A method and system for in-situ coal combustion heat extraction and carbon sequestration

Abstract

The application discloses a coal underground in-situ combustion heat extraction and carbon sequestration method and system, which comprises the following steps: determining coal seams and reasonably dividing a plurality of combustion units in a coal distribution area; drilling and completing a supply oxygen horizontal well and a heat extraction straight well in each combustion unit; preparing oxygen production, a coiled tubing and a temperature control oxygen supply pipe; injecting oxygen and controlling coal seam combustion by using the coiled tubing and the temperature control oxygen supply pipe; extracting carbon dioxide mixed gas generated by coal seam combustion to be converted into electric energy for utilization; and performing carbon dioxide sequestration in a combustion-out area, a depleted gas field or a deep trap. The application combines coal underground in-situ full combustion, carbon dioxide heat extraction and sequestration technologies, performs in-situ full combustion on coal which is not easy to be mined, extracts heat energy by using carbon dioxide mixed gas generated by combustion, and sequestrates carbon dioxide by using a combustion control area, a deep trap or a depleted gas field, so that the coal heat energy is fully utilized, the influence of carbon emission on the environment is reduced, and the environmental pollution in coal utilization is reduced.

Description

Technical Field

[0001] This invention relates to the field of underground coal pyrolysis technology, and in particular to a method and system for underground in-situ combustion heat extraction and carbon sequestration of coal. Background Technology

[0002] my country has abundant deep coal resources. The proven coal resources at depths shallower than 1,000 meters amount to 1,017.645 billion tons, the coal resources at depths of 1,000 to 2,000 meters are over 2.7 trillion tons, and the coal resources at depths of 1,000 to 3,000 meters are about 3.77 trillion tons. It is estimated that nearly 70% of my country's coal resources are distributed at depths of 1,000 meters or more.

[0003] Coal resources buried deeper than 1000 meters are difficult to mine economically and effectively using traditional methods due to rock bursts, heat hazards, and other factors. Coal resources buried shallower than 1000 meters are also subject to environmental and safety restrictions, with some provinces even imposing a complete ban on mining them. Deep mining generally presents a series of engineering and technical challenges, including water inrush from high-pressure, water-rich layers, gas or rockburst disasters, high-temperature heat hazards, rock bursts, and shaft rupture, which can easily lead to engineering accidents. It is predicted that, under current technological limitations, including environmental temperature at the coal face, roadway deformation control, and the potential for energy accumulation and disasters in the mined rock mass, the maximum mining depth for traditional underground coal mining is 1500 meters. Therefore, the utilization of abundant deep coal resources requires innovative development technologies and new approaches, as traditional technologies are insufficient for efficient and economical deep coal resource mining and utilization. Summary of the Invention

[0004] This invention aims to solve at least one of the technical problems existing in the prior art. To this end, this invention proposes a method for underground in-situ combustion heat recovery and carbon sequestration of coal, which solves the problem of the current difficulty in carrying out efficient and economical deep coal resource mining and utilization.

[0005] The present invention also provides a coal underground in-situ combustion heat recovery and carbon sequestration system.

[0006] The method for underground in-situ combustion heat recovery and carbon sequestration based on coal, according to a first aspect of the present invention, includes the following steps:

[0007] In the coal distribution area, coal seams are identified and multiple combustion units are rationally divided;

[0008] In each of the combustion units, oxygen supply horizontal wells and heat extraction vertical wells are drilled and completed.

[0009] Prepare oxygen generators, continuous oil tubing, and temperature-controlled oxygen supply tubing;

[0010] Oxygen is injected and coal seam combustion is controlled using the continuous tubing and the temperature-controlled oxygen supply pipe.

[0011] The carbon dioxide mixture produced by the combustion of coal seams is converted into electrical energy for use.

[0012] Carbon dioxide sequestration is carried out in gas-burning zones, depleted gas fields, or deep traps.

[0013] The method for underground in-situ combustion heat recovery and carbon sequestration based on coal according to embodiments of the present invention has at least the following beneficial effects:

[0014] By utilizing the method of this invention, in-situ underground combustion of coal can generate heat, and the resulting carbon dioxide mixture can be extracted to extract thermal energy and convert it into electrical energy. Simultaneously, the carbon dioxide can be sequestered. This invention combines in-situ full combustion of coal, carbon dioxide mixture heat extraction, and sequestration technologies. It enables in-situ full combustion of coal that is difficult to mine, extracting thermal energy from the high-temperature carbon dioxide mixture generated during combustion, sequestering some carbon dioxide in a combustion control zone, and sequestering the remaining carbon dioxide in deep, closed, or depleted gas fields. This fully utilizes the thermal energy of coal while reducing the environmental impact of carbon emissions, lowering environmental pollution and safety risks in coal utilization. Furthermore, the deformation of the combustion sludge zone after coal combustion has minimal impact on the surface, thus minimizing the impact on the geological environment. Therefore, it ultimately achieves the utilization of coal resources that are currently difficult to mine underground, resulting in a significant increase in usable coal resources.

