Method for analyzing pore diameter change of sandstone in acidic salt water reservoir based on nuclear magnetic resonance technology

Abstract

The invention provides a method for analyzing the pore diameter change of sandstone in an acidic saline water reservoir based on a nuclear magnetic resonance technology, and belongs to the technical field of CO2 geological sequestration. The method comprises the following steps: drying a sandstone core sample with target characteristics in a target area, and performing deionized water saturation treatment to obtain a first saturated sandstone core sample; performing a nuclear magnetic resonance test on the sandstone core sample after the first saturation to obtain a nuclear magnetic resonance test result before the reaction; drying the sandstone core sample after the first saturation, and placing the sandstone core sample under the simulated formation condition of the target area for reaction to obtain a reacted sandstone core sample; drying the reacted sandstone core sample, and performing saturation treatment to obtain a sandstone core sample after second saturation; performing a nuclear magnetic resonance test on the sandstone core sample after the second saturation to obtain a nuclear magnetic resonance test result after the reaction; and generating an analysis result of the pore diameter change rule of the sandstone core sample under the simulated formation condition by using the nuclear magnetic resonance test results before and after the reaction.

Description

Technical Field

[0001] The present invention relates to the technical field of CO2 geological storage, and in particular to a method for analyzing pore size changes of sandstone in acidic saline water reservoirs based on nuclear magnetic resonance technology. Background Art

[0002] CO2 geological storage is a more direct and cost-effective way to reduce CO2 emissions. At present, sandstone is a critical reservoir rock in CO2 geological storage technology. Sandstone is generally composed of quartz particles with high chemical stability and unstable geological minerals, such as feldspar and mica. Quartz has high chemical stability and is not easily corroded by acidic solutions, while minerals such as feldspar and mica are sensitive to acidic solutions. When encountering acidic conditions, acid corrosion may occur, resulting in the destruction or dissolution of the rock.

[0003] During the CO2 injection process, CO2 reacts with water to generate carbonic acid, which is easily decomposed into hydrogen ions, bicarbonate ions and carbonate ions under reservoir conditions, thus forming acidic conditions, causing chemical reactions between rock mineral components and acidic solutions, affecting the pore structure of the core, thereby affecting the porosity and permeability of the core, and further affecting the storage capacity of CO2. Therefore, providing an accurate and simple method to study the pore size change law of sandstone in acidic saline reservoirs is particularly important for studying the CO2 geological storage process. Summary of the invention

[0004] In view of this, in order to at least partially solve at least one of the above-mentioned technical problems, the present invention provides a method for analyzing pore size changes of acidic saline reservoir sandstone based on nuclear magnetic resonance technology.

[0005] According to an embodiment of one aspect of the present invention, a method for analyzing pore size changes in sandstone in an acidic saline reservoir based on nuclear magnetic resonance technology is provided, comprising: drying a sandstone core sample having target characteristics in a target area, and then saturating it with deionized water to obtain a first saturated sandstone core sample; performing a nuclear magnetic resonance test on the first saturated sandstone core sample to obtain a nuclear magnetic resonance test result before the reaction; drying the first saturated sandstone core sample, and placing it under simulated formation conditions for the target area for a preset reaction time to obtain a reacted sandstone core sample, wherein the simulated formation conditions include a simulated acidic saline solution, a simulated temperature, and a simulated pressure; drying the reacted sandstone core sample, and then saturating it with deionized water to obtain a second saturated sandstone core sample; performing a nuclear magnetic resonance test on the second saturated sandstone core sample to obtain a post-reaction nuclear magnetic resonance test result; and using the pre-reaction nuclear magnetic resonance test result and the post-reaction nuclear magnetic resonance test result to generate an analysis result of the pore size change law of the sandstone core sample under the simulated formation conditions.

[0006] According to an embodiment of the present invention, the method further comprises: configuring a simulated acidic saline solution according to formation water quality conditions in the target area; and determining a simulated temperature and a simulated pressure according to formation temperature and formation pressure in the target area.

[0007] According to an embodiment of the present invention, the simulated acidic saline solution is configured using the following steps: a NaCl solution with a mass concentration of 35 g / L is configured, and the pH value of the NaCl solution is adjusted to a preset value using the acidic solution to obtain a simulated acidic saline solution, wherein the preset value is determined according to the acidity of the formation water quality in the target area.

