Shallow shale gas reservoir cluster well group limit production well pattern structure

Abstract

The present application relates to a kind of shallow shale gas reservoir cluster well group limit well network structure, including double-row horizontal well in the ground preset well site, each row of horizontal well includes nine horizontal wells sequentially arranged according to numerical designation order, one row of horizontal well is inclined downward based on horizontal plane, and is provided with horizontal section along shale reservoir surface Ra, another row of horizontal well is inclined upward based on horizontal plane, and is provided with horizontal section along shale reservoir surface Rb, shale reservoir surface Ra and shale reservoir surface Rb are all optimal quality reservoir in the inside of shale gas reservoir development section R, shale reservoir surface Ra, shale reservoir surface Rb and gas reservoir development section R are parallel, and with horizontal plane, formation dip angle is arranged.Compared with prior art, the present application has the advantages of easy drilling, small construction difficulty, low drilling cost and the like.

Description

Technical Field

[0001] This invention relates to the field of shale gas reservoir development technology, and in particular to a cluster well network structure for the ultimate utilization of shallow shale gas reservoirs. Background Technology

[0002] Shale gas reservoirs are unconventional gas reservoirs with extremely low permeability. Their inherent seepage capacity is extremely low, making natural production impossible. Artificial fracturing technology is required to break up the reservoir and create artificial fractures to obtain industrial gas flow. Currently, multi-stage hydraulic volumetric fracturing is commonly used. Lateral hydraulic fractures extend along the direction of the minimum horizontal principal stress of the main rock, exhibiting a "star" shape. The main fracture extends horizontally along the vertical section of the reservoir surface, with a fracture length of approximately 300m. Longitudinal fractures extend vertically upwards and downwards along the vertical reservoir surface. The maximum fracture height at the vertical perforation point is approximately 30m, decreasing rapidly to the sides, with an average fracture height of 10m. Shallow shale gas reservoirs specifically refer to shale gas reservoirs with target layer depths of 600-1500m. Compared to medium-deep shale gas reservoirs (greater than 2000m), shallow shale gas reservoirs are characterized by lower development costs.

[0003] In existing technologies, the horizontal well network structure of shallow shale gas reservoirs typically adopts a single-row (well numbers: W1 / W2 / W3 / W4) or double-row (W1 / W2 / W3 / W4 / W5 / W6 / W7 / W8) cluster horizontal well network structure (e.g.) Figure 1 As shown), the length of the horizontal sections (C1 / C2 / C3 / C4 / C5 / C6 / C7 / C8) is uniformly 1000m, the planar projection distance l between adjacent horizontal sections in the same row is 350m, the distance L between row A and row B is 700m, the horizontal section targets are located within the same high-quality shale section (Ra), and the length F of the artificially inflated fracture is 300m (see attached). Figure 1 ).

[0004] However, existing single-row or double-row horizontal well network structures have many areas where reserves cannot be utilized. For example: 1. When the thickness of high-quality reservoirs in the vertical direction is large, exceeding the vertical extension height of artificial fractures, existing horizontal well network structures can only utilize reserves within an average range of 10m in the vertical direction, resulting in low vertical reserve utilization; 2. Under the existing 350m well spacing, there is a 50m wide area of ​​high-quality reserves between horizontal sections that cannot be utilized; 3. There is a 700m wide area of ​​high-quality reserves between double-row wells that cannot be utilized; 4. Existing technologies do not consider the impact of formation dip angle on drilling difficulty, and in actual implementation, there are differences in drilling difficulty between up-dip and down-dip wells. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a cluster well network structure for the ultimate utilization of shallow shale gas reservoirs. This structure can improve the utilization of shallow shale gas reservoir reserves and reduce the difficulty of drilling operations.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A cluster-type well network structure for the ultimate utilization of shallow shale gas reservoirs includes two rows of horizontal wellheads located within a pre-designated well site on the surface. Each row of horizontal wells comprises nine horizontal wells arranged in numerical order (well numbers 1 / 2 / 3 / 4 / 5 / 6 / 7 / 8 / 9 / 10 / 11 / 12 / 13 / 14 / 15 / 16 / 17 / 18).

