A method for improving co2 storage capacity estimation

Abstract

The application belongs to the technical field of carbon dioxide geological storage, and discloses a method for improving CO2 storage capacity estimation, which obtains the maximum throat radius of a cap layer and the minimum pore radius of a reservoir and the temperature and pressure of a storage site respectively; based on the temperature and pressure, the density of fresh water and the density of salt water are calculated respectively; the density difference between the salt water and the fresh water is calculated; based on the temperature, the pressure and the density difference, the fresh water-salt water interfacial tension is calculated; under the temperature and the pressure, the receding contact angle of the fresh water-salt water-rock system is measured; and the storage gas column height is calculated. The application has important significance for improving the accuracy of storage capacity estimation, and is helpful to build a more reliable storage capacity evaluation system and provide scientific basis and theoretical support for long-term safety prediction in a CGS project.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of carbon dioxide geological storage, and particularly relates to a method for improving estimation of CO2 storage capacity. BACKGROUND

[0002] Accurate calculation of the storable capacity is of great significance for carbon dioxide geological storage, and existing researches mostly use the volumetric method to estimate the CO2 structural storage capacity of a sedimentary basin, which is usually based on the average thickness of the reservoir. However, the physical mechanism of structural storage is essentially determined by the capillary pressure caused by the interfacial tension at the interface between two-phase fluids in the rock pore, which determines the upper limit of the CO2 gas column height that can be stored by the caprock. It is worth noting that the thickness of the reservoir mainly reflects the geometric characteristics and is not equal to the effective sealing gas column height limited by the capillary force.

[0003] The Young-Laplace equation can be used to calculate the capillary pressure difference, on the basis of which a formula for calculating the CO2 column storage height is formed, which is originally mainly used to calculate the height of the oil and gas column that can be blocked by the caprock, and is gradually applied to the evaluation of the structural storage capacity of CO2 and other fluids. The capillary pressure is the core control factor of the sealing capacity of the caprock, which is jointly affected by the contact angle, interfacial tension, density difference and pore throat radius and other parameters. The contact angle, interfacial tension and density difference all have corresponding relationships with temperature and pressure, and change with the change of the formation burial depth and thermodynamic environment. Scholars have systematically discussed the quantitative relationship between CO2 density and temperature and pressure conditions, and measured the change rule of the contact angle with the change of temperature and pressure conditions through various experimental methods, revealing the potential influence of wettability transition on storage stability. At the same time, it has also been shown that the interfacial tension has a significant correlation with temperature and pressure and density difference, and the corresponding empirical formula is proposed, which provides a theoretical and experimental basis for calculating the CO2 gas column height under different geological conditions. When the thickness of the reservoir exceeds the CO2 gas column height corresponding to the capillary sealing capacity of the caprock, the structural storage mechanism will fail and CO2 leakage will occur. Therefore, direct use of the reservoir thickness for calculation will lead to significant deviation, and in-depth study of the main control mechanism of the storable CO2 gas column height is the core prerequisite for scientific calculation of the CO2 storage potential.

[0004] Through the above analysis, the existing problems and defects of the prior art are that the volumetric method only calculates the storage capacity according to the reservoir thickness, without considering the control effect of the capillary pressure determined by the interfacial tension and pore throat structure, and ignoring the upper limit of the gas column height that can be stored by the caprock; at the same time, the changes of CO2 density, interfacial tension and contact angle under temperature and pressure conditions are not systematically coupled, resulting in overestimation of the capacity and inconsistency with the actual storage mechanism. SUMMARY

[0005] In order to overcome the problems in the prior art, the embodiment of the present application provides a method for improving CO2 storage capacity estimation, which is used for predicting the CO2 storage gas column height in the CO2 geological storage process to ensure that CO2 does not leak, and the technical scheme is as follows:

[0006] The present application is implemented as follows: the method for improving CO2 storage capacity estimation comprises the following steps:

[0007] S1, respectively acquiring the maximum throat radius of the cap rock and the minimum pore radius of the reservoir ;

[0008] S2, acquiring the temperature and pressure of the storage site;

[0009] S3, respectively calculating the density of CO2 and the density of salt water based on the temperature and pressure ;

[0010] S4, calculating the density difference between the salt water and CO2 , wherein,

[0011] S5, calculating the CO2-salt water interfacial tension based on the temperature , pressure and density difference ;

[0012] S6, measuring the receding contact angle of the CO2-salt water-rock system under the temperature and pressure ;

[0013] S7, calculating the CO2 storage gas column height based on the temperature , , , and ;

[0014] S8, comparing the CO2 storage gas column height with the maximum thickness of the reservoir to obtain the effective average thickness, and calculating the storage capacity.

