Shale gas two-layer development well bore structure design method and implementation method thereof

Abstract

The invention discloses a shale gas two-layer development well bore structure design method and an implementation method thereof. The well bore structure design method comprises the following steps that S1, the upper reservoir well casing windowing position H1 is determined, H1 is smaller than or equal to H2-R, H2 is the vertical depth of an upper reservoir well A target point, R is the borehole curvature radius, and alpha is the build-up rate; s2, determining the cement return depth H3 of the oil-string casing of the lower reservoir well, wherein H3 is greater than or equal to H1 + 10; s3, the lower depth H4 of the technical casing of the lower reservoir well is determined, and H4 is larger than or equal to H3 + 300; and S4, determining the depth of the surface casing of the lower reservoir well according to the constraint condition # imgabs0 # for preventing the overflow shut-in fracturing formation. According to the method, the windowing position of the casing of the upper reservoir well, the cement return height of the oil-string casing of the lower reservoir well, the lower depth of the technical casing of the lower reservoir well and the lower depth of the surface casing of the lower reservoir well are specially designed, so that effective exploitation of the two reservoirs is guaranteed, and the exploitation efficiency and economic benefits are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of wellbore structure design and optimization of oil and gas wells, and in particular to a shale gas two-layer development wellbore structure design method and an implementation method thereof. Background Art

[0002] The thickness of high-quality shale in a certain area of ​​my country is more than 80m. The "horizontal well + volume fracturing" development model is adopted. The current wellbore structure is designed to meet the needs of volume fracturing. Conventional methods such as setting mandatory sealing points, matching drill bits and casing sizes are used for design. However, they are limited to using one set of wellbore structures to develop a layer of high-quality shale reservoirs. Since the artificial fractures generated by the current volume fracturing only extend 20-30m in the vertical direction, a considerable portion of the resources in the high-quality shale reservoirs have not been effectively utilized in the vertical direction, which greatly affects the benefits of shale gas development. Summary of the invention

[0003] The purpose of the present invention is to overcome the problem that the existing wellbore structure design is mostly limited to using one set of wellbore structure to develop one layer of shale reservoir, resulting in a considerable portion of resources in the high-quality shale reservoir not being effectively utilized vertically, which greatly affects the benefits of shale gas development, and to provide a shale gas two-layer development wellbore structure design method and its implementation method.

[0004] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0005] A shale gas two-layer development wellbore structure design method is used to design a lower reservoir well and an upper reservoir well, comprising the following steps:

[0006] S1. Determine the position of the upper reservoir well casing window, the depth of the upper reservoir well casing window position is H1, unit m, H1≤H2-R, where H2 is the vertical depth of the upper reservoir well A target point, unit m; R is the wellbore curvature radius, unit m, R=18000 / (π*α), where α is the inclination rate, unit ° / 100m;

[0007] S2. Determine the depth H3 of the cement return height of the oil layer casing of the lower reservoir well, in meters; H3 ≥ H1 + 10;

[0008] S3. According to the requirements of the lower reservoir well oil layer casing cement return height into the technical casing and the segmented track design data of the deflection section, determine the lower depth H4 of the lower reservoir well technical casing, unit m, H4 ≥ H3 + 300;

[0009] S4. Based on the formation constraints of shut-in fracturing to prevent overflow: Determine the lower depth of the surface casing of the lower reservoir well, where ρ ffx is the safe formation fracture pressure equivalent density in the open hole section, g / cm3 ρ mmax is the maximum drilling fluid density in the open hole section, g / cm 3 ;D m is the top well depth corresponding to the maximum pore pressure equivalent density in the open hole section, m; D x is the depth of the surface casing of the lower reservoir well, m; S k is the overflow allowable value, g / cm 3 .

