Well group dynamic stress field change simulation method

Abstract

The invention provides a well group dynamic stress field change simulation method, and relates to the technical field of geological exploration, and the method comprises the following steps: carrying out four-dimensional ground stress field modeling under different development modes: establishing a water injection development oil reservoir-geomechanical coupling and fracturing development oil reservoir-geomechanical coupling numerical model, and dividing key stages according to age limit, analyzing the change condition of the minimum horizontal principal stress of the whole work area; analyzing a crustal stress change rule in a water injection development mode, and respectively carrying out dynamic stress field analysis on a typical water injection well and an oil production well in the work area under different development stage conditions; and analyzing a crustal stress change rule in a fracturing development mode, and carrying out dynamic stress field analysis on two fractured wells in a work area under different development stage conditions. According to the method, the stress states of different well layers after the formation pressure is attenuated are known by simulating and analyzing the change of the dynamic stress field of the well group, and the method is of great significance to old area repeated fracturing well layer selection and fracturing process optimization.

Description

Technical Field

[0001] The invention relates to the technical field of geological exploration, and in particular to a method for simulating changes in dynamic stress fields of a well group. Background Art

[0002] The basic principle of depletion development is to create a pressure difference in the reservoir to push oil and gas to the wellhead to improve the recovery rate. It maintains the pressure in the reservoir by injecting fracturing fluid, water drive or other pressurization means into the reservoir. Over time, the pressure in the reservoir gradually decreases, and the oil and gas production may decline. When the reservoir pressure drops to a level that cannot maintain economic production, the reservoir is considered "depleted". As the reservoir quality gradually deteriorates, the depletion development reservoir gradually increases. After a long period of development, the formation pressure decay affects the change of ground stress, that is, the dynamic stress field of the well group changes. By simulating and analyzing the changes in the dynamic stress field of the well group, the stress state of different well layers after the formation pressure decay can be understood. Lower principal stress may contribute to the formation of cracks, which helps to evaluate the potential for crack formation and prefer re-fractured well layers. By understanding the changes in the dynamic stress field, the direction of the fracturing crack can be optimized. Selecting a fracture direction that matches the principal stress direction helps to improve the stability and productivity of the fracture. Changes in the dynamic stress field may affect the propagation of the fracturing fluid in the formation, so the parameters of the fracturing fluid can be adjusted according to the characteristics of the stress field to improve the effective penetration of the liquid in the formation. Therefore, it is of great significance to clearly understand and grasp the changes in the dynamic stress field of the well group for the selection of well layers for repeated fracturing in old areas and the optimization of fracturing technology.

[0003] CN 106991236 B discloses a repeated fracturing layer selection method based on four-dimensional dynamic geostress changes. The method establishes a fracture extension calculation model, considers the impact of initial fracturing on reservoir seepage and mechanical state, and achieves a more accurate understanding of reservoir characteristics during repeated fracturing, effectively avoiding communication with aquifers. However, the method only focuses on the stress changes of a single well, and fails to reflect the changes in the geostress of the well group and the surrounding areas with the mining time and number of mining.

[0004] If the change rules of the well group and the ground stress field around the well are not mastered with the mining time and number, the fracturing effect of the well group will be poor, thus reducing the maximum production. In terms of fracturing effect, the change of the ground stress field of the well group and the ground stress field around the well may make it difficult for the cracks to expand in the expected direction and range. The expansion of the high stress area may lead to the early closure of the cracks, thereby reducing the persistence of the cracks and the permeability to the formation; in terms of maximum production, due to the restriction of the cracks, the increased risk of closure and the difficulty in controlling the path, it may eventually lead to a reduction in the production fracture area, thereby reducing the maximum production. Summary of the invention

[0005] The purpose of the present invention is to provide a method for simulating the change of dynamic stress field of a well group, establish a physical model of reservoir development mode-reservoir geomechanics coupling, explore the characteristics of four-dimensional geostress field under water injection and depletion development reservoir-geomechanics matching mode, analyze the maximum and minimum geostress change laws of two wells under water injection development and fracturing development modes respectively, and obtain the dynamic geostress change laws of well groups under different development modes, so as to facilitate the subsequent optimization of fracturing effect and increase the maximum production.

