A method for layered injection of carbon dioxide into a saline aquifer

Abstract

The application discloses a brine layer carbon dioxide layered injection method in the technical field of carbon dioxide storage, which comprises the following steps: calculating the effective carbon dioxide storage amount and the fracturing pressure of the upper injection layer and the lower injection layer; calculating the carbon dioxide injection pressure safety threshold of the upper injection layer and the lower injection layer according to the fracturing pressure; installing a carbon dioxide layered injection pipe column; injecting carbon dioxide into the lower injection layer and the upper injection layer in sequence through the carbon dioxide layered injection pipe column, calculating the real-time carbon dioxide injection pressure and the carbon dioxide injection amount of the upper injection layer and the lower injection layer, and judging whether the real-time carbon dioxide injection pressure is less than the carbon dioxide injection pressure safety threshold and whether the carbon dioxide injection amount is less than the effective carbon dioxide storage amount. The layered injection mode from the lower to the upper is adopted, which not only solves the problems of low storage efficiency and difficult site stability guarantee caused by the general carbon dioxide injection into the multi-layer non-homogeneous reservoir, but also has the advantages of simple method and convenient use.

Description

Technical Field

[0001] This invention relates to the field of carbon dioxide sequestration technology, and more specifically to a method for stratified carbon dioxide injection into a saline aquifer. Background Technology

[0002] In recent years, the massive consumption of fossil fuels and the resulting large-scale emissions of greenhouse gases, especially carbon dioxide, have significantly amplified the global greenhouse effect. Currently, CCUS (carbon dioxide capture, storage, and utilization) technology is a key technology for reducing carbon emissions and addressing global warming. Most of the sites in China capable of carbon dioxide storage exhibit heterogeneity and low permeability in their reservoirs. Practice has shown that general injection into multi-layered heterogeneous reservoirs results in low efficiency, making efficient storage difficult. Due to differences in the structure and physical properties of different reservoirs, carbon dioxide exhibits a surge phenomenon in high-permeability reservoirs. General injection into multi-layered heterogeneous reservoirs leads to low carbon dioxide storage efficiency, hindering safe and efficient carbon dioxide storage. Currently, the main technical challenges for carbon dioxide storage in multi-layered heterogeneous reservoirs are as follows:

[0003] (1) Due to the differences in reservoir structure and physical properties, the carbon dioxide sequestration rate also varies in different reservoirs. Reservoirs with higher permeability are injected first, while reservoirs with lower permeability cannot be used to the maximum extent, resulting in low carbon dioxide sequestration intensity.

[0004] (2) As a large amount of carbon dioxide is injected into the reservoir, pressure accumulation will occur in the deep saline water layer, affecting the mechanical stability of the reservoir. When injecting gas into multiple reservoirs at the same time, it is difficult to guarantee the mechanical stability of a single reservoir.

[0005] Therefore, how to improve the carbon dioxide sequestration strength and stability of multilayer heterogeneous reservoirs has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a method for stratified carbon dioxide injection in saline water layers to solve the technical problems of low carbon dioxide sequestration strength and poor reservoir mechanical stability in existing carbon dioxide injection methods.

[0007] The technical solution adopted in this invention is: a method for stratified carbon dioxide injection into a saline aquifer, the method comprising the following steps:

[0008] Step 1: Calculate the effective carbon dioxide storage capacity and rupture pressure of the upper and lower injection layers respectively;

[0009] Calculate the safe threshold values ​​for carbon dioxide injection pressure in the upper and lower injection layers based on the rupture pressure;

[0010] Step 2: Install the carbon dioxide stratified injection tubing;

[0011] Step 3: Inject carbon dioxide into the lower injection layer through the carbon dioxide stratified injection tubing, and calculate the real-time injection pressure and injection volume of the lower injection layer. The real-time injection pressure of the lower injection layer is less than the opening pressure of the constant pressure baffle on the carbon dioxide stratified injection tubing.

[0012] Determine whether the real-time carbon dioxide injection pressure of the lower injection layer is less than the safe threshold for carbon dioxide injection pressure of the lower injection layer, and whether the amount of carbon dioxide injected into the lower injection layer is less than the effective amount of carbon dioxide stored in the lower injection layer; if yes, continue to inject carbon dioxide into the lower injection layer; if no, stop injecting carbon dioxide into the lower injection layer, and inject carbon dioxide into the upper injection layer by opening the constant pressure baffle.

