CO2 flooding asphaltene blocking degree quantitative calculation method

Abstract

The invention discloses a CO2 flooding asphaltene blocking degree quantitative calculation method, and relates to the technical field of oil and gas field development. According to the technical scheme, the method comprises the following steps: executing on-line core in-situ condition nuclear magnetic testing: preparing a solution for saturating a core, preparing a saturated rock sample, determining a static pore throat nuclear magnetic T2 spectrum, determining a CO2 displacement process nuclear magnetic T2 spectrum, and determining a CO2 displacement post-nuclear magnetic T2 spectrum; the permeability damage rate and the porosity damage rate of the rock core are calculated by respectively obtaining static pore throat nuclear magnetic T2 spectrums and CO2 displacement process nuclear magnetic T2 spectrums of different rock cores, so that the CO2 displacement asphaltene blockage index is obtained. The method has the beneficial effects that the core in-situ condition on-line nuclear magnetic experiment is adopted, the micro-pore structure characteristics of the reservoir core are classified and researched, the CO2 displacement micro-dynamic process is observed by using the representative real core, the asphaltene and wax blocking degree of each stage can be quantitatively analyzed, the observation and operation are simple, the cost is low, and the method is suitable for large-scale popularization and application. And the support is provided for improving the recovery efficiency and reducing the residual oil distribution in the later-stage work of the oil field.

Description

Technical Field

[0001] This invention relates to the field of oil and gas field development technology, specifically to a method for monitoring the T2 spectrum of fluids in cores and quantitatively analyzing and evaluating the degree of bituminous and waxy blockage in cores at various stages of CO2 flooding in online nuclear magnetic resonance technology for CO2 displacement physical simulation experiments, and for evaluating the adaptability of different cores to CO2 flooding. Background Technology

[0002] CO2 flooding technology is a key technology for enhancing oil recovery in low-permeability reservoirs. By injecting CO2 into the reservoir, not only can the oil recovery rate be effectively improved, but CO2 can also be geologically stored. This dual benefit makes CO2 flooding technology an economical and environmentally friendly solution. This technology addresses the needs of energy extraction while promoting environmental protection, truly achieving a win-win situation. For example, Chinese patent application CN117552758A discloses a chemical system and method for controlling cross-flow and blocking gas in low-permeability reservoirs using CO2 flooding.

[0003] While CO2 flooding technology has been widely used in conventional reservoirs, its research and application in unconventional reservoirs are still insufficient. Currently, most research focuses on the production enhancement effect of CO2 flooding technology, while our understanding of key scientific issues such as the specific flow mechanism of CO2 in reservoir pores, the characteristics of hydrocarbon phase changes, and the laws governing asphaltene precipitation remains relatively vague.

[0004] Asphaltenes deposition is a significant problem in CO2 enhanced oil recovery (EOR) processes, as it can severely impact well operations and even lead to a substantial decrease in reservoir permeability. To gain a deeper understanding of this issue, Behbahani et al. employed advanced computed tomography (CT) scanning technology to visually analyze the impact of asphaltenes deposition on reservoir pores. Their results indicate that asphaltenes deposition is one of the main factors contributing to reduced reservoir permeability.

[0005] Therefore, when promoting and applying CO2 flooding technology in unconventional reservoirs in the future, we need to further strengthen research on the flow patterns of CO2 in the reservoir, the phase changes of oil and gas, and the precipitation mechanism of asphaltenes, in order to better control and manage these issues, improve reservoir recovery, and reduce environmental impact. Asphaltenes and carbonate minerals may be captured at throats or adsorbed on pore walls during displacement, a phenomenon particularly pronounced in low-permeability reservoirs with fine pore-throat structures. The accumulation of these precipitates gradually clogs pores and throats, leading to a significant decrease in reservoir permeability, thereby affecting oil and gas flow and recovery.