[0006] To achieve the above object, the present invention is implemented through the following technical solutions:

[0007] A method for simulating changes in dynamic stress fields of a well group, characterized in that it comprises the following steps:

[0008] Step S1: Modeling the four-dimensional geostress field in the water injection development mode and the fracturing development mode to obtain simulation data of the overall and local changes of geostress;

[0009] Step S2: Analyze the simulation data of the ground stress variation law under the water injection development mode to obtain the ground stress variation law of the well group and the surrounding areas;

[0010] Step S3: Analyze the simulation data of the ground stress variation law under the fracturing development mode to obtain the ground stress variation law of the well group and the surrounding areas.

[0011] Further: Step S1 specifically includes: establishing a numerical model of water injection development reservoir-geomechanical coupling and fracturing development reservoir-geomechanical coupling, and dividing the key stages according to years, simulating the model to obtain the temporal evolution data of the ground stress, obtaining the ground stress map and analyzing the change of the minimum horizontal principal stress of the entire work area.

[0012] Further: Step S2 specifically includes: obtaining the time evolution data of the ground stress from the simulation data to form a dynamic stress field diagram, and performing dynamic stress field analysis on a water injection well and an oil production well in the work area under different development stage conditions, extracting the maximum and minimum principal stress data of the water injection well and the oil production well, analyzing and deriving the change law.

[0013] Further: Step S3 specifically includes: obtaining the time evolution data of the ground stress from the simulation data to form a dynamic stress field diagram, and performing dynamic stress field analysis on the two fracturing wells in the work area under different development stage conditions, extracting the maximum and minimum principal stress data of the two fracturing wells, analyzing and deriving the change law.

[0014] Furthermore, the simulation formula of the waterflooding reservoir-geomechanical coupling numerical model can be expressed as:

[0015] Total induced stress = injection stress + production stress

[0016] Δσ h(x,y,t)=Δσ ji (x h ,y h ,t)+Δσ hp (x h ,y h ,t)

[0017] Δσ H (x,y,t)=Δσ ji (x H ,y H ,t)+Δσ hp (x H ,y H ,t)

[0018] Δσ v (x,y,t)=Δσ ji (x v ,y v ,t)+Δσ hp (x v ,y v ,t)

[0019] In the formula, Δσ h (x, y, t) is the induced stress generated in the direction of the minimum horizontal principal stress; Δσ H (x, y, t) is the induced stress generated in the direction of the maximum horizontal principal stress; Δσ v (x, y, t) is the induced stress in the vertical direction; Δσ ji (x h ,y h ,t) is the injection stress in the direction of the minimum horizontal principal stress; Δσ ji (x H ,y H ,t) is the injection stress in the direction of the maximum horizontal principal stress; Δσ ji (x v ,y v ,t) is the vertical injection stress; Δσ hp (x h ,y h ,t) is the production stress in the direction of the minimum horizontal principal stress; Δσ hp (x H ,y H ,t) is the production stress in the direction of the maximum horizontal principal stress; Δσ hp (x v ,y v ,t) is the vertical production stress.

[0020] Furthermore, the simulation formula of the coupled numerical model of reservoir-geomechanics for fracturing development can be expressed as:

[0021] Total induced stress = initial compressive stress + production stress

[0022] Δσ h (x,y,t)=Δσ hf (x h ,y h ,t)+Δσ hp (x h ,y h ,t)

[0023] Δσ H (x,y,t)=Δσ hf (x H ,y H ,t)+Δσ hp (x H ,y H ,t)

[0024] Δσ v (x,y,t)=Δσ hf (x v ,y v ,t)+Δσ hp (x v ,y v ,t)

