Exploitation method for implementing '3+2 'in extra-high water-containing oil field

Abstract

The invention provides a 3 + 2 mining method for an extra-high water-cut oil field, which specifically comprises the following steps of: S1, collecting and sorting oil reservoir geology and development dynamic data of a target block, and establishing a geologic model; s2, residual oil evolution in the chemical flooding process is simulated through a numerical simulation method; s3, establishing an evaluation method for the optimal enrichment window period of the remaining oil in the chemical flooding process; s4, establishing a three-field adaptation method of a target block pressure gradient field, a remaining oil saturation field and an oil-displacing agent concentration field; and S5, implementing oilfield exploitation according to the adaptive method. The utilization rate of the oil-displacing agent is fully improved, and the water-containing valley bottom period of chemical flooding is effectively prolonged, so that the effective peak period is prolonged, and the recovery efficiency and the economic benefit are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of oil production in oilfields, and particularly to a "3 + 2" production method implemented in extra-high water cut oilfields. Background Art

[0002] Chemical flooding is an effective technical method for improving oil recovery, and has been widely promoted and applied in oilfields in China. Currently, the annual oil production by chemical flooding in China reaches 16 million tons. The field practices in oilfields such as Shengli, Daqing, and Henan show that after implementing chemical flooding, the water cut in the reservoir decreases, and the oil production increases. During the peak period of effectiveness, the maximum water cut decreases by 10%, and the oil production more than doubles. The increased oil production and economic benefits account for more than 60% of the chemical flooding project. During the chemical flooding process, due to the displacement system expanding the swept volume and improving the oil washing efficiency, the highly dispersed remaining oil is secondarily enriched to form a high oil saturation zone, that is, the so-called "oil wall". As the "oil wall" migrates towards the oil well, the oil well enters the peak period of effectiveness, with a significant decrease in water cut and a significant increase in oil production. As time goes by, restricted by the fixed streamline caused by the unchanged well pattern, the enriched remaining oil is dispersed again, making it difficult to produce. Therefore, the peak period of effectiveness of conventional chemical flooding is short, only 2 - 5 years, and the oil recovery is increased by 8 - 15%. How to extend the peak period of effectiveness of chemical flooding and further improve the effect and economic benefits of chemical flooding is a problem that needs to be studied in depth.

[0003] Patent CN110344795B discloses a method for evaluating the applicability of a combined development method of polymer flooding and well pattern infilling, which is characterized by including the following contents: S1, establishing an economic evaluation model for polymer flooding and well pattern infilling combination; S2, conducting a technical evaluation on different combination modes of polymer flooding and well pattern infilling; S3, conducting an economic evaluation on different combination modes of polymer flooding and well pattern infilling according to the economic evaluation model to obtain the applicable oil price range of different combination modes; S4, based on the influence of different injection-production correspondence rates and well pattern densities, conducting a hierarchical evaluation on the oil prices of different combination modes of polymer flooding and well pattern infilling. The present invention proposes a method for evaluating the applicability of oil prices for different combined development methods of polymer flooding and well pattern infilling, providing a basis for determining a reasonable development method, and thus improving the oilfield development benefit.

[0004] Patent CN110714755B discloses a rapid prediction method for the secondary enrichment rate of remaining oil in a waterflood reservoir. The rapid prediction method for the secondary enrichment rate of remaining oil in a waterflood reservoir includes: Step 1, screening the well areas for applying the remaining oil secondary enrichment technology according to the reservoir development characteristics; Step 2, comprehensively determining the key parameter values affecting the secondary enrichment rate of remaining oil in the selected well areas by integrating seismic data, core test data, logging data, well test data, and development dynamic data; Step 3, predicting the secondary enrichment rate of remaining oil. The rapid prediction method for the secondary enrichment rate of remaining oil in a waterflood reservoir provides technical support for the potential tapping of remaining oil and the improvement of oil recovery in the later stage of waterflood reservoir development, especially for the development strategies, cyclic oil production countermeasures, determination of interlayer cyclic production periods, and secondary development of nearly abandoned reservoirs in the extra-high water cut period. Its popularization and application have broad prospects and remarkable economic and social benefits. Summary of the Invention

[0005] In view of the above problems, the present invention is proposed to provide a "3 + 2" production method for extra-high water cut oilfields to overcome or at least partially solve the above problems.