[0008] Both the Ra shale reservoir section and the Rb shale reservoir section are located inside the R shale reservoir. The R shale reservoir is 33m thick, the Ra reservoir section is 2m thick, the bottom of the Ra reservoir section is 4m from the bottom of the R reservoir section, the Rb reservoir section is 2m thick, the top of the Rb reservoir section is 15m from the top of the R reservoir section, and the bottom of the Rb reservoir section is 10m from the top of the Ra reservoir section.

[0009] The Ra reservoir layer, Rb reservoir layer, and R shale reservoir layer are parallel to each other and form an angle α with the horizontal plane, i.e., the dip angle of the formation, preferably 5~20°.

[0010] Each horizontal well numbered 1 / 3 / 5 / has a first horizontal section L1 set along the Ra reservoir section.

[0011] Each horizontal well numbered 2 / 4 has a second horizontal section L2 set along the Rb reservoir section.

[0012] Each horizontal well, numbered 6 / 8 / 10, has a third horizontal section L3 set along the Ra reservoir section.

[0013] Each horizontal well numbered 7 / 9 has a fourth horizontal section L4 set along the Rb reservoir section.

[0014] Each horizontal well numbered 12 / 14 / 15 / 17 has a fifth horizontal section L5 set along the Ra reservoir section.

[0015] Each of the horizontal wells numbered 11 / 13 / 16 / 18 has a sixth horizontal section L6 set along the Rb reservoir section.

[0016] Specifically, each of the following conditions applies: The length of each first-order pressure fracture F1 connected within L1 is less than or equal to 300m in the vertical-horizontal direction along the Ra shale reservoir surface; the length of each second-order pressure fracture F2 connected within L2 is less than or equal to 300m in the vertical-horizontal direction along the Rb shale reservoir surface; the length of each third-order pressure fracture F3 connected within L3 is less than or equal to 300m in the vertical-horizontal direction along the Ra shale reservoir surface; the length of each fourth-order pressure fracture F4 connected within L4 is less than or equal to 300m in the vertical-horizontal direction along the Rb shale reservoir surface; the length of each fifth-order pressure fracture F5 connected within L5 is less than or equal to 300m in the vertical-horizontal direction along the Ra shale reservoir surface; and the length of each sixth-order pressure fracture F6 connected within L6 is less than or equal to 300m in the vertical-horizontal direction along the Rb shale reservoir surface.

[0017] The orientation of the horizontal section of each of the above-mentioned horizontal wells is nearly perpendicular to the direction of the minimum principal stress of the reservoir.

[0018] Furthermore, the average height of the fracturing fractures extending in the direction perpendicular to the Ra reservoir surface of F1 / F3 / F5 is less than the vertical height difference between the bottom of the R reservoir and the bottom of the Rb reservoir, and the average height of the fracturing fractures extending in the direction perpendicular to the Rb reservoir surface of F2 / F4 / F6 is less than the vertical height difference between the top of the R reservoir and the top of the Ra reservoir.

[0019] In one possible implementation, the length H of the pre-set well site on the ground ranges from 100 to 150 m, and the width K ranges from 80 to 140 m.

[0020] In one possible implementation, the ground distance between any two adjacent horizontal wellheads in the same row ranges from 5 to 10 meters.

[0021] In one possible implementation, the distance between the wellheads of two adjacent rows of horizontal wells is 30m.

[0022] In one possible implementation, the horizontal projection distance l1 between any two adjacent wells located in different reservoir sections within the same row is 250m. For example, the horizontal projection distance between the horizontal segment of well number 1 and the horizontal segment of well number 2 is 250m. The horizontal projection distance between the horizontal segment of well number 2 and the horizontal segment of well number 3 is also 250m, and so on. The horizontal projection distance l2 between any two adjacent wells located in the same reservoir within the same row is 500m. For example, the horizontal projection distance between the horizontal segment of well number 1 and the horizontal segment of well number 3 is 500m. The horizontal projection distance between the horizontal segment of well number 2 and the horizontal segment of well number 4 is also 500m, and so on.