[0025] In the formula, Δσ h (x, y, t) is the induced stress generated in the direction of the minimum horizontal principal stress; Δσ H (x, y, t) is the induced stress generated in the direction of the maximum horizontal principal stress; Δσ v (x, y, t) is the induced stress in the vertical direction; Δσ hf (x h ,y h ,t) are the initial compressive stress in the direction of the minimum horizontal principal stress, i.e., the rigid deformation stress; Δσ hf (x H ,y H ,t) is the initial compressive stress in the direction of the maximum horizontal principal stress; Δσ hf (x v ,y v ,t) is the initial compressive stress in the vertical direction; Δσ hp (x h ,y h ,t) is the production stress in the direction of the minimum horizontal principal stress; Δσ hp (x H ,y H ,t) is the production stress in the direction of the maximum horizontal principal stress; Δσ hp (x v ,y v ,t) is the vertical production stress.

[0026] Furthermore: in the established geostress field model, the geostress field before repeated fracturing includes five links: isotropic in-situ stress field, anisotropic in-situ stress field, geostress field after initial pressure, stress field after production water injection and heavy pressure stress field; the static geomechanical model is combined with reservoir simulation and geomechanical model to realize fluid-solid parameter coupling, and finally the cross-iterative coupling method is used to solve the model to realize four-dimensional geostress simulation.

[0027] Further: the cross-iterative coupling method is used to solve the model obtained after the fluid-solid parameter coupling. The specific steps are: realize the data interaction of "corner point grid" and "tetrahedron grid" through the autonomous program, and realize the coupled loop solution of the model obtained after the fluid-solid parameter coupling; the steps and algorithms of the autonomous program specifically include:

[0028] Finite difference grid division of seepage field, input of geological parameters, fluid parameters and well control parameters, etc., and calculation of fluid pressure;

[0029] The "corner point" grid is the division of the stress field unstructured grid and the stress field is calculated, in which the output pressure of the seepage field is the input parameter of the stress field, and the interactive process of this autonomous program is realized;

[0030] When the next time step is performed, the seepage field and stress field are calculated according to the above steps and processes, and the solutions are cyclically solved in sequence.

[0031] Furthermore: water injection wells and oil production wells under the water injection development mode with a diamond inverted nine-point well pattern are selected, and the local grid units of the water injection wells and oil production wells are separated respectively; the stress field change law of the well group is analyzed as a whole through numerical simulation, and then the stress field change law around the water injection wells and oil production wells is analyzed and obtained respectively.

[0032] Furthermore: when analyzing the dynamic stress field of two fracturing wells in the work area under different development stage conditions, repeated fracturing operation was carried out on one of the wells; the errors of the numerical simulation results of formation pressure and ground stress and the field measured values ​​were analyzed to verify the feasibility of the model.

[0033] Compared with the original technology, the present invention has the following beneficial effects:

[0034] 1. This method establishes a physical model of reservoir development mode-reservoir geomechanics coupling, explores the characteristics of the four-dimensional geostress field under the water injection and depletion development reservoir-geomechanics matching mode, analyzes the maximum and minimum geostress variation laws of the two wells under the water injection development and fracturing development modes, and obtains the dynamic geostress variation laws of the well group under different development modes, so as to facilitate the subsequent optimization of fracturing effects and increase the maximum production.

[0035] 2. The seepage field is solved by the finite difference method, and the stress field is solved by the finite element method. The previous stress field and seepage field are solved separately and sequentially, which is innovated to interactive solution through grid. It solves the problem that different types of grids have significant differences in positioning, mapping and attribute interpolation, and realizes the coupled cycle solution of "seepage field-stress field". It only needs to add the corresponding well model to realize the coupled cycle solution of "seepage field-stress field", which is suitable for the analysis of the changing law of dynamic stress field of well groups with different development modes.

[0036] 3. Comparison of simulation results with field measurement data verifies the feasibility of the model and improves the credibility of the simulation method.

