Method for determining invalid water injection rate of oil reservoir by utilizing numerical simulation

Abstract

The invention belongs to the technical field of oilfield development, and relates to a method for determining the invalid water injection rate of an oil reservoir by utilizing numerical simulation, which comprises the following steps of: setting a virtual water layer and a virtual well in an oil reservoir numerical model, and splitting invalid water injection into the set virtual water layer, so that the formation pressure and water content fitting of the oil reservoir numerical model during invalid water injection is carried out; and finally, in the fitted reservoir numerical model, directly outputting the non-reservoir invalid water injection rate by the model. The shortages of large workload and long consumed time in digital-analog combination of a common water deduction method are overcome; the invalid water injection amount split to the virtual water layer can be directly output through the fitted model; the device is simple in structure, convenient to operate and short in consumed time, can greatly reduce the time and labor cost of invalid water injection numerical simulation research, and correspondingly improves the precision of an oil reservoir numerical model within limited time.

Description

Technical Field

[0001] The invention belongs to the technical field of oil field development, and in particular relates to a method for determining the ineffective water injection volume of an oil reservoir by utilizing numerical simulation. Background Art

[0002] Effective water injection refers to the amount of water injected into the reservoir by the water injection well; ineffective water injection refers to the part of the total water injection volume injected into the reservoir by the water injection well that cannot act on the reservoir. This part of ineffective water injection is usually lost or stored in non-reservoir layers due to structures (such as fractures, unconformities, edge and bottom water, etc.). Determining the ineffective water injection volume and analyzing the causes of ineffective water injection are of great significance to the evaluation of oilfield water injection effects and the optimization of development methods (Wang Xuezhong, 2007; Wang Qingtao et al., 2011; Xu Longhong, 2013). Usually, the calculation of ineffective water injection volume can be carried out by reservoir engineering method and numerical simulation method. The reservoir engineering method is based on the principle of material balance. The actual oil production, injection volume and underground expansion volume of the reservoir are brought into the material balance equation to calculate the effective water injection volume of the actual target layer, and then the difference is made with the actual total water injection volume to determine the ineffective water injection volume (Wen Guofeng et al., 2004). The use of numerical simulation method to calculate the ineffective water injection volume is a method generated on the basis of fitting the numerical model or in the process.

[0003] In the process of water injection development in oil fields, ineffective water injection cannot replenish formation energy, nor can it effectively displace oil and water, which makes the water injection volume of the water injection wells large, but the surrounding oil wells are ineffective, and the actual formation pressure does not change significantly at this time. However, in the numerical simulation research of the corresponding blocks, since the simulation software follows the material balance equation, the water injection wells have injection volume, and the software simulates the reservoir water absorption accordingly, thereby giving a very high formation pressure. At this time, the formation pressure and water content fitting accuracy are low (Ma Zhiyuan, 1992). Therefore, finding a way to split the ineffective water injection volume is a must in the historical fitting of numerical simulation research. Therefore, using numerical simulation methods to determine the ineffective water injection volume can simultaneously solve the two key problems of quantitative characterization of ineffective water injection volume and difficulty in simulating the number of ineffective water injection hours in the reservoir.

[0004] In the past, the method of deducting water injection volume was often used to determine the invalid water injection volume using numerical simulation technology (Ma Zhiyuan, 1992; Zhang Yuan et al., 2015), that is, by splitting the invalid water injection volume from the total injection volume and deducting it, the invalid water injection volume does not participate in the injection calculation of the numerical model, so as to make the model consistent with the actual water injection volume, and then fit the model. On the basis of the good model fitting, the invalid water injection volume of the reservoir is calculated by reverse calculation from the deducted injection water volume. This method is widely used, but it is very inconvenient in actual simulation operations. When fitting, the method of deducting water injection volume needs to modify the water injection volume of the injection wells one by one and one by one simulation time step. Even if this method fits the pressure and water content, the invalid water injection volume cannot be directly output from the fitted reservoir numerical model. It needs to be reversely calculated from the deducted water volume. The workload is large, the calculation is complicated, and it takes a lot of manpower and time, which restricts the numerical simulation research of invalid water injection to a certain extent. Summary of the invention

[0005] The purpose of the present invention is to provide a method for determining the ineffective water injection volume of an oil reservoir by using numerical simulation, which solves the problems of large workload, complex calculation, time-consuming and labor-intensive existing numerical simulation methods.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for determining the ineffective water injection volume of an oil reservoir by using numerical simulation comprises the following steps:

[0008] S1. Establishing a numerical reservoir model

[0009] A preliminary reservoir numerical model is established based on the acquired preliminary geological model, reservoir parameters, fluid properties and production history data;

[0010] S2. Fitting the reservoir numerical model

[0011] Adjust the parameters of the reservoir numerical model. If the conformity rate of one of the formation pressure, injection and production volume and water content index calculated by the reservoir numerical model is lower than the preset conformity rate, check whether it is caused by invalid water injection in the reservoir and proceed to S3.