[0023] In one possible implementation, the length of the horizontal segment L1 set along the downdip direction of the Ra reservoir is greater than the length of the horizontal segment L3 set along the updip direction of the Ra reservoir.

[0024] In one possible implementation, the length of the horizontal segment L2 set along the downdip direction of the Rb reservoir is greater than the length of the horizontal segment L4 set along the updip direction of the Rb reservoir.

[0025] In one possible implementation, the length of horizontal segment L5 along reservoir R is equal to the length of horizontal segment L6.

[0026] In one possible implementation, the length of the horizontal segment L1 set along the downdip direction of the Ra reservoir or the length of the horizontal segment L2 set along the downdip direction of the Rb reservoir is 1200m.

[0027] In one possible implementation, the length of the horizontal segment L3 set along the updip direction of the Ra reservoir or the length of the horizontal segment L4 set along the updip direction of the Rb reservoir is 1000m.

[0028] In one possible implementation, the length of the horizontal segment L5, which is set along the updip and / or downdip direction of the Ra reservoir, is 300m.

[0029] In one possible implementation, the length of the horizontal segment L6, which is set along the updip and / or downdip direction of the Rb reservoir, is 300m.

[0030] In one possible implementation, each horizontal segment L1 / L2 / L3 / L4 / L5 / L6 is divided into multiple sub-segments, and the length of each sub-segment ranges from 80 to 100m.

[0031] In one possible implementation, each sub-segment is provided with multiple perforation clusters, and the distance between any two adjacent perforation clusters is in the range of 10 to 15 m.

[0032] In one possible implementation, the length of each perforation cluster is in the range of 0.5m.

[0033] In one possible implementation, each perforation cluster has 3 to 5 perforations.

[0034] In one possible implementation, the sub-segments and perforation clusters within each adjacent horizontal segment are staggered.

[0035] Furthermore, the maximum height of the hydraulic fracture formed at each perforation cluster within the horizontal segment L1 / L2 / L3 / L4 is about 30m. The half-fracture height within a radius of 60m from the perforation cluster exceeds the vertical height of the Ra reservoir surface and the Rb reservoir surface. Further outward, the fracture height decreases, and the hydraulic fracture terminates at a radius of about 150m. The average fracture height is about 10m, and the average fracture length is 300m.

[0036] The shallow shale gas reservoir cluster well network structure provided by this invention has at least the following advantages compared to existing technologies:

[0037] 1) This invention adopts a double-row horizontal wellhead located in a pre-designated well site on the ground. Each row of horizontal wells has a downdip direction and an updip direction. Each horizontal well is set with a horizontal section along the shale reservoir to form a cluster well network structure. Compared with the well layout mode of single-row or double-row horizontal well groups commonly used in the prior art, drilling along the downdip direction of the shale reservoir is easier than drilling along the updip direction. The construction difficulty is small, the drilling cost is low, and the high-quality reserves in the area can be fully utilized as much as possible. It can maximize the utilization of planar reserves and avoid the interference between wells on the plane.

[0038] 2) The horizontal section of each well is divided into multiple sub-segments, and multiple perforation clusters are opened on each sub-segment. The height of the fracture half-fracture within the radius of the perforation cluster exceeds the vertical height of the reservoir surface. Further outward, the fracture height decreases. This can not only increase the effective utilization rate of the R shale reservoir between horizontal sections by more than 1 times, but also avoid the inter-well interference caused by fracturing.

[0039] 3) By setting up 8 horizontal wells with a horizontal section length of 300m within a range of L1 approximately 700 between the two rows of wells a, the horizontal sections of wells 11 / 13 / 16 / 18 are located within the Ra reservoir, and the horizontal sections of wells 12 / 14 / 15 / 17 are located within the Rb reservoir, which can add 1000m*600m area of ​​high-quality reserves for utilization.