[0006] Furthermore, due to the interlayer heterogeneity of reservoirs, the distribution of fluids varies significantly during displacement processes in reservoirs with different permeabilities. This difference, coupled with different displacement methods such as CO2 flooding and waterflooding, further increases the complexity of predicting remaining oil distribution and reservoir damage. Predicting reservoir damage and remaining oil distribution during displacement is a crucial task in reservoir management. However, due to the aforementioned complex factors, these predictions become exceptionally difficult. Therefore, it is necessary to find a method for calculating the degree of asphaltene blockage during CO2 flooding, thereby evaluating the adaptability of different regions to CO2 flooding and providing a theoretical basis for optimizing CO2 displacement methods for enhanced oil and gas recovery. This will enable more accurate prediction and management of reservoir damage, optimization of displacement strategies, and improvement of oil and gas recovery. Summary of the Invention

[0007] In order to solve the above-mentioned technical problems existing in the prior art, the present invention provides a quantitative evaluation method for the degree of blockage based on bituminous precipitation, thereby solving the problem that the existing methods do not fully consider the degree of damage caused by different core samples during the CO2 displacement process, and thus providing a basis for adjusting the next development strategy.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A method for quantitatively calculating the degree of asphalt blockage in CO2-driven asphalt, comprising the following steps:

[0010] S1. Perform in-situ online NMR testing of core samples;

[0011] S1.1, Prepare the solution for saturating the core;

[0012] S1.2, Prepare saturated rock samples;

[0013] S1.3, Determine the static pore throat NMR T2 spectrum;

[0014] S1.4 Determine the T2 NMR spectrum of the CO2 displacement process;

[0015] S1.3 Measure the T2 NMR spectrum after CO2 displacement;

[0016] S2. By obtaining the static pore throat NMR T2 spectrum and the CO2 displacement process NMR T2 spectrum of different core samples, the permeability damage rate and porosity damage rate of the core samples are calculated, thereby obtaining the CO2 displacement asphaltene blockage index.

[0017] Further, step S1.1 is specifically performed as follows: Based on the collected requirements for the salinity and type of formation water in the target block, calculate the mass of solute required to prepare X ml of solution; dry the solute at 100℃~120℃ to constant weight, and cool it to room temperature (15℃~25℃) in a desiccator; pour the weighed solute into an X ml volumetric flask, and then add... Add milliliters of distilled water to the volumetric flask, shake until the solute is completely dissolved, and then add distilled water to the mark of X milliliters while shaking.

[0018] Furthermore, in step S1.2, saturated rock samples are prepared according to the method of SY / T 5336 standard.

[0019] Furthermore, the specific steps in step S1.3 are as follows:

[0020] S1.3.1 Rock Sample Measurement - Lateral Relaxation Time T2 Measurement: Place the prepared rock sample into a non-magnetic container free of hydrogen and put it into the measurement chamber; the center of the rock sample should be located at the center of the magnetic field; select the appropriate pulse sequence according to the measurement content; set the measurement system parameters and echo interval, complete recovery time, number of echoes acquired, number of scans, and receiving gain; after confirming that the current parameters are accurate, start the measurement.

[0021] S1.3.1 Measurement Result Processing: After measuring the transverse relaxation time T2 using the CPMG pulse sequence, the distribution of the transverse relaxation time T2 is obtained by the processing program.

[0022] Furthermore, the specific steps in step S1.4 are as follows:

[0023] S1.4.1 T2 spectrum determination under saturated oil conditions: After the static pore throat NMR T2 spectrum determination is completed, the core is taken out, dried, and vacuumed. Under a certain pressure, a saturated deuterium water solution is used to displace the saturated deuterium water core with crude oil from the target block, and a T2 spectrum curve of the core with bound water saturation is established.

[0024] S1.4.2 T2 spectrum determination after CO2 displacement: The core with the established bound water saturation was placed in the core holder and a CO2 oil displacement experiment was carried out at a certain displacement flow rate. After the experiment, the nuclear magnetic resonance T2 spectrum curve of the core was measured.