[0037] 4. This method can explore the characteristics of the four-dimensional geostress field under the water injection and depletion development reservoir-geomechanical matching mode, and provide theoretical guidance and support for repeated fracturing screening in oil fields.

[0038] 5. This method models the four-dimensional geostress field under different development modes: numerical models of water injection development reservoir-geomechanical coupling and fracturing development reservoir-geomechanical coupling are established, and the four-dimensional geostress field under the water injection and depletion development reservoir-geomechanical matching modes is explored.

[0039] 6. This method analyzes the dynamic geostress field of the entire work area, one water injection well and one production well in the diamond inverse nine-point method, and two fracturing wells, and obtains the variation laws of the maximum and minimum principal stresses. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a flow chart of a method for studying the change of dynamic stress field of a well group under different depletion mode conditions of the present invention;

[0041] Figure 2 It is a distribution diagram of the formation pressure changes in the entire work area at different development stages according to the specific implementation of the present invention;

[0042] Figure 3 It is a numerical simulation grid distribution diagram of two research well groups specifically implemented by the present invention;

[0043] Figure 4 It is a schematic diagram of the change of the stress field of a well group under the water injection development conditions specifically implemented by the present invention;

[0044] Figure 5 It is a schematic diagram of cutting local grid units by a water injection well and an oil production well in a water injection development mode specifically implemented by the present invention;

[0045] Figure 6 It is a schematic diagram of stress field changes of a water injection well group and a histogram of minimum horizontal principal stress under a water injection development mode specifically implemented by the present invention;

[0046] Figure 7It is a schematic diagram of stress field changes of an oil well group under a water injection development mode specifically implemented by the present invention and a histogram of minimum horizontal principal stress;

[0047] Figure 8 It is a comparison diagram of the minimum horizontal principal stress drop law around the water injection well and the development well under the water injection development mode specifically implemented by the present invention;

[0048] Fig. 9 It is a simulation diagram of two fracturing wells in the fracturing development mode specifically implemented by the present invention;

[0049] Fig.10 It is a schematic diagram of stress field changes of two fracturing wells and a histogram of minimum horizontal principal stress in the fracturing development mode specifically implemented by the present invention;

[0050] Fig.11 It is a schematic diagram of the change of the local stress field caused by the change of stiffness in two fracturing wells under the fracturing development mode specifically implemented by the present invention and a comparison histogram of the two-way stress difference;

[0051] Fig.12 It is a schematic diagram of the error between the numerical simulation result of the formation pressure and the field measured value in the specific implementation of the present invention;

[0052] Fig.13 It is a schematic diagram of numerical simulation of repeated fracturing specifically implemented in the present invention. DETAILED DESCRIPTION

[0053] The technical solution of the present invention will be described clearly and completely below 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 creative work are within the scope of protection of the present invention.

[0054] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0055] like Figure 1 As shown: A method for simulating changes in dynamic stress fields of a well group includes the following steps:

[0056] Step S1: Modeling the four-dimensional geostress field under different development modes, establishing numerical models of water injection development reservoir-geomechanical coupling and fracturing development reservoir-geomechanical coupling, dividing key stages according to years, simulating the model to obtain geostress evolution data over time, further obtaining geostress diagrams and analyzing the changes in the minimum horizontal principal stress of the entire work area, and obtaining the overall and local changes in geostress;

[0057] The simulation formula of the waterflooding reservoir-geomechanics coupling numerical model can be expressed as:

[0058] Total induced stress = injection stress + production stress

[0059] Δσ h (x,y,t)=Δσ ji (x h ,y h ,t)+Δσ hp (x h ,y h ,t)

[0060] Δσ H (x,y,t)=Δσ ji (x H ,y H ,t)+Δσ hp (x H ,y H ,t)

[0061] Δσ v (x,y,t)=Δσ ji (x v ,y v ,t)+Δσ hp (x v ,y v ,t)