[0040] 4) By setting the lengths of the L2 and L4 horizontal sections in the updip direction of the formation to be shorter than the lengths of the L1 and L3 horizontal sections in the downdip direction, the drilling difficulty in formations with high water-to-vertical ratio can be reduced, and the well can be completed smoothly. Attached Figure Description

[0041] Figure 1 A schematic diagram of the structure of the existing horizontal well network in shallow shale gas reservoirs;

[0042] Figure 2 A schematic diagram of a shallow shale gas reservoir cluster well network structure for ultimate dynamic operation, provided as an embodiment of the present invention.

[0043] Figure 3 This is a three-dimensional schematic diagram of a cluster well network structure for extreme operation in a shallow shale gas reservoir, provided as an embodiment of the present invention.

[0044] The numbers in the diagram are as follows:

[0045] W1~W8: Original shale gas horizontal well numbers;

[0046] C1~C8: Horizontal sections of the original shale gas horizontal wells;

[0047] l: Spacing between adjacent horizontal sections of the original well network structure;

[0048] L: Spacing between adjacent rows in the original well network structure;

[0049] F: Original well network structure fracture morphology;

[0050] 1~18: Well numbers for invented shale gas horizontal wells;

[0051] L1: Level 1;

[0052] L2: Second level segment;

[0053] L3: Third level segment;

[0054] L4: Level 4;

[0055] L5: Level 5;

[0056] L6: Level 6;

[0057] F1: First pressure crack;

[0058] F2: Second pressure crack;

[0059] F3: Third pressure crack;

[0060] F4: Fourth pressure crack;

[0061] F5: Fifth pressure crack;

[0062] F6: Sixth pressure crack;

[0063] l1: The spacing between adjacent horizontal sections within different reservoirs in the invention well network structure;

[0064] l2: Spacing between adjacent horizontal sections within the same reservoir in the invention well network structure;

[0065] L1: Spacing between adjacent rows in the invention well network structure;

[0066] α: Dip angle of the formation;

[0067] R: Overall shale reservoir development section;

[0068] Ra: Ra shale reservoir development section;

[0069] Rb: Rb shale reservoir development section;

[0070] a: Target point a in the horizontal segment;

[0071] b: Target point b in horizontal segment;

[0072] K: Pre-set well site width on the ground;

[0073] H: Preset well site length on the ground. Detailed Implementation

[0074] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0075] This invention provides a cluster-type large well group three-dimensional development well network structure that can improve the planar and vertical utilization of shallow shale gas reservoirs.

[0076] Before providing a further detailed description of the embodiments of the present invention, the technical terms used in the embodiments of the present invention, such as "updip direction," "downdip direction," "horizontal segment a target point," and "horizontal segment b target point," are merely used to clearly describe the ultimate operational well network structure of shallow shale gas reservoir cluster well groups in the embodiments of the present invention, and are not intended to limit the scope of protection of the present invention. It is understood that the formation depth increases in the downdip direction and decreases in the updip direction; the horizontal segment a target point refers to the depth at which the well trajectory begins to enter the target layer, and the horizontal segment b target point refers to the final completion depth.

[0077] Unless otherwise defined, all technical terms used in the embodiments of this invention have the same meaning as commonly understood by those skilled in the art.

[0078] To make the technical solutions and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0079] This invention relates to a cluster well network structure for extreme dynamism in shallow shale gas reservoirs, such as... Figure 2 , Figure 3 As shown, the well network structure includes two rows of horizontal wells located in a pre-designated well site on the ground. Each row of horizontal wells includes 9 horizontal wells, which are numbered in the following order: downdip direction: 1 / 11 / 12 / 2 / 3 / 13 / 4 / 14 / 5, updip direction: 6 / 15 / 16 / 7 / 8 / 17 / 9 / 18 / 10.

[0080] Each horizontal well numbered 1 / 3 / 5 has a first horizontal section L1 along the Ra shale reservoir; each horizontal well numbered 2 / 4 has a second horizontal section L2 along the Rb shale reservoir; each horizontal well numbered 6 / 8 / 10 has a third horizontal section L3 along the Ra shale reservoir; each horizontal well numbered 7 / 9 has a fourth horizontal section L4 along the Rb shale reservoir; each horizontal well numbered 12 / 14 / 15 / 17 has a fifth horizontal section L5 along the Ra shale reservoir; and each horizontal well numbered 11 / 13 / 16 / 18 has a sixth horizontal section L6 along the Rb shale reservoir.