[0013] Calculate the real-time carbon dioxide injection pressure and carbon dioxide injection volume of the upper injection layer, and determine whether the real-time carbon dioxide injection pressure of the upper injection layer is less than the safe threshold of the carbon dioxide injection pressure of the upper injection layer, and whether the carbon dioxide injection volume of the upper injection layer is less than the effective carbon dioxide storage volume of the upper injection layer; if yes, continue to inject carbon dioxide into the upper injection layer; if no, stop injecting carbon dioxide.

[0014] Preferably, in step one, the formula for calculating the rupture pressure is:

[0015] Among them, P f P is the formation fracture pressure; μ is the formation Poisson's ratio; o The pressure of the overlying strata; P p This refers to the formation pore pressure.

[0016] Preferably, in step one, the formula for calculating the carbon dioxide injection pressure safety threshold is: P s =S×P f ;

[0017] Among them, P s P is the safe threshold for carbon dioxide injection pressure. f is the formation fracturing pressure; S is the safety factor.

[0018] Preferably, in step two, the carbon dioxide stratified injection string includes a wellhead injection device, a check valve, tubing, a completion string, an upper packer, a pressure-regulating baffle, a ball seat, a lower packer, and a bell mouth; the tubing is coaxially arranged inside the completion string, and the wellhead injection device is installed at the top of the tubing and the completion string; the upper packer is located above the upper injection layer and is installed between the tubing and the completion string; the lower packer is located between the upper and lower injection layers and is installed between the tubing and the completion string; the check valve is connected in series on the tubing and located above the upper packer, the pressure-regulating baffle is connected in series on the tubing and located between the upper and lower packers, the ball seat is connected in series on the tubing and located between the pressure-regulating baffle and the lower packer, and the bell mouth is installed at the bottom of the tubing.

[0019] Preferably, in step three, the formula for calculating the real-time carbon dioxide injection pressure is: P = P1 + ρ CO2 gh;

[0020] Where P is the injection pressure; P1 is the wellhead pressure; h is the depth of the saline aquifer; g is the acceleration due to gravity; ρ CO2 This represents the equivalent density of carbon dioxide in the wellbore.

[0021] Preferably, in step three, the formula for calculating the amount of carbon dioxide injected is:

[0022] Where W is the injection volume; T is the number of days of injection; υ i t represents the injection rate; i For injection time.

[0023] The beneficial effects of this invention are:

[0024] This invention employs a layered injection method. First, the effective carbon dioxide storage capacity, fracturing pressure, and safe threshold for carbon dioxide injection pressure in the upper and lower injection layers are theoretically calculated. Then, carbon dioxide is injected sequentially into each reservoir from bottom to top using a layered carbon dioxide injection string. This not only allows for the injection of different amounts of carbon dioxide into each reservoir based on its effective carbon dioxide storage capacity, ensuring efficient utilization of each reservoir, but also enables the determination of whether a single reservoir has reached the cessation of injection requirements based on changes in wellhead pressure during the injection process, ensuring the sealing of the caprock and the mechanical stability of the storage site. Simultaneously, it enables precise injection into only one saline layer at a time, improving injection efficiency and solving the problems of low carbon dioxide storage efficiency and difficulty in ensuring site stability in heterogeneous reservoirs with different strata due to indiscriminate injection. Attached Figure Description

[0025] Figure 1 A schematic diagram of a carbon dioxide stratified injection column.

[0026] Explanation of the reference numerals in the figure:

[0027] 1. Wellhead injection device; 2. Completion string; 3. Check valve; 4. Tubing; 5. Upper packer; 6. Pressure plate; 7. Ball seat; 8. Lower packer; 9. Bell mouth; 10. Casing shoe; 11. Upper injection layer; 12. Lower injection layer; 13. Surface. Detailed Implementation

[0028] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0029] In the description of this invention, it should be noted that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0030] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0031] Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0032] Examples, such as Figure 1 As shown, a method for stratified carbon dioxide injection into a saline aquifer includes the following steps:

[0033] Step 1: Calculate the effective carbon dioxide storage capacity and rupture pressure of the upper injection layer 11 and the lower injection layer 12 respectively, and calculate the safe threshold of carbon dioxide injection pressure for the upper injection layer 11 and the lower injection layer 12 respectively based on the rupture pressure.

