Coal seam in-situ gasification mining well pattern and mining method

Abstract

The invention discloses a coal seam in-situ gasification mining well pattern and a mining method. The well pattern comprises a plurality of injection wells and a production well; the multiple injection wells are designed in a well factory and are all horizontal wells, and well mouths are located on the same platform. The distance between the horizontal section of each injection well and the bottom plate of the coal seam is 10%-15% of the thickness of the coal seam and does not exceed 1 meter, and the distance between the horizontal sections of every two adjacent injection wells is 8-10 times of the thickness of the coal seam. In-situ gasification mining is conducted on the coal seam through the well pattern, operation is convenient and fast, combustion is stable, and mining economic benefits are high.

Description

Technical Field

[0001] The present invention relates to the technical field of clean utilization of coal, specifically to deep coal seam drilling and completion technology, gasification cavity injection and production well distribution design, multi-well linkage injection and production mode and other related technologies, and especially to a coal seam in-situ gasification production well network and production method. Background Art

[0002] Underground coal gasification technology is a cutting-edge and strategic new energy development technology. The construction of underground coal gasification furnaces is the key to the success of underground coal gasification projects. It is a comprehensive engineering technology involving the cross-integration of multiple disciplines such as drilling, cementing, materials, pipe mechanics, and machinery. my country's underground coal gasification research started late. Although preliminary exploratory tests have been carried out and successful shallow underground coal gasification tests have been carried out in a certain area, large-scale field tests have not yet been carried out.

[0003] In particular, underground gasification of deep coal seams with a burial depth of more than 2,200 meters is still a cutting-edge exploratory technology. There is no field test verification and the technology urgently needs to be tackled. Summary of the invention

[0004] In order to enrich the method to be applicable to more application scenarios, the present invention proposes a coal seam in-situ gasification mining well pattern and mining method.

[0005] In a first aspect, an embodiment of the present invention provides a coal seam in-situ gasification production well pattern, comprising a plurality of injection wells and a production well;

[0006] The multiple injection wells are designed by a well factory, and the injection wells are all horizontal wells with the wellheads on the same platform;

[0007] The distance between the horizontal section of each injection well and the bottom plate of the coal seam is 10% to 15% of the thickness of the coal seam and does not exceed 1 meter. The distance between the horizontal sections of two adjacent injection wells is 8 to 10 times the thickness of the coal seam.

[0008] In some embodiments, the connection point between each injection well and the production well is the same connection point.

[0009] In some embodiments, the injection well and the production well are connected by direct wellbore connection or by hydraulic fracturing.

[0010] In some embodiments, the horizontal section of the injection well is 500-700 meters long.

[0011] In some embodiments, the outer diameter of the production casing of the production well is not less than 224.5 mm.

[0012] In some embodiments, the production well is drilled through the coal seam, and the production well is completed using an open hole screen in the well section from the top of the coal seam to the bottom of the coal seam.

[0013] In some embodiments, a thermocouple is arranged every 20 to 50 meters in the oxygen injection annulus of the horizontal section of the injection well; and a thermocouple is arranged every 20 to 50 meters in the gas production pipe of the production well.

[0014] In some embodiments, the number of injection wells is 5 to 10.

[0015] In some embodiments, the production casing at the wellhead of the production well uses a corrugated pipe.

[0016] In some embodiments, a service well is also included for temperature and pressure monitoring and water injection to extinguish the fire under set conditions.

[0017] In a second aspect, an embodiment of the present invention provides a coal seam in-situ gasification mining method, comprising:

[0018] Through any of the above-mentioned coal seam in-situ gasification mining well networks, the coal seam is mined by in-situ gasification by adopting a mode in which multiple injection wells inject simultaneously and multiple combustion chambers work simultaneously.

[0019] In some embodiments, the ignition point of the first combustion chamber of the injection well is 10 to 15 times the thickness of the coal seam away from the connection point between the injection well and the production well.

[0020] In some embodiments, along a direction parallel to the coal seam floor, a minimum distance between two adjacent combustion chamber boundaries is greater than 5 times the coal seam thickness.

