Method for determining fracture length of oil well in compact oil reservoir fracturing anti-nine-point diamond well pattern

Abstract

The present application belongs to the field of oil and gas field development engineering, and discloses a method for determining the fracture length of a tight oil reservoir fracturing oil displacement anti-nine-point diamond well pattern, comprising the following steps: (1) determining the arrangement mode of the injection well and the oil well in the fracturing oil displacement anti-nine-point diamond injection-production well pattern; (2) obtaining the hydraulic fracture parameters generated in the process of water injection fracturing oil displacement; (3) obtaining the injection well displacement radius and the oil well drainage radius of the target reservoir after energy compensation of the injection well in the water injection fracturing oil displacement according to the reservoir basic parameters; (4) determining the water drive front of the injection well fracturing oil displacement; (5) according to the different orientations of the oil well affected in the anti-nine-point diamond injection-production well pattern, classifying the oil wells and respectively calculating the optimal half fracture length. The present application considers the oil-water effect difference caused by the position of the well pattern, classifies the oil wells and respectively calculates the fracturing fracture length of each type of oil well, which is more targeted and realizes the fine optimization of the fracturing fracture length.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas field development engineering, specifically a method for determining the fracture length of a tight oil reservoir fracturing well with a reverse nine-point rhomboid well pattern. Background Technology

[0002] For the development of low-permeability (tight) oil and gas reservoirs, fracturing is a key technical measure for production wells to achieve production or higher productivity. In recent years, oilfields have organically combined single-well fracturing technology, conventional waterflooding, and chemical flooding to propose an integrated "fracturing-injection-production" fracturing-flooding technology, also known as "fracturing-flooding," forming a complete set of continuous reservoir development processes. However, to achieve better development results, the parameter design of the fracturing-flooding process is particularly important. Especially after water injection wells inject large amounts of water and flooding agents under near-fracture pressure conditions to replenish formation energy, the optimized design or calculation of the fracture length in oil wells is a crucial factor affecting the overall productivity of the fracturing-flooding production well group in low-permeability (tight) oil and gas reservoirs.

[0003] Currently, the selection of fracture length in fracturing production well groups is mostly based on analogy with adjacent blocks or similar reservoirs, relying solely on operational experience. This lack of fundamental theoretical basis for process and parameter optimization fails to adequately guide field practice. Existing methods for optimizing well fracture length have the following limitations: First, if the fracture length is too short, the well fracturing is inadequate, leading to a failure to establish effective displacement between oil and water, and slow water drive effectiveness. Second, if the fracture length is too long, water flooding and channeling occur, causing the well to prematurely lose production capacity and be forced to shut down. Furthermore, because the ratio of oil to water wells in a diamond-shaped inverted nine-point well pattern is 3:1, the proportion of oil wells is relatively high, resulting in relatively high oilfield production in the early stages of development. Therefore, for relatively homogeneous, low-permeability oilfields with indistinct fracture directions and large fault areas, a diamond-shaped inverted nine-point well pattern is typically used for injection-production development. Therefore, in order to solve the problem of "inducing effect" of fracturing and oil displacement in production well groups, this invention mainly targets oil wells with a reverse nine-point rhomboid well pattern for fracturing and oil displacement in tight oil reservoirs, and proposes a method for calculating the production variation of oil well fracture length by combining geological understanding and field monitoring. Summary of the Invention

[0004] To overcome the problems in the existing technology, this invention provides a method for determining the fracture length of oil wells in a reverse nine-point diamond well pattern for fracturing and oil displacement in tight oil reservoirs. Based on determining the oil-water well spacing of the reverse nine-point diamond injection-production well pattern and monitoring the hydraulic fractures of the water injection wells through microseismic monitoring, this method calculates the oil well drainage radius and the water injection well displacement radius by combining the formation energy after fracturing and oil displacement, and optimizes the fracture length according to the well location, providing theoretical guidance for field fracturing operations.

[0005] The technical solution provided by this invention to solve the above-mentioned technical problems is: a method for determining the fracture length of a reverse nine-point diamond-pattern well in a tight oil reservoir, comprising the following steps: Step S1: Determine the arrangement of water injection wells (1) and oil wells (2) in the fracturing and oil displacement reverse nine-point diamond injection-production well network; Step S2: During the water injection fracturing and oil displacement process in the water injection well (1), microseismic fracture monitoring is performed to obtain the hydraulic fracture parameters generated during the water injection fracturing and oil displacement process. Step S3: Obtain the displacement radius of the water injection well and the oil well drainage radius of the target reservoir after fracturing and oil displacement in the water injection well (1) based on the basic parameters of the reservoir. Step S4: Determine the water drive front of the injection well (1) for fracturing and oil displacement based on the hydraulic fracture parameters monitored by the microseismic fractures in step S2 and the displacement radius of the injection well in step S3. Step S5: According to the different orientations of the oil wells (2) in the reverse nine-point diamond injection-production well network, classify the oil wells (2) and calculate the optimal half-fracture length for fracturing design for each.

