In-situ mining method of coal and oil shale interbed

Abstract

The application discloses an in-situ mining method for coal and oil shale interbeds, which comprises the following steps: step one, selecting a target mining area; step two, placing a heater in a heating well; step three, energy input; and step four, energy gain stage. The method has the beneficial effects of changing the problems of low utilization efficiency and poor economic benefits in previous resource mining, effectively developing low-value mineral resources of the coal and oil shale interbeds by utilizing the geological characteristics of the coal and oil shale interbeds, realizing the exchange of low-value coal resources for high-value oil and gas resources, and realizing the in-situ development of fossil resources, which conforms to the mining characteristics of being green, clean and efficient. Meanwhile, the method provides a new transformation route for cities that rely on coal resource mining and even face bankruptcy due to resource exhaustion.

Description

Technical Field

[0001] This invention relates to an in-situ mining method for underground resources, and more particularly to an in-situ mining method for interbedded coal and oil shale. Background Technology

[0002] Currently, in-situ mining technology refers to the input of energy underground to achieve in-situ extraction of mineral resources, also known as in-situ modification technology. In daily production and life, increasing the proportion of oil and gas utilization has become a development trend. However, domestic oil and gas production is low, and the dependence on foreign oil and gas has remained above 65% for many years. Oil shale, as a associated resource of coal, has huge reserves and can serve as a substitute for oil and gas. However, the sedimentary and occurrence conditions of domestic oil shale are poor, characterized by thin reservoirs, low oil content, and low thermal evolution. There are few oil shale layers suitable for independent in-situ extraction, and they are buried at great depths, resulting in extraction revenue far below economic benefits, which restricts the development of oil shale resources. In past mining processes, high-quality coal resources were prioritized for extraction, leaving lower-quality coal resources with some economic value, but far below the level of exploitability. National resource surveys show that such resources account for a significant portion of my country's resource reserves, and the effective development and utilization of these resources is a crucial issue in the field of resource extraction. Summary of the Invention

[0003] The purpose of this invention is to utilize the combustion reaction of underground coal resources to heat oil shale layers. By leveraging the interbedded and associated characteristics of coal and oil shale, the combustion reaction can be replaced, thereby achieving in-situ low-energy mining of oil shale resources and realizing the exchange of low-economic-value coal resources for high-value oil and gas resources. This invention provides an in-situ mining method for interbedded coal and oil shale.

[0004] The in-situ mining method for interbedded coal and oil shale provided by this invention includes the following steps:

[0005] Step 1: Select the target mining area and carry out drilling or well modification within the selected target area; deploy heating wells, production wells, and in-situ progress feedback monitoring wells in the target mining area, and set up the in-situ mining system;

[0006] Step 2: Place a heater in the heating well. The heater is an electric heater with a reinforced spiral structure, mainly used for gas heating and downhole ignition. A multi-functional monitoring device is installed in the in-situ progress feedback monitoring well. The multi-functional monitoring device includes a temperature sensor, a pressure sensor, and a gas concentration sensor. The heating well is connected to the gas injection system, and the in-situ progress feedback monitoring well is connected to the surface control system.

[0007] Step 3, energy input, the specific method is as follows:

[0008] After completing surface construction and sealing the wellhead, the gas injection system separates inert gas and transports compressed inert gas to the underground reservoir. The gas is heated to 550°C by an underground heater, causing the coal seam at the bottom of the well to reach its ignition point and undergo incomplete combustion, producing a large amount of carbon monoxide. Using the inert gas injected from the surface and the carbon monoxide produced by combustion as a heat transfer medium, the oil shale layer in the interlayer is heated through gas circulation. The mixed gas returning from underground is separated by a purification and separation system, and the inert gas is reinjected underground through the gas injection system for heating. The carbon monoxide is separated and stored, with part of the carbon monoxide used as the initial fuel gas in step four, and the other part used as an economical fuel gas, which is then finely processed to form coal gas to obtain economic benefits.