[0025] Furthermore, the specific steps in step S1.5 are as follows: after the displacement is completed, the oil is washed with petroleum ether and dried, then vacuumed and pressurized to saturate the formation water. After saturation, nuclear magnetic resonance scanning is performed to obtain the core pore distribution characteristics after asphaltene precipitation.

[0026] Furthermore, after obtaining the static pore throat NMR T2 spectra and the CO2 displacement process NMR T2 spectra of different cores, in step S2, NMR characteristic maps are generated using the static pore throat NMR T2 spectra and the CO2 displacement process NMR T2 spectra of different cores to compare the changes in pore size distribution between saturated cores and cores during displacement.

[0027] Furthermore, by combining the initial pore throat distribution, the pore throat distribution in the saturated oil state, and the pore throat radius distribution after the CO2 displacement, the trend of pore throat distribution change during CO2 displacement is analyzed, clarifying the impact of asphaltenes and wax blockage on pore size distribution at each stage during CO2 displacement of different cores under the same conditions.

[0028] Furthermore, the permeability damage rate and porosity damage rate of the core were calculated, and then the ratio of the permeability damage rate to the porosity damage rate of the core was obtained, which is the CO2 flooding bituminous blockage index.

[0029] Furthermore, the non-magnetic container is a glass test tube, and the measuring chamber is a core chamber or a sample chamber.

[0030] The beneficial effects of this invention are:

[0031] Compared with existing technologies, this method starts with the microscopic pore characteristics of the reservoir, uses in-situ online NMR experiments to classify and study the microscopic pore structure characteristics of reservoir cores, observes the microscopic dynamic process of CO2 displacement using representative real cores, and can quantitatively analyze the degree of asphaltenes and wax blockage at each stage. The method is simple to operate and low in cost, providing support for improving oil recovery and reducing residual oil distribution in later stages of oilfield operations. The quantitative calculation method for the degree of asphaltenes blockage during CO2 displacement described in this invention also has the following technical features or beneficial effects:

[0032] (1) Quantitative evaluation of asphaltene blockage degree: This invention provides a quantitative calculation method for the degree of asphaltene blockage during CO2 displacement based on nuclear magnetic resonance (NMR) testing. This method can accurately measure and evaluate the blockage of reservoir pores by asphaltene precipitation in different core samples during CO2 displacement. This solves the problem that existing technologies do not fully consider the degree of damage caused by different core samples during CO2 displacement, and provides more accurate data support for reservoir management.

[0033] (2) Enhanced Oil Recovery Strategy Optimization: By quantitatively evaluating the degree of asphaltene blockage, this invention helps identify areas susceptible to asphaltene precipitation during CO2 displacement, thus providing a theoretical basis for optimizing CO2 displacement enhanced oil recovery methods in the field. This helps optimize displacement strategies, reduce reservoir damage, and improve oil and gas recovery.

[0034] (3) Reduced environmental impact: CO2 enhanced oil recovery technology not only improves crude oil recovery but also achieves geological CO2 sequestration. This invention, by accurately assessing bituminous blockage, helps to utilize CO2 enhanced oil recovery technology more effectively, thereby reducing greenhouse gas emissions and environmental impact to a certain extent.

[0035] (4) Enhancing Research Level: This invention employs advanced nuclear magnetic resonance (NMR) testing technology, combined with detailed experimental procedures and data processing methods, providing a new perspective and means for the research of CO2 enhanced oil recovery technology. This helps to deepen the understanding of CO2 flow patterns in reservoirs, changes in oil and gas phases, and the precipitation mechanism of asphaltene, and promotes the further development of related research.

[0036] (5) Guiding practical applications: The technical solution of this invention is operable and practical, and can provide specific guidance and support for oilfield operations. By quantitatively evaluating the degree of asphaltene blockage, oilfield managers can more scientifically formulate and adjust development strategies, thereby improving the efficiency and effectiveness of reservoir management.

