Method for realizing pressure head moving forward by using preposed carbon dioxide slug assisted pressure drive water injection

Abstract

The application provides a method for realizing pressure head migration by using a front carbon dioxide slug to assist water injection, comprising the following steps: step 1, establishing a model of water injection assisted by a front carbon dioxide slug; step 2, calculating the required water injection volume for water injection according to a production scheme and reservoir production data, and combining a pressure distribution model to optimize the volume of the required carbon dioxide slug; step 3, injecting the carbon dioxide slug according to the calculation result of step 2 to realize pressure head migration; and step 4, after the carbon dioxide slug is injected, water injection development is carried out in the way of water injection to form a development model of water and carbon dioxide slug oil displacement. The method for realizing pressure head migration by using a front carbon dioxide slug to assist water injection combines the advantages of water injection and carbon dioxide displacement, achieves good oil displacement effect at a low cost, and has a great application prospect in the development of low-permeability reservoirs, tight reservoirs and fault block reservoirs.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of low-permeability oil reservoir pressure drive water injection development, in particular to a method for realizing pressure head migration by using a preposed carbon dioxide slug to assist pressure drive water injection. BACKGROUND

[0002] In China's future oil industry, enhancing oil recovery is becoming increasingly important, which will be an urgent and strategic task. China's oilfields are of various types and complex geology, so this technology should be diversified, especially for low-permeability oil reservoirs in China, which have geological reserves of more than 50×10 8 t, but the degree of utilization is poor. Because of the difficulty in water injection in low-permeability oil reservoirs, the formation energy is insufficient, making it difficult to effectively utilize. Therefore, new technologies are urgently needed to improve the recovery effect of low-permeability and tight oil reservoirs.

[0003] Pressure drive technology is a new technology that has been applied in recent years. Pressure drive uses fracturing pump trucks to inject a large amount of water to improve formation energy and improve development effect. However, pressure drive is different from fracturing, which uses specific fracturing fluid, proppant, etc. to press out hydraulic fractures according to the established plan. Pressure drive uses fracturing equipment to inject water at high pressure and fast. In field application, oil reservoirs that need to be replenished with energy for one year by conventional water injection can be completed by pressure drive water injection in one month, greatly shortening the injection time and having a huge effect on oil reservoirs with large formation energy deficit.

[0004] However, pressure drive also faces the problem of difficult pressure conduction in some formations. After pressure drive water injection, the production well can quickly respond, producing long-term self-flow or high recovery effect. However, some oil reservoirs have slow response after pressure drive water injection, or the bottom hole pressure of the base well quickly decreases after short-term self-flow, resulting in insignificant pressure drive effect.

[0005] In the Chinese patent application with application number CN202111186896.3, a method for grading characterization of carbon dioxide drive oil and gas channeling channels is disclosed. Based on the identification and quantitative characterization results of the heterogeneous reservoir advantage channel, a three-dimensional spatial distribution geometric model of the target reservoir advantage seepage channel is established. Through laboratory experiments and theoretical calculations, the amount of plugging agent and slug injection method are designed. Then, the plugging agent is injected through the injection well of the developed advantage seepage channel, and the pressure change, pressure drop curve shape, and water absorption index change during the injection process are closely monitored. After determining the obvious plugging control effect, carbon dioxide is injected for continuous displacement, thereby delaying the gas channeling time of the advantage large pore channel, improving the degree of utilization of weak water drive remaining oil, and achieving the purpose of balanced utilization of oil reservoirs.

[0006] In the Chinese patent application with the application number CN201410133734.7, a method for predicting carbon dioxide flooding reservoir index by material balance is disclosed, which comprises the following steps: step 1, giving the application conditions of the carbon dioxide flooding material balance equation; step 2, establishing the material balance equation suitable for carbon dioxide flooding; step 3, collecting reservoir parameters and determining calculation parameters; step 4, calculating the parameters corresponding to the time period, including oil production and gas injection; and step 5, determining the injection-production ratio and the recovery degree of these carbon dioxide flooding reservoir indexes by using the parameters calculated in step 4. The method for predicting carbon dioxide flooding reservoir index by material balance establishes the material balance equation suitable for carbon dioxide flooding considering the compressibility of reservoir rock fluid, and provides an application method of the material balance equation, which provides an effective method for predicting carbon dioxide flooding reservoir index.