[0008] According to an embodiment of the present invention, the acidic solution includes a nitric acid solution or a hydrochloric acid solution.

[0009] According to an embodiment of the present invention, the concentration range of the nitric acid solution or the hydrochloric acid solution is 40-50 g / L.

[0010] According to an embodiment of the present invention, the nuclear magnetic resonance test results before the reaction include a nuclear magnetic resonance imaging image (MRI imaging image) and a transverse relaxation time curve (T2 curve) of the sandstone core sample before the reaction; the nuclear magnetic resonance test results after the reaction include a nuclear magnetic resonance imaging image (MRI imaging image) and a transverse relaxation time curve (T2 curve) of the sandstone core sample after the reaction.

[0011] According to an embodiment of the present invention, the analysis results of the pore size change law include at least one of the following: the pore distribution change results of the sandstone core sample before the reaction and the sandstone core sample after the reaction; the pore structure change results of the sandstone core sample before the reaction and the sandstone core sample after the reaction.

[0012] According to an embodiment of the present invention, the method further includes: after drying the sandstone core sample with target characteristics in the target area, saturating it with deionized water, and before obtaining the first saturated sandstone core sample, cleaning the sandstone core sample with deionized water.

[0013] According to an embodiment of the present invention, the above method also includes: before using deionized water to clean the sandstone core sample, cutting the sandstone with target characteristics according to a preset size to obtain a sandstone core sample, wherein the preset size is determined according to the nuclear magnetic resonance testing equipment used for the nuclear magnetic resonance test.

[0014] According to an embodiment of the present invention, the target characteristics include at least one of the following: rock strength is lower than a first value, mud content is greater than a second value, and cement content is less than a third value.

[0015] According to an embodiment of the present invention, a nuclear magnetic resonance test is performed on a sandstone core sample before the reaction to obtain a nuclear magnetic resonance test result before the reaction, and then the formation conditions of the target area are simulated, and the sandstone core sample before the reaction is placed under the simulated formation conditions for a period of time, and then a nuclear magnetic resonance test is performed on the sandstone core sample after the reaction to obtain a nuclear magnetic resonance test result after the reaction, and finally, the law of pore size change of the acidic saltwater reservoir sandstone is analyzed in combination with the nuclear magnetic resonance test results before and after the reaction. The law of sandstone pore size change can provide an important reference for the CO2 geological storage process in the target area from the perspective of chemical reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

[0017] Figure 1 The present invention is a flowchart of a method for analyzing pore size changes of sandstone in acidic saline reservoirs based on nuclear magnetic resonance technology according to an embodiment of the present invention.

[0018] Figure 2 Schematic diagram of the structure of a high-temperature and high-pressure reactor according to an embodiment of the present invention.

[0019] Figure 3 It is a magnetic resonance imaging image (MRI imaging image) according to an embodiment of the present invention.

[0020] Figure 4 is a transverse relaxation time curve (T2 curve) according to an embodiment of the present invention.

[0021] Reference numerals:

[0022] 211: Intake valve;

[0023] 212: air release valve;

[0024] 213: Gas booster system;

[0025] 214: Gas tank;

[0026] 221: Electric motor;

[0027] 222: Rotating piece;

[0028] 231: reactor chamber;

[0029] 232: Constant temperature heating layer;

[0030] 233: cup holder;

[0031] 234: Sample;

[0032] 241: sampling valve;

[0033] 242: Sampling beaker. DETAILED DESCRIPTION

[0034] Below, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present invention. In the following detailed description, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of embodiments of the present invention. However, it is apparent that one or more embodiments may also be implemented without these specific details. In addition, in the following description, descriptions of known structures and technologies are omitted to avoid unnecessary confusion of concepts of the present invention.

[0035] The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. The term "comprising" used herein indicates the existence of features, steps, operations, but does not exclude the existence or addition of one or more other features.

[0036] In the case of using expressions such as "at least one of A, B, and C, etc.", it should generally be interpreted in accordance with the meaning of the expression generally understood by those skilled in the art (for example, "a system having at least one of A, B, and C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.). In the case of using expressions such as "at least one of A, B, or C, etc.", it should generally be interpreted in accordance with the meaning of the expression generally understood by those skilled in the art (for example, "a system having at least one of A, B, or C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.).