[0012] S3. Determine the invalid water injection well group

[0013] Determine whether there are invalid water injection well groups based on dynamic analysis, reservoir numerical model calculation results, and actual reservoir formation pressure analysis and comparison results;

[0014] When there is an invalid water injection well group, S4 is started;

[0015] S4. Modify the reservoir numerical model

[0016] On the basis of the reservoir numerical model, a virtual water layer is set at the bottom of the reservoir numerical model;

[0017] In addition to the actual perforated well section, the section where the virtual water layer of the water injection well in the invalid water injection well group is located is opened, and several water production wells using only the virtual water layer are set up around the water injection well, and the water injection wells, virtual water layers and virtual water production wells in the invalid water injection well group are connected to obtain a new reservoir numerical model;

[0018] S5. Fitting a new reservoir numerical model

[0019] Adjust the formation coefficient of the water injection wells in the virtual water layer and the water production of the virtual water production wells in the invalid water injection well group in the reservoir numerical model, fit the formation pressure, injection and production volume and water content of the whole area and the water injection wells, so that the formation pressure, injection and production volume and water content in the production history data are consistent with the formation pressure, injection and production volume and water content calculated by the new reservoir numerical model, then the fitting is completed and a well-fitted reservoir numerical model is obtained;

[0020] S6. Determine the amount of invalid water injection

[0021] By fitting the good reservoir numerical model, the invalid water injection volume split into the virtual water layer is directly output.

[0022] Furthermore, in S1, the early geological model includes reservoir structure, faults, porosity, permeability and fluid saturation.

[0023] Furthermore, in S1, numerical simulation software is used to simulate the fluid flow in the reservoir and establish a numerical model of the reservoir.

[0024] Furthermore, the digital modeling software is tNavigator, CMG or Eclipse.

[0025] Furthermore, in S2, the conformity rates of the formation pressure, injection and production volume, and water content indicators calculated by the reservoir numerical model are all lower than the preset conformity rates:

[0026] The conformity rate of production, pressure and water content simulated by the reservoir numerical model at the initial production stage, the initial water breakthrough stage and the current production stage with the actual production history data is less than 85%.

[0027] Further, in S3, determining whether there is an invalid water injection well group is specifically as follows:

[0028] In actual dynamic monitoring, as the water injection of the water injection well increases, the pressure of the surrounding corresponding oil production wells increases, and the oil well production also increases, which means that the water injection is effective and there is no invalid water injection well group;

[0029] If the pressure of the entire area calculated by the reservoir numerical model is higher than the actual reservoir formation pressure, and in actual dynamic monitoring, although the water injection volume is large, the pressure and liquid production of the surrounding oil wells do not show a large change trend, it means that there is an invalid water injection well group.

[0030] Furthermore, in S4, the reservoir conductivity of the virtual water layer is set to be 0, and the water saturation is equal to 1.

[0031] Furthermore, the constructed numerical model of the reservoir involves three types of thickness: simulated layer deposition thickness, sand body thickness and oil layer thickness, and the oil layer thickness is the effective thickness.

[0032] Furthermore, the simulated layer deposition thickness > sand body thickness > oil layer thickness.

[0033] Furthermore, in S5, the larger the formation coefficient value, the stronger the water absorption capacity of the set virtual water layer, the more the virtual water production well produces, and the greater the virtual water layer deficit. Thus, the more injected water the virtual water layer absorbs, the more invalid injected water is simulated to be lost.

