In-situ conversion development method for organic-rich rock

Abstract

The application discloses a method for in-situ conversion development of organic matter-rich rock. The method comprises the following steps: S1, obtaining basic data of the organic matter-rich reservoir; S2, deploying a three-dimensional well pattern with high conductivity in a target layer of the organic matter-rich reservoir, performing multi-stage fracturing, and forming a three-dimensional fracturing fracture network, the distal ends of the fracturing fracture network being connected to each other through micro-cracks; the three-dimensional well pattern comprises a heating well and a production well, one end of the heating well being connected to a heat production system, and one end of the production well being connected to an oil and gas post-processing system; injecting a working fluid into the heating well to heat the stratum for in-situ conversion, and extracting oil and gas through the production well. The method for in-situ conversion development of the organic matter-rich reservoir has simple principles, high feasibility and high operability, and can be conveniently used in field engineering practice based on other technologies in the field of shale oil and gas development, and the in-situ conversion efficiency is improved.

Description

Technical Field

[0001] This invention relates to a method for in-situ conversion and development of organic-rich rocks, belonging to the field of petroleum engineering, particularly oil and gas field development research. Background Technology

[0002] Immature and low-maturity hydrocarbon resources, including oil-rich coal, low-maturity shale oil, and low-maturity biogenic gas, are widely distributed in the formation. Conventional direct extraction methods are insufficient for large-scale, economically viable exploitation. In-situ conversion methods are needed to transform low-maturity organic rocks into exploitable oil and gas resources, which can then be extracted using advanced oil and gas extraction technologies. In-situ conversion technologies for organic-rich rocks or reservoirs, represented by low-maturity shale oil / oil-rich coal / low-maturity biogenic gas, hold immense potential and promising prospects, offering significant development potential for increasing oil and gas production in my country.

[0003] The main idea behind in-situ conversion of organic-rich rocks is to heat the low-maturity shale oil underground using various methods to generate large amounts of oil and gas, which are then developed through a well network. Currently, commonly used in-situ conversion technologies are classified into four types: reaction heat heating, convection heating, radiation heating, and conduction heating. These include localized chemical reaction (TSA) method, steam injection extraction (MTI) technology, near-critical water method (NCW) method, high-pressure-frequency electric heating method (HVF method), and fracturing combustion method for underground in-situ pyrolysis.

[0004] However, organic-rich rocks are poor conductors of heat. In existing technologies, the small contact area between the heat source and the formation makes large-scale heating difficult, resulting in low thermal conductivity, high energy consumption, and slow heat transfer, hindering the conditions for large-scale economic development. To efficiently and fully utilize immature and low-maturity hydrocarbon resources, it is necessary to establish a hot working fluid circulation mode within the fracture network, along with high thermal conductivity proppant materials, based on multi-stage fracturing in horizontal wells with a three-dimensional well network, fracture network control, and fracture network interference. This transforms traditional volumetric fracturing into an in-situ conversion system based on a volumetric fracturing network and heat flow circulation heating. The efficient heat conduction through the horizontal well's three-dimensional fracture network increases the contact area between the heat source and the rock, thereby increasing the volume of rock capable of pyrolysis, improving heat transfer efficiency, and increasing the conversion rate. This has significant implications for the large-scale promotion of in-situ conversion technology for oil-rich coal, low-maturity shale oil, and low-maturity biogas. Therefore, it is necessary to propose an in-situ conversion development method for organic-rich reservoirs, using a volumetric fracture network to heat the formation, achieving in-situ conversion, improving conversion efficiency, obtaining key parameters for field operations, and guiding field practice. Summary of the Invention

[0005] The purpose of this invention is to provide a method for in-situ development of organic-rich rocks. This method can achieve efficient development and evaluation of organic-rich rocks in situ through a complex well network and circulating heat injection system formed under controlled conditions.

[0006] The in-situ conversion and development method for organic-rich reservoirs provided by this invention includes the following steps:

[0007] S1. Obtain basic data on organic-rich reservoirs;

[0008] S2. Deploy a high-conductivity three-dimensional well network in the target layer rich in organic matter reservoir, perform multi-stage fracturing, and form a three-dimensional fracturing network. The distal ends of the fracturing network are interconnected through microfractures.

