A method and device for simulating the effect of fracturing operations on ground stress

Abstract

The application discloses a method and device for simulating the influence of fracturing construction on ground stress, which comprises the following steps: obtaining the design parameters and perforation parameters of a fracturing well; establishing a hydraulic pressure joint expansion model according to the design parameters of the fracturing well; establishing a numerical model of the influence of fracturing construction on a stratum according to the hydraulic pressure joint expansion model and the perforation parameters; and determining the ground stress variation law of the stratum around the fracturing well according to the numerical model of the influence of fracturing construction on the stratum. The method has the beneficial effects that the hydraulic pressure joint expansion model is established according to the design parameters of the fracturing well, the numerical model of the influence of fracturing construction on the stratum is established in combination with the perforation parameters, the ground stress variation law of the stratum around the fracturing well is determined according to the numerical model of the influence of fracturing construction on the stratum, and thus the ground stress variation law of the stratum around the fracturing well in the fracturing process can be obtained, which provides technical support for revealing the mechanism of the drilling interference caused by fracturing, and enriching and perfecting the related theory.

Description

Technical Field

[0001] The present invention relates to the field of drilling technology, and in particular to a method and device for simulating the influence of fracturing construction on ground stress. Background Art

[0002] In recent years, with the continued expansion of tight sandstone oil and gas reservoir development, advancements in drilling technology, and reductions in drilling costs, the combination of horizontal wells and staged fracturing has demonstrated significant advantages, leading to an increasingly widespread application of staged fracturing. Since 2016, large-scale production has been conducted using horizontal well technology in a key development area in my country. Initially drilled medium-deep horizontal wells have demonstrated relatively balanced technical performance and a low rate of downhole failures. Since 2017, large-scale volumetric fracturing has been implemented in completed horizontal wells in the area. However, during the volumetric fracturing operations, complications have arisen to varying degrees in some adjacent wells.

[0003] Volume fracturing technology refers to the use of segmented multi-cluster perforation technology, which utilizes the high net pressure within the fractures and the interference effect between fractures to achieve communication between artificial fractures and natural fractures and the generation of lateral fractures. It forms a complex fracture network in the three dimensions of length, width and height in the reservoir. The distance for oil and gas to seep from the matrix in any direction to the fractures is the "shortest", which greatly improves the overall permeability of the reservoir and increases the productivity and ultimate recovery rate of oil and gas wells in low-permeability unconventional reservoirs (see Chinese invention patent application number CN201610897188.3 for details).

[0004] With the widespread use of hydraulic fracturing in the development of tight sandstone oil and gas reservoirs, there is an urgent need to find solutions to the interference of hydraulic fracturing with drilling to ensure safe horizontal well drilling. During hydraulic fracturing, the in-situ stress of the formation surrounding the fractured well changes, disrupting the drilling of adjacent wells. Therefore, studying the dynamics of in-situ stress around the fractured well during fracturing is crucial for understanding the mechanisms of hydraulic fracturing interference with drilling and enriching and improving relevant theories.

[0005] However, in the prior art, there is a lack of research on the changing laws of ground stress in the formation around the fracturing well during the fracturing process. Summary of the Invention

[0006] In view of this, it is necessary to provide a method and device for simulating the impact of fracturing construction on ground stress, so as to study the change law of ground stress in the formation around the fracturing well during the fracturing process, thereby providing technical support for revealing the mechanism of fracturing interference on drilling and enriching and improving related theories.

[0007] To achieve the above object, the present invention provides a method for simulating the effect of hydraulic fracturing on ground stress, comprising:

[0008] obtaining design parameters and perforation parameters of the fracturing well;

[0009] establishing a hydraulic fracture propagation model according to the design parameters of the fracturing well;

[0010] establishing a numerical model of the influence of fracturing construction on the formation according to the hydraulic fracture propagation model and the perforation parameters;

[0011] determining the ground stress variation law of the formation around the fracturing well according to the numerical model of the influence of fracturing construction on the formation.

