Coal mine gas-heat damage combined treatment and terrestrial heat utilization method

Abstract

The invention provides a coal mine gas-heat damage combined treatment and terrestrial heat utilization method, which is based on a ground U-shaped well technology, by integrally arranging a gas-heat co-production well and a heat production well, coal seam gas and stratum heat energy are synchronously extracted before coal mining, gas emission and high-temperature heat damage are synergistically treated from the source, and meanwhile, the coal seam gas-heat damage combined treatment and terrestrial heat utilization are realized. Recycled gas and geothermal water are used as fuel gas and a heat source respectively for resource utilization, efficient operation is achieved through well group cooperation and injection-production regulation and control, a new coal-gas-heat multi-resource collaborative development mode is finally constructed, coal mine gas-heat damage combined treatment and geothermal utilization are achieved, and the coal mine gas-heat damage combined treatment and geothermal utilization are achieved. Benefits of disaster control and resource utilization are maximized, and safe, green and efficient mining of a coal mine is promoted.

Description

Technical Field

[0001] This invention belongs to the field of coal mining technology, specifically relating to a method for the combined management of coal mine gas and heat hazards and the utilization of geothermal energy. Background Technology

[0002] Coal mine gas is essentially produced by the chemical metamorphism of ancient plants during the long geological history of coal formation, through microbial decomposition and geothermal and geopressure processes. As an associated gas, it has coexisted with coal since its formation. Before mining, this gas is "locked" within the coal seam; once mining disrupts the original balance of the coal and rock mass, the gas is released through pressure differences and new fracture channels, entering the mine roadways and causing gas outbursts. When the concentration accumulates to a certain range (5%-16%), it explodes upon encountering an ignition source. Furthermore, with increasing coal mining depth, mine heat hazards become increasingly severe, posing a growing threat to miners' health and safety. High-temperature heat hazards have become a significant challenge restricting the safe and efficient mining of deep coal mines. The main heat sources in underground coal mining include heat dissipation from surrounding rocks, heat dissipation from underground hot fluids, oxidation heat dissipation, heat dissipation from mechanical and electrical equipment, natural air compression heat, heat generated by blasting operations, and heat dissipation from the human body. According to statistics, among the heat sources in deep mines, heat dissipation from surrounding rocks accounts for 40%-50%, followed by heat dissipation from mechanical and electrical equipment and oxidation heat dissipation. Therefore, solving the heat hazard from surrounding rocks has become an important issue in solving the high-temperature heat hazard in underground mines.

[0003] In summary, gas outbursts and heat hazards during deep coal mining are key factors restricting efficient and safe production. When coal mine gas content and mine temperature exceed prescribed limits, targeted control measures must be implemented. Traditional mine cooling measures, such as non-mechanical refrigeration, mechanical refrigeration, and the use of heat insulation materials and sprayed insulation layers for high-temperature rock strata heat hazard control, are not only costly, have limited applicability, and poor control effects, but also fail to rationally and effectively utilize natural clean geothermal resources such as high-temperature rock strata and high-temperature fluids, leading to a waste of mine geothermal resources. Currently, there is a lack of effective methods to combine gas and heat hazard control with geothermal extraction and utilization. Surface coalbed methane extraction, heat hazard control, and geothermal development and utilization are isolated operations, lacking systematic design and coordinated operation, making it difficult to maximize the benefits of disaster control and geothermal resource utilization. Summary of the Invention

[0004] To address the following problems mentioned in the background art: traditional mine cooling measures are costly, have limited applicability, poor treatment effects, and waste of mine geothermal resources; surface coalbed methane extraction, heat hazard control, and geothermal development and utilization are isolated operations, lacking systematic design and coordinated operation, making it difficult to maximize the benefits of disaster control and geothermal resource utilization. This invention provides a method for the joint control of coal mine gas and heat hazards and the utilization of geothermal resources. It selects an appropriate control scheme based on the gas content and heat hazard distribution characteristics, and uses surface U-shaped well technology to achieve gas and heat hazard control and geothermal utilization.

[0005] The method of the present invention includes: Based on the characteristics of coal seam gas occurrence, the thermal control geological model of the coal mining area, and the amount of geothermal resources, the layout scheme of the U-shaped well mining system in the coal mining planning area and the implementation scheme of the joint treatment of surface gas-heat hazards using U-shaped wells are determined. The joint treatment U-shaped wells include multiple surface gas-heat co-extraction U-shaped wells and multiple surface heat extraction U-shaped wells. The surface gas-heat co-extraction U-shaped wells include: H wells and gas and water extraction V wells. The surface heat extraction U-shaped wells include: cold water injection H wells and heat extraction V wells. Obtain user heat load demand, combine the heat extraction design of the U-shaped well joint treatment scheme for ground gas-heat hazards, and set up ground heating energy stations to provide heat energy to users; Develop extraction plans for gas-heat co-production wells and heat extraction wells: According to the gas-heat co-production well life cycle, it is divided into two stages: gas production-heat production and water injection-heat production. In the gas production-heat production stage, gas and geothermal water are extracted simultaneously through the gas production and water production V well. The geothermal water is heat exchanged through the surface heating energy station. After heat exchange, the heat energy is transferred to the heat consumption end. The cold water after heat exchange is treated to meet the standards before being discharged. After the gas production ends, it switches to the water injection-heat production stage. Cold water is injected into the formation through the cold water injection H well. After the water temperature reaches the standard, it is extracted and heat exchanged through the gas production and water production V well. The cycle is repeated until the formation temperature reaches the standard and then stops. The heating well is divided into two stages according to the formation water content: heating extraction and water injection-heat extraction. In the heating extraction stage, geothermal water is extracted through the heating extraction V well and transported to the surface heating energy station for heat exchange. After heat exchange, the heat energy is transferred to the heat consumption end. The cold water after heat exchange is treated to meet the standards before being discharged. When the hot water storage is insufficient, the system switches to the water injection-heat extraction stage. The cold water after heat exchange is injected into the formation for heat storage through the cold water injection H well. After the water temperature reaches the standard, it is extracted for heat exchange. The cycle continues until the formation temperature reaches the standard and then stops.

[0006] Specifically, based on the characteristics of coal seam gas occurrence, the thermal control geological model of the coal mining area, the amount of geothermal resources, the layout plan of the U-shaped well mining system in the coal mining planning area, the implementation plan for the joint treatment of surface gas-heat hazards by U-shaped wells, and the surface heating energy station, extraction plans for gas-heat co-extraction wells and heat extraction wells are formulated: Based on the production and drainage lifecycle, gas-heat co-production wells are divided into gas production-heat production stage and water injection-heat production stage. During the gas production-heat production stage, the system is regulated and monitored in real time according to the surface coalbed methane production patterns. Gas is extracted through the gas production and water production wells (V wells) and recycled at the surface gas gathering station. Simultaneously generated geothermal water is also discharged to the surface through these wells. The geothermal water undergoes heat exchange at the surface heating energy station, and the heat energy is then transferred to the heat-consuming end. The resulting low-temperature cold water is treated and discharged into a surface reservoir. After the coalbed methane production stage ends, the system switches to the water injection-heat production stage. Cold water is injected into the formation through the cold water injection well (H well). Once the formation water temperature reaches the design threshold, it is extracted to the surface through the gas production and water production wells (V wells) to complete the heat exchange. This process is repeated cyclically until the formation temperature drops to the design requirement value. Based on the differences in water content in the underlying strata, the geothermal well is divided into a geothermal extraction stage and a water injection-geothermal extraction stage. The geothermal water is extracted to the surface through the geothermal extraction V well. The geothermal water undergoes heat exchange at the surface heating energy station. After heat exchange, the heat energy is transferred to the heat-consuming end. The low-temperature cold water after heat exchange is treated and discharged into the surface reservoir. When the geothermal water reserves are insufficient or there is no hot water production, the system switches to the water injection-geothermal extraction stage. The low-temperature cold water after heat exchange is injected into the strata through the cold water injection H well. After injection, it stores heat for a certain period of time. Once the injected water absorbs heat from the strata and rises to the design temperature, it is extracted to the surface through the geothermal extraction V well to complete the heat exchange. This process is repeated cyclically until the strata temperature drops to the design requirement value and then stops.