[0037] In summary, this invention provides a quantitative calculation method for the degree of CO2-driven asphaltene blockage based on nuclear magnetic resonance (NMR) testing, which offers more accurate data support for reservoir management, helps optimize displacement strategies, improve oil recovery, reduce environmental impact, and promotes further development of related research. Attached Figure Description

[0038] To more clearly illustrate the technical solutions of the embodiments of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and detailed embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0039] Figure 1 This is a schematic diagram of the CO2 displacement NMR characteristics (core No. 1) of the present invention;

[0040] Figure 2 This is a schematic diagram of the nuclear magnetic resonance characteristics (core No. 1) before and after CO2 displacement according to the present invention;

[0041] Figure 3 This is a schematic diagram of the CO2 displacement NMR characteristics (core No. 4) of the present invention;

[0042] Figure 4 This is a schematic diagram of the nuclear magnetic resonance characteristics (core No. 4) before and after CO2 displacement according to the present invention;

[0043] Figure 5 This is a schematic diagram of the CO2 displacement NMR characteristics (core No. 6) of the present invention;

[0044] Figure 6 This is a schematic diagram of the nuclear magnetic resonance characteristics (core No. 6) before and after CO2 displacement according to the present invention;

[0045] Figure 7 This is a schematic diagram of the changes in the pore throat of the three blocks before and after CO2 displacement according to the present invention;

[0046] Figure 8 This is a schematic diagram of the CO2-driven bituminous blockage index in the core of this invention. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. The following description, in conjunction with the accompanying drawings... Figures 1-8 The method for quantifying the degree of asphalt blockage caused by CO2 flooding is further explained, and the technical solutions in the embodiments of this application are clearly and completely described. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0048] To explore the potential of CO2 injection for enhanced oil recovery in certain blocks of an oilfield, a laboratory experiment on CO2 displacement using long core samples was conducted. Online nuclear magnetic resonance (NMR) technology was used to monitor the T2 spectrum of the fluid within the cores before and after the displacement experiment. By comparing the amplitude differences in the T2 spectra, the degree of blockage in the pore-throat system during bituminous and wax deposition was quantitatively calculated, thereby determining the degree of damage in different core samples. This provides a theoretical basis for optimizing CO2 displacement methods for enhanced oil recovery in the field.

[0049] Example 1

[0050] This invention provides a method for in-situ online nuclear magnetic resonance (NMR) experiments and quantitative analysis of core samples to more accurately quantitatively analyze the deposition patterns of asphaltene and wax after the reaction of CO2 with crude oil. The overall technical solution is based on the physical properties of real core samples, selecting core sample preparation components with desired properties. A GeoSpec-53 NMR spectrometer is used to measure the resonance and signal generation characteristics of hydrogen nuclei in water within the rock in a magnetic field. Based on the decay and relaxation time relationship of hydrogen atoms under low-field conditions, parameters such as rock porosity and pore distribution can be quickly obtained through mathematical inversion. The NMR T2 spectrum is recorded and analyzed to obtain the variation law of pore throat radius in the core sample under different conditions. This method can clearly record the changes in pore throat during displacement, facilitating the quantitative analysis of the degree of blockage.

[0051] To achieve the above objectives, this invention provides a method for evaluating the adaptability of CO2 flooding based on asphaltene precipitation, which mainly includes the following steps:

[0052] (1) The specific steps for in-situ online NMR testing of core samples are as follows:

[0053] ①Preparation of solutions for saturated core samples

[0054] Based on the required salinity and type of formation water collected from the target block, the mass of solute needed to prepare 2000 mL of solution was calculated. The solute was dried to constant weight at 100℃–120℃ and then cooled to room temperature (15℃–25℃) in a desiccator. The weighed solute was poured into a 2000 mL volumetric flask, and approximately 1000 mL of distilled water was added. The flask was gently shaken until the solute was completely dissolved. Then, while shaking, distilled water was added to the 2000 mL mark to obtain a saturated solution.

