Method for improving CO2 storage capacity estimation

Abstract

The invention belongs to the technical field of carbon dioxide geological sequestration, and discloses a method for improving CO2 sequestration capacity estimation, which belongs to the technical field of carbon dioxide geological sequestration by respectively acquiring the maximum throat radius of a cover layer, and discloses a method for improving CO2 sequestration capacity estimation. According to the method, the maximum throat radius of a cap layer, the minimum pore radius of a reservoir and the temperature and pressure of a sealing site are obtained; respectively calculating the density and the density of the salt water based on the temperature and the pressure; calculating the density difference of the salt water; calculating-salt water interfacial tension based on the temperature, pressure and density difference; measuring a receding contact angle of a-salt water-rock system under temperature and pressure; calculating the height of the sealed air column. The method is of great significance in improving the accuracy of sealing capacity estimation, is beneficial for constructing a more reliable sealing capacity evaluation system, and provides a scientific basis and theoretical support for long-term safety prediction in a CGS project.

Description

Technical Field

[0001] This invention belongs to the field of carbon dioxide geological storage technology, and in particular relates to an improved method for estimating CO2 storage capacity. Background Technology

[0002] Accurate calculation of sequestration capacity is crucial for geological CO2 sequestration. Existing studies primarily employ the volumetric method to estimate the tectonic CO2 sequestration capacity of sedimentary basins, calculations typically based on the average reservoir thickness. However, the physical mechanism of tectonic sequestration essentially depends on the capillary pressure caused by interfacial tension at the interface between two-phase fluids within the rock pores. This capillary pressure determines the upper limit of the CO2 column height that can be sequestered. It is important to note that reservoir thickness primarily reflects geometric characteristics and is not equivalent to the effective sequestration column height limited by capillary forces.

[0003] The Young-Laplace equation can be used to calculate capillary pressure difference, and based on this, a formula for calculating the CO2 column storage height was developed. This formula was initially used primarily to calculate the height of the caprock capable of sealing the oil and gas column, and has gradually been extended to evaluate the structural storage capacity of CO2 and other fluids. Capillary pressure is the core controlling factor of caprock storage capacity, influenced by multiple parameters such as contact angle, interfacial tension, density difference, and pore throat radius. Contact angle, interfacial tension, and density difference all have corresponding relationships with temperature and pressure, and vary with formation depth and thermodynamic environment. Scholars have systematically explored the quantitative relationship between CO2 density and temperature and pressure conditions, and have measured the variation of contact angle with temperature and pressure conditions through various experimental methods, revealing the potential impact of wettability transformation on storage stability. Simultaneously, studies have shown a significant correlation between interfacial tension and temperature, pressure, and density difference, and corresponding empirical formulas have been proposed, providing a theoretical and experimental basis for calculating CO2 column height under different geological conditions. When the reservoir thickness exceeds the CO2 column height corresponding to the capillary sealing capacity of the caprock, the structural storage mechanism will fail, leading to CO2 leakage. Therefore, directly using reservoir thickness for calculation will lead to significant deviations. In-depth research on the main control mechanism of the height of the sequesterable CO2 gas column is the core prerequisite for scientifically calculating the CO2 sequestration potential.

[0004] Based on the above analysis, the problems and defects of the existing technology are as follows: the volumetric method only calculates the storage capacity based on the reservoir thickness, without considering the capillary pressure control effect determined by the interfacial tension and pore throat structure, and ignoring the upper limit of the height of the gas column that can be stored in the caprock; at the same time, it does not systematically couple the changes in CO2 density, interfacial tension and contact angle under temperature and pressure conditions, resulting in an overestimation of the capacity and inconsistency with the actual storage mechanism. Summary of the Invention