[0034] Compared with the prior art, the present invention has the following beneficial technical effects:

[0035] The present invention discloses a method for determining the invalid water injection volume of an oil reservoir by using numerical simulation. The method includes setting a virtual water layer and a virtual well in the numerical model of the oil reservoir, splitting the invalid water injection into the set virtual water layer, thereby fitting the formation pressure and water content of the numerical model of the oil reservoir when the invalid water injection occurs. Finally, in the fitted numerical model of the oil reservoir, the invalid water injection volume of the non-reservoir is directly output by the model. In the conventional process of determining the invalid water injection volume by using numerical simulation technology, the model fitting method has a large workload of modifying parameters and the operation takes a long time. The present invention sets a virtual water layer and a virtual water production well, splits the invalid water injection into the virtual water layer, realizes the accurate fitting of the numerical model of the oil reservoir, and thus determines the invalid water injection volume. The method solves the following two key problems: (1) quantitative characterization of invalid water injection volume; and (2) difficulty in fitting the numerical model when invalid water injection exists in the oil reservoir.

[0036] On the one hand, the present invention overcomes the shortcomings of the commonly used water deduction method in numerical simulation, such as large workload and long time consumption; on the other hand, the ineffective water injection volume split to the virtual water layer can be directly output from the fitted model. The operation is convenient and the time is short, which can greatly reduce the time and labor cost of the numerical simulation research of ineffective water injection, and accordingly improve the accuracy of the reservoir numerical model in a limited time. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 The possible structural factors in the cause of ineffective water injection are shown. a is the outcrop of Heiyu Mountain in Karamay; b is a crack; c is a fault; d is an unconformity surface;

[0038] Figure 2 The three thicknesses in the simulation model are shown: simulated layer deposition thickness, sand body thickness and oil layer thickness (effective thickness);

[0039] Figure 3A schematic diagram of the water deduction method commonly used in the model fitting process when conventionally using numerical simulation technology to determine the invalid water injection volume;

[0040] Figure 4 A schematic diagram of setting a virtual water layer and a virtual water production well, splitting the invalid water injection into the virtual water layer, and fitting the invalid water injection formation pressure;

[0041] Figure 5 This is the formation pressure fitting curve of the numerical model of the Kexia Formation reservoir in the Wu2 West Area of ​​Karamay Oilfield;

[0042] Figure 6 This is the variation curve of ineffective water injection volume in the Kexia Formation reservoir in the 5-2 West Area of ​​Karamay Oilfield over the years. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical solution and advantages of the present invention more clear, the following is further described in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention, that is, the embodiments described are only part of the embodiments of the present invention, not all embodiments.

[0044] The components described and shown in the drawings and embodiments of the present invention may be arranged and designed in various configurations. Therefore, the detailed description of the embodiments of the present invention provided in the following drawings is not intended to limit the scope of the claimed invention, but merely represents a selected embodiment of the present invention. Based on the drawings and embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0045] It should be noted that the terms "comprises", "includes" or any other variations are intended to cover non-exclusive inclusion, so that a process, element, method, article or equipment that includes a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to the process, element, method, article or equipment.

[0046] Numerical reservoir simulation is a method of using computer software to solve the mathematical model of the reservoir (commonly used numerical simulation software include tNavigator, CMG, Eclipse, etc.) to simulate the flow of fluids in the reservoir, thereby helping to determine the underground fluid distribution at a certain moment and predicting the future dynamic changes of the reservoir.

[0047] The invention discloses a method for determining the ineffective water injection volume of an oil reservoir by using numerical simulation, comprising the following steps:

[0048] S1. Establishing a numerical reservoir model

[0049] A preliminary reservoir numerical model is established based on the acquired preliminary geological model, reservoir parameters, fluid properties and production history data;

[0050] The early geological model includes properties such as reservoir structure, faults, porosity, permeability, and fluid saturation;

[0051] Production history data generally include well history, measures, well deviation, well group, production, pressure, water content and other data;

[0052] Reservoir parameters generally include parameters such as lithology, fluid PVT, density or relative permeability;

[0053] S2. Fitting the reservoir numerical model

[0054] By adjusting the reservoir numerical model parameters, the simulated oil (gas) reservoir development indicators are made close to the actual historical production dynamic data. If the conformity rate of the formation pressure, injection and production volume and water content indicators calculated by the reservoir numerical model is lower than the preset conformity rate, check whether it is caused by invalid water injection in the reservoir and proceed to S3.