[0034] Step 2: Install the carbon dioxide stratified injection tubing.

[0035] Step 3: Inject carbon dioxide into the lower injection layer 12 through the carbon dioxide stratified injection tubing, and calculate the real-time carbon dioxide injection pressure and carbon dioxide injection volume of the lower injection layer 12. The real-time carbon dioxide injection pressure of the lower injection layer 12 is less than the opening pressure of the constant pressure baffle 6 on the carbon dioxide stratified injection tubing.

[0036] Determine whether the real-time carbon dioxide injection pressure of the lower injection layer 12 is less than the safe threshold for carbon dioxide injection pressure of the lower injection layer 12, and whether the amount of carbon dioxide injected into the lower injection layer 12 is less than the effective amount of carbon dioxide stored in the lower injection layer 12; if yes, continue to inject carbon dioxide into the lower injection layer 12; if no, stop injecting carbon dioxide into the lower injection layer 12, and inject carbon dioxide into the upper injection layer 11 by opening the constant pressure baffle 6.

[0037] Calculate the real-time carbon dioxide injection pressure and carbon dioxide injection volume of the upper injection layer 11, and determine whether the real-time carbon dioxide injection pressure of the upper injection layer 11 is less than the safe threshold of the carbon dioxide injection pressure of the upper injection layer 11, and whether the carbon dioxide injection volume of the upper injection layer 11 is less than the effective carbon dioxide storage volume of the upper injection layer 11; if yes, continue to inject carbon dioxide into the upper injection layer 11; if no, stop injecting carbon dioxide.

[0038] This application employs a layered injection method. First, the effective carbon dioxide storage capacity, fracturing pressure, and safe threshold for carbon dioxide injection pressure of the upper injection layer 11 and the lower injection layer 12 are theoretically calculated. Then, carbon dioxide is injected sequentially into each reservoir from bottom to top using a layered carbon dioxide injection string. This not only allows for the injection of different amounts of carbon dioxide into each reservoir based on its effective carbon dioxide storage capacity, ensuring efficient utilization of each reservoir, but also allows for the determination of whether a single reservoir has reached the requirements for stopping injection based on changes in wellhead pressure during the injection process, ensuring the sealing of the caprock and the mechanical stability of the storage site. At the same time, it enables precise injection into only one saline layer at a time, improving injection efficiency and solving the problems of low carbon dioxide storage efficiency and difficulty in ensuring site stability in heterogeneous reservoirs with different layers due to general injection.

[0039] Specific embodiments, such as Figure 1 As shown, a method for stratified carbon dioxide injection into a saline aquifer includes the following steps:

[0040] Step 1: Calculate the effective carbon dioxide storage capacity M and rupture pressure P of the upper injection layer 11 and the lower injection layer 12 respectively. f .

[0041] Specifically: Geological carbon dioxide sequestration is an important indicator for evaluating the carbon dioxide sequestration capacity of saline aquifers. The effective carbon dioxide sequestration capacity is calculated using the CSLF (Carbon Sequestration Leadership Forum) method, and the calculation formula used in this method is as follows:

[0042] Where M represents the effective carbon dioxide sequestration in the saline aquifer, M1 represents the effective carbon dioxide sequestration in the upper injection layer, and M2 represents the effective carbon dioxide sequestration in the lower injection layer; ρ CO2 H is the density of carbon dioxide under saline water storage conditions; A is the effective storage area of ​​the saline water layer; H is the effective thickness of the saline water layer; H1 is the effective thickness of the upper injection layer; H2 is the effective thickness of the lower injection layer. The effective porosity of the saline aquifer; S w Where is the bound water saturation; E is the sequestration factor, for example, E = 3%.