[0005] To overcome the problems existing in related technologies, the present invention discloses an improved method for estimating CO2 storage capacity, used to predict the height of the CO2 storage gas column during CO2 geological storage to ensure that CO2 does not leak. The technical solution is as follows: This invention is implemented as follows, with improvements The method for estimating storage capacity includes the following steps: S1, obtain the maximum throat radius of the cap layer respectively. and the minimum pore radius of the reservoir ; S2, Obtain the temperature of the storage location. and pressure ; S3, based on the temperature and pressure Calculate separately density Density of salt water ; S4, Calculate saline water and density difference between ,in, ; S5, based on the temperature ,pressure and density difference ,calculate -Interfacial tension in saline water ; S6, at the temperature and pressure Below, measurement -Retreating contact angle of saline-lithic systems ; S7, based on the above , , , and ,calculate Storage column height ; S8, Storage column height The effective average thickness is obtained by comparing it with the maximum thickness of the reservoir, and the storage capacity is calculated.

[0006] In step S1, the maximum throat radius of the cap layer is obtained respectively. and the minimum pore radius of the reservoir ,include: The sample was milled layer by layer using focused ion beam scanning electron microscopy three-dimensional reconstruction technology, and the newly exposed surface was imaged with high resolution using an electron beam to obtain a continuous two-dimensional image sequence. The acquired images are imported into 3D reconstruction software. After registration, denoising, and thresholding, a 3D structural model of pores and skeleton is obtained. The three-dimensional structural model is subjected to skeletonization, connectivity analysis, and throat identification. The pore size and throat radius distribution are calculated, and the maximum throat radius of the cap layer is extracted. and the minimum pore radius of the reservoir .

[0007] In step S1, the maximum throat radius of the capping layer Less than 100nm; The minimum pore radius of the reservoir The range is from 1 μm to 100 μm.

[0008] In step S3, density The calculation uses the Batzle-Wang equation, specifically including: ; ; ; In the formula, For the specific gravity of the gas, take 1.5349; Let be the ideal gas constant, taken as 8.31441. ; Absolute temperature; It is the compression factor; Young's modulus; and They are respectively The pseudo-simplified pressure and pseudo-simplified temperature; For pressure; ; ; In the formula, for The pseudocritical pressure is taken as 7.4 MPa; for The pseudocritical temperature is taken as 31.1℃.

[0009] In step S3, the density of the salt water It is calculated by the following formula: ; ; ; ; ; In the formula, The density of saline water under standard conditions. The formation water volume factor under standard conditions is given by the reservoir pressure. and temperature Calculated; This represents the weight percentage of dissolved salts in formation water. Young's modulus; These are correction factors for pressure and temperature, respectively, used to describe the combined effect of pressure and temperature changes on the density of saline water; Pressure, unit: ; Temperature, unit: .

[0010] In step S5, -Interfacial tension in saline water The predictive relation is: ; In the formula, For pressure, For temperature, The salinity is for monovalent cations. The salinity of a divalent cation. for mole fraction, for exist impurity mole fraction, The square root function represents taking the square root of the quantity within the parentheses. It is the hyperbolic tangent function.

[0011] In step S6, measurement -Retreating contact angle of saline-lithic systems ,include: Under preset temperature conditions, the cleaned and dried mineral substrate was placed in a high-temperature and high-pressure test tank, and tested under simulated reservoir environment conditions. Circulating flushing removes impurities and facilitates gas replacement; A high-precision injection pump is used to smoothly raise the system pressure to the predetermined value and maintain it stable. After the temperature and pressure conditions stabilize, the degassed brine is dripped onto the surface of a mineral substrate at a pre-set tilt angle using a micro-syringe; the relationship between the solid surface and the brine is measured before the droplet begins to move. The included angle between the interfaces is used as the advancing contact angle, and the retreating contact angle is measured at the trailing edge of the droplet. The system synchronously records data using a high-definition camera system and calculates the contact angle value using image analysis software by extracting keyframe images.

[0012] further, The retreat contact angle θ of the saline-rock system ranges from 0° to 90°; when If the sealing mechanism fails, there is a risk to the sealing security.

[0013] In step S7, Storage column height Calculated using the following formula: ; In the formula, This is the acceleration due to gravity.

