A method for predicting casing deformation in staged fracturing of shale horizontal wells

Abstract

The present invention relates to a method for predicting casing deformation during staged fracturing of shale horizontal wells, comprising the following steps: S1. Based on the development of faults and natural fractures, as well as the pressure evolution of fractured rock and the hydraulic fractures caused by damage expansion under set injection and construction conditions, a first model is established, wherein the first model is a three-dimensional fluid-solid coupling damage numerical model that includes formation dimensions, and the first model is a global model; S2. Based on the development of formations, cement sheaths, and casing, a second model is established, wherein the second model is a formation-cement sheath-casing deformation model, and the second model is a sub-model; S3. The first model is used to simulate stress changes, the stress change results of the first model are transferred to the second model, and the second model is used to predict casing deformation. The present invention fully considers the three-dimensional structure of faults and natural fracture zones and the impact of staged fracturing on faults and natural fractures. By jointly simulating the global model and the sub-models, it helps to further accurately predict the risk of horizontal well casing deformation during staged fracturing of shale reservoirs.

Description

Technical Field

[0001] The present invention relates to the technical field of petroleum and natural gas engineering, and in particular to a method for predicting deformation of a shale horizontal well staged fracturing casing. Background Art

[0002] Shale gas, an unconventional energy resource characterized by abundant reserves and widespread production, has become a new focus of global oil and gas development and utilization in recent years. However, due to the deep burial depth of shale reservoirs, many of which are located in a geological environment rich in natural faults and fractures, achieving scalable and efficient development requires the use of horizontal wells and staged fracturing technology. During staged fracturing in horizontal wells, multiple segments and clusters of fractures can cause formation creep, altering the magnitude and direction of the in-situ stress field around the casing, thereby changing the stress field and causing casing deformation. This deformation severely impacts the efficient, safe, and economic development of shale gas wells.

[0003] Slippage in faults and natural fractures has long been considered the primary cause of casing deformation. Domestic and international scholars have conducted a series of simulations and analyses of slippage in these fractures. These simulations typically use finite element models that integrate the fault, fracture, and casing dimensions. Slippage manifests primarily as damage in localized weak locations, which intensifies with increasing stress, leading to a gradual increase in fault deformation. These models ignore the slip trends of the entire fault and fracture, as well as the cross-scale issues between faults, fractures, and casing, resulting in inaccurate results. Summary of the Invention

[0004] In order to overcome the problems in the prior art, the present invention provides a method for predicting casing deformation in staged fracturing of shale horizontal wells. To achieve the above object, the present invention provides the following solutions:

[0005] A method for predicting casing deformation in staged fracturing of a shale horizontal well comprises the following steps:

[0006] S1. Based on the development of faults and natural fractures, as well as the pressure evolution of fractured rock and the hydraulic fractures caused by damage extension under set injection and construction conditions, a first model is established. The first model is a three-dimensional fluid-solid coupling damage numerical model that includes formation dimensions. The first model is a global model.

[0007] S2. Establishing a second model based on relevant conditions of the formation, cement sheath, and casing, wherein the second model is a formation-cement sheath-casing deformation model, and the second model is a sub-model;

[0008] S3. Use the first model to simulate stress changes, transfer the stress change results of the first model to the second model, and use the second model to predict casing deformation.

[0009] A further technical solution is that the cracks include natural cracks and hydraulic cracks.

[0010] A further technical solution is to use ant bodies and set injection and construction conditions to analyze the pressure evolution and damage expansion of fractured rocks to obtain the occurrence of faults and all cracks.

[0011] A further technical solution is that the first model size is larger than the second model size.

[0012] A further technical solution is that the first model uses the augmented Lagrangian method and the Coulomb friction model to simulate the friction slip generated by the fault and the natural crack.

[0013] A further technical solution is that the first model is a cuboid, and corresponding boundary loads are set on its top, front and right sides respectively, and the other sides are set as constraint conditions with displacement only in the tangential direction, and the cracks are set as construction loads.

[0014] A further technical solution is that the second model uses hexahedron face mapping to control the grid, the grid is "sparse outside and dense inside", and the casing and cement ring are refined using boundary distribution.