[0010] In traditional shale gas development, it is usually limited to using one wellbore structure to develop one shale reservoir. The development of multiple layers requires re-drilling, which increases the mining cost, time and resource waste. However, through the shale gas two-layer development wellbore structure design method provided by the present invention, two layers of the reservoir can be mined in one wellbore, achieving efficient utilization of the reservoir, while also reducing the costs of drilling, completion, testing, supporting facilities, etc., effectively improving economic benefits. At the same time, the method designs the window position of the upper reservoir well casing, which can avoid interference between different reservoirs and further improve the oil and gas collection efficiency; the method designs the depth of the surface casing of the lower reservoir well according to the formation constraint conditions for preventing overflow, shut-in and fracturing, which can ensure that the well body will not have problems such as well leakage during the exploitation process, thereby ensuring the safety of development. In summary, the method can ensure the effective exploitation of the two reservoirs by specially designing the window position of the upper reservoir well casing, the cement return height of the oil layer casing of the lower reservoir well, the technical casing depth of the lower reservoir well and the surface casing depth of the lower reservoir well, thereby improving the exploitation efficiency and economic benefits.

[0011] Preferably, the slope rate α ranges from 5 to 25° / 100m.

[0012] Preferably, S k The value range is 0.05g / cm 3 ~0.1g / cm 3 .

[0013] A method for implementing a two-layer shale gas development wellbore structure comprises the following steps:

[0014] A1. Designing the lower reservoir well and the upper reservoir well by using the above-mentioned two-layer shale gas development wellbore structure design method;

[0015] A2. Lower the surface casing of the lower reservoir well to the depth of H5, lower the technical casing of the lower reservoir well to the depth of H4, drill the lower reservoir horizontal section, lower the oil layer casing of the lower reservoir well throughout the entire section of the lower reservoir well, control the cement return height of the oil layer casing of the lower reservoir well to the depth of H3, cement and construct the wellbore of the lower reservoir well, and develop the lower reservoir;

[0016] A3. After the gas production in the lower reservoir is completed, the oil layer casing section of the lower reservoir well that is not sealed with cement above the H3 depth is taken out, and the window opening whipstock is lowered into the upper reservoir well to the H3 depth. A window is opened and the upper reservoir horizontal section is side-drilled from the H1 depth position. The oil layer casing of the upper reservoir well is lowered into the entire well section and then cemented to construct the wellbore of the upper reservoir well to develop the upper reservoir.

[0017] The implementation method of the shale gas two-layer development wellbore structure of the present invention adopts the concept of batch development to develop the lower reservoir and the upper reservoir, first implements the drilling and development of the horizontal section of the lower reservoir well, and after the gas production of the lower reservoir well is completed, the oil layer casing of the unsealed section of the lower reservoir well is cut out, and the upper reservoir window side drilling and development are carried out by using the lower reservoir wellbore and ground equipment. Two different reservoirs can be mined in the same wellbore, which reduces the cost and mining difficulty, can greatly reduce the comprehensive well construction cost, and improve the shale gas development benefits. At the same time, it also reduces the occupied area and environmental damage. Due to the use of the whipstock window side drilling upper horizontal section, the upper reservoir can be effectively prevented from being affected by the lower reservoir, ensuring the mining efficiency and output of the upper reservoir.

[0018] Preferably, both the lower reservoir and the upper reservoir are developed by volume fracturing.

[0019] Volume fracturing can form a complex fracture system in the reservoir, increase the contact area between the reservoir and the wellbore and the production area, and improve the production and recovery rate of the well. At the same time, volume fracturing can also effectively change the permeability and porosity of the reservoir, especially for some low-permeability shale gas reservoirs. Therefore, the use of volume fracturing for both the upper and lower reservoirs can increase the production of shale gas, bring higher economic benefits and better investment returns.

[0020] Preferably, both the lower reservoir well and the upper reservoir well adopt a depletion development method.

[0021] By adopting depletion-type development, we can make full use of the reservoir's own pressure, reduce gas production costs and investment costs, and thus improve recovery rates and economic benefits.