[0055] ② Preparation of saturated rock samples

[0056] Saturated rock samples were prepared according to the method specified in SY / T 5336.

[0057] ③ Static pore throat T2 NMR spectrum determination

[0058] 1) Rock sample measurement - transverse relaxation time T2 measurement

[0059] Place the prepared rock sample into a non-magnetic container (such as a glass test tube) free of hydrogen and put it into the measurement chamber (core chamber or sample chamber). The center of the rock sample should be located at the center of the magnetic field. Select the appropriate pulse sequence according to the measurement content (for MARAN type instruments: use the CPMG pulse sequence to measure transverse relaxation time). Set the measurement system parameters and acquisition parameters such as echo interval, complete recovery time, number of acquired echoes, number of acquisition scans, and receiver gain. After confirming that the current parameters are accurate, start the measurement.

[0060] 2) Measurement result processing

[0061] After measuring the transverse relaxation time T2 using the CPMG pulse sequence, the distribution of the transverse relaxation time T2 is obtained by a processing program (such as WinDxp used by MARAN type instruments).

[0062] ④ Determination of T2 NMR spectrum during CO2 displacement process

[0063] 1) T2 spectrum determination under saturated oil conditions

[0064] After the static pore throat NMR T2 spectrum measurement was completed, the core was taken out, dried, and vacuumed. The core was then saturated with deuterium water at 23 MPa and replaced with crude oil from the target block. The T2 spectrum curve of the core was established based on the determination of bound water saturation.

[0065] 2) T2 spectrum determination after CO2 displacement is completed

[0066] The core with the bound water saturation was placed in the core holder and a CO2 flooding experiment was carried out at a displacement flow rate of 0.1 ml / min. After the experiment, the nuclear magnetic resonance T2 spectrum curve of the core was measured.

[0067] ⑤ NMR T2 spectrum determination after CO2 displacement

[0068] After displacement, the oil was washed with petroleum ether (asphaltite is insoluble in petroleum ether) and dried. The formation water was then re-vacuumed and pressurized to saturate. After saturation, nuclear magnetic resonance (NMR) scanning was performed to obtain the core pore distribution characteristics after asphaltite precipitation.

[0069] (2) Experimental Data Analysis

[0070] Static pore throat NMR T2 spectra and CO2 displacement process NMR T2 spectra of different cores were obtained, and NMR characteristic maps were plotted to compare the changes in pore size distribution of saturated cores and cores during displacement.

[0071] By combining the initial pore throat distribution, the pore throat distribution in the saturated oil state, and the pore throat radius distribution after the CO2 displacement, the trend of pore throat distribution change during CO2 displacement is analyzed, clarifying the impact of asphaltenes and wax blockage on pore size distribution at each stage during CO2 displacement of different cores under the same conditions.

[0072] The permeability damage rate and porosity damage rate of the core were calculated. This patent innovatively proposes a CO2 flooding bituminous plugging index for cores, which is the ratio of the permeability damage rate to the porosity damage rate of the core. The larger the ratio, the greater the permeability damage under the unit porosity damage condition, thereby evaluating the adaptability of different cores to CO2 flooding.

[0073] Example 2

[0074] This embodiment, in conjunction with the accompanying drawings, clearly and completely describes the technical solutions of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0075] Figure 1 A schematic diagram of a nuclear magnetic resonance (NMR) experimental measurement instrument for rock samples, representing an exemplary embodiment of the present invention, is shown. The steps of the invention are described below using an example based on a CO2 displacement physics simulation experiment and online NMR technology and quantitative analysis.

[0076] Step (1): Taking a certain block in an oilfield as an example, crude oil samples were taken from the wellheads of blocks Y, P, and J, and simulated oil was prepared based on the gas-oil ratio; the experimental cores were taken from the core bank, and the cores were washed and cut; the experimental formation water was prepared in the laboratory according to the formation water composition. In this embodiment, seven columnar samples of the original cores were selected, numbered 1, 2, 3, 4, 5, 6, and 7. After washing, the porosity and permeability of the cores were tested, and the core parameters under in-situ online NMR testing are shown in Table 1.