[0043] The rupture pressure P of the injection layer f Determining the injection pressure is crucial; the injection pressure must exceed the rupture pressure P. f This poses a safety risk to the airtightness of the caprock and site stability; calculate the rupture pressure P. f The most commonly used method is the Eaton method, which uses the following calculation formula:

[0044] Among them, P f P is the formation fracture pressure. f1 P is the fracture pressure of the upper injection layer. f2 The fracture pressure of the lower injection layer is μ; the formation Poisson's ratio is P. o For the pressure of the overlying strata, P o1 P represents the pressure of the overlying strata of the upper injection layer. o2 The pressure of the overlying strata of the lower injection layer; P p This refers to the formation pore pressure.

[0045] According to the rupture pressure P f Calculate the safe threshold P of carbon dioxide injection pressure for the upper injection layer 11 and the lower injection layer 12 respectively. s The calculation formula is: P s =S×P f ;

[0046] Among them, P s P is the safe threshold for carbon dioxide injection pressure. f is the formation fracture pressure; S is the safety factor, with a value ranging from 0.85 to 0.9.

[0047] Step 2: Install the carbon dioxide stratified injection tubing.

[0048] Specifically, the carbon dioxide stratified injection string includes a wellhead injection device 1, a check valve 3, tubing 4, a completion string 2, an upper packer 5, a pressure-regulating baffle 6, a ball seat 7, a lower packer 8, a bell mouth 9, and a casing shoe 10. The tubing 4 is coaxially installed inside the completion string 2. The wellhead injection device 1 is installed on the surface 13 and connected to the top of the tubing 4 and the completion string 2 for carbon dioxide injection and real-time wellhead pressure measurement. The upper packer 5 is located above the upper injection layer 11 and is installed between the tubing 4 and the completion string 2, separating the upper and lower annulus of the upper injection layer 11. The lower packer 8 is located between the upper injection layer 11 and the lower injection layer 12 and is installed between the tubing 4 and the completion string 2, separating the lower injection layer. The upper and lower annulus of layer 12; the one-way valve 3 is connected in series at the upper part of the tubing 4 and located above the upper packer 5, used to control the flow rate and direction of carbon dioxide; the pressure-regulating baffle 6 is connected in series in the middle of the tubing 4 and located between the upper packer 5 and the lower packer 8, used to control the stratified injection of carbon dioxide, so that the tubing 4 can be connected to the upper injection layer 11 by opening the pressure-regulating baffle 6, for injecting carbon dioxide into the upper injection layer 11; the ball seat 7 is connected in series on the tubing 4 and located between the pressure-regulating baffle 6 and the lower packer 8, which can block carbon dioxide from entering the tubing 4 below the ball seat 7; the bell mouth 9 is installed at the bottom end of the tubing 4 so that the bottom end of the tubing 4 can be connected to the lower injection layer 12, for injecting carbon dioxide into the lower injection layer 12; the casing shoe 10 is installed at the bottom end of the completion string 2, used to fix the completion string 2.

[0049] Step 3: Open the check valve 3 and ball seat 7 on the carbon dioxide stratified injection line, and close the constant pressure baffle 6. Inject carbon dioxide into the lower injection layer 12 through the carbon dioxide stratified injection line, and calculate the real-time carbon dioxide injection pressure P2 and carbon dioxide injection volume W2 of the lower injection layer 12. The real-time carbon dioxide injection pressure P2 of the lower injection layer 12 is less than the opening pressure of the constant pressure baffle 6 on the carbon dioxide stratified injection line.

[0050] Specifically: the wellhead pressure P of carbon dioxide k The injection volume W can serve as an important criterion for whether to stop injection in a single injection layer, when the wellhead pressure P k When the maximum allowable wellhead pressure is exceeded or the carbon dioxide injection volume W has reached the effective storage capacity of the site, it indicates that the injection layer has reached its limit injection volume. Injection in this layer should be stopped and the layer should be sealed. The constant pressure baffle 6 should be opened by adjusting the injection pressure to inject carbon dioxide into other injection layers.

[0051] The formula for calculating the real-time carbon dioxide injection pressure P is: P = P k +ρ CO2 gh;

[0052] Where P is the real-time carbon dioxide injection pressure, P1 is the real-time carbon dioxide injection pressure of the upper injection layer, and P2 is the real-time carbon dioxide injection pressure of the lower injection layer; k ρ is the wellhead pressure; h is the saline aquifer depth, h1 is the saline aquifer depth of the upper injection layer, h2 is the saline aquifer depth of the lower injection layer; g is the acceleration due to gravity; ρ CO2 This represents the equivalent density of carbon dioxide in the wellbore.