[0009] Step 4, Energy Gain Stage, the specific method is as follows:

[0010] When the ground control system receives the first signal, it stops injecting inert gas; it then injects a mixture of gas, mainly carbon monoxide and low-oxygen gas, which is used to ignite the coal seam through an underground heater, heating the oil shale layer and causing it to crack, producing light oil and gas. The oil and gas are then extracted to the surface through gas circulation. The mixed products undergo static three-phase separation to separate the gas, oil, and solids. The combustible oil and gas are separated and stored. The bottom layer of coal and oil shale is burned, heating or even igniting the upper layer of coal and oil shale, continuing the above reaction and forming a chain reaction.

[0011] The in-situ mining system includes a surface control system, a gas injection system, a purification and separation system, and a monitoring system. The gas injection system includes an air compressor, a gas separation device, and a high-pressure buffer tank. One end of the air compressor is connected to an external power source to drive its operation, and the other end is connected to the gas separation device, which is also connected to the high-pressure buffer tank. The gas separation device can separate inert gases from the air, compress them through pipelines via the air compressor, and then input them into the target formation for in-situ mining through pipelines connected to the high-pressure buffer tank. The downhole heater heats the input gas to 550°C. The heating well is drilled in the target formation for in-situ mining. The heating well and the mining well adopt a one-injection-one-production or one-injection-multiple-production well layout. The heating well and the mining well are connected to the surface equipment through gas injection pipelines.

[0012] The ground control system consists of a sensor signal conversion device, a PLC automatic data acquisition and analysis device, and a computer. One end of the ground control system is connected to an external power source, which supplies power to the system. The other end is connected to the gas injection system, the purification and separation system, and the monitoring system. The purification and separation system includes a static three-phase separator, a gas storage tank, a gas separation and filtration device, a carbon monoxide storage tank, and a pyrolysis gas storage tank. The inlet of the static three-phase separator is connected to the production well via a pipeline, and the outlet is connected to the gas separation and filtration device. The gas separation and filtration device is also connected to the gas storage tank, the carbon monoxide storage tank, and the pyrolysis gas storage tank. The production well is drilled to the same depth as the heating well. Through gas circulation, the underground circulating gas... The incoming mixed gas is separated by a static three-phase separator and a gas separation and filtration device. The gas to be reinjected underground and the economically viable gas are stored in carbon monoxide storage tanks and cracked gas storage tanks, respectively. The monitoring system includes an in-situ progress feedback monitoring well and a multi-functional monitoring device. The in-situ progress feedback monitoring well is less than 5m away from the heating well to ensure the accuracy of the monitoring data. The multi-functional monitoring device is installed in the in-situ progress feedback monitoring well and arranged in series according to the formation thickness. The multi-functional monitoring device is connected to the ground control system via wires and transmits key parameters such as temperature, pressure and gas concentration in real time. This allows for the adjustment of the operating parameters of each system and the control of in-situ mining. The heating well and the mining well are located at the bottom layer of the target formation for in-situ mining to ensure the maximization of in-situ mining.

[0013] The target mining area is a mineral layer that has not been mined after geological exploration. Among them, the average oil content of the oil shale layer is less than 5%, the average thickness is less than 3m, or the remaining mineral layer that has been mined and has no mining benefits. The mining revenue of the two should be less than 20% of the overall mining value.

[0014] Drilling projects or well modification projects shall be carried out to the lowest level of the target mining area; heating wells, production wells and in-situ progress feedback monitoring wells shall be deeper than 10m. When drilling down into strata that have been previously mined, rich coal seams or oil and gas layers with mining value shall be avoided and the distance between them shall be 10m; the distance between in-situ progress feedback monitoring wells and heating wells shall not exceed 5m.

[0015] The first signal is a control signal fed back to the surface control system based on the downhole gas concentration results, specifically when the carbon dioxide concentration reaches 15%.

[0016] The well layout method of one injection and one production is adopted. The concentration ratio of combustible gas in the mixed gas injected into the well in step four is adjusted by the downhole gas concentration sensor to control the downhole reaction process. The well layout method of one injection and multiple production is adopted. Based on the above method and the opening and closing status of the production well, the downhole reaction process and the production area are controlled.

[0017] An array of sensors is deployed in the in-situ progress feedback monitoring well; the sensors in the same well are evenly spaced along the vertical direction.