[0015] According to some embodiments of the present invention, the conversion of the carbon dioxide mixture produced by the combustion of the extracted coal seam into electrical energy for utilization includes the following steps:

[0016] The high-temperature carbon dioxide mixture produced by coal seam combustion is extracted to generate electricity through heat utilization.

[0017] The low-temperature carbon dioxide mixture after heat utilization is recycled to generate electricity from the waste heat of the combustion chamber.

[0018] According to some embodiments of the present invention, the process of extracting high-temperature carbon dioxide mixture from coal seam combustion to generate electricity by extracting thermal energy includes the following steps:

[0019] Establish a balance relationship for combustion and heat recovery control. The balance relationship includes at least the balance relationship between coal combustion rate, oxygen supply rate and high-temperature carbon dioxide production rate, as well as the balance relationship between combustion air zone pressure, oxygen injection pressure and carbon dioxide mixture production pressure.

[0020] The amount of gas extracted from the high-temperature carbon dioxide mixture is controlled according to the pressure requirements of maintaining the combustion zone.

[0021] The high-temperature carbon dioxide mixture is extracted from the heating well and brought to the wellhead, where it is then used for power generation after heat exchange.

[0022] According to some embodiments of the present invention, determining the coal seam and rationally dividing it into multiple combustion units in a coal distribution area includes the following steps:

[0023] In the coal distribution area, coal seams are identified, and the coal seams must at least meet the requirements for coal seam burial depth, coal seam thickness, stable and continuous distribution of coal seams, and water-proofing of coal seams.

[0024] In the coal seam, multiple combustion units are divided according to the continuity and stability of the coal seam, the needs of surface drilling construction, and the needs of equipment deployment.

[0025] According to some embodiments of the present invention, the drilling and completion of the oxygen supply horizontal well and the heat extraction vertical well in each of the combustion units includes the following steps:

[0026] Drill horizontal wells for oxygen supply in the target coal seam of each combustion unit;

[0027] Drill the heating vertical well in the bottom area of ​​each of the oxygen supply horizontal wells and complete the bottom connection between the oxygen supply horizontal wells and the heating vertical wells, so that the oxygen supply horizontal wells and the heating vertical wells on each of the combustion units form a well pair, which is used to control coal seam combustion and heat extraction.

[0028] According to some embodiments of the present invention, if the combustion unit is a multi-layered combustion unit, the well pair adopts a multi-branch well pair, the multi-layered combustion unit represents a combustion unit divided under multiple superimposed coal seams, and the multi-branch well pair consists of multiple oxygen supply horizontal wells and multiple heat extraction vertical wells.

[0029] According to some embodiments of the present invention, the preparation of the oxygen generator, continuous oil tubing, and temperature-controlled oxygen supply tubing includes the following steps:

[0030] Prepare an air separation oxygen generator with sufficient oxygen content;

[0031] The vertical section of the temperature-controlled oxygen supply pipe is made of seamless steel pipe, and the horizontal section is made of a special temperature-controlled screen pipe with sieve holes made of seamless steel pipe.

[0032] The temperature-controlled oxygen supply pipe is run into the oxygen supply horizontal well, and the coiled tubing is run into the temperature-controlled oxygen supply pipe.

[0033] According to some embodiments of the present invention, the oxygen injection and control of coal seam combustion using the continuous tubing and the temperature-controlled oxygen supply pipe includes the following steps:

[0034] An ignition device is inserted into the temperature-controlled oxygen supply pipe.

[0035] Oxygen is injected into the coal seam at the bottom of the well through the coiled tubing;

[0036] The ignition device is activated to ignite the coal seam, so that the coal seam can continue to burn fully and generate heat energy.

[0037] According to some embodiments of the present invention, a protective coal column is provided between the plurality of combustion units.

[0038] A coal underground in-situ combustion heat recovery and carbon sequestration system according to a second aspect embodiment of the present invention includes:

[0039] Combustion zone determination unit, used to determine coal seams and rationally divide multiple combustion units in coal distribution areas;

[0040] A drilling unit for drilling and completing oxygen supply horizontal wells and thermal extraction vertical wells in each of the combustion units;

[0041] The preparation unit is used to prepare oxygen generators, continuous oil lines, and temperature-controlled oxygen supply lines.

[0042] A combustion unit is implemented for injecting oxygen and controlling coal seam combustion using the continuous oil pipe and the temperature-controlled oxygen supply pipe;

[0043] Energy extraction unit, used to extract carbon dioxide mixture produced by coal seam combustion and convert it into electrical energy for use;

[0044] A storage unit is used for carbon dioxide sequestration in fuel-air zones, depleted gas fields, or deep traps.