[0062] In the formula, Δσ h (x, y, t) is the induced stress generated in the direction of the minimum horizontal principal stress; Δσ H (x, y, t) is the induced stress generated in the direction of the maximum horizontal principal stress; Δσ v (x, y, t) is the induced stress in the vertical direction; Δσ ji (x, y, t) are the minimum and maximum horizontal principal stress directions and the vertical injection stress respectively; Δσ hp (x, y, t) are the minimum and maximum horizontal principal stress directions and the production stress in the vertical direction, respectively;

[0063] The simulation formula of the coupled numerical model of reservoir-geomechanics for fracturing development can be expressed as:

[0064] Total induced stress = initial compressive stress (rigid deformation stress) + production stress

[0065] Δσ h (x,y,t)=Δσ hf (x h ,y h ,t)+Δσ hp (x h ,y h ,t)

[0066] Δσ H (x,y,t)=Δσ hf (x H ,y H ,t)+Δσ hp (x H ,y H ,t)

[0067] Δσ v (x,y,t)=Δσ hf (x v ,y v ,t)+Δσ hp (x v ,y v ,t)

[0068] In the formula, Δσ hf (x, y, t) are the initial compressive stress in the direction of minimum and maximum horizontal principal stress and vertical direction, i.e., rigid deformation stress.

[0069] The geostress field before repeated fracturing involves five links: isotropic in-situ stress field, anisotropic in-situ stress field, geostress field after initial pressure, stress field after production water injection, and heavy pressure stress field. The key to realizing four-dimensional geostress simulation is to use static geomechanical model as the main model, and then combine reservoir simulation and geomechanical model to realize fluid-solid parameter coupling, and finally use cross-iterative coupling method to solve the model. The specific steps of using cross-iterative coupling method to solve the model obtained after fluid-solid parameter coupling are: realize the data interaction of "corner point grid" and "tetrahedron grid" through autonomous program, and realize the coupled loop solution of the model obtained after fluid-solid parameter coupling; the steps and algorithms of autonomous program specifically include:

[0070] Finite difference grid division of seepage field, input of geological parameters, fluid parameters and well control parameters, etc., and calculation of fluid pressure;

[0071] The "corner point" grid is the division of the stress field unstructured grid and the stress field is calculated, in which the output pressure of the seepage field is the input parameter of the stress field, and the interactive process of this autonomous program is realized;

[0072] When the next time step is performed, the seepage field and stress field are calculated according to the above steps and processes, and the solutions are cyclically solved in sequence.

[0073] Step S2: Analyze the variation law of ground stress under the water injection development mode, obtain the time evolution data of ground stress from the simulation data to form a dynamic stress field diagram, and perform dynamic stress field analysis on a water injection well and an oil production well in the work area under different development stages, extract the maximum and minimum principal stress data of the water injection well and the oil production well and analyze their variation law, and obtain the variation law of ground stress in the well group and around the well;

[0074] The water injection wells and oil production wells in the water injection development mode with diamond inverted nine-point well pattern are selected, and the local grid units of the water injection wells and oil production wells are separated respectively. The stress field variation law of the well group is analyzed as a whole through numerical simulation, and then the stress field variation law around the water injection wells and oil production wells is analyzed separately.

[0075] Step S3: Analyze the variation law of geostress under the fracturing development mode, obtain the temporal evolution data of geostress from the simulation data to form a dynamic stress field diagram, and perform dynamic stress field analysis on two fracturing wells in the work area under different development stage conditions, extract the maximum and minimum principal stress data of the two fracturing wells and analyze their variation law, and obtain the variation law of geostress in the well group and around the wells.

[0076] A fracturing development model was selected for numerical simulation, and the dynamic stress field analysis of two fracturing wells in the work area under different development stages was studied. Repeated fracturing operation was carried out on one of the wells.

[0077] In the dynamic stress field analysis under the fracturing development mode, the pressure and pump-off pressure curves of well test interpretation at different time nodes are used to reversely calculate the minimum horizontal principal stress at different development times, and analyze the errors between the numerical simulation results of formation pressure and ground stress and the field measured values. Based on the calculation of dynamic stress field by geomechanics, repeated fracturing numerical simulation is carried out, and production prediction is performed.