[0009] The three-dimensional well network includes heating wells and production wells. One end of the heating well is connected to a heat production system, and one end of the production well is connected to an oil and gas post-processing system.

[0010] Working fluid is injected into the heating well to heat the formation in situ for in-situ conversion, and oil and gas are extracted through the production well.

[0011] In the above development method, in step S1, the basic parameters are obtained based on preliminary well logging, geophysical exploration and engineering information, laboratory experiments, etc. The basic parameters include: target layer physical properties, target layer geostress magnitude and direction, formation thermal conductivity, formation temperature, etc.

[0012] In the above-mentioned development method, the working fluid can be molten salt, oil, water, polymer solution or high-pressure steam, which has good thermal conductivity and high specific heat capacity, and can continuously keep the formation above the threshold temperature for in-situ conversion of organic matter into a large amount of hydrocarbon generation and has stable properties, and continuously transfer heat to the target layer rock.

[0013] The support material used is a mixture of copper foam balls and quartz sand, or graphene-doped ceramic, which has high thermal conductivity and can quickly transfer heat to the far end of the mesh.

[0014] In the above development method, the injection and conduction of the working fluid are carried out in the following three ways:

[0015] 1. The heating well is provided with an annulus. The working fluid is injected from the inner pipe and returned from the annulus, thereby heating the working fluid in the near-wellbore fracture. The working fluid conducts heat to the entire fracture network and the surrounding rocks, and further pyrolyzes the rocks in the formation to produce light hydrocarbons, which are then extracted by the fracture network of the production well.

[0016] 2. The heating well is equipped with an annulus. The working fluid is injected from the inner tube and then injected into the fracture network through the perforation. Mass transfer occurs at the distal end through the connecting fracture network and the matrix. After the working fluid flows into the adjacent fracture network, it returns to the surface through the annulus, forming a closed loop of convective heat transfer between adjacent fractures. This creates a hydrothermal circulation for the distal fracture network, continuously heating the formation and causing the organic-rich formation to undergo pyrolysis to produce light hydrocarbons. These light hydrocarbons are then pumped into the production well through the fracture network of the production well, ultimately producing the pyrolyzed light hydrocarbons from the formation.

[0017] 3. The working fluid is injected from the heating well, then flows into the fracture network through the perforation, and flows into the adjacent well's fracture network through mass transfer via the connecting fracture network and matrix at the distal end. Finally, it flows into the adjacent well, forming a closed loop of convective heat transfer between the adjacent wells, heating the rock volume between the two wells. The working fluid forms a cycle, continuously heating the formation, causing the organic-rich formation to pyrolyze and produce light hydrocarbons, which are then pumped into the production well through the fracture network of the adjacent production well, ultimately producing the pyrolyzed light hydrocarbons from the formation.

[0018] Preferably, the three-dimensional well network can be either a horizontal well network or a vertical well network;

[0019] The three-dimensional well network includes multiple wells distributed in an interlaced manner (the main well trajectories are parallel to each other, and multiple layers are designed perpendicular to the cross-section of the well trajectory, with each layer of well trajectory arranged in an interlaced manner). Under the action of fracturing, each well forms an interlaced fracture network.

[0020] The fracture networks formed by each well are not aligned with each other, and the main fractures extend along the horizontal maximum principal stress.

[0021] Preferably, the arrangement of the three-dimensional well network around and above and below the formation can reduce heat loss caused by dynamic bottom water generated during the production process and external natural water intrusion, and reduce heat loss from non-target layer rocks to target layer rocks, as shown in the following structure:

[0022] The target area is arranged with an interlaced three-dimensional well network consisting of the production wells and the heating wells, while the target area is surrounded and bottomed with vertical wells, horizontal wells, or a combination of vertical and horizontal wells.

[0023] The working section of the vertical well covers the target layer and the depth of the dynamic bottom water below it;

[0024] The top of the working section of the vertical well is higher than the top of the target layer and its dynamic bottom water, and the bottom of the working section of the vertical well is deeper than the bottom of the target layer and its dynamic bottom water.

