Method for optimizing injection rate of carbon dioxide slug before pressure flooding water injection

Abstract

The invention relates to the technical field of low-permeability reservoir pressure-drive water injection development, and provides a method for optimizing the injection rate of a carbon dioxide slug before pressure-drive water injection. The method comprises the following steps: establishing a three-dimensional geologic model according to pre-acquired oil reservoir data of a target block; carrying out numerical simulation by utilizing the model, obtaining the accumulated oil production of each pressure-driving water injection parameter in a preset time period, and calculating the difference value between the accumulated oil production of different preposed carbon dioxide slug pressure-driving water injection parameters and the accumulated oil production of conventional pressure-driving water injection parameters to obtain the relative accumulated oil increase of different pressure-driving water injection parameters; and on the basis of the oil reservoir geological reserves and the total carbon dioxide injection amount of the target block, the recovery efficiency improvement range, the oil change rate and the final corresponding pressure flooding water injection preposed carbon dioxide slug injection amount are obtained. By means of the method, the relation between the injection amount of the carbon dioxide slug before pressure flooding water injection and the improved recovery efficiency range and oil change rate can be predicted, and the influence on the low-permeability oil reservoir development effect is reflected.

Description

Technical Field

[0001] This invention relates to the field of pressure-driven water injection development technology for low-permeability reservoirs, and particularly to a method for optimizing the injection volume of a carbon dioxide slug before pressure-driven water injection. Background Technology

[0002] Low-permeability reservoirs suffer from low water injection capacity or difficulty due to their low reservoir permeability. Pressure-driven water injection technology can increase the water injection rate in low-permeability reservoirs from 20m³ / h. 3 / d increased to 1000-2000m 3 / d, effectively solving the problem of difficult water injection in low-permeability reservoirs. However, water injection under pressure also faces problems such as small water drive sweep area and low reservoir recovery during application. After water injection is implemented in the target oil layer, the production wells in the mainstream direction quickly become effective, but due to the presence of dynamic fractures in the oil layer, the injected water advances rapidly along the dynamic fractures, resulting in a small displacement sweep volume and low reservoir recovery.

[0003] Carbon dioxide flooding (CO2) is one of the most widely used technologies for enhancing oil recovery in low-permeability reservoirs. CO2 can penetrate nanoscale pores, effectively expanding the displacement sweep volume. Simultaneously, CO2 reduces interfacial tension, and after miscibility, it can significantly improve reservoir recovery. Field practice shows that the amount of CO2 injected affects reservoir development effectiveness and economic benefits. Therefore, accurately determining the optimal CO2 injection rate is a key factor in the success of CO2 flooding projects. It is necessary to obtain the CO2 slug injection rate before water injection in pressure flooding; however, this value is difficult to determine.

[0004] Currently, the existing methods for optimizing the injection volume of pre-CO2 slugs in pressure-driven water injection mainly rely on calculations based on seepage theory formulas. However, this method cannot reflect the impact of the injection volume of pre-CO2 slugs on the development effect of low-permeability reservoirs, nor can it predict the relationship between the injection volume of pre-CO2 slugs and the increase in oil recovery and oil exchange rate. Summary of the Invention

[0005] In view of this, the present invention provides an optimization method for the injection volume of pre-CO2 slug in pressure-driven water injection, in order to solve the technical problems in the prior art that the optimization method for the injection volume of pre-CO2 slug in pressure-driven water injection cannot reflect the impact of the size of the pre-CO2 slug on the development effect of low-permeability reservoirs, and cannot predict the relationship between the injection volume of pre-CO2 slug and the increase in oil recovery and oil exchange rate.

[0006] This invention provides a method for optimizing the injection volume of a pre-pressure water injection carbon dioxide slug, comprising:

[0007] S1. Based on the reservoir data of the target block obtained in advance, establish a three-dimensional geological model;

[0008] S2. Based on multiple pre-set pre-coal slug pressure drive water injection parameters, numerical simulation is performed using the three-dimensional geological model to obtain the cumulative oil production of each pre-coal slug pressure drive water injection parameter over a preset period. The pre-coal slug pressure drive water injection parameters include conventional pressure drive water injection parameters and multiple different pre-coal slug pressure drive water injection parameters. For each different pre-coal slug pressure drive water injection parameter, the difference between the cumulative oil production of the different pre-coal slug pressure drive water injection parameter and the cumulative oil production of the conventional pressure drive water injection parameter is calculated to obtain the relative cumulative oil increase of the different pre-coal slug pressure drive water injection parameters.