[0018] The heater, multi-functional monitoring device, temperature sensor, pressure sensor, gas concentration sensor, ground control system, air compressor, gas separation device, high-pressure buffer tank, external power supply, static three-phase separation device, gas storage tank, gas separation and filtration device, carbon monoxide storage tank and pyrolysis gas storage tank mentioned above are all assemblies of existing equipment. Therefore, the specific models and specifications are not described in detail.

[0019] The beneficial effects of this invention are:

[0020] This invention provides an in-situ mining method for interbedded coal and oil shale layers, overcoming the problems of low utilization efficiency and poor economic benefits associated with previous resource extraction methods. Utilizing the geological characteristics of co-existing coal and oil shale sedimentary layers, it effectively develops low-value mineral resources within these layers, enabling the exchange of low-value coal resources for high-value oil and gas resources. Furthermore, it achieves in-situ development of fossil resources, aligning with the characteristics of green, clean, and efficient mining. Simultaneously, it provides a new transformation path for cities reliant on coal resource extraction, or even facing bankruptcy due to resource depletion.

[0021] The average mining cost of one ton of ordinary coal in China is between 300 and 550 yuan. If the coal seam is thinner, the mining cost will increase; for thin-layered (1.3m) coal, the mining cost will increase by 100-150 yuan per ton, an increase of approximately 18%-34%. Meanwhile, the mining cost of one ton of oil shale is approximately 4300 yuan per ton, and the cost of dry distillation of one ton of oil shale is approximately 1245.69 yuan per ton. Due to the low and unstable oil content of oil shale, and the fact that the price of oil and gas (gasoline or diesel) in China is generally around 230 yuan per ton, the economic benefits of mining oil shale alone are low and unstable, excluding the economic costs of surface equipment. The mining and utilization of these two mineral resources are accompanied by large amounts of waste gas emissions, causing environmental pollution, and the cost of treating this waste gas is approximately 1500-2500 yuan per ton. Considering the economic benefits of extracting the aforementioned geological resources, which are approximately RMB 330 per ton, the profit margin for this resource is relatively low. Based on practical considerations, the profit per ton may decrease by about 5%. Furthermore, this extraction method still causes irreversible environmental impacts. Conversely, the extraction method described in this invention greatly protects the environment. Considering environmental costs, the cost of producing oil and gas resources is approximately RMB 700 per barrel (US$96 per barrel), demonstrating a certain economic advantage. In addition, the carbon monoxide produced during the extraction process also has economic value, further increasing extraction profits by approximately 3%.

[0022] In summary, the comparison of the two mining methods shows that the latter has an economic benefit that is about 15% greater than the former. The latter has exploitable technological potential and provides a prospect and impetus for the transformation of coal resource-depleted cities. Taking into account various factors such as the environment, the economic benefits of the technical solution provided by this invention will be further increased. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the overall structure of the in-situ mining system described in this invention.

[0024] The annotations in the image above are as follows:

[0025] 1. Heating well; 2. Production well; 3. In-situ progress feedback monitoring well; 4. Heater.

[0026] 5. Multifunctional monitoring device; 6. Ground control system; 7. Air compressor; 8. Gas separation device.

[0027] 9. High-pressure buffer tank; 10. External power supply; 11. Static three-phase separator; 12. Gas storage tank.

[0028] 13. Gas separation and filtration device; 14. Carbon monoxide storage tank; 15. Pyrolysis gas storage tank. Detailed Implementation

[0029] Please see Figure 1 As shown:

[0030] The in-situ mining method for interbedded coal and oil shale provided by this invention includes the following steps:

[0031] Step 1: Select the target mining area and carry out drilling or well modification within the selected target area; deploy heating well 1, mining well 2 and in-situ progress feedback monitoring well 3 in the target mining area, and set up the in-situ mining system;

[0032] Step 2: Heater 4 is placed in heating well 1. Heater 4 is an electric heater with a reinforced spiral structure, mainly used for gas heating and downhole ignition. Multifunctional monitoring device 5 is installed in in-situ progress feedback monitoring well 3. Multifunctional monitoring device 5 includes temperature sensor, pressure sensor and gas concentration sensor. Heating well 1 is connected to the gas injection system. In-situ progress feedback monitoring well 3 is connected to the ground control system 6.

