Hydraulic fracturing method for shale gas reservoirs based on flow field structure

Abstract

The present disclosure provides a shale gas reservoir hydraulic fracturing method based on flow field structure, comprising: forming a horizontal well along the minimum horizontal principal stress direction of the target reservoir; determining at least one drilling area of the first type of radial borehole, the drilling density and the drilling height of each drilling area according to the reservoir conditions of the target reservoir; determining the drilling point position, drilling angle and drilling distance of the second type of radial borehole according to the fracturing parameters and ground stress conditions of the horizontal well; forming the first type of radial borehole based on the determined drilling area, drilling density and drilling height of the first type of radial borehole; the first type of radial borehole extends along the direction perpendicular to the horizontal plane of the horizontal section wellbore of the horizontal well; forming the second type of radial borehole based on the determined drilling point position, drilling angle and drilling distance of the second type of radial borehole; and performing fracturing operation on the horizontal well. The method can expand the flow field volume, increase the effective development of the reservoir, optimize the flow field structure, and realize the efficient development of the shale gas reservoir.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of oil and gas well stimulation, and particularly relates to a shale gas reservoir hydraulic fracturing method based on flow field structure. BACKGROUND

[0002] The shale gas reservoir has obvious low porosity and low permeability characteristics, and has almost no commercial development value without reservoir fracturing reconstruction. The size of the reservoir reconstruction area and the complexity of the fracture formation in the reconstruction area are main factors affecting the development efficiency and ultimate recovery degree of the shale gas reservoir. According to the comprehensive development effect and the theoretical calculation result, the main producing range of the shale gas reservoir is limited in the gas reservoir range which is subjected to fracturing reconstruction. Therefore, how to expand the fracture reconstruction range is a key technical point of the shale gas reservoir hydraulic fracturing. SUMMARY

[0003] Embodiments of the present disclosure provide a shale gas reservoir hydraulic fracturing method based on flow field structure, so as to expand the flow field volume and increase the effective production of the reservoir, thereby realizing efficient development of the shale gas reservoir.

[0004] Some embodiments of the present disclosure provide a shale gas reservoir hydraulic fracturing method based on flow field structure, which comprises:

[0005] forming a horizontal well along the direction of the minimum horizontal principal stress of the target reservoir;

[0006] determining at least one drilling area of the first type of radial drilling hole, the drilling density of each drilling area and the drilling height of each drilling area according to the reservoir conditions of the target reservoir;

[0007] determining the drilling point, the drilling angle and the drilling distance of the second type of radial drilling hole according to the fracturing parameters of the horizontal well and the ground stress condition;

[0008] forming the first type of radial drilling hole based on the determined at least one drilling area of the first type of radial drilling hole, the drilling density of each drilling area and the drilling height of each drilling area; the first type of radial drilling hole extends along the direction perpendicular to the horizontal section wellbore horizontal plane of the horizontal well;

[0009] forming the second type of radial drilling hole based on the determined drilling point, the drilling angle and the drilling distance of the second type of radial drilling hole;

[0010] performing fracturing operation on the horizontal well.

[0011] In some embodiments, determining at least one drilling area of the first type of radial drilling hole according to the reservoir conditions of the target reservoir comprises:

[0012] According to the total organic carbon content, effective porosity, brittleness index and total gas content of the target reservoir, the target reservoir is divided into a first type reservoir, a second type reservoir and a third type reservoir;

[0013] The first type reservoir and the second type reservoir are combined, and a region in the combined reservoir that satisfies a first preset condition for reservoir thickness is determined as a drilling region of a first type radial well.

[0014] In some embodiments, the first type reservoir satisfies the following conditions:

[0015] The first type reservoir satisfies the following conditions: total organic carbon content ≥ 3%, effective porosity ≥ 5%, brittleness index ≥ 55% and total gas content ≥ 3m 3 / t;

[0016] The second type reservoir satisfies the following conditions: total organic carbon content 2-3%, effective porosity 3-5%, brittleness index 45-55% and total gas content 2-3m 3 / t;

[0017] The third type reservoir satisfies the following conditions: total organic carbon content 1-2%, effective porosity 2-3%, brittleness index 30-45% and total gas content 1-2m 3 / t.