[0045] The underground in-situ combustion heat recovery and carbon sequestration system based on coal according to embodiments of the present invention has at least the following beneficial effects:

[0046] By utilizing the system of this invention, in-situ underground combustion of coal can generate heat, and the resulting carbon dioxide mixture can be extracted to extract thermal energy and convert it into electrical energy. Simultaneously, the carbon dioxide can be sequestered. The system of this embodiment combines in-situ full combustion of coal, carbon dioxide mixture heat extraction, and sequestration technologies. It enables in-situ full combustion of coal that is difficult to mine, extracting thermal energy from the high-temperature carbon dioxide mixture generated during combustion, sequestering some carbon dioxide in a combustion control zone, and sequestering the remaining carbon dioxide in deep, closed, or depleted gas fields. While fully utilizing the thermal energy of coal, it reduces the environmental impact of carbon emissions, lowers environmental pollution and safety risks in coal utilization, and minimizes the impact of the combustion sludge deformation on the surface, thus reducing the impact on the geological environment. Therefore, it ultimately realizes the utilization of coal resources that are currently difficult to mine underground, significantly increasing the available coal resources.

[0047] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description

[0048] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0049] Figure 1 This is a flowchart of an embodiment of the present invention of a method for in-situ underground combustion heat recovery and carbon sequestration of coal;

[0050] Figure 2 This is a structural diagram of a well pair consisting of one oxygen supply horizontal well and one heat extraction vertical well, according to an embodiment of the present invention.

[0051] Figure 3 This is a structural diagram of a well pair consisting of two oxygen supply horizontal wells and two heat extraction vertical wells according to an embodiment of the present invention;

[0052] Figure 4 This is a structural diagram of a well pair consisting of a dual-branch oxygen supply horizontal well and a thermal extraction vertical well, according to an embodiment of the present invention.

[0053] Figure 5 This is a structural diagram of a well pair consisting of a multi-coal-seam, multi-branch oxygen supply horizontal well and a thermal extraction vertical well, according to an embodiment of the present invention.

[0054] Figure label:

[0055] 100 on the surface;

[0056] Coal seam 200;

[0057] 300mm oxygen supply horizontal well;

[0058] 400m vertical well for heat extraction. Detailed Implementation

[0059] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals characterize the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0060] In the description of this invention, the use of terms such as "first," "second," etc., is for the purpose of distinguishing technical features only and should not be construed as indicating or implying relative importance, or implicitly indicating the number of technical features indicated, or implicitly indicating the order of the technical features indicated.

[0061] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, etc., are based on the orientation or positional relationship shown in the drawings and are only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0062] In the description of this invention, it should be noted that, unless otherwise explicitly defined, terms such as "setting," "installation," and "connection" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0063] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are some embodiments of the present invention, not all embodiments.

[0064] See Figure 1 The diagram shows a flowchart of a method for in-situ underground combustion heat recovery and carbon sequestration of coal according to an embodiment of the present invention. The method includes the following steps:

[0065] In the coal distribution area, coal seam 200 was identified and multiple combustion units were rationally divided.

[0066] In each combustion unit, an oxygen supply horizontal well (300) and a heat extraction vertical well (400) were drilled and completed.

[0067] Prepare oxygen generators, continuous oil tubing, and temperature-controlled oxygen supply tubing;

[0068] Oxygen was injected and the combustion of coal seam 200 was controlled using coiled tubing and temperature-controlled oxygen supply pipes.

[0069] The carbon dioxide mixture produced by burning coal seam 200 is converted into electrical energy for use.

[0070] Carbon dioxide sequestration is carried out in gas-burning zones, depleted gas fields, or deep traps.

[0071] Specifically, such as Figure 1As shown, firstly, coal seams 200 are identified in the coal distribution area. Specifically, coal seams 200 that meet the requirements for in-situ full combustion, carbon dioxide heat recovery, and carbon sequestration are selected. After delineating the area of ​​coal seam 200, it is divided into multiple combustion units. It can be understood that each combustion unit can implement underground in-situ combustion of coal and carbon dioxide heat recovery. Therefore, oxygen supply horizontal wells 300 and heat recovery vertical wells 400 are drilled and completed in each combustion unit. In some embodiments, the horizontal section of the oxygen supply horizontal well 300 is about 1000 meters long, and it encounters coal seam 200 100%. After drilling and completion, the bottom of the heat recovery vertical well 400 and the oxygen supply horizontal well 300 are connected. The heat recovery vertical well 400 is cemented with high-temperature resistant insulation material, and the oxygen supply horizontal well 300 serves as the installation space for temperature-controlled oxygen supply pipes.

[0072] Furthermore, oxygen production is prepared, and in some embodiments, air separation can be used for oxygen production. It is understood that by using oxygen as a combustion aid, the combustion product is primarily carbon dioxide, which can only be extracted through the thermal well 400, resulting in low collection costs and easy reuse or burial disposal, significantly reducing the environmental impact of carbon dioxide. Simultaneously, coiled tubing is selected, and temperature-controlled oxygen supply pipes are manufactured and installed. Oxygen is then injected into the coal seam 200 at the bottom of the well, and orderly oxygen supply is achieved using the coiled tubing and temperature-controlled oxygen supply pipes, thereby controlling the combustion of coal seam 200. The remaining CO2 mixture is injected into the natural gas reservoir using existing injection wells in the depleted gas field near the combustion zone.