[0015] ​​​​​​​​​​​​In step S1, the maximum throat radius of the cap layer is obtained respectively. and the minimum pore radius of the reservoir ,include:

[0016] 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.

[0017] The acquired images are imported into 3D reconstruction software. After registration, denoising, and thresholding, a 3D structural model of pores and skeleton is obtained.

[0018] 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 .

[0019] In step S1, the maximum throat radius of the capping layer Less than 100nm;

[0020] The minimum pore radius of the reservoir The range is from 1 μm to 100 μm.

[0021] In step S3, density The calculation uses the Batzle-Wang equation, which specifically includes:

[0022] ;

[0023] ;

[0024] ;

[0025] 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;

[0026] ;

[0027] ;

[0028] In the formula, for The pseudocritical pressure is taken as 7.4 MPa; for The pseudocritical temperature is taken as 31.1℃.

[0029] In step S3, the density of the salt water It is calculated by the following formula:

[0030] ;

[0031] ;

[0032] ;

[0033] ;

[0034] ;

[0035] 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: .

[0036] In step S5, -Interfacial tension in saline water The predictive relation is:

[0037] ;

[0038] 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, This is the square root function, which represents taking the square root of the quantity within the parentheses. It is the hyperbolic tangent function.

[0039] In step S6, measurement -Retreating contact angle of saline-lithic systems ,include:

[0040] 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;

[0041] A high-precision injection pump is used to smoothly raise the system pressure to the predetermined value and maintain it stable.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] In step S7, Storage column height Calculated using the following formula:

[0046] ;

[0047] In the formula, This is the acceleration due to gravity.

[0048] 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 ability 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.

[0049] Another object of the present invention is to provide an improvement as described above. Methods for estimating storage capacity in Application in the optimal selection of geological storage sites, the evaluation of caprock effectiveness and the prediction of long-term storage safety.

[0050] In combination with all the technical solutions described above, the present application has the following beneficial effects:

[0051] Firstly, based on the interfacial physical parameters (density difference, interfacial tension and contact angle) and pore throat structure characteristics, the present application systematically analyzes the variation law of CO2 structural storage capacity under different burial depths, and reveals the influence mechanism of pore throat scale on the storage height. The experimental results show that the caprock throat radius is the dominant factor controlling the storage height, and its influence is significantly stronger than that of the reservoir pore radius, and the two are strictly inversely proportional; at the same time, temperature and pressure as environmental variables have a nonlinear regulation effect on the storage capacity. The temperature and pressure rise caused by the increase of burial depth promotes the increase of storage height within a certain range, but when the contact angle exceeds 90°, the wettability change of CO2 to the caprock will lead to the failure of the structural storage mechanism, and there is a potential leakage risk. Overall, the optimization of the structural storage capacity depends on the matching of the caprock nanoscale throat size and the moderate thermodynamic environment.

[0052] The method for improving the estimation of storage capacity provided by the present application can quantitatively predict the CO2 storage gas column height in the process of CO2 geological storage, so as to ensure that CO2 does not leak. By comparing the CO2 storage gas column height with the maximum thickness of the reservoir, the effective average thickness is obtained, and the storage capacity is calculated, so as to ensure that CO2 does not leak in the process of geological storage.

[0053] Secondly, the present application establishes a gas column height calculation formula, introduces the Batzle-Wang equation and the multi-parameter interfacial tension empirical formula to accurately calculate the CO2 physical properties and interfacial tension; the caprock contact angle is measured under high temperature and high pressure experimental conditions to reflect the wettability of the real storage environment; at the same time, the key parameters of rock pores and throats are extracted by using the focused ion beam-scanning electron microscope (FIB-SEM) three-dimensional reconstruction technology, so as to comprehensively improve the reliability and applicability of the prediction results. The present application is suitable for various geological storage scenes, and can provide reliable technical support and parameter basis for safe and long-term storage of CO2.

[0054] Thirdly, by improving the accuracy of the evaluation of CO2 storage capacity, the present application can significantly reduce the uncertainty of site selection and operation, reduce the storage risk, and realize safer and more economical CO2 geological storage engineering; at the same time, it can be used for storage site evaluation, design optimization and monitoring and early warning, and has wide engineering applicability and popularization value. The present application compares and constrains the reservoir geometric thickness with the CO2 storage gas column height controlled by the interfacial physical properties and pore throat structure, effectively avoids the deviation caused by the estimation based on the reservoir thickness only, fundamentally improves the accuracy of the prediction of the storage capacity and significantly reduces the leakage risk.