[0009] S3. For the relative cumulative oil increase of each different pre-coal slug squeegee water injection parameter, based on the reservoir geological reserves of the target block and the total amount of carbon dioxide injected in the different pre-coal slug squeegee water injection parameters, respectively obtain the recovery rate increase and oil exchange rate of the different pre-coal slug squeegee water injection parameters.

[0010] S4. Based on the project economic limit index preset for the target block, obtain the amount of pre-carbon dioxide slug injection in the pre-carbon dioxide slug injection parameters that satisfy the project economic limit index from the enhanced oil recovery rate and oil exchange rate corresponding to different pre-carbon dioxide slug pressure water injection parameters.

[0011] Optionally, the reservoir data for the target block includes: well data for geological modeling, geological graphic data, reserve reports, and production dynamic data.

[0012] Optionally, the expression for the increase in recovery rate is as follows:

[0013]

[0014] Optionally, the expression for the oil change rate is as follows:

[0015]

[0016] Optionally, this also includes obtaining different pre-positioned carbon dioxide slug injection volumes, including:

[0017] Based on numerical simulation schemes with different pre-coal dioxide slug injection volumes, the volume of the pre-coal dioxide slug under underground reservoir conditions is calculated.

[0018] Based on the volume of the pre-CO2 slug under underground reservoir conditions, the volume of the pre-CO2 slug under standard conditions is calculated according to the ideal gas equation of state.

[0019] Based on the volume of the pre-positioned carbon dioxide slug under standard conditions, and according to the conversion coefficient between volume and mass under standard conditions, the injection volume of different pre-positioned carbon dioxide slugs is calculated.

[0020] Optionally, the volume of the pre-mounted carbon dioxide slug under underground reservoir conditions is expressed as follows:

[0021]

[0022] Among them, V res This indicates the volume of the pre-mounted carbon dioxide slug under underground reservoir conditions. V represents the size of the pre-mounted carbon dioxide slug, and V represents the target reservoir pore volume.

[0023] Optionally, the volume of the pre-mounted carbon dioxide slug under standard conditions is expressed as follows:

[0024]

[0025] Among them, V std P represents the volume of the pre-CO2 slug under standard conditions. res T represents the pressure under underground oil reservoir conditions. std P represents temperature under standard conditions. std T represents pressure under standard conditions. res This indicates the temperature under underground oil reservoir conditions.

[0026] Optionally, the expressions for the different pre-positioned carbon dioxide slug injection volumes are as follows:

[0027] Q CO2 =V std / Z std

[0028] in, Z represents the pre-load carbon dioxide slug injection volume. std This indicates the volume of 1 ton of carbon dioxide under standard conditions.

[0029] Optionally, the pre-CO2 slug injection volume in the pre-CO2 slug pressure-driven water injection parameters corresponding to the improved recovery rate and oil exchange rate meeting the economic limit indicators of the project, and the numerical simulation scheme of the pre-CO2 slug injection volume corresponding to the pressure-driven water injection, is the numerical simulation scheme of the target pressure-driven water injection pre-CO2 slug injection volume.

[0030] Optionally, the determination of the numerical simulation scheme for the target pressure-driven water injection pre-carbon dioxide slug injection volume includes:

[0031] The relative cumulative oil increase of the pre-carbon dioxide slug pressure drive water injection parameters is the highest, as are the enhanced oil recovery rate and oil exchange rate.

[0032] The advantages of this invention compared to the prior art are:

[0033] 1. This invention establishes a three-dimensional geological model of the target block reservoir and uses the model to conduct numerical simulations to establish the relationship between different injection volumes of carbon dioxide slugs before water injection and the extent of enhanced oil recovery and oil exchange rate, and obtains the necessary parameters, namely, different injection volumes of carbon dioxide slugs before water injection.