[0006] According to one aspect of the present invention, there is provided a "3 + 2" production method for extra-high water cut oilfields. The production method specifically includes:

[0007] Step S1: Collect and organize the reservoir geology and development dynamic data of the target block, and establish a geological model;

[0008] Step S2: Use numerical simulation methods to simulate the evolution of remaining oil during chemical flooding;

[0009] Step S3: Establish an evaluation method for the optimal enrichment window period of remaining oil during chemical flooding;

[0010] Step S4: Establish a three-field matching method for the pressure gradient field, remaining oil saturation field, and displacing agent concentration field of the target block;

[0011] Step S5: Implement oilfield production using the "3 + 2" production method according to the matching method.

[0012] Optionally, the collection and organization of the reservoir geology and development dynamic data of the target block specifically include:

[0013] Single-well drilling data, sub-layer data, layered data, porosity, permeability, geological reserves, high-pressure physical properties data of crude oil, core well data, and rock parameters.

[0014] Optionally, the establishment of the geological model specifically includes: Conducting fine geological research on the reservoir of the target block and establishing a geological model reflecting the dynamic heterogeneity of the reservoir.

[0015] Optionally, step S2: Simulating the evolution of remaining oil during chemical flooding using numerical simulation methods specifically includes:

[0016] Using numerical simulation methods to perform historical matching of the target block, correcting and adjusting geological and chemical agent parameters, and simulating the evolution of remaining oil during chemical flooding.

[0017] Optionally, the use of numerical simulation methods to perform historical matching of the target block, correcting and adjusting geological and chemical agent parameters specifically includes:

[0018] Designing fitting principles;

[0019] Dynamically adjusting the injection and production volumes and fitting pressures of boundary wells according to the fitting principles;

[0020] Adjusting the permeability and relative permeability curves to fit the water cut of individual wells.

[0021] Optionally, the fitting principles are:

[0022] Adopting the method of first overall and then local to ensure relative unity in the whole area and between individual layers;

[0023] First meeting the fitting accuracy of the total indicators and then pursuing the fitting accuracy of individual wells.

[0024] Optionally, the simulation of the evolution of remaining oil during chemical flooding specifically includes:

[0025] During fitting, all high-yield and important individual wells need to be fully fitted to obtain fitting results;

[0026] Based on the fitting results and combined with dynamic data analysis, accurately simulate the underground remaining oil distribution status.

[0027] Optionally, step S3: Establishing an evaluation method for the optimal enrichment window period of remaining oil during chemical flooding specifically includes:

[0028] Defining that when the oil saturation is greater than 20% of the oil saturation before chemical flooding as the optimal enrichment window period, the remaining oil distribution state in the optimal enrichment window period is defined as an "oil wall", and the scale of the "oil wall" is characterized by the remaining oil aggregation degree, where the remaining oil aggregation degree refers to the ratio of the difference between the current oil saturation and the oil saturation before chemical flooding to the oil saturation before chemical flooding, formula 1;

[0029] With the increase of the sweep efficiency after chemical flooding, an "oil wall" will form near the effective wells. Defining the remaining oil aggregation degree to characterize this phenomenon, and defining that when the remaining oil aggregation degree is greater than 20% as the optimal enrichment window period;

[0030]

[0031] Among them, C sois the remaining oil accumulation degree; S o is the current remaining oil saturation; S oi is the oil saturation before chemical flooding.

[0032] Optionally, the step S4: the method for establishing the three-field adaptation of the pressure gradient field, the remaining oil saturation field, and the displacing agent concentration field in the target block specifically includes:

[0033] As shown in Formula 2, based on Formula 2, the high remaining oil saturation areas with development potential are divided into four zones, and the zone with a high pressure gradient field and a high displacing agent concentration field is defined as the optimal zone;

[0034]

[0035] In the formula, n is the number of grids, an integer; K i is the permeability of the i-th grid, mD; S wi is the water saturation of the i-th grid, a decimal; K ro (S wi ) is the oil-phase relative permeability corresponding to the water saturation S wi a decimal; K rw (S wi ) is the water-phase relative permeability corresponding to the water saturation S wi a decimal; μ o is the underground crude oil viscosity, mPa·s; μ w is the formation water viscosity, mPa·s; R i is the seepage resistance of the i-th grid, MPa, is the Hamilton operator, used to represent the gradient and divergence; P i is the pressure of the i-th grid, MPa.