[0014] In step S8, Storage column height Compared with the maximum reservoir thickness, if the maximum reservoir thickness is greater than the resilient reservoir thickness... At the air column height, storage and sealing are adopted. Gas column height is calculated based on average effective thickness; maximum reservoir thickness is less than the resilient reservoir thickness. The gas column height indicates that the caprock has the capability to completely seal the gas column height within the maximum thickness of the reservoir. The average effective thickness is calculated using the maximum thickness of the reservoir, and the storage capacity is estimated accordingly.

[0015] Another object of the present invention is to provide an improvement as described above. Methods for estimating storage capacity in Applications in the selection of geological storage sites, assessment of caprock effectiveness, and prediction of long-term storage safety.

[0016] Combining all the above technical solutions, the beneficial effects of this invention are as follows: First, this invention, based on interfacial physical parameters (density difference, interfacial tension, and contact angle) and pore-throat structural characteristics, systematically analyzes the variation law of CO2 structural storage capacity under different burial depths and reveals the influence mechanism of pore-throat scale on storage height. Experimental results show that the caprock throat radius is the dominant factor controlling storage height, and its influence is significantly stronger than that of reservoir pore radius, with the two showing a strict inverse relationship. Meanwhile, temperature and pressure, as environmental variables, have a nonlinear regulatory effect on storage capacity. The increase in temperature and pressure caused by increased burial depth promotes the increase in storage height within a certain range, but when the contact angle exceeds 90°, the transformation of CO2 to caprock wettability will lead to the failure of the structural storage mechanism, posing a potential leakage risk. Overall, the optimization of structural storage capacity depends on the matching of the caprock nanoscale throat scale with a suitable thermodynamic environment.

[0017] The improved method for estimating CO2 storage capacity provided by this invention can quantitatively predict the height of the CO2 storage column during CO2 geological storage, thereby ensuring that CO2 does not leak. By comparing the CO2 storage column height with the maximum reservoir thickness to obtain the effective average thickness, the storage capacity is calculated, thus guaranteeing that CO2 does not leak during geological storage.

[0018] Secondly, this invention establishes a formula for calculating the gas column height, introduces the Batzle-Wang equation and a multi-parameter empirical formula for interfacial tension to accurately calculate CO2 properties and interfacial tension; it measures the caprock contact angle under high-temperature and high-pressure experimental conditions to reflect the wettability of the actual storage environment; and it utilizes focused ion beam scanning electron microscopy (FIB-SEM) three-dimensional reconstruction technology to extract key parameters of rock pores and throats, thereby comprehensively improving the reliability and applicability of the prediction results. This invention is applicable to various geological storage scenarios and can provide reliable technical support and parameter basis for the safe and long-term storage of CO2.

[0019] Third, by improving the accuracy of CO2 storage capacity assessment, this invention can significantly reduce the uncertainty of site selection and operation, reduce storage risks, and achieve safer and more economical CO2 geological storage projects. It can also be used for storage site evaluation, design optimization, and monitoring and early warning, possessing broad engineering applicability and promotional value. This invention systematically compares and constrains the reservoir geometric thickness with the CO2 storage gas column height controlled by interface properties and pore throat structure, effectively avoiding deviations caused by estimating solely based on reservoir thickness, fundamentally improving the accuracy of storage capacity prediction and significantly reducing leakage risks.

[0020] Traditional views generally consider reservoir thickness as the primary control parameter for structural storage capacity, thus neglecting the fact that capillary pressure, determined by interfacial tension, contact angle, and pore-throat structure, is the fundamental factor limiting CO2 column height. This invention breaks through the inherent assumption that "thickness equals storage capacity," introducing capillary plugging mechanisms into the capacity calculation framework. Through quantitative verification using experimental physical properties and pore-throat structure data, it successfully overcomes industry misconceptions in storage assessment, achieving storage capacity predictions that more accurately reflect real geological processes. Attached Figure Description

