A method and system for determining wellbore skin permeability
By establishing zoned seepage equations and numerical models near the wellbore, and combining physical experiments and numerical simulations, the permeability coefficient of the wellbore skin is determined, solving the problems of insufficient accuracy and high cost in traditional methods, and realizing the accurate calculation of the wellbore permeability coefficient.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HUAINAN MINING IND GRP
- Filing Date
- 2026-01-05
- Publication Date
- 2026-05-29
AI Technical Summary
Traditional numerical models, which do not design zonal seepage equations, cannot reconstruct the three-dimensional flow field near the wellbore, resulting in insufficient accuracy in calculating the wellbore permeability coefficient. Existing methods lack a unified standard for quantifying relative errors, and the calculation results are highly subjective and have poor repeatability.
By simulating the groundwater flow field near the wellbore using a physical experimental device, the zoned seepage equations for the aquifer and the wellbore skin region are established. The permeability coefficient of the wellbore skin region is adjusted by combining a numerical model, and the degree of fitting is quantified using a preset relative error formula. Finally, the permeability coefficient of the wellbore skin region is determined.
It enables accurate determination of wellbore permeability coefficient, avoiding the accuracy limitations and high costs of traditional methods, and provides a convenient and low-cost solution.
Smart Images
Figure CN122108880A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of hydrogeology, specifically to a method and system for determining the permeability coefficient of a wellbore skin. Background Technology
[0002] In groundwater extraction, oil extraction, and other engineering projects, the study of the hydrogeological characteristics of the area near pumping wells is of great significance. Among these, the permeability coefficient of the well casing, as a key factor affecting the performance of pumping wells, has always received considerable attention. However, due to the complexity of the hydraulic characteristics of the well casing area, the permeability coefficient is usually difficult to obtain accurately. Traditional experimental methods are limited by field conditions and cannot provide accurate permeability coefficient values, while existing numerical simulation methods often rely on assumptions and simplified models, failing to effectively reproduce the actual water flow conditions near the well casing.
[0003] In practical engineering, the wellbore permeability coefficient is usually lower than that of the aquifer. This difference can lead to significant changes in the water flow velocity in the pumping well area, thus significantly impacting the wellbore's extraction efficiency, energy consumption, and the stability of the seepage field. Ignoring the influence of the wellbore permeability coefficient on the flow field will result in errors in groundwater flow velocity, thereby affecting the design and optimization of pumping wells. Especially during groundwater extraction, if the variation in the wellbore permeability coefficient is not fully considered, it means that extracting the same amount of water requires more energy; in oil extraction, this manifests as a decrease in oil well production. Furthermore, ignoring the influence of the wellbore permeability coefficient on the flow field will also interfere with the analysis of seepage and related parameters near the pumping well. For example, when determining the aquifer permeability coefficient through pumping tests, due to the skin effect, complex flow states such as three-dimensional flow and turbulent flow may occur near the pumping well, making it impossible for traditional calculation formulas to accurately determine the aquifer permeability coefficient.
[0004] Existing numerical simulation methods mostly employ homogeneous simplified models and fail to design specific seepage equations for the regional hydraulic characteristics of the "skin zone-aquifer" near the well. This makes it impossible to reconstruct the three-dimensional flow field characteristics, resulting in significant deviations between the model calculation results and the actual flow field. The inversion accuracy of the skin permeability coefficient is insufficient. Furthermore, existing numerical simulation methods often rely on empirical judgment to adjust the skin permeability coefficient, lacking a unified standard for quantifying relative errors. This makes it impossible to determine the skin permeability coefficient that minimizes the error between the simulated wellbore flow velocity and the actual wellbore flow velocity, leading to highly subjective calculation results and poor repeatability. Summary of the Invention
[0005] The purpose of this invention is to provide a method and system for determining the permeability coefficient of wellbore skin, so as to solve the problems mentioned in the background art, such as insufficient accuracy and poor coordination between experiments and models caused by the traditional numerical model not being designed with zonal seepage equations to restore the three-dimensional flow field.