[0025] The horizontal well is a single-layer or multi-layer horizontal well, and its horizontal part is the working section, located in the target layer or its dynamic bottom water;

[0026] The working section can increase the heat to generate a high-temperature thermal wall at the bottom and around the dense target layer, or it can inject heat-insulating foam into the formation to make it difficult for external natural water to flow into the target area, while isolating dynamic bottom water from the target area. This can slow down the temperature drop and heat loss of the target layer in the target area, thereby preventing the reduction of the target layer conversion rate caused by cooling, and ultimately achieving the goal of improving the in-situ conversion efficiency of the rock in the target area.

[0027] The working section of the heating well is the part of the well section that heats the formation.

[0028] In the above development method, the reasonable well spacing and cluster spacing of the three-dimensional well network are determined according to the following method:

[0029] 1) In the direction perpendicular to the wellbore, within a given time t, determine the maximum distance x1 from the lowest temperature point to the threshold temperature for in-situ conversion of a large amount of hydrocarbon generation;

[0030] 2) Along the wellbore direction, within a given time t, determine the maximum distance x2 from the lowest temperature point to the threshold temperature for in-situ conversion of large amounts of hydrocarbons;

[0031] 3) The reasonable well spacing L is obtained according to the following formula. d and cluster spacing L c ;

[0032] L d =αL f +2x1

[0033] L c =2x2

[0034] Where α is the safety factor, obtained based on engineering experience; L f The half-fracture length is obtained from field monitoring data (generally microseismic monitoring and well test analysis).

[0035] In step 1), the maximum distance x1 is obtained by the following formula;

[0036]

[0037] Where, T1, T i These are the wellbore wall temperature and the original formation temperature, respectively, which can be obtained from downhole sensors; T r The threshold temperature for large-scale hydrocarbon generation can be obtained through indoor rock sample pyrolysis experiments; ρ and C are the average formation rock density and specific heat capacity, respectively; λ1 is the average effective thermal conductivity of the formation perpendicular to the wellbore direction, which can be obtained through indoor core experiments; erf is the error function, and its expression is: t represents the heating time for the in-situ conversion development, which is determined according to the development plan;

[0038] In step 2), the maximum distance x2 is obtained using the following formula;

[0039]

[0040] Where T2 is the fluid temperature in the fracture, which can be obtained through downhole sensors; λ2 is the formation's average effective thermal conductivity along the wellbore direction, which can be obtained through indoor core experiments; T r The threshold temperature for large-scale hydrocarbon generation can be obtained through indoor rock sample pyrolysis experiments; ρ and C are the average formation rock density and specific heat capacity, respectively, and erf is the error function, whose expression is: t represents the heating time for the in-situ conversion development, which is determined according to the development plan;

[0041] In step 3), α is 1 to 1.5.

[0042] The basic principle of this invention is to construct a hydrothermal circulation system under the condition of horizontal well three-dimensional fracture network fracturing. Through devices such as high-pressure pumps, heating wells, well networks, fracture network systems, and separators, a hot working fluid circulation system is constructed between and within volumetric fractures in the formation. This increases the contact area between the heat source and the formation, overcomes the difficulty of low thermal conductivity of the formation, continuously heats the formation, and achieves high-efficiency in-situ conversion.

[0043] This invention relates to an in-situ conversion and development method for organic-rich reservoirs. In this method, heat conduction within the fracture network conforms to the heat conduction equation. To ensure that the temperature at the lowest point in the formation (generally the midpoint between two parallel heat sources) reaches the threshold temperature for the in-situ conversion of organic-rich rocks into a large amount of hydrocarbons within a given time period, the heat conduction process is simplified to an isothermal boundary unsteady-state heat conduction problem. The appropriate well spacing L can then be calculated using the heat conduction equation. d and cluster spacing L c To achieve a reasonable well spacing L d Cluster spacing L c The optimal approach is as follows: In constructing complex fracture networks, a combination of in-situ stress, flow rate, and perforation technology can create simple fractures near the wellbore and complex fractures further away. Specifically: a. In the near-wellbore zone, use flow-limited perforation. After vertical directional perforation, rapidly increase the flow rate to the maximum permissible level. When injecting fracturing fluid, use a pulsed variable flow rate method, employing a high-viscosity, large-slug-type fracturing fluid; b. Inject low-viscosity slickwater in the far-wellbore zone. When adding proppant, use the maximum permissible flow rate, continuously adding small-diameter proppant with gradually increasing concentration; c. In the later stages of fracturing, use a multi-diameter proppant mixture to fill the near-wellbore fractures, providing support. Add fibers to the fluid to enhance proppant suspension.