[0007] In the Chinese patent application with the application number CN201811469493.8, a method for improving recovery based on trapped gas is disclosed, which comprises the following steps: step 1, stopping water injection after water flooding to the limit water content in the target reservoir; step 2, determining the position and number of gas injection wells according to the characteristics of the target reservoir; step 3, injecting gas into the gas injection well, closing the gas injection well and the production well for a first predetermined time to form trapped gas; step 4, stopping water injection after water flooding to the limit water content in the target reservoir, and recording the recovery of the target reservoir during this process; step 5, setting a number threshold and a recovery increase threshold, determining whether the number of gas injection reaches the number threshold, if yes, the oil production is completed, if not, step 6 is performed; step 6, determining whether the increase of recovery is less than the recovery increase threshold, if not, repeating steps 3-5, if yes, the oil production is completed. The invention improves the water control of high water cut reservoir by establishing trapped gas in the reservoir, thereby improving the recovery and economic benefit.

[0008] The above prior art has great difference from the present application and cannot solve the technical problems we want to solve, therefore we invent a new method for realizing pressure head migration by using pre-positioned carbon dioxide slug assisted pressure drive water injection. SUMMARY

[0009] The purpose of the present application is to provide a method for realizing pressure head migration by using pre-positioned carbon dioxide slug assisted pressure drive water injection, which makes the pressure distribution of pressure drive through the pressure drive well and the production well, and realizes the continuous high-yield production of the production well.

[0010] The purpose of the present application can be realized by the following technical measures: a method for realizing pressure head migration by using pre-positioned carbon dioxide slug assisted pressure drive water injection, which comprises the following steps:

[0011] Step 1, establishing a pre-positioned carbon dioxide slug assisted pressure drive water injection model;

[0012] Step 2, according to the exploitation scheme and the reservoir exploitation data, the required water injection amount of pressure drive is calculated; combined with the pressure distribution model of pressure drive, the volume of the required carbon dioxide slug is optimized;

[0013] Step 3, according to the calculation result of step 2, the carbon dioxide slug is injected to realize the pressure head migration;

[0014] Step 4, after injecting the carbon dioxide slug, the water injection development is carried out in the mode of pressure drive, and the development model of water and carbon dioxide slug displacement is formed.

[0015] The object of the application can also be achieved by the following technical measures:

[0016] In step 1, the preposed carbon dioxide slug assisted pressure drive water injection model is established, the reservoir pressure distribution is calculated combined with the reservoir exploitation history, and the pressure distribution curve is drawn.

[0017] In step 1, the carbon dioxide slug is injected first, and then the well is injected by pressure drive; the physical model is divided into three regions, from the pressure drive well to the oil production well, which are water injection section, carbon dioxide slug and crude oil section.

[0018] In step 1, the pressure distribution between the water injection well and the inner boundary of the carbon dioxide slug can be approximated as:

[0019]

[0020] Wherein, q is the displacement flow rate; mu1 is the viscosity of water; k1 is the permeability around the pressure drive well; h is the oil layer height; r is the distance; h is the oil layer height P wf The pressure of the injection well is r w The well radius is G, and the starting pressure gradient is.

[0021] In step 1, after the carbon dioxide slug contacts with the crude oil, the miscible effect occurs between the carbon dioxide slug and the crude oil, which reduces the viscosity of the crude oil, expands the volume of the crude oil, and makes the oil flow easily; the distance from the inner boundary of the carbon dioxide slug to the water injection well is R1(t), and the pressure distribution in the carbon dioxide slug can be approximated as:

[0022]

[0023] In the formula, mu2 is the viscosity of the carbon dioxide and crude oil after miscible phase; k2 is the permeability in the carbon dioxide slug.