[0034] 2. This invention establishes the relationship between different pre-injection volumes of carbon dioxide slugs for pressure-driven water injection and the increase in oil recovery and oil exchange rate, demonstrating the profound impact of pre-injection volumes of carbon dioxide slugs on the development of low-permeability reservoirs. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in this invention, the accompanying drawings used in the description of the embodiments or prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a flowchart of a method for optimizing the injection volume of a pre-pressure water injection carbon dioxide slug provided in an embodiment of the present invention;

[0037] Figure 2 This is a schematic diagram showing the relationship between different sizes of the pre-coal dioxide slug for pressure-driven water injection and the increase in oil recovery and oil exchange rate, as provided in the embodiments of the present invention. Detailed Implementation

[0038] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will understand that the invention can be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods are omitted so as not to obscure the description of the invention with unnecessary detail.

[0039] The following will describe in detail, with reference to the accompanying drawings, a method for optimizing the injection volume of a pre-pressure water injection carbon dioxide slug according to the present invention.

[0040] Figure 1 This is a flowchart of a method for optimizing the injection volume of a pre-pressure water injection carbon dioxide slug provided in an embodiment of the present invention.

[0041] like Figure 1 As shown, the method for optimizing the injection volume of the pre-pressure water injection carbon dioxide slug includes:

[0042] S1. Based on the reservoir data of the target block obtained in advance, establish a three-dimensional geological model;

[0043] In one embodiment, the reservoir data of the target block is known, and various historical data encountered during the work are used to establish the three-dimensional geological model in the selected target block using numerical simulation software based on the reservoir data of the target block. The target block refers to a specific selected block.

[0044] The reservoir data for the target block includes: well data for geological modeling, geological graphic data, reserve reports, and production dynamic data.

[0045] S2. Based on multiple pre-set pre-coal slug pressure drive water injection parameters, numerical simulation is performed using the three-dimensional geological model to obtain the cumulative oil production of each pre-coal slug pressure drive water injection parameter over a preset period. The pre-coal slug pressure drive water injection parameters include conventional pressure drive water injection parameters and multiple different pre-coal slug pressure drive water injection parameters. For each different pre-coal slug pressure drive water injection parameter, the difference between the cumulative oil production of the different pre-coal slug pressure drive water injection parameter and the cumulative oil production of the conventional pressure drive water injection parameter is calculated to obtain the relative cumulative oil increase of the different pre-coal slug pressure drive water injection parameters.

[0046] Among them, several different pre-coal slug pressure drive water injection parameters include: pre-coal slug injection volume, number of carbon dioxide injection cycles, total carbon dioxide injection volume, etc. Conventional pressure drive water injection parameters include: total pressure drive water injection volume.

[0047] In one embodiment, numerical simulation is performed using the three-dimensional geological model to obtain the cumulative oil production of different pre-CO2 slug injection parameters over a preset time period. Based on the cumulative oil production of different pre-CO2 slug injection parameters over the preset time period, the difference between the cumulative oil production of the different pre-CO2 slug injection parameters and the cumulative oil production of the conventional injection parameters is calculated to obtain the relative cumulative oil increase of the different pre-CO2 slug injection parameters. Each relative cumulative oil increase of different pre-CO2 slug injection parameters corresponds to a numerical simulation scheme of different pre-CO2 slug injection volume for injection. The pre-CO2 slug injection parameters include conventional injection parameters and multiple different pre-CO2 slug injection parameters.

[0048] S3. For the relative cumulative oil increase of each different pre-coal slug squeegee water injection parameter, based on the reservoir geological reserves of the target block and the total amount of carbon dioxide injected in the different pre-coal slug squeegee water injection parameters, respectively obtain the recovery rate increase and oil exchange rate of the different pre-coal slug squeegee water injection parameters.

[0049] In one embodiment, based on the relative cumulative oil gain of different pre-CO2 slug injection parameters, a relationship is established between the injection volume of the pre-CO2 slug and the enhanced oil recovery rate and oil exchange rate. Following the principle that the target block's production wells have the same operating regime, the same total injection volume, and the same total CO2 injection volume, but different pre-CO2 slug injection volumes, since the relative cumulative oil gain of each different pre-CO2 slug injection parameter is different, for each different pre-CO2 slug injection parameter, based on the reservoir geological reserves of the target block and the total CO2 injection volume in the different pre-CO2 slug injection parameters, the enhanced oil recovery rate and oil exchange rate of the different pre-CO2 slug injection parameters can be obtained respectively. Here, the operating regime of the target block's production wells refers to the production time.