[0055] Whether the established reservoir numerical model can be used for subsequent research depends on whether it can truly and reliably reflect the dynamic changes of the actual reservoir. Therefore, the reliability of the model is verified by comparing the previous reservoir production data (generally referred to as historical data) with the production data calculated by the reservoir numerical model. When the consistency rate of the oil and water production, pressure changes, etc. involved in the comparison between the two is greater than 85%, the model is considered reliable. How to adjust the reservoir numerical model parameters to make the production history data consistent with the production data calculated by the reservoir numerical model is called the history fitting process.

[0056] In historical matching, there is no clear regulation on the rate of conformity, which is usually based on the principle of satisfying research. Due to the limitations of simulation working time, quality of reservoir production data and other factors, reservoir simulation engineers will pay more attention to the rate of conformity of historical matching in the early stage of reservoir production, the early stage of water breakthrough, and the current production.

[0057] S3. Determine the invalid water injection well group

[0058] Based on the dynamic analysis, the calculation results of the reservoir numerical model, and the obtained actual reservoir formation pressure analysis and comparison results, determine whether there are invalid water injection well groups; specifically:

[0059] When there are invalid water injection well groups in the reservoir, the pressure of the entire model area will be significantly higher than the actual reservoir formation pressure. These well groups can be found from the model single well and well group pressure change curves. Then, it is necessary to combine dynamic analysis, that is, based on the dynamic monitoring response of the actual mine, to determine whether the pressure fitting anomalies of these well group models are caused by invalid water injection.

[0060] In actual dynamic monitoring, when water injection is effective, as the water injection of the injection wells increases, the pressure of the surrounding corresponding oil wells will increase, and the energy of the oil wells will be replenished. At the same time, as the injected water drives oil, the oil well production will also increase. On the contrary, if there is ineffective water injection, although the water injection volume is large, there is no significant change trend in the pressure and liquid production of the surrounding oil wells.

[0061] S4. Modify the reservoir numerical model

[0062] like Figure 4 As shown, based on the initial reservoir numerical model, a virtual water layer is set at the bottom of the model, and the conductivity of the top of the virtual water layer is set to 0, that is, there is no energy exchange between the virtual water layer and the reservoir;

[0063] In addition to the actual perforated well section, the section where the virtual water layer of the water injection well in the invalid water injection well group is located is opened, and several water production wells that only use the virtual water layer are set up around the water injection well. By connecting the water injection wells, virtual water layers and virtual water production wells in the invalid water injection well group, a new reservoir numerical model is obtained;

[0064] S5. Fitting a new reservoir numerical model

[0065] Adjust the formation coefficient Kh of the injection wells in the virtual water layer and the water production of the virtual water production wells in the invalid injection well group in the numerical model, and fit the formation pressure, injection and production volume and water content of the whole area and the injection wells; make the formation pressure, injection and production volume and water content in the production history data consistent with the formation pressure, injection and production volume and water content calculated by the new reservoir numerical model, then the fitting is completed and a well-fitted reservoir numerical model is obtained;

[0066] The larger the Kh value is, the stronger the water absorption capacity of the virtual water layer is, the more the virtual water well produces, and the greater the virtual water layer deficit is. Therefore, the more injected water the virtual water layer absorbs, the more invalid injected water is simulated to be lost.

[0067] S6. Determine the amount of invalid water injection

[0068] By fitting the good reservoir numerical model, the invalid water injection volume split into the virtual water layer is directly output from the numerical simulation software.

[0069] The features and performances of the present invention are further described in detail below in conjunction with the embodiments.

[0070] Figure 1 The reasons for the large difference between the historical fitting formation pressure and the actual formation pressure in the numerical simulation study when ineffective water injection occurs in the reservoir are shown, and several structural factors that may exist in the causes of ineffective water injection are shown. Figure 1 (a) is the outcrop of Karamay Black Oil Mountain. Figure 1 (b) Figure 1 (c) Figure 1(d) Due to the cracks, faults and unconformity structures in the strata, the ineffective injection water is not absorbed by the water-absorbing layer as designed by the mine, but flows along these structures, resulting in leakage, and has no actual effect on the oil reservoir;

[0071] Figure 2 Three types of thickness in the simulation model are shown: simulated layer deposition thickness, sand body thickness and oil layer thickness (effective thickness). Figure 2 The sand body thickness of the water injection well layer in the area shown in the figure is 2.3 times the effective thickness. Because the effective thickness is used in the reservoir numerical model, the thickness of the ineffective reservoir in the sand body is not considered. In fact, the water injection well can absorb water in the sand body, while in the model, it only absorbs water in the effective thickness, which causes a huge difference between the actual and simulated formation pressures.