[0015] In another aspect, the present invention provides a shale horizontal well staged fracturing casing deformation prediction system, comprising the following modules:

[0016] A global model building module, wherein the global model building module establishes a first model based on the development of faults and natural fractures, as well as the pressure evolution of fractured rock and hydraulic fractures caused by damage extension under set injection and construction conditions, without considering the wellbore material. The first model is a three-dimensional fluid-solid coupling damage numerical model that does not consider the wellbore material including the formation size. The first model is a global model;

[0017] A sub-model construction module, wherein the sub-model construction module establishes a second model based on relevant conditions such as the formation, cement sheath, casing material, size, etc., wherein the second model is a formation-cement sheath-casing deformation model, and the second model is a sub-model;

[0018] The casing deformation prediction module transfers the stress change result predicted by the global model under the combined action of rock deformation and fluid to the sub-model, and uses the sub-model to predict casing deformation.

[0019] On the other hand, the present invention provides a computer device comprising a memory, a processor, and a computer program stored in the memory and running on the processor, characterized in that when the processor executes the computer program, the steps of the shale horizontal well staged fracturing casing deformation prediction method described in any one of the above claims are implemented.

[0020] On the other hand, the present invention provides a computer-readable storage medium having a computer program stored thereon, characterized in that when the computer program is executed by a processor, the steps of the method for predicting casing deformation of shale horizontal well staged fracturing as described in any one of the above claims are implemented.

[0021] The present invention has the following advantages: the present invention fully considers the existence of three-dimensional structures of faults and natural fracture zones and the impact of staged fracturing on faults and natural fractures. By jointly simulating the global model and sub-models, it helps to further accurately predict the risk of horizontal well casing deformation during staged fracturing of shale reservoirs, thereby taking targeted casing deformation prevention and control measures. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 Schematic diagram of the method flow of the present invention;

[0024] Figure 2 A two-dimensional display diagram of the first model in an embodiment of the present invention;

[0025] Figure 3 A schematic diagram and a mesh division diagram of a first model in one embodiment of the present invention;

[0026] Figure 4 Schematic diagram and mesh division diagram of the second model in one embodiment of the present invention;

[0027] Figure 5 This is a diagram showing the casing deformation simulation results in one embodiment of the present invention. DETAILED DESCRIPTION

[0028] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0029] The purpose of the present invention is to provide a method for predicting casing deformation in staged fracturing of shale horizontal wells. In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0030] During staged fracturing, the stress load changes around the faults and natural fractures cause them to slip, which in turn causes casing deformation. In addition, considering the small size of the casing and cement sheath, there is a cross-scale problem between the faults and natural fractures, which will lead to inaccurate simulation of casing deformation. Figure 1 As shown, the present invention provides a method for predicting casing deformation in staged fracturing of a shale horizontal well, comprising the following steps:

[0031] S1. Based on the development of faults and natural fractures, as well as the pressure evolution of fractured rock and the hydraulic fractures caused by damage extension under set injection and construction conditions, a first model is established. The first model is a three-dimensional fluid-solid coupling damage numerical model that includes formation dimensions. The first model is a global model.

[0032] Specifically, ant bodies can be used to determine the occurrence and size of faults and natural fractures near the wellbore. Based on the actual formation and construction parameters, the hydraulic fracturing operation parameters and geological parameters are obtained. Using numerical simulation software, the occurrence and size of hydraulic fractures caused by the pressure evolution and damage expansion of the fractured rock during the injection process under the designed operation parameters can be determined.

[0033] Specifically, fault parameters include fault strike, dip, inclination, etc.; natural fracture parameters include fracture length, fracture width, etc.; fracturing construction parameters include displacement, liquid volume, etc.; geological parameters include elastic modulus, Poisson's ratio, principal stress, porosity, permeability, etc.; hydraulic fracture parameters simulated under set injection conditions include fracture length, fracture width, etc.

[0034] When establishing the first model, the size of the formation model is determined in combination with the target block conditions. The size of the first model is larger than that of the second model, and the number and distribution of the model grid sizes are determined by the size of the formation model. Preferably, in the first model, the grid is refined at the junction of the fracture network to enhance the accuracy of the model simulation.

[0035] After determining the boundary load and initial value of the first model, the Mohr-Coulomb failure principle was used to simulate the hydraulic fracture propagation morphology under the set injection conditions and construction parameters:

[0036] |τ|=p n tanφ+C

[0037] Where τ is the shear stress on the failure surface (crack surface), p n is the compressive stress acting normal to the failure surface, is the friction angle, and C is the cohesive strength before failure.