[0021] In some embodiments, the combustion chamber of the injection well adopts an alternating backward combustion mode.

[0022] In some embodiments, during the process of extinguishing a combustion chamber or igniting a non-first combustion chamber, nitrogen is injected through a corresponding injection well to keep the internal pressure of the combustion chamber no lower than the internal pressure of other combustion chambers that are burning.

[0023] In some embodiments, the combustion chamber retreat operation of multiple injection wells is performed by a concentric coiled tubing operation vehicle.

[0024] The beneficial effects of the above technical solution provided by the embodiment of the present invention include at least:

[0025] (1) The coal seam in-situ gasification mining well network provided by the embodiment of the present invention has multiple injection wells designed by a well factory. The injection wells are all horizontal wells, and the wellheads are on the same platform, which is convenient for the injection of oxygen, water and nitrogen protective gas and continuous pipe operation, and the operation is convenient; the distance between the horizontal section of each injection well and the bottom plate of the coal seam is 10% to 15% of the average thickness of the coal seam, and does not exceed 1 meter, which can ensure the maximum combustion efficiency; the distance between the horizontal sections of two adjacent injection wells is 8 to 10 times the thickness of the coal seam, which ensures that the gas pressures between the combustion chambers are independent of each other during the mining process. Through this well network, the coal seam is mined by in-situ gasification, which is convenient to operate, has stable combustion, and has high economic benefits.

[0026] (2) In the coal seam in-situ gasification production well network provided in the embodiment of the present invention, the production casing at the wellhead of the production well uses a bellows, which can offset the wellhead uplift caused by thermal stress during operation of the production well to a certain extent.

[0027] (3) The coal seam in-situ gasification mining method provided in the embodiment of the present invention adopts a mode of simultaneous injection of multiple wells and simultaneous operation of multiple combustion chambers, which reduces the unit cost of produced gas and greatly increases the total produced gas volume.

[0028] (4) In the coal seam in-situ gasification mining method provided by the embodiment of the present invention, the ignition point of the first combustion chamber of the injection well is 10 to 15 times the thickness of the coal seam at the connection point between the injection well and the production well. The minimum ignition distance is designed to ensure that the formation's own seepage and physical and chemical reactions are used for pyrolysis and cooling; the maximum distance is designed to prevent the coal from pyrolyzing at temperatures below 450 degrees. Pyrolysis of coal below 450 degrees will produce a large amount of tar, which may block the air flow channel. In addition, the distance between the connection point of the combustion chamber and the production well is large enough to ensure that the produced gas is naturally cooled and depressurized by the formation, which is more suitable for high temperature and high pressure conditions in the deep coal gasification process.

[0029] (5) In the coal seam in-situ gasification mining method provided by the embodiment of the present invention, the combustion chambers of multiple injection wells adopt an alternating retreat mode to ensure the stable supply of gas produced by the production wells. At the same time, the chambers are arranged at intervals, which can improve the utilization rate of the coal seam.

[0030] (6) In the coal seam in-situ gasification mining method provided in an embodiment of the present invention, during the process of extinguishing a combustion chamber or igniting a combustion chamber other than the first combustion chamber, nitrogen is injected through a corresponding injection well to maintain the internal pressure of the combustion chamber at least equal to the internal pressure of other combustion chambers that are burning, thereby preventing the gas in other operating chambers from flowing back into the extinguished chamber.

[0031] (7) The coal seam in-situ gasification mining method provided by the embodiment of the present invention takes into account the stability of the internal cavity after the combustion of the combustion chamber. During the underground gasification process of deep coal seams, the designed width of the ore pillar (the minimum distance between the boundaries of two adjacent combustion chambers in the direction parallel to the coal seam floor) is not less than 5 times the thickness of the coal seam. Generally speaking, after the underground gasification cavity of a deep coal seam is burned and abandoned, the hydrostatic pressure inside the cavity and the ash left by the combustion can largely support the mechanical stability of the combustion cavity, and due to the deep burial depth, the collapse of the flat cavity generally does not cause any impact on the ground.