[0078] The following examples are provided to further illustrate the scheme and effects of the present invention:

[0079] Carry out four-dimensional geostress field modeling under different development modes, establish numerical models of reservoir-geomechanics coupling for water injection development and reservoir-geomechanics coupling for fracturing development, divide key stages according to years, simulate the model to obtain data on the evolution of geostress over time, further obtain geostress diagrams and analyze the changes in the minimum horizontal principal stress of the entire work area, and derive the overall and local changes in geostress;

[0080] like Figure 2As shown, in one embodiment, the entire time period of 44 years (1977-2021) is divided into four key stages: 1977, 1992, 2007, and 2021. It can be seen from the figure that the pore pressure (ground stress) decreases as a whole, and the local changes vary greatly.

[0081] like Figure 3 As shown in the figure, two numerical simulation grid distribution maps of well group 1 (water injection development mode) and well group 2 (fracturing depletion development mode) are selected for research, and the dynamic stress field change law caused by different development modes is analyzed in combination with a single well.

[0082] Analyze the variation law of ground stress under the water injection development mode, obtain the time evolution data of ground stress from the simulation data to form a dynamic stress field diagram, and conduct dynamic stress field analysis under different development stages for a water injection well and an oil production well in the work area, extract the maximum and minimum principal stress data of the water injection well and the oil production well and analyze their variation law, and obtain the variation law of ground stress in the well group and around the well;

[0083] like Figure 4 As shown in the figure, with the continuous development of water injection, the size of the ground stress shows a downward pattern, the area of ​​decline is gradually increasing, and a larger ground stress decline zone appears near the oil wells; the overall ground stress decline trend in the well group is affected by the water injection relationship, and the decline trend around each well is relatively uniform.

[0084] Figure 5 It shows a schematic diagram of cutting local grid units of a typical water injection well (8759) and oil production well (T86861) in the work area under the water injection development mode (diamond inverted nine points).

[0085] like Figure 6 As shown, for the water injection well (8759), with the continued development, the maximum and minimum horizontal stresses show a decreasing trend; the histogram of the minimum principal stress in the work area shifts to the left, decreasing by about 2MPa from 1977 to 1992.

[0086] like Figure 7 As shown in the figure, for the development well (T86861), with the continued development, the maximum and minimum horizontal stresses show a decreasing trend; the histogram of the minimum principal stress in the work area shifts to the left, decreasing by about 5 MPa from 1977 to 1992.

[0087] like Figure 8As shown in the figure, by comparing the decrease law of the minimum horizontal principal stress around the injection well (8759) and the development well (T86861), it can be seen that the decrease range of the average ground stress around the injection well (16.6%) is relatively smaller than the decrease range of the average ground stress value of the development well (22.7%); at the same time, the decrease trend of the ground stress of the injection well is more moderate than that of the development well, which confirms that the water injection of the water injection well has a certain recovery effect on the formation pressure.

[0088] The changing law of geostress under the fracturing development mode is analyzed, and the time evolution data of geostress is obtained from the simulation data to form a dynamic stress field diagram. The dynamic stress field of two fracturing wells in the work area under different development stage conditions is analyzed, and the maximum and minimum principal stress data of the two fracturing wells are extracted and their changing laws are analyzed, thus obtaining the changing law of geostress in the well group and around the wells.

[0089] Fig. 9 A schematic diagram of the dynamic stress field analysis of two fracturing wells (T85231) and (T86004) in the study area under different development stage conditions under the fracturing development mode is shown.

[0090] like Fig.10 As shown in the figure, under different development stages of the two fracturing wells (T85231) and (T86004), the two wells have similar geostress decline trends, and the decline distance area is mainly concentrated near the wells. The overall minimum horizontal principal stress decline is about 12MPa.