[0038] Since the change of surrounding external loads during the fracturing process of faults and natural fractures will cause slip, the augmented Lagrangian method and Coulomb friction model are used to simulate the friction slip generated by faults and natural fractures:

[0039] μ=μ dyn +(μ stat -μ dyn )e -a|v|

[0040] Where μ is the friction coefficient, μdyn is the kinetic friction coefficient, μstat is the static friction coefficient, a is the friction attenuation coefficient, and v is the slip velocity.

[0041] Specifically, the first model is a set of multiple equations that control the mutual coupling of stress field and seepage field, including solid mechanics equations, fluid seepage equations, and fracture displacement equations. Among them, the solid mechanics equations are for fractures, setting a surface load with a crack surface pressure equal to the bottom hole flow pressure to perform fracturing. The elastic thin layer boundary condition is suitable for simulating systems containing very thin elastic layers. This boundary condition has elastic and damping properties. It simulates an elastic thin layer with specified stiffness and damping properties by acting between two parts. The fault is regarded as an elastic thin layer, and the equation is:

[0042] F L =-k A d(u u -u d -u0)

[0043] Among them F L is the force per unit length, k A is the spring constant per unit area, u u is the upper displacement, u d is the lower displacement, and u0 is the initial displacement.

[0044] Specifically, the fluid flow equations are based on the different porosity and permeability characteristics of the matrix and natural fractures, and establish a matrix seepage field mathematical model and a fracture seepage field mathematical model respectively. Among them, the matrix system equation is:

[0045]

[0046] Among them: K m is the bedrock permeability; p m is the bedrock pore system pressure; μ is the fluid viscosity.

[0047] The governing equation of the crack system is:

[0048]

[0049] Specifically, the crack displacement model is as follows, and the normal stiffness under crack compression exhibits nonlinear behavior:

[0050] b n =b r +(b0-b r )exp(-ξσ′ n )

[0051]

[0052] Among them, b n is the normal hole, b0 is the initial hole, b r is the residual hole, σ′ n =σ n -p is the effective normal compressive stress, σ n is the total normal stress, p is the fluid pressure, ξ is the stress-void correlation coefficient, which is 1 / [K n0 (b0-b r )],K n0 is the initial normal stiffness. The shear behavior of rock cracks is based on Coulomb's friction law:

[0053]

[0054] τ p =σ′ n tanφ f

[0055] u p =τ p / K s

[0056] Among them, τ s is the shear stress, u s is the shear displacement, K s is the fracture shear stiffness, τ p is the peak shear stress, φ f is the friction angle, u p is the peak shear displacement at which the fracture starts to slip.

[0057] The first model can be used to simulate the frictional sliding around faults and natural fracture zones under fluid-solid coupling damage, as well as the resulting stress changes near the fractures, thereby improving the accuracy and comprehensiveness of the simulation.

[0058] S2. Establishing a second model based on the relevant conditions of the formation, cement sheath, and casing, wherein the second model is a formation-cement sheath-casing deformation model, and the second model is a sub-model;

[0059] Specifically, the parameters related to the casing and cement sheath include corresponding size and material parameters, including: inner diameter, wall thickness, length, material density, elastic modulus, Poisson's ratio, and yield strength.

[0060] During the construction process, the magnitude of the ground stress near the wellbore will change, including: the faults and natural cracks change from a stable state to a critical sliding state, and finally to unstable sliding. During this process, the creep of the stratum causes the ground stress near the wellbore to change continuously.

[0061] S3. Use the first model to simulate stress changes, transfer the stress change results of the first model to the second model, and use the second model to predict casing deformation.

[0062] By calculating the pore pressure caused by the formation fluid in the first model and simulating the pore pressure as external stress through an interpolation function, the fluid-solid coupling damage of the three-dimensional model is realized, and finally the stress value and its changes around the wellbore under the influence of the slip of faults and natural fractures are obtained.

[0063] Specifically, the simulation results of the first three-dimensional fluid-solid coupling damage model containing faults and natural fractures are transferred to the second model containing formation-cement sheath-casing deformation using a generalized stretching operator to transfer the ground stress data as the initial condition. That is, the field variables of the first model are specified as boundary conditions, and the results are assigned to the second model. The ratio of the source point of the first model (global model) to the source point of the second model (sub-model) is assigned to the target mapping position in the second model (sub-model). Since the generalized stretching operator is used for data transfer, the simulation results of the first model (i.e., the global model) are assigned to the second model (sub-model) as the initial value, which makes the key part of the casing deformation simulated in the second model obtain higher accuracy.