[0032] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the written description, claims, and drawings.

[0033] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0035] Figure 1 This is a schematic diagram of the distribution of the well pattern for in-situ gasification of coal seams in Example 1 of the present invention;

[0036] Figure 2 Schematic diagram of the temperature field around the combustion chamber in the second embodiment of the present invention. DETAILED DESCRIPTION

[0037] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0038] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0039] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the art to which the invention belongs. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0040] In the description of the present invention, it should be noted that the terms "include", "including", "have", "contain" and the like are open terms, meaning including but not limited to.

[0041] In order to achieve efficient in-situ gasification and mining of deep coal seams (the main application scenario is coal seams with a burial depth greater than 2,200 meters and a thickness of 5 to 20 meters), an efficient design method for the distribution of injection and production wells and cavity types for underground gasification of deep coal seams is established, and the design of well groups and cavity groups for underground gasification of deep coal seams is carried out to achieve efficient and clean utilization of deep coal seams. An embodiment of the present invention provides a coal seam in-situ gasification mining well network and mining method.

[0042] Embodiment 1

[0043] Embodiment 1 of the present invention provides a coal seam in-situ gasification mining well pattern, referring to Figure 1 As shown, it includes multiple injection wells and one production well.

[0044] 1. Characteristics of the distribution design of multi-horizontal injection wells and single production wells

[0045] (1) Multiple injection wells are designed using a well factory. All injection wells are horizontal wells with wellheads on the same platform.

[0046] (2) The distance between the horizontal section of each injection well and the bottom of the coal seam is 10% to 15% of the thickness of the coal seam and does not exceed 1 meter.

[0047] Preferably, the distance between the horizontal section of each injection well and the bottom plate of the coal seam is 15% of the average thickness of the coal seam and does not exceed 1 meter.

[0048] The coal seam thickness in the embodiment of the present invention refers to the average thickness of the coal seam.

[0049] (3) The distance between the horizontal sections of two adjacent injection wells is 8 to 10 times the thickness of the coal seam.

[0050] Preferably, the distance between the horizontal sections of two adjacent injection wells is 10 times the thickness of the coal seam, and the combustion chambers are designed to be arranged at intervals.

[0051] In the coal seam in-situ gasification mining well network provided in the first embodiment of the present invention, multiple injection wells are designed by a well factory, and the injection wells are all horizontal wells, with the wellheads on the same platform, which is convenient for the injection of oxygen, water and nitrogen protective gas and continuous pipe operation, and the operation is convenient; the distance between the horizontal section of each injection well and the bottom plate of the coal seam is 10% to 15% of the average thickness of the coal seam, and does not exceed 1 meter, which can ensure the maximum combustion efficiency; the distance between the horizontal sections of two adjacent injection wells is 8 to 10 times the thickness of the coal seam, which ensures that the gas pressures between the combustion chambers are independent of each other during the mining process. Through the well network, the coal seam is mined by in-situ gasification, which is convenient to operate, has stable combustion, and has high economic benefits.

[0052] (4) The horizontal section length of the injection well is 500 to 700 meters. If technical and safety conditions permit and the gasification volume can cover the drilling cost, the horizontal section length should be increased as much as possible to increase the single well production efficiency.

[0053] (5) The outer diameter of the production casing of the injection well is 114.3 mm. Since the production well receives synthetic gas from multiple combustion chambers, the outer diameter of the production casing is designed to be no less than 224.5 mm.

[0054] (6) The production well is drilled through the coal seam, and the production well is completed using an open hole high-strength and high-temperature resistant screen pipe in the well section from the top of the coal seam to the bottom of the coal seam.

[0055] (7) The number of injection wells is 5 to 10.

[0056] (8) A vertical well service well is set up about 10 meters near the production well for temperature and pressure monitoring and water injection to extinguish the fire under set conditions.

[0057] 2. The connection method between injection well and production well

[0058] See also Figure 1 As shown, the connection point between each injection well and the production well is the same connection point.