[0081] It is understandable that both the Ra and Rb shale reservoirs are the relatively highest-quality reservoirs within the R shale gas reservoir, which can be obtained through preliminary comprehensive geological evaluation. The Ra reservoir layer, Rb reservoir layer, and R shale reservoir layer are parallel to each other, forming an angle α with the horizontal plane, i.e., the dip angle, generally 5~20°. The Ra layer is 2m thick and serves as the target layer for L1 / L3 / L5, while the Rb layer is 2m thick and serves as the target layer for L2 / L4 / L6. R represents the entire high-quality shale development section, with a thickness of 33m. Simultaneously, the strike of L1 / L3 / L5 should be as close as possible to the direction of the minimum horizontal principal stress of Ra, and the strike of L2 / L4 / L6 should be as close as possible to the direction of the minimum horizontal principal stress of Rb. The directions of the minimum horizontal principal stresses of Ra and Rb can be obtained through geological evaluation.

[0082] Specifically, the first hydraulic fracture F1 formed by fracturing on the first horizontal segment L1 has a length of less than or equal to 300m along the Ra reservoir surface in the direction perpendicular to the horizontal segment L1; the second hydraulic fracture F2 formed by fracturing on the second horizontal segment L2 has a length of less than or equal to 300m along the Rb reservoir surface in the direction perpendicular to the horizontal segment L2; the third hydraulic fracture F3 formed by fracturing on the third horizontal segment L3 has a length of less than or equal to 300m along the Ra reservoir surface in the direction perpendicular to the horizontal segment L3; the fourth hydraulic fracture F4 formed by fracturing on the fourth horizontal segment L4 has a length of less than or equal to 300m along the Rb reservoir surface in the direction perpendicular to the horizontal segment L4; the fifth hydraulic fracture F5 formed by fracturing on the fifth horizontal segment L5 has a length of less than or equal to 300m along the Ra reservoir surface in the direction perpendicular to the horizontal segment L5; and the sixth hydraulic fracture F6 formed by fracturing on the sixth horizontal segment L6 has a length of less than or equal to 300m along the Rb reservoir surface in the direction perpendicular to the horizontal segment L6.

[0083] The average height of each F1 / F3 / F5 fracturing fracture extending in the direction perpendicular to the Ra reservoir surface is less than the vertical height difference between the bottom of the R reservoir and the bottom of the Rb reservoir. The average height of each F2 / F4 / F6 fracturing fracture extending in the direction perpendicular to the Rb reservoir surface is less than the vertical height difference between the top of the R reservoir and the top of the Ra reservoir.

[0084] Understandably, after all wells are drilled, the horizontal sections L1 / L2 / L3 / L4 / L5 / L6 of each well need to be fracturing and stimulated in stages to create artificial gas reservoirs, thus enabling the shale gas wells to produce gas industrially. Figure 2 , 3 The diagram shown illustrates the artificial fracture morphology formed by high-pressure hydraulic fracturing of the Ra and / or Rb shale reservoirs, specifically the 1st / 2nd / 3rd / 4th / 5th / 6th hydraulic fractures F1 / F2 / F3 / F4 / F5 / F6 extending within the Ra and / or Rb shale reservoirs. This is achieved through segmentation and perforation within each cluster, followed by fracturing of the formation.

[0085] After hydraulic fracturing, the artificial fracture network is distributed in a star shape within the reservoir. The main fracture extends horizontally along the vertical section of the reservoir surface, with a fracture length of about 300m. The longitudinal fractures extend vertically along the vertical direction of the reservoir surface, with the fractures extending up to about 30m at the vertical perforation point, and then rapidly decreasing in size to both sides, with an average fracture height of 10m.