[0018] In some embodiments, the first preset condition is:

[0019] H p ≥ 1.5H(x)

[0020] wherein H p is the reservoir thickness, m;

[0021] The fracture extension height H(x) is obtained by integrating the following formula:

[0022]

[0023]

[0024] In the formula, p f is the fluid pressure in the fracture, Pa;

[0025] g is the acceleration of gravity;

[0026] S1 is the minimum horizontal principal stress of the reservoir, Pa;

[0027] S2 is the maximum horizontal principal stress of the reservoir, Pa;

[0028] H(x) is the fracture height at any position in the length direction of the fracture, m;

[0029] K ICThe critical value of stress intensity factor, i.e. fracture toughness, can be calculated by petrophysical parameters, Pa.m 1 / 2 ;

[0030] E is the elastic modulus of shale rock, GPa;

[0031] μ is the Poisson's ratio of shale rock, dimensionless;

[0032] γ is the specific surface energy of shale rock, N / m.

[0033] In some embodiments, the drilling density in any drilling area is determined according to the following formula:

[0034]

[0035] In the formula, n is the drilling density;

[0036] L w is the horizontal well length, m;

[0037] m f is the number of fracturing sections;

[0038] L di is the length of the i-th drilling area.

[0039] In some embodiments, the drilling height in any drilling area is determined according to the following formula:

[0040]

[0041] In the formula, S3 is the vertical principal stress of the reservoir, Pa.

[0042] In some embodiments, the drilling point of the second type of radial drilling is determined, including: determining the starting position of the drilling section of the second type of radial drilling along the wellbore direction of the horizontal well according to the fracturing parameters of the horizontal well;

[0043] wherein the fracturing parameters include the fracturing perforation section position coordinates, the number of perforation clusters, the single cluster perforation length and the perforation cluster spacing; and the starting position is determined according to the following formula:

[0044]

[0045] In the formula, x i is the relative starting position of the drilling of the i-th fracturing section along the wellbore direction of the horizontal well;

[0046] r i is the position coordinate of the i-th fracturing section closest to the well site along the wellbore direction;

[0047] L ci is the perforation cluster spacing of the i-th fracturing section, m;

[0048] L b is the perforation cluster length, m;

[0049] n i is the number of perforation clusters of the i-th fracturing section.

[0050] In some embodiments, the drilling distance is determined according to the following formula:

[0051]

[0052] wherein: L i is the drilling distance of the i-th fracturing section, m.

[0053] In some embodiments, the drilling angle is determined according to the following formula:

[0054]

[0055] wherein: θ is the drilling angle, representing the included angle between the horizontal wellbore extension direction and the drilling direction;

[0056] S1 is the horizontal minimum principal stress of the reservoir, MPa;

[0057] S2 is the horizontal maximum principal stress of the reservoir, MPa;

[0058] S3 is the vertical principal stress of the reservoir, MPa.

[0059] In some embodiments, the fracturing operation is performed on the horizontal well, comprising:

[0060] The first type of radial borehole is subjected to separate independent fracturing operation, and the second type of radial borehole is directly subjected to fracturing operation.