[0021] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure; Figure 1 This is a flowchart of the improved CO2 storage capacity estimation method provided in the embodiments of the present invention; Figure 2 This is a schematic diagram illustrating the change of CO2-water interfacial tension with temperature and pressure conditions, provided in an embodiment of the present invention. Figure 3This is a schematic diagram illustrating the change of CO2 density with temperature and pressure conditions provided in an embodiment of the present invention; Figure 4 This is a graph showing the relationship between depth and sealing height provided in an embodiment of the present invention. Detailed Implementation

[0022] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0023] The innovation of this invention lies in the fact that it breaks through the traditional approach of using reservoir thickness as the core indicator of storage capacity estimation. Instead, it systematically compares and constrains the reservoir geometric thickness with the CO2 storage column height controlled by interface properties and pore throat structure. This effectively avoids the deviation caused by estimating storage capacity solely based on reservoir thickness, fundamentally improves the accuracy of storage capacity prediction, and significantly reduces the risk of leakage.

[0024] Example 1, such as Figure 1 As shown, the improved CO2 storage capacity estimation method provided in this embodiment of the invention includes the following steps: S1, obtain the maximum throat radius of the cap layer respectively. and the minimum pore radius of the reservoir ; S2, Obtain the temperature of the storage location. and pressure ; S3, based on the temperature and pressure Calculate separately density Density of salt water ; S4, Calculate saline water and density difference between ,in, ; S5, based on the temperature ,pressure and density difference ,calculate -Interfacial tension in saline water ; S6, at the temperature and pressure Below, measurement -Retreating contact angle of saline-lithic systems ; S7, based on the above , , , and ,calculate Storage column height ; S8, Storage column height The effective average thickness is obtained by comparing it with the maximum thickness of the reservoir, and the storage capacity is calculated.

[0025] In step S1, the maximum throat radius of the cap layer is obtained respectively. and the minimum pore radius of the reservoir ,include: The sample was milled layer by layer using focused ion beam scanning electron microscopy three-dimensional reconstruction technology, and the newly exposed surface was imaged with high resolution using an electron beam to obtain a continuous two-dimensional image sequence. The acquired images are imported into 3D reconstruction software. After registration, denoising, and thresholding, a 3D structural model of pores and skeleton is obtained. The three-dimensional structural model is subjected to skeletonization, connectivity analysis, and throat identification. The pore size and throat radius distribution are calculated, and the maximum throat radius of the cap layer is extracted. and the minimum pore radius of the reservoir .

[0026] The maximum throat radius of the capping layer Less than 100nm, preferably less than 10nm; The minimum pore radius of the reservoir The range is from 1 μm to 100 μm.

[0027] The Young-Laplace equation can be expressed as: ; In the formula, For capillary pressure, For interfacial tension, The contact angle between CO2, saline water, and rock. This refers to the pore radius or throat radius of the rock.

[0028] The formula for calculating the height of the CO2 column is: ; In the formula, It is the acceleration due to gravity. This refers to the air column sealing height. The difference in density between saltwater and CO2. The radius of the capillary throat. The reservoir pore radius is denoted as .

[0029] ; In the formula, The density of salt water, The density of CO2.

[0030] As shown in formula (2), the CO2 column height is directly affected by parameters such as interfacial tension, contact angle, density difference, caprock throat radius, and reservoir pore radius. Among these parameters, the caprock throat radius and reservoir pore radius are generally not significantly affected by external environmental factors, and their values ​​remain relatively stable once the storage location is determined. In contrast, other parameters are more susceptible to external influences and exhibit a certain degree of variability. The calculation methods and specific value bases of the above parameters will be described in detail below to support the construction and application of the subsequent evaluation system.

[0031] In step S3, density The calculation uses the Batzle-Wang equation, specifically including: ; ; ; In the formula, Specific gravity is defined as the ratio of gas density to air density under standard conditions (18℃ and 1 atm). The specific gravity of CO2 gas is 1.5349. Let be the ideal gas constant, taken as 8.31441. mol·K; Absolute temperature; It is the compression factor; Young's modulus; and They are respectively The pseudo-simplified pressure and pseudo-simplified temperature; For pressure; and These are the pseudo-simplified pressure and pseudo-simplified temperature of the gas, respectively.