[0006] A further technical solution is that, in step S1, the arrangement of the water injection well (1) and the oil well (2) is such that the long semi-axis of the line connecting the water injection well (1) and the oil well (2) is consistent with the direction of the maximum horizontal principal stress of the formation, and the short semi-axis of the line connecting the water injection well (1) and the oil well (2) is perpendicular to the direction of the maximum horizontal principal stress of the formation.

[0007] A further technical solution is that, in step S2, the hydraulic fracture parameters obtained by microseismic fracture monitoring include fracture network half-length, fracture network half-width, fracture network height, and fracture network orientation.

[0008] A further technical solution is that, in step S3, the calculation methods for the displacement radius of the water injection well and the drainage radius of the oil well are as follows: r =3.226 ( P e - P w )*( K / μ ) 0.5992 In the formula: r The control radius is expressed in meters (m). P e To maintain the hydraulic pressure for fracturing and oil displacement at a level, the unit is MPa; P w The bottomhole flowing pressure of a fracturing oil well is expressed in MPa. K This refers to matrix permeability, expressed in units of 10. -3 μm 2 ; μ The viscosity of the formation crude oil is expressed in mPa·s.

[0009] A further technical solution is that, in step S4, determining the water drive front of the fracturing oil displacement of the injection well (1) further includes: summing the half length of the hydraulic fracture network monitored by the microseismic fracture and the displacement radius of the injection well (1), and using the summation result as the water drive front of the fracturing oil displacement of the injection well (1).

[0010] A further technical solution is that, in step S5, classifying the oil wells (2) and calculating the optimal half-fracture length for fracturing design for each well also includes: classifying the two wells at the long axis position of the inverted nine-point rhombus well network as Class I corner wells, wherein the half-fracture length of the fracturing fracture of the Class I corner wells is ≥ oil well spacing - water drive front edge - oil well drainage radius, and the half-fracture length of the fracturing fracture is < oil well spacing - water drive front edge.

[0011] A further technical solution is that, in step S5, classifying the oil wells (2) and calculating the optimal half-fracture length for fracturing design respectively also includes: classifying the two wells at the short axis position of the inverted nine-point diamond well network as Class II corner wells, and the half-fracture length of the fracturing fracture of the Class II corner wells is the optimal half-fracture length for production capacity numerical simulation fracturing.

[0012] A further technical solution is that, in step S5, classifying the oil wells (2) and calculating the optimal half-fracture length for fracturing design includes: classifying the four wells on the edge of the inverted nine-point diamond well network as Class III edge wells, drawing a circle with the oil well drainage radius as the radius in the direction of fracture extension, and when the circle is tangent to the water drive front edge of the injection well, taking the corresponding half-fracture length of the fracturing fracture as the optimal half-fracture length.

[0013] Compared with the prior art, the advantages of the present invention are: (1) This invention is designed for the different positions of oil wells in the reverse nine-point diamond well network for fracturing and oil displacement in tight oil reservoirs. It takes into account the differences in oil and water effects caused by the position of the oil wells, classifies the oil wells and calculates the fracture length of each type of oil well. It is more targeted and achieves fine optimization of fracture length.

[0014] (2) For Class I corner wells with the long axis position of the inverted nine-point rhomboid well network, the method for determining the fracture length provided by the present invention can not only establish an effective displacement between oil wells and water wells, but also reduce the risk of water channeling.

[0015] (3) For Class II corner wells at the short axis position of the inverted nine-point rhombus well network, taking into full account the characteristic that this type of well is less affected by the fracturing oil displacement well, the numerical simulation optimization method is directly used to determine the fracture length, which is more convenient and faster.

[0016] (4) For Class III edge wells located on the edge of the reverse nine-point diamond well network, the method of gradually drawing circles in the direction of fracture extension is adopted to seek the optimal fracture length, which can not only fully establish effective displacement, but also reduce the risk of water channeling and flooding. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the reverse nine-point rhomboid well pattern of the present invention.

[0019] Figure 2 This is a schematic diagram of the numbering of oil wells in the reverse nine-point diamond well network of the present invention.

[0020] Figure 3 This is a schematic diagram of calculating the fracture half-length for a Class I corner well according to the present invention.

