In-situ development method of gravity drainage using inverted seven-point horizontal well pattern for medium-low maturity oil shale

Abstract

The present invention discloses an in-situ development method for low-maturity oil shale using an inverted seven-point horizontal well network with gravity drainage, which belongs to the field of in-situ shale development. The method arranges an inverted seven-point horizontal well network containing injection wells and production wells in a target area for exploitation of low-maturity oil shale, and utilizes the horizontal well sections of the production wells to generate a preheating zone for an in-situ conversion reaction to collect mobile oil generated by cracking and draining due to gravity. The inverted seven-point horizontal well network includes at least one well network unit, each well network unit includes an injection well located at the center of a regular hexagon, and horizontal well sections of the production wells located at the six sides of the regular hexagon. Heat is provided by the injection wells to perform gravity drainage in the horizontal well sections of the production wells, thereby improving the mobile oil production efficiency. The in-well temperature and pressure monitoring device can provide real-time feedback on the production process, and at the same time can provide a basis for adjusting the injection flow rate and the temperature of the injected fluid of the injection well, so that the heated fluid injected into the formation is fully utilized.

Description

Technical Field

[0001] The present invention belongs to the field of shale in-situ development, and in particular relates to an in-situ development method for low-maturity oil shale using an inverted seven-point horizontal well pattern gravity drainage. Background Art

[0002] Low- to medium-maturity oil shale, comprising the bulk of China's continental shale oil, is one of the most realistic scalable replacement resources for conventional oil and gas, with enormous development potential. Commercializing low- to medium-maturity oil shale can fundamentally address my country's energy security challenges, ensuring stable and even increased crude oil production.

[0003] Underground in-situ conversion technology involves artificially heating shale reservoirs to 350°C to 500°C, cracking the solid organic matter and retained hydrocarbons within the shale into small-molecule oil and gas. This is then extracted to the surface through oil recovery processes. This technology offers significant advantages in clean production, scale, and output quality, and is a key trend in the development of the shale oil industry. Over the past 20 years, driven by national energy needs, domestic universities, research institutes, and energy companies have all conducted research and development in in-situ conversion technologies for oil shale, developing a variety of new technologies tailored to the specific characteristics of my country's oil shale resources.

[0004] Jilin University has proposed a method for the in-situ conversion of low- to medium-maturity, organic-rich shale using autogenous heat for oil shale development and utilization. (See patent document CN114017032B.) This method primarily involves locally preheating a well-reformed shale formation near an injection well and injecting ambient air into the preheated formation. This stimulates and establishes a chemical reaction zone consisting of a residue zone, an autogenous heat zone, a thermal cracking zone, and a preheating zone. The residue produced by kerogen thermal cracking undergoes an oxidation reaction, releasing heat to achieve convection heating of the shale formation. The oil and gas products produced by kerogen thermal cracking enter the production well through fractures. The current main research direction of this technology focuses on the triggering and progression of the reaction. Related in-situ development process directions also focus on improving overall heating and heat transfer efficiency. Both methods propose a lattice layout of injection and production wells, but do not specify the method for setting up production wells. At the same time, there is no clear solution to the problem of easy clogging of cracking products generated during the in-situ conversion development process. The technology for improving the recovery efficiency of production wells also needs to be further deepened. There is relatively little research on the production well location and well network layout technology. There is a lack of systematic single-well temperature and pressure monitoring system to timely visualize the production process. The problem of injected gas breakthrough also needs to be further solved.

[0005] In order to solve the problem of heavy hydrocarbon products produced by cracking being prone to clogging, a steam-assisted gravity drainage method for a single horizontal well under fracturing has been proposed in the prior art. See Chinese patent document CN102518415A. During the production phase, steam is continuously injected into a vertical well to produce the steam-heated crude oil from the horizontal well by its own gravity. This method uses steam to assist the drainage of heavy hydrocarbons, which can increase the utilization of the horizontal well section and improve the recovery rate and development effect of the oil reservoir. However, large amounts of steam injection may cause the temperature around the production well to be too high during the in-situ conversion and development process. The in-situ development process of low- and medium-maturity oil shale has already injected high-temperature gas into the formation. At the same time, the production well will also be affected by the high-temperature gas from the injection well during the recovery process. Therefore, heavy hydrocarbons can be produced from the horizontal well by using the heat conducted by the formation and its own gravity during the in-situ conversion and development process.