[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for determining the permeability coefficient of a wellbore skin, comprising the following steps: S1: Simulate the groundwater flow field near the well using a physical experimental device; the physical experimental device includes an experimental water tank for filling porous media, a well cylinder set in the experimental water tank, and a water stabilizing tank for regulating the water level at both ends of the experimental water tank. S2: By adjusting the height of the two end water tanks to provide different head differences, the unconfined aquifer system under different flow velocities is simulated, and the actual flow velocity in the wellbore under different head difference conditions and the actual flow velocity of the aquifer measured at the outlet of the experimental water tank are obtained. S3: Based on the geometric parameters of the physical experimental setup, the head difference, and the permeability coefficient of the porous medium, a three-dimensional steady-flow numerical model of the confined aquifer is established. The numerical model divides the area near the well into the aquifer region and the well skin region. S4: Adjust the permeability coefficient of the wellbore skin region in the numerical model, calculate the corresponding simulated wellbore flow velocity output by the numerical model, and determine the permeability coefficient of the wellbore skin region used when the relative error between the simulated wellbore flow velocity and the actual flow velocity in the wellbore is minimized.
[0007] Optionally, in step S3, the groundwater seepage equation for the aquifer region is applicable to r s The region ≤ r < ∞, where r is the distance from the center of the wellbore. s The radius of the wellbore surface area, in meters, is expressed as: ; In the above formula, H is the water head, and K is the water head. ax K ay K az These are the permeability coefficients of the aquifer along the x, y, and z directions, respectively, in m / d. The groundwater seepage equation for the surface region is applicable to r w ≤r<r s The region where r w The radius of the wellbore is in meters (m), and its expression is: ; In the above formula, K sx K sy K sz These are the permeability coefficients of the epidermal region along the x, y, and z directions, respectively, in m / d; In the numerical model, the left and right boundaries of the confined aquifer are set as constant head boundaries, and the front and rear boundaries are set as flux boundaries. The expression is: ; ; In the above formula, S1 and S2 are constant head boundaries; S3 and S4 are flux boundaries; n is the outward normal direction of boundary S3; H1 is the head of boundary S1; and H2 is the head of boundary S2.
[0008] Optionally, in step S4, the relative error between the simulated wellbore flow velocity and the actual flow velocity inside the wellbore is calculated using a preset relative error formula. The preset relative error formula is as follows: ; In the above formula, v obs v is the actual flow velocity inside the wellbore in step S2. sim The simulated wellbore flow velocity is output by the numerical model in step S4.
[0009] A system for determining the permeability coefficient of a wellbore skin includes a physical experimental setup and a numerical simulation and inversion subsystem, wherein... The physical experimental setup includes: The experimental water tank is filled with a porous medium for measuring the permeability coefficient. The well is vertically installed in the experimental water tank and inserted into the porous medium, and the lower part of the well has a hole that communicates with the porous medium. There are two water level stabilizers, which are connected to the two ends of the experimental water tank respectively, and are used to adjust the water level at the two ends of the experimental water tank to form different head differences; The flow velocity monitoring unit inside the well is installed inside the well and is used to monitor the actual flow velocity inside the well. The aquifer velocity monitoring unit is located at the outlet of the experimental water tank and is used to monitor the actual velocity of the aquifer. The numerical simulation and inversion subsystem includes: The data processing and storage unit is used to receive and store data from the wellbore flow velocity monitoring unit and the aquifer flow velocity monitoring unit; The numerical modeling unit is used to establish a three-dimensional steady flow numerical model of a confined aquifer based on the geometric parameters of the physical experimental device, the head difference, and the permeability coefficient of the porous medium, and to divide the area near the well into the aquifer region and the well skin region. The parameter inversion unit is used to adjust the permeability coefficient of the wellbore skin region and perform simulation. The simulated wellbore flow velocity is compared with the actual flow velocity in the well to calculate the fitting error. The wellbore skin permeability coefficient that minimizes the fitting error is obtained through iterative optimization.
[0010] Optionally, water tanks for water level buffering are installed at both ends of the experimental water tank, and the water level stabilizing tanks at both ends are connected to the water tanks at both ends. The function of the water tanks is to smoothly transmit the water level changes of the water level stabilizing tanks to the aquifer, avoiding excessive water flow impact and sand layer disturbance caused by the water level stabilizing tanks being directly connected to the porous medium.
[0011] Optionally, a filter screen is provided at the interface between the water storage tank and the porous medium to prevent the porous medium from entering the water storage tank. The filter screen is used to isolate the water storage unit from the porous medium, ensure unobstructed water flow, and prevent the porous medium from entering the water storage unit due to water flow and causing blockage.