[0059] The injection well and the production well can be connected in the following two ways:

[0060] (1) Direct connection with the wellbore

[0061] Using long-distance needle-threading magnetic guidance technology, when the bottom of the horizontal injection well approaches the production vertical well to a certain distance, a drill bit with an artificial magnetic source is lowered into the horizontal well to generate a rotating magnetic field while drilling, and a probe pipe (set near the connection point) is lowered into the production well to collect signals and transmit them to the ground. The relative position relationship of the two wells is calculated by an algorithm, and the horizontal well continues to drill while adjusting the trajectory, ultimately achieving connectivity at the target well depth (at the connection point).

[0062] (2) Connecting by fracturing

[0063] When the horizontal well is drilled to the connection point 1 to 3 meters away from the production well, the drilling is stopped and the connection is made by micro-fracturing with a displacement of no more than 5 cubic meters per minute. When this connection method is selected, the well needs to be drilled along the maximum horizontal principal stress.

[0064] 3. Injection well injection and concentric coiled tubing design

[0065] (1) The injection well is designed with concentric coiled tubing and production casing. The annulus between the inner and outer pipes of the concentric coiled tubing is kept clean for oxygen injection, and the annulus between the outer pipe of the concentric coiled tubing and the production casing is used for water injection. An automatic cut-off system is installed in the oxygen injection annulus to ensure that the oxygen supply is automatically stopped immediately when there is any abnormality in the well. Oxygen is transported by liquid oxygen tanker and injected underground after being gasified on the ground. A nozzle is designed at the bottom of the concentric coiled tubing to mix the oxygen and water injected by the concentric coiled tubing.

[0066] (2) Multiple injection wells are monitored by a set of concentric coiled tubing operation vehicles. When the ignition point needs to be retreated, the coiled tubing operation vehicle lowers the coiled tubing and uses a combustible (triethylborane, etc.) to melt through the casing to retreat the injection point.

[0067] 4. Both the injection well and the production well are equipped with thermocouple monitoring

[0068] Among them, a thermocouple is arranged every 20 to 50 meters in the oxygen injection annulus of the horizontal section of the injection well; and a thermocouple is arranged every 20 to 50 meters in the gas production pipe of the production well.

[0069] The production well uses a component monitoring device to monitor the produced gas in real time. The thermocouple used can withstand high temperatures above 1500 degrees Celsius.

[0070] 5. Use high temperature resistant cement to ensure wellbore integrity

[0071] Under high temperature conditions, silicate cement hydration products are prone to differences, poor structural stability, and severe strength decline. The wellbore of the production well uses high-temperature reinforced special materials with good rheological properties, strong crystal structure induction ability, and stable performance at 600℃. The high-temperature silicate cement slurry system meets the requirements of 600℃ resistance. The compressive strength of cement stone in a high-temperature environment of 600℃ for 14 days is 36.1MPa, 39MPa for 28 days, and 15.8MPa for 800℃ for 14 days.

[0072] 6. Anti-corrosion design of injection and production wells

[0073] Corrosion considerations need to be taken into account for injection wells and production wells. For injection wells, the main consideration is high-pressure dissolved oxygen corrosion, while for production wells, the main consideration is high-temperature and high-pressure hydrogen corrosion, carbon dioxide, water vapor, and hydrogen sulfide corrosion.

[0074] (1) The injection well pressure is always higher than the cavity operating pressure to prevent corrosion perforation caused by the backflow of high-pressure dissolved oxygen and to prevent the backflow explosion of the mixture of combustible gas and oxygen.

[0075] (2) The parameters for the production well corrosion condition are as follows: 500 degrees at the bottom of the production well and 300 degrees at the wellhead. A back pressure valve made of high-temperature and corrosion-resistant nickel-based alloy is used at the bottom of the production well to control the bottom pressure of the production well. The bottom pressure of the production well should be controlled below 22MPa to prevent the occurrence of supercritical water in the production well from corroding the pipe column due to high temperature and high pressure. At the same time, the temperature and pressure of the production well should be kept in the steam phase of water as much as possible to prevent corrosion caused by carbon dioxide and other substances dissolved in water.