[0024] In step 1, it is assumed that the pressure at the outer boundary radius R e is P e , and the pressure distribution from the outer boundary of the carbon dioxide slug to the reservoir boundary is:

[0025]

[0026] wherein μ3 is the viscosity of the crude oil; k3 is the permeability of the crude oil section.

[0027] In step 1, the pressure distribution in the process of prepositioning carbon dioxide slug by pressure drive is calculated by using the above-mentioned model approximation; the model needs the viscosities of water, carbon dioxide slug and crude oil in the calculation; after extraction and mutual solubility of carbon dioxide slug and crude oil after contact, the viscosity will change; the viscosity calculation model of oil and gas reservoir fluid-carbon dioxide system derived based on PR state equation is used:

[0028]

[0029] In the calculation of the viscosity of carbon dioxide-crude oil mixed system, the parameters in the formula use the mixing criterion

[0030] a m =∑z i a i

[0031] b m =∑z i b i

[0032]

[0033]

[0034] wherein T is temperature; p is pressure; μ is the viscosity of the system; z is the mole fraction of component i; k is the binary interaction coefficient; a is the component parameter of component i; b is the component mixture parameter; b' is the function of temperature and pressure; b' is the intermediate parameter in the state equation; r' is the gas constant of component i; and r' is the gas constant of the mixed gas. m i ij i i m m i m i m

[0035] In step 2, based on the geological conditions of the reservoir, the reasonable water injection amount of the block in the process of pressure drive is designed according to the reservoir formation depletion and the pressure maintenance level to be restored after pressure drive; on the basis of this, in order to ensure that the injected water does not break through the carbon dioxide slug, a certain length and width of the carbon dioxide slug need to be ensured; by injecting a certain amount of carbon dioxide slug, the pressure head of the pressure distribution curve is moved forward, and the pressure distribution between injection and production wells is improved, so that the pressure conduction between injection and production wells is continuous.

[0036] ​​​​​​​​​​​In step 2, according to the cumulative liquid production and the cumulative water injection data of the oil reservoir block, the oil reservoir deficit is calculated; at the same time, according to the original formation pressure and the pressure maintenance level to be restored to, the amount of water to be injected is calculated:

[0037]

[0038] Wherein, p i is the original formation pressure; p is the current formation pressure; p M is the pressure maintenance level; Q k is the deficit; Q is the amount of water to be injected. With the injection, the preposed carbon dioxide slug thickness becomes smaller and smaller; through volume conservation, combined with the oil reservoir conditions such as porosity and oil saturation, the carbon dioxide slug length under different injection water, carbon dioxide amount ratios can be approximately calculated; in order to ensure the effect of carbon dioxide injection, the minimum width of the carbon dioxide slug is 1 meter, and through volume conservation, the amount of preposed carbon dioxide under different water injection conditions Q C1 .

[0039] In step 2, through step 1, the pressure distribution between injection and production wells is calculated; in the pressure drive process of low permeability oil reservoir, there is a situation of pressure conduction disconnection, so a preposed carbon dioxide slug is injected, and because the viscosity of carbon dioxide is very low, it will cause the pressure head of the pressure distribution curve to move forward, thereby making the overall pressure in the oil reservoir rise and making the pressure conduction range larger; in the calculation, first, the amount of carbon dioxide injection Q C1 is designed according to the pressure deficit and the pressure maintenance level, to ensure the width and effect of the carbon dioxide slug; then, the pressure distribution curve is drawn according to step 1, if the pressure conduction is connected, the amount of carbon dioxide injection is finally designed as Q C1 ; if the amount of carbon dioxide injection Q C1 is not enough to make the pressure connected, the amount of carbon dioxide injection is continuously increased to Q C2 , until the pressure conduction is connected.