[0033] Step 3, energy input, the specific method is as follows:

[0034] After completing surface construction and sealing the wellhead, the gas injection system separates inert gas and transports compressed inert gas to the underground reservoir. The gas is heated to 550°C by the downhole heater 4, causing the coal seam at the bottom of the well to reach its ignition point and undergo incomplete combustion, producing a large amount of carbon monoxide. Using the inert gas injected from the surface and the carbon monoxide produced by combustion as a heat transfer medium, the oil shale layer in the interlayer is heated through gas circulation. The mixed gas returning from underground is separated by the purification and separation system, and the inert gas is reinjected underground through the gas injection system for heating. The carbon monoxide is separated and stored, with part of the carbon monoxide used as the initial fuel gas in step four and the other part used as economic fuel gas, which is then finely processed to form coal gas to obtain economic benefits.

[0035] Step 4, Energy Gain Stage, the specific method is as follows:

[0036] When the ground control system 6 receives the first signal, it stops injecting inert gas; it injects a mixed gas mainly composed of carbon monoxide and low-content oxygen-containing gas, which is ignited by the downhole heater 4 to heat the coal seam and the oil shale layer, causing cracking and producing light oil and gas. The oil and gas are extracted to the surface through gas circulation. The mixed products pass through the static three-phase separator 11 for static separation of gas, oil and solids. The combustible oil and gas are separated and stored. The bottom layer of coal and oil shale is burned, heating or even igniting the upper layer of coal and oil shale, continuing the above reaction and forming a chain reaction.

[0037] The in-situ mining system includes a surface control system 6, a gas injection system, a purification and separation system, and a monitoring system. The gas injection system includes an air compressor 7, a gas separation device 8, and a high-pressure buffer tank 9. One end of the air compressor 7 is connected to an external power source 10, which serves as the power source for driving the air compressor 7. The other end of the air compressor 7 is connected to the gas separation device 8, which is also connected to the high-pressure buffer tank 9. The gas separation device 8 can separate inert gases from the air, compress them through a pipeline via the air compressor 7, and then input them into the target formation for in-situ mining through the pipeline connected to the high-pressure buffer tank 9. The downhole heater 4 heats the input gas to 550°C. The heating well 1 is drilled in the target formation for in-situ mining. The heating well 1 and the mining well 2 are laid out in a one-injection-one-mining or one-injection-multiple-mining manner. The heating well 1 and the mining well 2 are connected to the surface equipment through gas injection pipelines.

[0038] The ground control system 6 consists of a sensor signal conversion device, a PLC automatic acquisition and analysis device, and a computer. One end of the ground control system 6 is connected to an external power supply 10, which supplies power to the ground control system 6. The other end of the ground control system 6 is connected to the gas injection system, the purification and separation system, and the monitoring system. The purification and separation system includes a static three-phase separator 11, a gas storage tank 12, a gas separation and filtration device 13, a carbon monoxide storage tank 14, and a cracked gas storage tank 15. The inlet of the static three-phase separator 11 is connected to the production well 2 via a pipeline, and the outlet of the static three-phase separator 11 is connected to the gas separation and filtration device 13. The gas separation and filtration device 13 is also connected to the gas storage tank 12, the carbon monoxide storage tank 14, and the cracked gas storage tank 15. The drilling depth of the production well 2 is the same as that of the heating well 1. Gas circulation... The system separates the mixed gas from the underground circulation via a static three-phase separator 11 and a gas separation and filtration device 13. The gas reinjected underground and the economically viable gas are stored in a carbon monoxide storage tank 14 and a pyrolysis gas storage tank 15, respectively. The monitoring system includes an in-situ progress feedback monitoring well 3 and a multi-functional monitoring device 5. The in-situ progress feedback monitoring well 3 is less than 5m away from the heating well 1 to ensure the accuracy of the monitoring data. The multi-functional monitoring device 5 is installed in the in-situ progress feedback monitoring well 3 and arranged in series according to the formation thickness. The multi-functional monitoring device 5 is connected to the ground control system 6 via wires and transmits key parameters such as temperature, pressure and gas concentration in real time. This allows for the adjustment of the operating parameters of each system and the control of in-situ mining. The heating well 1 and the mining well 2 are located at the bottom layer of the target formation for in-situ mining to ensure the maximization of in-situ mining.