[0061] Some embodiments of the present disclosure provide a shale gas reservoir hydraulic fracturing method based on flow field structure. According to the reservoir conditions of the target reservoir, the fracturing parameters of the horizontal well and the ground stress conditions, the drilling area (drilling point) suitable for the first type of radial drilling and the second type of radial drilling is screened out, and the drilling density and drilling height of the first type of radial drilling are optimized, and the drilling angle and drilling distance of the second type of radial drilling are optimized. On the basis of the conventional horizontal well fracturing mode, by setting the first type of radial drilling and the second type of radial drilling, the flow field volume is expanded and the effective reservoir production is increased, thereby solving the technical problems of serious energy dissipation and limited flow field range of the conventional horizontal well fracturing, and realizing efficient development of the shale gas reservoir. The first type of radial drilling is drilled in the direction of the formation perpendicular to the horizontal plane of the horizontal section of the horizontal well, which can extend the volume reconstruction range and achieve the effect of deep acidification and directional fracturing. The second type of radial drilling is drilled in the direction at a certain angle with the horizontal well, which can change the stress conditions of the reservoir and increase the complexity of the fracture network in the main reconstruction range. At the same time, different fracturing modes are adopted for different drilling forms, so that the fracture network structure formed by the first type of radial drilling and the second type of radial drilling is superimposed to form a more complex fracture network structure. The composite fracture network can expand the flow field area and enhance the flow field spreading effect, and can optimize the flow field structure of the shale gas reservoir, thereby improving the production capacity and further improving the recovery of the reservoir. BRIEF DESCRIPTION OF DRAWINGS

[0062] The accompanying drawings illustrate exemplary embodiments of the present disclosure, and together with the general description given above, and the detailed description given below, serve to explain the principles of the present disclosure. These drawings are included herewith and constitute a part of this specification.

[0063] Figure 1 It is a schematic diagram of the multi-stage fracturing horizontal well fracture network form and flow field structure in the related art.

[0064] Figure 2 It is a schematic diagram of the composite fracture network form and flow field structure formed by a shale gas reservoir hydraulic fracturing method based on flow field structure according to some embodiments.

[0065] Figure 3 It is a stratigraphic section of a certain block in Sichuan Basin.

[0066] Figure 4 It is a production curve comparison diagram of the composite fracture network formed by the embodiments of the present disclosure and the conventional fracture network. DETAILED DESCRIPTION

[0067] The present disclosure will be described in further detail below with reference to the drawings and embodiments. It can be understood that the specific embodiments described herein are only intended to explain the relevant content and are not intended to limit the present disclosure. In addition, it should be noted that only parts related to the present disclosure are shown in the drawings for ease of description.

[0068] It should be noted that the embodiments and features in the present disclosure can be combined with each other without conflict. The present disclosure will be described in further detail below with reference to the drawings and embodiments.

[0069] In the related art, the direction of the horizontal well is generally drilled along the direction of the minimum horizontal principal stress, so as to form a planar fracture perpendicular to the wellbore direction in the fracturing process, and to expand the fracture volume as much as possible. However, due to the strong ground stress and the large difference between the horizontal stresses, hydraulic energy is easily dissipated seriously, the range of the reconstruction is limited, and the fracture mode formed is simple, which further leads to a small flow field control area and a single flow field structure of the shale gas reservoir, and most of the regions cannot be effectively developed. At the same time, the multi-stage fracturing horizontal well technology is mainly used for the construction of the "double sweet spot" region of the geological sweet spot and the engineering sweet spot, and the regions adjacent to the region with poor gas-bearing property are usually not developed due to the poor economic benefits of the infill horizontal well.

[0070] Therefore, the core of the development of the shale gas reservoir and other ultra-low permeability oil and gas reservoirs is the formation of an effective fracture network, and the multi-stage fracturing technology of the horizontal well in the related art has the defects of limited reconstruction range and simple fracture structure in the reconstruction range, which leads to a single flow field structure. As shown in FIG. 1, after the conventional horizontal well multi-stage fracturing design and construction, the flow field formed has a limited sweep range and loose flow lines. Figure 1

[0071] Based on this, the present disclosure proposes a shale gas reservoir hydraulic fracturing method based on a flow field structure, selects reasonable drilling points according to the reservoir conditions and the fracturing design scheme, and optimizes the drilling angle, height and other schemes. Different fracturing modes are used for different drilling forms, which can expand the flow field area and enhance the flow field sweep effect.