[0032] ; ; In the formula, for The pseudocritical pressure is taken as 1072 psi (7.4 MPa). for The pseudocritical temperature is taken as 31.1℃.

[0033] The density of saltwater can be calculated using the following formula: density of salt water It is calculated by the following formula: ; ; ; ; ; In the formula, The density of saline water under standard conditions. The formation water volume factor under standard conditions is given by the reservoir pressure. and temperature Calculated; This represents the weight percentage of dissolved salts in formation water. Young's modulus; These are correction factors for pressure and temperature, respectively, used to describe the combined effect of pressure and temperature changes on the density of saline water; Pressure, unit: ; Temperature, unit: .

[0034] Parameters such as temperature and pressure need to be measured according to the actual conditions of the storage location to ensure that the calculated parameters are consistent with the on-site working conditions.

[0035] Interfacial tension The predictive relation is expressed as: ; In the formula, For pressure, For temperature, The salinity is for monovalent cations, in units of ; The salinity of divalent cations, in units of ; for mole fraction, for exist impurity mole fraction, The square root function represents taking the square root of the quantity within the parentheses. It is the hyperbolic tangent function.

[0036] The wettability of the caprock plays a crucial role in its sealing effect, with the retreat contact angle being closely related to the structural sealing performance. To obtain reliable contact angle data, appropriate mineral samples need to be selected based on the mineral composition of the caprock and reservoir at the sealing site, and measurements are performed under high temperature and high pressure conditions. The specific method is as follows: Under preset temperature conditions, a cleaned and dried mineral substrate is placed in a high-temperature and high-pressure test chamber, and the chamber is flushed with CO2 circulation for approximately 10 minutes under simulated reservoir conditions to remove impurities and achieve gas replacement. Subsequently, a high-precision injection pump is used to steadily increase the system pressure to a predetermined value and maintain stability. After the temperature and pressure conditions stabilize, brine that has been degassed under vacuum for more than 12 hours is slowly dripped onto the surface of the mineral substrate at a pre-set inclination angle using a micro-syringe, controlling the droplet volume and drip rate to avoid disturbance. The angle between the solid surface and the brine-CO2 interface is measured as the advancing contact angle just before the droplet begins to move, and the retreat contact angle is measured at the trailing edge of the droplet. The entire process is synchronously recorded by a high-definition camera system. After the experiment, keyframe images are extracted and combined with image analysis software to accurately calculate the contact angle.

[0037] Representative rock samples were selected, processed into flat small pieces or thin slices, and dried under vacuum conditions. If necessary, a conductive coating was applied to the samples to reduce charge accumulation. Focused ion beam scanning electron microscopy (FIB-SEM) was used to mill the samples layer by layer, and simultaneously, high-resolution imaging of the newly exposed surfaces was performed using an electron beam to acquire a continuous sequence of two-dimensional images. The acquired images were imported into 3D reconstruction software, and after registration, denoising, and thresholding, a 3D structural model of the pores and framework was obtained. This 3D model was then subjected to framework reconstruction, connectivity analysis, and throat identification. The pore size and throat radius distribution were calculated, and key parameters such as the "minimum pore radius" and "maximum throat radius" could be extracted as needed.

[0038] This invention achieves quantitative prediction of CO2 storage column height by comprehensively considering information such as the maximum throat radius of the caprock, the minimum pore radius at the bottom of the reservoir, burial depth, and physical parameters of the CO2-saline interface. It breaks through the traditional approach of using reservoir thickness as the core indicator of storage capacity, systematically comparing and constraining the reservoir's geometric thickness with the CO2 storage column height controlled by interface properties and pore throat structure. This effectively avoids the bias caused by estimating storage capacity solely based on reservoir thickness, fundamentally improving the accuracy of storage capacity prediction and significantly reducing leakage risk, thus ensuring that CO2 does not leak during geological storage. This invention is applicable to various geological storage scenarios and can provide reliable technical support and parameter basis for the safe and long-term storage of CO2.

