Fractured-vuggy reservoir structure identification method based on Fluent

Abstract

The invention relates to a Fluent-based fractured-vuggy reservoir structure identification method. The method comprises the following steps: constructing a three-dimensional fractured-vuggy reservoir mechanism model as a to-be-tested model; performing grid division on the to-be-tested model to obtain a grid file; the grid file is imported into Fluent software, and transient calculation is carried out; the upper end of a shaft is used as a speed inlet, the mixing speed is 0.1 m / s, and the volume fraction of water is 1; setting a pressure-speed coupling solution algorithm, and outputting pressure data of a speed inlet once every other time step; calculating required water injection time, setting time steps, ending calculation when the total water injection rate or the water injection time is reached, returning the inlet speed to zero, and recalculating; selecting standard initialization calculation; judging whether convergence occurs or not, and if yes, continuously calculating to obtain the time required for convergence; and after the calculation is finished, drawing a double logarithmic diagram of the pressure drop and the pressure drop derivative of the to-be-tested model in the well shut-in stage. The method can help to identify fracture-vug structure types and guide fracture-vug type oil reservoir water injection oil replacement development well selection.

Description

Technical Field

[0001] The invention relates to the field of oil reservoir identification, and in particular to a method for identifying fracture-cavity oil reservoir structure based on Fluent. Background Art

[0002] Carbonate reservoirs account for more than half of the world's total oil and gas resources, most of which are fracture-cave reservoirs. my country's fracture-cave reservoirs are mainly distributed in the Tarim Basin. In fracture-cave reservoirs, large caves are the main storage space for oil and gas resources, and fractures are the main seepage channels. This type of reservoir has the characteristics of strong heterogeneity, complex spatial relationship between fracture-cave reservoirs, discrete distribution, and irregular morphology. The internal fluid flow is complex and irregular, which makes development difficult.

[0003] In the early stage of production, fracture-cave oil reservoirs rely on natural energy for exploitation. As the production time increases, the natural energy gradually decreases, resulting in a rapid decrease in production and a low recovery rate. At this time, water injection for oil replacement is one of the important development methods to improve the recovery rate. It is necessary to inject water into the oil reservoir through the production well, shut down the well after the water injection is completed, and use gravity separation during the well shut-in process to replace oil and water, increase the formation pressure, and open the well for production after the oil and water are fully replaced. After multiple rounds of water injection for oil replacement, the recovery of crude oil is gradually improved. However, the injected water can easily break through to form a dominant channel, resulting in a limited range of water drive, and the effect of water injection for oil replacement gradually deteriorates. The water injection for oil replacement development effects of different fracture-cave unit structures are also different.

[0004] At present, researchers have conducted a large number of physical simulation experiments to divide fracture-cavity units. However, due to the incomplete geological data, the difficulty of describing the fracture-cavity structure and understanding the reserves, the experiments cannot accurately reflect the impact of the fracture-cavity spatial relationship on the effect of water injection to replace oil, and cannot select water injection wells with water injection to replace oil technology, thus causing certain economic losses. Therefore, it is necessary to propose a simulation method for accurately identifying fracture-cavity structures and understanding the flow law of fluids inside fracture-cavity reservoirs and the mechanism of water injection to replace oil. Summary of the invention

[0005] The present invention solves the problem that it is currently impossible to accurately understand the influence of the spatial relationship between fractures and caves on the effect of water injection for oil replacement, and it is impossible to select water injection wells equipped with water injection for oil replacement technology, thereby affecting the effect of water injection for oil replacement and causing economic losses. A Fluent-based fracture-cavity oil reservoir structure identification method is provided to solve the technical problem. The Fluent software is used to visualize the process of water injection for oil replacement in a single well of a fracture-cavity oil reservoir, enriching the mechanism research of water injection for oil replacement, and according to the characteristics of the drawn pressure drop curve, the structural type of the fracture cave can be identified in the actual process of water injection for oil replacement, thereby guiding the well selection for water injection for oil replacement development in fracture-cavity oil reservoirs and improving production efficiency.