[0021] Figure 4 This is a schematic diagram for calculating the fracture half-length of a Class II corner well according to the present invention.

[0022] Figure 5 This is a schematic diagram of calculating the fracture half-length for a Class III side well according to the present invention.

[0023] In the diagram, 1—water injection well; 2—oil well. Detailed Implementation

[0024] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] This invention provides a method for determining the fracture length in a tight oil reservoir using a reverse nine-point diamond-pattern well pattern, comprising the following steps: Step S1: Determine the arrangement of water injection well 1 and oil well 2 in the fracturing and oil displacement reverse nine-point diamond injection-production well network; like Figure 1 The diagram shown is a schematic representation of a rhomboid inverted nine-point well network in this field. In this network, the center is a water injection well (1), surrounded by eight oil wells (2). The oil wells (2) can be numbered according to their positions within the network. Figure 2As shown, the eight oil wells 2 are numbered #1, #2, #3, #4, #5, #6, #7, and #8 respectively. Among them, the two oil wells 2 with well numbers #1 and #5 are located on the long axis of the inverted nine-point diamond well network, the two oil wells 2 with well numbers #3 and #7 are located on the short axis of the inverted nine-point diamond well network, and the four oil wells 2 with well numbers #2, #4, #6, and #8 are located on the edge of the inverted nine-point diamond well network. Those skilled in the art can determine parameters such as the spacing between oil and water wells in the fracturing and oil displacement inverted nine-point diamond injection-production well network based on reservoir parameters, geological parameters, etc., and then establish the corresponding inverted nine-point diamond injection-production well network. In the inverted nine-point diamond well network, the major semi-axis of the line connecting oil and water wells is nearly aligned with the direction of the maximum horizontal principal stress in the formation, while the minor semi-axis of the line connecting oil and water wells is nearly perpendicular to the direction of the maximum horizontal principal stress in the formation. Step S2: During the water injection fracturing and oil displacement process in the water injection well 1, microseismic fracture monitoring is performed to obtain hydraulic fracture parameters generated during the water injection fracturing and oil displacement process. Step S3: Obtain the displacement radius of the water injection well and the oil well drainage radius of the target reservoir after fracturing and oil displacement in the water injection well 1, based on the basic reservoir parameters. Those skilled in the art can use the oil supply radius formula for low-permeability reservoirs to determine the displacement radius of water injection wells and the drainage radius of oil wells. The calculation orientation of the displacement control radius of water injection wells and the drainage control radius of oil wells is consistent. The following formula is selected for calculation: r =3.226 ( P e - P w )*( K / μ ) 0.5992 In the formula: r The control radius is expressed in meters (m). P e To maintain the hydraulic pressure for fracturing and oil displacement at a level, the unit is MPa; P w The bottomhole flowing pressure of a fracturing oil well is expressed in MPa. K This refers to matrix permeability, expressed in units of 10. -3 μm 2 ; μ The viscosity of the crude oil in the formation is expressed in mPa·s. Step S4: Determine the pre-fracturing water drive parameters of the injection well 1 based on the hydraulic fracture parameters monitored by the microseismic fractures in step S2 and the displacement radius of the injection well in step S3; Step S5: Based on the different effective orientations of oil wells 2 in the reverse nine-point diamond injection-production well network, classify the oil wells 2 and calculate the optimal half-fracture length for fracturing design for each.

[0026] Based on the effective well orientation of oil well 2 in the reverse nine-point diamond injection-production well network, oil well 2 is divided into three categories, and the optimal half-fracture length for fracturing design is calculated for each category. Among them, the two wells on the long axis of the reverse nine-point diamond well network are classified as Class I corner wells, the two wells on the short axis of the reverse nine-point diamond well network are classified as Class II corner wells, and the four wells on the edge of the reverse nine-point diamond well network are classified as Class III edge wells.

[0027] For Class I corner wells, such as Figure 3 As shown, A represents the location of injection well 1, AB represents the half-length of the hydraulic fracture in the injection well (or the half-length of the fracture network) in the water-drive microseismic monitoring, BC represents the displacement radius of the injection well, AC represents the water drive front, E represents the location of Class I oil wells, AE represents the distance between oil and water wells, CD represents the oil well drainage radius, and DE represents the half-length of the fracturing fracture. The optimal half-length of the fracturing fracture is calculated as follows: when effective displacement between oil and water wells is established, the half-length of the fracturing fracture should be greater than or equal to the difference between the oil well distance, the water drive front, and the oil well drainage radius; to reduce the risk of water channeling, the half-length of the fracturing fracture should be less than the difference between the oil well distance and the water drive front.