[0006] During the in-situ conversion and development of low- to medium-maturity oil shale, injected gas can break through the formation and flow directly into the horizontal well, creating a pathway between the injection well and the production well, leading to the escape of the injected high-temperature gas. A systematic single-well temperature and pressure monitoring system can effectively monitor the production process, accurately measure the temperature and pressure processes in various parts of the horizontal well, and effectively determine the location of the local breakthrough in the production well. Temperature detection can also effectively determine the extent of oil leakage.

[0007] In summary, exploring a feasible in-situ production well recovery process for oil shale and its well pattern layout method to improve the oil and gas recovery efficiency generated by in-situ conversion is an important means to achieve the exploitation of medium- and low-maturity oil shale. Summary of the Invention

[0008] To address the aforementioned issues with the in-situ conversion of low- to medium-maturity oil shale using autogenous heat, the present invention proposes a method for in-situ development of low- to medium-maturity oil shale using gravity drainage via an inverted seven-point horizontal well pattern. This method primarily plans and arranges production wells by placing an inverted seven-point horizontal well pattern at the end of a preheating zone, utilizing heat generated by the formation itself to transfer to the production wells, achieving gravity drainage. Because in-situ conversion of oil shale only requires local preheating near the injection well, with heat then transferred to the production wells via the formation, the method is relatively cost-effective.

[0009] The technical solution adopted by the present invention to achieve the above-mentioned object is: an in-situ development method of low-maturity oil shale using a reverse seven-point horizontal well pattern gravity drainage, which includes the following steps:

[0010] Step 1: Determine the target area for in-situ conversion and development of medium-low maturity oil shale autothermal energy, and arrange an inverted seven-point horizontal well pattern containing injection wells and production wells in the target area. The production wells include a continuously arranged vertical production well section and a horizontal production well section. The horizontal production well section is located in the medium-low maturity oil shale formation. The inverted seven-point horizontal well pattern includes at least one well pattern unit, each well pattern unit includes an injection well located at the center of a regular hexagon and production wells located on the six sides of the regular hexagon.

[0011] Step 2: Conduct multiple time-sharing fracturing operations in sequence in the injection well, complete the downhole heater operation, inject gas and start the heater simultaneously to begin heating the low-maturity oil shale formation, thereby forming a chemical reaction zone consisting of a residue zone, an autogenous heat zone, a thermal cracking zone and a preheating zone in the low-maturity oil shale formation between the injection well and the production well;

[0012] The aforementioned injection well fracturing process, heater installation and startup procedures, and chemical reaction zone delineation are based on the autogenous heat in-situ conversion and development method for low-maturity, organic-rich shale described in Chinese Patent CN114017032B. The residue zone, autogenous heat zone, thermal cracking zone, and preheating zone are defined based on the temperature profile and oxygen concentration differences within the reaction zone as it progresses.

[0013] Step 3: Arrange a horizontal section of a production well parallel to the dip direction of the medium-low maturity oil shale formation at the edge of the preheating zone described in Step 2, and simultaneously arrange production pipelines and temperature and pressure monitoring devices in the production well. After the production well is arranged, temperature and pressure data monitoring is carried out on the ground in the horizontal section of the production well;

[0014] Step 4: When the preheating zone where the production well is located reaches the temperature and pressure required for gravity drainage, the mobile oil generated by cracking enters the horizontal well section of the production well through the fractures and flows into the production pipeline, allowing the next step of oil production.

[0015] Step 5: In order to cope with the breakthrough of gas injected into the formation by the injection well, which causes a sudden change in temperature and pressure in the well, a packer is installed in the vertical section of the production well to ensure that the pressure in the well maintains the oil drainage process.