[0012] Optionally, a water tank is installed below the experimental water tank to replenish the aquifer within the tank. The water tank ensures the stability of the water level and head difference during the experiment, preventing fluctuations in the water flow field due to insufficient water volume.
[0013] Optionally, the flow velocity monitoring unit inside the well is a groundwater flow velocity and direction meter, including a controller, cables and a monitoring probe, wherein the monitoring probe is fixed in the well by a steel cable and the front end of the monitoring probe is immersed in water.
[0014] The beneficial effects of this invention are as follows: By establishing a three-dimensional steady-flow numerical model that includes the seepage equations and corresponding boundary conditions for the aquifer region and the wellbore skin region, the three-dimensional flow field characteristics near the well are restored, avoiding the accuracy limitations of traditional homogeneous simplified models. By constructing a numerical model consistent with experimental parameters, the permeability coefficient of the wellbore skin is iteratively adjusted, and the degree of fitting is quantified by a preset relative error formula. Finally, the permeability coefficient of the wellbore skin region used when the relative error between the simulated wellbore flow velocity and the actual flow velocity in the wellbore is minimized is determined. The system utilizes a physical experimental setup and a numerical simulation and inversion subsystem working in tandem. The physical experimental setup uses quartz sand to simulate porous media and sets a groundwater level to recreate the environment of a shallow aquifer. It is paired with a perforated wellbore to reproduce the hydraulic connection between the real well and the aquifer. Furthermore, it adjusts the head difference in the stabilizing tank to create a stable flow field with different velocities within the aquifer, buffers water level changes in the storage tank, mitigates disturbances in the filter sand layer, and manages the water supply to the tank. Combined with flow velocity monitoring units and aquifer flow velocity monitoring units, it ensures stable and reliable multi-dimensional measured data. The numerical simulation and inversion subsystem constructs a three-dimensional numerical model based on experimental parameters and iteratively optimizes the wellbore skin permeability coefficient to achieve a fit between the simulated and measured flow velocities. This system can adjust the height of the stabilizing tank to achieve multi-condition experiments and avoids the problems of geological scene disconnect, large data errors, and high costs associated with traditional methods, thus successfully determining the skin permeability coefficient. Attached Figure Description
[0015] Figure 1 This is a flowchart illustrating a method for determining the permeability coefficient of a wellbore skin according to the present invention. Figure 2 This is a schematic diagram of the physical experimental apparatus of the present invention; Figure 3 This is a three-dimensional mesh partitioning diagram of the numerical model of a method for determining the permeability coefficient of a wellbore skin according to the present invention. Figure 4The figure shows the experimental results of a method for determining the permeability coefficient of a wellbore skin according to the present invention. Figure 5 Aquifer flow velocity fitting diagram for a method of determining the permeability coefficient of a wellbore skin according to the present invention; Figure 6 This is a flow velocity fitting diagram inside the wellbore, which is part of the method for determining the permeability coefficient of the wellbore skin according to the present invention.
[0016] Figure 2 The components are: 1. Experimental water tank; 2. Water storage tank; 3. Porous medium; 4. Stabilizing tank; 5. Water tank; 6. Groundwater level line; 7. Well shaft; 8. Aquifer flow velocity monitoring unit; 9. Controller; 10. Cable; 11. Monitoring probe; 12. Steel rope. Detailed Implementation
[0017] The present application will now be described in further detail with reference to the accompanying drawings. It should be noted that the following specific embodiments are only used to further illustrate the present application and should not be construed as limiting the scope of protection of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application based on the above application content.
[0018] Example 1 Refer to the instruction manual appendix Figure 1 This embodiment discloses a method for determining the permeability coefficient of a wellbore skin, including the following steps: S1: Simulate the groundwater flow field near the well using a physical experimental device; the physical experimental device includes an experimental water tank for filling with porous media, a well cylinder set in the experimental water tank, and a water stabilizing tank for regulating the water level at both ends of the experimental water tank.
[0019] S2: By adjusting the height of the two end water tanks to provide different head differences, the system of unconfined aquifers under different flow velocities is simulated, and the actual flow velocity in the wellbore under different head difference conditions and the actual flow velocity of the aquifer measured at the outlet of the experimental water tank are obtained.
[0020] S3: Based on the geometric parameters of the physical experimental setup, the head difference, and the permeability coefficient of the porous medium, a three-dimensional steady-flow numerical model of the confined aquifer was established using COMSOL Multiphysics software. Refer to the attached instruction manual for the numerical model diagram. Figure 3 The numerical model divides the area near the wellbore into an aquifer region and a wellbore skin region.