[0012] In some embodiments, the design parameters of the fracturing well include well location distribution data of the fracturing well and wellbore trajectories of each fracturing well.

[0013] In some embodiments, the hydraulic fracture propagation model is established according to the design parameters of the fracturing well, specifically including:

[0014] determining the range of the hydraulic fracture propagation model according to the design parameters of the fracturing well;

[0015] establishing the hydraulic fracture propagation model within the range of the hydraulic fracture propagation model based on a fracture propagation criterion according to the design parameters of the fracturing well, wherein the fracture propagation criterion is a maximum energy release rate criterion.

[0016] In some embodiments, the range of the hydraulic fracture propagation model is determined according to the design parameters of the fracturing well, specifically including:

[0017] determining the actual fracturing construction initiation point position of the target well and projecting it onto a plane to obtain a planar projection map of the fracturing construction well according to the design parameters of the fracturing well;

[0018] determining the range of the hydraulic fracture propagation model according to the planar projection map.

[0019] In some embodiments, the numerical model of the influence of fracturing construction on the formation is established according to the hydraulic fracture propagation model and the perforation parameters, specifically including:

[0020] adding a liquid injection point in the hydraulic fracture propagation model according to the perforation parameters;

[0021] setting a Cohesive unit at each liquid injection point in the hydraulic fracture propagation model;

[0022] calculating the fracture propagation parameters on the Cohesive unit for each Cohesive unit to obtain the numerical model of the influence of fracturing construction on the formation.

[0023] In some embodiments, the cohesive unit is a COH3D8P unit type.

[0024] In some embodiments, the crack propagation parameters include stress, displacement, damage factor, and crack width.

[0025] In some embodiments, determining the ground stress variation pattern of the formation surrounding the fracturing well based on a numerical model of the impact of fracturing operation on the formation includes:

[0026] The numerical model of the impact of fracturing construction on the formation was imported into the finite element analysis software to carry out numerical simulation calculations, and the ground stress data along the length direction of the hydraulic fracture at different injection construction times were obtained:

[0027] Based on the geostress data along the length of the hydraulic fracture at different injection times, the control range and variation law of the horizontal geostress difference caused by fracturing injection are obtained, thereby determining the variation law of the geostress in the formation around the fracturing well.

[0028] The present invention also provides a device for simulating the impact of fracturing construction on ground stress, including a processor and a memory, wherein a computer program is stored in the memory. When the computer program is executed by the processor, the method of simulating pore pressure changes during the fracturing process is implemented.

[0029] The present invention also provides a computer-readable storage medium storing one or more programs, which can be executed by one or more processors to implement the steps in the method for simulating the impact of fracturing construction on ground stress.

[0030] Compared with the existing technology, the beneficial effects of the technical solution proposed in the present invention are: a hydraulic fracture expansion model is established through the design parameters of the fracturing well, and then a numerical model of the impact of fracturing construction on the formation is established in combination with the perforation parameters. Then, based on the numerical model of the impact of fracturing construction on the formation, the ground stress change law of the formation around the fracturing well is determined, thereby obtaining the ground stress change law in the formation around the fracturing well during the fracturing process, providing technical support for revealing the mechanism of fracturing interference on drilling and enriching and improving related theories. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a flow chart of an embodiment of a method for simulating the effect of hydraulic fracturing on ground stress provided by the present invention;

[0032] Figure 2 yes Figure 1 Schematic diagram of the process of step S2;

[0033] Figure 3 yes Figure 2Flow diagram of step S21;

[0034] Figure 4 yes Figure 1 Schematic diagram of the process of step S3;

[0035] Figure 5 yes Figure 1 Schematic diagram of the process of step S4;

[0036] Figure 6 It is a plan projection diagram of the fracturing well;

[0037] Figure 7 This is a schematic diagram of the changes in formation stress along the length of the fracture caused by the extension of the hydraulic fracture during the hydraulic fracturing injection process;

[0038] Figure 8 It is the curve of the horizontal stress difference in the crack extension length direction at different time points during the entire injection process.