[0040] In step 3, according to the calculation results of step 2, the volume of carbon dioxide to be injected is determined, and then the measures of injecting carbon dioxide are taken in the project to form a carbon dioxide slug around the injection well; after the carbon dioxide contacts with the crude oil, the miscibility effect occurs, the viscosity is reduced, and the flow is easy, so that the pressure head moves forward and the pressure distribution of the oil reservoir is improved.

[0041] In step 4, the water injection by pressure drive is to use a fracturing pump truck to inject a large amount of liquid, to improve the formation energy and improve the development effect; in the preliminary understanding of the mine field, through the pressure drive injection, the energy is rapidly increased, on the one hand, the formation energy is increased, the production pressure difference and the oil well productivity are improved; on the other hand, the oil reservoir sweep efficiency and the oil displacement efficiency are improved, thereby the oil reservoir recovery is improved, and it has a wide application prospect.

[0042] The method for realizing pressure head migration by using preposed carbon dioxide slug assisted water injection and displacement of the application calculates the reasonable injection amount of carbon dioxide slug from the reservoir engineering point of view. The method combines the advantages of water injection and displacement and carbon dioxide displacement, achieves better oil displacement effect at lower cost, and has great application prospect in low permeability reservoir, tight reservoir and fault block reservoir development. The method for realizing pressure head migration by using preposed carbon dioxide slug assisted water injection and displacement overcomes the problem of difficult pressure conduction in the existing water injection and displacement process, obtains a method for realizing water injection and displacement pressure head migration by injecting carbon dioxide slug, makes the water injection and displacement pressure distribution through the water injection well and the production well, and realizes the continuous high-yield production of the production well. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 The flow chart of a specific embodiment of the method for realizing pressure head migration by using preposed carbon dioxide slug assisted water injection and displacement of the application;

[0044] Figure 2 The physical model schematic diagram of the method for realizing pressure head migration by using preposed carbon dioxide slug assisted water injection and displacement in a specific embodiment of the application;

[0045] Figure 3 The dynamic change schematic diagram of carbon dioxide slug of the method for realizing pressure head migration by using preposed carbon dioxide slug assisted water injection and displacement in a specific embodiment of the application. DETAILED DESCRIPTION

[0046] It should be noted that the following detailed description is exemplary and is intended to provide further description of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0047] It should be noted that the terms used herein are only for the purpose of describing specific embodiments, and are not intended to limit the exemplary embodiments according to the application. As used herein, the singular form is intended to include the plural form unless the context clearly indicates otherwise, and furthermore, it should be understood that when the terms "comprise" and / or "include" are used in the specification, there is a feature, step, operation and / or combination thereof.

[0048] Carbon dioxide flooding (CO2) technology involves injecting carbon dioxide into the oil reservoir to enhance oil recovery. However, CO2 injection is significantly more expensive than water injection. Therefore, to save costs and maximize efficiency, CO2 slug injection is employed. Since carbon dioxide is a gas with high solubility in both oil and water, when dissolved in large quantities in crude oil, it causes the crude oil to expand in volume, decrease viscosity, and reduce interfacial tension between oil and water, thus facilitating flow. By injecting CO2 slugs, the pressure head is moved forward, improving the pressure distribution during hydraulic displacement and enabling pressure transmission between the injection well and the production well, overcoming the problem of poor performance in the production well.

[0049] The following are several specific embodiments of the application of the present invention.

[0050] Example 1

[0051] In a specific embodiment 1 of the present invention, such as Figure 1 As shown, Figure 1 This is a flowchart of the method for achieving head forward movement using a pre-mounted carbon dioxide slug-assisted pressure-driven water injection according to the present invention. The method includes the following steps:

[0052] S1. Establish a pre-loaded carbon dioxide slug-assisted pressure-driven water injection model, and calculate the reservoir pressure distribution based on the reservoir exploitation history, and plot the pressure distribution curve.