[0073] Furthermore, the carbon dioxide produced after the combustion of coal seam 200 will be extracted as thermal energy through the thermal well 400 and ultimately converted into electrical energy for utilization. In some embodiments, in-situ coal combustion occurs in a confined underground space where the surrounding rocks and strata have low thermal conductivity and low heat loss rate. The maximum influence range formed by the heating of the surrounding strata and rocks is 20 meters. After the continuous combustion units have completed combustion, the heated rocks and strata can be regarded as hot dry rock, so the thermal energy can be extracted using hot dry rock thermal extraction technology.

[0074] Furthermore, controlled combustion of gasified gas from deep coal seams (up to 200 meters underground) can create numerous safe and reliable sealed underground combustion chambers. These combustion chambers can be used for underground gas storage and carbon dioxide sequestration. Therefore, carbon dioxide sequestration can be directly achieved using these combustion chambers. Simultaneously, existing injection wells in depleted gas fields near the combustion chambers can be used to inject the remaining carbon dioxide mixture into the natural gas reservoir. If no depleted gas fields are nearby, the remaining carbon dioxide mixture can be injected into deep traps for sequestration.

[0075] In some embodiments, since multiple combustion units are divided, multiple combustion units can be used for simultaneous combustion for thermal power generation or sequential combustion for thermal power generation, so as to meet the needs of different scales of underground coal in-situ combustion for thermal power generation and carbon sequestration.

[0076] In this embodiment, the method of the present invention enables in-situ combustion of coal underground to generate heat, and the heat energy from the carbon dioxide produced during combustion can be extracted and converted into electrical energy for use. Simultaneously, the carbon dioxide can be sequestered. This method combines in-situ full combustion of coal underground with carbon dioxide heat extraction and sequestration technologies. It allows for the in-situ full combustion of coal that is difficult to mine, extracting heat energy from the high-temperature carbon dioxide produced during combustion, sequestering part of the carbon dioxide in a combustion control zone, and sequestering the remaining carbon dioxide in deep, closed, or depleted gas fields. While fully utilizing the thermal energy of coal, it reduces the environmental impact of carbon emissions, lowers environmental pollution during coal utilization, and minimizes the impact of the combustion sump deformation on the surface (100°), thus reducing the geological environment impact. Therefore, it ultimately achieves the utilization of coal resources that are currently difficult to mine underground, resulting in a significant increase in usable coal resources.

[0077] In some embodiments, the carbon dioxide mixture produced by the combustion of coal seam 200 is converted into electrical energy for utilization, including the following steps:

[0078] The high-temperature carbon dioxide mixture produced by the combustion of coal seam 200 is used to generate electricity through heat utilization.

[0079] The low-temperature carbon dioxide mixture after heat recovery is recycled to generate electricity from the waste heat of the combustion chamber.

[0080] Specifically, it can be understood that when coal seam 200 is burned, the oxygen supply and pressure are first controlled to ensure that coal seam 200 is fully burned and forms a high-temperature carbon dioxide mixture. Then, the pressure control device at the wellhead of the thermal well 400 is used to control the pressure of the high-temperature carbon dioxide mixture to be slightly higher than the gas pressure in the formation, so as to extract heat energy from the high-temperature carbon dioxide mixture and transfer the heat energy to the power generation working medium through the heat exchange device for power generation.

[0081] Furthermore, after each combustion unit has completed combustion, the low-temperature carbon dioxide mixture formed after the first heat utilization is injected into the combustion air zone through an oxygen supply pipe, then reheated in the combustion air zone, and the waste heat of the combustion air zone is recycled for power generation and comprehensive utilization. In some embodiments, when the temperature of the combustion air zone drops below 50 degrees Celsius, the waste heat extraction from the combustion air zone is stopped.

[0082] In some embodiments, the high-temperature carbon dioxide mixture produced by the combustion of coal seam 200 is extracted to generate electricity from the extracted heat energy, including the following steps:

[0083] Establish balance relationships for combustion and heat recovery control. The balance relationships should include at least the balance relationships between coal combustion rate, oxygen supply rate and high-temperature carbon dioxide production rate, as well as the balance relationships between combustion air zone pressure, oxygen injection pressure and carbon dioxide mixture production pressure.

[0084] Control the amount of high-temperature carbon dioxide mixture produced based on the pressure requirements of the combustion zone.

[0085] High-temperature carbon dioxide mixture is extracted from the 400-meter vertical well and brought to the wellhead. After heat exchange treatment, it is used for power generation.

[0086] Specifically, it can be understood that by establishing a balance relationship, the full combustion of coal seam 200 can be controlled more precisely and scientifically, so that a large amount of high-temperature carbon dioxide thermal energy can be extracted, thereby achieving efficient energy recovery and utilization.

[0087] In some embodiments, determining a coal seam 200 in a coal distribution area and rationally dividing it into multiple combustion units includes the following steps:

[0088] In the coal distribution area, coal seam 200 is determined. Coal seam 200 must at least meet the requirements for burial depth, thickness, stable and continuous distribution, and water resistance.