[0072] It should be noted that the target reservoir refers to a reservoir in which the first type of radial drilling operation and / or the second type of radial drilling operation mentioned in the present disclosure are required, and there can be multiple horizontal wells in the target reservoir. The application object of the method of the present disclosure is a single horizontal well, and the first type of radial drilling and the second type of radial drilling are both drilling on the well wall of the horizontal section wellbore of the horizontal well.

[0073] Some embodiments of the present disclosure provide a shale gas reservoir hydraulic fracturing method based on a flow field structure, which includes S1-S6.

[0074] S1, forming a horizontal well along the direction of the minimum horizontal principal stress of the target reservoir.​

[0075] After drilling a horizontal well along the direction of the minimum horizontal principal stress, hydraulic fracturing is performed to reduce the resistance during the opening and extending of the fractures, so as to reduce the complex fracture friction, increase the net pressure at the far end of the fracture, and communicate the secondary fractures far from the well.

[0076] S2, determining at least one drilling area of the first type of radial drilling hole, a drilling density of each drilling area, and a drilling height of each drilling area according to reservoir conditions of the target reservoir.

[0077] Here, the target reservoir generally refers to one reservoir or an overall body composed of multiple small layers with small variation ranges. The reservoir conditions include reservoir thickness, gas content, porosity (Ⅱ type reservoir standard), etc. Specifically, the reservoir conditions can be total organic carbon content, effective porosity, brittleness index, and total gas content of the target reservoir. The reservoir condition data of the target reservoir can be obtained through microseismic interpretation data, well logging interpretation data, and indoor core testing.

[0078] In some embodiments, the target reservoir can be determined to be three classifications according to the classification of the shale gas reservoir according to the reservoir conditions of the target reservoir, and the classification standards are shown in Table 1.

[0079] Table 1

[0080]

[0081] In some embodiments, at least one drilling area of the first type of radial drilling hole is determined according to the reservoir conditions of the target reservoir, including:

[0082] According to the total organic carbon content, effective porosity, brittleness index, and total gas content of the target reservoir, the target reservoir is divided into a Ⅰ type reservoir, a Ⅱ type reservoir, and a Ⅲ type reservoir;

[0083] The Ⅰ type reservoir and the Ⅱ type reservoir are combined, and a region in the combined reservoir with a reservoir thickness satisfying a first preset condition is determined as a drilling area of the first type of radial drilling hole.

[0084] In some embodiments, the first preset condition is:

[0085] H p ≥1.5H(x)

[0086] wherein H p is the reservoir thickness, m;

[0087] The fracture extension height H(x) is obtained by integrating the following formula:

[0088]

[0089]

[0090] wherein p f is the fluid pressure in the fracture, Pa;

[0091] g is the acceleration of gravity;

[0092] S1 is the minimum horizontal principal stress of the reservoir, Pa;

[0093] S2 is the maximum horizontal principal stress of the reservoir, Pa;

[0094] H(x) is the height of the fracture at any position along the length of the fracture, m;

[0095] K IC is the critical value of the stress intensity factor, i.e., the fracture toughness, which can be calculated by rock physics parameters, Pa-m 1 / 2 ;

[0096] E is the elastic modulus of the shale rock, GPa;

[0097] μ is the Poisson's ratio of the shale rock, dimensionless;

[0098] γ is the specific surface energy of the shale rock, N / m.

[0099] In some embodiments, the drilling density in any drilling region is determined according to the following formula:

[0100]

[0101] wherein n is the drilling density;

[0102] L w is the length of the horizontal well, m;

[0103] m f is the number of fracturing sections;

[0104] L di is the length of the i-th drilling region.

[0105] It should be noted that the drilling density refers to the number of drilled holes on the wall surface of the horizontal well in the drilling region, which refers to the linear density here.

[0106] In some embodiments, the drilling height in any drilling region is determined according to the following formula:

[0107]

[0108] wherein S3 is the vertical principal stress of the reservoir, Pa.

[0109] For the first type of radial drilling, since the main direction of the drilling is drilling into the formation in the direction perpendicular to the horizontal plane of the horizontal section of the wellbore, the first type of radial drilling can extend the volume of the reformation range, and achieve the effect of deep acidizing and directional fracturing.