[0086] To make the first fracturing fracture F1 clearly visible, in Figure 3 The first fracturing fracture F1 morphology was only shown at the end of the horizontal section L1 in wells 1 / 3 / 5; to clearly see the second fracturing fracture F2, in Figure 3 The second fracturing fracture, F2, was only observed at the end of the horizontal section L2 in the 2 / 4 section of the well; to clearly visualize the third fracturing fracture, F3, [fracturing was performed in...]. Figure 3 The third fracturing fracture, F3, was only observed at the end of the horizontal section L3 in well 10; to clearly visualize the fourth fracturing fracture, F4, [fracturing was performed in...]. Figure 3 The fourth fracturing fracture, F4, was only observed at the end of the horizontal section L4 in well 9; to clearly visualize the fifth fracturing fracture, F5, [fracturing was performed in...]. Figure 3 The fifth fracturing fracture, F5, was only observed at the end of the horizontal section L5 in well 14; to clearly visualize the sixth fracturing fracture, F6, [fracturing was performed in...]. Figure 3 The data shows that the sixth fracturing fracture, F6, was only observed at the end of the horizontal section L6 in Well 18. However, in actual production, multiple corresponding fracturing fractures F1 / F2 / F3 / F4 / F5 / F6 were designed on each horizontal section L1 / L2 / L3 / L4 / L5 / L6.

[0087] Furthermore, by setting up 8 horizontal wells with a horizontal section length of 300m within a range of approximately 800m between points a of the two rows of wells, as mentioned above, the horizontal sections of wells 11 / 13 / 16 / 18 are located within the Ra reservoir, and the horizontal sections of wells 12 / 14 / 15 / 17 are located within the Rb reservoir, an additional 1000m*600m area of ​​high-quality reserves can be utilized.

[0088] Furthermore, by setting the lengths of the L2 and L4 horizontal sections in the updip direction to be shorter than the lengths of the L1 and L3 horizontal sections in the downdip direction, the drilling difficulty in formations with high water-to-vertical ratio is reduced, and the well is successfully completed.

[0089] The following is a further description of the ultimate operational well network structure for shallow shale gas reservoir cluster well groups according to an embodiment of the present invention:

[0090] The selected surface well sites are determined based on a comprehensive assessment of both surface and subsurface conditions. Subsurface conditions require the development of a high-quality shale reservoir segment with a vertical extension greater than 30m. Within a 2km radius of this reservoir, a pre-selected surface well site is determined. The surface area should be a gently sloping region with a length of 100-150m and a width of 80-140m, with convenient transportation and sufficient water supply. In practice, the location of the pre-selected surface well site can be determined through field exploration.

[0091] In a pre-designed well site, the distance between the wellheads of any two adjacent horizontal wells within the same row ranges from 5 to 10 meters. The distance between the wellheads of two adjacent rows of horizontal wells is 30 meters, which is intended to facilitate on-site construction and minimize development costs.

[0092] L1 / L3 are located within the Ra high-quality reservoir section, and L2 / L4 are located within the Rb high-quality reservoir section. Both the Ra and Rb high-quality reservoirs are located within the R shale reservoir. The R shale reservoir is 33m thick, the Ra high-quality reservoir is 2m thick vertically, and the Rb high-quality reservoir is 2m thick vertically. The bottom of the a shale reservoir is 4m from the bottom of the R reservoir, the top of the b shale reservoir is 15m from the top of the R reservoir, and the bottom of the b shale reservoir is 10m from the top of the a reservoir.

[0093] Within the same row, any adjacent horizontal segments L1 and L2 are staggered, with a longitudinal offset of at least 12m, greater than the average fracture height of artificial fractures F1 and F2. Similarly, any adjacent horizontal segments L3 and L4 within the same row are staggered, with a longitudinal offset of at least 12m, greater than the average fracture height of artificial fractures F3 and F4. Likewise, any adjacent horizontal segments L5 and L6 within the same row are staggered, with a longitudinal offset of at least 12m, greater than the average fracture height of artificial fractures F5 and F6. This arrangement ensures full utilization of vertical reserves while avoiding the impact of vertical pressure channeling.