[0006] In order to solve the above technical problems, the technical solution of the present invention is as follows:

[0007] A method for identifying fracture-cavity reservoir structure based on Fluent includes the following steps:

[0008] S1. Use the Design Modeler software of the Ansys workbench platform to construct a three-dimensional fracture-cavity reservoir mechanism model with a wellbore, and save the mechanism model as a model to be tested;

[0009] S2. Use Mesh software to mesh the model to be tested, add boundary layer meshes through Insert-Inflation settings, name different fluid domains and boundaries, and save them as mesh files;

[0010] S3. Import the grid file into Fluent software, select double precision, check the grid, then select the pressure-based solver for transient calculation, select laminar flow and multiphase flow models, set the fluid domain and related parameters, and set the fluid material and properties of the model to be tested, the fluid includes crude oil, water, and gas;

[0011] S4. The upper end of the wellbore is taken as the velocity inlet, the mixing velocity is 0.1 m / s, and the volume fraction of water is 1;

[0012] S5. Set the pressure-velocity coupling solution algorithm, and set the residual of the continuity equation to 0.0001, create a monitoring surface in the grid file, set the pressure data at the velocity inlet to be output once every time step; select the standard initialization calculation, and set the animation surface for real-time monitoring;

[0013] S6. Calculate the required injection time according to the following formula, set the time step size, time step number and maximum number of iterations, end the calculation when the total injection volume or injection time is reached, change the inlet speed to 0, restart the calculation and enter the well shut-in stage.

[0014]

[0015] Where Q is the total water injection volume (m 3 ), v is the injection velocity (m / s), r is the wellbore radius (m);

[0016] S7. Determine whether the process has converged. If it has converged, continue to calculate the time required to reach convergence. If it has not converged, appropriately reduce the relaxation factor or modify the pressure-velocity coupling algorithm and recalculate.

[0017] S8. After the calculation is completed, CFD-Post post-processing is used to view the dynamic change process of the oil-water interface during the water injection stage and the shut-in stage. According to the inlet pressure data output by Fluent, a double logarithmic graph of the pressure drop and the pressure drop derivative of the model to be tested during the shut-in stage is drawn.

[0018] Preferably, in step S3, the cracks of the crack holes are set as porous medium regions, and then the porosity of the porous medium region and the viscous resistance coefficients in three directions of x, y and z are input, where the viscous resistance coefficient is the inverse of the permeability of the porous medium.

[0019] Preferably, when checking the mesh quality in step S3, the average value of the element quality is required to be greater than 0.8; the skewness is required to be less than 0.9; the aspect ratio is required to be less than 5, and the boundary layer is required to be less than 10. If any of these conditions is not met, return to step S2 to re-divide the mesh.

[0020] Preferably, in step S6, the SIMPLE method is selected as the pressure-velocity coupling algorithm for solution, and the spatial discretization methods are: the gradient is the least squares unit, the pressure is PRESTO!, the density, momentum, and energy are the second-order upwind format, the volume fraction is the geometric reconstruction, and the transient formula is the first-order implicit.

[0021] Preferably, in step S6, the input initial pressure of the standard initialization is the bottom hole pressure before water injection, and the volume fractions of water and gas are 0; if the reservoir contains gas before water injection, a marked area should be created in advance through Cell Registers-New-Region, and the area should be initialized in combination with Patch, and the volume fraction of gas in the area should be set to 1.

[0022] Preferably, when setting the animation surface in step S6, first

[0023] Set up a cloud map of the oil or water phase volume fraction in Results-Graphics-Contour, then add the cloud map in Solution-Calculation activities-Solution Animations, enter the update frequency, and set the oil or water volume fraction to update every N time steps to monitor the changes in the oil-water interface in real time.

[0024] Preferably, after obtaining the double logarithmic graph of the pressure drop and the pressure drop derivative of the model to be tested in the shut-in stage, the model to be tested is modified to obtain the double logarithmic graphs of the pressure drop and the pressure drop derivative of various fracture-vuggy reservoir mechanism models in the shut-in stage,

[0025] In actual production, the water injection pressure drop curve characteristics of the oil well are tested while the oil well is being injected with water to replace oil. The double logarithmic graph of the pressure drop and the pressure drop derivative in the shut-in stage of the above-mentioned various fracture-cavity reservoir mechanism models is compared to determine the fracture-cavity unit type corresponding to the oil well, so as to select a suitable oil well for water injection to replace oil.