[0044] This invention presents a simple, feasible, and highly operable in-situ conversion and development method for organic-rich reservoirs. Based on existing technologies in other shale oil and gas development fields, it can be easily implemented in field engineering. Unlike existing publicly available technologies, this method utilizes horizontal well multi-stage fracturing technology and fracture network morphology control technology to expand the contact surface with the rock. This large contact surface serves as a heat source, creating a three-dimensional heating effect on the rock, effectively increasing the contact area between the heat source and the formation, thereby improving in-situ conversion efficiency. This overcomes the problems of low thermal conductivity, high energy consumption, and slow heat transfer caused by the poor thermal conductivity of organic-rich rocks in traditional technologies, which makes large-scale economical development difficult. Furthermore, this invention innovatively constructs multiple thermal fluid circulation modes, including working fluid circulation within the pipe + fracture heat conduction, external circulation + single-well adjacent fracture network circulation, and external circulation + multi-well fracture network circulation, maintaining a continuous high temperature within the circulation system and effectively increasing in-situ conversion efficiency. Furthermore, the working fluid with high specific heat and high thermal conductivity, and the proppant made of high thermal conductivity materials, can effectively deliver the heat source to the deep rock formation through various methods such as heat conduction, forced convection, and thermal radiation, thereby effectively increasing the in-situ conversion efficiency. In addition, the volumetric fracture network formed by multi-stage fracturing in the production well in this invention can effectively increase the contact area with the formation, efficiently and economically extracting the light hydrocarbons converted in situ from the formation, thus improving the in-situ conversion efficiency. Attached Figure Description

[0045] Figure 1 This is one of the circulation methods for the working fluid in the method of the present invention.

[0046] Figure 2 This is the second circulation method for the working fluid in the method of the present invention.

[0047] Figure 3 This is the third circulation mode of the working fluid in the method of the present invention.

[0048] Figure 4 This refers to the three-dimensional well network in the method of this invention.

[0049] Figure 5 This is a three-dimensional well network layout diagram in the method of the present invention; wherein, the left figure is a top view and the right figure is a front view.

[0050] Figure 6 This is a horizontal well network in the method of the present invention; wherein, the left figure is a schematic diagram of the characterization of each parameter, and the right figure is a simplified schematic diagram of heat transfer and its coordinates.

[0051] Figure 7 This describes the conversion effect of the method of the present invention under specific parameters. Detailed Implementation

[0052] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0053] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0054] The in-situ conversion and development method for organic-rich reservoirs provided by this invention includes the following steps:

[0055] (1) Obtain basic data. Based on preliminary well logging, geophysical exploration and engineering information, indoor experiments, etc., obtain basic parameters, including: target layer physical properties, target layer geostress magnitude and direction, formation thermal conductivity, formation temperature, etc.

[0056] (2) Deploy a high-conductivity three-dimensional well network in the target layer, perform multi-stage fracturing to form a three-dimensional fracturing network with interconnected micro-fractures at the distal ends; divide the three-dimensional well network into heating wells and production wells; inject working fluid into the heating wells to heat the formation and perform in-situ transformation, and extract oil and gas through the production wells; the specific steps are as follows:

[0057] a. The working fluid is injected into the formation through a heated well, which heats the formation. After being heated, the formation is converted in situ to produce oil and gas, which is then extracted through production wells.

[0058] b. The working fluid has good thermal conductivity and high specific heat capacity, which can continuously keep the formation above the threshold temperature for in-situ conversion of organic matter into a large amount of hydrocarbon generation and has stable properties. It continuously transfers heat to the target rock layer. The working fluids that can be selected include, but are not limited to, molten salt, oil, water, polymer solution, high-pressure steam, etc.