[0053] S2. Based on the extraction plan and reservoir extraction data, calculate the required water injection volume for pressure drive. Optimize the volume of the carbon dioxide slug to be injected based on the pressure drive pressure distribution model.

[0054] S3, inject the carbon dioxide volume calculated in S2 to form a carbon dioxide slug.

[0055] S4. A large amount of water is injected using a pressure-driven water injection method to form a development model for water and carbon dioxide sluice-driven oil displacement.

[0056] Example 2

[0057] In a specific embodiment 2 of the present invention, the method of using a pre-mounted carbon dioxide slug-assisted pressure-driven water injection to achieve head forward movement includes:

[0058] Step 1, establish a pre-coal slug-assisted pressure-driven water injection model; the specific steps for establishing the pre-coal slug-assisted pressure-driven water injection model include:

[0059] The process of installing a pre-installed CO2 slug in pressure-driven well injection involves first injecting the CO2 slug, followed by water injection into the pressure-driven well. Therefore, the physical model is divided into three regions: the water injection zone, the CO2 slug zone, and the crude oil zone, from the pressure-driven well to the production well. The pressure distribution between the water injection well and the inner boundary of the CO2 slug can be approximated as follows:

[0060]

[0061] where q is the displacement flux; μ1 is the viscosity of water; k1 is the permeability around the water injection well; h is the oil layer height; r is the distance; h is the oil layer height P wf is the pressure of the injection well.

[0062] After the carbon dioxide slug contacts the crude oil, miscibility effect occurs between the carbon dioxide and the crude oil, which reduces the viscosity of the crude oil, expands the volume of the crude oil, and makes the oil flow easily. The distance from the inner boundary of the carbon dioxide slug to the water injection well is R1(t), and the pressure distribution in the carbon dioxide slug can be approximated as

[0063]

[0064] where μ2 is the viscosity of the carbon dioxide and the crude oil after miscibility; k2 is the permeability in the carbon dioxide slug.

[0065] Suppose the pressure at the outer boundary radius R e is P e , then the pressure distribution from the outer boundary of the carbon dioxide slug to the reservoir boundary is

[0066]

[0067] where μ3 is the viscosity of the crude oil; k2 is the permeability in the crude oil slug.

[0068] The above model can be used to approximately calculate the pressure distribution in the process of pre-displacing the carbon dioxide slug. The model requires the viscosities of the water, the carbon dioxide slug, and the crude oil in the calculation. After the carbon dioxide slug contacts the crude oil, extraction and mutual solubility occur, and the viscosity changes. The viscosity calculation model of the carbon dioxide-oil system in the oil and gas reservoir is derived based on the PR state equation

[0069]

[0070] In the calculation of the viscosity of the carbon dioxide-crude oil mixed system, the parameters in the formula are calculated using the mixing rule

[0071] a m =∑z i a i

[0072] b m =∑z i b i

[0073]

[0074]

[0075] where T is temperature; p is pressure; μ m is the viscosity of the system; z i is the mole fraction of component i; k ij is the binary interaction coefficient, and the remaining variables are intermediate variables of the component model.

[0076] Step 2, optimizing the injection amount of the pre-positioned carbon dioxide slug;

[0077] The specific steps of optimizing the injection amount of the pre-positioned carbon dioxide slug include:

[0078] The cost of injecting carbon dioxide is much higher than that of injecting the same volume of water, so it is necessary to use as little carbon dioxide as possible to achieve the pressure head advance, so that the pressure propagation between the injection and production wells is continuous. Considering two aspects, first, based on the geological conditions of the reservoir, according to the reservoir voidage, the pressure maintenance level to be restored after pressure drive, the reasonable water injection amount of the block is designed, and on this basis, in order to ensure that the injected water does not break through the carbon dioxide slug, a certain length and width of the carbon dioxide slug needs to be ensured. Second, by injecting a certain amount of carbon dioxide slug, the pressure head of the pressure distribution curve is advanced, and the pressure distribution between the injection and production wells is improved, so that the pressure conduction between the injection and production wells is continuous.