[0055] 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

[0056] 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;

[0057] Figure 1 This is a flowchart of the improved CO2 storage capacity estimation method provided in the embodiments of the present invention;

[0058] 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;

[0059] Figure 3 This is a schematic diagram illustrating the change of CO2 density with temperature and pressure conditions provided in an embodiment of the present invention;

[0060] Figure 4 This is a graph showing the relationship between depth and sealing height provided in an embodiment of the present invention. Detailed Implementation

[0061] 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.

[0062] 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.

[0063] Example 1, as Figure 1 As shown, the improved CO2 storage capacity estimation method provided in this embodiment of the invention includes the following steps:

[0064] S1, obtain the maximum throat radius of the cap layer respectively. and the minimum pore radius of the reservoir ;

[0065] S2, Obtain the temperature of the storage location. and pressure ;

[0066] S3, based on the temperature and pressure Calculate separately density Density of salt water ;

[0067] S4, Calculate saline water and density difference between ,in, ;

[0068] S5, based on the temperature ,pressure and density difference ,calculate -Interfacial tension in saline water ;

[0069] S6, at the temperature and pressure Below, measurement -Retreating contact angle of saline-lithic systems ;

[0070] S7, based on the above , , , and ,calculate Storage column height ;

[0071] 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.

[0072] In step S1, the maximum throat radius of the cap layer is obtained respectively. and the minimum pore radius of the reservoir ,include:

[0073] 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.

[0074] The collected images are imported into three-dimensional reconstruction software, and after registration, denoising and threshold segmentation, the three-dimensional structure model of the pore and skeleton is obtained;

[0075] The three-dimensional structure model is skeletonized, analyzed for connectivity and identified for throat, the pore diameter and pore throat radius distribution are calculated, and the maximum throat radius of the cap layer and the minimum pore radius of the reservoir are extracted . .

[0076] The maximum throat radius of the cap layer is less than 100 nm, preferably less than 10 nm;

[0077] The minimum pore radius of the reservoir is 1-100 μm.

[0078] The Young-Laplace equation can be expressed as:

[0079] ;

[0080] In the formula, is the capillary pressure, is the interfacial tension, is the contact angle of CO2-salt water-rock, is the pore radius or throat radius of the rock.

[0081] The calculation formula of the CO2 gas column height is:

[0082] ;

[0083] In the formula, is the acceleration of gravity, is the gas column storage height, is the difference between the densities of salt water and CO2, is the cap layer throat radius, is the reservoir pore radius.

[0084] ;

[0085] In the formula, is the density of salt water, is the density of CO2.

[0086] From equation (2), it can be seen that the CO2 gas column height is directly affected by the interfacial tension, contact angle, density difference, cap rock throat radius and reservoir pore radius, etc. Among the above parameters, the cap rock throat radius and reservoir pore radius are usually not significantly affected by external environmental factors, and once the storage site is determined, their values remain basically stable. In contrast, other parameters are easily affected by external parameters and exhibit certain variability. Next, the calculation method of the above parameters and the specific value basis will be introduced in detail to support the construction and application of the subsequent evaluation system.

[0087] In step S3, the density of the salt water The calculation of the density of the salt water adopts the Batzle-Wang equation, which specifically includes:

[0088] ;

[0089] ;

[0090] ;

[0091] In the formula, is the gas specific gravity, defined as the ratio of the gas density to the air density under standard conditions (18°C and 1 atm), and the CO2 gas specific gravity is 1.5349; is the ideal gas constant, taking 8.31441 mol·K; is the absolute temperature; is the compressibility factor; is the Young's modulus; and are the pseudo-reduced pressure and pseudo-reduced temperature of respectively; is the pressure;

[0092] and are the pseudo-reduced pressure and pseudo-reduced temperature of the gas respectively.

[0093] ;

[0094] ;

[0095] In the formula, is the pseudo-critical pressure of , taking 1072 psi (7.4 MPa); is the pseudo-critical temperature of , taking 31.1°C.

[0096] The density of the salt water can be obtained by the following formula:

[0097] The density of the salt water is calculated from the following formula:

[0098] ;

[0099] ;

[0100] ;

[0101] ;

[0102] ;

[0103] where, is the density of 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 percentage 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 salt water; is the pressure in ; is the temperature in .

