower group of coal in the coal-bearing reservoir with a lower layer and thicker thickness as the target (mining) coal seam 1, design the mining area, and determine the main key layer 2, sub-key layer 3, and key layer 4 that plays a role in blocking water and gas in the coal seam overburden based on the theoretical method of key layer controlling the rock formation.

[0092] 3) Based on the scope of the mining area, the layout spacing of the surface wells is reasonably designed. For the injection well 5 and the production wells 6-9, vertical wells are used to enter the target coal seam 1 at a depth of more than 1500m, and the bottom of the well is drilled to the bottom rock layer 10 of the target coal seam.

[0093] 4) Based on the physical and mechanical properties of the coal-rock interface zone obtained by laboratory measurements, a suitable fracturing medium is selected, and repeated fracturing is carried out along the coal-rock interface zone of the coal-rock layer, and proppant 12 is injected to achieve interconnection between the injection well 5 and the production wells 6-9, providing a channel for underground pyrolysis of the coal seam.

[0094] 5) Supercritical water (>600°C) is injected into the interface zone 13 to flow along the interface zone and preheat the coal body. Oxygen is then injected to cause oxidation-reduction reaction in the coal seam. The temperature decreases along the gasification channel, including the ultra-high temperature zone 14 and the high temperature zone 15, to produce a mixed gas mainly composed of hydrogen and carbon dioxide.

[0095] 6) Since the coal seam gasification in the interface zone 13 will cause the upper coal seam 1 to unload and rupture, resulting in an increase in the pores and cracks in the coal body and an increase in the area of ​​the gasification channel, it is necessary to continue to inject supercritical water into the coal seam, gradually gasify it from bottom to top along the height direction of the coal seam, and realize upward gasification and control of hydrogen.

[0096] 7) During the gasification process, high-water filling slurry 16 is simultaneously injected into the gasification cavity 11. The water in the slurry generates supercritical water at high temperature and participates in the reduction reaction. At the same time, the dehydrated solid filling material supports the coal skeleton in the reaction zone, thereby preventing the roof surrounding rock from collapsing.

[0097] 8) The gas produced by gasification is discharged from the production well 6-9 and separated on the ground to obtain hydrogen, and the separated carbon dioxide is sealed in the deep ground 17.

[0098] 9) Monitor the temperature and pressure distribution of gasification cavity 11 and the changes in the key rock layers of the roof surrounding rock in real time, integrate the migration and dynamic change laws of the temperature field, seepage field, and fracture field in the coal-bearing reservoir between different vertical layers and different horizontal factors, analyze the development, update, evolution, and iteration laws of the temperature field of the gasification cavity throughout its life cycle, construct a multi-mechanism collaborative evolution mechanism, and form a dynamic evolution model of the temperature field during the gasification process of the gasification cavity 11 throughout its life cycle.

[0099] 10) Integrate multi-source data such as coal-bearing geology and well group injection and production processes to establish a synchronous digital twin model; based on big data mining technology, study the changes in the flow field and temperature field of the gasification cavity at different injection and production stages or life cycles, determine the relevant influencing factors and weights with gas production volume and gas production efficiency as the targets, and design dynamic and efficient gasification methods for different life cycles.

[0100] 11) Based on the intelligent monitoring data of gasification, an intelligent linkage model of the injection and production of a group of wells and the flow field and temperature field of the gasification cavity is constructed. Deep learning technology is proposed to clarify the intelligent parameter adjustment linkage relationship of the injection and production system of a group of wells, and an intelligent linkage control model for the entire life cycle is established.

[0101] 12) Utilize digital twin technology and knowledge generation mechanism to organically integrate gasification mechanism models, empirical knowledge and big data, and establish an efficient gasification smart platform with real-time optimization of gasification schemes, intelligent regulation of gasification systems, intelligent diagnosis of gasification systems, and automatic evaluation of gasification compliance, forming an efficient gasification intelligent system with full perception, real-time interconnection, analysis and decision-making, autonomous learning, dynamic evolution, and collaborative control throughout the entire life cycle.

[0102] 13) During the gasification mining process, the efficient gasification intelligent system 18 monitors the temperature distribution of the gasification chamber in real time:

[0103] If the fluid temperature is lower than the critical threshold of the reduction reaction, the control valve 20 of the injection well is opened by the controller 19, and oxygen is injected into the gasification chamber 11 from the injection well;

[0104] If the fluid temperature increases and exceeds the critical threshold of the reduction reaction, the control valve 20 of the injection well is closed by the controller 19 to stop injecting oxygen into the gasification chamber 11.

[0105] Thereby, intelligent control of the opening / closing state of the injection well is achieved.

[0106] Similarly, the opening / closing state of the production well is also controlled in the same way.

[0107] In addition, the fluid pressure change in the gasification chamber can also be monitored by the pressure sensor 22, thereby realizing intelligent control. Therefore, the injection well and the production well are selected in an intelligent interval rotation, and the injection interval and ratio of supercritical water and oxygen are selected, thereby regulating the uniform expansion of the reaction zone and realizing intelligent control and exploitation of the gasification zone group wells.