[0016] Furthermore, in step 1, the formation conditions of the target area are formation vitrinite reflectance less than 1, formation oil content greater than 5%, formation thickness greater than 15m, formation water content less than 5% and formation burial depth less than 2000m.

[0017] Furthermore, the ratio of injection wells to production wells in the inverted seven-point horizontal well network with a single injection well is 1:6; the ratio of injection wells to production wells in the inverted seven-point horizontal well network containing multiple injection wells is 1:3, which improves oil production efficiency while reducing well network layout costs.

[0018] Furthermore, in order to ensure oil recovery efficiency and ensure that the autogenous heat in-situ conversion reaction can effectively affect the formations near the horizontal section of the production well, while avoiding the interconnection of the horizontal sections of the production well, the relative relationship between the injection well and the production well in a single well network unit in the inverted seven-point horizontal well pattern is arranged as follows: the injection well is located in the center of the chemical reaction zone, the regular hexagon is tangent to the original rock area at the edge of the chemical reaction zone, the drilling direction of the horizontal section of the production well is arranged clockwise along the regular hexagon, and the center point of the horizontal section of the production well coincides with the midpoint of the regular hexagon. The length of the horizontal section of the production well is less than or equal to 30m; the closest point distance between the injection well and the production well is less than 50m, the distance between adjacent injection wells is 80m to 100m, and the closest point distance between the horizontal sections of the two production wells is greater than 10m.

[0019] Furthermore, in order to fully utilize the production wells in each group of inverted seven-point horizontal well patterns, in the inverted seven-point horizontal well pattern formed by combining multiple well pattern units, when multiple hexagonal well patterns are combined, only one production well is arranged in the overlapping part.

[0020] Furthermore, the temperature and pressure monitoring device uses a fiber Bragg grating temperature and pressure sensor to ensure that the entire horizontal section of the production well can be monitored at low cost and high efficiency.

[0021] Furthermore, in step 4, the temperature range of the horizontal section of the production well is 200°C to 300°C, and the bottom hole pressure of the horizontal section of the production well is controlled to 5MPa, so as to maximize the oil drainage efficiency. The temperature and pressure control is achieved by adjusting the injection gas flow rate of the injection well.

[0022] According to a specific embodiment of the present invention, the heat injection area is located at the bottom of the injection well, and the top of the horizontal well section of the production well is 3m to 5m lower than the bottom of the heat injection area.

[0023] According to a specific embodiment of the present invention, the production pipeline includes a screen pipe and an oil production pipe. The screen pipe is sleeved on the outside of the oil production pipe, and the two are arranged concentrically and coaxially. The screen pipe is a wire-wound screen pipe in which a filter layer is formed by winding metal wire on the sleeve. The flowing oil enters the screen pipe through the filter layer. The oil production pipe is provided with oil production holes at intervals, and the flowing oil enters the oil production pipe through the oil production holes.

[0024] The production holes on the production pipe are located in the horizontal section of the production well, and adjacent holes are arranged with an interval of 0.5m.

[0025] According to a specific embodiment of the present invention, the packer is located in the vertical well section of the production well and is installed 5m to 10m above the medium-low maturity oil shale formation.

[0026] Through the above design scheme, the present invention can bring the following beneficial effects:

[0027] First, a method for in-situ development of low- to medium-maturity oil shale using gravity drainage in an inverted seven-point horizontal well pattern is proposed. Within the target area for low- to medium-maturity oil shale development, one injection well and six production wells are drilled to form an inverted seven-point horizontal well pattern. Heat provided by the injection wells is used to gravity drain the horizontal sections of the production wells, producing oil and gas and improving oil and gas production efficiency.

[0028] Second, the in-well temperature and pressure monitoring device can provide real-time feedback on the production process, adjust the reasonable drainage speed, make full use of the heating fluid injected into the formation, and provide a basis for adjusting the injection gas flow rate of the injection well. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The accompanying drawings herein are used to provide a further understanding of the present invention and constitute a part of the present application. The exemplary embodiments of the present invention and their descriptions are used to understand the present invention and do not constitute improper limitations of the present invention. In the accompanying drawings:

[0030] Figure 1 Schematic diagram of the relative positions of the in-situ conversion reaction zone and the wellhead.