[0039] Figure 9 This is a curve showing the change of the impact range of the horizontal stress difference along the fracture propagation direction with injection time for a well with a depth of 3000m, with the horizontal stress difference increasing to 1.5MPa as a dangerous situation.

[0040] Figure 10 It is the curve of the horizontal stress difference along the length of the first hydraulic fracture at different time points during the entire second hydraulic fracture injection process.

[0041] Figure 11 This is a curve showing the change of the horizontal stress difference affected by the second stage of fracturing along the crack propagation direction with the injection time, with the horizontal stress difference increasing to 1.5 MPa as a dangerous situation for a well with a depth of 3000m. DETAILED DESCRIPTION

[0042] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, and are not used to limit the scope of the present invention.

[0043] Please refer to Figure 1 The present invention provides a method for simulating the influence of fracturing construction on ground stress, comprising:

[0044] S1. Obtaining design parameters and perforation parameters of the fracturing well;

[0045] Specifically, the design parameters of the fracturing wells include well location distribution data of the fracturing wells and the wellbore trajectory of each fracturing well.

[0046] S2. Establishing a hydraulic fracture expansion model based on the design parameters of the fractured well;

[0047] S3. Establishing a numerical model of the impact of hydraulic fracturing on the formation based on the hydraulic fracture expansion model and the perforation parameters;

[0048] S4. Based on the numerical model of the impact of fracturing construction on the formation, determine the change law of the ground stress of the formation around the fracturing well.

[0049] The technical solution provided by the present invention establishes a hydraulic fracture expansion model through the design parameters of the fracturing well, and then combines the perforation parameters to establish a numerical model of the impact of fracturing construction on the formation. Then, based on the numerical model of the impact of fracturing construction on the formation, the change law of the ground stress in the formation around the fracturing well is determined, thereby obtaining the change law of the ground stress in the formation around the fracturing well during the fracturing process, providing technical support for revealing the mechanism of fracturing interference on drilling and enriching and improving related theories.

[0050] Please refer to Figure 2 , step S2 specifically includes the following steps:

[0051] S21, determining the range of the hydraulic fracture expansion model according to the design parameters of the fracturing well;

[0052] S22. Establishing a hydraulic fracture expansion model within the scope of the hydraulic fracture expansion model according to the design parameters of the fracturing well and based on a fracture expansion judgment criterion, wherein the fracture expansion judgment criterion is a maximum energy release rate criterion.

[0053] The maximum energy release rate criterion can be expressed as:

[0054]

[0055] The crack tip shows tensile failure and is easy to expand;

[0056] Shear failure occurs at the crack tip and the crack is able to expand;

[0057] and The crack tip is prone to expansion due to simultaneous tensile and shear failure; G is the area under the traction separation curve, representing the fracture energy of the crack; C is the bond breaking energy caused by tensile failure at the crack tip; GI is the bond breaking energy caused by shear failure at the crack tip.

[0058] Please refer to Figure 3 , step S21 specifically includes the following steps:

[0059] S211, determining the actual fracturing initiation point of the target well according to the design parameters of the fracturing well, and projecting it onto a plane to obtain a plane projection diagram of the fracturing well;

[0060] S212: Determine the range of the hydraulic fracture expansion model according to the plan projection diagram.

[0061] Please refer to Figure 4 , step S3 specifically includes the following steps:

[0062] S31, adding injection points in the hydraulic fracture expansion model according to the perforation parameters;

[0063] S32, setting a cohesive unit at each injection point in the hydraulic fracture expansion model, specifically, the cohesive unit is a COH3D8P unit type;

[0064] S33. Calculate the crack propagation parameters on each cohesive unit to obtain a numerical model of the impact of fracturing construction on the formation, wherein the crack propagation parameters include stress, displacement, damage factor and crack width.

[0065] Please refer to Figure 5 , step S4 specifically includes the following steps:

[0066] S41. The numerical model of the impact of hydraulic fracturing on the formation is imported into the finite element analysis software to carry out numerical simulation calculations, and the ground stress data along the length direction of the hydraulic fracture at different injection construction times are obtained:

[0067] S42. Based on the ground stress data along the length direction of the hydraulic fracture at different injection construction times, the control range and change law of the horizontal ground stress difference caused by the fracturing injection are obtained, thereby determining the ground stress change law of the formation around the fracturing well.