[0110] S3, determining the drilling point, drilling angle and drilling distance of the second type of radial drilling according to the fracturing parameters of the horizontal well and the ground stress condition.

[0111] Here, the fracturing parameters of the horizontal well can be obtained from the fracturing design scheme. The fracturing parameters include the position coordinates of the fracturing perforation section, the number of perforation clusters, the length of a single perforation cluster and the perforation cluster spacing, etc. The ground stress condition includes the minimum horizontal principal stress of the reservoir, the maximum horizontal principal stress of the reservoir and the vertical principal stress of the reservoir.

[0112] The second type of radial drilling refers to drilling near the fracturing section to form a more complex fracture network condition in the formation.

[0113] In some embodiments, the drilling point of the second type of radial drilling is determined, including: determining the starting position of the drilling section of the second type of radial drilling along the wellbore direction of the horizontal well according to the fracturing parameters of the horizontal well.

[0114] The starting position is determined according to the following formula:

[0115]

[0116] In the formula, x i is the relative starting position of the drilling of the i-th fracturing section along the wellbore direction of the horizontal well (with the starting position of the horizontal section as the origin and the extension direction of the horizontal well as the x-axis);

[0117] r i is the position coordinate of the i-th fracturing section closest to the well site along the wellbore direction;

[0118] L ci is the perforation cluster spacing of the i-th fracturing section, m;

[0119] L b is the length of the perforation cluster, m;

[0120] n i is the number of perforation clusters of the i-th fracturing section.

[0121] In some embodiments, the drilling distance is determined according to the following formula:

[0122]

[0123] In the formula, L i is the drilling distance of the drilling of the i-th fracturing section, m.

[0124] In some embodiments, the drilling angle is determined according to the following formula:

[0125]

[0126] wherein θ is the drilling angle, representing the angle between the horizontal wellbore extension direction and the drilling direction;

[0127] S1 is the horizontal minimum principal stress of the reservoir, MPa;

[0128] S2 is the horizontal maximum principal stress of the reservoir, MPa;

[0129] S3 is the vertical principal stress of the reservoir, MPa.

[0130] For the second type of radial borehole, the main direction of the radial borehole is the drilling direction at a certain angle with the horizontal wellbore, and the second type of radial borehole can change the stress condition of the reservoir and increase the complexity of the fracture network in the main reconstruction range.

[0131] S4, forming the first type of radial borehole based on the determined at least one borehole region of the first type of radial borehole, the drilling density of each borehole region, and the drilling height of each borehole region; the first type of radial borehole extends in a direction perpendicular to the horizontal plane of the horizontal section wellbore of the horizontal well.

[0132] S5, forming the second type of radial borehole based on the determined drilling point position, drilling angle, and drilling distance of the second type of radial borehole.

[0133] S6, performing a fracturing operation on the horizontal well.

[0134] In some embodiments, the fracturing operation on the horizontal well includes:

[0135] The first type of radial borehole is subjected to separate independent fracturing operation, and the second type of radial borehole is directly subjected to fracturing operation.

[0136] For example, when performing the fracturing operation on the horizontal well, a fracturing tool can be lowered into the wellbore, and the fracturing is performed according to the fracturing design scheme, wherein the first type of radial borehole is subjected to separate independent fracturing operation, and a bridge plug, a packer, or other process means is used to perform segmented independent fracturing in the specified region. The second type of radial borehole is directly subjected to fracturing operation. The sequence of fracturing can be determined according to the distance from the vertical wellbore of the horizontal well, and the fracturing is performed from the far end (far from the vertical wellbore) first, and then gradually towards the near end.

[0137] The fracture network formed after fracturing is as shown in Figure 2 Compared with the conventional multi-stage fracturing horizontal well fracture network Figure 1 It can be seen that it significantly increases the reservoir producing degree and the fracture network complexity.