[0050] The expression for the increase in recovery rate is as follows:

[0051]

[0052] The expression for the oil change rate is as follows:

[0053]

[0054] The different pre-positioned CO2 slug injection volumes were obtained by:

[0055] Based on numerical simulation schemes with different pre-coal dioxide slug injection volumes, the volume of the pre-coal dioxide slug under underground reservoir conditions is calculated.

[0056] Based on the volume of the pre-CO2 slug under underground reservoir conditions, the volume of the pre-CO2 slug under standard conditions is calculated according to the ideal gas equation of state.

[0057] Based on the volume of the pre-positioned carbon dioxide slug under standard conditions, and according to the conversion coefficient between volume and mass under standard conditions, the injection volume of different pre-positioned carbon dioxide slugs is calculated.

[0058] The volume expression for the pre-loaded carbon dioxide slug under underground reservoir conditions is as follows:

[0059]

[0060] Among them, Vres This indicates the volume of the pre-loaded carbon dioxide slug under underground reservoir conditions. V represents the size of the pre-mounted carbon dioxide slug, and V represents the target reservoir pore volume.

[0061] The volume of the pre-mounted carbon dioxide slug under standard conditions is expressed as follows:

[0062]

[0063] Among them, V std P represents the volume of the pre-CO2 slug under standard conditions. res T represents the pressure under underground oil reservoir conditions. std P represents temperature under standard conditions. std T represents pressure under standard conditions. res This indicates the temperature under underground oil reservoir conditions.

[0064] The expressions for the different pre-positioned carbon dioxide slug injection volumes are as follows:

[0065] Q CO2 =V std / Z std

[0066] in, Z represents the pre-load carbon dioxide slug injection volume. std This indicates the volume of 1 ton of carbon dioxide under standard conditions.

[0067] S4. Based on the project economic limit index preset for the target block, obtain the amount of pre-carbon dioxide slug injection in the pre-carbon dioxide slug injection parameters that satisfy the project economic limit index from the enhanced oil recovery rate and oil exchange rate corresponding to different pre-carbon dioxide slug pressure water injection parameters.

[0068] The numerical simulation scheme for the pre-CO2 slug injection volume in the pre-CO2 slug injection parameters corresponding to the improved oil recovery rate and oil exchange rate that meet the economic limit indicators of the project is the numerical simulation scheme for the target pre-CO2 slug injection volume in water injection for water injection.

[0069] In one embodiment, for each set of enhanced oil recovery rate and oil exchange rate, the pre-coal slug injection volume in the pre-coal slug pressure injection parameters is selected. The pre-coal slug injection volume in the pre-coal slug pressure injection parameters corresponding to the enhanced oil recovery rate and oil exchange rate meeting the project's economic limit indicators is selected. The pre-coal slug injection volume numerical simulation scheme to which this pre-coal slug injection volume belongs is the required pre-coal slug injection volume numerical simulation scheme, i.e., the target pressure injection water pre-coal slug injection volume numerical simulation scheme.

[0070] The determination of the numerical simulation scheme for the target pressure-driven water injection pre-carbon dioxide slug injection volume includes:

[0071] The relative cumulative oil increase of the pre-carbon dioxide slug pressure drive water injection parameters is the highest, as are the enhanced oil recovery rate and oil exchange rate.

[0072] This invention establishes a three-dimensional geological model of the target reservoir and uses this model for numerical simulation to establish the relationship between different CO2 slug injection volumes before water injection and the enhanced oil recovery rate and oil exchange rate. It obtains the necessary parameters, namely, different CO2 slug injection volumes before water injection. By establishing the relationship between different CO2 slug injection volumes before water injection and the enhanced oil recovery rate and oil exchange rate, the invention demonstrates the profound impact of CO2 slug injection volume on the development effect of low-permeability reservoirs.

[0073] Example 1

[0074] Step 1. Based on the pre-acquired reservoir data of the target block, establish a three-dimensional geological model;

[0075] Step 2. Based on multiple pre-set pre-coal slug pressure drive water injection parameters, numerical simulation is performed using the three-dimensional geological model to obtain the cumulative oil production of each pre-coal slug pressure drive water injection parameter over a preset period. The pre-coal slug pressure drive water injection parameters include conventional pressure drive water injection parameters and multiple different pre-coal slug pressure drive water injection parameters. For each different pre-coal slug pressure drive water injection parameter, the difference between the cumulative oil production of the different pre-coal slug pressure drive water injection parameter and the cumulative oil production of the conventional pressure drive water injection parameter is calculated to obtain the relative cumulative oil increase of the different pre-coal slug pressure drive water injection parameters.