[0007] Furthermore, by using methods including geophysical exploration, drilling, and laboratory testing and analysis, the geological structure, strata, coal body structure, development of coal seam fracture system, and coalbed methane content and distribution characteristics of the coal mining area were determined. Using data including hydrogeological drilling and pumping tests, combined with the geothermal field characteristics and geothermal flow distribution patterns in the coal mining area, and considering the influence of various geological factors on the geothermal field, the main controlling factors of the geothermal anomaly zone in the coal mining area, as well as the geological and geothermal characteristics, a heat-controlling geological model for the coal mining area was determined, and the geothermal resources in the coal mining area were assessed.

[0008] Furthermore, based on the characteristics of coal seam gas occurrence, the thermal control geological model of the coal mining area, and the amount of geothermal resources, the layout scheme of the U-shaped well mining system in the coal mining planning area is determined: the U-shaped well mining system in the coal mining planning area adopts a simultaneous overall deployment of multiple U-shaped wells, and the layout scheme of the U-shaped well mining system, including well sites, drilling strata, and number, is determined; the U-shaped wells in the coal mining planning area are divided into gas-heat co-extraction U-shaped wells and thermal extraction U-shaped wells according to their functions; gas-heat co-extraction U-shaped wells are used to extract coal seam gas and extract formation heat energy; thermal extraction U-shaped wells are used to extract heat energy from the underlying rock strata; The horizontal section of the gas-heat co-mining U-shaped well is located near the central axis of the working face in the coal mining planning area. The wellbore trajectory of the horizontal section of the gas-heat co-mining U-shaped well H is located in the coal seam or in the roof of the coal seam. If the coal seam is a broken and soft coal seam, the wellbore trajectory of the horizontal section of the gas-heat co-mining U-shaped well H is located in the roof of the coal seam, and the distance between the wellbore trajectory and the roof of the coal seam is 0-2m. If the coal body structure is intact and the coal seam firmness coefficient is large, the wellbore trajectory of the horizontal section of the gas-heat co-mining U-shaped well H is located in the coal seam. Based on the geological, hydrological, and geothermal characteristics of the underlying strata, it is determined whether a heat extraction U-shaped well should be installed in the underlying strata. If the geothermal energy in the underlying strata is not abundant, and the heat hazard in the coal seam and surrounding rock can be reduced through gas-heat co-extraction U-shaped wells, then it is not necessary to install a heat extraction U-shaped well in the underlying strata. Conversely, if the geothermal energy is abundant, then it is necessary to install a heat extraction U-shaped well in the underlying strata to extract heat energy from the underlying formation. The horizontal section of the heating U-shaped well H is located in the underlying rock strata near the central axis of the planned coal mining face. The distance between the wellbore trajectory of the horizontal section and the bottom of the coal seam is determined according to the specific circumstances. Based on the geological and geothermal characteristics of the underlying strata, determine whether the gas-heat co-extraction U-shaped well and the heat extraction U-shaped well share a single V-well for extraction. If the underlying strata are not rich in water and have poor permeability, the gas-heat co-extraction U-shaped well and the heat extraction U-shaped well can share a single V-well; otherwise, the gas-heat co-extraction U-shaped well and the heat extraction U-shaped well use separate V-wells for extraction.

[0009] Furthermore, based on the characteristics of coal seam gas occurrence, the thermal control geological model of the coal mining area, and the amount of geothermal resources, combined with the layout plan of the U-shaped well mining system in the coal mining planning area, a joint treatment implementation plan for surface gas-heat hazards using U-shaped wells is formulated: the joint treatment U-shaped wells include multiple surface gas-heat co-extraction U-shaped wells and multiple surface heat extraction U-shaped wells; the surface gas-heat co-extraction U-shaped wells include: well H and gas-water extraction V-shaped wells; well H adopts a three-section wellbore structure, and the horizontal section of well H uses a cable pump bridge plug + perforation combined operation process for segmented perforation and segmented fracturing construction. The perforation orientation is determined according to the specific wellbore trajectory, and the segmented fracturing construction parameters and pumping construction procedures are determined according to specific geological conditions; the gas-water extraction V-shaped wells adopt a two-section or three-section wellbore structure according to the formation conditions. The gas-water extraction V-shaped wells serve as drainage wells, with gas extraction in the annulus between the casing and the tubing, and water extraction in the tubing, using an electric submersible screw pump for drainage; The surface heating U-shaped well includes a cold water injection H well and a heating V well. The cold water injection H well adopts a three-section wellbore structure. The horizontal section of the cold water injection H well is constructed using a combined cable pump bridge plug and perforation process for segmented perforation and segmented fracturing. The perforation azimuth, segmented fracturing parameters, and pumping procedures are determined according to specific geological conditions. As a cold water injection well, cold water enters the formation through the production casing of the cold water injection H well via perforation holes and fracturing fractures. The heating V well is a heating well. Depending on the formation conditions, the heating V well adopts a two-section or three-section wellbore structure and uses a submersible pump to extract formation hot water.

[0010] Furthermore, the ground heating energy station uses a heat source that couples geothermal energy with peak-shaving boilers to provide heat to users: when the user's heat load is low, geothermal energy heating mode is used; when the user's heat load exceeds the theoretical design load of geothermal energy, geothermal energy and peak-shaving boiler combined heating mode is used. The operation process of the ground heating energy station is as follows: The extracted geothermal water is purified by a water treatment device and then converted into high-quality hot water and low-temperature cold water through an energy conversion system. The high-quality hot water is transported to the heat-consuming end through an insulated transmission pipeline network to meet the diverse heat needs of the mining area and surrounding areas for heating, bathing, hot spring development, aquaculture insulation, and wellhead frost prevention. The low-temperature cold water is transported to a centralized water treatment station through a reinjection pipeline and then treated in two ways: surface reservoir discharge or ground reinjection.

[0011] Furthermore, the ground heating energy station adopts differentiated heating process paths based on the temperature characteristics of geothermal water extraction to ensure that the output heat quality meets the demand: when the geothermal water extraction temperature is high, the heating design parameters can be achieved through a single heat exchange via a plate heat exchanger, and the low-temperature water after heat exchange is directly connected to the cold water reinjection pipeline; when the geothermal water extraction temperature is low, a combined process of "one-time heat exchange via plate heat exchanger + secondary and above heating via heat pump unit" is adopted to gradually improve the heat quality to the user's required standards.

[0012] Furthermore, the energy efficiency management of the ground heating energy station combines the geothermal water extraction temperature with the user's real-time heat load to implement refined heat extraction and heat exchange control: when the geothermal water extraction temperature is high and the user's heat load is low, the heating demand can be met by a single heat exchange through a primary plate heat exchanger, and the low-temperature water enters the reinjection pipeline after heat exchange; when the geothermal water extraction temperature is high and the user's heat load is high, a multi-stage extraction of geothermal heat is achieved by using "preliminary heat exchange through a primary plate heat exchanger and deep heat enhancement through a secondary plate heat exchanger + heat pump unit"; when the geothermal water extraction temperature is low, it is directly connected to a secondary plate heat exchanger, and the heat pump unit is used to improve the heat quality until the user's heat load and heat quality requirements are met.

[0013] Furthermore, the ground heating energy station is designed with a redundancy guarantee mechanism for extreme operating conditions: when encountering extreme low temperatures, depletion of extracted geothermal energy resources, or other extreme conditions that cause the user's heat load to exceed the theoretical design load of geothermal energy, the coupled peak-shaving boiler heating system is activated to reheat the hot water after heat exchange, ensuring that the output heat quality and heat load meet the needs of the heat user.

[0014] Furthermore, gas-heat co-production wells are divided into gas production-heat production stage and water injection-heat production stage based on their drainage life cycle: The gas extraction-heat extraction stage is based on the production patterns of surface coalbed methane and adopts an operation strategy of "gas extraction as the main focus and heat extraction as a supplement." During this stage, coalbed methane enters the surface gas gathering station from the bottom of the well through the casing annulus of the gas and water extraction V well for recycling. The geothermal water generated simultaneously is discharged to the surface through the oil pipes of the gas and water extraction V well, and is purified by a water treatment device and then exchanged for heat at the surface heating energy station. After heat exchange, the heat energy is transferred to the heat consumption end. The low-temperature cold water generated after heat exchange is transported to the centralized water treatment station through the reinjection pipeline. After treatment to meet standards, it is discharged into the surface reservoir. Formation reinjection is not implemented in this stage. Operation and control requirements for the gas extraction-heat extraction stage: A closed loop for real-time monitoring and control of parameters is established in the gas extraction-heat extraction stage. The key indicators of bottom hole flowing pressure, casing pressure, gas production, water production, and water production temperature are monitored. Based on the monitoring data, the extraction system and key flow parameters are dynamically adjusted to ensure the continuous and stable gas and water production process. After the coalbed methane production stage is completed, the process switches to the water injection-heat production stage. Cold water is injected into the formation through the perforation holes of the production casing of the cold water injection well H to achieve formation heat exchange and extraction. The operation and management requirements for the water injection-heat production stage are as follows: Based on the pumping test data and numerical simulation results, the heat storage time of the injected cold water is set. After the formation water temperature rises to the design threshold, the water is extracted to the surface through the tubing of the gas production and water production well V to complete the heat exchange. During the operation, the formation water temperature and bottom hole flowing pressure are monitored in real time, and the matching relationship between the injection pressure, the amount of injected cold water and the amount of produced hot water is adjusted. This process is repeated periodically until the formation temperature drops to the design requirement value, at which point it stops.