[0138] Some embodiments of the present disclosure provide a shale gas reservoir hydraulic fracturing method based on flow field structure. According to the reservoir conditions of the target reservoir, the fracturing parameters of the horizontal well and the ground stress conditions, drilling regions (drilling points) suitable for first type radial drilling and second type radial drilling are screened out, and the drilling density and drilling height of the first type radial drilling are optimized, and the drilling angle and drilling distance of the second type radial drilling are optimized. On the basis of the conventional horizontal well fracturing mode, by setting the first type radial drilling and the second type radial drilling, the flow field volume is expanded and the effective reservoir production is increased, thereby solving the technical problems of serious energy dissipation and limited flow field range of the conventional horizontal well fracturing, and achieving efficient development of the shale gas reservoir. The first type radial drilling is drilled in the direction of the formation perpendicular to the horizontal plane of the horizontal section of the horizontal well, which can extend the volume reconstruction range and achieve the effect of deep acidification and directional fracturing. The second type radial drilling is drilled in the direction at a certain angle with the horizontal well, which can change the stress conditions of the reservoir and increase the complexity of the fracture network in the main reconstruction range. At the same time, different fracturing modes are adopted for different drilling forms, so that the fracture network structure formed by the first type radial drilling and the second type radial drilling is superimposed to form a more complex fracture network structure. The composite fracture network can expand the flow field area and enhance the flow field spreading effect, and the composite fracture network can optimize the flow field structure of the shale gas reservoir, thereby improving the productivity and further improving the recovery of the reservoir.

[0139] The technical effects achieved by the technical solutions of the present disclosure are further illustrated below by taking a shale gas block in the Sichuan Basin as an example. The reservoir profile structure of the example block is shown in Figure 3 , and the shale gas reservoir hydraulic fracturing method based on flow field structure of the present disclosure is used for fracturing construction. The original length of the wellbore is 1500m, and 20 sections are fractured. Finally, 5 first type radial drilling points and 20 second type radial drilling points are determined, the average drilling distance is 75m, and the average drilling angle is 39°.

[0140] The physical modeling is performed on the scheme using the shale gas reservoir hydraulic fracturing method based on flow field structure of the present disclosure and the scheme using the conventional reservoir fracturing method, and the production results are compared by using numerical simulation technology. Under the condition of simulating production for 500 days, the conventional bottom hole flowing pressure is depleted. The result comparison curve is shown in Figure 4 . It can be seen that the daily gas production of the composite fracture network formed by the method of the present disclosure is obviously higher than that of the traditional fracturing mode, the daily water production changes little, the effective improvement of the reservoir production degree is achieved, and the effect of improving the recovery of the shale gas reservoir is achieved.

[0141] In the description of the specification, the description of the terms "one embodiment / way", "some embodiments / ways", "example", "specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment / way or example are included in at least one embodiment / way or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment / way or example. Also, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments / ways or examples. In addition, the person skilled in the art can combine and combine the different embodiments / ways or examples described in the specification and the features of the different embodiments / ways or examples, without contradiction.

[0142] In addition, the terms "first", "second" are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include at least one of the features. In the description of the present disclosure, the meaning of "a plurality of" is at least two, for example, two, three, etc., unless otherwise explicitly specified. "And / or" is only to describe the relationship between the associated objects, which means three relationships, for example, A and / or B, which means: A exists alone, A and B exist together, and B exists alone.

[0143] The person skilled in the art should understand that the above-mentioned embodiments are only for clearly illustrating the present disclosure, and are not intended to limit the scope of the present disclosure. Based on the above disclosure, other changes or modifications can also be made by those skilled in the art, and these changes or modifications are still within the scope of the present disclosure.