[0031] Figure 2 This is a schematic cross-sectional diagram of the vertical section and horizontal section of the production well.

[0032] Figure 3 Schematic diagram of the gravity drainage process in the horizontal section of a production well.

[0033] Figure 4 Schematic diagram of the reverse seven-point horizontal well pattern layout with a single well pattern unit.

[0034] Figure 5 Schematic diagram of the inverted seven-point horizontal well pattern layout formed by combining multiple well pattern units.

[0035] Figure 6 This is a graph of the cumulative flowing oil production of a single production well in an inverted seven-point horizontal well pattern with a single well pattern unit.

[0036] Figure numbers: 1 is a production well; 2 is an injection well; 3 is a residue zone; 4 is an autogenous heat zone; 5 is a thermal cracking zone; 6 is a preheating zone; 7 is a protolith zone; 8 is a medium-low maturity oil shale formation; 9 is a production pipe; 10 is a screen pipe; 11 is a temperature and pressure monitoring device; 12 is a packer; 13 is a horizontal well section of a production well; 14 is a vertical well section of a production well; 15 is a heat injection area; 16 is a gravity drainage curve. DETAILED DESCRIPTION

[0037] In order to make the objects, features, and advantages of the present invention more apparent and understandable, the technical solutions of the present invention are clearly and completely described below in conjunction with the embodiments of the present invention and the accompanying drawings. Obviously, the present invention is not limited to the following embodiments, and specific implementation methods can be determined based on the technical solutions of the present invention and actual conditions. In order to avoid obscuring the essence of the present invention, well-known methods, processes, and procedures are not described in detail.

[0038] The method for in-situ development of low-maturity oil shale using a reverse seven-point horizontal well pattern with gravity drainage is designed. The horizontal well section 13 of the production well and its well pattern arrangement mainly act on the edge of the preheating zone 6 formed by the in-situ conversion reaction of the low-maturity oil shale. The residue generated by the thermal cracking of the kerogen in the low-maturity oil shale undergoes an oxidation reaction to release heat, thereby heating the low-maturity oil shale formation 8. The mobile oil generated by the thermal cracking of the kerogen enters the horizontal well section 13 of the production well through the cracks. The heat generated by convection assists the heavy hydrocarbon components to enter the horizontal well section 13 of the production well by gravity drainage. Figure 1 The figure shows the relative positions of the in-situ conversion reaction zone and the wellhead.

[0039] like Figure 1 、 Figure 2 、 Figure 3 、 Figure 4 and Figure 5 As shown in the figure, the in-situ development method of low-mature oil shale using gravity drainage with an inverted seven-point horizontal well pattern is provided. The process implementation system based on the method includes a horizontal well drainage system and an inverted seven-point horizontal well pattern system.

[0040] First, target areas for autogenous heat in-situ conversion of low- to medium-maturity oil shale are identified based on formation conditions, including formation vitrinite reflectance less than 1, formation oil content greater than 5%, formation thickness greater than 15m, formation water content less than 5%, and formation depth less than 2000m.

[0041] The reverse seven-point horizontal well pattern system is deployed in the target area for medium-low maturity oil shale development, such as Figure 1 As shown, the injection well 2 is located in the center of the area, and the layout of the six production wells 1 adopts the conventional regular hexagonal layout method in the field of oil development. The direction from A to A′ in the figure corresponds to the direction of progress of the chemical reaction zone, that is, the direction of the arrow represents the direction of the reaction. Multiple time-sharing fracturing operations are carried out in sequence in the injection well 2, and the downhole heater is lowered into the well. The heater is started to heat the medium-low maturity oil shale formation 8, thereby forming a chemical reaction zone composed of a residue zone 3, an autogenous heat zone 4, a thermal cracking zone 5 and a preheating zone 6 in sequence in the medium-low maturity oil shale formation 8 between the injection well 2 and the production well 1, as well as a parent rock zone 7 at the edge of the chemical reaction zone. The production wells 1 are located in the preheating zone 6 and are arranged in a regular hexagon around the injection well 2. Figure 1AA′ is the side length of the regular hexagonal well pattern, which is less than or equal to 50 m, which is less than the farthest reaction distance of in-situ conversion development.