[0015] Furthermore, based on the differences in water content in the underlying strata, thermal wells are divided into thermal extraction stage and water injection-thermal extraction stage: When the formation contains enough hot water to meet extraction requirements, the process enters the heat extraction stage. Hot water is extracted to the surface via pumps from the heat extraction V-well. After purification by a water treatment unit, it is sent to a surface heating energy station for heat exchange. The heat is then transferred to the heat-consuming end. The cooled water after heat exchange is sent to a centralized water treatment station via reinjection pipelines. After treatment to meet standards, it is discharged into a surface reservoir. Formation reinjection is not implemented during this stage. Control requirements for the heat extraction stage include: real-time monitoring of the relationship between key parameters such as water temperature, pumping rate, wellbore level, and bottom-hole flowing pressure; dynamic adjustment of the extraction rate to ensure the stability of heat extraction. When the hot water reserves in the formation are insufficient or there is no hot water production, the process switches to the water injection-heat extraction stage. The low-temperature cold water after heat exchange is injected into the formation through the perforation holes via the production casing of the cold water injection well H. After injection, the water is stored for a certain period of time. Once the injected water absorbs heat from the formation and rises to the design temperature, it is pumped to the surface through the pump pipe of the heat extraction well V to complete the heat exchange. The requirements for full-process control of the heat extraction stage and the water injection-heat extraction stage of the heat extraction well are as follows: real-time monitoring of the relationship between the injected water volume and the water production volume, as well as key parameters such as water temperature, bottom hole flowing pressure, injection pressure, and heat storage time, and maximizing heat extraction efficiency through dynamic control. This process is repeated periodically until the formation temperature drops to the design requirement value, at which point it stops.

[0016] Compared with the prior art, the present invention has the following advantages: (1) Achieving source-coordinated management of gas and heat hazards: Traditional mine management usually deals with gas outbursts and heat hazards separately. This invention uses a U-shaped well system on the surface to perform integrated extraction of gas and geothermal energy from the coal seam and surrounding rock before mining. Gas extraction reduces the gas pressure and content in the coal seam, while hot water extraction directly removes heat from the rock strata, reducing gas outbursts and heat dissipation intensity from the source, transforming the "passive response" underground into "active prevention and control" on the surface. (2) Improve resource utilization efficiency and economic benefits: By recovering gas as a gas resource and converting geothermal water into heat energy through a ground energy station, it can not only efficiently reduce the gas content of coal seams and reduce the heat dissipation intensity of surrounding rocks, but also recycle gas and geothermal resources in a resource-based manner, realizing the simultaneous recovery and cascade utilization of gas and geothermal resources; compared with the traditional governance model that only invests in the cost of disaster treatment and abandoned geothermal resources, this invention realizes the combination of "disaster treatment" and "resource utilization", improving the overall economic benefits; (3) Adopting surface U-shaped joint management and reducing underground engineering: Based on the characteristics of gas occurrence and geothermal distribution, multiple U-shaped wells (gas-heat co-extraction wells and heat extraction wells) with complementary functions are centrally deployed on the surface of the coal mining planning area to form a "well factory" model for regional collaborative management; this arrangement can cover a large area through surface drilling, which can reduce the regional gas content and formation heat in a targeted manner, while reducing the number of surface well sites and reducing complex engineering such as underground dedicated extraction roadways and refrigeration systems, thus saving investment and operation and maintenance costs; (4) Multi-purpose well and flexible operation and control: Gas-heat co-production wells can switch functions at different stages: gas and hot water are extracted simultaneously first, and after gas production is completed, they switch to cold water injection-heat production mode to continuously reduce rock temperature. Heat production wells can also switch between direct heat production and water injection-heat production cycle according to water-bearing conditions; this design extends the service cycle of a single well, improves equipment utilization, and can dynamically adjust the operation strategy according to the formation response; (5) Effectively block the upward conduction of deep heat source: The present invention arranges a heat-collecting U-shaped well in the high-temperature rock layer under the coal seam, and extracts deep heat energy through the circulating injection and extraction method, directly reducing the rock mass temperature in the direction of the coal seam floor, forming a "heat insulation layer" effect, thereby blocking or weakening the conduction of deep geothermal energy to the overlying coal seam and mine roadway, and alleviating mine heat damage from the root. (6) Constructing a new model for the coordinated development of coal-gas-heat resources: This invention systematically integrates coal mining planning, gas control, heat hazard prevention and geothermal utilization, and realizes the advanced coordinated development of multiple resources through surface well groups; ultimately forming a green and efficient development system with safe coal mining as the core and gas and geothermal as value-added resources, and constructing a new green, clean and efficient development model for the coordinated governance and integrated utilization of coal-gas-heat resources, which is in line with the development trend of clean and resource-oriented mines.

[0017] In summary, this invention, based on surface U-shaped well technology, integrates gas-heat co-extraction wells and geothermal wells to simultaneously extract coal seam gas and ground heat energy before coal mining. This addresses gas outbursts and high-temperature heat hazards at the source. Simultaneously, the recovered gas and geothermal water are utilized as fuel and heat sources, respectively. Efficient operation is achieved through well cluster coordination and injection-production regulation. Ultimately, this invention constructs a new model for the coordinated development of multiple resources—coal, gas, and heat—realizing the joint management of coal mine gas and heat hazards and geothermal utilization. This maximizes the benefits of disaster management and resource utilization, promoting safe, green, and efficient coal mining. Attached Figure Description

[0018] Figure 1 This is a flowchart of the method in this application.

[0019] Figure 2 This is a schematic diagram of the U-shaped well mining system in Example 1.

[0020] Figure 3 This is a schematic diagram of the gas-heat extraction stage of well U1 and the heat extraction stage of well U5 in Example 1.

[0021] Figure 4 This is a schematic diagram of the water injection-heat extraction stage of the gas-heat co-production U1 well and the water injection-heat extraction stage of the heat extraction U5 well in Example 1.

[0022] Explanation of reference numerals in the attached drawings: 1-Surface casing; 2-Technical casing; 3-Production casing; 4-Oil pipe; 5-Pump pipe; 6-Electric submersible screw pump; 7-Submersible pump; 8-Coalbed methane; 9-Gas gathering station; 10-Water treatment unit; 11-First-stage plate heat exchanger; 12-Second-stage plate heat exchanger; 13-Heat pump unit; 14-Gas boiler; 15-Cold water reinjection pipeline; 16-Heat end; 17-Centralized water treatment station; 18, 19, 20, 21, 22, 23, and 24 are all valves. Detailed Implementation

[0023] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0024] This application provides a method for the combined control of coal mine gas and heat hazards and geothermal utilization, the flowchart of which is shown below. Figure 1 As shown, the details are as follows.

[0025] First, determine the characteristics of coal seam gas occurrence, the heat-controlling geological model of the coal mining area, and the amount of geothermal resources.

[0026] Specifically, methods including geophysical exploration, drilling, and laboratory testing and analysis were used to determine the coalbed methane occurrence characteristics, including the geological structure, strata, coal body structure, coal seam fracture system development, and coalbed methane content and distribution characteristics of the coal mining area. Combining the geothermal field characteristics and geothermal flow distribution patterns of the coal mining area, the influence of various geological factors on the geothermal field, the main controlling factors of the coal mine geothermal anomaly zone, and geological and geothermal characteristics, a heat-controlling geological model for the coal mining area was determined, and the geothermal resource quantity of the coal mining area was assessed.

[0027] Then, based on the characteristics of coal seam gas occurrence, the thermal control geological model of the coal mining area and the amount of geothermal resources, the layout scheme of the U-shaped well mining system in the coal mining planning area is determined. The U-shaped wells in the coal mining planning area include multiple U-shaped wells, including gas-heat co-mining U-shaped wells and heat mining U-shaped wells.