[0036] For the potential zone with a low pressure gradient field and a low displacing agent concentration field, according to the optimal enrichment window period of the remaining oil determined in step S3, implement the "2" in the "3 + 2" enhanced oil recovery technology;

[0037] Design different "2" schemes during the optimal enrichment window period of the remaining oil, implement the streamline adjustment method alone or in combination, and use reservoir numerical simulation to compare the streamline, water cut change, and cumulative oil increment index of different schemes to optimize the best "2" scheme.

[0038] Optionally, the "2" in the "3 + 2" enhanced oil recovery technology includes the streamline adjustment methods of new well drilling, sidetracking well drilling, and injection-production allocation.

[0039] Optionally, the step S4: the method for establishing the three-field adaptation of the pressure gradient field, the remaining oil saturation field, and the displacing agent concentration field in the target block further includes:

[0040] In the thief zone with a low pressure gradient field and a high displacing agent concentration field, implement the "3" in the "3 + 2" enhanced oil recovery technology to inhibit the occurrence of thief zone phenomena and cultivate and upgrade to the optimal zone.

[0041] Optionally, the implementation of the "3" in the "3 + 2" enhanced oil recovery technology specifically includes: the change of the displacing system, the optimization of the slug size, and the optimization of the injection method.

[0042] An oil production method for implementing "3 + 2" in an extra-high water cut oilfield provided by the present invention specifically includes: Step S1: Collect and organize the reservoir geology and development dynamic data of the target block and establish a geological model; Step S2: Use numerical simulation methods to simulate the evolution of remaining oil during chemical flooding; Step S3: Establish an evaluation method for the best enrichment window period of remaining oil during chemical flooding; Step S4: Establish a three-field matching method for the pressure gradient field, remaining oil saturation field, and displacing agent concentration field of the target block; Step S5: Implement oilfield production according to the matching method. Fully improve the utilization rate of the displacing agent, effectively extend the "water cut valley period" of chemical flooding, thereby extending the peak response period and improving oil recovery and economic benefits.

[0043] The above description is only an overview of the technical solution of the present invention. In order to be able to understand the technical means of the present invention more clearly, it can be implemented according to the content of the specification. And in order to make the above and other purposes, features and advantages of the present invention more obvious and understandable, the following specifically describes the embodiments of the present invention. Brief Description of the Drawings

[0044] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0045] Figure 1 It is a flowchart of an oil production method for implementing "3 + 2" in an extra-high water cut oilfield provided by an embodiment of the present invention;

[0046] Figure 2 It is a schematic diagram of a three-field matching partition method provided by an embodiment of the present invention. Detailed Description of the Embodiments

[0047] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the drawings. Although the exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0048] In the embodiments of the specification, claims, and drawings of the present invention, the terms "comprising", "having", and any variations thereof are intended to cover non-exclusive inclusion. For example, including a series of steps or units.

[0049] The following further describes the technical solutions of the present invention in detail in conjunction with the drawings and embodiments.

[0050] As Figure 1 shown, a "3 + 2" production method for ultra-high water cut oilfields includes the steps:

[0051] Step 1: Collect and organize the reservoir geology and development dynamic data of the target block, including: single well drilling data, sub-layer data, layered data, porosity, permeability, geological reserves, high-pressure physical properties data of crude oil, coring well data, rock-related parameters (Table 1), and establish a static and dynamic reservoir model.

[0052] Table 1 Reservoir fluid parameters (a certain area in Shengli Oilfield)

[0053]

[0054]

[0055] Step 2: Fine analyze and organize the historical production and injection data of the block, use numerical simulation methods to conduct historical fitting of the target block, correct and adjust geological and chemical agent parameters, and simulate the evolution of remaining oil during the chemical flooding process;

[0056] Fitting principle: 1. First overall then local, ensuring relative unity across the whole area and between single layers; 2. First meet the fitting accuracy of the total index, and then pursue the fitting accuracy of single wells; Fitting method: 1. Dynamically adjust the injection and production volumes of boundary wells to fit the pressure; 2. Adjust the permeability and relative permeability curves to fit the water cut of single wells. All high-yield and important single wells need to be fitted during the fitting. Based on numerical simulation means and combined with dynamic data analysis, accurately simulate the distribution of underground remaining oil.