[0104] Temperature and pressure parameters need to be measured according to the actual conditions of the storage site to ensure that the calculated parameters are consistent with the on-site working conditions.

[0105] The interfacial tension is predicted by the following relationship:

[0106] ;

[0107] where, is the pressure, is the temperature, is the salinity of monovalent cations in ; is the salinity of divalent cations in ; is the mole fraction of , is the mole fraction of impurities in , is the square root function, which represents the square root of the quantity inside the parentheses, is the hyperbolic tangent function.

[0108] ​The wettability of the cap rock plays an important role in its sealing effect, and the receding contact angle is closely related to the sealing effect. To obtain reliable contact angle data, the corresponding mineral samples need to be selected according to the mineral composition of the cap rock and the reservoir at the sealing site, and the measurement is carried out under high temperature and high pressure conditions. The specific method is as follows: under the preset temperature condition, the washed and dried mineral substrate is placed in a high temperature and high pressure test tank, and the chamber is circulated and flushed with CO2 for about 10 minutes under the simulated reservoir environment condition to remove impurities and achieve gas replacement; then the system pressure is smoothly increased to the predetermined value by using a high-precision injection pump and kept stable; after the temperature and pressure conditions are stable, the salt water which has been vacuum degassed for more than 12 hours is slowly added to the mineral substrate surface with a preset inclination angle by using a micro-injector, and the drop volume and drop speed are controlled to avoid disturbance. The angle between the solid surface and the salt water-CO2 interface is measured as the advancing contact angle before the droplet moves, and the receding contact angle is measured at the trailing position of the droplet. The whole process is recorded by a high-definition camera system, and the contact angle is accurately calculated by extracting key frame images and using image analysis software after the test is completed.

[0109] Representative rock samples are selected, processed into flat small blocks or slices and dried under vacuum conditions; if necessary, the samples are conductive plated to reduce charge accumulation. The sample is milled layer by layer by using a focused ion beam-scanning electron microscope (FIB-SEM) imaging technology, and the newly exposed surface is imaged by using an electron beam at the same time, so that a continuous two-dimensional image sequence is obtained. The collected images are imported into three-dimensional reconstruction software, and after registration, denoising, threshold segmentation and other processes, a three-dimensional structure model of pores and skeletons is obtained. The three-dimensional model is skeletonized, analyzed for connectivity and identified for throat, the pore size and throat radius distribution are calculated, and key parameters such as "minimum pore radius" and "maximum throat radius" can be extracted according to actual needs.

[0110] The present application realizes quantitative prediction of the CO2 sealing gas column height by comprehensively sealing the maximum throat radius of the cap rock, the minimum pore radius of the reservoir bottom, the burial depth condition, and the temperature, pressure and CO2-salt water interface physical parameters, breaks through the traditional estimation idea of taking the reservoir thickness as the core index of sealing capacity, systematically compares and constrains the reservoir geometric thickness with the CO2 sealing gas column height controlled by the interface physical properties and pore throat structure, effectively avoids the deviation caused by estimating the sealing capacity only by the reservoir thickness, fundamentally improves the accuracy of the sealing capacity prediction and significantly reduces the leakage risk. To ensure that CO2 does not leak during the geological sealing process. The present application is suitable for various geological sealing scenes, and can provide reliable technical support and parameter basis for safe and long-term sealing of CO2.

[0111] Figure 3The variation of CO2 density with pressure at different temperatures is shown, and the CO2 density increases significantly with the increase of pressure; at the same pressure, the increase of temperature leads to the decrease of CO2 density.

[0112] The value of the sealing height changing with the depth is shown in the quartz mineral and pure water as an example. Figure 4

[0113] In embodiment 2, the application of the method for improving the estimation of the CO2 sealing capacity to the selection of the CO2 geological storage site, the evaluation of the effectiveness of the cap rock and the long-term safety prediction is provided.

[0114] The Smeaheia project in the north of the Norwegian North Sea is taken as a typical case for calculation and analysis. As a key site for carbon capture and storage in Europe, Smeaheia has detailed geological exploration data and typical structural characteristics, and is an ideal object for testing the theoretical model.

[0115] According to the measured data, the temperature at a depth of 1200 m is 51.5 °C, and the temperature at a depth of 1500 m is 62.6 °C, and the obtained geothermal gradient is 37 ℃ / km. The pressure of the cap rock at 32 / 4-1 is 12.12 MPa, and the temperature is 51.9 °C, and the pressure of the cap rock at 32 / 2-1 is 8.58 MPa, and the temperature is 39.6 °C.