[0028] In one embodiment, based on the characteristics of coal seam gas occurrence and the thermal control geological model of the coal mining area, the U-shaped well mining system in the coal mining planning area adopts the simultaneous overall deployment of multiple U-shaped wells, and determines the layout scheme of the U-shaped well mining system, including the well site, drilling strata, and number; U-shaped wells are divided into gas-heat co-extraction U-shaped wells and heat extraction U-shaped wells according to their functions; gas-heat co-extraction U-shaped wells are used to extract coal seam gas and extract formation heat energy; heat extraction U-shaped wells are used to extract heat energy from the underlying rock strata.

[0029] In practical applications, the horizontal section of the gas-heat co-mining U-shaped well is located near the central axis of the working face in the coal mining planning area, and the wellbore trajectory of the horizontal section of the gas-heat co-mining U-shaped well H is located in the coal seam or in the coal seam roof. If the coal seam is a broken and soft coal seam, the wellbore trajectory of the horizontal section of the gas-heat co-mining U-shaped well H is located in the coal seam roof, and the distance between the wellbore trajectory and the coal seam roof is 0-2m. If the coal body structure is intact and the coal seam firmness coefficient is large, the wellbore trajectory of the horizontal section of the gas-heat co-mining U-shaped well H is located in the coal seam.

[0030] In practical applications, the geological, hydrological, and geothermal characteristics of the underlying strata are considered when determining whether a U-shaped well for heat extraction should be installed in the underlying strata. If the geothermal energy in the underlying strata is not abundant, and the heat hazard in the coal seam and surrounding rock can be reduced through a gas-heat co-extraction U-shaped well, then it is not necessary to install a U-shaped well for heat extraction in the underlying strata. Conversely, if the geothermal energy is abundant, then a U-shaped well for heat extraction should be installed in the underlying strata to extract heat energy from the underlying formation. In practical applications, the horizontal section of the heating U-shaped H-shaped well is arranged in the underlying rock strata near the central axis of the planned coal mining face. The distance between the wellbore trajectory of the horizontal section and the bottom of the coal seam is determined according to specific circumstances. In practical applications, the geological and geothermal characteristics of the underlying strata of the coal seam are considered to determine whether the gas-heat co-extraction U-shaped well and the heat extraction U-shaped well share a single V-well for extraction. If the underlying strata are not rich in water and have poor permeability, the gas-heat co-extraction U-shaped well and the heat extraction U-shaped well can share a single V-well; otherwise, a separate V-well is used for extraction.

[0031] If a coal mining area has multiple minable coal seams, when deploying a U-shaped well mining system, the gas and heat hazards of each minable coal seam should be considered vertically to achieve multi-layer combined mining and maximize benefits.

[0032] Then, based on the characteristics of coal seam gas occurrence, the thermal control geological model of the coal mining area, the amount of geothermal resources, and the layout plan of the U-shaped well mining system in the coal mining planning area, a joint treatment implementation plan for surface gas-heat hazards using U-shaped wells is formulated. The joint treatment U-shaped wells include multiple surface gas-heat co-extraction U-shaped wells and multiple surface heat extraction U-shaped wells. The surface gas-heat co-extraction U-shaped wells include: H wells and gas and water extraction V wells. The surface heat extraction U-shaped wells include: cold water injection H wells and heat extraction V wells.

[0033] In one embodiment, the surface gas-heat co-production U-shaped well includes: an H well and a gas- and water-producing V well; the H well adopts a three-section wellbore structure, and the horizontal section of the H well is constructed using a cable-pumped bridge plug + perforation combined operation process for segmented perforation and segmented fracturing. The perforation azimuth is determined according to the specific wellbore trajectory, and the segmented fracturing construction parameters and pumping construction procedures are determined according to specific geological conditions; the gas- and water-producing V well adopts a two- or three-section wellbore structure according to the formation conditions. The gas- and water-producing V well serves as a drainage well, with gas production in the annulus between the casing and the tubing, and water production in the tubing, using an electric submersible screw pump for drainage.

[0034] In one embodiment, the surface heating U-shaped well includes: a cold water injection H well and a heating V well; the cold water injection H well adopts a three-section wellbore structure, and the horizontal section of the cold water injection H well is constructed by segmented perforation and segmented fracturing using a cable pump bridge plug + perforation combined process. The perforation azimuth, segmented fracturing parameters and pumping construction procedures are determined according to specific geological conditions. As a cold water injection well, cold water enters the formation through the production casing of the cold water injection H well via perforation holes and fracturing fractures; the heating V well is a heating well, and the heating V well adopts a two-section or three-section wellbore structure according to the formation conditions, and uses a submersible pump to extract formation hot water.

[0035] Next, the user's heat load demand is obtained, and the heat extraction capacity is designed based on the U-shaped well combined treatment scheme for ground gas-heat hazards to set up a ground heating energy station to provide heat energy to the user. This application scientifically arranges the ground heating energy station according to the theoretical geothermal energy extraction capacity and the user's heat load demand, realizing the efficient cascade utilization of geothermal energy. The ground heating energy station includes a heat exchange station. The extracted geothermal water is purified by a water treatment device and then exchanged through the heat exchange station before being transported to the heat-consuming end.

[0036] In practical applications, ground heating energy stations use a heat source that couples geothermal energy with peak-shaving boilers to provide heat to users: when the user's heat load is low, geothermal energy heating mode is used; when the user's heat load exceeds the theoretical design load of geothermal energy, a combined geothermal energy and peak-shaving boiler heating mode is used.

[0037] In practical applications, the operation process of a ground heating energy station is as follows: The extracted geothermal water is purified by a water treatment device and then converted into high-quality hot water and low-temperature cold water through an energy conversion system. The high-quality hot water is transported to the heat-consuming end through an insulated transmission pipeline network to meet the diverse heat needs of the mining area and surrounding areas for heating, bathing, hot spring development, aquaculture insulation, and wellhead frost prevention. The geothermal energy utilization efficiency is maximized through a full-chain cascade utilization model. The low-temperature cold water is transported to a centralized water treatment station through a reinjection pipeline. After deep treatment, it is disposed of either by surface reservoir discharge or ground reinjection.

[0038] In practical applications, ground heating energy stations adopt differentiated heating process paths based on the temperature characteristics of geothermal water extraction to ensure that the output heat quality meets the demand: when the geothermal water extraction temperature is high, the heating design parameters can be achieved through a single heat exchange via a plate heat exchanger, and the low-temperature water after heat exchange is directly connected to the cold water reinjection pipeline; when the geothermal water extraction temperature is low, a combined process of "one-time heat exchange via plate heat exchanger + secondary and above heating via heat pump unit" is adopted to gradually improve the heat quality to the user's required standards.

[0039] In practical applications, the energy efficiency management of ground heating energy stations combines the geothermal water extraction temperature with the real-time heat load of users to implement refined heat extraction and heat exchange control: when the geothermal water extraction temperature is high and the user heat load is low, the heating demand can be met by a single heat exchange through a primary plate heat exchanger, and the low-temperature water enters the reinjection pipeline after heat exchange; when the geothermal water extraction temperature is high and the user heat load is high, a multi-stage extraction of geothermal heat is achieved by using a "primary heat exchange through a primary plate heat exchanger and a secondary plate heat exchanger + heat pump unit for deep heat enhancement"; when the geothermal water extraction temperature is low, it is directly connected to a secondary plate heat exchanger, and the heat quality is improved by using a heat pump unit until the user's heat load and heat quality requirements are met.

[0040] In practical applications, ground heating energy stations are designed with redundant protection mechanisms for extreme operating conditions: when encountering extreme low temperatures, depletion of extracted geothermal energy resources, or other extreme conditions that cause the user's heat load to exceed the theoretical design load of geothermal energy, the coupled peak-shaving boiler heating system is activated to raise the temperature of the hot water after heat exchange, ensuring that the output heat quality and heat load meet the needs of the heat user and ensuring the continuity and stability of the heating system.