[0059] c. The proppant in the crack has high thermal conductivity and can quickly transfer heat to the far end of the crack mesh. Optional materials include, but are not limited to, a mixture of foamed copper balls and quartz sand, graphene-doped ceramics, etc.

[0060] d. Systems that inject working fluid to heat the formation include a heat production system 1, a heating well 2, a fracture network of the heating well 3, a fracture network of the production well 4, a production well 5, and an oil and gas post-processing system 6. There are three typical injection methods:

[0061] d1. The heated well has an annulus. Hot working fluid is injected from the inner tube and returns from the annulus, heating the rocks near the heated well. Simultaneously, the highly thermally conductive working fluid and proppant heat the fracture network, transferring heat to the entire fracture network and surrounding rocks, further pyrolyzing the rocks in the formation to produce light hydrocarbons. These light hydrocarbons are then extracted through the fracture network of the production well. Figure 1 As shown;

[0062] d2. The heated well has an annulus. Hot working fluid is injected downhole from the inner tube and then into the fracture network through perforations. Mass transfer occurs at the distal end through the connecting fracture network and matrix. After flowing into adjacent fracture networks, the working fluid returns to the surface through the annulus, forming a convective heat transfer cycle between adjacent fractures. This creates a hydrothermal circulation in the distal fracture network, continuously heating the formation and causing pyrolysis of the organic-rich formation to produce light hydrocarbons. These hydrocarbons are then pumped into the production well through the fracture network, ultimately producing the pyrolyzed light hydrocarbons from the formation. Figure 2 As shown;

[0063] d3. The hot working fluid is injected into the heated well, then flows into the fracture network through perforations. At the distal end, it is transferred through the connecting fracture network and matrix, flowing into the fracture network of the adjacent well, and finally into the next well, forming a convective heat transfer cycle between the adjacent wells. This heats the rock volume between the two wells, creating a circulation of the working fluid that continuously heats the formation, causing the organic-rich formation to pyrolyze and produce light hydrocarbons. These light hydrocarbons are then pumped into the production well through the fracture network of the adjacent production well, ultimately producing the pyrolyzed light hydrocarbons from the formation. For example... Figure 3 As shown.

[0064] The three-dimensional well network in this invention can be either horizontal or vertical, consisting of multiple wells 7 staggered (the main well trajectories are parallel to each other, and multiple layers are designed perpendicular to the well trajectory tangent, with each layer of well trajectories arranged alternately). Each well uses multi-stage fracturing technology to form multiple staggered fracture networks. The fracturing fractures created by the perforations 8 of each well are not directly opposite each other, and the main fracture extends along the horizontal maximum principal stress; for example... Figure 4 As shown, when the well pattern is horizontal, the left figure is a top view and the right figure is a vertical section. When the well pattern is vertical, the left figure is a front view perpendicular to the formation and the right figure is a top view.

[0065] The three-dimensional well network of the present invention, when arranged around and above and below the formation, can reduce heat loss caused by dynamic bottom water generated during the production process and external natural water intrusion, and reduce heat loss from non-target layer rocks to target layer rocks. Its characteristic is that it includes... Figure 5The diagram shows: Vertical well 9, production well 10a, heating well 10b, horizontal well 11, target layer 12, and dynamic bottom water 13; a staggered three-dimensional well network consisting of production wells 10a and heating wells 10b is arranged inside the target area; vertical wells 9, horizontal wells 11, or a combination of vertical wells 9 and horizontal wells 11 are drilled at the periphery and bottom of the target area; the working section of vertical well 9 covers the target layer 12 and the depth of its lower dynamic bottom water 13, i.e., the top of the working section of vertical well 9 is higher than the top of the target layer 12 and its lower dynamic bottom water 13, and the bottom of the working section of vertical well 9 is deeper than the bottom of the target layer and its lower dynamic bottom water; horizontal well 1... 1 is a single-layer or multi-layer horizontal well, the horizontal part of which is the working section, located inside the target layer 12 or its dynamic bottom water 13; the working section can be heated to generate a high-temperature thermal wall at the bottom and around the dense target layer, or can inject heat-insulating foam into the formation to make it difficult for external natural water to flow into the target area, while isolating the dynamic bottom water from the target area, which can slow down the temperature drop and heat loss of the target layer in the target area, thereby preventing the reduction of the target layer conversion rate caused by cooling, and ultimately achieving the purpose of improving the in-situ conversion efficiency of the rock in the target area; the working section of the heated well 10b is the part of the well section that heats the formation.