[0072] Figure 3 A schematic diagram of the process of deducting water volume commonly used in the model fitting process when conventionally using numerical simulation technology to determine the invalid water injection volume, in which the modification of the deducted water volume used to simulate the invalid water injection volume in the actual reservoir requires manual modification of the water injection volume at each time step in the production history of a single well in the model, which means that if there are 10 single well injection parameters that need to be modified, the ideal state is to modify it once at a time step to meet the fitting standard, and the single well water injection volume needs to be modified at least 10 times; if the model needs to fit a time step of 120 (if it is in months, then it will be simulated backward for 10 years), the water injection volume at each time step of the 10 wells needs to be compared and adjusted step by step according to the pressure change in 10 years, and the calculation is too complicated.

[0073] Figure 4 A schematic diagram of splitting invalid water injection to the virtual water layer by setting up a virtual water layer and a virtual water production well, and fitting the invalid water injection formation pressure is provided, that is, a virtual water layer with a conductivity of 0 and a water saturation of 1 similar to that of the upper reservoir is set below the reservoir, and a virtual water production well with only the virtual water layer opened is set in the periphery, and at the same time, the layer section where the virtual water layer of the water production well in the invalid water injection well group is located is opened, the water injection well, the virtual water layer and the virtual water production well are connected, and the numerical model pressure and water content are fitted by adjusting the Kh value of the virtual water layer of the water injection well and the water production of the water production well. Finally, on the basis of completing the model history fitting, the software directly quantitatively outputs the size of the invalid water injection amount split to the virtual water layer.

[0074] The technology provided in this embodiment of fitting reservoir formation pressure and determining invalid water injection volume by using virtual water layer and virtual water production well has been well applied in the numerical simulation research of the lower Ke formation reservoir in the 52 west area of ​​Karamay Oilfield. The specific embodiments are as follows:

[0075] (1) The sand layer thickness of the Kexia Formation oil reservoir in the Wu2 West Area is generally 2 to 3 times the effective thickness, and the oil layer is seriously heterogeneous. After water injection development, due to the existence of ineffective water injection, the reservoir plane pressure difference is large, the pressure distribution is extremely uneven, the injection well pressure is high, and the oil well pressure is low. The initial model formation pressure of the numerical simulation model reaches 48MPa, which is twice as high as the actual formation pressure of 24MPa. In addition, the pressure difference between the injection and production wells is small, and the oil well pressure is much higher than the current actual pressure.

[0076] (2) By comparing the preliminary numerical model results with the actual pressure, single factor and multi-factor analysis including permeability, conductivity, water-like thickness, relative permeability curve, and compressibility coefficient was conducted, and it was found that water absorption by non-oil-bearing sand bodies was the reason for the huge difference between the actual and model results.

[0077] (3) Setting up virtual water layers and virtual water production wells for the well group simulating abnormal formation pressure, and fitting the model formation pressure and water content by adjusting the Kh value of the injection well in the virtual water layer and the water production of the virtual water production well;

[0078] (4) The formation pressure and water content in the whole model area are well fitted (see Figure 5 ), the single well fitting coincidence rate exceeds 85%, and according to the invalid water injection volume output by the model, the current water injection efficiency of the reservoir is only 70% (see Figure 6 ), the error between this value and the value calculated by reservoir engineering method is 2%. Then, combined with geological and dynamic analysis, the main reasons for the outflow of the remaining 30% of the ineffective water injection volume in the reservoir are outflow from unclosed boundaries, entering the bedrock along unconformity surfaces, entering bottom water along cracks, and outflow from channel wells.

[0079] (5) Based on numerical simulation research and water injection effectiveness evaluation, the oil field carried out a scheme demonstration of periodic water injection combined with measures to tap the potential. After the implementation of the scheme, the reservoir liquid production structure was adjusted, the liquid production level increased by 46t / d, the water content increase rate was effectively controlled, the invalid water circulation was reduced, the reservoir water storage rate increased by 4.8%, the formation pressure configuration gradually became reasonable, and the injection-production pressure difference dropped from 13MPa to 9.8MPa.