[0041] Finally, based on the characteristics of coal seam gas occurrence, the thermal control geological model of the coal mining area, the amount of geothermal resources, the layout plan of the U-shaped well mining system in the coal mining planning area, the implementation plan for the joint treatment of surface gas-heat hazards by U-shaped wells, and the surface heating energy station, the extraction plans for gas-heat co-extraction wells and heat extraction wells are formulated: According to the gas-heat co-production well life cycle, it is divided into two stages: gas production-heat production and water injection-heat production. In the gas production-heat production stage, gas and geothermal water are extracted simultaneously through the gas production and water production V well. The geothermal water is heat exchanged through the surface heating energy station. After heat exchange, the heat energy is transferred to the heat consumption end. The cold water after heat exchange is treated to meet the standards before being discharged. After the gas production ends, it switches to the water injection-heat production stage. Cold water is injected into the formation through the cold water injection H well. After the water temperature reaches the standard, it is extracted and heat exchanged through the gas production and water production V well. The cycle is repeated until the formation temperature reaches the standard and then stops. The heating well is divided into two stages according to the formation water content: heating extraction and water injection-heat extraction. In the heating extraction stage, geothermal water is extracted through the heating extraction V well and transported to the surface heating energy station for heat exchange. After heat exchange, the heat energy is transferred to the heat consumption end. The cold water after heat exchange is treated to meet the standards before being discharged. When the hot water storage is insufficient, the system switches to the water injection-heat extraction stage. The cold water after heat exchange is injected into the formation for heat storage through the cold water injection H well. After the water temperature reaches the standard, it is extracted for heat exchange. The cycle continues until the formation temperature reaches the standard and then stops.

[0042] Specifically, the gas-heat co-production well is divided into a gas production-heat production stage and a water injection-heat production stage according to its production life cycle. In the gas production-heat production stage, the production is regulated and monitored in real time according to the production pattern of coalbed methane on the surface. Gas is extracted through the gas production and water production V well and sent to the surface gas gathering station for recycling. The geothermal water produced simultaneously is also discharged to the surface through the gas production and water production V well. The geothermal water undergoes heat exchange through the surface heating energy station. After heat exchange, the heat energy is transferred to the heat consumption end. The low-temperature cold water after heat exchange is treated and discharged to the surface reservoir. After the coalbed methane production stage ends, the system switches to the water injection-heat production stage. Cold water is injected into the formation through the cold water injection H well. After the formation water temperature rises to the design threshold, it is extracted to the surface through the gas production and water production V well to complete the heat exchange. This process is repeated cyclically until the formation temperature drops to the design requirement value and then stops. Specifically, the geothermal well is divided into a geothermal extraction stage and a water injection-geothermal extraction stage based on the difference in water content in the underlying strata. The geothermal water is extracted to the surface through the geothermal extraction V well. The geothermal water undergoes heat exchange at the surface heating energy station. After heat exchange, the heat energy is transferred to the heat-consuming end. The low-temperature cold water after heat exchange is treated and discharged into the surface reservoir. When the geothermal water reserves are insufficient or there is no hot water production, the system switches to the water injection-geothermal extraction stage. The low-temperature cold water after heat exchange is injected into the strata through the cold water injection H well. After injection, it is stored for a certain period of time. After the injected water absorbs the heat from the strata and rises to the design temperature, it is extracted to the surface through the geothermal extraction V well to complete the heat exchange. This process is repeated cyclically until the strata temperature drops to the design requirement value and then stops.

[0043] In one embodiment, a gas-heat co-production well is divided into a gas-heat production stage and a water-heat injection stage based on its drainage life cycle: The gas extraction-heat extraction stage is based on the production patterns of surface coalbed methane and adopts an operation strategy of "gas extraction as the main focus and heat extraction as a supplement." During this stage, coalbed methane enters the surface gas gathering station from the bottom of the well through the casing annulus of the gas and water extraction V well for recycling. The geothermal water generated simultaneously is discharged to the surface through the oil pipes of the gas and water extraction V well, and then undergoes purification through a water treatment device and heat exchange at the surface heating energy station. The heat energy after heat exchange is then transferred to the heat-consuming end. The low-temperature cold water generated after heat exchange is transported to a centralized water treatment station through reinjection pipelines. After treatment to meet standards, it is discharged into the surface reservoir. Formation reinjection is not implemented during this stage. Operation and control requirements for the gas extraction-heat extraction stage: A closed-loop system for real-time parameter monitoring and control is established during the gas extraction-heat extraction stage. The key indicators of bottom hole flowing pressure, casing pressure, gas production, water production, and water production temperature are monitored. Based on the monitoring data, the extraction system and key flow parameters are dynamically adjusted to ensure the continuous and stable production of gas and water, and to achieve efficient gas and heat synergy. After the coalbed methane production stage is completed, the process switches to the water injection-heat extraction stage. Cold water is injected into the formation through the perforation holes in the production casing of the cold water injection well H to achieve formation heat energy exchange and extraction. The operation and management requirements for the water injection-heat extraction stage are as follows: Based on the pumping test data and numerical simulation results, the heat storage time of the injected cold water is set. After the formation water temperature rises to the design threshold, it is extracted to the surface through the tubing of the gas production and water production well V to complete the heat exchange. During the operation, the formation water temperature and bottom hole flowing pressure are monitored in real time, and the matching relationship between the injection pressure, the amount of injected cold water and the amount of produced hot water is adjusted to maximize the heat energy extraction efficiency. This process is repeated periodically until the formation temperature drops to the design requirement value, at which point it stops.

[0044] In one embodiment, the thermal well is divided into a thermal extraction stage and a water injection-thermal extraction stage based on the difference in water content in the underlying strata: When the formation contains enough hot water to meet extraction requirements, the process enters the heat extraction stage. Hot water is extracted to the surface via pumps from the heat extraction V-well. After purification by a water treatment unit, it is sent to a surface heating energy station for heat exchange. The heat is then transferred to the heat-consuming end. The cooled water after heat exchange is sent to a centralized water treatment station via reinjection pipelines. After treatment to meet standards, it is discharged into a surface reservoir. Formation reinjection is not implemented during this stage. Control requirements for the heat extraction stage include: real-time monitoring of the relationship between key parameters such as water temperature, pumping rate, wellbore level, and bottom-hole flowing pressure; dynamic adjustment of the extraction rate to ensure the stability of heat extraction. When the hot water reserves in the formation are insufficient or there is no hot water production, the process switches to the water injection-heat extraction stage. The low-temperature cold water after heat exchange is injected into the formation through the perforation holes via the production casing of the cold water injection well H. After injection, the water is stored for a certain period of time. Once the injected water absorbs heat from the formation and rises to the design temperature, it is pumped to the surface through the pump pipe of the heat extraction well V to complete the heat exchange. The requirements for full-process control of the heat extraction stage and the water injection-heat extraction stage of the heat extraction well are as follows: real-time monitoring of the relationship between the injected water volume and the water production volume, as well as key parameters such as water temperature, bottom hole flowing pressure, injection pressure, and heat storage time, and maximizing heat extraction efficiency through dynamic control. This process is repeated periodically until the formation temperature drops to the design requirement value, at which point it stops.

[0045] Example 1 For a certain coal mine, the following methods are adopted to jointly manage coal mine gas and heat hazards, and to coordinate with geothermal utilization.

[0046] Step 1: Determine the characteristics of coal seam gas occurrence, the heat-controlling geological model of the coal mining area, and the amount of geothermal resources.

[0047] By utilizing geophysical exploration, drilling, and laboratory testing and analysis, combined with geological survey characteristics of other coal mining faces in the coal mining area, we can identify the structural features of faults, collapse columns, etc. in the coal mining planning area, determine the geological structure, strata, coal body structure, coal seam fracture system development, geostress distribution, coalbed methane content and distribution, etc., and identify the dominant geological factors affecting the occurrence characteristics of coalbed methane, thereby determining the occurrence characteristics of coalbed methane.

[0048] Using data from hydrogeological drilling and pumping tests, combined with the geothermal field characteristics and geothermal heat flow distribution patterns in coal mining areas, this study elucidates the influence of various geological factors on the geothermal field, focuses on analyzing the main controlling factors in geothermal anomaly zones in coal mining areas, determines the heat-controlling geological model of coal mining areas based on geological and geothermal characteristics, and assesses the amount of geothermal resources in coal mining areas.

[0049] Step 2: Deploy a U-shaped well mining system for the combined treatment of coalbed methane and heat hazards and the utilization of geothermal energy.

[0050] Based on the characteristics of coal seam gas occurrence and the thermal control geological model of the coal mining area, the surface U-shaped well mining system in the coal mining planning area adopts a multi-U-shaped well deployment to form a well factory and a large-scale gas-heat hazard control effect in the region. U-shaped wells are divided into gas-heat co-extraction U-shaped wells and thermal extraction U-shaped wells according to their functions. Gas-heat co-extraction U-shaped wells are used to extract coal seam gas and extract formation heat energy; thermal extraction U-shaped wells are used to extract heat energy from the underlying rock strata.