[0076] In the absence of special corrosion research, casing, casing head, blowout preventer, and concentric coiled tubing meet the following corrosion requirements:

[0077] Casing: API 5CT

[0078] Wellhead: API 6A.PSL 1PR1

[0079] Blowout Preventer: API RP 53

[0080] Concentric coiled pipe: API 5CLP

[0081] 7. Lifting of the wellhead of the production well

[0082] The production casing at the wellhead of the production well uses a bellows, which can offset the wellhead uplift caused by thermal stress during the operation of the production well to a certain extent.

[0083] Embodiment 2

[0084] Embodiment 2 of the present invention provides a coal seam in-situ gasification mining method, comprising:

[0085] Through the above-mentioned coal seam in-situ gasification mining well network, the coal seam is mined by in-situ gasification by adopting a mode in which multiple injection wells inject simultaneously and multiple combustion chambers work simultaneously.

[0086] The mode of simultaneous injection of multiple wells and simultaneous operation of multiple combustion chambers is adopted to reduce the unit gas production cost and greatly increase the total gas production.

[0087] In the process of in-situ gasification production, the injection well cavity successive combustion has the following characteristics:

[0088] (1) The ignition point of the first combustion chamber of the injection well is 10 to 15 times the thickness of the coal seam away from the connection point between the injection well and the production well.

[0089] During the combustion process, the temperature field around the combustion chamber is as follows: Figure 2As shown in the figure, the interior is the outline of the gasification cavity, and the external shadow is the range that the temperature field of the gasification cavity can affect. The temperature outside the cavity is basically at normal formation temperature 50 meters away, and the temperature is relatively limited due to heat transfer from the formation rock.

[0090] When the raw coal gas flows from the combustion chamber to the production well, the gas temperature will drop due to three reasons: endothermic gasification reaction, pyrolysis coal absorption and formation heat transfer cooling. In order to cool the raw coal gas as much as possible after entering the production well, when the first cavity is burned, the first cavity ignition point of all injection wells is designed to be 10 to 15 times the coal seam thickness from the connection point of the production well. The minimum ignition distance is designed to ensure that the formation's own seepage and physical and chemical reactions are used for pyrolysis cooling; the maximum distance is designed to prevent coal from pyrolysis below 450 degrees. Pyrolysis of coal below 450 degrees will produce a large amount of tar, which may block the airflow channel.

[0091] (2) The combustion chambers of multiple injection wells adopt an alternating backward combustion mode.

[0092] When a single cavity of the injection well is extinguished and a back-off operation is performed to re-ignite a new cavity, the remaining cavities are in working condition to ensure a stable supply of produced gas from the production well.

[0093] (3) Taking into account the deviation of the outer contour of the combustion chamber, the distance between the ignition points of the two chambers is designed to be more than 10 times the thickness of the coal seam to ensure that the gas pressures between the chambers are independent of each other during operation.

[0094] (4) During the process of extinguishing a combustion chamber or igniting a non-first combustion chamber, nitrogen is injected through the corresponding injection well to keep the internal pressure of the combustion chamber no lower than the internal pressure of other combustion chambers that are burning, thereby preventing the gas from other operating chambers from flowing back into the extinguished chamber.

[0095] (5) The minimum distance between the boundaries of two adjacent combustion chambers in the direction parallel to the coal seam floor is greater than 5 times the thickness of the coal seam.

[0096] Considering the stability of the internal cavity after combustion, during the underground gasification process of deep coal seams, the designed width of the pillar (the minimum distance between the boundaries of two adjacent combustion cavities in the direction parallel to the coal seam floor) is not less than 5 times the thickness of the coal seam. Generally speaking, after the underground gasification cavity of deep coal seams is burned and abandoned, the hydrostatic pressure inside the cavity and the ash left by the combustion can largely support the mechanical stability of the combustion cavity, and due to the deep burial depth, the collapse of the flat cavity generally does not cause any impact on the ground.