[0066] In the method of this invention, the reasonable well spacing and cluster spacing of the high thermal conductivity three-dimensional well network can be determined by calculation. The reasonable well spacing L d Cluster spacing L c The optimal arrangement principle is to ensure that, while maintaining economic efficiency, the temperature at the lowest point of the target layer within a given time t reaches the threshold temperature for large-scale hydrocarbon generation from in-situ conversion of organic matter, thus guaranteeing that the temperature of the entire target layer reaches the threshold temperature T for large-scale hydrocarbon generation. r The preferred method for determination is as follows, such as... Figure 6 As shown:

[0067] a. Calculate the maximum distance x1 from the lowest temperature point to the in-situ hydrocarbon generation threshold temperature within a given time t, perpendicular to the wellbore direction. The calculation method is as follows:

[0068] The limiting half-length x1 perpendicular to the wellbore direction is calculated using the following equation:

[0069]

[0070] Where, T1, T i These are the wellbore wall temperature and the original formation temperature, respectively, which can be obtained from downhole sensors; T r The threshold temperature for large-scale hydrocarbon generation can be obtained through indoor rock sample pyrolysis experiments; ρ and C are the average formation rock density and specific heat capacity, respectively; λ1 is the average effective thermal conductivity of the formation perpendicular to the wellbore direction, which can be obtained through indoor core experiments; erf is the error function, and its expression is: t is the heating time for the in-situ conversion development, which is determined according to the development plan; there is only one unknown in the above formula, x1, which can be obtained through trial calculation or other gradual methods.

[0071] b. Due to the heterogeneity of the rock, fractures are generally distributed along the maximum horizontal principal stress. The heterogeneity of natural geostress leads to a greater number of micro-fractures perpendicular to the wellbore direction than those along the wellbore direction. Therefore, the effective thermal conductivity λ1 perpendicular to the wellbore direction is inconsistent with the effective thermal conductivity λ2 along the wellbore direction. Therefore, the maximum distance x2 from the lowest temperature point to the in-situ conversion threshold temperature for a large amount of hydrocarbon generation within a given time t is calculated along the vertical direction of the wellbore. The calculation method is to solve the following equation:

[0072]

[0073] Where T2 is the fluid temperature in the fracture, which can be obtained through downhole sensors; λ2 is the formation's average effective thermal conductivity along the wellbore direction, which can be obtained through indoor core experiments; the other parameters are defined in the same way as in step a.

[0074] c. Calculate the reasonable well spacing L according to the following formula. d Cluster spacing L c :

[0075] L d =αL f +2x1

[0076] L c =2x2

[0077] Where α is the safety factor, which is obtained from engineering experience, and the preferred value range is 1 to 1.5; L f The half-fracture length is obtained from field monitoring data (generally microseismic monitoring and well test analysis).

[0078] The basic principle of this invention is to construct a hydrothermal circulation system under the condition of horizontal well three-dimensional fracture network fracturing. Through devices such as high-pressure pumps, heating wells, well networks, fracture network systems, and separators, a hot working fluid circulation system is constructed between and within volumetric fractures in the formation. This increases the contact area between the heat source and the formation, overcomes the difficulty of low thermal conductivity of the formation, continuously heats the formation, and achieves high-efficiency in-situ conversion.