[0042] The production horizontal well oil drainage system includes a horizontal well system, an in-well monitoring system and an in-well isolation system. The specific arrangement is as follows: Figure 2 As shown, the horizontal section 13 of the production well is arranged parallel to the dip direction of the medium-low maturity oil shale formation 8 and is located at the lower part of the medium-low maturity oil shale formation 8. The entire horizontal section 13 of the production well is located within the preheating zone 6 during the in-situ conversion process and has a length of less than or equal to 30m. The production pipe 9 and the screen 10 are coaxially arranged in the horizontal section 13 of the production well to form a production pipeline. The screen 10 is a wire-wound screen, which uses metal wire wrapped around the casing to form a filter layer. It has a large flow area and strong corrosion resistance. After the flowing oil enters the screen 10 through the filter layer, it enters the production pipe 9 through the production hole, preventing the rock debris components from entering the production pipe 9 and blocking the oil and gas production channel. The in-well monitoring system is a temperature and pressure monitoring device 11, which is installed in the middle section of the horizontal section 13 of the production well. The temperature and pressure monitoring device 11 uses a fiber Bragg grating temperature and pressure sensor, which is a commercially available product and will not be described in detail. The in-well isolation system is located in the vertical well section 14 of the production well, and a packer 12 is installed 5m to 10m above the medium- and low-maturity oil shale formation 8. The packer 12 here adopts the combined packer for high-temperature and high-pressure working conditions of the existing technology, that is, the combined packer for high-temperature and high-pressure working conditions published in CN107605422B, to adapt to the high-temperature and high-pressure environment in the production well.

[0043] When the temperature and pressure monitoring device 11 detects a sharp change in the internal pressure, the packer 12 is closed to ensure that the pressure in the well is maintained during the oil drainage process.

[0044] Figure 3 The figure shows the gravity drainage process of the horizontal well section 13 of the production well during the in-situ conversion reaction. Figure 4 A cross-sectional view of the formation and well locations at point BB', viewed from southwest to northeast. Injection well 2 is located in the center of the area, with heat injection zone 15 at its base. The left production well is the northwest production well, and the right production well is the southeast production well. Heat injection zone 15 heats the low- to medium-maturity oil shale formation 8, forming an in-situ conversion chemical reaction zone. Gravity drainage curve 16 illustrates the migration direction of cracked materials during the reaction. The top of the horizontal section 13 of the production well is 3 to 5 meters below the bottom of the heat injection zone 15. The mobile oil produced by cracking reaches the horizontal section 13 of the production well. After entering the horizontal section 13 due to gravity drainage, it is produced through production pipe 9.

[0045] Figure 4The diagram shows the relative relationship between injection well 2 and production well 1 in a single well pattern unit in the inverted seven-point horizontal well pattern. Injection well 2 is located in the center of the chemical reaction zone, and the regular hexagon is tangent to the in-situ rock area 7 at the edge of the chemical reaction zone. The horizontal section 13 of the production well is drilled clockwise along the regular hexagon, with the center point of the production well section 13 coinciding with the midpoint of the regular hexagon. The length of the production well section 13 is less than or equal to 30 meters. Figure 5 In the inverted seven-point horizontal well pattern formed by combining multiple well pattern units, the relative position relationship between production well 1 and injection well 2 remains unchanged. When multiple hexagons are combined, only one production well is retained in the overlapping part of the production wells, and the drilling direction of the horizontal well section 13 of the production well is ensured to be arranged clockwise along the regular hexagon as much as possible.

[0046] This example selects the shale in the Songliao Basin of China as the research object. The test area is a representative reservoir of China's shallow and medium-deep oil shale resources, with an oil content of 3% to 6%, which is a low-grade, low-permeability reservoir.