Claims

1. A hydraulic fracturing method for shale gas reservoirs based on flow field structure, characterized in that, The method includes: A horizontal well is formed along the direction of the minimum horizontal principal stress of the target reservoir; Based on the reservoir conditions of the target reservoir, determine at least one borehole region of the first type of radial borehole, the borehole density of each borehole region, and the borehole height of each borehole region; Based on the fracturing parameters and geostress conditions of the horizontal well, determine the drilling location, drilling angle, and drilling distance of the second type of radial borehole; The first type of radial borehole is formed based on at least one borehole region of the first type of radial borehole, the borehole density of each borehole region, and the borehole height of each borehole region; the first type of radial borehole extends along the horizontal plane of the horizontal section of the wellbore perpendicular to the horizontal plane of the horizontal well. Based on the determined drilling points, drilling angles, and drilling distances of the second type of radial borehole, the second type of radial borehole is formed, and the second type of radial borehole is drilled along a direction at a certain angle to the horizontal wellbore; The horizontal well was subjected to fracturing operations; The drilling angle is determined according to the following formula: In the formula: The drilling angle represents the angle between the extension direction of the horizontal wellbore and the drilling direction. S 1 represents the minimum horizontal principal stress of the reservoir, in MPa; S 2 represents the maximum horizontal principal stress in the reservoir, in MPa; S 3 represents the vertical principal stress of the reservoir, in MPa.

2. The hydraulic fracturing method for shale gas reservoirs based on flow field structure according to claim 1, characterized in that, Based on the reservoir conditions of the target reservoir, at least one borehole region for the first type of radial borehole is determined, including: Based on the total organic carbon content, effective porosity, brittleness index, and total gas content of the target reservoir, the target reservoir is divided into Class I, Class II, and Class III reservoirs. The Class I reservoir and the Class II reservoir are merged, and the area in the merged reservoir whose reservoir thickness meets the first preset condition is determined as the drilling area of ​​the first type of radial borehole.

3. The hydraulic fracturing method for shale gas reservoirs based on flow field structure according to claim 2, characterized in that, The Class I reservoirs must meet the following conditions: total organic carbon content ≥3%, effective porosity ≥5%, brittleness index ≥55%, and total gas content ≥3m³. 3 / t; The Class II reservoirs must meet the following conditions: total organic carbon content 2-3%, effective porosity 3-5%, brittleness index 45-55%, and total gas content 2-3 m³ / s. 3 / t; The Class III reservoirs must meet the following conditions: total organic carbon content 1-2%, effective porosity 2-3%, brittleness index 30-45%, and total gas content 1-2 m³. 3 / t.

4. The hydraulic fracturing method for shale gas reservoirs based on flow field structure according to claim 2, characterized in that, The first preset condition is: in, Let be the reservoir thickness, in meters (m). Crack extension height By integrating the following equation, we obtain: In the formula: p f The fluid pressure within the crack is expressed in Pa. The fluid density within the crack; g is the acceleration due to gravity; S 1 represents the minimum horizontal principal stress of the reservoir, in Pa; S 2 represents the maximum horizontal principal stress of the reservoir, in Pa; H(x) Let be the crack height at any position along the crack length direction, in meters (m). K IC The critical value of the stress intensity factor, i.e., fracture toughness, can be calculated from rock physical parameters, in Pa·m. 1 / 2 ; E The elastic modulus of shale rock, in GPa; μ Poisson's ratio for shale rock, dimensionless; γ is the specific surface energy of shale rock, N / m.

5. The hydraulic fracturing method for shale gas reservoirs based on flow field structure according to any one of claims 1 to 4, characterized in that, The borehole density within any borehole region is determined according to the following formula: In the formula: n Drilling density; L w The length of the horizontal well is in meters (m). m f This refers to the number of fracturing stages; L di For the first i The length of each borehole area.

6. The hydraulic fracturing method for shale gas reservoirs based on flow field structure according to claim 4, characterized in that, The borehole height within any borehole area is determined according to the following formula: In the formula: S 3 represents the vertical principal stress of the reservoir, in Pa.

7. The hydraulic fracturing method for shale gas reservoirs based on flow field structure according to claim 1, characterized in that, Performing fracturing operations on the horizontal well includes: Separate and independent fracturing operations are performed on the first type of radial boreholes, while fracturing operations are performed directly on the second type of radial boreholes.

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