[0028] For Class II corner wells, such as Figure 4 As shown, A is the location of water injection well 1, AB is the half-axis of the fracture in the water-drive microseismic monitoring well, BC is the displacement radius of the water injection well, AC is the water drive front, D is the location of the Class II oil well, and AD is the distance between the oil and water wells. The calculation method for the optimal half-fracture length is as follows: the extension direction of the fracture in the Class II oil well is parallel to the direction of the fracture network of the water injection well 1, and it is less affected by the fractured oil well. Therefore, the half-fracture length is optimized by numerical simulation of production capacity. Since the numerical simulation optimization method of fracture is existing technology, it will not be described in detail in this application.

[0029] For Class III edge wells, such as Figure 5 As shown, A represents the location of injection well 1, AB represents the semi-major axis of the fracture in the water-drive microseismic monitoring injection well, AC represents the semi-minor axis of the water-drive front, AD represents the semi-minor axis of the fracture in the water-drive microseismic monitoring injection well, AE represents the semi-minor axis of the water-drive front monitoring, F represents the location of Class III oil wells, AF represents the distance between oil and water wells, and FG represents the half-fracture length of the fracturing fracture. The optimal half-fracture length is calculated as follows: If the half-fracture length of oil well 2 is too small, the matrix distance between the fracture tip and the water-drive front increases, making effective displacement impossible. Figure 5 The leftmost dashed circle in the direction of the fracture is shown; if the fracture half-fracture length of oil well 2 is too large, and the fracture tip is too close to the water drive front, there is a risk of water channeling and water flooding. Figure 5 The rightmost dashed circle in the direction of the fracture is shown; therefore, when the circle with the oil well's drainage radius is tangent to the water drive front edge of the injection well in the direction of fracture extension, the optimal half-fracture length can be obtained, as shown below. Figure 5 The solid circle at the center of the crack direction is shown.

[0030] To facilitate a deeper understanding of the technical solution of this invention by those skilled in the art, a calculation example is provided for illustration. The calculation example first determines the fracturing and oil recovery reverse nine-point diamond injection-production well pattern based on reservoir parameters, geological parameters, etc., where Table 1 shows the oil-water well spacing for fracturing and oil recovery in a certain reverse nine-point diamond well group.

[0031] Table 1 Statistical Results of Oil and Water Well Spacing

[0032] During the fracturing and oil displacement process of injection well 1 in this well group, water-drive microseismic fracture monitoring was carried out, and the monitoring results are shown in Table 2.

[0033] Table 2. Monitoring results of water-driven microseismic cracks

[0034] Step S5: Calculate the displacement radius of the water injection well and the drainage radius of the oil well after fracturing and replenishing the oil in the target reservoir using the low-permeability reservoir supply radius formula: r =3.226 ( P e - P w )*( K / μ ) 0.5992 In the formula: r The control radius is expressed in meters (m). P e To maintain the hydraulic pressure for fracturing and oil displacement at a level, the unit is MPa; P w The bottomhole flowing pressure of a fracturing oil well is expressed in MPa. K This refers to matrix permeability, expressed in units of 10. -3 μm 2 ; μ The viscosity of the formation crude oil is expressed in mPa·s.

[0035] in, P e - P w =15 MPa; K =2×10 -3 μ m 2 ; μ = 0.5 mPa·s, and the calculated displacement radius of the water injection well and the oil drainage radius of the oil well are both 110 m.

[0036] The sum of the hydraulic fracture half-length and the displacement radius of the injection well, as measured by microseismic monitoring, is the water drive front of the fracturing oil displacement in injection well 1. The calculation results are shown in Table 3. Table 3 Calculation results of the water drive front

[0037] Based on the effective well orientation of the reverse nine-point diamond injection-production well network, oil well 2 is divided into three categories, and the optimal half-fracture length for fracturing design is calculated for each category. The classification results of oil well 2 are shown in Table 4.

[0038] Table 4 Oil well classification results

[0039] For the calculation method of the optimal half-fracture length for Class I corner wells, taking well #1 as an example, when effective displacement between oil and water wells is established, the half-fracture length of the fracturing fracture is ≥ oil well spacing - water drive front edge - oil well drainage radius = 166 m; to reduce the risk of water channeling, the half-fracture length of the fracturing fracture is < oil well spacing - water drive front edge = 276 m. For the calculation method of the optimal half-fracture length for Class II corner wells, taking well #3 as an example, the extension direction of the fracture in well #3 is parallel to the direction of the fracture network of the water injection well 1, and is less affected by the fracture network of the water injection well 2. The optimal half-fracture length for production capacity numerical simulation is 140 m. Regarding the calculation method for the optimal half-fracture length of Class III edge wells, taking well #2 as an example, if the half-fracture length of the oil well is too small, the distance between the fracture tip and the water drive front increases, making it impossible to establish effective displacement; if the half-fracture length of oil well #2 is too large, the fracture tip and the water drive front are too close, posing a risk of water channeling and water flooding; when the circle with the oil well drainage radius as the radius is tangent to the water drive front of the injection well, the optimal half-fracture length is 110 m.