[0079] Preferably, according to the cumulative liquid production and the cumulative water injection of the reservoir block, the reservoir voidage is calculated. At the same time, according to the original formation pressure and the pressure maintenance level to be restored, the amount of water to be injected is calculated

[0080]

[0081] where p i is the original formation pressure; p is the current formation pressure; p M is the pressure maintenance level; Q k is the voidage. As the injection proceeds, the thickness of the pre-positioned carbon dioxide slug becomes smaller and smaller. Through volume conservation, combined with the reservoir conditions such as oil layer porosity and oil saturation, the length of the carbon dioxide slug under different injection water and carbon dioxide amount ratios can be approximately calculated. In order to ensure the effect of injecting carbon dioxide, the minimum width of the carbon dioxide slug is 1 meter, and through volume conservation, the amount of pre-positioned carbon dioxide Q C1 under different water injection amounts can be obtained.

[0082] Preferably, through step 1), the pressure distribution between the injection and production wells is calculated. During the pressure drive process of the low permeability reservoir, there is a situation of disconnected pressure conduction, so the pre-positioned carbon dioxide slug is injected. Due to the low viscosity of carbon dioxide, it will cause the pressure head of the pressure distribution curve to advance, so that the overall pressure in the reservoir is lifted, and the pressure conduction range is larger. In the calculation, first, according to the pressure voidage and the pressure maintenance level, Q C1to ensure the width and effect of the carbon dioxide slug. Then, the pressure distribution curve is drawn according to step 1), and if the pressure conduction is connected, the final amount of injected carbon dioxide is Q C1 If the amount of injected carbon dioxide is insufficient to make the pressure conduction connected, the amount of injected carbon dioxide is continuously increased to Q C2 until the pressure conduction is connected.

[0083] Step 3, according to the calculation result of step 2), a carbon dioxide slug is injected to realize the pressure head migration; the specific steps of injecting the carbon dioxide slug according to the calculation result of step 2) to realize the pressure head migration include:

[0084] According to the calculation result of step 2), the volume of the injected carbon dioxide is determined, and then the injection of carbon dioxide is taken in the project to form a carbon dioxide slug around the injection well. After the carbon dioxide contacts the crude oil, the miscible effect occurs, the viscosity is reduced, and the flow is easy, so that the pressure head migrates and the reservoir pressure distribution is improved.

[0085] Step 4, after the carbon dioxide slug is injected, water injection development is carried out in the way of pressure drive water injection.

[0086] The specific steps of carrying out water injection development in the way of pressure drive water injection after the carbon dioxide slug is injected include:

[0087] After the carbon dioxide slug is injected, the water injection development is carried out in the way of pressure drive water injection. The pressure drive water injection is to inject a large amount of liquid by using a fracturing pump truck to improve the formation energy and improve the development effect. Compared with the conventional water injection development technology, the injection capacity of the pressure drive water injection is greatly increased, and the water injection time is greatly reduced. In the preliminary understanding of the mine field, the pressure drive water injection is used to quickly increase the energy, which on the one hand increases the formation energy, improves the production pressure difference and the oil well productivity; on the other hand, improves the reservoir sweep efficiency and the oil displacement efficiency, and then improves the reservoir recovery, and has a wide application prospect.

[0088] Embodiment 3

[0089] In a specific embodiment 3 of the application, as shown in Figure 2 CO2 is added before pressure drive to form a CO2 slug between water and crude oil. Because the viscosity of CO2 is low and the pressure transmission performance is good, the overall pressure in the reservoir is lifted, the pressure propagation is farther, and the problem of difficult pressure propagation in the current low permeability reservoir is overcome. Through the pressure deficit formula in step 2, the amount of injected water Q winj cubic meters is calculated, and the radius r winj of water is calculated by the amount of water injection. At this time, the radius of the large circle including the CO2 slug is r winj + 1 meter. The volume of the annular ring is calculated by the circular area formula, and the volume Q c1Under different reservoir development conditions, the pressure deficit is different, and the water injection amount is different at this time, such as shown in Figure 3 According to different reservoir conditions, different water injection amounts are calculated, so that different CO2 injection volumes Q c1 .