[0021] Among them, the groundwater seepage equation for the aquifer region is applicable to r s The region ≤ r < ∞, where r is the distance from the center of the wellbore. s The radius of the wellbore surface area, in meters, is expressed as: ; In the above formula, H is the water head, and K is the water head. ax K ay K az These are the permeability coefficients of the aquifer along the x, y, and z directions, respectively, in m / d. The groundwater seepage equation for the surface region is applicable to r w ≤r<r s The region where r w The radius of the wellbore is in meters (m), and its expression is: ; In the above formula, K sx K sy K sz These are the permeability coefficients of the epidermal region along the x, y, and z directions, respectively, in m / d; In the numerical model, the left and right boundaries of the confined aquifer are set as constant head boundaries, and the front and rear boundaries are set as flux boundaries. The expression is: ; ; In the above formula, S1 and S2 are constant head boundaries; S3 and S4 are flux boundaries; n is the outward normal direction of boundary S3; H1 is the head of boundary S1; and H2 is the head of boundary S2.
[0022] S4: Adjust the permeability coefficient of the wellbore skin region in the numerical model, calculate the corresponding simulated wellbore flow velocity output by the numerical model, and determine the permeability coefficient of the wellbore skin region used when the relative error between the simulated wellbore flow velocity and the actual flow velocity in the wellbore is minimized.
[0023] Optionally, in step S4, the relative error between the simulated wellbore flow velocity and the actual flow velocity inside the wellbore is calculated using a preset relative error formula, which is: In the above formula, v obs v is the actual flow velocity inside the wellbore in step S2. sim The simulated wellbore flow velocity is output by the numerical model in step S4.
[0024] To make the technical solution of the present invention clearer and easier to understand, the following detailed description is provided in conjunction with specific examples.
[0025] The head difference between the two ends of the experimental water tank was adjusted by using a stabilizing tank to achieve head differences of 6.6 cm, 4.7 cm, and 3.1 cm for the aquifer within the water tank. After the groundwater flow field corresponding to each head difference stabilized, the actual flow velocity inside the well and the actual flow velocity of the aquifer measured at the outlet of the experimental water tank were monitored. The monitoring results are shown in the appendix to the instruction manual. Figure 4 .
[0026] The permeability coefficient of the wellbore skin region in the numerical model was iteratively adjusted using a trial-and-error method (adjustment range: 4~8 m / d, step size: 1 m / d). The fitting error between the simulated wellbore flow velocity and the actual flow velocity inside the wellbore was calculated using a preset relative error formula, thereby achieving the inversion of the wellbore skin permeability coefficient. The fitting results are shown in the appendix to the instruction manual. Figure 5 , Figure 6 As shown in Table 1, the results indicate that when the permeability coefficient of the wellbore surface is 4, 5, 6, 7, and 8 m / d, the average relative errors are 0.315, 0.170, 0.094, 0.173, and 0.142, respectively. When the permeability coefficient of the wellbore surface is 6 m / d, the fitting error between the simulated wellbore flow velocity and the actual flow velocity inside the wellbore is the smallest.
[0027] Table 1 details the inverted wellbore skin permeability coefficient, simulated aquifer velocity, simulated wellbore velocity, actual aquifer velocity, actual wellbore velocity, and fitting error (E) of the wellbore velocity under different head differences (h1, h2). j (and other data.)
[0028] Table 1. Parameter Inversion Results ; Note: h1 and h2 are both in cm; the units for the inverted wellbore surface permeability coefficient, simulated aquifer velocity, simulated wellbore velocity, actual aquifer velocity, and actual wellbore velocity are all in m / d; E j The fitting error (dimensionless) represents the flow velocity within the wellbore.
[0029] This method for determining the skin permeability coefficient of a wellbore involves establishing a three-dimensional steady-flow numerical model that includes the seepage equations and corresponding boundary conditions for the aquifer region and the wellbore skin region. This model reconstructs the three-dimensional flow field characteristics near the well, avoiding the accuracy limitations of traditional homogeneous simplified models. By constructing a numerical model consistent with experimental parameters, the skin permeability coefficient is iteratively adjusted using a trial-and-error method. The degree of fitting is quantified using a preset relative error formula. Ultimately, a skin permeability coefficient of 6 m / d is determined to minimize the fitting error between the simulated wellbore flow velocity and the actual flow velocity within the wellbore, thus achieving the inversion of the skin permeability coefficient. Furthermore, the entire method relies on controlled indoor experiments, eliminating the need for on-site construction. It is convenient to operate, low in cost, and can simulate different heterogeneous geological conditions by adjusting the characteristics of porous media. This solves the problems of uncontrollable geological conditions, high cost, and long time consumption in traditional on-site experiments, providing a technical solution for the study of the wellbore skin effect and the calculation of the skin permeability coefficient.