[0053] The formula for calculating the carbon dioxide injection volume W is:

[0054] Where W is the carbon dioxide injection volume, W1 is the carbon dioxide injection volume of the upper injection layer, W2 is the carbon dioxide injection volume of the lower injection layer; T is the number of injection days; υ i t represents the injection rate; i For injection time.

[0055] Determine whether the real-time carbon dioxide injection pressure P2 of the lower injection layer 12 is less than the safe threshold P of the carbon dioxide injection pressure of the lower injection layer 12. s2 And whether the amount of carbon dioxide injected into the lower injection layer 12, W2, is less than the effective amount of carbon dioxide stored in the lower injection layer 12, M2.

[0056] If so, continue injecting carbon dioxide into the lower injection layer 12; that is, the real-time carbon dioxide injection pressure P2 of the lower injection layer 12 is less than the safe threshold P of the carbon dioxide injection pressure of the lower injection layer 12. s2 If the amount of carbon dioxide injected into the lower injection layer 12, W2, is less than the effective amount of carbon dioxide stored in the lower injection layer 12, then carbon dioxide will continue to be injected into the lower injection layer 12.

[0057] If not, then stop injecting carbon dioxide into the lower injection layer 12 and inject carbon dioxide into the upper injection layer 11 by opening the constant pressure diaphragm 6; that is, the real-time carbon dioxide injection pressure P2 of the lower injection layer 12 is not less than the safe threshold P of the carbon dioxide injection pressure of the lower injection layer 12. s2 If the amount of carbon dioxide injected into the lower injection layer 12, W2, is not less than the effective carbon dioxide storage amount, M2, then the ball-throwing and closing ball seat 7 stops injecting carbon dioxide into the lower injection layer 12, the gas injection into the lower injection layer 12 ends, and the constant pressure baffle 6 is opened by increasing the injection pressure to inject carbon dioxide into the upper injection layer 11.

[0058] It should be noted that the pressure of the constant pressure baffle 6 is 40MPa. When the fluid pressure inside the carbon dioxide injection string exceeds 40MPa, the pressure constant pressure baffle 6 will open, so that the oil pipe 4 and the upper injection layer 11 of the carbon dioxide injection string are always in a connected state.

[0059] Calculate the real-time carbon dioxide injection pressure P1 and carbon dioxide injection volume W1 of the upper injection layer 11, and determine whether the real-time carbon dioxide injection pressure P1 of the upper injection layer 11 is less than the safe threshold P of the carbon dioxide injection pressure of the upper injection layer 11. s1 And whether the amount of carbon dioxide injected into the upper injection layer 11, W1, is less than the effective amount of carbon dioxide stored in the upper injection layer, M1.

[0060] If so, continue injecting carbon dioxide into the upper injection layer 11; that is, the real-time carbon dioxide injection pressure P1 of the upper injection layer 11 is less than the safe threshold P of the carbon dioxide injection pressure of the upper injection layer 11. s1 If the amount of carbon dioxide injected into the upper injection layer 11, W1, is less than the effective amount of carbon dioxide stored in the upper injection layer 11, then carbon dioxide will continue to be injected into the upper injection layer 11.

[0061] If not, then stop injecting carbon dioxide by closing the single-flow valve 3; that is, the real-time carbon dioxide injection pressure P1 of the upper injection layer 11 is not less than the safe threshold P of the carbon dioxide injection pressure of the upper injection layer 11. s1 If the amount of carbon dioxide injected into the upper injection layer 11, W1, is not less than the effective carbon dioxide storage amount, M1, then the injection of carbon dioxide into the upper injection layer 11 is stopped, and the injection of carbon dioxide into the upper injection layer 11 is stopped by closing the one-way valve 3, and the gas injection into the upper injection layer 11 ends.

[0062] Compared with the prior art, this application has at least the following beneficial technical effects:

[0063] 1. Based on the carbon dioxide sequestration potential of reservoirs with different physical properties, this application injects a corresponding amount of carbon dioxide to achieve efficient carbon dioxide sequestration in different reservoirs.