[0022] Preferably, the sizes of the surface casing of the lower reservoir well, the technical casing of the lower reservoir well, the oil layer casing of the lower reservoir well, and the oil layer casing of the upper reservoir well are all determined with reference to the drill bit and casing size information of the construction wells in the adjacent area.

[0023] Based on the drill bit and casing size information of neighboring wells, existing resources can be used to the greatest extent, and previous drilling and completion experience can be fully utilized. It can better adapt to local geological conditions and environment, reduce the probability of accidents during construction, reduce construction difficulty, and thus improve the success rate of construction and wellbore stability.

[0024] Preferably, the surface casing of the lower reservoir well is cemented back up to the surface.

[0025] The surface casing cement of the lower reservoir well is returned to the ground, which can better isolate the groundwater layer, reinforce the well wall of the upper loose rock layer, protect the wellbore, and comprehensively ensure the safety of the well body and reduce the probability of safety accidents.

[0026] Preferably, the technical casing of the lower reservoir well is cemented back up to the surface.

[0027] The casing cement of the lower reservoir well technology is returned to the ground, which can protect and isolate the difficult-to-control complex formations above the shale gas layer, such as isolating the upper high-pressure oil (gas, water) layer, leakage layer or collapse layer, to ensure the smooth progress of drilling.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The shale gas two-layer development wellbore structure design method provided by the present invention can exploit two layers of the reservoir in one wellbore, realize the efficient utilization of the reservoir, and also reduce the costs of drilling, completion, testing, supporting facilities, etc., effectively improving the economic benefits. At the same time, the method designs the window position of the upper reservoir well casing, which can avoid the interference between different reservoirs and further improve the oil and gas collection efficiency; the method designs the depth of the surface casing of the lower reservoir well according to the formation constraint conditions to prevent overflow, shut-in and fracturing, which can ensure that the wellbore will not have problems such as well leakage during the exploitation process, thereby ensuring the safety of development. In summary, the method can ensure the effective exploitation of the two reservoirs by specially designing the window position of the upper reservoir well casing, the cement return height of the oil layer casing of the lower reservoir well, the depth of the technical casing of the lower reservoir well, and the depth of the surface casing of the lower reservoir well, thereby improving the exploitation efficiency and economic benefits.

[0030] 2. The implementation method of the two-layer shale gas development wellbore structure of the present invention adopts the concept of batch development to develop the lower reservoir and the upper reservoir, first implements the drilling and development of the horizontal section of the lower reservoir well, and after the gas production of the lower reservoir well is completed, the oil layer casing of the unsealed section of the lower reservoir well is cut out, and the upper reservoir window side drilling and development are carried out by using the lower reservoir wellbore and ground equipment. Two different reservoirs can be mined in the same wellbore, which reduces the cost and mining difficulty, can greatly reduce the comprehensive well construction cost, and improve the benefits of shale gas development. At the same time, it also reduces the occupied area and environmental damage. Due to the use of the whipstock window side drilling of the upper horizontal section, the upper reservoir can be effectively prevented from being affected by the lower reservoir, ensuring the mining efficiency and output of the upper reservoir. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a flow chart of the wellbore structure design method for two-layer shale gas development in Example 1;

[0032] Figure 2 This is a flow chart of the implementation method of the wellbore structure for the two-layer development of shale gas in Example 2;

[0033] Figure 3 This is a schematic diagram of the wellbore structure of the lower reservoir well;

[0034] Figure 4 Schematic diagram of the wellbore structure of the upper reservoir well.

[0035] Figure markings: 1-lower reservoir well, 11-surface casing of lower reservoir well, 12-technical casing of lower reservoir well, 13-oil layer casing of lower reservoir well, 14-cement return height of oil layer casing of lower reservoir well, 2-upper reservoir well, 21-target point A of upper reservoir well, 22-window opening position of casing of upper reservoir well, 23-window opening bevel device of upper reservoir well, 24-oil layer casing of upper reservoir well. DETAILED DESCRIPTION

[0036] The present invention is further described in detail below in conjunction with test examples and specific implementation methods. However, this should not be understood as the scope of the above subject matter of the present invention being limited to the following embodiments, and all technologies realized based on the content of the present invention belong to the scope of the present invention.