[0030] Example 2 Refer to the instruction manual appendix Figure 2This embodiment discloses a system for determining the permeability coefficient of a wellbore skin, including a physical experimental device and a numerical simulation and inversion subsystem. The physical experimental device includes an experimental water tank 1, a wellbore 7, a water stabilization tank 4, a flow velocity monitoring unit and an aquifer flow velocity monitoring unit 8. The numerical simulation and inversion subsystem includes a data processing and storage unit, a numerical modeling unit and a parameter inversion unit.
[0031] The experimental water tank 1 is filled with a porous medium 3 for measuring permeability. The experimental water tank 1 provides a physical space for simulating groundwater aquifers. In this embodiment, the experimental water tank 1 is made of a transparent material to facilitate observation of the internal water flow and sand layer distribution. The porous medium 3 is made of quartz sand. During the experiment, water is injected into the experimental water tank 1 until the quartz sand is saturated, so that the water level is lower than a preset distance below the top interface of the quartz sand, forming a groundwater level line 6 to simulate the hydrological conditions of a groundwater aquifer.
[0032] The well shaft 7 is vertically installed in the experimental water tank 1 and inserted into the porous medium 3. The lower part of the well shaft 7 has a hole that communicates with the porous medium 3, so that the water in the aquifer in the porous medium 3 can enter the well shaft 7 through the hole.
[0033] Two water level stabilizing tanks 4 are provided, connected to both ends of the experimental water tank 1 respectively, to regulate the water level at both ends of the experimental water tank 1 to create different head differences. Each end of the experimental water tank 1 is equipped with a water storage tank 2 for water level buffering. The two water level stabilizing tanks 4 and the two water storage tanks 2 are connected by flexible hoses. During operation, the height of the two water level stabilizing tanks 4 can be adjusted by manually raising them. The function of the water storage tanks 2 is to smoothly transmit the water level changes of the water level stabilizing tanks 4 to the aquifer, avoiding excessive water flow impact and sand layer disturbance caused by the direct connection of the water level stabilizing tanks 4 to the porous medium 3. By adjusting the height difference between the two water level stabilizing tanks 4, the water level of the water storage tanks 2 is changed, thereby creating a stable flow field with different flow velocities in the aquifer, enabling multi-condition experiments.
[0034] As a preferred embodiment, a filter screen is provided at the junction of the water storage tank 2 and the porous medium 3 to prevent the porous medium 3 from entering the water storage tank 2. The filter screen is used to isolate the water storage tank 2 and the porous medium 3, ensuring unobstructed water flow and preventing the porous medium 3 from entering the water storage tank 2 due to water flow and causing blockage.
[0035] When the height of the water stabilizing tank 4 is adjusted, the water storage tank 2 first receives the water delivered by the water stabilizing tank 4. After its own water level stabilizes, it slowly replenishes or drains water into the aquifer through the filter screen at the interface with the porous medium 3. Finally, a stable head difference is formed in the experimental water tank 1, which provides driving force for the stable flow of groundwater.
[0036] As a preferred option, a water tank 5 is installed below the experimental water tank 1 to replenish the water level of the aquifer in the experimental water tank 1. The water tank 5 is connected to the water stabilizing tank 4. The water tank 5 ensures the stability of the water level and head difference during the experiment and avoids fluctuations in the water flow field due to insufficient water.
[0037] A flow velocity monitoring unit is installed inside the wellbore 7 to monitor the actual flow velocity within the wellbore 7. The flow velocity monitoring unit uses a groundwater flow velocity and direction meter, including a controller 9, a cable 10, and a monitoring probe 11. A steel cable 12 is installed above the wellbore 7, and the monitoring probe 11 is fixed inside the wellbore 7 by the steel cable 12 with its tip immersed in water. The tip of the monitoring probe 11 is a high-definition downhole television. The controller 9 controls the switching of the monitoring probe 11 and also has data transmission capabilities and an interface, allowing system data to be transmitted externally via built-in wireless and external communication interfaces. Furthermore, the controller 9 is connected to a cable reel, and the cable 10 is wound on the reel's spool.