[0039] Figure 3The study demonstrates the variation of CO2 density with pressure at different temperatures, showing that CO2 density increases significantly with increasing pressure; meanwhile, under the same pressure conditions, increasing temperature leads to a decrease in CO2 density.

[0040] Taking quartz minerals and pure water as examples, the values ​​of the storage height changing with depth are as follows: Figure 4 As shown.

[0041] Example 2: This embodiment of the invention provides an application of the improved CO2 storage capacity estimation method in the selection of CO2 geological storage sites, assessment of caprock effectiveness, and prediction of long-term storage safety.

[0042] The Smeaheia project in the northern Norwegian North Sea is used as a typical case study for computational analysis. As a key site for carbon capture and storage in Europe, Smeaheia possesses detailed geological exploration data and typical structural features, making it an ideal object for testing theoretical models.

[0043] Based on measured data, the temperature at a depth of 1200 m is 51.5 °C, and the temperature at 1500 m is 62.6 °C, resulting in a geothermal gradient of 37 °C / km. The pressure of the caprock at location 32 / 4-1 was obtained as 12.12 MPa and the temperature as 51.9 °C, while the pressure of the caprock at location 32 / 2-1 was obtained as 8.58 MPa and the temperature as 39.6 °C.

[0044] Previous researchers measured the pore throat radius of the Draupne formation and found that the median pore throat radius was 13.5 nm. When calculating the height of the sequesterable CO2 column, a pore throat radius of 13.5 nm was used.

[0045] The formation contains 11 wt% NaCl. The density of the saline water is obtained using formula (9), and the density of CO2 is obtained using formula (4), thus the density difference is calculated. The interfacial tension is obtained using formula (14). The data in Table 1 are obtained. Then the gas column height is compared with the corresponding reservoir thickness at each location.

[0046] Table 1 Data Parameter Table

[0047] The reservoir thickness at location 32 / 4-1 is 580 m, less than the sequesterable CO2 column height of 768.69 m. The reservoir thickness at location 32 / 2-1 is 330 m, also less than the sequesterable CO2 column height of 765.28 m. Since the reservoir thickness at both locations is less than the sequesterable CO2 column height, the average effective reservoir thickness can be used for volume calculation. This contributes to the optimal selection of CO2 geological storage sites, the assessment of caprock effectiveness, and long-term safety prediction.

[0048] Example 3, as Figure 2 As shown, density difference ( Compared to interfacial tension ( It exhibits stronger environmental response characteristics. Based on this, a pressure of 10 MPa and a temperature of 100℃ was selected. and For constant parameters ( =35.243mN / m, =731.795kg / m 3 Since the contact angle has no functional relationship with temperature and pressure, the contact angles listed in Table 2 are used as a reference. Threshold standards, set =70°.

[0049] Table 2 data confirms the radius of the apex throat ( ) on the sealing height ( It has a dominant control, and its influence significantly exceeds that of the reservoir pore radius. ).when From 10nm to 100nm, The altitude dropped sharply from 332.5-335.8m to 30.2-33.5m, a decrease of 90%. This contrasts sharply with the previous situation... Under fixed conditions, Increasing from 1 μm to 100 μm (on the order of magnitude × 100) only causes a weak perturbation: for a 10 nm throat, Only an increase of 3.32m (relative increase ≈ 1%); for a 100nm throat, the same Under change It only increased by 3.32m (although the relative increase was approximately 10% due to the smaller base, the absolute increase remained at 3.27m). The above cross-order-of-magnitude experiments demonstrate that... right Highly sensitive to variation. Based on right The dominant control effect requires that the caprock selection must meet the following condition: the critical throat radius of the dominant seepage channel. <100nm, and the optimization objective is <10nm.

[0050] Table 2. Quantitative influence of caprock throat radius and reservoir pore radius on storage height

[0051] Example 4, Table 3 shows the relationship between wettability and contact angle. When the contact angle exceeds 90°, the cosine of the contact angle is negative, indicating that the sealing structure has failed and CO2 is leaking.