[0037] It should be explained that acid saline reservoir is a common term in CO2 storage, oil and gas exploration or environmental science. Its specific meaning needs to be understood in the context of geology, chemistry and engineering. The following is a detailed analysis:

[0038] 1. Basic definition: Acidic saline reservoirs refer to underground rock pores or fractures with high salinity (salty water) and acidic gases, which can store and allow fluids (water, oil and gas, etc.) to flow. Such reservoirs are usually related to oil and gas reservoirs, geothermal resources or deep groundwater systems. Their "acidic" characteristics mainly come from dissolved acidic gases (such as hydrogen sulfide H2S, carbon dioxide CO2, etc.), rather than the strong acidity of the water itself (the pH value may be close to neutral or weak acidity).

[0039] Formation mechanism: In anoxic environments, microorganisms decompose organic matter to produce CO2 or H2S. Sulfide minerals (such as pyrite) are oxidized to produce sulfuric acid (H2SO4). Magmatic activity or hydrothermal activity releases acidic gases such as CO2 and H2S. Evaporation of water in closed basins leads to salt enrichment (such as salt lake deposition). Seawater in coastal areas infiltrates underground aquifers. Salt rocks (such as rock salt and gypsum) in the strata dissolve and release Cl - 、Na + , Ca 2+ Plasma.

[0040] 3. Engineering and environmental significance: Acidic saline reservoirs have the advantage of high storage capacity as potential storage sites. + , Ca 2+ Mg 2+ Plasma) can dissolve with CO2 to generate HCO3 - Combined with each other, the formation of stable carbonate minerals (such as calcite and dolomite) can achieve long-term mineral storage. The reservoir has a certain porosity and permeability and can accommodate a large amount of supercritical CO2. The low pH environment of the reservoir itself may accelerate the reaction of CO2 with rock minerals (such as the dissolution of feldspar and clay minerals), thereby enhancing the efficiency of mineral storage. 2+ Mg 2+ ) can dissolve with CO2 to produce H + Exchange occurs, further promoting carbonate precipitation. Acidic saline water reservoirs are mostly found in deep sedimentary basins (such as abandoned oil and gas fields, deep brine layers), far away from human activities, and have high storage safety.

[0041] Acidic saline reservoirs are complex geological-chemical systems, and their research involves multiple fields such as CO2 storage and oil and gas exploration. Understanding their characteristics is of great significance for reducing engineering risks, formulating pollution prevention and control strategies, and developing new resources.

[0042] At present, CO2 geological storage is the most direct and cost-effective way to reduce CO2 emissions. Loose sandstone is a critical reservoir rock in CO2 geological storage technology. Due to its geological characteristics, loose sandstone has a lower rock strength. This rock is usually located in shallower formations, so it is subject to less pressure from the overlying rocks and has a weaker compaction effect. Due to poor sorting, loose sandstone is mainly mud-cemented, and the strength of this cementation is relatively weak. The combined effect of these factors makes loose sandstone easy to break when subjected to external stress, and acid corrosion may occur when encountering acidic conditions, leading to rock destruction and dissolution. In addition, sandstone may also contain pores and microcracks, which will expand under acidic solutions, further increasing the erosion rate of the rock.

[0043] When sandstone encounters an acidic solution, the first thing that happens is the chemical reaction between the acid and the mineral. For example, the hydrogen ions in the acidic solution will combine with the hydroxide bonds on the surface of the mineral to trigger the dissolution of the hydrogen ions, thereby reducing the volume of the mineral. At the same time, the hydrogen ions in the acidic solution will also react with the metal ions in the mineral to form soluble metal salts. These chemical reactions will lead to the dissolution and destruction of sandstone. Through optical microscopic observation, it was found that during the acid corrosion process, pores and caves of various shapes will form on the surface of the mineral. These pores and caves have different shapes and sizes, such as spherical pores, linear cracks, etc., which depends on the permeability and rate of acid corrosion. In addition, the bonding phase between the individual mineral particles in the sandstone will also be corroded, resulting in a loose structure between the particles. Therefore, under acidic conditions, the chemical reaction between the rock mineral components and the solution will affect the pore structure of the core, and then affect the porosity and permeability of the core.