[0026] Beneficial technical effects of the technical solution of the present invention:

[0027] (I) Construct a three-dimensional fracture-cavity reservoir mechanism model, divide the model into grids, and then import the grid file into Fluent software for testing. Use the inlet pressure data output by Fluent to draw a double logarithmic graph of the pressure drop and the pressure drop derivative during the shut-in stage of the model. In actual production, when water-flooding oil wells, the pressure drop curve characteristics of the oil wells can be compared with the double logarithmic graph of the pressure drop and the pressure drop derivative of the model to identify and determine the fracture-cavity structure that is subject to water-flooding treatment, determine the fracture-cavity unit type, and guide the selection of wells for water-flooding oil replacement development in fracture-cavity reservoirs to improve production efficiency.

[0028] (ii) Add a cloud chart in Solution-Calculation activities-Solution Animations and enter the update frequency. You can visually see the changes in the volume fraction of the oil phase or water phase during the calculation process.

[0029] (III) While injecting water to displace oil in the oil well, the water injection pressure drop curve characteristics of the oil well are tested, and compared with the double logarithmic graph of the pressure drop and the pressure drop derivative of various fracture-cavity reservoir mechanism models measured in this scheme during the shut-in stage, the fracture-cavity unit type corresponding to the oil well can be easily determined, so as to select the appropriate oil well for water injection to displace oil. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A structural schematic diagram of a fracture-cavity reservoir structure identification method based on Fluent in an embodiment of the present invention is shown;

[0031] Figure 2 A schematic diagram of the structure of a single crack hole model in an embodiment of the present invention is shown;

[0032] Figure 3 A schematic structural diagram of a double-slit-hole model in an embodiment of the present invention is shown.

[0033] Markings in the accompanying drawings:

[0034] 1-Cave; 2-Crack; 3-Entrance. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical scheme and advantages of the present invention clearer, the following is a further detailed description of a method for identifying fracture-cavity reservoir structure based on Fluent proposed by the present invention in combination with the accompanying drawings and specific embodiments. According to the following description, the advantages and features of the present invention will be clearer. It should be noted that the accompanying drawings are in a very simplified form and use non-precise proportions, which are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention. In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, please refer to the accompanying drawings. It should be noted that the structure, proportion, size, etc. illustrated in the drawings of this specification are only used to match the content disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the present invention, so they have no technical substantive significance. Any modification of the structure, change of the proportional relationship or adjustment of the size, without affecting the effect that the present invention can produce and the purpose that can be achieved, should still fall within the scope of the technical content disclosed by the present invention.

[0036] Example

[0037] The following will be combined with the attached Figure 1 The technical solution of a method for identifying fracture-cavity reservoir structure based on Fluent of the present invention is described in detail with specific embodiments.

[0038] like Figure 1 As shown, a method for identifying fracture-cavity reservoir structure based on Fluent in this embodiment includes the following steps:

[0039] S1. Use the Design Modeler software of the Ansys workbench platform to construct a three-dimensional fracture-cavity reservoir mechanism model with a wellbore, and save the mechanism model as a model to be tested.

[0040] In this step, when constructing the mechanism model, different fracture-cavity structures should be constructed according to the actual situation, such as single cave, single fracture-cavity, double fracture-cavity and triple fracture-cavity, etc., and the two situations of the well inside and outside the cave should also be considered. In the constructed mechanism model, cave 1 can be represented by a cylinder or a cube with a filled interior, while fracture 2 is represented by a slender cylinder or a cuboid, and the wellbore is connected to fracture 2 or cave 1.

[0041] S2. Use Mesh software to mesh the model to be tested, add boundary layer meshes through Insert-Inflation settings, name different fluid domains and boundaries, and save them as mesh files.

[0042] In addition, when performing mesh division, it is also necessary to modify the size of the mesh cells and encrypt the mesh according to the size of the model to be tested.