[0051] Based on the results determined in step 1, a layout scheme for the U-shaped well production system, including well site, drilling strata, and number of wells, is designed. The following is a more detailed explanation of the U-shaped well production system in step 2 of this embodiment: (Refer to...) Figure 2A coal mining area in a certain mine has two working faces (C1 and C2). Based on the gas occurrence characteristics and geothermal resources of the area, a total of four gas-heat co-extraction U-shaped wells (U1, U2, U3, U4) and four heat extraction U-shaped wells (U5, U6, U7, U8) are designed for gas-heat hazard control. The gas-heat co-extraction U-shaped wells utilize wells V1, V2, V3, and V4 for gas and heat extraction; the heat extraction U-shaped wells utilize wells V5, V6, V7, and V8 for extraction. The U-shaped well mining system has a total of six well sites, with wells V1 and V5, V2 and V6, H1, H5, V3 and V7, H2, H6, V4 and V8, H3 and H7, and H4 and H8 sharing one well site. U-shaped wells are designed to avoid areas with well-developed structures such as faults and collapse columns. The horizontal wellbore trajectory is arranged along the strike of the coal seam and intersects the direction of the main formation fracture at a certain angle. V-shaped wells are located in the downdip direction of the coal seam. For gas-heat co-production U-shaped wells H-wells (H1, H2, H3, and H4), the horizontal sections are located near the central axis of the overlying strata on the planned coal mining face, with the wellbore trajectory (h1) between 0 and 2 meters from the top of the coal seam. For heat-producing U-shaped wells H-wells (H5, H6, H7, and H8), the horizontal sections are located in the underlying strata near the central axis of the planned coal mining face, with the wellbore trajectory (h2) between the bottom of the coal seam.

[0052] Step 3: Develop an implementation plan for U-shaped wells for surface gas-heat hazard control.

[0053] In this embodiment, the U-shaped well scheme for surface gas-heat hazard control is illustrated using the gas-heat co-production U1 well and the heat production well U5 well as examples. Figure 3 and Figure 4 The U1-type surface gas-heat co-production well includes well H1 and vertical well V1. Wells H1 and V1 are connected in the cavity-building section. Well H1 adopts a three-section wellbore structure, with surface casing 1, technical casing 2, and production casing 3 installed separately. The horizontal section of well H1 uses a combined cable-pumped bridge plug and perforation process for segmented perforation and fracturing. The perforation azimuth is determined according to the actual wellbore trajectory using different perforation schemes: vertical downward perforation is used when the horizontal wellbore trajectory is more than 2m away from the coal seam in the roof strata; a combination of oblique downward and vertical downward perforation is used when the distance is 0-2m from the coal seam; and spiral perforation is used within the coal seam. The fracturing parameters and pumping procedures for each section are determined according to specific geological conditions. Well V1 adopts a two-section wellbore structure based on formation conditions, with surface casing 1 and production casing 3 installed separately. Well V1 serves as the drainage well. Gas is produced in the annulus between production casing 3 and tubing 4, and water is produced in tubing 4. Drainage is carried out using an electric submersible screw pump 6.

[0054] In this embodiment, the surface heating well U5 includes well H5 and well V5. Well H5 and well V5 are connected in the cavity-building section. Well H5 serves as a cold water injection well and adopts a three-section wellbore structure, with a surface casing 1, a technical casing 2, and a production casing 3 installed separately. The horizontal section of well H5 uses a cable-pumped bridge plug + perforation combined operation process for segmented perforation and segmented fracturing. The perforation azimuth adopts a spiral perforation method. The fracturing parameters and pumping operation procedures for each segment are determined according to specific geological conditions. Well V5 serves as a heating well and adopts a two-section wellbore structure according to the formation conditions, with a surface casing 1 and a production casing 3 installed separately. A submersible pump 6 is used to extract formation hot water, which is pumped to the surface through pump pipe 5.

[0055] In this embodiment, the gas-heat co-production well and the heat production well have different functions and different geological conditions of the horizontal wellbore trajectory, so the perforation, fracturing and other mining schemes will also be different; the fracturing scale and number of fracturing sections of the horizontal section of the heat production U5 type well are smaller than those of the gas-heat co-production U1 type well.

[0056] Step 4: Based on the designed geothermal energy extraction volume and user heat load requirements, arrange ground heating energy stations to achieve efficient cascade utilization of geothermal energy.

[0057] In this embodiment, the ground-based geothermal energy station provides heat to users using a heat source that couples geothermal energy with a peak-shaving boiler, ensuring the reliability and stability of the heat source. When the user's heat load is low, the geothermal energy heating mode is used; when the user's heat load exceeds the theoretical design load of the geothermal system, a combined geothermal energy and peak-shaving boiler heating mode is used. In this embodiment, a gas-fired boiler 14 is used, see [link to documentation]. Figure 3 and Figure 4 .

[0058] In this embodiment, based on the theoretical pre-extraction amount of geothermal energy in the coal mining area and the user's heat load demand, the load parameters of the core equipment of the energy station are scientifically matched and designed. The energy station includes equipment such as a primary plate heat exchanger 11, a secondary plate heat exchanger 12, a heat pump unit 13, and a gas boiler 14. The operation process of the energy station is as follows: The extracted geothermal water is purified by the water treatment device 10 and then generates high-quality hot water and low-temperature cold water through the energy conversion system. The high-quality hot water is transported to the heat-consuming end 16 through the insulated transmission pipeline network to meet the diverse heat demands of the mining area and surrounding areas, such as heating, bathing, hot spring development, aquaculture insulation, and wellhead frost prevention. The geothermal energy utilization efficiency is maximized through the full-chain cascade utilization mode. The low-temperature cold water is transported to the centralized water treatment station 17 through the reinjection pipeline 15, and after deep treatment, it is discharged to the surface reservoir or reinjected into the formation.

[0059] In this embodiment, when the local hot water extraction temperature is high and the user's heat load is low, valves 18 and 20 are opened and valve 19 is closed. The extracted water only needs to undergo heat exchange once through the primary plate heat exchanger 11 to meet the heating demand. The low-temperature cold water after heat exchange enters the cold water reinjection pipeline 15. When the local hot water extraction temperature is high and the user's heat load is high, valve 18 is opened and valves 19 and 20 are closed. The extracted water first passes through the primary plate heat exchanger 11, and the outlet water then passes through the secondary plate heat exchanger 12 and is further heated by the heat pump unit 13, realizing multi-stage extraction of extracted water. When the local hot water extraction temperature is low, valves 18 and 19 are opened and valve 20 is closed. The extracted water directly enters the secondary plate heater 12 and is heated by the heat pump unit 13 to improve the heat quality until the user's heating demand is met.

[0060] In this embodiment, if extreme cold weather or geothermal energy decay occurs and the heat demand exceeds the theoretical design load of geothermal energy, the coupled peak-shaving gas boiler heating system is started, valve 21 is closed and valve 22 is opened, and the hot water generated after heat exchange is heated by gas boiler 14 to ensure that the output heat quality and heat load meet the heat demand of the heat user end and is delivered to the heat user end 16 to ensure the continuity and stability of the heating system.

[0061] Step 5: Develop extraction plans for gas-heat co-production wells and heat extraction wells.

[0062] In this embodiment, the gas-heat co-production well is divided into two management stages based on its production lifecycle: gas production-heat production and water injection-heat production. The gas production-heat production stage uses the production patterns of surface coalbed methane as the core control basis, with gas production as the primary focus and heat production as a secondary measure. See also... Figure 3 In this stage, coalbed methane enters the surface gas gathering station 9 from the bottom of the well via the casing annulus for recovery and utilization; the geothermal water generated simultaneously is discharged to the surface via oil pipe 4, and after being purified by water treatment device 10 and converted by energy at the heat exchange station, the heat energy is transported to the heat-using end 16; the low-temperature cold water generated after heat exchange is transported to the centralized water treatment station 17 via reinjection pipeline 15, and after treatment to meet standards, it is discharged to the surface reservoir. In this stage, the cold water is not reinjected into the formation. The operation and management requirements for this stage are as follows: a closed loop of real-time parameter monitoring and control needs to be established in the gas production-heat production stage, focusing on monitoring key indicators such as bottom hole flowing pressure, casing pressure, gas production, water production, and water production temperature. Based on the monitoring data, the extraction system, flow rate, and other key parameters are dynamically adjusted to ensure the continuous and stable gas and water production process and achieve efficient gas and heat synergy.

