Shale horizontal well staged fracturing casing deformation prediction method

Abstract

The invention relates to a shale horizontal well staged fracturing casing deformation prediction method, which comprises the following steps of S1, establishing a first model based on fault and natural fracture development related conditions and hydraulic fractures expanded by pressure evolution and damage of fractured rocks under set liquid injection and construction conditions, the first model is a three-dimensional fluid-structure interaction damage numerical model containing the stratum size, and the first model is a global model; s2, based on related conditions of the stratum, the cement sheath and the casing pipe, a second model is established, the second model is a stratum-cement sheath-casing pipe deformation model, and the second model is a sub-model; and S3, performing stress change simulation by adopting the first model, transmitting a stress change result of the first model to the second model, and performing casing deformation prediction by utilizing the second model. According to the method, the existence of the three-dimensional structure of the fault and the natural fracture zone and the influence of staged fracturing on the fault and the natural fracture are fully considered, and the horizontal well casing deformation risk in the shale reservoir staged fracturing process can be further accurately predicted in a mode of common simulation of the global model and the sub-model.

Description

Technical Field

[0001] The 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] As an unconventional energy resource with rich reserves and wide distribution of production areas, shale gas has become a new focus of global oil and gas resource development and utilization in recent years. However, due to the deep burial of shale reservoirs, which are mostly in a geological environment with developed natural faults and fractures, horizontal wells and staged fracturing technology are needed to achieve large-scale and efficient development. During the staged fracturing of horizontal wells, multiple segments and clusters of fractures will cause formation creep, change the size and direction of the in-situ stress field around the casing, and thus change the casing force field and cause casing deformation. Casing deformation seriously affects the efficient, safe and economic development of shale gas wells.

[0003] The slip of faults and natural fractures has always been regarded as the main cause of casing deformation. Domestic and foreign scholars have made a series of simulations and analyses on the slip of faults and natural fractures. Usually, a finite element model that includes faults, fractures and casing dimensions is established. The slip is mainly manifested as damage in local weak places, and as the stress increases, this damage will be further strengthened, causing the fault deformation to gradually increase. This model ignores the slip trend of the entire fault and natural fracture, as well as the cross-scale problem between faults, fractures and casing, so the results are not accurate. 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 purpose, the present invention provides the following solutions:

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

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

[0007] S2. Based on the relevant conditions of the formation, cement sheath 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;

[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 study 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 fracture.

[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 hexahedral 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] On the other hand, 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 does not consider the wellbore material, and establishes a first model based on the development of faults and natural fractures, as well as the pressure evolution of fractured rocks and hydraulic fractures caused by damage expansion under set injection and construction conditions. 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 building module, wherein the sub-model building module builds a second model based on relevant conditions such as formation, cement ring, casing material, size, etc., wherein the second model is a formation-cement ring-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 for staged fracturing of shale horizontal wells 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 influence of staged fracturing on faults and natural fractures, and through the joint simulation of the global model and the sub-model, it helps to further accurately predict the risk of casing change of horizontal wells during staged fracturing of shale reservoirs, so as to take targeted casing change 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 drawings required for use in the embodiments will be briefly introduced below. 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 creative labor.

[0023] Figure 1 It is a 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 A schematic diagram and a mesh division diagram of a second model in one embodiment of the present invention;

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

[0028] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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 creative work 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 in conjunction with 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 results in 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 of shale horizontal well staged fracturing, comprising the following steps:

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

[0032] Specifically, the ant body can be used to obtain the occurrence and size of faults and natural cracks near the wellbore. Through the actual parameters of the formation and construction, the fracturing construction parameters and geological parameters are obtained. Using numerical simulation software for simulation, 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 construction parameters can be obtained.

[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 and other parameters; hydraulic fracture parameters simulated under set injection conditions include fracture length, fracture width and other parameters.

[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 grid sizes of the model 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 is used to simulate the hydraulic fracture propagation morphology under the set injection conditions and construction parameters:

[0036] |τ|=p n tanφ+C

[0037] Among them, τ is the shear stress on the failure surface (crack surface), p n is the compressive stress acting in the normal direction of 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 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 ) -a|v|

[0040] Among them, μ is the friction coefficient, μdyn is the dynamic 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 plurality of equations of mutual coupling and control of stress field and seepage field, including: solid mechanics equation, fluid seepage equation, fracture displacement equation. Among them, the solid mechanics equation is for fractures, setting a crack surface pressure as a surface load of bottom hole flow pressure for fracturing. The elastic thin layer boundary condition is suitable for simulating a system containing a very thin elastic layer. The 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 an elastic thin layer, and there is an equation:

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

[0043] where 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 equation establishes a matrix seepage field mathematical model and a fracture seepage field mathematical model according to the different porosity and permeability characteristics of the matrix and natural fractures. Among them, the matrix system equation is:

[0045]

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

[0047] The control 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 friction sliding around faults and natural fracture zones under fluid-solid coupling damage and the resulting stress changes near the fractures, thereby improving the accuracy and comprehensiveness of the simulation.