[0057] Step 3: Establish an evaluation method for the optimal enrichment window period of remaining oil during the chemical flooding process. Define that when the oil saturation is greater than 20% of the oil saturation before chemical flooding as the optimal enrichment window period. The distribution state of the remaining oil during this period is defined as an "oil wall". The scale of the "oil wall" is characterized by the degree of remaining oil aggregation. The degree of remaining oil aggregation is the ratio of the difference between the current oil saturation and the oil saturation before chemical flooding to the oil saturation before chemical flooding (Formula 1);

[0058] Due to the increase in the sweep efficiency after chemical flooding, an "oil wall" will form near the effective wells. Therefore, the degree of remaining oil accumulation is defined to characterize this phenomenon. The degree of remaining oil accumulation in the whole area is statistically analyzed, and the remaining oil accumulation area is found. When the degree of remaining oil accumulation is greater than 20%, it is defined as the optimal enrichment window period.

[0059]

[0060] C so is the degree of remaining oil accumulation; S o is the current oil saturation; S oi is the oil saturation before chemical flooding.

[0061] Step 4: Establish a three-field matching method for the pressure gradient field, remaining oil saturation field, and displacing agent concentration field in the target block, as shown in Formula 2. Based on Formula 2, the remaining oil high-saturation areas with development potential are divided into four zones. The zone with a high pressure gradient field and a high displacing agent concentration field is defined as the optimal zone, as Figure 2 shown.

[0062] For the potential zone with a low pressure gradient field and a low displacing agent concentration field, according to the optimal enrichment window period of the remaining oil determined in Step 3, start implementing the "2" in the "3 + 2" enhanced oil recovery technology. The above-mentioned "2" includes, but is not limited to, new well drilling, sidetracking, and injection-production allocation streamline adjustment methods.

[0063]

[0064] In the formula, n is the number of grids, an integer; K i is the permeability of the i-th grid, mD; S wi is the water saturation of the i-th grid, a decimal; K ro (S wi ) is the relative permeability of the oil phase corresponding to the water saturation S wi , a decimal; K rw (S wi ) is the relative permeability of the water phase corresponding to the water saturation S wi , a decimal; μ o is the underground crude oil viscosity, mPa·s; μ w is the formation water viscosity, mPa·s; R i is the seepage resistance of the i-th grid, MPa, is the Hamilton operator, used to represent the gradient and divergence; P i is the pressure of the i-th grid, MPa.

[0065] Finally, different "2" schemes are designed during the optimal enrichment window period of remaining oil. This scheme can implement streamline adjustment methods individually or in combination, and use reservoir numerical simulation to compare indicators such as streamlines, water cut changes, and cumulative oil increment of different schemes, so as to optimize the best "2" scheme.

[0066] Step 5, for the thief zone with a low pressure gradient field and a high displacing agent concentration field, it is necessary to implement the "3" in the "3 + 2" enhanced oil recovery technology, including the change of the displacing agent system, the optimization of slug size, the optimization of injection rate, etc., to inhibit the occurrence of thief zone phenomena and quickly cultivate and upgrade to the optimal zone ( Figure 2 ).

[0067] The optimization of chemical agent injection parameters is first the optimization of the injection system. In this optimization, a heterogeneous composite displacing agent system with stronger profile control ability is obtained; the second is the design optimization of the total volume of chemical flooding injection, that is, the slug size (Table 2). Four schemes with total injection slug volumes of 0.5PV, 0.7PV, 0.9PV, and 1.1PV are designed for optimization. It can be seen from the numerical simulation optimization results that as the injection slug increases, the enhanced oil recovery value gradually increases, but the increasing trend first increases and then decreases. The comprehensive index is the largest at 0.9PV. Therefore, the recommended optimal total injection slug is 0.9PV. The third is the design and optimization of the injection rate (Table 3). On the basis of the optimized design of the slug size, the injection rate optimization of the target area is carried out. Since the block has good injection capacity, five injection rates of 0.08, 0.09, 0.1, 0.11, and 0.12PV / a are designed respectively. The numerical simulation calculation results show that the five injection rates have little influence on the displacement effect. At the same time, the study of the chemical agent propulsion under different injection rates shows that the greater the injection rate, the faster the chemical agent advances and the easier it is to occur channeling and aggregation. Therefore, the recommended injection rate for this block is 0.1PV / a. Finally, the best injection system parameters suitable for field application are recommended.