[0077] Table 1 Core parameters obtained from NMR tests

[0078]

[0079] Step (2): Based on the required mineralization and type of the formation water collected from Block Y, calculate the mass of solute needed to prepare 2000 mL of solution. Dry the solute at 100℃~120℃ to constant weight and cool it to room temperature (15℃~25℃) in a desiccator. Pour the weighed solute into a 2000 mL volumetric flask, add approximately 1000 mL of distilled water, and gently shake the flask until the solute is completely dissolved. Then, while shaking, add distilled water to the 2000 mL mark to obtain a saturated solution. Prepare 7 saturated rock samples according to the method specified in SY / T 5336.

[0080] Step (3): Place the prepared rock sample into a non-magnetic container (such as a glass test tube) free of hydrogen and put it into the measurement chamber (core chamber or sample chamber). The center of the rock sample should be located at the center of the magnetic field. After confirming that the current parameters are accurate, start the measurement and obtain the static pore throat characteristics of the NMR T2 spectrum, as shown below. Figure 2 , 3 As shown in Figure 4, the static characteristics of the T2 NMR spectra of cores with different permeabilities in blocks Y, P, and J are as follows: the presence of single and double peaks in the T2 spectra indicates strong heterogeneity among the cores; the double-peak structure of the T2 NMR spectra of the rock samples in the three blocks indicates poor core sorting; the volume of small pore throats with pore throat radii of 0.01–0.1 μm accounts for 48.58%, 53.52%, and 24.96% of the total pore throat volume, respectively.

[0081] Step (4): After the static pore throat NMR T2 spectrum measurement is completed, the core is taken out, dried, and vacuumed. The core is then saturated with deuterium water at 23 MPa and replaced with crude oil from block Y to establish the T2 spectrum curve of the core for measuring the saturation of bound water.

[0082] Step (5): Place the core sample with the established bound water saturation into the core holder and conduct a CO2 flooding experiment at a displacement flow rate of 0.1 ml / min. After the experiment, measure the nuclear magnetic resonance T2 spectrum curve of the core sample. Establish a comparison diagram of the T2 spectrum distribution curves in the initial state, saturated oil state, and CO2 flooding end state, as shown below.Figure 5 , 6 7. The T2 NMR characteristics of CO2 displacement cores from blocks Y, P, and J at different permeabilities show that the average bound water saturation of the cores in the three blocks is 25.6%, 39.30%, and 25.92%, respectively; and the oil displacement efficiencies are 67.29%, 68.45%, and 74.73%, respectively.

[0083] Step (6): After displacement, the oil was washed with petroleum ether (asphaltene is insoluble in petroleum ether) and dried. The formation water was then re-vacuumed and pressurized. After saturation, nuclear magnetic resonance (NMR) scanning was performed to obtain the core pore distribution characteristics after asphaltene precipitation. A comparison of T2 spectrum distribution curves before and after CO2 displacement was established, as shown in the figure. The NMR characteristics of T2 spectra before and after CO2 displacement of cores with different permeabilities in blocks Y, P, and J show that: in block Y, after CO2 displacement, the proportion of macropore throats decreased by 1.07%, mesopore throats decreased by 1.03%, micropore throats increased by 0.61%, and micropore throats increased by 1.50%; in block P, after CO2 displacement, the proportion of macropore throats decreased by 2.44%, mesopore throats decreased by 1.38%, micropore throats increased by 1.79%, and micropore throats increased by 2.04%; in block J, after CO2 displacement, the proportion of macropore throats decreased by 0.42%, mesopore throats decreased by 0.05%, micropore throats increased by 0.27%, and micropore throats increased by 0.19%.