[0094] Furthermore, the horizontal projection distance between any two adjacent wells in different reservoir sections within the same row is set at 250m, and the horizontal projection distance between any two adjacent wells in the same reservoir section within the same row is set at 500m. Specifically: on the plane, the horizontal projection distance between any two adjacent wells L1 and L2, L3 and L4, L5 and L6 in different reservoir sections within the same row is 250m, and the horizontal projection distance between any two adjacent wells L1 and L1, L2 and L2, L3 and L3, L4 and L4, L5 and L5, L6 and L6 in the same reservoir section within the same row is 500m. This forms a horizontal projection distance of 250m between wells in adjacent reservoirs (Ra and Rb) and 500m between wells in the same reservoir (Ra or Rb), which can maximize the utilization of planar reserves while avoiding interference between wells on the plane.

[0095] Regarding the length settings for horizontal sections, the length of horizontal section L1 along the downdip direction of the Ra reservoir or the length of horizontal section L2 along the downdip direction of the Rb reservoir is 1200m. The length of horizontal section L3 along the updip direction of the Ra reservoir or the length of horizontal section L4 along the updip direction of the Rb reservoir is 1000m. The length of horizontal section L5 along the updip and / or downdip direction of the Ra reservoir is 300m. The length of horizontal section L6 along the updip and / or downdip direction of the Rb reservoir is 300m. This setting is because, during construction, drilling along the downdip direction of shale-developed reservoirs is easier than drilling along the updip direction, resulting in less construction difficulty and lower drilling costs.

[0096] Furthermore, in this embodiment, the horizontal sections (L1 / L2 / L3 / L4 / L5 / L6) of each well are divided into multiple sub-segments. The length of each sub-segment ranges from 80 to 100 m, and multiple perforation clusters are formed on each sub-segment. The distance between any two adjacent perforation clusters ranges from 10 to 15 m, the length of each perforation cluster ranges from 0.5 m, and there are 3 to 5 perforations within each perforation cluster. The sub-segments and perforation clusters within each adjacent horizontal section are staggered. Through the staggered distribution of sub-segments and perforation clusters within each adjacent horizontal section, the maximum fracture height formed at each perforation cluster is about 30 m. The fracture half-fracture height within a radius of 60 m from the perforation cluster exceeds the vertical height between the Ra shale reservoir surface and the Rb reservoir surface. Further outward, the fracture height decreases, and the fracture terminates at a radius of about 150 m, with an average fracture height of about 10 m. It can increase the effective utilization rate of R shale reservoirs between horizontal sections by more than 100%, and avoid the inter-well interference caused by fracturing.

[0097] The maximum height of the hydraulic fractures formed at each perforation cluster in the horizontal sections L1 and L2 is about 30m. The half-fracture height of the hydraulic fractures within a radius of 60m from the perforation cluster exceeds the vertical height of the Ra reservoir surface and the Rb reservoir surface. Further outward, the fracture height decreases and terminates at a radius of about 150m. The average fracture height is about 10m and the average fracture length is 300m.

[0098] In this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. The term "a plurality" refers to two or more unless otherwise expressly defined.

[0099] This invention employs a double-row horizontal wellhead located within a pre-designated well site on the surface. Each row of horizontal wells has both downdip and updip directions. Each horizontal well is arranged along a horizontal section of the shale reservoir to form a cluster-like well network structure. Compared to the commonly used single-row or double-row horizontal well group layout in existing technologies, drilling along the downdip direction of the shale reservoir is easier, less difficult, and less costly. It also allows for the full utilization of high-quality reserves within the affected area, maximizing the utilization of planar reserves while avoiding inter-well interference. Each well's horizontal section is divided into multiple sub-segments, each with multiple perforation clusters. The fracture half-fracture height within the radius of the perforation cluster exceeds the vertical height of the reservoir surface, decreasing further outwards. This approach not only increases the effective utilization rate of the R-shale reservoir between horizontal sections by more than double but also avoids inter-well interference caused by fracturing.