[0076] In specific application scenarios, numerical simulation designs are carried out using the three-dimensional geological model for different pre-injection carbon dioxide slug injection volumes for pressure-driven water injection. The numerical simulation designs for different pre-injection carbon dioxide slug injection volumes are calculated based on a 20-year production period for the target block reservoir.

[0077] Table 1 shows the numerical simulation of increased oil production for different pressure-driven water injection pre-carbon dioxide slug injection volumes.

[0078] Table 1. Oil Increase under Numerical Simulation Schemes with Different Pressure-Driven Water Injection Pre-Carbon Dioxide Slug Injection Volumes

[0079]

[0080] Figure 2 This is a schematic diagram showing the relationship between different sizes of the pre-coal dioxide slug for pressure-driven water injection and the increase in oil recovery and oil exchange rate, as provided in the embodiments of the present invention.

[0081] Step 3. For the relative cumulative oil increase of each different pre-coal slug squeegee water injection parameter, based on the reservoir geological reserves of the target block and the total amount of carbon dioxide injected in the different pre-coal slug squeegee water injection parameters, obtain the improved recovery rate and oil exchange rate of the different pre-coal slug squeegee water injection parameters respectively.

[0082] The economic threshold for oil exchange rate determined by the economic evaluation of the oilfield enhanced oil recovery project is 0.70 t / t. Step 3 is used to establish... Figure 2 The figure shows the relationship between different sizes of the pre-coal slug in pressure-driven water injection and the increase in oil recovery and oil exchange rate.

[0083] Table 2. Enhanced Oil Recovery and Oil Replacement Rate with Different Pre-CO2 Slug Plug Injection Parameters for Water Injection.

[0084]

[0085] Step 4. Based on the preset economic limit indicators for the target block, obtain the amount of pre-coal slug injection in the pre-coal slug injection parameters that satisfy the economic limit indicators for the target block, from the enhanced oil recovery rate and oil exchange rate corresponding to different pre-coal slug injection parameters.

[0086] The numerical simulation scheme for the pre-CO2 slug injection volume in the pre-CO2 slug injection parameters corresponding to the improved oil recovery rate and oil exchange rate that meet the economic limit indicators of the project is the numerical simulation scheme for the target pre-CO2 slug injection volume in water injection for water injection.

[0087] The determination of the numerical simulation scheme for the target pressure-driven water injection pre-carbon dioxide slug injection volume includes:

[0088] The relative cumulative oil increase of the pre-carbon dioxide slug pressure drive water injection parameters is the highest, as are the enhanced oil recovery rate and oil exchange rate.

[0089] Depend on Figure 2It can be seen that when the size of the pre-CO2 slug before water injection in pressure-driven oil recovery is 0.02 PV, the reservoir's enhanced oil recovery and oil exchange rate are both at their highest. At this point, the injection volume of the pre-CO2 slug before water injection in pressure-driven oil recovery is 1.9 × 10⁻⁶. 4 Therefore, the injection rate of the carbon dioxide slug before pressure-driven water injection is 1.9 × 10⁻⁶. 4 The numerical simulation scheme for the injection volume of the pre-coal dioxide slug at the location of t is the numerical simulation scheme for the injection volume of the pre-coal dioxide slug of the target pressure-driven water injection system.

[0090] All of the above-mentioned optional technical solutions can be combined in any way to form the optional embodiments of this application, and will not be described in detail here.