[0063] After the coalbed methane production stage ceases, the system switches to the water injection-heat extraction stage. Since most of the water in the formation has been extracted during the production-heat extraction stage, cold water is injected into the formation through perforations via the production casing 3 of well H1 to achieve formation heat exchange and extraction. See also... Figure 4After opening valve 23, the cooled water, having undergone heat exchange, is injected into the formation from the centralized water treatment station 17 through the perforation of the production casing 3 in well H1. It stores heat for a period, and once the water temperature reaches a certain level, it is discharged to the surface through the tubing 4 of well V1. This cycle repeats until the formation temperature drops to the design requirements. Operational control requirements for this stage: To ensure efficient heat extraction, the heat storage time of the injected cold water must be scientifically set based on pumping test data and numerical simulation results. Once the formation water temperature reaches the design threshold, it is pumped to the surface through the tubing 4 of well V1 to complete heat exchange. During operation, key parameters such as formation water temperature and bottom hole flowing pressure are monitored in real time, and the injection pressure, the amount of injected cold water, and the amount of produced hot water are precisely controlled to maximize heat extraction efficiency.

[0064] In this embodiment, the underlying formation beneath the heat extraction well has a high water content, and the treatment process is divided into a heat extraction stage and a water injection-heat extraction stage. See also Figure 3 During the heat extraction phase, the extracted hot water is pumped to the surface via pump pipe 5 from well V5. After treatment by water treatment device 10, it enters the heat exchange station, where the heat energy is transferred to the heat-consuming end 16. Cold water is transported via reinjection pipeline 15 to the centralized water treatment station 17 for treatment before being discharged into the surface reservoir. During this phase, the cold water is not reinjected into the formation. Heat extraction process control requirements: Real-time monitoring of key parameters such as water temperature, pumping rate, wellbore level, and bottom-hole flowing pressure; dynamic adjustment of the pumping speed to ensure the stability of heat extraction.

[0065] Water injection-heat extraction stage, see Figure 4 After heat exchange, the cooled water is injected into the formation through perforations in the production casing 3 of well H5. Once the injected water temperature rises to a certain level, it is then pumped to the surface from pump pipe 5 of well V5. This cycle repeats until the formation temperature drops to the design requirements. The entire heat extraction process requires real-time monitoring of the relationship between injected water volume and production water volume, as well as key parameters such as water temperature, bottom hole flowing pressure, injection pressure, and heat storage time. Dynamic control is used to maximize heat extraction efficiency.

[0066] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0067] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A method for combined control of coal mine gas and heat hazards and geothermal utilization, characterized in that, Includes the following steps: Determine the characteristics of coalbed methane occurrence, the heat-controlling geological model of the coal mining area, and the amount of geothermal resources; Based on the characteristics of coal seam gas occurrence, the thermal control geological model of coal mining area and the amount of geothermal resources, the layout scheme of U-shaped well mining system in the coal mining planning area and the implementation scheme of joint treatment of surface gas-heat hazards in U-shaped wells are determined. The joint treatment U-shaped wells include multiple surface gas-heat co-extraction U-shaped wells and multiple surface heat extraction U-shaped wells. The surface gas-heat co-extraction U-shaped well includes: an H well and a gas and water extraction V well; the surface heat extraction U-shaped well includes: a cold water injection H well and a heat extraction V well. Obtain user heat load demand, combine the heat extraction design of the U-shaped well joint treatment scheme for ground gas-heat hazards, and set up ground heating energy stations to provide heat energy to users; Develop extraction plans for gas-heat co-production wells and heat extraction wells: The gas-heat co-production well is divided into two stages according to the production and drainage life cycle: gas production-heat production and water injection-heat production. In the gas production-heat production stage, gas and geothermal water are extracted simultaneously through the gas production and water production V well. The geothermal water is exchanged for heat through the surface heating energy station. After heat exchange, the heat energy is transferred to the heat consumption end. The cold water after heat exchange is treated to meet the standards before being discharged. After the gas production ends, the system switches to the water injection-heat production stage. Cold water is injected into the formation through the cold water injection H well. After the water temperature reaches the standard, it is extracted and exchanged for heat through the gas production and water production V well. The cycle is repeated until the formation temperature reaches the standard and then stops. The heating well is divided into two stages according to the formation water content: heating extraction and water injection-heat extraction. In the heating extraction stage, the heating extraction V well extracts geothermal water and transports it to the surface heating energy station for heat exchange. After heat exchange, the heat energy is transferred to the heat consumption end. The cold water after heat exchange is treated to meet the standards before being discharged. When the hot water storage is insufficient, the system switches to the water injection-heat extraction stage. The cold water after heat exchange is injected into the formation for heat storage through the cold water injection H well. After the water temperature reaches the standard, it is extracted for heat exchange. The cycle continues until the formation temperature reaches the standard and then stops.

2. The method for combined control of coal mine gas and heat hazards and geothermal utilization according to claim 1, characterized in that: Using methods including geophysical exploration, drilling, and laboratory testing and analysis, we determined the geological structure, strata, coal body structure, coal seam fracture system development, and coalbed methane content and distribution characteristics of the coal mining area. Using data including hydrogeological drilling and pumping tests, combined with the geothermal field characteristics and geothermal flow distribution patterns in the coal mining area, and considering the influence of various geological factors on the geothermal field, the main controlling factors of the geothermal anomaly zone in the coal mining area, as well as the geological and geothermal characteristics, a heat-controlling geological model for the coal mining area was determined, and the geothermal resources in the coal mining area were assessed.

3. The method for combined control of coal mine gas and heat hazards and geothermal utilization according to claim 1, characterized in that: Based on the characteristics of coal seam gas occurrence, the thermal control geological model of the coal mining area, and the amount of geothermal resources, the layout scheme of the U-shaped well mining system in the coal mining planning area is determined: the U-shaped well mining system in the coal mining planning area adopts a simultaneous overall deployment of multiple U-shaped wells, and the layout scheme of the U-shaped well mining system, including well sites, drilling strata, and number, is determined; the U-shaped wells in the coal mining planning area are divided into gas-heat co-extraction U-shaped wells and thermal extraction U-shaped wells according to their functions; gas-heat co-extraction U-shaped wells are used to extract coal seam gas and extract formation heat energy; thermal extraction U-shaped wells are used to extract heat energy from the underlying rock strata; The horizontal section of the gas-heat co-mining U-shaped well is located near the central axis of the working face in the coal mining planning area. The wellbore trajectory of the horizontal section of the gas-heat co-mining U-shaped well H is located in the coal seam or in the roof of the coal seam. If the coal seam is a broken and soft coal seam, the wellbore trajectory of the horizontal section of the gas-heat co-mining U-shaped well H is located in the roof of the coal seam, and the distance between the wellbore trajectory and the roof of the coal seam is 0-2m. If the coal body structure is intact and the coal seam firmness coefficient is large, the wellbore trajectory of the horizontal section of the gas-heat co-mining U-shaped well H is located in the coal seam. In conjunction with the geological, hydrological, and geothermal characteristics of the underlying rock strata, it is determined whether a heat-collecting U-shaped well should be installed in the underlying rock strata. If the geothermal energy in the underlying rock strata is not abundant, and the heat hazard in the coal seam and surrounding rock can be reduced by gas-heat co-extraction U-shaped wells, then it is not necessary to install a heat-collecting U-shaped well in the underlying rock strata. Conversely, a U-shaped well for heat extraction needs to be installed in the underlying rock strata to extract heat energy from the underlying formation. The horizontal section of the heating U-shaped well H is located in the underlying rock strata near the central axis of the planned coal mining face. The distance between the wellbore trajectory of the horizontal section and the bottom of the coal seam is determined according to the specific circumstances. Based on the geological and geothermal characteristics of the underlying strata, determine whether the gas-heat co-extraction U-shaped well and the heat extraction U-shaped well share a single V-well for extraction. If the underlying strata are not rich in water and have poor permeability, the gas-heat co-extraction U-shaped well and the heat extraction U-shaped well can share a single V-well; otherwise, the gas-heat co-extraction U-shaped well and the heat extraction U-shaped well use separate V-wells for extraction.