[0084] Step (7): After measuring the permeability and porosity of the core sample following the CO2 displacement experiment, and comparing them with the initial permeability and porosity, the permeability damage rate and porosity damage rate of the core sample are quantitatively calculated. The formula for calculating the permeability damage rate is as follows: Where: a - core permeability damage rate, %, K1 - permeability before experiment, mD, K2 - permeability after experiment, mD; the formula for calculating porosity damage rate is: b - Core porosity damage rate, % -Porosity of the core sample before testing, %; - Porosity after core experiments, %. Calculations show that the permeability damage rate of core samples from block Y is 12.51%, and the porosity damage rate is 4.41%; the permeability damage rate of core samples from block P is 10.08%, and the porosity damage rate is 4.05%; and the permeability damage rate of core samples from block J is 4.89%, and the porosity damage rate is 2.62%.

[0085] Finally, the CO2-driven asphalt clogging index was calculated.

[0086]

[0087] c-CO2-driven asphaltene blockage index;

[0088] a-Core permeability damage rate;

[0089] b - Core porosity damage rate.

[0090] The CO2 flooding bituminous plugging indices of the seven core samples were 3.39, 2.77, 2.32, 2.3, 2.67, 2.06, and 2.08, respectively. The CO2 flooding bituminous plugging indices for blocks Y, P, and J were 2.82, 2.485, and 2.07, respectively. This is because the bituminous precipitation after CO2 flooding led to different levels of pore-throat damage in the three blocks, resulting in varying degrees of permeability impairment. Figure 7 As can be seen, this is because after CO2 displacement in block Y, the proportion of macropore throats in the core decreased by 1.07%, mesopore throats decreased by 1.03%, micropore throats increased by 0.61%, and micropore throats increased by 1.50%. The decrease in macropore throats and mesopore throats was more significant, while the increase in micropore throats was more significant, resulting in greater damage to permeability. After CO2 displacement in block P, the proportion of macropore throats in the core decreased by 2.44%, mesopore throats decreased by 1.38%, micropore throats increased by 1.79%, and micropore throats increased by 2.04%. Block P had the largest decrease in macropore throats and mesopore throats and the largest increase in micropore throats. After CO2 displacement in block J, the proportion of macropore throats in the core decreased by 0.42%, mesopore throats decreased by 0.05%, micropore throats increased by 0.27%, and micropore throats increased by 0.19%. Block J had the smallest decrease in macropore throats and mesopore throats and the smallest increase in micropore throats. Block Y exhibits the highest CO2 flooding asphaltene blockage index. Combined with the variation in the proportion of different pore throat levels observed in the experiment, this indicates that this block generates the highest permeability damage rate per unit porosity damage rate. Block P shows the second highest CO2 flooding asphaltene blockage index, while Block J has the lowest. Therefore, Block Y is the least adaptable to CO2 flooding, followed by Block P, and Block J is the most adaptable. This aligns with the reservoir damage assessment results in the industry standard SY / T 5358-2010 "Evaluation Method for Reservoir Sensitivity Flow Experiments." The CO2 flooding asphaltene blockage index evaluation further refines the adaptability of different blocks to CO2 flooding.

[0091] 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 equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for quantitatively calculating the degree of asphalt blockage in CO2-driven asphalt, characterized in that, The steps are as follows: S1. Perform in-situ online NMR testing of core samples; S1.1, Prepare the solution for saturating the core; S1.2, Prepare saturated rock samples; S1.3, Determine the static pore throat NMR T2 spectrum; S1.4 Determine the T2 NMR spectrum of the CO2 displacement process; S1.3 Measure the T2 NMR spectrum after CO2 displacement; S2. By obtaining the static pore throat NMR T2 spectrum and the CO2 displacement process NMR T2 spectrum of different core samples, the permeability damage rate and porosity damage rate of the core samples are calculated, thereby obtaining the CO2 displacement asphaltene blockage index.