[0038] The aquifer velocity monitoring unit 8 is located at the outlet of the experimental water tank 1 and is used to monitor the actual flow velocity of the aquifer. A flow meter can be selected as the aquifer velocity monitoring unit 8. (Refer to the attached instruction manual.) Figure 2 In this embodiment, the right side of the experimental water tank 1 is used as the inlet, and the left side of the experimental water tank 1 is used as the outlet. The height of the right-side water stabilization tank 4 is higher than that of the left-side water stabilization tank 4. The water flows from the right side to the left side. The water flows from the left-side water storage tank 2 into the left-side water stabilization tank 4. At this time, the aquifer water flows into the water tank 5 through the flow meter. The overall flow velocity of the aquifer is calculated by measuring the outlet flow rate, providing measured data for the verification of the numerical model.
[0039] As a preferred option, an external data storage device is installed in the experimental water tank 1. The data storage device is used to continuously record monitoring data and provide a complete dataset for subsequent analysis. The monitoring probe 11 is connected to the data storage device through the cable 10. After the monitoring probe 11 collects the flow velocity data in the well 7, it is stored in real time by the data storage device to ensure that the dynamic changes of water flow are captured and to meet the time accuracy requirements for fitting the numerical model and experimental data.
[0040] The data processing and storage unit is used to receive and store data from the flow velocity monitoring unit inside the wellbore 7 and the aquifer flow velocity monitoring unit 8; the numerical modeling unit is used to establish a three-dimensional steady flow numerical model of the confined aquifer based on the geometric parameters of the physical experimental device, the head difference and the permeability coefficient of the porous medium 3, and divide the area near the wellbore 7 into the aquifer region and the wellbore skin region; the parameter inversion unit is used to adjust the permeability coefficient of the wellbore skin region and perform simulation, calculate the fitting error between the simulated flow velocity in the wellbore 7 and the actual flow velocity inside the well, and obtain the wellbore skin permeability coefficient that minimizes the fitting error through iterative optimization.
[0041] This wellbore skin permeability coefficient determination system works collaboratively with a physical experimental setup and a numerical simulation and inversion subsystem. The physical experimental setup uses quartz sand to simulate porous media (3), establishes a groundwater level line (6) to recreate the unconfined aquifer environment, and employs a perforated wellbore (7) to reproduce the actual well-aquifer hydraulic connection. Furthermore, it utilizes the head difference of a stabilizing tank (4) to adjust the flow field at different velocities within the aquifer, a water storage tank (2) to buffer water level changes, a filter screen to prevent sand disturbance, and a water supply to a water tank (5). Combined with a flow velocity monitoring unit and an aquifer flow velocity monitoring unit (8), it ensures stable and reliable multi-dimensional measured data. The numerical simulation and inversion subsystem constructs a three-dimensional numerical model based on experimental parameters and iteratively optimizes the wellbore skin permeability coefficient to achieve a fit between the simulated and measured flow velocities. This system can adjust the height of the stabilizing tank (4) to achieve multi-condition experiments and avoids the problems of geological scene disconnect, large data errors, and high costs associated with traditional methods, thus successfully determining the wellbore skin permeability coefficient.
[0042] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.
Claims
1. A method for determining the permeability coefficient of a wellbore skin, characterized in that, Includes the following steps: S1: Simulate the groundwater flow field near the well using a physical experimental device; the physical experimental device includes an experimental water tank for filling with porous media, a well cylinder set in the experimental water tank, and a water stabilizing tank for regulating the water level at both ends of the experimental water tank. S2: By adjusting the height of the two end water tanks to provide different head differences, simulate the unconfined aquifer system under different flow velocities, and obtain the actual flow velocity in the wellbore under different head difference conditions and the actual flow velocity of the aquifer measured at the outlet of the experimental water tank. S3: Based on the geometric parameters of the physical experimental device, the head difference, and the permeability coefficient of the porous medium, a three-dimensional steady flow numerical model of the confined aquifer is established. The numerical model divides the area near the well into an aquifer region and a well skin region. S4: Adjust the permeability coefficient of the wellbore skin region in the numerical model, run the simulation and obtain the corresponding simulated wellbore flow velocity, and determine the permeability coefficient of the wellbore skin region used when the fitting error between the simulated wellbore flow velocity and the actual flow velocity in the wellbore is minimized.