[0058] S2. Based on the relevant conditions of the formation, cement sheath 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;

[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 fractures change from a stable state to a critical sliding state, and finally to unstable sliding. During this process, the ground stress near the wellbore continues to change due to the creep of the strata.

[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 the interpolation function, the fluid-solid coupling damage of the three-dimensional model is realized, and finally the stress value and its change around the wellbore under the influence of the slip of faults and natural fractures are obtained.

[0063] Specifically, the simulation results of the first model of three-dimensional fluid-solid coupling damage including faults and natural fractures are transferred to the second model including 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 designated as boundary conditions, and the results are assigned to the second model, and the ratio of the source points of the first model (global model) to the source points 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 enables the key part of the casing deformation simulated in the second model to 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, and s and d are the subscripts of the source and target points, respectively.

[0069] Application Examples

[0070] The data used in this application example comes from the actual construction project example of Well X in Block X. According to the on-site construction situation, taking into account the effects of casing changes and natural fractures, a total of 26 sections / 110 clusters were divided after adjustment, with a section length of 47-118m and an average of 67.9m, 3-6 perforation clusters, 5.5-20m cluster spacing, and 13-33m section spacing, with an average of 21m (excluding lost section layers).

[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 side 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] According to the distribution of ant bodies and the pressure evolution of fractured rocks and the hydraulic fractures caused by damage extension 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 This is a 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, hexahedral face mapping is used to control the grid, the grid is "sparse outside and dense inside", and the casing and cement ring are refined by boundary distribution.

[0081] The geostress variation model is used as the global model, and the formation-cement sheath-casing model is used as the sub-model. The changes in the stress field around the fracture under different influencing factors are calculated through the geostress variation model, and then the stress data is transferred to the formation-cement sheath-casing model to obtain the casing deformation.

[0082] Based on the logging and seismic interpretation data, the correspondence between the deformation points of the casing-deformed wells and the natural fractures in this area was statistically analyzed (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 communicate with the horizontal wellbore.

[0083] Table 3 Casing and natural fractures

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

[0085] Correspondingly, such as Figure 5 As shown, the simulation results of the present invention also show that casing deformation occurs in the 4th, 6th, 8th, 16th and 19th natural fracture development areas. This is because during the hydraulic fracture expansion process, due to the stress concentration effect, a fracture expansion action area is formed at the fracture tip. When encountering a natural fracture, the natural fracture surface is affected by shear stress and normal stress at the same time, and the natural fracture slips and produces 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 influence of different fracturing displacements and liquid volumes on casing deformation through crack damage and expansion under different injection conditions, thereby providing technical qualifications 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 casing change of horizontal wells during the staged fracturing of shale reservoirs, and facilitates the adoption of targeted casing change prevention and control measures.

[0088] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for predicting casing deformation in staged fracturing of shale horizontal wells, comprising the following steps: S1. Based on the development of faults and natural fractures, and the pressure evolution of fractured rocks and hydraulic fractures caused by damage expansion under set injection and construction conditions, a first model is established. The first model is a three-dimensional fluid-solid coupling damage numerical model including formation dimensions. The first model is a global model. S2. Based on the relevant conditions of the formation, cement sheath 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. 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.

2. According to the method for predicting casing deformation of shale horizontal well staged fracturing according to claim 1, the fractures include natural fractures and hydraulic fractures.

3. According to the method for predicting casing deformation in staged fracturing of shale horizontal wells as described in claim 1, hydraulic fractures are obtained by using the pressure evolution and damage extension of fractured rocks.

4. According to the method for predicting casing deformation of shale horizontal well staged fracturing according to claim 1, the first model size is larger than the second model size.

5. According to the method for predicting casing deformation of shale horizontal well staged fracturing according to claim 1, the first model uses the augmented Lagrangian method and the Coulomb friction model to simulate the friction slip generated by faults and natural fractures.

6. According to the method for predicting deformation of shale horizontal well segmented fracturing casing in claim 1, the first model is a cuboid, and corresponding boundary loads are set on its top, front and right sides respectively, and the other side faces are set as constraint conditions that only have displacement in the tangential direction, and the cracks are set as construction loads.

7. The method for predicting casing deformation in staged fracturing of shale horizontal wells according to claim 1, wherein the second model uses hexahedral 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.

8. 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 builds 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; A sub-model construction module, wherein the sub-model construction module establishes a second model based on the formation, cement ring, and casing related conditions, wherein the second model is a formation-cement ring-casing deformation model, and the second model is a sub-model; The casing deformation prediction module transfers the stress change result predicted by the global model to the sub-model, and uses the sub-model to predict the casing deformation.

9. 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 for staged fracturing of a shale horizontal well according to any one of claims 1 to 7 are implemented.

10. 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 for staged fracturing of a shale horizontal well according to any one of claims 1 to 7 are implemented.

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