[0068] Table 2 Optimization of injection volume (a certain area in Shengli Oilfield)

[0069] Injection volume, PV Enhanced oil recovery, % 0.5 49.1 0.7 51.3 0.9 53.8 1.1 55.0

[0070] Table 3 Optimization of injection rate (a certain area in Shengli Oilfield)

[0071] Injection rate, PV / a Enhanced oil recovery, % 0.08 52.8 0.09 52.6 0.1 52.5 0.11 52.5 0.12 52.4

[0072] Use numerical simulation to predict the oil increment effect of "3 + 2" enhanced oil recovery. Through example calculation, in this block of Shengli Oilfield, when the water cut reaches 98%, the heterogeneous composite flooding can increase the oil recovery by 15.4% (7.3% higher than the original scheme design), and the cumulative oil increment is 54.3×10 4 t, and the converted oil increment per ton of polymer is 18.8t / t. The ultimate oil recovery is 52.76%.

[0073] Aiming at the problem that the validity period of the existing economic evaluation method is not suitable, an economic evaluation method adapted to the "3+2" technology for significantly improving oil recovery is established. The main financial evaluation indicators (such as the internal rate of return on investment after tax, net present value of finance, static investment payback period, etc.) should meet the benchmark income requirements of the petroleum industry, that is, it is economically feasible.

[0074] Beneficial effects: The method of the present invention adds a method for identifying the optimal enrichment window period of remaining oil during the tertiary oil recovery process: carry out fine geological research on the target block reservoir and establish a geological model that can reflect the reservoir heterogeneity. Based on numerical simulation, accurately simulate the underground remaining oil distribution, and define the period when the oil saturation is more than 20% higher than the average oil saturation as the optimal enrichment window period of remaining oil. Secondly, it adds a three-field matching method for the pressure gradient field, remaining oil saturation field, and displacing agent concentration field in the target block, and guides the implementation of the "3+2" technology for significantly improving oil recovery by dividing different evaluation areas; finally, the optimal plan is obtained through reservoir numerical simulation and economic evaluation, and the oil increment effect is predicted and the economic benefits are calculated.

[0075] The evaluation method of the present invention is reliable and effective, and can be widely applied to the development effect evaluation and optimization during the implementation of various chemical oil displacement technologies, and can also be used to guide the design of well pattern adjustment plans during the development of chemical oil displacement in the oilfield. The "3+2" technology for significantly improving oil recovery constructs new flow lines through "2", increases the oil drainage channels while balancing the pressure field, strengthens the planar sweep and its effect, and rationally designs the dosage and injection method of the displacing agent system through "3" to fully improve the utilization rate of the displacing agent. This technology can effectively extend the "water cut valley period" of chemical flooding, thereby extending the peak response period and further improving the oil recovery and economic benefits.

[0076] The above specific implementation manners further elaborate in detail the purpose, technical solution and beneficial effects of the present invention. It should be understood that the above are only the specific implementation manners of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A "3 + 2" production method for extra-high water cut oilfields, characterized in that, The described production method specifically includes: Step S1: Collect and collate the reservoir geology and development dynamic data of the target block, and establish a geological model; Step S2: Use numerical simulation methods to simulate the evolution of remaining oil during chemical flooding; Step S3: Establish an evaluation method for the optimal enrichment window period of remaining oil during chemical flooding; Step S4: Establish a three-field matching method for the pressure gradient field, remaining oil saturation field, and displacing agent concentration field in the target block; Step S5: Implement oilfield production using the "3 + 2" production method according to the described matching method.

2. The "3 + 2" production method for extra-high water cut oilfields according to claim 1, characterized in that, The collection and collation of the reservoir geology and development dynamic data of the target block specifically include: Single-well drilling data, sub-layer data, layered data, porosity, permeability, geological reserves, high-pressure physical properties data of crude oil, core well data, and rock parameters.

3. The "3 + 2" production method for extra-high water cut oilfields according to claim 1, characterized in that, The establishment of the geological model specifically includes: Conduct fine geological research on the reservoir in the target block and establish a geological model reflecting the dynamic heterogeneity of the reservoir.

4. The "3 + 2" production method for extra-high water cut oilfields according to claim 1, characterized in that, The described Step S2: Using numerical simulation methods to simulate the evolution of remaining oil during chemical flooding specifically includes: Use numerical simulation methods to conduct history matching for the target block, correct and adjust geological and chemical agent parameters, and simulate the evolution of remaining oil during chemical flooding.