[0040] The above description is not intended to limit the present invention in any way. Although the present invention has been disclosed through the above embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for determining the fracture length of a well in a compact oil reservoir fracture flooding inverted nine-spot rhombus well pattern, characterized in that, Includes the following steps: Step S1: Determine the arrangement of water injection wells (1) and oil wells (2) in the fracturing and oil displacement reverse nine-point diamond injection-production well network; In step S1, the arrangement of the water injection well (1) and the oil well (2) is as follows: the major semi-axis of the line connecting the water injection well (1) and the oil well (2) is consistent with the direction of the maximum horizontal principal stress of the formation, and the minor semi-axis of the line connecting the water injection well (1) and the oil well (2) is perpendicular to the direction of the maximum horizontal principal stress of the formation. Step S2: During the water injection fracturing and oil displacement process in the water injection well (1), microseismic fracture monitoring is performed to obtain the hydraulic fracture parameters generated during the water injection fracturing and oil displacement process. Step S3: Obtain the displacement radius of the water injection well and the oil well drainage radius of the target reservoir after fracturing and oil displacement in the water injection well (1) based on the basic reservoir parameters; Step S4: Determine the water drive front of the injection well (1) for fracturing and oil displacement based on the hydraulic fracture parameters monitored by the microseismic fractures in step S2 and the displacement radius of the injection well in step S3. Step S5: According to the different orientations of the oil wells (2) in the reverse nine-point diamond injection-production well network, classify the oil wells (2) and calculate the optimal half-fracture length for fracturing design for each well. In step S5, classifying the oil wells (2) and calculating the optimal half-fracture length for fracturing design for each well also includes classifying the two wells at the long axis position of the inverted nine-point rhombus well network as Class I corner wells. The half-fracture length of the fracturing fractures of the Class I corner wells is greater than or equal to the oil well spacing - water drive front edge - oil well drainage radius, and the half-fracture length of the fracturing fractures is less than the oil well spacing - water drive front edge. The classification of the oil wells (2) and the calculation of the optimal half-fracture length for fracturing design also include: classifying the two wells at the short axis position of the inverted nine-point diamond well network as Class II corner wells, and the half-fracture length of the fracturing fracture of the Class II corner wells is the optimal half-fracture length for production capacity numerical simulation fracturing; The classification of the oil wells (2) and the calculation of the optimal half-fracture length for fracturing design also include: classifying the four wells on the edge of the inverted nine-point diamond well network as Class III edge wells, drawing a circle with the oil well drainage radius as the radius in the direction of fracture extension, and taking the corresponding half-fracture length of the fracturing fracture as the optimal half-fracture length when the circle is tangent to the water drive front edge of the injection well.

2. The method for determining fracture length of oil well fractured by compact reservoir fracturing drive oil anti-nine-point diamond well pattern according to claim 1, characterized in that, In step S2, the hydraulic fracture parameters obtained by microseismic fracture monitoring include fracture network half-length, fracture network half-width, fracture network height, and fracture network orientation.

3. The method of determining fracture length for compact reservoir fracturing and oil displacement reverse nine-spot rhombus well pattern oil well according to claim 1, characterized in that, In step S3, the calculation methods for the displacement radius of the water injection well and the drainage radius of the oil well are as follows: ； In the formula: To control the radius, the unit is... ; To maintain the fracturing oil displacement pressure at a level, the unit is... ; The bottom hole flowing pressure of a fracturing oil well is expressed in units of... ; The value is the matrix permeability, in units of... ; The viscosity of the formation crude oil is expressed in units of... .

4. The method for determining the fracture length of a tight oil reservoir fracturing well with a reverse nine-point diamond-shaped well pattern according to claim 1, characterized in that, In step S4, determining the water drive front of the fracturing oil displacement of the injection well (1) further includes: summing the half length of the hydraulic fracture network monitored by the microseismic fracture and the displacement radius of the injection well (1), and taking the summing result as the water drive front of the fracturing oil displacement of the injection well (1).

Images