[0064] The generalized stretch operator can transfer simulation results from one geometry to another. The source points of the first model correspond to the target points of the second model, so we get:

[0065] x s =ax d

[0066] y s =by d

[0067] z s =cz d

[0068] Where a, b, and c are the ratios of the x, y, and z coordinates of the source and target points, respectively. Finally, enter the right side of the above equation (without subscripts) in the x, y, and z expressions of the target mapping. s and d are the subscripts of the source and target points, respectively.

[0069] Application Examples

[0070] This application example uses data from an actual construction project in Well X, Block X. Based on on-site construction conditions and taking into account the effects of casing deformation and natural fractures, the data was adjusted to 26 segments / 110 clusters. Segment lengths range from 47 to 118 meters, with an average length of 67.9 meters. The number of perforation clusters ranged from 3 to 6, with cluster spacing ranging from 5.5 to 20 meters. The segment spacing ranged from 13 to 33 meters, with an average length of 21 meters (excluding lost segments).

[0071] The basic data collected for the simulation include: (1) initial geostress field, including formation parameters, geostress magnitude, pumping procedure, etc. (2) elastic modulus, Poisson's ratio, density, and yield strength of the formation, cement sheath, and casing.

[0072] Specifically, the size of the first model is 3000m×100m×30m, and the size of the second model is 3000m×1m×1m. The specific basic parameters are shown in Table 1-2.

[0073] Table 1 Basic parameters of the first model

[0074]

[0075]

[0076] Table 2 Basic parameters of the second model

[0077] Material Elastic modulus E(GPa) Poisson's ratio <![CDATA[Density (kg / m 3 )]]> Yield strength (MPa) Reservoir 32 0.24 2600 — cement ring 12 0.16 1950 — casing 210 0.3 7850 758

[0078] The boundary conditions of the first model are set as follows: the top surface is the ground, with a stress load of 68 MPa; the right side is a stress load of 74 MPa; the front is a stress load of 90 MPa; the other surfaces are set as roller supports, and there are no other load conditions; the cracks are set as construction loads.

[0079] Based on the distribution of ant bodies and the pressure evolution of fractured rocks and the hydraulic fractures caused by damage under the set injection and construction conditions, the first model including fault-natural fracture-hydraulic fracture was established. Figure 2 is a two-dimensional display diagram of the first model. Figure 3 Schematic diagram and mesh division diagram of the first model.

[0080] Figure 4 The schematic diagram and mesh division diagram of the second model (including casing-cement sheath-stratum), in which the inner diameter of the casing is set to 0.1m, the wall thickness is 0.01m, and the material density is 7850kg / m 3 The inner diameter of the cement ring is 0.11m, the wall thickness is 0.04m, and the material density is 1950kg / m 3In the second model, hexahedron face mapping is used to control the mesh, which is “sparse outside and dense inside”. The casing and cement sheath are refined using boundary distribution.

[0081] The geostress variation model is used as the global model, and the formation-cement sheath-casing model as a sub-model. The geostress variation model calculates the stress field changes around the fracture under different influencing factors. This stress data is then transferred to the formation-cement sheath-casing model to determine the casing deformation.

[0082] Based on the comprehensive logging and seismic interpretation data, a statistical analysis was conducted on the consistency between the deformation points of the casing-deformed wells in this area and the natural fractures (Table 3). It can be seen from the table that the casing-deformed points are all located in the natural fracture development zone or relatively developed zone, especially where the fractures connect with the horizontal wellbore.

[0083] Table 3 Correlation between casing and natural fractures

[0084] Serial number Number of segments Development of natural cracks at casing deformation points 1 Paragraph 3 Cracks are well developed 2 Paragraph 4 Fractures are well developed and connect the horizontal wellbore 3 Paragraph 6 Cracks are well developed 4 Paragraph 8 Crack development 5 Paragraph 14 Cracks are well developed 6 Paragraph 16 Crack development 7 Paragraph 19 Crack development

[0085] Correspondingly, such as Figure 5 As shown in the simulation results using the present invention, casing deformation also occurs in the natural fracture development areas of sections 4, 6, 8, 16, and 19. This is because during hydraulic fracture propagation, stress concentration creates a crack propagation zone at the fracture tip. When encountering a natural fracture, the natural fracture surface is simultaneously affected by shear stress and normal stress, causing the natural fracture to slip and cause casing deformation. Therefore, there is a certain correlation between natural fractures and casing deformation.

[0086] In addition, the method for predicting casing deformation in staged fracturing of horizontal wells provided by the present invention can also predict the effects of different fracturing displacements and liquid volumes on casing deformation through crack damage and expansion under different injection conditions, thereby providing technical expertise for analyzing and evaluating casing deformation risk zones and preventing casing deformation in horizontal wells.