2. The method for determining the permeability coefficient of a wellbore skin according to claim 1, characterized in that, In step S3, the groundwater seepage equation for the aquifer region is applicable to r s The region ≤ r < ∞, where r is the distance from the center of the wellbore. s The radius of the wellbore surface area, in meters, is expressed as: ； In the above formula, H is the water head, and K is the water head. ax K ay K az These are the permeability coefficients of the aquifer along the x, y, and z directions, respectively, in m / d; The groundwater seepage equation for the skin region is applicable to r w ≤r<r s The region where r w The radius of the wellbore, in meters, is expressed as: ； In the above formula, K sx K sy K sz These are the permeability coefficients of the epidermal region along the x, y, and z directions, respectively, in m / d; In the numerical model, the left and right boundaries of the confined aquifer are set as constant head boundaries, and the front and rear boundaries are set as flux boundaries. The expression is: ； ； In the above formula, S1 and S2 are constant head boundaries; S3 and S4 are flux boundaries; n is the outward normal direction of boundary S3; H1 is the head of boundary S1; and H2 is the head of boundary S2.
3. The method for determining the permeability coefficient of a wellbore skin according to claim 1, characterized in that, In step S4, the fitting error between the simulated wellbore flow velocity and the actual flow velocity inside the wellbore is calculated using a preset relative error formula. The preset relative error formula is as follows: ； In the above formula, v obs v is the actual flow velocity inside the wellbore in step S2. sim The simulated wellbore flow velocity is output by the numerical model in step S4.
4. A system for determining the permeability coefficient of a wellbore skin for implementing the method of any one of claims 1-3, characterized in that, It includes physical experimental setups and numerical simulation and inversion subsystems, among which, The physical experimental apparatus includes: The experimental water tank (1) is filled with a porous medium (3) for measuring the permeability coefficient. The well shaft (7) is vertically installed in the experimental water tank (1) and inserted into the porous medium (3), and the lower part of the well shaft (7) is provided with a hole communicating with the porous medium (3); There are two water tanks (4), which are respectively connected to the two ends of the experimental water tank (1) to adjust the water level at both ends of the experimental water tank (1) to form different head differences; A flow velocity monitoring unit is installed inside the well (7) to monitor the actual flow velocity inside the well. An aquifer flow velocity monitoring unit (8) is installed at the outlet of the experimental water tank (1) to monitor the actual flow velocity of the aquifer. The numerical simulation and inversion subsystem includes: A data processing and storage unit is used to receive and store data from the wellbore flow velocity monitoring unit and the aquifer flow velocity monitoring unit (8); The numerical modeling unit is used to establish a three-dimensional steady flow numerical model of the confined aquifer based on the geometric parameters of the physical experimental device, the head difference and the permeability coefficient of the porous medium (3), and to divide the area near the well (7) into the aquifer area and the well skin area. The parameter inversion unit is used to adjust the permeability coefficient of the wellbore skin region and perform simulation. The simulated wellbore flow velocity is compared with the actual flow velocity in the well to calculate the fitting error. The wellbore skin permeability coefficient that minimizes the fitting error is obtained through iterative optimization.
5. The system for determining the permeability coefficient of a wellbore skin according to claim 4, characterized in that, The experimental water tank (1) is equipped with water storage tanks (2) at both ends for water level buffering, and the water stabilizing tanks (4) at both ends are connected to the water storage tanks (2) at both ends respectively.
6. The system for determining the permeability coefficient of a wellbore skin according to claim 5, characterized in that, A filter screen is provided at the junction of the water storage tank (2) and the porous medium (3) to prevent the porous medium (3) from entering the water storage tank (2).
7. The system for determining the permeability coefficient of a wellbore skin according to claim 4, characterized in that, Below the experimental water tank (1) is a water tank (5) that provides water replenishment to the aquifer in the experimental water tank (1).
8. The system for determining the permeability coefficient of a wellbore skin according to claim 4, characterized in that, The flow velocity monitoring unit inside the well (7) is a groundwater flow velocity and direction meter, including a controller (9), a cable (10) and a monitoring probe (11), wherein the monitoring probe (11) is fixed in the well (7) by a steel rope (12) and the front end of the monitoring probe (11) is immersed in water.