[0091] like Fig.11 As shown in the figure, the formation of fracturing cracks around the two fracturing wells (T85231) and (T86004) caused deformation caused by stiffness, which further changed the local stress field. It can be seen that the stress drop presents an elliptical pattern. By counting the two-dimensional stress differences at different production stages, it can be found that the continuous production causes the horizontal two-dimensional stress difference to increase.

[0092] like Fig.12 As shown in the figure, the minimum horizontal principal stress at different development times is inversely calculated using the well test interpretation pressure and pump-off pressure curves at different time nodes, and the errors between the numerical simulation results of formation pressure and ground stress and the field measured values ​​are analyzed. The error is verified to be less than 15%, confirming the reliability of the model.

[0093] like Fig.13 As shown, based on the results of geomechanical calculation of dynamic stress field, repeated fracturing numerical simulation was carried out and production prediction was performed. The comparison table between the simulation results and the field measured data is shown in Table 1 below. It can be seen that the simulation results are consistent with the field measured data, which further verifies the reliability of the model.

[0094] Table 1: Comparison of simulation results and field measured data

[0095]

[0096] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent transformation or modification made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for simulating changes in dynamic stress fields of a well group, characterized by: The following steps are involved: Step S1: Modeling the four-dimensional geostress field in the water injection development mode and the fracturing development mode to obtain simulation data of the overall and local changes of geostress; Step S2: Analyze the simulation data of the ground stress variation law under the water injection development mode to obtain the ground stress variation law of the well group and the surrounding areas; Step S3: Analyze the simulation data of the ground stress variation law under the fracturing development mode to obtain the ground stress variation law of the well group and the surrounding areas.

2. A method for simulating changes in dynamic stress fields of a well group according to claim 1, characterized in that: Step S1 specifically includes: A water injection reservoir-geomechanical coupling numerical model and a fracturing reservoir-geomechanical coupling numerical model were established, and the key stages were divided according to the years. After simulating the model, the temporal evolution data of the geostress were obtained, and the geostress diagram was obtained and analyzed to obtain the change of the minimum horizontal principal stress in the entire work area.

3. A method for simulating changes in dynamic stress field of a well group according to claim 1, characterized in that: Step S2 specifically includes: The time evolution data of geostress are obtained from the simulation data to form a dynamic stress field diagram, and the dynamic stress field analysis of a water injection well and an oil production well in the work area under different development stages is carried out respectively. The maximum and minimum principal stress data of the water injection well and the oil production well are extracted and analyzed to derive the variation law.

4. A method for simulating changes in dynamic stress fields of a well group according to claim 1, characterized in that: Step S3 specifically includes: The time evolution data of geostress are obtained from the simulation data to form a dynamic stress field diagram, and the dynamic stress field analysis of two fracturing wells in the work area under different development stage conditions is carried out. The maximum and minimum principal stress data of the two fracturing wells are extracted and analyzed to derive the change law.

5. A method for simulating changes in dynamic stress field of a well group according to claim 2, characterized in that: The simulation formula of the waterflooding reservoir-geomechanics coupling numerical model can be expressed as: Total induced stress = injection stress + production stress Board h (x,y,t)=Δσ ji (x h ,y h ,t)+Δσ hp (x h ,y h ,t) Board H (x,y,t)=Δσ ji (x H ,y H ,t)+Δσ hp (x H ,y H ,t) Board v (x,y,t)=Δσ ji (x v ,y v ,t)+Δσ hp (x v ,y v ,t) In the formula, Δσ h (x, y, t) is the induced stress generated in the direction of the minimum horizontal principal stress; Δσ H (x, y, t) is the induced stress generated in the direction of the maximum horizontal principal stress; Δσ v (x, y, t) is the induced stress in the vertical direction; Δσ ji (x h ,y h ,t) is the injection stress in the direction of the minimum horizontal principal stress; Δσ ji (x H ,y H ,t) is the injection stress in the direction of the maximum horizontal principal stress; Δσ ji (x v ,y v ,t) is the vertical injection stress; Δσ hp (x h ,y h ,t) is the production stress in the direction of the minimum horizontal principal stress; Δσ hp (x H ,y H ,t) is the production stress in the direction of the maximum horizontal principal stress; Δσ hp (x v ,y v ,t) is the vertical production stress.