[0079] This invention relates to an in-situ conversion and development method for organic-rich reservoirs. In this method, heat conduction within the fracture network conforms to the heat conduction equation. To ensure that the temperature at the lowest point in the formation (generally the midpoint between two parallel heat sources) reaches the threshold temperature for the in-situ conversion of organic-rich rocks into a large amount of hydrocarbons within a given time period, the heat conduction process is simplified to an isothermal boundary unsteady-state heat conduction problem. The appropriate well spacing L can then be calculated using the heat conduction equation. dand cluster spacing L c To achieve a reasonable well spacing L d Cluster spacing L c The optimal approach is as follows: In constructing complex fracture networks, a combination of in-situ stress, flow rate, and perforation technology can create simple fractures near the wellbore and complex fractures further away. Specifically: a. In the near-wellbore zone, use flow-limited perforation. After vertical directional perforation, rapidly increase the flow rate to the maximum permissible level. When injecting fracturing fluid, use a pulsed variable flow rate method, employing a high-viscosity, large-slug-type fracturing fluid; b. Inject low-viscosity slickwater in the far-wellbore zone. When adding proppant, select the maximum permissible flow rate, continuously adding small-diameter proppant with gradually increasing concentration; c. In the later stages of fracturing, use a multi-diameter proppant mixture to fill the near-wellbore fractures, providing support. Add fibers to the fluid to enhance proppant suspension.

[0080] The method of this invention was used to carry out in-situ conversion and development of low-maturity oil shale in a certain formation in Qinghai. The threshold temperature for large-scale hydrocarbon generation was determined to be 500℃ through laboratory experiments, and the density of the formation oil shale was 1900 kg / m³. 3 The specific heat capacity is 1000 J / (Kg·K), the thermal conductivity is 0.3 W / (mK), the initial formation temperature is 90℃, and the circulating fluid temperature is 900℃. Based on the method of this invention, x1 and x2 can be directly calculated within a given time t. The following shows the temperature variation with distance under different t conditions. The horizontal line represents the threshold temperature Tr for large-scale hydrocarbon generation. For example, when t = 10000 h, the intersection of the curve and the horizontal line represents the farthest distance at which the temperature reaches Tr: 2.5 m. When t = 20000 h, the farthest distance of Tr is approximately 3.5 m, and so on. When t = 50000 h, the farthest distance of Tr is approximately 5.5 m. Accordingly, as... Figure 7 As shown:

[0081] When t = 10000h, and the safety factor α is taken as 1.5, the half-fracture length L of the hydraulic fracturing fracture is... f When the depth is 30m, the reasonable well spacing L d =1.5×30+2×2.5=50m, cluster spacing L c =2 × 2.5 = 5m;

[0082] When t = 20000h, and the safety factor α is taken as 1.5, the half-fracture length L of the hydraulic fracturing crack is... f When the depth is 30m, the reasonable well spacing L d =1.5×30+2×3.5=52m, cluster spacing L c =2 × 3.5 = 7m;

[0083] When t = 50000h, and the safety factor α is taken as 1.5, the half-fracture length L of the hydraulic fracturing fracture is... f When the depth is 30m, the reasonable well spacing L d=1.5×30+2×5.5=56m, cluster spacing L c =2 × 5.5 = 11m.

[0084] In the actual development process described above, taking into account both the production cycle and development costs, a development scheme with a heating time of t = 10000h was selected for the pilot test well, with L... d =50m, L c A pilot test well was set up with parameters of 5m. After heating for approximately 10,000 hours, the overall in-situ conversion rate of shale oil in this area reached 37%. In the same reservoir of a similar block in this area, under traditional development scheme parameters (L... d =200m, L c =20m), the overall in-situ conversion efficiency of shale oil at 10000h was only 11.2%. Therefore, the optimization method of this invention can significantly improve the conversion efficiency after optimizing the well pattern and well spacing.