[0090] Finally, it should be noted that the above only for the preferred embodiments of the present application, and is not intended to limit the present application, although the foregoing detailed description of the present application is made with reference to the foregoing examples, for those skilled in the art, it still can be modified, or part of the technical features of the equivalent replacement. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included within the scope of the present application.

[0091] In addition to the technical features described in the specification, they are known to those skilled in the art.

Claims

1. A method for advancing the pressure head by using a pre-mounted carbon dioxide slug-assisted pressure-driven water injection, characterized in that, The method of using a pre-mounted carbon dioxide slug-assisted pressure-driven water injection to achieve head forward movement includes: Step 1, establish a pre-CO2 slug-assisted pressure-driven water injection model, including: The pressure distribution between the injection well and the inner boundary of the carbon dioxide slug can be approximated as follows: ； Where q is the displacement flow; Where: is the viscosity of water; k1 is the permeability around the pressure-driven well; h is the reservoir height; r is the distance; h is the reservoir height. For injection well pressure, Where G is the well radius and G is the starting pressure gradient; When the carbon dioxide slug comes into contact with crude oil, it undergoes a miscibility effect, reducing the crude oil's viscosity and causing it to expand in volume, making the oil easier to flow. If the distance from the inner boundary of the carbon dioxide slug to the injection well is R1(t), then the pressure distribution within the carbon dioxide slug can be approximated as follows: ； In the formula k1 represents the viscosity of the carbon dioxide and crude oil mixture; k2 represents the permeability within the carbon dioxide slug. Assuming the outer boundary radius R e The pressure at the point is P e The pressure distribution from the outer boundary of the carbon dioxide plug to the reservoir boundary is as follows: ； In the formula k is the viscosity of the crude oil; k3 is the permeability within the crude oil segment; Step 2: Calculate the required water injection volume for pressure drive based on the extraction plan and reservoir extraction data; optimize the volume of the carbon dioxide slug to be injected based on the pressure drive water injection model, including: designing a reasonable water injection volume for pressure drive in this block based on reservoir geological conditions, reservoir formation depletion, and the pressure level to be restored after pressure drive; ensuring a certain length and width of the carbon dioxide slug to prevent the injected water from breaking through the carbon dioxide slug; and shifting the pressure head of the pressure distribution curve forward by injecting a certain amount of carbon dioxide slug to improve the pressure distribution between injection and production wells, thereby ensuring continuous pressure transmission between injection and production wells. Step 3: Based on the calculation results in Step 2, inject carbon dioxide slugs to move the pressure head forward; Step 4: After injecting the carbon dioxide slug, water injection is carried out using pressure-driven water injection to form a development model of water and carbon dioxide slug oil displacement.

2. The method for advancing the pressure head by using a pre-mounted carbon dioxide slug-assisted pressure-driven water injection according to claim 1, characterized in that, In step 1, a pre-coal dioxide slug-assisted pressure drive water injection model is established. Based on the reservoir exploitation history, the reservoir pressure distribution is calculated, and the pressure distribution curve is plotted.

3. The method for advancing the pressure head by using a pre-mounted carbon dioxide slug-assisted pressure-driven water injection according to claim 2, characterized in that, In step 1, a carbon dioxide slug is injected first, followed by water injection into the pressure-driven well. The physical model is divided into three regions, namely the water injection section, the carbon dioxide slug section, and the crude oil section, from the pressure-driven well to the production well.