2. The method for quantitatively calculating the degree of CO2-driven asphalt blockage as described in claim 1, characterized in that, Step S1.1 is specifically performed as follows: Based on the collected requirements for the salinity and type of formation water in the target block, calculate the mass of solute required to prepare X ml of solution; dry the solute at 100℃~120℃ to constant weight, and cool it to room temperature (15℃~25℃) in a desiccator; pour the weighed solute into an X ml volumetric flask, and then add... Add milliliters of distilled water to the volumetric flask, shake until the solute is completely dissolved, and then add distilled water to the mark of X milliliters while shaking.

3. The method for quantitatively calculating the degree of CO2-driven asphalt blockage as described in claim 1, characterized in that, In step S1.2, saturated rock samples are prepared according to the method of SY / T 5336 standard.

4. The method for quantitatively calculating the degree of CO2-driven asphalt blockage as described in claim 1, characterized in that, The specific steps in step S1.3 are as follows: S1.3.1 Rock Sample Measurement—Transverse Relaxation Time T2 Measurement: Place the prepared rock sample into a non-magnetic container free of hydrogen and put it into the measurement chamber; the center of the rock sample should be located at the center of the magnetic field; select the appropriate pulse sequence according to the measurement content; set the measurement system parameters and echo interval, complete recovery time, number of echoes acquired, number of scans, and receiving gain; after confirming that the current parameters are accurate, start the measurement. S1.3.1 Measurement Result Processing: After measuring the transverse relaxation time T2 using the CPMG pulse sequence, the distribution of the transverse relaxation time T2 is obtained by the processing program.

5. The method for quantitatively calculating the degree of CO2-driven asphalt blockage as described in claim 1, characterized in that, The specific steps in step S1.4 are as follows: S1.4.1 T2 spectrum determination under saturated oil conditions: After the static pore throat NMR T2 spectrum determination is completed, the core is taken out, dried, and vacuumed. Under a certain pressure, a saturated deuterium water solution is used to displace the saturated deuterium water core with crude oil from the target block, and a T2 spectrum curve of the core with bound water saturation is established. S1.4.2 T2 spectrum determination after CO2 displacement: The core with the established bound water saturation was placed in the core holder and a CO2 oil displacement experiment was carried out at a certain displacement flow rate. After the experiment, the nuclear magnetic resonance T2 spectrum curve of the core was measured.

6. The method for quantitatively calculating the degree of CO2-driven asphalt blockage as described in claim 1, characterized in that, The specific steps in step S1.5 are as follows: After the displacement is completed, the oil is washed with petroleum ether and dried. The formation water is then re-vacuumed and pressurized to saturate. After saturation, nuclear magnetic resonance scanning is performed to obtain the core pore distribution characteristics after asphaltene precipitation.

7. The method for quantitatively calculating the degree of CO2-driven asphalt blockage as described in any one of claims 1-6, characterized in that, After obtaining the static pore throat NMR T2 spectra and the CO2 displacement process NMR T2 spectra of different cores, in step S2, NMR characteristic maps are generated using the static pore throat NMR T2 spectra and the CO2 displacement process NMR T2 spectra of different cores to compare the changes in pore size distribution of saturated cores and cores during displacement.

8. The method for quantitatively calculating the degree of CO2-driven asphalt blockage as described in claim 7, characterized in that, By combining the initial pore throat distribution, the pore throat distribution in the saturated oil state, and the pore throat radius distribution after the CO2 displacement, the trend of pore throat distribution change during CO2 displacement is analyzed, clarifying the impact of asphaltenes and wax blockage on pore size distribution at each stage during CO2 displacement of different cores under the same conditions.

9. The method for quantitatively calculating the degree of CO2-driven asphalt blockage as described in claim 7, characterized in that, The permeability damage rate and porosity damage rate of the core were calculated, and then the ratio of the permeability damage rate to the porosity damage rate of the core was obtained, which is the CO2 flooding bituminous blockage index.

10. The method for quantitatively calculating the degree of CO2-driven asphalt blockage as described in claim 4, characterized in that, The non-magnetic container is a glass test tube, and the measuring chamber is a core chamber or a sample chamber.

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