[0039] The target mining area is a mineral layer that has not been mined after geological exploration. Among them, the average oil content of the oil shale layer is less than 5%, the average thickness is less than 3m, or the remaining mineral layer that has been mined and has no mining benefits. The mining revenue of the two should be less than 20% of the overall mining value.

[0040] The drilling project or well modification well is drilled to the bottom layer of the target mining area; the depth of heating well 1, mining well 2 and in-situ progress feedback monitoring well is greater than 10m. When drilling down into a previously mined stratum, avoid rich coal seams or oil and gas layers with mining value, and keep a distance of 10m between them; the in-situ progress feedback monitoring well is no more than 5m away from the heating well.

[0041] The first signal is a control signal generated by feeding back the downhole gas concentration results to the surface control system 6, specifically when the carbon dioxide concentration reaches 15%.

[0042] The well layout method of one injection and one production is adopted. The concentration ratio of combustible gas in the mixed gas injected into the well in step four is adjusted by the downhole gas concentration sensor to control the downhole reaction process. The well layout method of one injection and multiple production is adopted. Based on the above method and the opening and closing status of the production well, the downhole reaction process and the production area are controlled.

[0043] An array of sensors is arranged in well 3 for in-situ progress feedback monitoring; the sensors in the same well are evenly spaced along the vertical direction.

[0044] The heater 4, multi-functional monitoring device 5, temperature sensor, pressure sensor, gas concentration sensor, ground control system 6, air compressor 7, gas separation device 8, high-pressure buffer tank 9, external power supply 10, static three-phase separation device 11, gas storage tank 12, gas separation and filtration device 13, carbon monoxide storage tank 14, and pyrolysis gas storage tank 15 mentioned above are all assemblies of existing equipment. Therefore, their specific models and specifications are not described in detail.

Claims

1. A method for in-situ mining of interbedded coal and oil shale, characterized in that: The method includes the following steps: Step 1: Select the target mining area and carry out drilling or well modification within the selected target area; deploy heating wells, production wells, and in-situ progress feedback monitoring wells in the target mining area, and set up the in-situ mining system; Step 2: Place a heater in the heating well. The heater is an electric heater with a reinforced spiral structure, mainly used for gas heating and downhole ignition. A multi-functional monitoring device is installed in the in-situ progress feedback monitoring well. The multi-functional monitoring device includes a temperature sensor, a pressure sensor, and a gas concentration sensor. The heating well is connected to the gas injection system, and the in-situ progress feedback monitoring well is connected to the surface control system. Step 3, energy input, the specific method is as follows: After completing surface construction and sealing the wellhead, the gas injection system separates inert gas and transports compressed inert gas to the underground reservoir. The gas is heated to 550°C by an underground heater, causing the coal seam at the bottom of the well to reach its ignition point and undergo incomplete combustion, producing a large amount of carbon monoxide. Using the inert gas injected from the surface and the carbon monoxide produced by combustion as a heat transfer medium, the oil shale layer in the interlayer is heated through gas circulation. The mixed gas returning from underground is separated by a purification and separation system, and the inert gas is reinjected underground through the gas injection system for heating. The carbon monoxide is separated and stored, with part of the carbon monoxide used as the initial fuel gas in step four, and the other part used as an economical fuel gas, which is then finely processed to form coal gas to obtain economic benefits. Step 4, Energy Gain Stage, the specific method is as follows: When the ground control system receives the first signal, it stops injecting inert gas; it then injects a mixture of gas, mainly carbon monoxide and low-oxygen gas, which is used to ignite the coal seam through an underground heater, heating the oil shale layer and causing a cracking reaction to produce light oil and gas. The oil and gas are then extracted to the surface through gas circulation. The mixed products undergo static three-phase separation to separate the gas, oil, and solids. The combustible oil and gas are separated and stored. The bottom layer of coal and oil shale is burned, heating or even igniting the upper layer of coal and oil shale, continuing the above reaction and forming a chain reaction.