[0091] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0092] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A method for optimizing the injection volume of a pre-pressure water injection carbon dioxide slug, characterized in that, include: S1. Based on the reservoir data of the target block obtained in advance, establish a three-dimensional geological model; S2. Based on multiple pre-set pre-coal slug pressure drive water injection parameters, numerical simulation is performed using the three-dimensional geological model to obtain the cumulative oil production of each pre-coal slug pressure drive water injection parameter over a preset period. The pre-coal slug pressure drive water injection parameters include conventional pressure drive water injection parameters and multiple different pre-coal slug pressure drive water injection parameters. For each different pre-coal slug pressure drive water injection parameter, the difference between the cumulative oil production of the different pre-coal slug pressure drive water injection parameter and the cumulative oil production of the conventional pressure drive water injection parameter is calculated to obtain the relative cumulative oil increase of the different pre-coal slug pressure drive water injection parameters. S3. For the relative cumulative oil increase of each different pre-coal slug squeegee water injection parameter, based on the reservoir geological reserves of the target block and the total amount of carbon dioxide injected in the different pre-coal slug squeegee water injection parameters, respectively obtain the recovery rate increase and oil exchange rate of the different pre-coal slug squeegee water injection parameters. S4. Based on the project economic limit index preset for the target block, obtain the amount of pre-carbon dioxide slug injection in the pre-carbon dioxide slug injection parameters that satisfy the project economic limit index from the enhanced oil recovery rate and oil exchange rate corresponding to different pre-carbon dioxide slug pressure water injection parameters.

2. The method for optimizing the injection volume of the pre-pressure-driven water injection carbon dioxide slug according to claim 1, characterized in that, The reservoir data for the target block includes: well data for geological modeling, geological graphic data, reserve reports, and production dynamic data.

3. The method for optimizing the injection volume of the pre-pressure water injection carbon dioxide slug as described in claim 1, characterized in that, The expression for the increase in recovery rate is as follows:

4. The method for optimizing the injection volume of the pre-pressure water injection carbon dioxide slug according to claim 1, characterized in that, The expression for the oil change rate is as follows:

5. The method for optimizing the injection volume of the pre-pressure water injection carbon dioxide slug according to claim 1, characterized in that, This also includes obtaining different pre-positioned carbon dioxide slug injection volumes, including: Based on numerical simulation schemes with different pre-coal dioxide slug injection volumes, the volume of the pre-coal dioxide slug under underground reservoir conditions is calculated. Based on the volume of the pre-CO2 slug under underground reservoir conditions, the volume of the pre-CO2 slug under standard conditions is calculated according to the ideal gas equation of state. Based on the volume of the pre-positioned carbon dioxide slug under standard conditions, and according to the conversion coefficient between volume and mass under standard conditions, the injection volume of different pre-positioned carbon dioxide slugs is calculated.

6. The method for optimizing the injection volume of the pre-pressure water injection carbon dioxide slug according to claim 5, characterized in that, The volume expression for the pre-loaded carbon dioxide slug under underground reservoir conditions is as follows: Among them, V res This indicates the volume of the pre-mounted carbon dioxide slug under underground reservoir conditions. V represents the size of the pre-mounted carbon dioxide slug, and V represents the target reservoir pore volume.

7. The method for optimizing the injection volume of the pre-pressure water injection carbon dioxide slug according to claim 6, characterized in that, The volume of the pre-mounted carbon dioxide slug under standard conditions is expressed as follows: Among them, V std P represents the volume of the pre-CO2 slug under standard conditions. res T represents the pressure under underground oil reservoir conditions. std P represents temperature under standard conditions. std T represents pressure under standard conditions. res This indicates the temperature under underground oil reservoir conditions.

8. The method for optimizing the injection volume of the pre-pressure water injection carbon dioxide slug according to claim 7, characterized in that, The expressions for the different pre-positioned carbon dioxide slug injection volumes are as follows: in, Z represents the pre-load carbon dioxide slug injection volume. std This indicates the volume of 1 ton of carbon dioxide under standard conditions.

9. The method for optimizing the injection volume of the pre-pressure water injection carbon dioxide slug according to claim 1, characterized in that, The numerical simulation scheme for the pre-CO2 slug injection volume in the pre-CO2 slug injection parameters corresponding to the improved oil recovery rate and oil exchange rate that meet the economic limit indicators of the project is the numerical simulation scheme for the target pre-CO2 slug injection volume in water injection for water injection.

10. The method for optimizing the injection volume of the pre-pressure water injection carbon dioxide slug according to claim 9, characterized in that, The determination of the numerical simulation scheme for the target pressure-driven water injection pre-carbon dioxide slug injection volume includes: The relative cumulative oil increase of the pre-carbon dioxide slug pressure drive water injection parameters is the highest, as are the enhanced oil recovery rate and oil exchange rate.

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