[0037] Example 1

[0038] At present, the Sichuan Basin and its surrounding areas are rich in shale gas resources, but the existing design and construction methods for shale gas well bodies are mostly limited to using one set of well bodies to develop a layer of high-quality shale reservoirs. Since the artificial fractures generated by the current volume fracturing only extend 20-30m in the vertical direction, a considerable portion of the resources in the high-quality shale reservoirs have not been effectively utilized in the vertical direction, which greatly affects the benefits of shale gas development.

[0039] like Figure 1 , 3 As shown in , 4, the present invention provides a method for designing a wellbore structure for two-layer development of shale gas, the method being used to design a lower reservoir well 1 and an upper reservoir well 2, comprising the following steps:

[0040] S1. Determine the window position 22 of the upper reservoir well casing. The depth of the window position 22 of the upper reservoir well casing is H1, in m, H1≤H2-R, where H2 is the vertical depth of the target point 21 of the upper reservoir well A, in m; R is the wellbore curvature radius, in m, R=18000 / (π*α), where α is the inclination rate. In general, the inclination rate ranges from 5 to 25° / 100m. The value of the inclination rate is adjusted dynamically during the construction process according to the actual construction requirements;

[0041] S2. Determine the depth of the cement return height 14 of the oil layer casing of the lower reservoir well as H3, in meters; H3 ≥ H1 + 10;

[0042] S3. According to the requirements of the technical casing of the oil layer casing cement return height of the lower reservoir well 1 (refer to the "Petroleum and Natural Gas Industry Standard of the People's Republic of China", SY / T 5431-2017) and the segmented track design data of the deflection section, determine the lower depth H4 of the technical casing 12 of the lower reservoir well, unit m, H4 ≥ H3 + 300;

[0043] S4. Based on the formation constraints of shut-in fracturing to prevent overflow: where ρ ffx is the safe formation fracture pressure equivalent density in the open hole section, g / cm 3 ρ mmax is the maximum drilling fluid density in the open hole section, g / cm 3 ;D m is the top well depth corresponding to the maximum pore pressure equivalent density in the open hole section, m; D x is the depth of the surface casing 11 of the lower reservoir well, m; S k is the overflow allowable value. Generally, S k The value range is 0.05g / cm 3 ~0.1g / cm 3 , determine the lower depth of the surface casing 11 of the lower reservoir well.

[0044] Through the shale gas two-layer development wellbore structure design method provided by the present invention, two layers of the reservoir can be exploited in one wellbore, achieving efficient utilization of the reservoir, while also reducing the costs of drilling, completion, testing, supporting facilities, etc., and effectively improving economic benefits. At the same time, the method designs the window position 22 of the upper reservoir well casing, which can avoid interference between different reservoirs and further improve the efficiency of oil and gas collection; the method designs the depth of the surface casing 11 of the lower reservoir well according to the formation constraint conditions for preventing overflow and shutting in the well for fracturing, which can ensure that the wellbore will not have problems such as well leakage during the exploitation process, thereby ensuring the safety of development. In summary, the method can ensure the effective exploitation of the two reservoirs by specially designing the window position 22 of the upper reservoir well casing, the cement return height 14 of the lower reservoir well oil layer casing, the depth of the technical casing 12 of the lower reservoir well, and the depth of the surface casing 11 of the lower reservoir well, thereby improving the exploitation efficiency and economic benefits.