2. The in-situ mining method for interbedded coal and oil shale according to claim 1, characterized in that: The in-situ mining system includes a surface control system, a gas injection system, a purification and separation system, and a monitoring system. The gas injection system includes an air compressor, a gas separation device, and a high-pressure buffer tank. One end of the air compressor is connected to an external power source to drive its operation, and the other end is connected to the gas separation device, which is also connected to the high-pressure buffer tank. The gas separation device can separate inert gases from the air, compress them through a pipeline, and then input them into the target formation for in-situ mining through a pipeline connected to the high-pressure buffer tank. The downhole heater heats the input gas to 550°C. The heating well is drilled in the target formation for in-situ mining. The heating well and the mining well are arranged in a one-injection-one-mining or one-injection-multiple-mining configuration. The heating well and the mining well are connected to the surface equipment through gas injection pipelines. The ground control system consists of a sensor signal conversion device, a PLC automatic data acquisition and analysis device, and a computer. One end of the ground control system is connected to an external power source, which supplies power to the system. The other end is connected to the gas injection system, the purification and separation system, and the monitoring system. The purification and separation system includes a static three-phase separator, a gas storage tank, a gas separation and filtration device, a carbon monoxide storage tank, and a pyrolysis gas storage tank. The inlet of the static three-phase separator is connected to the production well via a pipeline, and the outlet is connected to the gas separation and filtration device. The gas separation and filtration device is also connected to the gas storage tank, the carbon monoxide storage tank, and the pyrolysis gas storage tank. The production well is drilled to the same depth as the heating well. Through gas circulation, the underground circulating gas... The incoming mixed gas is separated by a static three-phase separator and a gas separation and filtration device. The gas to be reinjected underground and the economically viable gas are stored in carbon monoxide storage tanks and cracked gas storage tanks, respectively. The monitoring system includes an in-situ progress feedback monitoring well and a multi-functional monitoring device. The in-situ progress feedback monitoring well is less than 5m away from the heating well to ensure the accuracy of the monitoring data. The multi-functional monitoring device is installed in the in-situ progress feedback monitoring well and arranged in series according to the formation thickness. The multi-functional monitoring device is connected to the ground control system via wires and transmits key parameters such as temperature, pressure and gas concentration in real time. This allows for the adjustment of the operating parameters of each system and the control of in-situ mining. The heating well and the mining well are located at the bottom layer of the target formation for in-situ mining to ensure the maximization of in-situ mining.

3. The in-situ mining method for interbedded coal and oil shale according to claim 1, characterized in that: The target mining area refers to mineral layers that have not been geologically explored and are not worth mining. Among them, the average oil content of the oil shale layer is less than 5%, the average thickness is less than 3m, or the remaining mineral layers that have been mined and are not worth mining. The mining revenue of the two should be less than 20% of the overall mining value.

4. The in-situ mining method for interbedded coal and oil shale according to claim 1, characterized in that: The drilling project or well modification shall be carried out to the bottom layer of the target mining area; the depth of the heating well, the production well and the in-situ progress feedback monitoring well shall be greater than 10m. When drilling down into the formation that has been mined, the rich coal seam or oil and gas layer with mining value shall be avoided and the two shall be 10m apart; the in-situ progress feedback monitoring well shall be no more than 5m away from the heating well.

5. The in-situ mining method for interbedded coal and oil shale according to claim 1, characterized in that: The first signal is a control signal fed back to the surface control system based on the downhole gas concentration result, specifically when the carbon dioxide concentration reaches 15%.

6. The in-situ mining method for interbedded coal and oil shale according to claim 2, characterized in that: The well layout method of one injection and one production is described, in which the concentration ratio of combustible gas in the mixed gas injected into the well in step four is adjusted by the downhole gas concentration sensor to control the downhole reaction process; the well layout method of one injection and multiple production is described, in which the downhole reaction process and the production area are controlled according to the above method and the opening and closing status of the production well.

7. The in-situ mining method for interbedded coal and oil shale according to claim 1, characterized in that: An array of sensors is arranged in the in-situ progress feedback monitoring well; the sensors in the same well are evenly spaced along the vertical direction.

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