[0089] In coal seam 200, multiple combustion units are divided according to the continuity and stability of coal seam 200, the needs of surface drilling construction, and the needs of equipment deployment.

[0090] Specifically, it is understood that in some embodiments, the coal distribution area is first determined by prioritizing coal seams 200 with a burial depth of 600 to 1000 meters, a thickness greater than 2 meters, stable and continuous structure, a distance of more than 30 meters from water-bearing faults, and water-resistant roof and floor. Then, within the coal distribution area, combustion units are divided according to the continuity and stability of the coal seam 200, the requirements of surface drilling construction and equipment deployment, with a length of 1000 meters and a width of 70 meters. Further, in some embodiments, when costs are reduced, stable and continuous coal seams 200 with a thickness of less than 2 meters can be selected.

[0091] In some embodiments, drilling and completion of an oxygen supply horizontal well 300 and a heat extraction vertical well 400 in each combustion unit includes the following steps:

[0092] In each combustion unit, drill 300 horizontal wells for oxygen supply in the target coal seam at a depth of 200;

[0093] Drill a heating vertical well 400 in the bottom area of ​​each oxygen supply horizontal well 300 and complete the bottom connection between the oxygen supply horizontal well 300 and the heating vertical well 400 so that the oxygen supply horizontal well 300 and the heating vertical well 400 on each combustion unit form a well pair, which is used to control the combustion and heating of coal seam 200.

[0094] Specifically, it can be understood that existing drilling and completion technologies for oil and gas, shale oil and gas, and coal seam 200 gas are utilized, and based on the extension direction of the thermal recovery unit, an oxygen supply horizontal well 300 is drilled in the target coal seam 200. The horizontal well section is approximately 1000 meters long to provide installation space for the temperature-controlled oxygen supply pipe. In the bottom area of ​​the oxygen supply horizontal well 300, a thermal recovery vertical well 400 is drilled, achieving bottom-hole connection between the two wells. In some embodiments, the thermal recovery vertical well 400 employs high-temperature resistant casing and cementing completion.

[0095] In some embodiments, if the combustion unit is a multi-layered combustion unit, the well pair adopts a multi-branch well pair. The multi-layered combustion unit refers to the combustion unit divided under multiple superimposed coal seams 200. The multi-branch well pair consists of multiple oxygen supply horizontal wells 300 and multiple heat extraction vertical wells 400.

[0096] Specifically, it can be understood that within a combustion unit, a well pair consisting of an oxygen supply horizontal well 300 ("L"-shaped well or multi-branched well) and a heating vertical well 400 is drilled along the extension direction to provide installation space for the oxygen supply conduit, oxygen supply coiled tubing, and heating pipe. For a single coal seam 200, a well pair consisting of one oxygen supply horizontal well 300 and one heating vertical well 400 can be drilled in each combustion unit, or a well pair consisting of two branched oxygen supply horizontal wells 300 and two heating vertical wells 400 can be used. For multiple coal seams 200, depending on the distribution characteristics of the combustion units, a well pair consisting of a unidirectional multi-branched horizontal well and a heating vertical well 400, or a bidirectional multi-branched horizontal well and a heating vertical well 400 can be used.

[0097] Furthermore, in conjunction with references Figures 2 to 5 , Figures 2 to 5 The diagram illustrates various well pairs arranged between the surface 100 and the coal seam 200 under different embodiments. Each well pair consists of a different oxygen supply horizontal well 300 and a heat extraction vertical well 400. In some embodiments, such as Figure 2 As shown, when the coal seam 200 is stable and continuous, and the length of the combustion unit is approximately 1000 meters, a well pair consisting of one oxygen supply horizontal well 300 and one heat extraction vertical well 400 is used for in-situ underground combustion and heat extraction of the coal. Specifically, the oxygen supply horizontal well 300 is drilled from one side of the combustion unit to the other, and a heat extraction vertical well 400 is drilled on the other side of the combustion unit and connected to the bottom of the oxygen supply well. The oxygen supply horizontal well 300 is ignited for combustion, and heat is extracted through the heat extraction vertical well 400.

[0098] Furthermore, such as Figure 3 As shown, when the coal seam 200 is stable and continuous, and the length of the combustion unit can be continuously extended to about 2000 meters, a well pair consisting of two oxygen supply horizontal wells 300 and one heat extraction vertical well 400 is used for in-situ combustion and heat extraction of the coal seam underground. Specifically, oxygen supply horizontal wells 300 are drilled from both sides of the combustion unit toward the center, and a heat extraction vertical well 400 is drilled in the center of the combustion unit and connected to the bottom of the two oxygen supply wells. The two oxygen supply horizontal wells 300 are ignited and combusted simultaneously, and heat is extracted simultaneously through the heat extraction vertical well 400 in the center.