[0043] S3. Import the mesh file into Fluent software, select double precision, check the mesh, then select the pressure-based solver for transient calculations, select laminar and multiphase flow models, set the fluid domain and related parameters, and set the fluid material and properties of the model to be tested. The fluids include crude oil, water, and gas.

[0044] In this step, based on the problem addressed by this solution, select the VOF model in the laminar flow model and the multiphase flow model. In order to realize the calculation test of the oil-water interface distribution, the VOF model should be selected, the number of phases is 3 (crude oil, water, and gas), and the Implicit Body Force option should be activated. Select the continuous surface tension and wall adhesion in the surface tension model, and input the surface tension coefficients between oil and water, gas and oil, and gas and water as 0.045N / m, 0.04N / m, and 0.072N / m, respectively.

[0045] The above VOF model is mainly applicable to non-steady multiphase flow models, which can simulate the flow of immiscible fluids. All fluids share a set of momentum equations and track the volume fraction of each phase in each calculation unit in the entire flow domain. Assume that the volume fraction of phase j is α j , with α j It represents the ratio of the volume of unit phase j to the total volume of the unit. In the entire flow basin, the sum of the volume fractions of all phases is 1, that is,

[0046]

[0047] For phase j, the mass conservation equation is:

[0048]

[0049] In the formula, m ij is the mass transfer from phase i to phase j.

[0050] The fluid materials in the model of this embodiment have three phases, namely crude oil, water, and gas. Water and crude oil are set as compressible liquids. Among them: gas is an ideal gas (there is a preset ideal_gas in Fluent, and its default properties can be used directly); water is liquid water in the Fluent material database, the input reference pressure is the original formation pressure of 2.3×107Pa, and the reference density is 998.2kg / m 3 , the reference bulk modulus is the inverse of the compressibility coefficient 4.5×10 10 Pa, the density index is 1; the properties of crude oil are modified from the properties of water, and the input reference pressure is set to 2.3×10 7 Pa, reference density is 800kg / m 3 , the reference bulk modulus is 2.7×10 9 Pa, density index is 1.

[0051] There are two fluid domains in the fracture-cavity structure model. The fluid flow in the fracture-cavity reservoir is coupled flow. The flow in the fracture 2 is seepage, which can be set as a porous medium area. The flow in the cave 1 is free flow, which is similar to pipe flow. The present invention uses the Brinkman equation to achieve a unified characterization of seepage and free flow in fracture-cavity reservoirs:

[0052]

[0053] Where ρ is the fluid density, μ is the fluid viscosity, u is the fluid velocity vector, and ρg is the gravity term. is the porosity, K -1 is the permeability tensor, which depends on the medium type. For the free flow region, K=∞, for porous media region, is the regional porosity, K is the regional permeability, K -1 It is called the viscous drag coefficient.

[0054] S4. The upper end of the wellbore is taken as velocity inlet 3, the mixing velocity is 0.1 m / s, and the volume fraction of water is 1;

[0055] S5. Set the pressure-velocity coupling solution algorithm, and set the residual of the continuity equation to 0.0001, create a monitoring surface in the grid file, and set the pressure data at the velocity inlet 3 to be output once every time step; select the standard initialization calculation, and set the animation surface for real-time monitoring.

[0056] In this embodiment, the pressure-velocity coupling algorithm is set to SIMPLE method, and the spatial discretization methods are: the gradient is the least squares unit, the pressure is PRESTO!, the density, momentum, and energy are the second-order upwind format, the volume fraction is the geometric reconstruction, and the transient formula is the first-order implicit.

[0057] Fluent's default convergence criteria are that the residual values ​​of all equations except energy are less than 0.001, and the residual value of energy is less than 1e-6. In general, the default criteria are sufficient. The continuity equation residual is set to 0.0001 here to strictly require and improve calculation accuracy.

[0058] After setting the animation surface in this embodiment, the volume fraction cloud map of oil or water can be updated every N time steps. In actual operation, first set the cloud map of the volume fraction of the oil phase or water phase in Results-Graphics-Contour. Here we set the volume fraction change cloud map of which phase of the entire model we want to monitor; then add the cloud map in Solution-Calculation activities-Solution Animations, enter the update frequency, and you can intuitively see the volume fraction changes of the oil phase or water phase during the calculation process. In addition, set the calculation process to be saved every N time steps in Autosave, which can facilitate viewing the cloud map and animation of the selected time point during post-processing.