Claims

1. A method for in-situ conversion and development of organic-rich reservoirs, comprising the following steps: S1. Obtain basic data on organic-rich reservoirs; S2. Deploy a high-conductivity three-dimensional well network in the target layer rich in organic matter reservoir, perform multi-stage fracturing, and form a three-dimensional fracturing network. The distal ends of the fracturing network are interconnected through microfractures. The three-dimensional well network includes heating wells and production wells. One end of the heating well is connected to a heat production system, and one end of the production well is connected to an oil and gas post-processing system. Working fluid is injected into the heating well to heat the formation in situ for in-situ conversion, and oil and gas are extracted through the production well. The reasonable well spacing and cluster spacing of the three-dimensional well network are determined according to the following method: 1) Perpendicular to the wellbore direction, at a given time Within, determine the maximum distance from the lowest temperature point to the threshold temperature for large-scale in-situ hydrocarbon generation. ; The maximum distance is obtained using the following formula. ; ； in, , These are the wellbore temperature and the original formation temperature, respectively. This is the threshold temperature for large-scale hydrocarbon generation; C and C represent the average density and specific heat capacity of the formation rocks, respectively. The average effective thermal conductivity of the formation perpendicular to the wellbore direction is given by: erf is the error function, expressed as: t represents the heating time for in-situ conversion under given heating conditions, which is determined according to the development plan. The maximum distance is obtained using the following formula. ; ； in, The temperature of the fluid in the crack; The average effective thermal conductivity of the formation along the wellbore direction; This is the threshold temperature for large-scale hydrocarbon generation; C and C represent the average formation rock density and specific heat capacity, respectively, and erf is the error function, whose expression is: t represents the heating time for in-situ conversion under given heating conditions, which is determined according to the development plan. 2) Along the shaft direction, at a given time Within, determine the maximum distance from the lowest temperature point to the threshold temperature for large-scale in-situ hydrocarbon generation. ; 3) The reasonable well spacing is obtained according to the following formula. and cluster spacing ; ； ； in, The safety factor is derived from engineering experience; The half-fracture length of the hydraulic fracturing fracture was obtained from field monitoring data. It is 1~1.

5.

2. The development method according to claim 1, characterized in that: The working fluid is molten salt, oil, water, polymer solution, or high-pressure steam; The proppant used is a mixture of copper foam balls and quartz sand, or graphene-doped ceramics.

3. The development method according to claim 1 or 2, characterized in that: The injection and conduction methods of the working fluid are as follows: The heating well is provided with an annulus. The working fluid is injected from the inner pipe and returned from the annulus, thereby heating the working fluid in the near-wellbore fractures. The working fluid conducts heat to the entire fracture network.

4. The development method according to claim 1 or 2, characterized in that: The injection and conduction methods of the working fluid are as follows: The heating well is provided with an annulus. The working fluid is injected from the inner tube and then injected into the fracture network through the perforation. Mass transfer is carried out at the distal end through the connecting fracture network and the matrix. After the working fluid flows into the adjacent fracture network, it returns to the surface through the annulus, forming a closed loop of convective heat transfer between adjacent fractures.

5. The development method according to claim 1 or 2, characterized in that: The injection and conduction methods of the working fluid are as follows: The working fluid is injected from the heating well, then flows into the fracture network through the perforation, and flows into the adjacent well fracture network through mass transfer via the connecting fracture network and matrix at the distal end, and finally flows into the adjacent well, forming a closed loop of convective heat transfer between adjacent wells.

6. The development method according to claim 1 or 2, characterized in that: The three-dimensional well network can be a horizontal well network or a vertical well network; The three-dimensional well network includes multiple wells distributed in an interlaced manner. Under the action of fracturing, each well forms an interlaced network of fractures. The fracture networks formed by each well are not aligned with each other, and the main fractures extend along the horizontal maximum principal stress.

7. The development method according to claim 1 or 2, characterized in that: The structure of the three-dimensional well network is as follows: The target area is arranged with an interlaced three-dimensional well network consisting of the production wells and the heating wells, while the outer perimeter and bottom of the target area are arranged with a combination of vertical and horizontal wells. The depth to which the vertical well working section covers the target layer and the dynamic bottom water below it; The horizontal well is a single-layer or multi-layer horizontal well, and its horizontal part is the working section, located in the target layer or its dynamic bottom water; The working section of the heating well is the part of the well section that heats the formation.

8. The development method according to claim 7, characterized in that: The top of the working section of the vertical well is higher than the top of the target layer and its dynamic bottom water, and the bottom of the working section of the vertical well is deeper than the bottom of the target layer and its dynamic bottom water.

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