[0080] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for determining the ineffective water injection volume of an oil reservoir using numerical simulation, characterized in that: The following steps are involved: S1. Establishing a numerical reservoir model A preliminary reservoir numerical model is established based on the acquired preliminary geological model, reservoir parameters, fluid properties and production history data; S2. Fitting the reservoir numerical model Adjust the parameters of the reservoir numerical model. If the conformity rate of one of the formation pressure, injection and production volume and water content index calculated by the reservoir numerical model is lower than the preset conformity rate, check whether it is caused by invalid water injection in the reservoir and proceed to S3. S3. Determine the invalid water injection well group Determine whether there are invalid water injection well groups based on dynamic analysis, reservoir numerical model calculation results, and actual reservoir formation pressure analysis and comparison results; When there is an invalid water injection well group, S4 is started; S4. Modify the reservoir numerical model On the basis of the reservoir numerical model, a virtual water layer is set at the bottom of the reservoir numerical model; In addition to the actual perforated well section, the section where the virtual water layer of the water injection well in the invalid water injection well group is located is opened, and several water production wells using only the virtual water layer are set up around the water injection well, and the water injection wells, virtual water layers and virtual water production wells in the invalid water injection well group are connected to obtain a new reservoir numerical model; S5. Fitting a new reservoir numerical model Adjust the formation coefficient of the water injection wells in the virtual water layer and the water production of the virtual water production wells in the invalid water injection well group in the reservoir numerical model, fit the formation pressure, injection and production volume and water content of the whole area and the water injection wells, so that the formation pressure, injection and production volume and water content in the production history data are consistent with the formation pressure, injection and production volume and water content calculated by the new reservoir numerical model, then the fitting is completed and a well-fitted reservoir numerical model is obtained; S6. Determine the amount of invalid water injection By fitting the good reservoir numerical model, the invalid water injection volume split into the virtual water layer is directly output.

2. A method for determining the ineffective water injection volume of an oil reservoir by using numerical simulation according to claim 1, characterized in that: In S1, the early geological model includes reservoir structure, faults, porosity, permeability and fluid saturation.

3. The method for determining the ineffective water injection volume of an oil reservoir by numerical simulation according to claim 1, characterized in that: In S1, numerical simulation software is used to simulate the fluid flow in the reservoir and establish a numerical model of the reservoir.

4. A method for determining the ineffective water injection volume of an oil reservoir by using numerical simulation according to claim 3, characterized in that: The digital modeling software is tNavigator, CMG or Eclipse.

5. The method for determining the ineffective water injection volume of an oil reservoir by numerical simulation according to claim 1, characterized in that: In S2, one of the conformity rates of formation pressure, injection and production volume, and water content calculated by the reservoir numerical model is lower than the preset conformity rate: The conformity rate between the production, pressure and water content simulated by the reservoir numerical model at the initial production stage, the initial water breakthrough stage and the current production stage and the actual production history data is less than 85%.

6. The method for determining the ineffective water injection volume of an oil reservoir by numerical simulation according to claim 1, characterized in that: In S3, determining whether there is an invalid water injection well group is specifically as follows: In actual dynamic monitoring, as the water injection of the water injection well increases, the pressure of the surrounding corresponding oil production wells increases, and the oil well production also increases, which means that the water injection is effective and there is no invalid water injection well group; If the pressure of the entire area calculated by the reservoir numerical model is higher than the actual reservoir formation pressure, and in actual dynamic monitoring, although the water injection volume is large, the pressure and liquid production of the surrounding oil wells do not show a large change trend, it means that there is an invalid water injection well group.

7. The method for determining the ineffective water injection volume of an oil reservoir by numerical simulation according to claim 1, characterized in that: In S4, the reservoir conductivity of the virtual water layer is set to be 0, and the water saturation is equal to 1.

8. The method for determining the ineffective water injection volume of an oil reservoir by numerical simulation according to claim 1, characterized in that: The constructed reservoir numerical model involves three types of thickness: simulated layer deposition thickness, sand body thickness and oil layer thickness, and the oil layer thickness is the effective thickness.

9. The method for determining the ineffective water injection volume of an oil reservoir by numerical simulation according to claim 9, characterized in that: Simulated layer deposition thickness > sand body thickness > oil layer thickness.

10. The method for determining the ineffective water injection volume of an oil reservoir by using numerical simulation according to claim 1, characterized in that: In S5, the larger the formation coefficient value is, the stronger the water absorption capacity of the set virtual water layer is, the more the virtual water production well produces, the greater the virtual water layer deficit is, and the more injected water the virtual water layer absorbs, the more invalid injected water is simulated to be lost.

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