[0064] 2. This application determines whether a single reservoir has reached the requirements for stopping injection based on the changes in wellhead pressure during the injection process, thus ensuring the airtightness of the caprock and the stability of the storage site.

[0065] 3. This application achieves precise injection of only one saline layer at a time by using a layered injection string, which improves injection efficiency and solves the problem of low carbon dioxide sequestration efficiency caused by general injection.

[0066] 4. This application adopts a bottom-to-top layered injection method, which not only solves the problems of low storage efficiency and difficulty in ensuring site stability caused by general carbon dioxide injection in multi-layered heterogeneous reservoirs, but also has the advantages of simple method and easy use, and can provide technical support for carbon dioxide geological storage.

[0067] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and substitutions can be made without departing from the technical principles of the present invention, and these improvements and substitutions should also be considered within the scope of protection of the present invention.

Claims

1. A method for stratified carbon dioxide injection into a saline aquifer, characterized in that, The method includes the following steps: Step 1: Calculate the effective carbon dioxide storage capacity and rupture pressure of the upper and lower injection layers respectively; Calculate the safe threshold values ​​for carbon dioxide injection pressure in the upper and lower injection layers based on the rupture pressure; Step 2: Install the carbon dioxide stratified injection tubing; Step 3: Inject carbon dioxide into the lower injection layer through the carbon dioxide stratified injection tubing, and calculate the real-time injection pressure and injection volume of the lower injection layer. The real-time injection pressure of the lower injection layer is less than the opening pressure of the constant pressure baffle on the carbon dioxide stratified injection tubing. Determine whether the real-time carbon dioxide injection pressure of the lower injection layer is less than the safe threshold for carbon dioxide injection pressure of the lower injection layer, and whether the amount of carbon dioxide injected into the lower injection layer is less than the effective amount of carbon dioxide stored in the lower injection layer; if yes, continue to inject carbon dioxide into the lower injection layer; if no, stop injecting carbon dioxide into the lower injection layer, and inject carbon dioxide into the upper injection layer by opening the constant pressure baffle. Calculate the real-time carbon dioxide injection pressure and carbon dioxide injection volume of the upper injection layer, and determine whether the real-time carbon dioxide injection pressure of the upper injection layer is less than the safe threshold of the carbon dioxide injection pressure of the upper injection layer, and whether the carbon dioxide injection volume of the upper injection layer is less than the effective carbon dioxide storage volume of the upper injection layer; if yes, continue to inject carbon dioxide into the upper injection layer; if no, stop injecting carbon dioxide. The formula for calculating the rupture pressure is: Among them, P f P is the formation fracture pressure; μ is the formation Poisson's ratio; o P represents the pressure of the overlying strata. p Formation pore pressure; The formula for calculating the carbon dioxide injection pressure safety threshold is: P s =S×P f ; Among them, P s P is the safe threshold for carbon dioxide injection pressure. f S is the formation fracture pressure; S is the safety factor. The formula for calculating the real-time carbon dioxide injection pressure is: P = P1 + ρ CO2 gh; Where P is the injection pressure; P1 is the wellhead pressure; h is the depth of the saline aquifer; g is the acceleration due to gravity; ρ CO2 This represents the equivalent density of carbon dioxide in the wellbore. The formula for calculating the amount of carbon dioxide injected is: Where W is the injection volume; T is the number of days of injection; υ i t represents the injection rate; i For injection time.

2. The method for stratified carbon dioxide injection into a saline aquifer according to claim 1, characterized in that, In step two, the carbon dioxide stratified injection string includes a wellhead injection device, a check valve, tubing, a completion string, an upper packer, a pressure-regulating baffle, a ball seat, a lower packer, and a bell mouth. The tubing is coaxially arranged inside the completion string, and the wellhead injection device is installed at the top of the tubing and the completion string. The upper packer is located above the upper injection layer and is installed between the tubing and the completion string. The lower packer is located between the upper and lower injection layers and is installed between the tubing and the completion string. The check valve is connected in series with the tubing and is located above the upper packer. The pressure-regulating baffle is connected in series with the tubing and is located between the upper and lower packers. The ball seat is connected in series with the tubing and is located between the pressure-regulating baffle and the lower packer. The bell mouth is installed at the bottom of the tubing.

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