[0068] The present invention also provides a device for simulating the impact of fracturing construction on ground stress, including a processor and a memory, wherein a computer program is stored in the memory. When the computer program is executed by the processor, the method of simulating pore pressure changes during the fracturing process is implemented.

[0069] The present invention also provides a computer-readable storage medium storing one or more programs, which can be executed by one or more processors to implement the steps in the method for simulating the impact of fracturing construction on ground stress.

[0070] In order to verify the feasibility and technical effect of the technical solution provided by the present invention, a simulation of the pore pressure changes during the actual fracturing process was carried out on a well area. The specific process is as follows:

[0071] (1) Obtaining design parameters and perforation parameters of the fracturing well;

[0072] Statistical analysis is performed on wells that have undergone on-site fracturing and drilling operations in a specific block to screen target wells. Fracturing well parameters (such as perforation parameters, segmentation and clustering data, etc.) and drilling parameters (such as drilling fluid density) are obtained from the oil field site in the specific block during the same time period. Statistical analysis is then performed on the working conditions, and target wells are screened based on the statistical analysis results.

[0073] (2) establishing a hydraulic fracture expansion model based on the design parameters of the fractured well;

[0074] First, the range of the hydraulic fracture expansion model is determined according to the design parameters of the fracture well;

[0075] Based on the rock mechanical parameters of the selected target well, the fracturing construction design adopts the perforation bridge plug combined fracturing process, and uses the cable pumping bridge plug and perforation method to perform segmentation and perforation. According to the sand addition scale of each section of the example well, the fracturing construction is carried out with limited pressure but not limited displacement; according to the target well fracturing construction design and wellbore trajectory map, the actual fracturing starting point of the target well is determined and projected in the CAD (such as Figure 6 Based on the planar projection of the fracturing initiation point in CAD, the entire area is approximately 8,700 meters long from east to west and 3,000 meters long from north to south. The two fracturing wells are located slightly left of the center of the entire area. To optimize the calculation and consider the overall size of the model, the model scale is 1 / 2 of the entire area, so the model dimensions are 6,000 meters by 300 meters by 600 meters.

[0076] Then, according to the design parameters of the fracturing well and based on the fracture expansion judgment criterion, a hydraulic fracture expansion model is established within the scope of the hydraulic fracture expansion model.

[0077] According to the fracturing construction design and modeling scope, the Cohesive constitutive model is selected;

[0078] Cohesive-based constitutive models can be used to simulate material failure, especially interfacial failure involving interfacial materials. The hydraulic fracture propagation model uses the fraction-separation criterion to describe material failure, employing a bilinear constitutive model. This model assumes that the viscous surface is initially intact, without any relative displacement. When the traction force reaches the cohesive unit strength or the equivalent separation displacement is exceeded, reversible linear elastic behavior is exhibited. When the separation displacement is exceeded, the traction force decreases linearly to zero, and the load-traction displacement relationship during this process is irreversible. Based on the cohesive hydraulic fracture propagation model, the maximum energy release rate criterion is used as the fracture propagation criterion.

[0079] (3) establishing a numerical model of the impact of hydraulic fracturing on the formation based on the hydraulic fracture expansion model and the perforation parameters;

[0080] The grid size was determined based on the Cohesive hydraulic fracturing expansion model. In actual calculations, a too small grid size would result in an excessive number of cells, requiring excessive server computing resources and slowing down the calculation speed. A too large grid size would result in too few cells, further compromising the accuracy of the calculation results. After multiple preliminary trials and analyses, a global grid size of 25 meters and a global grid count of 726,600 cells were determined.

[0081] Based on the perforation parameters of the example well, nine injection points were set on the left side of the model, each located on a cohesive element, to simulate multi-stage fracturing. Based on the numerical model, the C3D8P element type was used for the solid element mesh, and the COH3D8P element type was used for the cohesive element mesh to simulate fracture propagation during hydraulic fracturing. The output results include stress S, displacement U, damage factor SDEG, and fracture width PFOPEN during the fracture propagation process.