[0052] Table 3 Wettability of the Rock-CO2-Saline Water System

[0053] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0054] To further demonstrate the positive effects of the above embodiments, the present invention conducts the following experiment based on the above technical solution. In this experiment, at a location where CO2 geological sequestration is planned, geological parameters such as the mineral composition and pore structure of the caprock and reservoir are determined based on drilling, core, and testing data. Representative caprock samples are selected, and a three-dimensional structural model of the pores and throats is obtained using focused ion beam scanning electron microscopy (FIB-SEM) imaging technology. The maximum throat radius is then extracted. Select representative reservoir samples to obtain the minimum pore radius. .

[0055] Subsequently, the density of the saline water was determined based on the on-site measurements of burial depth, temperature, and pressure. The retreat contact angle of CO2-saline water-rock was measured under corresponding temperature and pressure conditions. The contact angle was measured using a high-temperature, high-pressure contact angle testing device. The cleaned and dried mineral substrate was placed in a high-pressure test tank at a preset temperature and rinsed with CO2 circulation for approximately 10 minutes. Then, a high-precision injection pump was used to steadily raise the system pressure to a predetermined value and maintain it. Next, brine that had been degassed under vacuum for more than 12 hours was slowly dripped onto the substrate surface at a set tilt angle. The advancing contact angle was measured just before the droplet moved, and the retreating contact angle was measured at the trailing edge of the droplet. The entire process was recorded by a high-definition camera system and processed using image analysis software.

[0056] The density of CO2 can be used Calculation, interfacial tension according to Calculation of density difference. It can be by The calculation shows that substituting the above parameters into... The predicted value of the CO2 sequestration column height at the sequestration site was obtained.

[0057] Then, the predicted value of the sequesterable CO2 column height is compared with the maximum reservoir thickness. If the maximum reservoir thickness is greater than the sequesterable CO2 column height, directly using the maximum reservoir thickness to calculate the average effective thickness will lead to an overestimation of the storage capacity, and may even result in breakthroughs and leaks during actual injection. Therefore, in such cases, the sequesterable CO2 column height should be used as the equivalent thickness in capacity calculation. If the maximum reservoir thickness is less than the sequesterable CO2 column height, it indicates that the caprock has the capacity to completely seal the gas column height within the maximum reservoir thickness. In this case, the maximum reservoir thickness can be used to calculate the average effective thickness and estimate the storage capacity accordingly.

[0058] The method of this invention can be used to quantitatively predict the height of CO2 storage gas columns under different geological conditions, thereby providing reliable technical support for the safe and long-term storage of CO2.

[0059] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention and within the spirit and principles of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method of improving the estimation of CO2 storage capacity, characterized by, The method comprises the following steps: S1, respectively acquiring the maximum throat radius of the cap rock and the minimum pore radius of the reservoir ; S2, obtaining temperature of sequestration site and pressure ; S3, based on the temperature and pressure , respectively calculate the density of the fresh water and the density of the salt water; S4, calculating the density difference between the salt water and the fresh water wherein, ;​ S5, calculating the saltwater interfacial tension based on the temperature , pressure , and density difference ;​​ S6, at said temperature and pressure under which the - receding contact angle of the saltwater-rock system ; S7, based on the , , , and , calculate the height of the gas column ; S8, will Sealing gas column height The effective average thickness is compared with the maximum thickness of the reservoir to calculate the sealing capacity.

2. The method for improving the estimation of the CO2 storage capacity according to claim 1, characterized in that, In step S1, the maximum throat radius of the cap rock is acquired respectively and the minimum pore radius of the reservoir , comprising: The sample is milled layer by layer by using a focused ion beam-scanning electron microscope three-dimensional reconstruction technology, the newly exposed surface is imaged at high resolution by using an electron beam, and a continuous two-dimensional image sequence is obtained; The collected images are imported into three-dimensional reconstruction software, and after registration, denoising and threshold segmentation processing, a three-dimensional structure model of the pores and the skeleton is obtained; The three-dimensional structure model is skeletonized, connectivity analyzed and throat identified, aperture and pore throat radius distribution are calculated, and the maximum throat radius of the cap rock is extracted and the minimum pore radius of the reservoir .