[0099] Furthermore, such as Figure 4 As shown, when the coal seam 200 is stable and continuous, and the combustion unit length can extend continuously for more than 3000 meters, a well pair consisting of a double-branch horizontal well and a 400-meter heating vertical well is used for in-situ coal combustion and heat extraction. Specifically, at 1000 meters and 3000 meters of the combustion unit, a double-branch oxygen-supplying horizontal well 300 is drilled, forming four oxygen-supplying horizontal well sections 300. At both ends of the combustion unit and at 2000 meters, a heating vertical well 400 is drilled, connecting to the bottom of the four oxygen-supplying horizontal well sections. The four oxygen-supplying horizontal well sections are ignited and combusted simultaneously, and heat is extracted simultaneously through the three 400-meter heating vertical wells.

[0100] Furthermore, such as Figure 5 As shown, for coal seams 200 with multiple layers available for in-situ combustion, different vertical multi-branch horizontal wells and heating vertical wells 400 can be designed based on the above basic well pairs, forming multi-branch well pairs. Specifically, multiple horizontal sections of oxygen supply wells are drilled simultaneously in multiple coal seams 200, and one heating vertical well 400 is simultaneously established to connect with multiple coal seams 200. The multiple coal seams 200 are then sequentially ignited for heat extraction from top to bottom.

[0101] In some embodiments, preparing an oxygen generator, a continuous oil tubing, and a temperature-controlled oxygen supply tubing includes the following steps:

[0102] Prepare an air separation oxygen generator with sufficient oxygen content;

[0103] The vertical section of the temperature-controlled oxygen supply pipe is made of seamless steel pipe, and the horizontal section is made of a special temperature-controlled screen pipe with sieve holes made of seamless steel pipe.

[0104] A temperature-controlled oxygen supply pipe is run into the oxygen supply horizontal well within 300 meters, and then a coiled tubing is run into the temperature-controlled oxygen supply pipe.

[0105] Specifically, it is understood that in some embodiments, commercially available air separation oxygen production equipment is used to ensure an oxygen content of over 95%; the vertical section of the oxygen supply pipe is made of seamless steel pipe; its horizontal section is a specially designed temperature-controlled screen pipe, with seamless steel pipe used to make the screen holes, which are evenly distributed in four rows, with a hole spacing of 10cm per row and a hole diameter of 0.5cm. Except for the bottom 10 meters of the horizontal well, all oxygen supply holes are sealed with a self-melting material at around 700℃, which automatically melts and opens the screen holes to supply oxygen at the corresponding temperature; continuous tubing is run into the oxygen supply pipe as a channel for injecting oxygen downhole. When the oxygen supply horizontal well is completed at 300, the temperature-controlled oxygen supply pipe is run in, the vertical section of the temperature-controlled oxygen supply pipe is cemented and completed, and the horizontal section is completed with the oxygen supply screen pipe.

[0106] In some embodiments, oxygen injection and control of coal seam 200 combustion using coiled tubing and temperature-controlled oxygen supply tubing include the following steps:

[0107] Insert the ignition device into the temperature-controlled oxygen supply pipe;

[0108] Oxygen was injected into the coal seam 200 at the bottom of the well via coiled tubing;

[0109] The ignition device is activated to ignite the coal seam 200, so that the coal seam 200 can continue to burn fully and generate heat energy.

[0110] Specifically, it can be understood that in some embodiments, firstly, a continuous tubing with an ignition device at the front end is lowered into the temperature-controlled oxygen supply pipe to the bottom of the oxygen supply horizontal well 300. Then, an air compressor is used to inject oxygen into the coal seam 200 at the bottom of the well through the continuous tubing, and the ignition device is activated to ignite the coal seam 200. The coal seam 200 continues to burn and generate heat energy. When the temperature near the sealed oxygen supply hole reaches about 700°C, the material sealing the oxygen supply hole melts, the sealed oxygen supply hole opens, and the continuous tubing is moved back to the vicinity of the newly opened oxygen supply hole to supply oxygen, so that the coal seam 200 burns fully along the oxygen supply pipe and continues to generate heat energy. Since the combustion unit is a closed space with a temperature of over 1200°C, the heat energy is mainly stored in the carbon dioxide mixture produced by combustion and in the rocks and strata within 20 meters around it. It cannot be dissipated in a short time, there is no heat energy leakage channel, and the amount of heat energy loss is small.

[0111] In some embodiments, a protective coal pillar is provided between multiple combustion units.

[0112] Specifically, in some embodiments, a protective coal pillar with a width of about 10 meters is left between adjacent combustion units to reduce the risk of roof collapse and prevent cross-contamination of combustion products.