5. The "3 + 2" production method for extra-high water cut oilfields according to claim 4, characterized in that, The use of numerical simulation methods to conduct history matching for the target block and correct and adjust geological and chemical agent parameters specifically includes: Design the matching principle; Dynamically adjust the injection and production volumes and fitting pressures of boundary wells according to the described matching principle; Adjust the permeability and relative permeability curves to fit the water cut of a single well.

6. The "3 + 2" production method for extra-high water cut oilfields according to claim 5, characterized in that, The described matching principle is: Adopt the method of first overall and then local to ensure relative unity in the whole area and between single layers; First meet the fitting accuracy of the total index, and then pursue the fitting accuracy of a single well.

7. The "3 + 2" production method for extra-high water cut oilfields according to claim 4, characterized in that, The described simulation of the evolution of remaining oil during chemical flooding specifically includes: All high-yield and important single wells need to be fully fitted during the fitting to obtain the fitting results; Based on the described fitting results and combined with the analysis of dynamic data, simulate the accurate distribution of underground remaining oil.

8. The "3 + 2" production method for extra-high water cut oilfields according to claim 1, characterized in that, The described Step S3: Establish an evaluation method for the optimal enrichment window period of remaining oil during chemical flooding specifically includes: Define that when the oil saturation is greater than 20% of the oil saturation before chemical flooding as the optimal enrichment window period. The remaining oil distribution state during the optimal enrichment window period is defined as an "oil wall", and the scale of the "oil wall" is characterized by the degree of remaining oil aggregation. The degree of remaining oil aggregation refers to the ratio of the difference between the current oil saturation and the oil saturation before chemical flooding to the oil saturation before chemical flooding, Formula 1; With the increase of the sweep efficiency after chemical flooding, an "oil wall" will form near the effective wells. Define the degree of remaining oil aggregation to characterize this phenomenon, and define that when the degree of remaining oil aggregation is greater than 20% as the optimal enrichment window period; Among them, C so is the remaining oil accumulation degree; S o is the current remaining oil saturation; S oi is the oil saturation before chemical flooding.

9. A method for implementing "3 + 2" in an extra-high water cut oilfield according to claim 1, characterized in that, The described Step S4: Establish a three-field matching method for the pressure gradient field, remaining oil saturation field, and displacing agent concentration field in the target block specifically includes: As shown in Formula 2, based on Formula 2, divide the remaining oil high-saturation areas with development potential into four zones, and define the zone with a high pressure gradient field and a high displacing agent concentration field as the optimal zone; where n is the number of grids, an integer; K i is the permeability of the i-th grid, mD; S wi is the water saturation of the i-th grid, a decimal; K ro (S wi ) is the relative permeability of the oil phase corresponding to the water saturation S wi , a decimal; K rw (S wi ) is the relative permeability of the water phase corresponding to the water saturation S wi , a decimal; μ o is the viscosity of underground crude oil, mPa·s; μ w is the viscosity of formation water, mPa·s; R i is the seepage resistance of the i-th grid, MPa, is the Hamilton operator, used to represent gradient and divergence; P i is the pressure of the i-th grid, MPa. For the potential zone with a low pressure gradient field and a low displacing agent concentration field, implement the "2" in the "3 + 2" enhanced oil recovery technology according to the optimal enrichment window period of remaining oil determined in Step S3; Design different "2" schemes during the optimal enrichment window period of remaining oil, implement the streamline adjustment method alone or in combination, and use reservoir numerical simulation to compare the streamline, water cut change and cumulative oil increment index of different schemes, so as to optimize the best "2" scheme.

10. A method for implementing "3 + 2" in an extra-high water cut oilfield according to claim 9, characterized in that, The "2" in the "3 + 2" enhanced oil recovery technology includes the streamline adjustment methods of new well drilling, sidetracking well drilling and injection-production allocation.

11. A method for implementing "3 + 2" in an extra-high water cut oilfield according to claim 9, characterized in that, The step S4: The three-field adaptation method for establishing the pressure gradient field, remaining oil saturation field and displacing agent concentration field in the target block further includes: In the channeling agent area with a low pressure gradient field and a high displacing agent concentration field, implement the "3" in the "3 + 2" enhanced oil recovery technology to inhibit the occurrence of channeling agent phenomenon and cultivate and upgrade it to the optimal area.

12. A method for implementing "3 + 2" in an extra-high water cut oilfield according to claim 11, characterized in that, The implementation of the "3" in the "3 + 2" enhanced oil recovery technology specifically includes: the change of the displacing system, the optimization of the slug size, and the optimization of the injection method.

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