3. The method for improving the estimation of the CO2 storage capacity according to claim 1, characterized in that, In step S1, the maximum throat radius of the cap layer is less than 100 nm; the minimum pore radius of the reservoir is 1 pm to 100 pm.

4. The method for improving the estimation of CO2 storage capacity according to claim 1, wherein, In step S3, the density The calculation employs the Batzle-Wang equation, in particular comprising: ； ； ； In the formula, For the specific gravity of the gas, take 1.5349; Let be the ideal gas constant, taken as 8.31441. ; Absolute temperature; It is the compression factor; Young's modulus; and They are respectively The pseudo-simplified pressure and pseudo-simplified temperature; For pressure; ； ； In the formula, for The pseudocritical pressure is taken as 7.4 MPa; for The pseudocritical temperature is taken as 31.1℃.

5. The method for improving the estimation of CO2 storage capacity according to claim 1, wherein, In step S3, the density of the salt water is calculated from the following formula: ； ； ； ； ； wherein is the density of the salt water under standard conditions, is the formation water volume factor under standard conditions, calculated from the given reservoir pressure and temperature ; is the weight percent of dissolved salts in the formation water, is the Young's modulus; are the correction factors for pressure and temperature, respectively, used to describe the combined effect of pressure and temperature changes on the density of the salt water; is the pressure in ; is the temperature in .

6. The method for improving the estimation of the CO2 storage capacity according to claim 1, characterized in that, In step S5, - the saltwater interfacial tension The predictive relationship is: ； ； ； ； ； ； wherein is pressure, is temperature, is salinity of monovalent cations, is salinity of divalent cations, is mole fraction, is mole fraction of impurities in is a square root function, indicating taking the square root of the quantity inside the parentheses, is a hyperbolic tangent function.​ 7. The method for improving the estimation of CO2 storage capacity according to claim 1, wherein, In step S6, the measurement - the receding contact angle of the saltwater-rock system comprising: The cleaned and dried mineral substrates are placed in a high temperature and high pressure test cell under pre-set temperature conditions and subjected to a simulated reservoir environment under pre-set temperature and pressure conditions using Circulating flushing to drive off impurities and achieve gas displacement; The system pressure is smoothly increased to a predetermined value by a high-precision injection pump and kept stable; After the temperature and pressure conditions are stable, the salt water that has been vacuum degassed is added dropwise to the mineral substrate surface with a preset angle of inclination through a microsyringe; the angle between the solid surface and the salt water interface is measured as the advancing contact angle before the droplet moves, and the receding contact angle is measured at the rear position of the droplet; interface is measured as the advancing contact angle before the droplet moves, and the receding contact angle is measured at the rear position of the droplet; The contact angle value is calculated by extracting key frame images by using image analysis software through synchronous recording by a high-definition camera system; - the receding contact angle of the saltwater-rock system, Θ, ranges from 0° to 90°; when the receding contact angle of the saltwater-rock system, Θ, ranges from 0° to 90°; when 8. The method for improving the estimation of CO2 storage capacity according to claim 1, wherein, In step S7, Sequestering gas column height This is calculated by the equation: ； In the formula, g is the acceleration due to gravity.

9. The method for improving the estimation of CO2 storage capacity according to claim 1, wherein, In step S8, the Sealing gas column height Compared with the maximum thickness of the reservoir, if the maximum thickness of the reservoir is greater than the sealable gas column height, the average effective thickness is calculated by using the sealable gas column height; if the maximum thickness of the reservoir is less than the sealable gas column height, it indicates that the cap rock has the ability to completely seal the gas column height within the maximum thickness of the reservoir, and the average effective thickness is calculated by using the maximum thickness of the reservoir, and the sealing capacity is estimated accordingly.

10. Use of the method for improving the estimation of the CO2 storage capacity according to any one of claims 1 to 9 in the selection of a CO2 geological storage site, the evaluation of the effectiveness of the cap rock and the prediction of the long-term storage safety.

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