[0045] Example 2

[0046] like Figure 2 , 3 As shown in , 4, the present invention also provides a method for implementing a shale gas two-layer development wellbore structure, the method comprising the following steps:

[0047] A1. The lower reservoir well 1 and the upper reservoir well 2 are designed using the shale gas two-layer development well structure design method of Example 1;

[0048] A2. Lower the surface casing 11 of the lower reservoir well to the depth of H5, cement the surface casing 11 of the lower reservoir well back to the ground, lower the technical casing 12 of the lower reservoir well to the depth of H4, cement the technical casing 12 of the lower reservoir well back to the ground, then, after drilling the lower reservoir horizontal section, lower the oil layer casing 13 of the lower reservoir well 1 in the entire section, control the cement return height 14 of the oil layer casing of the lower reservoir well to the depth of H3, cement and construct the wellbore of the lower reservoir well, adopt volume fracturing, and use the depletion development method to develop the lower reservoir;

[0049] A3. After the gas production of the lower reservoir well 1 is completed, the lower reservoir well oil layer casing 13 section that is not cemented above the H3 depth is taken out, and the window opening whipstock 23 of the upper reservoir well is lowered to the H3 depth. The upper reservoir horizontal section is side-drilled from the H1 depth position through the window. The upper reservoir well oil layer casing 24 is lowered into the entire section of the upper reservoir well 2, and then cemented to construct the upper reservoir wellbore. Volume fracturing is adopted, and the upper reservoir is developed using the depletion development method.

[0050] In this embodiment, the sizes of the surface casing 11 of the lower reservoir well, the technical casing 12 of the lower reservoir well, the oil layer casing 13 of the lower reservoir well, and the oil layer casing 24 of the upper reservoir well are all determined by referring to the drill bit casing size information of the construction wells in the adjacent area.

[0051] The implementation method of the shale gas two-layer development wellbore structure of the present invention adopts the concept of batch development to implement the development of the lower reservoir and the upper reservoir, and first implements the horizontal section drilling and development of the lower reservoir well 1. After the gas production of the lower reservoir well 1 is completed, the oil layer casing of the unsealed section of the cement of the lower reservoir well 1 is cut out, and the upper reservoir window side drilling and development are implemented by using the lower reservoir well 1 wellbore and ground equipment. Two different reservoirs can be mined in the same wellbore, which reduces the cost and mining difficulty, can greatly reduce the comprehensive well construction cost, and improve the shale gas development benefits. At the same time, it also reduces the occupied area and environmental damage. Due to the use of the whipstock window side drilling upper horizontal section, the upper reservoir can be effectively prevented from being affected by the lower reservoir, ensuring the mining efficiency and output of the upper reservoir.

[0052] Example 3

[0053] On the basis of Examples 1 and 2, the present invention is described by taking a shale gas well with a vertical depth of less than 3500m in a certain block of the Sichuan Basin as an example.

[0054] The block adopts exhaustion gas production. Most gas wells have low gas production after 3 years and basically no economic benefits. The vertical geological stratigraphic data of shale gas wells in this block are shown in Table 1. The target distance between the upper and lower reservoir A targets is 350m, and the horizontal section length is 1500m. The construction wells in the neighboring area use a three-opening wellbore structure. The size of the first opening drill bit is 406.4mm and the surface casing size is 339.7mm; the size of the second opening drill bit is 311.2mm and the technical casing size is 244.5mm; the size of the third opening drill bit is 215.9mm and the oil layer casing size is 139.7mm; the cement of the construction wells in the neighboring area is returned to the wellhead and put into production by volume fracturing.

[0055] Based on the geological stratigraphic data table of shale gas wells in a block of the Sichuan Basin provided in Table 1, the segmented trajectory design data table of the upper reservoir well and the lower reservoir well provided in Table 2, and the wellbore structure characteristic parameters of the construction wells in the adjacent area, the upper and lower reservoir A target point data of the target reservoir (Longmaxi Formation) were obtained, and it was determined that the size of the surface casing 11 of the lower reservoir well was 339.7 mm, and the size of the first opening drill bit was 406.4 mm; the size of the technical casing 12 of the lower reservoir well was 244.5 mm, and the size of the second opening drill bit was 311.2 mm; the size of the oil layer casing 13 of the lower reservoir well was 139.7 mm, and the size of the third opening drill bit was 215.9 mm; the size of the oil layer casing 24 of the upper reservoir well was 139.7 mm, and the size of the third opening drill bit was 215.9 mm.