[0116] The previous measurement of the pore throat radius of the Draupne formation found that the median pore throat radius is 13.5 nm, and when calculating the sealable CO2 gas column height, the pore throat radius of 13.5 nm is used for calculation.

[0117] The salt water in the formation is 11 wt% NaCl. The salt water density is obtained by formula (9), the CO2 density is obtained by formula (4), and the density difference is obtained. The interfacial tension is obtained by formula (14). The data in Table 1 is obtained. Then the gas column height is compared with the corresponding reservoir thickness at each place.

[0118] Table 1 Data Parameter Table

[0119]

[0120] The corresponding reservoir thickness at 32 / 4-1 is 580 m, which is less than the sealable CO2 gas column height of 768.69 m, and the corresponding reservoir thickness at 32 / 2-1 is 330 m, which is less than the sealable CO2 gas column height of 765.28 m. The reservoir thickness at both places is less than the sealable CO2 gas column height. Therefore, when calculating the volume, the average effective thickness of the reservoir can be used for calculation. Therefore, the CO2 geological storage site selection, the evaluation of the effectiveness of the cap rock and the long-term safety prediction contribute.​

[0121] 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°.

[0122] 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.

[0123] Table 2. Quantitative influence of caprock throat radius and reservoir pore radius on storage height

[0124]

[0125] 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.

[0126] Table 3 Wettability of rock-CO2-saline water system

[0127]

[0128] In the above embodiments, the description of each embodiment has its own focus, and the parts not described or recorded in detail in a certain embodiment can be referred to the relevant description of other embodiments.

[0129] To further prove the positive effect of the above embodiments, the present application based on the above technical solutions carries out the following experiments. In a place where CO2 geological storage is to be carried out, the geological parameters such as mineral composition and pore structure of the cap rock and reservoir are determined according to drilling, core and test data. Representative cap rock samples are selected, and three-dimensional structure model of pores and throats is obtained by focused ion beam-scanning electron microscope (FIB-SEM) imaging technology, and the maximum throat radius is extracted .

[0130] Subsequently, the density of saline water is determined according to the measured burial depth, temperature and pressure conditions , and the receding contact angle of CO2-saline water-rock is determined under the corresponding temperature and pressure conditions . The contact angle is measured by using a high temperature and high pressure contact angle testing device. The cleaned and dried mineral substrate is placed in a high pressure test cell at a preset temperature, and then the system pressure is smoothly increased to a predetermined value and kept stable by using a high precision syringe pump after being washed with CO2 for about 10 min. Then, the saline water degassed for more than 12 h is slowly added to the surface of the substrate with a set inclination, and the advancing contact angle is measured before the droplet moves, and the receding contact angle is measured after the droplet moves. The whole process is recorded by a high-definition camera system and processed by image analysis software.

[0131] The density of CO2 can be calculated by , the interfacial tension is calculated according to , and the density difference can be calculated by . By substituting the above parameters into , the predicted value of the CO2 sealable gas column height of the storage site is obtained.

[0132] 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.

[0133] 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.

[0134] 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. An improved method for estimating CO2 storage capacity, characterized in that, The method 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. In step S7, Storage column height Calculated using the following formula: ； In the formula, It is the acceleration due to gravity; In step S8, Storage column height Compared with the maximum reservoir thickness, if the maximum reservoir thickness is greater than the resilient reservoir thickness... When the air column height is reached, a sealable method is used. 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 ability 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.

2. The improved method for estimating CO2 storage capacity according to claim 1, characterized in that, 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 .

3. The improved method for estimating CO2 storage capacity according to claim 1, characterized in that, 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.

4. The improved method for estimating CO2 storage capacity according to claim 1, characterized in that, 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℃.

5. The improved method for estimating CO2 storage capacity according to claim 1, characterized in that, 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: .

6. The improved method for estimating CO2 storage capacity according to claim 1, characterized in that, 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, This is the square root function, which represents taking the square root of the quantity within the parentheses. It is the hyperbolic tangent function.

7. The improved method for estimating CO2 storage capacity according to claim 1, characterized in that, 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 contact angle value is calculated using image analysis software by synchronously recording with a high-definition camera system and extracting key frame images. 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.

8. An application of the method as described in any one of claims 1-7 in the selection of CO2 geological storage sites, assessment of caprock effectiveness, and prediction of long-term storage safety.

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