[0087] It can be seen that the present invention fully considers the three-dimensional structure of faults and natural fracture zones and the impact of the staged fracturing process on faults and natural fractures. Through the joint simulation of the global model and the sub-model, it helps to further accurately predict the risk of horizontal well casing deformation during the staged fracturing of shale reservoirs, making it easier to take targeted casing deformation prevention and control measures.

[0088] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only intended to help understand the method and core concept of the present invention. At the same time, those skilled in the art will find that the specific implementation methods and application scopes may vary based on the concept of the present invention. In summary, the contents of this specification should not be construed as limiting the present invention.

Claims

1. A method for predicting casing deformation in staged fracturing of a shale horizontal well, comprising the following steps: S1. Based on the development of faults and natural fractures, as well as the pressure evolution of fractured rock and the hydraulic fractures caused by damage extension under set injection and construction conditions, a first model is established. The first model is a three-dimensional fluid-solid coupling damage numerical model that includes formation dimensions. The first model is a global model. The first model uses the augmented Lagrangian method and the Coulomb friction model to simulate the friction slip generated by faults and natural fractures; ； in, μ is the friction coefficient, μ dyn is the coefficient of kinetic friction, μ stat is the static friction coefficient, a is the friction attenuation coefficient, v is the slip velocity; S2. Establishing a second model based on relevant conditions of the formation, cement sheath, and casing, wherein the second model is a formation-cement sheath-casing deformation model, and the second model is a sub-model; S3. Using the first model to simulate stress changes, using a generalized stretching operator to transfer the stress change results of the first model to the second model, and using the second model to predict casing deformation; The data transfer method of the generalized stretch operator is: ； ； ； in, a 、 b 、 c The source and target points x 、 y 、 z Ratio of axis coordinates; s 、 d are the source and target points, respectively.

2. The method for predicting casing deformation in staged fracturing of shale horizontal wells according to claim 1, wherein the fractures include natural fractures and hydraulic fractures.

3. The method for predicting casing deformation in staged fracturing of shale horizontal wells according to claim 1, wherein hydraulic fractures are obtained by using the pressure evolution and damage extension of fractured rocks. 4 . The method for predicting casing deformation in staged fracturing of shale horizontal wells according to claim 1 , wherein the first model size is larger than the second model size.

5. According to the method for predicting casing deformation of staged fracturing of shale horizontal wells in claim 1, the first model is a rectangular parallelepiped, and corresponding boundary loads are set on its top, front and right sides respectively, and the other sides are set as constraint conditions with displacement only in the tangential direction, and the cracks are set as construction loads.

6. The method for predicting casing deformation in staged fracturing of shale horizontal wells according to claim 1 , wherein the second model uses a hexahedron face mapping control grid, with a "sparse outside and dense inside" grid, and the casing and cement sheath are refined using boundary distribution.

7. A shale horizontal well staged fracturing casing deformation prediction system, comprising the following modules: A global model building module, wherein the global model building module establishes a first model based on the development of faults and fractures, wherein the first model is a three-dimensional fluid-solid coupling damage numerical model including formation dimensions, and the first model is a global model; The first model uses the augmented Lagrangian method and the Coulomb friction model to simulate the friction slip generated by faults and natural fractures; ， in, μ is the friction coefficient, μ dyn is the coefficient of kinetic friction, μ stat is the static friction coefficient, a is the friction attenuation coefficient, v is the slip velocity; A sub-model construction module, wherein the sub-model construction module establishes a second model based on the relevant conditions of the formation, cement sheath, and casing, wherein the second model is a formation-cement sheath-casing deformation model, and the second model is a sub-model; A casing deformation prediction module uses a generalized stretching operator to transfer the stress change result predicted by the global model to the sub-model, and uses the sub-model to predict casing deformation; The data transfer method of the generalized stretch operator is: ； ； ； in, a 、 b 、 c The source and target points x 、 y 、 z Ratio of axis coordinates; s 、 d are the source and target points, respectively.

8. A computer device comprising a memory, a processor, and a computer program stored in the memory and running on the processor, characterized in that: When the processor executes the computer program, the steps of the method for predicting casing deformation of staged fracturing of a shale horizontal well according to any one of claims 1 to 6 are implemented.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method for predicting casing deformation of staged fracturing of a shale horizontal well according to any one of claims 1 to 6 are implemented.

Images