[0056] The shale gas two-layer development wellbore structure design method in Example 1 is adopted. According to Table 1, it is known that the vertical depth H2 of the target point 21 of the upper reservoir well A is 2844m. According to the inclination rate of 18-20° / 100m and the dynamic adjustment requirements during the implementation process, and taking into account the convenience of construction, it is concluded that the vertical depth from the target point 21 of the upper reservoir well A should not be less than 300m, and the depth H1 of the upper reservoir well casing window position 22 is determined to be 2544m.

[0057] Table 1 Geological stratigraphic data of shale gas wells in a certain area of ​​Sichuan Basin

[0058]

[0059] Table 2 Data table of segmented track design for upper reservoir wells and lower reservoir wells

[0060]

[0061] According to the depth H1=2544m of the window position 22 of the upper reservoir well casing, and the requirement of reserving 10m of space downward for the window opening whipstock 23 of the upper reservoir well, the depth H3=2554m of the cement return height 14 of the oil layer casing of the lower reservoir well is determined. Combined with the requirement that the cement slurry of the oil layer casing enters the upper casing no less than 300m in the shale gas well body structure design and the segmented track design data of the lower reservoir well 1, the lower depth H4≥2854m (corresponding to a vertical depth of 2822m) of the technical casing 12 of the lower reservoir well is determined downward.

[0062] According to the formation pore pressure, formation fracture pressure and formation collapse pressure profile of the lower reservoir well 1 from the wellhead to the depth of the lower reservoir well technical casing 12, a bottom-up design method is adopted to prevent overflow and shut-in fracturing formation constraints: where ρ ffx is the safe formation fracture pressure equivalent density in the open hole section, g / cm 3 ρ mmax is the maximum drilling fluid density in the open hole section, g / cm 3 ;D m is the top well depth corresponding to the maximum pore pressure equivalent density in the open hole section, m; D x is the depth of the surface casing 11 of the lower reservoir well, m; S k is the overflow allowable value, g / cm 3 , determine the lower depth of the surface casing 11 of the lower reservoir well.

[0063] In this embodiment, ffx The value is 1.96g / cm 3 , ρ mmax The value is 1.55g / cm 3 , D m The value is 2470m, S k The value is 0.05g / cm 3 , D can be calculated x ≥301m, for the convenience of actual construction, we take D x It is 300m.

[0064] Combined with the acquired wellbore structural characteristic parameters of the adjacent well construction area and the designed wellbore depth of 4550m for the lower reservoir well 1 track and 4550m for the upper reservoir well 2 track, a two-layer development wellbore structural design scheme can be designed as shown in Table 3 below:

[0065] Based on the two-layer development wellbore structure design scheme designed in Table 3, the surface casing 11 of the lower reservoir well is lowered to 300 m, and the technical casing 12 of the lower reservoir well is lowered to a well depth of 2854 m. After the lower reservoir horizontal section is drilled to a well depth of 4550 m, the oil layer casing 13 of the lower reservoir well is lowered to a well depth of 4548 m in the entire well section. The cement return height 14 of the oil layer casing of the lower reservoir well is controlled to a well depth of 2554 m to construct the wellbore, and then volume fracturing is used to develop the lower reservoir.

[0066] Table 3 Two-layer development wellbore structure design scheme

[0067]

[0068] After the gas production of the lower reservoir well 1 is completed, the oil layer casing of the lower reservoir well oil layer casing cement return height 14 and above the cement unsealed section is removed by cutting, and the upper reservoir well window opening whipstock 23 is lowered to the well depth of 2554m. The casing window is opened from the position H1=2544m, and the upper reservoir horizontal section is side-drilled to a well depth of 4550m. The upper reservoir well oil layer casing 24 is lowered to a well depth of 4548m in the entire well section, and then the wellbore is cemented to construct the wellbore, and volume fracturing is used to develop the upper reservoir.