[0113] In some embodiments, by utilizing the method of the present invention, a combustion unit 1000 meters long, 3 meters thick, and 30 meters wide can burn approximately 125,000 tons of coal. The calorific value of the coal is 5500 kcal / kg = 23.1 MJ / kg, the thermal efficiency is calculated at 70% (the efficiency of existing domestic thermal power plant boilers is around 90%), and the electricity conversion efficiency is 30% (the efficiency of existing domestic steam turbine power generation systems is around 40%). Without considering combined heat and power (CHP), the power generation is calculated based on pure condensation power generation, the electricity price is calculated at 0.4 yuan / kWh, and 10% is used for self-consumption. 125,000 tons of coal, through underground in-situ combustion for heat recovery and power generation, can produce 150 million kWh of sellable electricity, generating 60 million yuan in revenue. If the combustion width is 60 meters, it can produce 300 million kWh of sellable electricity, generating 120 million yuan in revenue. Therefore, the embodiments of the present invention have good economic benefits.

[0114] In addition, one embodiment of the present invention provides a coal underground in-situ combustion heat recovery and carbon sequestration system. The system includes: a combustion zone determination unit, a drilling unit, a preparation unit, a combustion implementation unit, an energy recovery unit, and a sequestration unit. The combustion zone determination unit is used to determine the coal seam 200 in the coal distribution area and rationally divide it into multiple combustion units; the drilling unit is used to drill and complete the oxygen supply horizontal well 300 and the heat recovery vertical well 400 in each combustion unit; the preparation unit is used to prepare oxygen production, coiled tubing, and temperature-controlled oxygen supply pipes; the combustion implementation unit is used to inject oxygen and control the combustion of coal seam 200 using coiled tubing and temperature-controlled oxygen supply pipes; the energy recovery unit is used to extract the carbon dioxide mixture generated by the combustion of coal seam 200 and convert it into electrical energy for utilization; the sequestration unit is used to sequestrate carbon dioxide in the combustion zone, depleted gas field, or deep trap.

[0115] Specifically, it is understood that the coal underground in-situ combustion heat recovery and carbon sequestration system in this application embodiment is used to implement the coal underground in-situ combustion heat recovery and carbon sequestration method. The coal underground in-situ combustion heat recovery and carbon sequestration system in this application embodiment corresponds to the aforementioned coal underground in-situ combustion heat recovery and carbon sequestration method. For the specific processing procedure, please refer to the aforementioned coal underground in-situ combustion heat recovery and carbon sequestration method, which will not be repeated here.

[0116] In this embodiment, the system of the present invention enables in-situ combustion of coal underground to generate heat, and the resulting carbon dioxide mixture is extracted to extract thermal energy and convert it into electrical energy. Simultaneously, the carbon dioxide can be sequestered. This system combines in-situ full combustion of coal underground, carbon dioxide mixture heat extraction, and sequestration technologies. It allows for the in-situ full combustion of coal that is difficult to mine, extracting thermal energy from the high-temperature carbon dioxide mixture generated during combustion, sequestering some carbon dioxide in a combustion control zone, and sequestering the remaining carbon dioxide in deep, closed, or depleted gas fields. This fully utilizes the thermal energy of coal while reducing the environmental impact of carbon emissions, lowering environmental pollution and safety risks in coal utilization. Furthermore, the deformation of the combustion zone after coal combustion has minimal impact on the surface area, thus minimizing the impact on the geological environment. Therefore, it ultimately achieves the utilization of coal resources that are currently difficult to mine underground, resulting in a significant increase in usable coal resources.

[0117] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0118] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

[0119] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for underground in-situ combustion heat recovery and carbon sequestration of coal, characterized in that, Includes the following steps: In the coal distribution area, the coal seam is identified and multiple combustion units are rationally divided; protective coal pillars are set between the multiple combustion units. In each combustion unit, an oxygen supply horizontal well and a heat extraction vertical well are drilled and completed, and the heat extraction vertical well is cemented with thermal insulation cement. Prepare oxygen generators, continuous oil tubing, and temperature-controlled oxygen supply tubing; Oxygen is injected and coal seam combustion is controlled using the continuous tubing and the temperature-controlled oxygen supply pipe. The carbon dioxide mixture produced by the combustion of coal seams is converted into electrical energy for use. Carbon dioxide is stored in the combustion zone, depleted gas field, or deep trap. In the combustion zone, carbon dioxide is stored while the remaining carbon dioxide mixture is injected into the natural gas reservoir using existing injection wells in the depleted gas field near the combustion zone. If there is no depleted gas field nearby, the remaining carbon dioxide mixture is injected into the deep trap for storage. The process of converting the carbon dioxide mixture produced by burning the extracted coal seam into electrical energy includes the following steps: The high-temperature carbon dioxide mixture produced by coal seam combustion is extracted to generate electricity through heat utilization. The low-temperature carbon dioxide mixture after heat utilization is recycled to generate electricity from the waste heat of the combustion chamber. The process of generating electricity from the high-temperature carbon dioxide mixture produced by burning the extracted coal seam includes the following steps: Establish a balance relationship for combustion and heat recovery control. The balance relationship includes at least the balance relationship between coal combustion rate, oxygen supply rate and high-temperature carbon dioxide production rate, as well as the balance relationship between combustion air zone pressure, oxygen injection pressure and carbon dioxide mixture production pressure. The amount of gas extracted from the high-temperature carbon dioxide mixture is controlled according to the pressure requirements of maintaining the combustion zone. The high-temperature carbon dioxide mixture is extracted from the heating well and brought to the wellhead, where it is then used for power generation after heat exchange.