[0108] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for fracturing and connecting coal seam wells based on supercritical water injection pyrolysis and gasification, characterized in that: The mining steps include: Step S1: Investigate the geological conditions of typical coal-measure gas deposits with a burial depth greater than 1500m, establish a reservoir geometry model based on geological drilling data and geomechanics theory, obtain the lithology, physical and mechanical properties, and permeability parameters of rocks at different layers of the coal-measure reservoir and the interface of the coal-rock layer under ultra-high temperature and complex stress conditions, and establish a coal-measure reservoir geometry model; Step S2: Based on the coal-bearing reservoir geometric model, the lower coal group with low layer position and thick thickness in the coal-bearing reservoir is selected as the target gasification mining coal seam, the mining area is designed, and the lithological characteristics of the coal seam gasification zone are analyzed according to the rock stratum control key layer theory method to determine the stratigraphic distribution of the overburden key layer; Step S3: Based on the mining area, the spacing of the surface wells is designed. Each well is drilled vertically into the coal seam with a depth of 1500m or more, and the bottom of the well is drilled to the bottom rock layer of the target gasification mining coal seam; Step S4: selecting appropriate fracturing media according to the physical and mechanical properties of the coal-rock mass at the coal-rock interface area, and performing repeated fracturing along the coal-rock interface area of ​​the coal-rock layer to achieve interconnection between wells and provide a channel for underground pyrolysis of the coal seam; Step S5: injecting supercritical water with a temperature greater than 600°C into the interface area, allowing it to flow along the interface area and preheat the coal body, and then injecting oxygen to cause an oxidation-reduction reaction in the coal seam to produce a mixed gas mainly composed of hydrogen and carbon dioxide, thereby completing the pre-gasification work; Step S6: continue to inject supercritical water into the coal seam, gradually gasify it from bottom to top along the height direction of the coal seam, and realize upward gasification and control of hydrogen; Step S7: during the gasification process, a filling slurry is synchronously injected into the gasification chamber, so that the water in the slurry self-generates supercritical water at high temperature to participate in the reduction reaction; Step S8: The gas produced by gasification is discharged from the production well and separated on the ground to obtain hydrogen, and the separated carbon dioxide is stored deep underground; Step S9: real-time monitoring and collection of gasification cavity temperature and pressure distribution data, as well as rock mass change data of key layers of roof surrounding rock; Step S10: Based on the monitoring data, a gasification chamber temperature field evolution model is established, a gasification method is designed, and an intelligent linkage control model is established to realize automatic selection of injection well and production well interval rotation, automatic selection of supercritical water and oxygen injection intervals and ratios, and uniform expansion of the reaction zone.

2. The method for fracturing and connecting coal seam wells based on supercritical water injection pyrolysis and gasification according to claim 1 is characterized in that: The geological conditions of typical coal-measure gas deposits investigated in step S1 specifically include: fault distribution characteristics, aquifer level, aquifer water pressure, coal seam level, and coal seam thickness; The lithological characteristics and physical and mechanical properties of different reservoir layers and coal-rock interface zones obtained in step S1 specifically include: mineral composition, porosity, elastic modulus, Poisson's ratio, uniaxial compressive strength, triaxial compressive strength, cohesion, internal friction angle, fracture characteristics, and heat transfer characteristics; In the process of establishing the coal-bearing reservoir geometric model in step S1, the model lithology parameters are adjusted and the model is verified and corrected by comparing the measured data of borehole water pressure of aquifers in different layers with the numerical simulation data.

3. The method for fracturing and connecting coal seam wells based on supercritical water injection pyrolysis and gasification according to claim 1, characterized in that: The key overburden layers determined in step S2 specifically include: a key layer with the lowest permeability that functions as a water barrier and a gas barrier, and a key layer with the highest mechanical strength that functions as a rock layer control.

4. The method for fracturing and connecting coal seam wells based on supercritical water injection pyrolysis and gasification according to claim 1, characterized in that: The fracturing medium selected in step S4 includes a fluid fracturing medium, specifically supercritical carbon dioxide, water or nitrogen foam.

5. The method for fracturing and connecting coal seam wells based on supercritical water injection pyrolysis and gasification according to claim 1, characterized in that: The specific process of injecting oxygen in step S5 to cause the coal seam to undergo oxidation-reduction reaction is as follows: When injecting oxygen, the injection is controlled according to the temperature change of the reaction chamber. When the temperature of the reaction chamber is lower than the reduction reaction threshold, oxygen is injected. When the temperature of the reaction chamber is lower than the reduction reaction threshold, the injection of oxygen is stopped. Oxygen reacts with coal to produce carbon dioxide. This reaction is an exothermic reaction. The accumulation of heat generated by the reaction will cause the coal temperature to reach the critical threshold of the reduction reaction. At this time, supercritical water reacts with the coal to produce carbon dioxide and hydrogen.

6. The method for fracturing and connecting coal seam wells based on supercritical water injection pyrolysis and gasification according to claim 1, characterized in that: The specific methods for deep underground storage of carbon dioxide in step S8 include coal seam storage, ultrabasic rock storage, and aquifer storage. Ultrabasic rock storage specifically involves injecting carbon dioxide into deep ultrabasic rock formations to cause a chemical reaction between carbon dioxide and ultrabasic rocks to achieve solidification and storage.

7. The method for fracturing and connecting coal seam wells based on supercritical water injection pyrolysis and gasification according to claim 1, characterized in that: The rock mass change data of the key layers of the roof surrounding rock monitored and collected in step S9 are specifically the deformation of the key layers of water blocking and gas isolating and the key layers of rock stratum control during the gasification process and the range of the plastic failure zone of the surrounding rock.

8. The method for fracturing and connecting coal seam wells based on supercritical water injection pyrolysis and gasification according to claim 1, characterized in that: The specific method for establishing the gasification cavity temperature field evolution model in step S10 is: By obtaining the spatial distribution of coal-bearing reservoirs at different levels and the deformation characteristics of overlying rocks at different coal seam gasification stages, integrating the migration and dynamic change laws of temperature field, seepage field, and fracture field in coal-bearing reservoirs between different vertical layers and different horizontal factors, the development, update, evolution, and iteration laws of the temperature field of the gasification cavity throughout its life cycle are analyzed, and a multi-mechanism collaborative evolution mechanism is constructed, ultimately forming a dynamic evolution model of the temperature field in the gasification process of the gasification cavity throughout its life cycle.

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