[0100] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and such modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A cluster well network structure for extreme utilization in shallow shale gas reservoirs, characterized in that, It includes two rows of horizontal wells located in a pre-designated well site on the ground. Each row of horizontal wells includes nine horizontal wells arranged in numerical order. One row of horizontal wells is inclined downwards based on the horizontal plane and has a horizontal section along the shale reservoir layer Ra. The other row of horizontal wells is inclined upwards based on the horizontal plane and has a horizontal section along the shale reservoir layer Rb. Both the shale reservoir layer Ra and the shale reservoir layer Rb are the highest quality reservoirs within the shale gas reservoir development section R. The shale reservoir layer Ra and the shale reservoir layer Rb are parallel to each other and have a stratigraphic dip angle with the horizontal plane. Each horizontal well numbered 1 / 3 / 5 has a first horizontal section L1 set along the shale reservoir surface Ra; each horizontal well numbered 2 / 4 has a second horizontal section L2 set along the shale reservoir surface Rb; each horizontal well numbered 6 / 8 / 10 has a third horizontal section L3 set along the shale reservoir surface Ra; each horizontal well numbered 7 / 9 has a fourth horizontal section L4 set along the shale reservoir surface Rb; each horizontal well numbered 12 / 14 / 15 / 17 has a fifth horizontal section L5 set along the shale reservoir surface Ra; and each horizontal well numbered 11 / 13 / 16 / 18 has a sixth horizontal section L6 set along the shale reservoir surface Rb. The extension length of the fracture along the shale reservoir surface perpendicular to the horizontal section is less than or equal to 300m. For a horizontal wellhead inclined downwards based on a horizontal plane, the average height of the hydraulic fractures extending in the direction perpendicular to the shale reservoir surface Ra in each horizontal segment is less than the vertical height difference between the bottom of the gas reservoir development segment R and the bottom of the shale reservoir surface Ra. For a horizontal wellhead inclined upwards based on a horizontal plane, the average height of the hydraulic fractures extending in the direction perpendicular to the shale reservoir surface Rb in each horizontal segment is less than the vertical height difference between the top of the gas reservoir development segment R and the top of the shale reservoir surface Rb. The length of the horizontal segment L1 set along the downdip direction of the shale reservoir surface Ra or the length of the horizontal segment L2 set along the downdip direction of the shale reservoir surface Rb is 1200m; the length of the horizontal segment L3 set along the updip direction of the shale reservoir surface Ra or the length of the horizontal segment L4 set along the updip direction of the shale reservoir surface Rb is 1000m; the length of the horizontal segment L5 set along the updip and / or downdip direction of the shale reservoir surface Ra is 300m; and the length of the horizontal segment L6 set along the updip and / or downdip direction of the shale reservoir surface Rb is 300m.

2. The shallow shale gas reservoir cluster well network structure with ultimate operational capability according to claim 1, characterized in that, The dip angle of the strata is 5~20°.

3. The shallow shale gas reservoir cluster well network structure with ultimate operational capability according to claim 1, characterized in that, The horizontal section of each horizontal well is oriented perpendicular to the direction of the minimum principal stress of the shale reservoir layer in which it is located.

4. The shallow shale gas reservoir cluster well network structure for ultimate operational use according to claim 1, characterized in that, The horizontal distance between any two adjacent horizontal wells located in different reservoir sections within the same row is 250m.

5. The shallow shale gas reservoir cluster well network structure for ultimate operational use according to claim 1, characterized in that, Each horizontal segment L1 / L2 / L3 / L4 / L5 / L6 is divided into multiple sub-segments, and multiple perforation clusters are opened on each sub-segment. The sub-segments and perforation clusters in each adjacent horizontal segment are staggered.

6. The shallow shale gas reservoir cluster well network structure for ultimate operational use according to claim 1, characterized in that, The length of the pre-set well site on the ground ranges from 100 to 150 m, and the width ranges from 80 to 140 m.

7. The shallow shale gas reservoir cluster well network structure for ultimate operational use according to claim 1, characterized in that, The distance between any two adjacent horizontal wellheads in the same row and the ground is 5 to 10 meters, and the distance between two adjacent rows of horizontal wellheads is 30 meters.

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