2. The method for underground in-situ combustion heat recovery and carbon sequestration of coal according to claim 1, characterized in that, The process of identifying coal seams and rationally dividing them into multiple combustion units in a coal distribution area includes the following steps: In the coal distribution area, coal seams are identified, and the coal seams must at least meet the requirements for coal seam burial depth, coal seam thickness, stable and continuous distribution of coal seams, and water-proofing of coal seams. In the coal seam, multiple combustion units are divided according to the continuity and stability of the coal seam, the needs of surface drilling construction, and the needs of equipment deployment.

3. The method for underground in-situ combustion heat recovery and carbon sequestration of coal according to claim 1, characterized in that, The drilling and completion of the oxygen supply horizontal well and the heat extraction vertical well in each of the combustion units includes the following steps: Drill horizontal wells for oxygen supply in the target coal seam of each combustion unit; Drill the heating vertical well in the bottom area of ​​each of the oxygen supply horizontal wells and complete the bottom connection between the oxygen supply horizontal wells and the heating vertical wells, so that the oxygen supply horizontal wells and the heating vertical wells on each of the combustion units form a well pair, which is used to control coal seam combustion and heat extraction.

4. The method for underground in-situ combustion heat recovery and carbon sequestration of coal according to claim 3, characterized in that, If the combustion unit is a multi-layered combustion unit, the well pair adopts a multi-branch well pair. The multi-layered combustion unit refers to the combustion unit divided under multiple superimposed coal seams. The multi-branch well pair consists of multiple oxygen supply horizontal wells and multiple heat extraction vertical wells.

5. The method for underground in-situ combustion heat recovery and carbon sequestration of coal according to claim 1, characterized in that, The preparation of the oxygen generator, continuous oil tubing, and temperature-controlled oxygen supply tubing includes the following steps: Prepare an air separation oxygen generator with sufficient oxygen content; The vertical section of the temperature-controlled oxygen supply pipe is made of seamless steel pipe, and the horizontal section is made of a special temperature-controlled screen pipe with sieve holes made of seamless steel pipe. The temperature-controlled oxygen supply pipe is run into the oxygen supply horizontal well, and the coiled tubing is run into the temperature-controlled oxygen supply pipe.

6. The method for underground in-situ combustion heat recovery and carbon sequestration of coal according to claim 1, characterized in that, The process of injecting oxygen and controlling coal seam combustion using the continuous tubing and the temperature-controlled oxygen supply pipe includes the following steps: An ignition device is inserted into the temperature-controlled oxygen supply pipe. Oxygen is injected into the coal seam at the bottom of the well through the coiled tubing; The ignition device is activated to ignite the coal seam, so that the coal seam can continue to burn fully and generate heat energy.

7. A coal underground in-situ combustion heat recovery and carbon sequestration system, characterized in that, include: Combustion zone determination unit, used to determine coal seams and rationally divide multiple combustion units in coal distribution areas; Protective coal pillars are provided between the multiple combustion units; A drilling unit is used to drill and complete oxygen supply horizontal wells and heat extraction vertical wells in each of the combustion units, wherein the heat extraction vertical wells are cemented with insulating cement. The preparation unit is used to prepare oxygen generators, continuous oil lines, and temperature-controlled oxygen supply lines. A combustion unit is implemented for injecting oxygen and controlling coal seam combustion using the continuous oil pipe and the temperature-controlled oxygen supply pipe; Energy extraction unit, used to extract carbon dioxide mixture produced by coal seam combustion and convert it into electrical energy for use; The storage unit is used for carbon dioxide storage in the combustion zone, depleted gas field, or deep trap. In the combustion zone, carbon dioxide is stored while the remaining carbon dioxide mixture is injected into the natural gas reservoir using existing injection wells in the depleted gas field near the combustion zone. If there is no depleted gas field nearby, the remaining carbon dioxide mixture is injected into the deep trap for storage. The process of converting the carbon dioxide mixture produced by burning the extracted coal seam into electrical energy includes the following steps: The high-temperature carbon dioxide mixture produced by coal seam combustion is extracted to generate electricity through heat utilization. The low-temperature carbon dioxide mixture after heat utilization is recycled to generate electricity from the waste heat of the combustion chamber. The process of generating electricity from the high-temperature carbon dioxide mixture produced by burning the extracted coal seam includes the following steps: Establish a balance relationship for combustion and heat recovery control. The balance relationship includes at least the balance relationship between coal combustion rate, oxygen supply rate and high-temperature carbon dioxide production rate, as well as the balance relationship between combustion air zone pressure, oxygen injection pressure and carbon dioxide mixture production pressure. The amount of gas extracted from the high-temperature carbon dioxide mixture is controlled according to the pressure requirements of maintaining the combustion zone. The high-temperature carbon dioxide mixture is extracted from the heating well and brought to the wellhead, where it is then used for power generation after heat exchange.

Images