[0044] In the process of realizing the concept of the present invention, the inventors found that during the injection of CO2 into the reservoir, CO2 reacts with water to generate carbonic acid, which is easily decomposed into hydrogen ions, bicarbonate ions and carbonate ions under reservoir conditions to form acidic conditions, causing a chemical reaction between the rock mineral components and the acidic solution, affecting the pore structure of the core, thereby affecting the porosity and permeability of the core, and further affecting the storage amount of CO2.

[0045] Based on this, the present invention provides a method for analyzing the pore size change law of acidic saline water reservoir sandstone based on nuclear magnetic resonance technology, by performing nuclear magnetic resonance test on the sandstone core sample before reaction to obtain the nuclear magnetic resonance test result before reaction, then simulating the formation conditions of the target area, placing the sandstone core sample before reaction under the simulated formation conditions for a period of time, then performing nuclear magnetic resonance test on the sandstone core sample after reaction to obtain the nuclear magnetic resonance test result after reaction, and finally combining the nuclear magnetic resonance test results before and after reaction to analyze the pore size change law of acidic saline water reservoir sandstone. This method can provide an important reference for the CO2 geological storage process from the perspective of chemical reaction.

[0046] Figure 1 The present invention is a flowchart of a method for analyzing pore size changes of sandstone in acidic saline reservoirs based on nuclear magnetic resonance technology according to an embodiment of the present invention.

[0047] like Figure 1 As shown, the method for analyzing pore size changes of acidic saline reservoir sandstone based on nuclear magnetic resonance technology in this embodiment includes operations S110 to S160.

[0048] In operation S110, the sandstone core sample with target characteristics in the target area is dried and then saturated with deionized water to obtain a first saturated sandstone core sample.

[0049] In operation S110, the target feature may be a feature of loose sandstone, for example, the target feature includes at least one of the following: rock strength is lower than a first value, mud content is greater than a second value, and cement content is less than a third value. The first value, the second value, and the third value may be set according to actual needs.

[0050] According to an embodiment of the present invention, in operation S110, drying the sandstone core sample may be placing the sandstone core sample in a drying machine and drying it at a set temperature, such as 100° C., until the sandstone core sample is completely dried. After the drying is completed, the sandstone core sample is taken out and allowed to cool naturally to room temperature. At this time, the sandstone core sample is considered to be in a dry state and is ready for subsequent experiments.

[0051] According to an embodiment of the present invention, in operation S110, the deionized water saturation treatment may be to repeatedly saturate the sandstone core sample with deionized water using a vacuum pressurization device, which may specifically include: (1) preparing the vacuum pressurization saturation device: checking whether the sealing and pressure system of the vacuum pressurization saturation device are normal to ensure that the device can operate normally. At the same time, preparing the required deionized water to ensure that its purity meets the experimental requirements. (2) installing the sandstone core sample: installing the dried sandstone core sample in the vacuum pressurization saturation device to ensure that the sandstone core sample is firmly installed and the connection with the device is well sealed to avoid leakage during the saturation process. (3) setting the saturation conditions: according to the experimental requirements, the pressure of the vacuum pressurization saturation device is set to, for example, 21 MPa. Before starting the saturation, the device is first vacuumed to remove the air in the device to ensure that the deionized water can fully enter the core pores during the saturation process. (4) sandstone core saturation process: at the set pressure, deionized water is injected into the vacuum pressurization saturation device to fully saturate the sandstone core sample with deionized water at a pressure of 21 MPa. The saturation time is 12 hours, during which the pressure of the device is ensured to remain stable to ensure the saturation effect. After the saturation is completed, the device is closed and the sandstone core sample after the first saturation is taken out.

[0052] In operation S120, a nuclear magnetic resonance test is performed on the sandstone core sample after the first saturation to obtain a nuclear magnetic resonance test result before the reaction.

[0053] The NMR test results before the reaction may include a NMR image (MRI image) and a transverse relaxation time curve (T2 curve) of the sandstone core sample before the reaction. In step S120, the NMR test of the sandstone core sample after the first saturation may include: (1) checking the performance of the NMR test equipment to ensure that the various parameters of the equipment are set accurately and the test can be performed normally. At the same time, prepare relevant test accessories and recording equipment so that the test data can be accurately recorded during the test. (2) Installing the sandstone core sample: Install the sandstone core sample after the first saturation on the sample rack of the NMR test equipment to ensure that the sandstone core sample is installed in the correct position and can be well matched with the magnetic field and detector components of the equipment. (3) Performing a NMR test: Start the NMR test equipment and perform the test according to the operating procedures of the equipment. During the test, the equipment will automatically collect the NMR signal of the sandstone core sample and generate a NMR image (MRI image) and a transverse relaxation time curve (T2 curve). After the test is completed, the test results, i.e., the nuclear magnetic resonance test results before the reaction, are saved, and the nuclear magnetic resonance imaging (MRI imaging) and transverse relaxation time curve (T2 curve) are preliminarily analyzed to record the pore size distribution characteristics and pore structure information of the sandstone core sample at the first saturation.