[0047] The first step is to conduct underground and surface engineering construction and commissioning for in-situ conversion. After the preliminary work is completed, in-situ conversion begins. First, the medium-mature oil shale formation 8 is preheated at injection well 2. After preheating, high-temperature nitrogen, heated to 350°C to 500°C on the surface, is injected into the medium-mature oil shale formation 8 to trigger a small-scale pre-cracking reaction. Once the pre-cracking reaction stabilizes, ambient temperature air is injected to trigger the in-situ conversion reaction in the medium-mature oil shale, creating the initial conditions for oil and gas to flow through fractures and into the horizontal well section 13 of the production well by gravity.

[0048] In the second step, based on the location of injection well 2, the first inverse seven-spot horizontal well pattern was deployed. Horizontal section 13 of the production wells was drilled in a clockwise direction. This section was 30 meters long, and the closest distance between injection well 2 and production well 1 was 42 meters. The second and subsequent inverse seven-spot horizontal well patterns were combined with the existing inverse seven-spot horizontal well pattern, with the existing production wells used to complete the overlapping portions of the inverse seven-spot horizontal well pattern.

[0049] The third step involves drilling the production well and installing the equipment within it. This includes the installation of the production tubing 9 and screen 10, as well as the installation and commissioning of the temperature and pressure monitoring device 11 in the horizontal section 13 of the production well and the packer 12 in the vertical section 14 of the production well. Simultaneously, monitoring is carried out on the surface. Once the well temperature reaches above 200°C and the bottomhole pressure in the horizontal section 13 of the production well reaches approximately 5 MPa, the packer 12 is activated. The reaction process is regulated by adjusting the injected gas flow rate at injection well 2, thereby maintaining a constant temperature between 200°C and 300°C in the horizontal section 13 of the production well and a constant bottomhole pressure around 5 MPa, for optimal efficiency.

[0050] In the fourth step, eight days after the in-situ conversion reaction begins, gravity drainage occurs due to the in-situ self-heating reaction near the horizontal section 13 of the production well. The pressure within the horizontal section 13 of the production well is monitored. When the temperature and pressure exceed the range set in the previous step, the injection gas flow rate is adjusted based on the feedback data. Once the temperature and pressure remain within a stable range, the flowing oil enters the screen 10 through the filter layer and then enters the production pipe 9 through the production hole, at which point oil production begins.

[0051] Step 5. Figure 6 The cumulative flowing oil production diagram of a single production well in an inverted seven-point horizontal well network with a single well network unit is shown. The oil production operation is maintained for no less than 30 days, and the flowing oil approaches the maximum value on the 25th day. The average oil recovery rate of the flowing oil of a single production well in the inverted seven-point horizontal well network with a single well network unit reaches 63%.