4. The method for combined control of coal mine gas and heat hazards and geothermal utilization according to claim 3, characterized in that: Based on the characteristics of coal seam gas occurrence, the thermal control geological model of the coal mining area, and the amount of geothermal resources, and combined with the layout plan of the U-shaped well mining system in the coal mining planning area, a joint treatment implementation plan for surface gas-heat hazards using U-shaped wells is formulated. The joint treatment U-shaped wells include multiple surface gas-heat co-extraction U-shaped wells and multiple surface heat extraction U-shaped wells. The surface gas-heat co-extraction U-shaped wells include: well H and gas-water extraction V-shaped wells. Well H adopts a three-section wellbore structure. The horizontal section of well H uses a cable pump bridge plug + perforation combined operation process for segmented perforation and segmented fracturing. The perforation orientation is determined according to the specific wellbore trajectory. The segmented fracturing construction parameters and pumping construction procedures are determined according to specific geological conditions. The gas-water extraction V-shaped wells adopt a two-section or three-section wellbore structure according to the formation conditions. The gas-water extraction V-shaped wells serve as drainage wells, with gas extraction in the annulus between the casing and the tubing, and water extraction in the tubing, using an electric submersible screw pump for drainage. The surface heating U-shaped well includes a cold water injection H well and a heating V well. The cold water injection H well adopts a three-section wellbore structure. The horizontal section of the cold water injection H well is constructed using a combined cable pump bridge plug and perforation process for segmented perforation and segmented fracturing. The perforation azimuth, segmented fracturing parameters, and pumping procedures are determined according to specific geological conditions. As a cold water injection well, cold water enters the formation through the production casing of the cold water injection H well via perforation holes and fracturing fractures. The heating V well is a heating well. Depending on the formation conditions, the heating V well adopts a two-section or three-section wellbore structure and uses a submersible pump to extract formation hot water.

5. The method for combined control of coal mine gas and heat hazards and geothermal utilization according to claim 1, characterized in that: The ground heating energy station provides heat to users by using a heat source that couples geothermal energy with peak-shaving boilers: when the user's heat load is low, geothermal energy heating mode is used; when the user's heat load exceeds the theoretical design load of geothermal energy, a combined geothermal energy and peak-shaving boiler heating mode is used. The operation process of the ground heating energy station is as follows: The extracted geothermal water is purified by a water treatment device and then converted into high-quality hot water and low-temperature cold water through an energy conversion system. The high-quality hot water is transported to the heat-consuming end through an insulated transmission pipeline network to meet the diverse heat needs of the mining area and surrounding areas for heating, bathing, hot spring development, aquaculture insulation, and wellhead frost prevention. The low-temperature cold water is transported to a centralized water treatment station through a reinjection pipeline and then treated in two ways: surface reservoir discharge or ground reinjection.

6. The method for combined control of coal mine gas and heat hazards and geothermal utilization according to claim 5, characterized in that: Based on the characteristics of geothermal water extraction temperature, the ground heating energy station adopts differentiated heating process paths to ensure that the output heat quality meets the demand: when the geothermal water extraction temperature is high, the heating design parameters can be achieved through a single heat exchange via a plate heat exchanger, and the low-temperature water after heat exchange is directly connected to the cold water reinjection pipeline; when the geothermal water extraction temperature is low, a combined process of "plate heat exchanger primary heat exchange + heat pump unit secondary and above heating" is adopted to gradually improve the heat quality to the user's required standards.

7. The method for combined control of coal mine gas and heat hazards and geothermal utilization according to claim 6, characterized in that: The energy efficiency management of the ground heating energy station combines the geothermal water extraction temperature with the real-time heat load of users to implement refined heat extraction and heat exchange control: when the geothermal water extraction temperature is high and the user heat load is low, the heating demand can be met by a single heat exchange through a primary plate heat exchanger, and the low-temperature water enters the reinjection pipeline after heat exchange; when the geothermal water extraction temperature is high and the user heat load is high, a multi-stage extraction of geothermal heat is achieved by using "preliminary heat exchange through a primary plate heat exchanger and deep heat enhancement through a secondary plate heat exchanger + heat pump unit"; when the geothermal water extraction temperature is low, it is directly connected to a secondary plate heat exchanger, and the heat quality is improved by using a heat pump unit until the user's heat load and heat quality requirements are met.

8. The method for combined control of coal mine gas and heat hazards and geothermal utilization according to claim 7, characterized in that: The ground heating energy station is designed with a redundancy guarantee mechanism for extreme operating conditions: when encountering extreme low temperatures, depletion of extracted geothermal energy resources, or other extreme operating conditions that cause the user's heat load to exceed the theoretical design load of geothermal energy, the coupled peak-shaving boiler heating system is activated to reheat the hot water after heat exchange, ensuring that the output heat quality and heat load meet the needs of the heat user.

9. The method for combined control of coal mine gas and heat hazards and geothermal utilization according to claim 1, characterized in that: Gas-heat co-production wells are divided into gas-heat production stage and water-heat injection stage according to their drainage life cycle: The gas extraction-heat extraction stage is based on the production patterns of surface coalbed methane and adopts an operation strategy of "gas extraction as the main focus and heat extraction as a supplement." During this stage, coalbed methane enters the surface gas gathering station from the bottom of the well through the casing annulus of the gas and water extraction V well for recycling. The geothermal water generated simultaneously is discharged to the surface through the oil pipes of the gas and water extraction V well, and is purified by a water treatment device and then exchanged for heat at the surface heating energy station. After heat exchange, the heat energy is transferred to the heat consumption end. The low-temperature cold water generated after heat exchange is transported to the centralized water treatment station through the reinjection pipeline. After treatment to meet standards, it is discharged into the surface reservoir. Formation reinjection is not implemented in this stage. Operation and control requirements for the gas extraction-heat extraction stage: A closed loop for real-time parameter monitoring and control is established in the gas extraction-heat extraction stage. The key indicators of bottom hole flowing pressure, casing pressure, gas production, water production, and water production temperature are monitored. Based on the monitoring data, the extraction system and key flow parameters are dynamically adjusted to ensure the continuous and stable gas and water production process. After the coalbed methane production stage is completed, the process switches to the water injection-heat production stage. Cold water is injected into the formation through the perforation holes of the production casing of the cold water injection well H to achieve formation heat exchange and extraction. The operation and management requirements for the water injection-heat production stage are as follows: Based on the pumping test data and numerical simulation results, the heat storage time of the injected cold water is set. After the formation water temperature rises to the design threshold, the water is extracted to the surface through the tubing of the gas production and water production well V to complete the heat exchange. During the operation, the formation water temperature and bottom hole flowing pressure are monitored in real time, and the matching relationship between the injection pressure, the amount of injected cold water and the amount of produced hot water is adjusted. This process is repeated periodically until the formation temperature drops to the design requirement value, at which point it stops.

10. The method for combined control of coal mine gas and heat hazards and geothermal utilization according to claim 1, characterized in that: Based on the differences in water content in the underlying strata, thermal wells are divided into two stages: thermal extraction stage and water injection-thermal extraction stage. When the formation contains enough hot water to meet extraction requirements, the process enters the heat extraction stage. Hot water is extracted to the surface via pumps from the heat extraction V-well. After purification by a water treatment unit, it is sent to a surface heating energy station for heat exchange. The heat is then transferred to the heat-consuming end. The cooled water after heat exchange is sent to a centralized water treatment station via reinjection pipelines. After treatment to meet standards, it is discharged into a surface reservoir. Formation reinjection is not implemented during this stage. Control requirements for the heat extraction stage include: real-time monitoring of the relationship between key parameters such as water temperature, pumping rate, wellbore level, and bottom-hole flowing pressure; dynamic adjustment of the extraction rate to ensure the stability of heat extraction. When the hot water reserves in the formation are insufficient or there is no hot water production, the process switches to the water injection-heat extraction stage. The low-temperature cold water after heat exchange is injected into the formation through the perforation holes via the production casing of the cold water injection well H. After injection, the water is stored for a certain period of time. Once the injected water absorbs heat from the formation and rises to the design temperature, it is pumped to the surface through the pump pipe of the heat extraction well V to complete the heat exchange. The requirements for full-process control of the heat extraction stage and the water injection-heat extraction stage of the heat extraction well are as follows: real-time monitoring of the relationship between the injected water volume and the water production volume, as well as key parameters such as water temperature, bottom hole flowing pressure, injection pressure, and heat storage time, and maximizing heat extraction efficiency through dynamic control. This process is repeated periodically until the formation temperature drops to the design requirement value, at which point it stops.

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