[0059] S6. Calculate the required water injection time according to the following formula, set the time step size, time step number and maximum number of iterations, end the calculation when the total water injection volume or water injection time is reached, change the inlet 3 speed to 0, restart the calculation, and enter the well shut-in stage.

[0060]

[0061] Where Q is the total water injection volume (m 3 ), v is the injection velocity (m / s), and r is the wellbore radius (m).

[0062] When setting the time step size, if the time step method is Fixed, set the time step size and number of steps according to the required time. The initial step size is set to 0.0001, and then increase the step size appropriately after the calculation converges. If the time step method is Variable, the step size is automatically adjusted according to the convergence situation.

[0063] S7. Determine whether the process has converged. If it has converged, continue to calculate the time required to reach convergence. If it has not converged, appropriately reduce the relaxation factor or modify the pressure-velocity coupling algorithm and recalculate.

[0064] S8. After the calculation is completed, CFD-Post post-processing is used to view the dynamic change process of the oil-water interface during the water injection stage and the shut-in stage. According to the inlet 3 pressure data output by Fluent, a double logarithmic graph of the pressure drop and the pressure drop derivative of the model to be tested during the shut-in stage is drawn.

[0065] After the convergence is determined, the calculation is continued until the time required for water injection, and then the velocity of inlet 3 is changed to 0 to simulate the shut-in stage. At this time, the operation of outputting the pressure at inlet 3 every other time step still exists, so the output is the pressure data at inlet 3 during all simulation time, and the final analysis is the pressure at the shut-in stage.

[0066] Specifically, in step S3, since the fluid flow mode in fracture 2 is Darcy flow, fracture 2 of the fracture hole is set as a porous medium region, and then the porosity of the porous medium region and the viscous resistance coefficients in the x, y, and z directions are input. The viscous resistance coefficient is the inverse of the permeability of the porous medium region, i.e., fracture 2.

[0067] Specifically, when checking the mesh quality in step S3, it is necessary to ensure that the average value of the element quality is greater than 0.8; the skewness is less than 0.9; the aspect ratio is less than 5, and the boundary layer is less than 10. If any of these conditions are not met, return to step S2 to re-divide the mesh. If the mesh is incorrect or of poor quality, it will cause non-convergence at the beginning or in the middle of the subsequent calculation.

[0068] Specifically, in step S6, the input initial pressure of the standard initialization is the bottom hole pressure before water injection, and the volume fractions of water and gas are 0; if the reservoir contains gas before water injection, a marked area should be created in advance through Cell Registers-New-Region, and the area should be initialized in combination with Patch, and the volume fraction of gas in the area should be set to 1.

[0069] After obtaining the double logarithmic graph of the pressure drop and the pressure drop derivative of the model to be tested during the shut-in stage, the model to be tested is modified to obtain the double logarithmic graphs of the pressure drop and the pressure drop derivative of various fracture-vuggy reservoir mechanism models during the shut-in stage.

[0070] In actual production, the water injection pressure drop curve characteristics of the oil wells are tested while water is injected to replace oil. The double logarithmic graphs of the pressure drop and the pressure drop derivative of the above-mentioned various fracture-cavity reservoir mechanism models in the shut-in stage are compared with the double logarithmic graphs in the actual water injection process to determine the fracture-cavity unit type corresponding to the oil well, so as to select the appropriate oil well for water injection to replace oil.