[0082] (4) Based on the numerical model of the impact of fracturing construction on the formation, determine the change law of the ground stress in the formation around the fracturing well.

[0083] Based on the numerical simulation results, the variation pattern and control range of the in-situ stress in the direction of the current construction section are obtained. That is, by extracting the in-situ stress data along the length of the hydraulic fracture at different injection construction times, the simulation software can be used to obtain the control range and variation pattern of the horizontal in-situ stress difference caused by fracturing injection in the direction of the current construction section.

[0084] Please refer to Figure 7 During the hydraulic fracturing injection process, the extension of the hydraulic fracture will cause the formation stress to change along the length of the fracture. Figure 7 As shown in the figure, the arrow line is located in the length direction of the hydraulic fracture. By extracting the ground stress change data in the length direction of the hydraulic fracture at different injection construction times, the control range and change law of the ground stress change in the direction of the current construction section can be obtained.

[0085] Based on the numerical simulation results, the variation patterns and control range of inter-stage interference on in-situ stress were determined. Specifically, after importing and processing parameters through simulation software, a curve of the horizontal in-situ stress difference along the length of the first hydraulic fracture at different time points along the length of the fracture extension during the entire second-stage fracturing and injection process was obtained. Based on these numerical simulation results, a numerical simulation analysis of the impact of fracturing operation on in-situ stress during drilling was completed.

[0086] Analysis results:

[0087] Please refer to Figure 8 , Figure 8 is the curve of the horizontal stress difference along the crack extension length at different time points during the entire injection process. Figure 8 It can be seen that the horizontal stress difference is affected by hydraulic fracturing construction along the length of the crack, and its influence can be divided into four stages:

[0088] ① Stable stage: In the longitudinal direction, starting from the perforation injection point, the horizontal geostress difference remains roughly unchanged, with a maximum value of 11.7 MPa. ② Sudden drop stage: The horizontal geostress difference suddenly drops sharply, and the point where the sharp drop begins is the tip of the hydraulic fracture in the longitudinal direction. ③ Slow drop stage: After the sudden drop of the horizontal geostress difference, the horizontal geostress difference begins to decrease slowly. ④ Re-stabilization stage: After the horizontal geostress difference slowly decreases, the horizontal geostress difference tends to stabilize, and the stable horizontal geostress difference is close to but not lower than the original initial horizontal geostress difference of 7.41 MPa.

[0089] Please refer to Figure 9 , Figure 9 This is a curve showing the change of the horizontal stress difference influence range along the crack expansion direction with the injection time for a well with a depth of 3000m, when the horizontal stress difference increases to 1.5MPa, which is considered a dangerous situation. Figure 9 As injection progresses, the crack expands, and the impact of horizontal geostress gradually expands. The distance affected by the horizontal geostress difference along the length of the crack is linearly related to the injection time. The maximum impact distance during this injection process is 800 meters from the injection point.

[0090] Please refer to Figure 10 , Figure 10 This is the curve of the horizontal stress difference along the length of the first hydraulic fracture at different time points during the entire second hydraulic fracture injection process. Figure 10 It can be seen that the horizontal geostress difference is affected by the second hydraulic fracturing operation along the length of the fracture, and its influence pattern can be divided into four stages. ① Stable stage: Along the length direction, starting from the perforation injection point, the horizontal geostress difference remains roughly unchanged, but its maximum value is lower than the 11.7 MPa before the second hydraulic fracturing operation. Under the influence of the second hydraulic fracturing, its maximum value is 10.5 MPa. ② Sudden drop stage: The horizontal geostress difference suddenly drops sharply, and the point of the sharp drop begins at the tip of the hydraulic fracture length. ③ Slow drop stage: After the sudden drop in the horizontal geostress difference, the horizontal geostress difference begins to slowly decrease. ④ Re-stabilization stage: After the horizontal geostress difference slowly decreases, the horizontal geostress difference tends to stabilize, and the stable horizontal geostress difference is close to but not lower than the initial horizontal geostress difference of 7.41 MPa.