[0052] Finally, it should be noted that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or substitute equivalents for some of the technical features. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. An in-situ development method for low-mature oil shale using a reverse seven-point horizontal well pattern with gravity drainage, characterized in that: The method comprises the following steps: Step 1: Determine the target area for in-situ conversion and development of medium-low maturity oil shale autothermal energy, and arrange an inverted seven-point horizontal well pattern containing injection wells and production wells in the target area. The production wells include a continuously arranged vertical production well section and a horizontal production well section. The horizontal production well section is located in the medium-low maturity oil shale formation. The inverted seven-point horizontal well pattern includes at least one well pattern unit, each well pattern unit includes an injection well located at the center of a regular hexagon and production wells located at six sides of the regular hexagon; Step 2: Conduct multiple time-sharing fracturing operations in sequence in the injection well, complete the downhole heater operation, inject gas and start the heater simultaneously to begin heating the low-maturity oil shale formation, thereby forming a chemical reaction zone consisting of a residue zone, an autogenous heat zone, a thermal cracking zone and a preheating zone in the low-maturity oil shale formation between the injection well and the production well; Step 3: Arrange a horizontal section of a production well parallel to the dip direction of the medium-low maturity oil shale formation at the edge of the preheating zone described in Step 2, and simultaneously arrange production pipelines and temperature and pressure monitoring devices in the production well. After the production well is arranged, temperature and pressure data monitoring is carried out on the ground in the horizontal section of the production well; Step 4: When the preheating zone where the production well is located reaches the temperature and pressure required for gravity drainage, the mobile oil generated by cracking enters the horizontal well section of the production well through the fractures and flows into the production pipeline, allowing the next step of oil production. Step 5: To cope with the sudden change in temperature and pressure in the well caused by the breakthrough of gas injected into the formation by the injection well, a packer is installed in the vertical section of the production well to ensure that the well pressure maintains the oil drainage process; The relative relationship between the injection well and the production well in a single well pattern unit in the inverted seven-point horizontal well pattern is as follows: the injection well is located in the center of the chemical reaction zone, the regular hexagon is tangent to the original rock area at the edge of the chemical reaction zone, the drilling direction of the horizontal section of the production well is arranged clockwise along the regular hexagon, and the center point of the horizontal section of the production well coincides with the midpoint of the regular hexagon, and the length of the horizontal section of the production well is less than or equal to 30m; the closest point distance between the injection well and the production well is less than 50m, the distance between adjacent injection wells is 80m~100m, and the closest point distance between the horizontal sections of two production wells is greater than 10m.

2. The method for in-situ development of low-maturity oil shale using a reverse seven-point horizontal well pattern gravity drainage according to claim 1, characterized in that: In step 1, the formation conditions of the target area are: formation vitrinite reflectance less than 1, formation oil content greater than 5%, formation thickness greater than 15m, formation water content less than 5% and formation burial depth less than 2000m.

3. The in-situ development method for low-maturity oil shale using an inverted seven-point horizontal well pattern gravity drainage according to claim 1, characterized in that: The ratio of injection wells to production wells in the inverted seven-point horizontal well network with a single injection well is 1:6; the ratio of injection wells to production wells in the inverted seven-point horizontal well network containing multiple injection wells is 1:

3.

4. The in-situ development method for low-maturity oil shale using an inverted seven-point horizontal well pattern gravity drainage according to claim 1, characterized in that: In the inverted seven-point horizontal well pattern formed by combining multiple well pattern units, when multiple hexagonal well patterns are combined, only one production well is arranged in the overlapping part.

5. The method for in-situ development of low-maturity oil shale using a reverse seven-point horizontal well pattern gravity drainage according to claim 1, characterized in that: The temperature and pressure monitoring device adopts a fiber grating temperature and pressure sensor.

6. The method for in-situ development of low-maturity oil shale using a reverse seven-point horizontal well pattern gravity drainage according to claim 1, characterized in that: In step 4, the temperature range of the horizontal section of the production well is 200°C to 300°C, and the bottom hole pressure of the horizontal section of the production well is controlled to be 5 MPa.

7. The method for in-situ development of low-maturity oil shale using a reverse seven-point horizontal well pattern gravity drainage according to claim 1, characterized in that: The heat injection area is located at the bottom of the injection well, and the top of the horizontal section of the production well is 3m~5m lower than the bottom of the heat injection area.

8. The method for in-situ development of low-maturity oil shale using a reverse seven-point horizontal well pattern gravity drainage according to claim 1, characterized in that: The production pipeline includes an oil production pipe and a screen pipe. The screen pipe is sleeved on the outside of the oil production pipe, and the two are arranged concentrically and coaxially. The screen pipe is a wire-wound screen pipe in which a filter layer is formed by winding metal wire around the casing. Oil production holes are distributed at intervals on the oil production pipe, and the area where the oil production holes are located corresponds to the horizontal section of the production well. Adjacent oil production holes are arranged at intervals of 0.5m.

9. The method for in-situ development of low-maturity oil shale using a reverse seven-point horizontal well pattern gravity drainage according to claim 1, characterized in that: The packer is located in the vertical section of the production well and is installed 5m to 10m above the medium-low maturity oil shale formation.

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