[0071] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0072] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for identifying fracture-cavity reservoir structure based on Fluent, characterized in that: The following steps are involved: S1. Use the Design Modeler software of the Ansys workbench platform to construct a three-dimensional fracture-cavity reservoir mechanism model with a wellbore, and save the mechanism model as a model to be tested; S2. Use Mesh software to mesh the model to be tested, add boundary layer meshes through Insert-Inflation settings, name different fluid domains and boundaries, and save them as mesh files; S3. Import the grid file into Fluent software, select double precision, check the grid, then select the pressure-based solver for transient calculation, select laminar flow and multiphase flow models, set the fluid domain and related parameters, and set the fluid material and properties of the model to be tested, the fluid includes crude oil, water, and gas; S4. The upper end of the wellbore is taken as the velocity inlet, the mixing velocity is 0.1 m / s, and the volume fraction of water is 1; S5. Set the pressure-velocity coupling solution algorithm, and set the residual of the continuity equation to 0.0001, create a monitoring surface in the grid file, set the pressure data at the velocity inlet to be output once every time step; select the standard initialization calculation, and set the animation surface for real-time monitoring; S6. Calculate the required injection time according to the following formula, set the time step size, time step number and maximum number of iterations, end the calculation when the total injection volume or injection time is reached, change the inlet speed to 0, restart the calculation and enter the well shut-in stage. Where Q is the total water injection volume (m 3 ), v is the injection velocity (m / s), r is the wellbore radius (m); S7. Determine whether the process has converged. If it has converged, continue to calculate the time required to reach convergence. If it has not converged, appropriately reduce the relaxation factor or modify the pressure-velocity coupling algorithm and recalculate. S8. After the calculation is completed, CFD-Post post-processing is used to view the dynamic change process of the oil-water interface during the water injection stage and the shut-in stage. According to the inlet pressure data output by Fluent, a double logarithmic graph of the pressure drop and the pressure drop derivative of the model to be tested during the shut-in stage is drawn.

2. A method for identifying fracture-cavity reservoir structure based on Fluent according to claim 1, characterized in that: In step S3, the cracks of the crack holes are set as porous medium regions, and then the porosity of the porous medium region and the viscous resistance coefficients in the x, y and z directions are input, where the viscous resistance coefficient is the inverse of the permeability of the porous medium.

3. A method for identifying fracture-cavity reservoir structure based on Fluent according to claim 1, characterized in that: When checking the mesh quality in step S3, the average value of the element quality is required to be greater than 0.8; the skewness is required to be less than 0.9; the aspect ratio is required to be less than 5, and the boundary layer is required to be less than 10. If any of these conditions is not met, return to step S2 to re-divide the mesh.

4. A method for identifying fracture-cavity reservoir structure based on Fluent according to claim 1, characterized in that: In step S6, the SIMPLE method is selected as the pressure-velocity coupling algorithm for solution, and the spatial discretization methods are: the gradient is the least squares unit, the pressure is PRESTO!, the density, momentum, and energy are the second-order upwind format, the volume fraction is the geometric reconstruction, and the transient formula is the first-order implicit.

5. The method for identifying fracture-cavity reservoir structure based on Fluent according to claim 1, characterized in that: In step S6, the input initial pressure of the standard initialization is the bottom hole pressure before water injection, and the volume fractions of water and gas are 0; if there is gas in the reservoir before water injection, a marked area should be created in advance through CellRegisters-New-Region, and the area should be initialized in combination with Patch, and the volume fraction of gas in the area should be set to 1.

6. A method for identifying fracture-cavity reservoir structure based on Fluent according to claim 1, characterized in that: When setting the animation surface in step S6, first set the cloud map of the oil phase or water phase volume fraction in Results-Graphics-Contour, then add the cloud map in Solution-Calculation activities-Solution Animations, enter the update frequency, and set the oil or water volume fraction to update every N time steps to monitor the change process of the oil-water interface in real time.

7. A method for identifying fracture-cavity reservoir structure based on Fluent according to claim 1, characterized in that: After obtaining the double logarithmic graph of the pressure drop and the pressure drop derivative of the model to be tested in the shut-in stage, the model to be tested is modified to obtain the double logarithmic graphs of the pressure drop and the pressure drop derivative of various fracture-cavity reservoir mechanism models in the shut-in stage. In actual production, the water injection pressure drop curve characteristics of the oil well are tested while the oil well is being injected with water to replace oil. The double logarithmic graph of the pressure drop and the pressure drop derivative in the shut-in stage of the above-mentioned various fracture-cavity reservoir mechanism models is compared to determine the fracture-cavity unit type corresponding to the oil well, so as to select a suitable oil well for water injection to replace oil.

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