4. The method for advancing the pressure head by using a pre-mounted carbon dioxide slug-assisted pressure-driven water injection according to claim 1, characterized in that, In step 1, the pressure distribution during the pre-pressure drive carbon dioxide slug process is approximated using the above model. This model requires the viscosity of the fluids—water, carbon dioxide slug, and crude oil—for calculation. After extraction and miscibility occur upon contact between the carbon dioxide slug and crude oil, the viscosity will change. A viscosity calculation model for the reservoir fluid-carbon dioxide system derived from the PR equation of state is used. ； When calculating the viscosity of the carbon dioxide-crude oil mixture, the parameters in the formula adopt the mixing criterion: ； ； ； ； In the formula, T is temperature; p is pressure; z is the viscosity of the system. i k is the mole fraction of component i; ij Let a be the binary interaction coefficient. i ,b i Let a be the component parameter of component i. m ,b m For parameters of the component mixture, It is a function of temperature and pressure. These are intermediate parameters of the state equation. Let i be the gas constant of component i. is the gas mixture constant.

5. The method for advancing the pressure head by using a pre-mounted carbon dioxide slug-assisted pressure-driven water injection according to claim 1, characterized in that, In step 2, the reservoir deficit is calculated based on the cumulative fluid production and cumulative water injection data of the reservoir block; simultaneously, the amount of water to be injected is calculated based on the balance between the original formation pressure and the pressure to be restored. ； Where, p i p represents the original formation pressure; p represents the current formation pressure; p M To maintain pressure levels; Q k Let Q be the deficit; Q be the amount of water to be injected; as injection progresses, the thickness of the pre-installed CO2 slug decreases; by conserving volume and considering reservoir conditions such as reservoir porosity and oil saturation, the length of the CO2 slug under different injection water-to-CO2 ratios can be approximately calculated; to ensure the effectiveness of CO2 injection, the CO2 slug width is set to a minimum of 1 meter, and the amount of pre-installed CO2 Q under different injection rates can be obtained by conserving volume. C1 .

6. The method for advancing the pressure head by using a pre-mounted carbon dioxide slug-assisted pressure-driven water injection according to claim 5, characterized in that, In step 2, the pressure distribution between injection and production wells is calculated based on step 1. In low-permeability reservoirs, pressure transmission is often disrupted during pressure drive; therefore, a pre-installed carbon dioxide slug is injected. Due to the low viscosity of carbon dioxide, the pressure head on the pressure distribution curve shifts forward, resulting in an overall increase in reservoir pressure and a wider pressure transmission range. In the calculation, Q is first designed based on pressure deficit and maintaining a horizontal pressure level. C1 The amount of carbon dioxide injected is determined to ensure the width and effectiveness of the carbon dioxide slug; then, a pressure distribution curve is plotted based on step 1. If the pressure transmission is continuous, the final designed amount of carbon dioxide injected is Q. C1 If Q C1 If the amount of carbon dioxide injected is insufficient to achieve pressure connectivity, the amount of carbon dioxide injected will be increased until conductive connectivity is achieved on the pressure distribution diagram. At this point, the amount of carbon dioxide injected is Q. C2 .

7. The method for advancing the pressure head by using a pre-mounted carbon dioxide slug-assisted pressure-driven water injection according to claim 1, characterized in that, In step 3, based on the calculation results of step 2, the volume of carbon dioxide to be injected is determined, and then carbon dioxide injection measures are taken in the project to form a carbon dioxide slug around the injection well; after carbon dioxide comes into contact with crude oil, a miscibility effect occurs, the viscosity decreases, and it is easy to flow, which causes the pressure head to move forward and improves the reservoir pressure distribution.

8. The method for advancing the pressure head by using a pre-mounted carbon dioxide slug-assisted pressure-driven water injection according to claim 1, characterized in that, In step 4, hydraulic water injection involves injecting large volumes of fluid using a fracturing pump truck to increase formation energy and improve development results. In the initial understanding of the mine, hydraulic water injection can rapidly increase formation energy, thereby increasing production pressure differential and well productivity. On the other hand, it can also improve reservoir sweep efficiency and oil displacement efficiency, thus improving reservoir recovery rate, and has broad application prospects.

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