[0097] (6) The combustion chamber retreat operation of multiple injection wells can be realized through the inspection of a concentric coiled tubing operation vehicle. The inspection operation of a single concentric coiled tubing operation vehicle can further reduce the unit gas production cost.

[0098] (7) This design cannot determine which injection well injection point needs to be retreated by the quality fluctuation of the produced gas, so the timing of retreat is determined by the quality of the injected oxygen and water. The specific timing is determined based on the coal seam properties such as coal rank, ash content, and coal seam thickness.

[0099] Embodiment 3

[0100] Embodiment 3 of the present invention provides a method for designing the distribution of injection and production wells and cavity groups for in-situ gasification of deep coal seams.

[0101] See also Figure 1 As shown, in this embodiment, the injection well and the production well adopt the mode of multiple horizontal injection wells and a single production vertical well. The bottom of the injection well is connected with the bottom of the production well. The distance between the horizontal sections of adjacent injection wells is 100 meters (10 times the thickness of the coal seam), the length of the horizontal section is 500 meters, and the distance between the horizontal section of the horizontal well and the bottom plate of the coal seam is 15% of the average thickness of the coal seam, and the thickness of the coal seam is 5 meters. A vertical well service well is set about 10 meters near the production well for temperature and pressure monitoring and water injection and flameout under emergency conditions. The injection well adopts tubing and casing design. The tubing is kept clean for oxygen injection, and the tubing and casing annulus are used for water injection. The oxygen injection pipe is equipped with an automatic cut-off system to ensure that the oxygen supply is automatically stopped immediately when there is any abnormality underground; oxygen is transported by liquid oxygen tank trucks and injected into the ground after gasification on the ground; liquid water is injected into the annulus of the inner and outer pipes of the concentric continuous pipe; the bottom of the concentric continuous pipe adopts a nozzle design to mix the oxygen and water injected by the concentric continuous pipe. Multiple injection wells use a set of concentric coiled tubing operation vehicles to monitor. When the ignition point needs to be retreated, the coiled tubing operation vehicle will lower the coiled tubing and use combustibles (such as triethylborane) to melt through the oil pipe and casing to retreat the injection point. Thermocouple monitoring is set up for both the injection well and the production well, and a thermocouple is arranged every 20 meters in the horizontal section. High-temperature resistant cement is used to ensure the integrity of the wellbore. At the same time, the injection well pressure is always guaranteed to be higher than the cavity operating pressure. The back pressure valve made of high-temperature and corrosion-resistant nickel-based alloy is used at the bottom of the production well to control the bottom pressure of the production well. Bellows are used for the casing of the wellhead. The combustion chamber is semi-drop-shaped, and the combustion chamber is designed to be arranged at intervals.

[0102] The embodiment of the present invention also introduces a method for designing the distribution of deep coal underground gasification injection and production wells and cavity groups. The above process includes:

[0103] Step S1: Multiple horizontal injection wells are connected to a single vertical production well. The bottom of the injection well is connected to the bottom of the production well. The distance between the horizontal injection wells is 100 meters, and the length of the horizontal section is 500 meters. A vertical well service well is set 10 meters near the production well.

[0104] Step S2: During ignition, the first cavity ignition point of all injection wells should be 50 meters away from the bottom of the production well.

[0105] Step S3: After the first cavity of the injection well is extinguished, a retreat operation is required. When a new cavity is re-ignited, multiple injection wells are extinguished / ignited alternately, and the retreat distance of each injection point is 50 meters.

[0106] Step S4: After the combustion is finished, the injection well stops injecting oxygen, and water is injected into the combustion chamber through the service well to lower its temperature until the reaction stops.

[0107] It should be understood that the specific order or hierarchy of steps in the disclosed process is an example of an exemplary method. Based on design preferences, it should be understood that the specific order or hierarchy of steps in the process can be rearranged without departing from the scope of protection of the present disclosure. The attached method claims present the elements of the various steps in an exemplary order and are not intended to be limited to the specific order or hierarchy described.