[0069] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for designing a wellbore structure for two-layer development of shale gas, characterized in that: The method is used for designing a lower reservoir well (1) and an upper reservoir well (2), comprising the following steps: S1. Determine the upper reservoir well casing window position (22), the depth of the upper reservoir well casing window position (22) is H1, unit m, H1≤H2-R, where H2 is the vertical depth of the upper reservoir well A target point (21), unit m; R is the wellbore curvature radius, unit m, R = 18000 / (π*α), where α is the inclination rate, unit ° / 100m; S2. Determine the depth H3 of the cement return height (14) of the oil layer casing of the lower reservoir well, in meters; H3 ≥ H1 + 10; S3. According to the requirements of the lower reservoir well (1) oil layer casing cement return high into the technical casing and the segmented track design data of the deflection section, determine the lower depth H4 of the lower reservoir well technical casing (12), unit m, H4 ≥ H3 + 300; S4. Based on the formation constraints of shut-in fracturing to prevent overflow: Determine the lower depth of the surface casing (11) of the lower reservoir well, where ρ ffx is the safe formation fracture pressure equivalent density in the open hole section, g / cm 3 ρ mmax is the maximum drilling fluid density in the open hole section, g / cm 3 ;D m is the top well depth corresponding to the maximum pore pressure equivalent density in the open hole section, m; D x is the depth of the surface casing (11) of the lower reservoir well, m; S k is the overflow allowable value, g / cm 3 .

2. A shale gas two-layer development wellbore structure design method according to claim 1, characterized in that: The value range of the slope rate α is 5 to 25° / 100m.

3. A method for designing a wellbore structure for two-layer development of shale gas according to claim 1, characterized in that: S k The value range is 0.05g / cm 3 ~0.1g / cm 3 .

4. A method for implementing a two-layer shale gas development wellbore structure, characterized in that: The steps include: A1. Designing the lower reservoir well (1) and the upper reservoir well (2) by using a shale gas two-layer development wellbore structure design method as described in any one of claims 1 to 3; A2. Lower the surface casing (11) of the lower reservoir well to a depth of H5, lower the technical casing (12) of the lower reservoir well to a depth of H4, drill the lower reservoir horizontal section, lower the oil layer casing (13) of the lower reservoir well (1) throughout the entire section, control the cement return height (14) of the oil layer casing of the lower reservoir well to a depth of H3, cement and construct the wellbore of the lower reservoir well (1), and develop the lower reservoir; A3. After the gas production in the lower reservoir is completed, the section of the lower reservoir well oil layer casing (13) that is not cemented above the H3 depth is removed, and the window opening whipstock (23) of the upper reservoir well is lowered to the H3 depth. A window is opened and the upper reservoir horizontal section is side-drilled from the H1 depth position. The upper reservoir well oil layer casing (24) is lowered into the entire section of the upper reservoir well (2) and cemented to construct the wellbore of the upper reservoir well (2) and develop the upper reservoir.

5. A method for implementing a shale gas two-layer development wellbore structure according to claim 4, characterized in that: The lower reservoir and the upper reservoir are both developed by volume fracturing.

6. A method for implementing a shale gas two-layer development wellbore structure according to claim 4, characterized in that: The lower reservoir well (1) and the upper reservoir well (2) both adopt a depletion development method.

7. A method for implementing a shale gas two-layer development wellbore structure according to claim 4, characterized in that: The sizes of the surface casing (11) of the lower reservoir well, the technical casing (12) of the lower reservoir well, the oil layer casing (13) of the lower reservoir well, and the oil layer casing (24) of the upper reservoir well are all determined by referring to the drill bit casing size information of the adjacent construction well.

8. A method for implementing a shale gas two-layer development wellbore structure according to claim 4, characterized in that: The surface casing (11) of the lower reservoir well is cemented back to the ground.

9. A method for implementing a shale gas two-layer development wellbore structure according to claim 8, characterized in that: The technical casing (12) of the lower reservoir well is cemented back to the surface.

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