6. A method for simulating changes in dynamic stress field of a well group according to claim 2, characterized in that: The simulation formula of the coupled numerical model of reservoir-geomechanics for fracturing development can be expressed as: Total induced stress = initial compressive stress + production stress Board h (x,y,t)=Δσ hf (x h ,y h ,t)+Δσ hp (x h ,y h ,t) Board H (x,y,t)=Δσ hf (x H ,y H ,t)+Δσ hp (x H ,y H ,t) Board v (x,y,t)=Δσ hf (x v ,y v ,t)+Δσ hp (x v ,y v ,t) In the formula, Δσ h (x, y, t) is the induced stress generated in the direction of the minimum horizontal principal stress; Δσ H (x, y, t) is the induced stress generated in the direction of the maximum horizontal principal stress; Δσ v (x, y, t) is the induced stress in the vertical direction; Δσ hf (x h ,y h ,t) are the initial compressive stress in the direction of the minimum horizontal principal stress, i.e., the rigid deformation stress; Δσ hf (x H ,y H ,t) is the initial compressive stress in the direction of the maximum horizontal principal stress; Δσ hf (x v ,y v ,t) is the initial compressive stress in the vertical direction; Δσ hp (x h ,y h ,t) is the production stress in the direction of the minimum horizontal principal stress; Δσ hp (x H ,y H ,t) is the production stress in the direction of the maximum horizontal principal stress; Δσ hp (x v ,y v ,t) is the vertical production stress.

7. A method for simulating changes in dynamic stress field of a well group according to claim 2, characterized in that: In step S1: in the established Siwei geostress field model, the geostress field before repeated fracturing includes five stress fields: isotropic in-situ stress field, anisotropic in-situ stress field, geostress field after initial pressure, stress field after production water injection, and heavy pressure stress field; the static geomechanical model is combined with the reservoir simulation and the geomechanical model to realize fluid-solid parameter coupling, and finally the cross-iterative coupling method is used to solve the model obtained after fluid-solid parameter coupling to realize four-dimensional geostress simulation and obtain simulation data.

8. A method for simulating changes in dynamic stress fields of a well group according to claim 7, characterized in that: The specific steps of solving the model obtained after fluid-solid parameter coupling using the cross-iterative coupling method are as follows: realizing the data interaction between "corner point grid" and "tetrahedron grid" through the autonomous program, and realizing the coupled cyclic solution of the model obtained after fluid-solid parameter coupling; The steps and algorithms of the autonomous program specifically include: Finite difference grid division of seepage field, input of geological parameters, fluid parameters and well control parameters, etc., and calculation of fluid pressure; "Corner point grid" is the division of the unstructured grid of the stress field and the calculation of the stress field, in which the output pressure of the seepage field is the input parameter of the stress field, and the interactive process of this autonomous program is realized; When the next time step is performed, the seepage field and stress field are calculated according to the above steps and processes, and the solutions are cyclically solved in sequence.

9. A method for simulating changes in dynamic stress fields of a well group according to claim 3, characterized in that: In step S2: water injection wells and oil production wells in a water injection development mode with a diamond-shaped inverted nine-point well pattern are selected, and the local grid units of the water injection wells and oil production wells are separated respectively; the stress field variation law of the well group is analyzed as a whole through numerical simulation, and then the stress field variation law around the water injection wells and oil production wells is analyzed and obtained respectively.

10. A method for simulating changes in dynamic stress field of a well group according to claim 4, characterized in that: In step S3: when the dynamic stress field analysis is performed on two fracturing wells in the work area under different development stage conditions, repeated fracturing operation is carried out on one of the wells; the formation pressure and ground stress numerical simulation results and the errors of the field measured values ​​are analyzed to verify the feasibility of the model.

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