[0108] In the above detailed description, various features are grouped together in a single embodiment to simplify the disclosure. This method of disclosure should not be interpreted as reflecting an intention that the embodiments of the claimed subject matter require more features than are clearly stated in each claim. On the contrary, as reflected in the appended claims, the invention is in a state of having less than all the features of the disclosed individual embodiments. Therefore, the appended claims are hereby expressly incorporated into the detailed description, with each claim standing on its own as a separate preferred embodiment of the invention.

[0109] The above description includes examples of one or more embodiments. Of course, it is impossible to describe all possible combinations of components or methods for the purpose of describing the above embodiments, but it should be recognized by those skilled in the art that the various embodiments may be further combined and arranged. Therefore, the embodiments described herein are intended to cover all such changes, modifications and variations that fall within the scope of protection of the appended claims. In addition, with respect to the term "comprising" used in the specification or claims, the word is covered in a manner similar to the term "including", just as "including," is explained as a transitional word in the claims. In addition, any term "or" used in the specification of the claims is intended to mean "non-exclusive or".

Claims

1. A coal seam in-situ gasification mining well pattern, characterized in that: It includes multiple injection wells and one production well; The multiple injection wells are designed by a well factory, and the injection wells are all horizontal wells with the wellheads on the same platform; The distance between the horizontal section of each injection well and the bottom plate of the coal seam is 10% to 15% of the thickness of the coal seam and does not exceed 1 meter. The distance between the horizontal sections of two adjacent injection wells is 8 to 10 times the thickness of the coal seam.

2. The well pattern according to claim 1, characterized in that: The connection point between each injection well and the production well is the same connection point.

3. The well pattern according to claim 1, characterized in that: The injection well and the production well are connected by direct wellbore connection or by hydraulic fracturing.

4. The well pattern according to claim 1, characterized in that: The horizontal section of the injection well is 500 to 700 meters long.

5. The well pattern according to claim 1, characterized in that: The outer diameter of the production casing of the production well is not less than 224.5 mm.

6. The well pattern according to claim 1, characterized in that: The production well is drilled through the coal seam, and the production well is completed using an open hole screen pipe in the well section from the top of the coal seam to the bottom of the coal seam.

7. The well pattern according to claim 1, characterized in that: A thermocouple is arranged every 20 to 50 meters in the oxygen injection annulus of the horizontal section of the injection well; A thermocouple is arranged every 20 to 50 meters in the gas production pipe of the production well.

8. The well pattern according to any one of claims 1 to 7, characterized in that: The number of injection wells is 5 to 10.

9. The well pattern according to any one of claims 1 to 7, characterized in that: The production casing at the wellhead of the production well uses a corrugated pipe.

10. The well pattern according to any one of claims 1 to 7, characterized in that: It also includes a service well for temperature and pressure monitoring and water injection to shut down the flame under set conditions.

11. A coal seam in-situ gasification mining method, characterized in that: include: Through the coal seam in-situ gasification mining well network described in any one of claims 1 to 10, a mode of simultaneous injection of multiple injection wells and simultaneous operation of multiple combustion chambers is adopted to carry out in-situ gasification mining of the coal seam.

12. The method according to claim 11, characterized in that The ignition point of the first combustion chamber of the injection well is 10 to 15 times the thickness of the coal seam away from the connection point between the injection well and the production well.

13. The method according to claim 11, characterized in that The minimum distance between the boundaries of two adjacent combustion chambers along the direction parallel to the coal seam bottom plate is greater than 5 times the thickness of the coal seam.

14. The method according to claim 11, characterized in that The combustion chambers of multiple injection wells adopt an alternating backward combustion mode.

15. The method according to claim 14, characterized in that During the process of extinguishing a combustion chamber or igniting a combustion chamber other than the first one, nitrogen is injected through the corresponding injection well to keep the internal pressure of the combustion chamber no lower than the internal pressure of other combustion chambers that are burning.

16. The method according to claim 14, characterized in that The combustion chamber retreat operation of multiple injection wells is realized by a concentric coiled tubing operation vehicle.

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