[0091] Please refer to Figure 11 , Figure 11 For a well with a depth of 3000m, the horizontal stress difference is considered dangerous when it increases to 1.5MPa. The curve of the influence range of the horizontal stress difference affected by the second stage fracturing along the crack propagation direction changes with the injection time. Figure 11 As injection progresses, the crack propagates forward, and the impact of horizontal geostress gradually expands. The distance affected by the horizontal geostress difference along the length of the crack is linearly related to the injection time. The maximum impact distance during this injection process is 1700 meters from the injection point.

[0092] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A method for simulating the effect of hydraulic fracturing on ground stress, characterized in that: include: Obtain design parameters and perforation parameters of the fracturing well; Establishing a hydraulic fracture expansion model according to the design parameters of the fractured well; Establishing a numerical model of the impact of hydraulic fracturing on the formation based on the hydraulic fracture expansion model and the perforation parameters; Based on the numerical model of the impact of fracturing construction on the formation, the change law of the ground stress in the formation around the fracturing well is determined; Determine the scope of the hydraulic fracture expansion model based on the design parameters of the fracturing well, specifically including: According to the design parameters of the fracturing well, the actual fracturing starting point of the target well is determined and projected onto a plane to obtain a plane projection diagram of the fracturing well; Determining the scope of the hydraulic fracture expansion model according to the plan projection diagram; Based on the hydraulic fracture expansion model and the perforation parameters, a numerical model of the impact of fracturing on the formation is established, specifically including: adding injection points in the hydraulic fracture expansion model according to the perforation parameters; A cohesive unit is set at each injection point in the hydraulic fracture expansion model; The fracture propagation parameters on each cohesive unit are calculated to obtain a numerical model of the impact of fracturing on the formation. Based on the numerical model of the impact of fracturing construction on the formation, the change law of the ground stress in the formation around the fracturing well is determined, including: The numerical model of the impact of fracturing construction on the formation was imported into the finite element analysis software to carry out numerical simulation calculations, and the ground stress data along the length direction of the hydraulic fracture at different injection construction times were obtained: Based on the geostress data along the length of the hydraulic fracture at different injection construction times, the control range and variation law of the horizontal geostress difference caused by fracturing injection are obtained, thereby determining the variation law of the geostress in the formation around the fracturing well.

2. The method for simulating the influence of hydraulic fracturing on ground stress according to claim 1, characterized in that: The design parameters of the fracturing wells include the well location distribution data of the fracturing wells and the wellbore trajectory of each fracturing well.

3. The method for simulating the influence of hydraulic fracturing on ground stress according to claim 1, characterized in that: According to the design parameters of the fracturing well, a hydraulic fracture expansion model is established, which specifically includes: Determining the range of a hydraulic fracture expansion model based on design parameters of the fractured well; According to the design parameters of the fracturing well and based on the fracture expansion judgment criterion, a hydraulic fracture expansion model is established within the scope of the hydraulic fracture expansion model, wherein the fracture expansion judgment criterion is a maximum energy release rate criterion.

4. The method for simulating the influence of hydraulic fracturing on ground stress according to claim 1, characterized in that: The cohesive unit is a COH3D8P unit type.

5. The method for simulating the influence of hydraulic fracturing on ground stress according to claim 1, characterized in that: The crack extension parameters include stress, displacement, damage factor and crack width.

6. A device for simulating the effect of hydraulic fracturing on ground stress, characterized in that: The method comprises a processor and a memory, wherein a computer program is stored in the memory, and when the computer program is executed by the processor, the method for simulating pore pressure changes during fracturing according to any one of claims 1 to 5 is implemented.

7. A computer-readable storage medium, characterized in that The computer-readable storage medium stores one or more programs, and the one or more programs can be executed by one or more processors to implement the steps in the method for simulating the impact of fracturing construction on ground stress as described in any one of claims 1 to 5.

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