[0054] In operation S130, the first saturated sandstone core sample is dried and then placed under simulated formation conditions for the target area to react for a preset time to obtain a reacted sandstone core sample, wherein the simulated formation conditions include simulated acidic saline solution, simulated temperature and simulated pressure.

[0055] The preset time can be set according to actual needs, for example, the preset time can be 14 days, 30 days, etc. The simulated acidic saline solution can be the same as the formation water quality condition of the target area, the simulated temperature can be the same as the formation temperature of the target area, and the simulated pressure can be the same as the formation pressure of the target area.

[0056] According to an embodiment of the present invention, operation S130 may be performed in a high-temperature and high-pressure reactor, and may specifically include: (1) placing a reaction solution and installing a sandstone core sample: pouring the prepared simulated acidic salt water solution into the reactor, and then placing the sandstone core sample on the sample rack in the reactor, ensuring that the sandstone core sample is completely immersed in the solution. After installing the sandstone core sample, seal the reactor to ensure that its sealing performance is good. (2) Setting reaction conditions: setting the temperature of the reactor to the simulated temperature and the pressure to the simulated pressure. After setting the reaction conditions, start the reactor to react according to the set conditions. (3) Monitoring the reaction process: during the reaction process, regularly record the changes in parameters such as the temperature and pressure of the reactor to ensure the stability and safety of the reaction process. The reaction time may be 400 hours. During this period, the operating status of the reactor should be closely monitored, and any abnormal situation should be handled in a timely manner. (4) End of reaction and sample removal: after the reaction is completed, close the reactor and wait for it to cool naturally to room temperature. Then open the reactor and carefully remove the sandstone core sample, taking care to prevent the sandstone core sample from being affected by external factors and changing. The sandstone core samples taken out were numbered and marked for subsequent experimental operations and result analysis.

[0057] In operation S140, the reacted sandstone core sample is dried and then saturated with deionized water to obtain a second saturated sandstone core sample.

[0058] According to an embodiment of the present disclosure, the drying process and the deionized water saturation process of operation S140 are the same as the drying process and the deionized water saturation process of the above-mentioned operation S110 , and are not described in detail herein.

[0059] In operation S150, a nuclear magnetic resonance test is performed on the sandstone core sample after the second saturation to obtain a nuclear magnetic resonance test result after the reaction.

[0060] In operation S150, performing a nuclear magnetic resonance test on the sandstone core sample after the second saturation may include: (1) checking the performance of the nuclear magnetic resonance test equipment to ensure that the various parameters of the equipment are set accurately and the test can be performed normally. At the same time, prepare relevant test accessories and recording equipment so that the test data can be accurately recorded during the test. (2) Installing the sandstone core sample: Install the sandstone core sample after the second saturation on the sample rack of the nuclear magnetic resonance test equipment to ensure that the sandstone core sample is installed in the correct position and can cooperate well with the magnetic field and detector components of the equipment. (3) Performing a nuclear magnetic resonance test: Start the nuclear magnetic resonance test equipment and perform the test according to the operating procedures of the equipment. During the test, the equipment will automatically collect the nuclear magnetic resonance signal of the sandstone core sample and generate a nuclear magnetic resonance imaging image (MRI imaging image) and a transverse relaxation time curve (T2 curve). After the test is completed, the test results, i.e. the nuclear magnetic resonance test results after the reaction, are saved, and the nuclear magnetic resonance imaging (MRI imaging) and transverse relaxation time curve (T2 curve) are preliminarily analyzed to record the pore size distribution characteristics and pore structure information of the sandstone core sample at the second saturation.

[0061] In operation S160, the analysis results of the pore size variation law of the sandstone core sample under the simulated formation conditions are generated by using the nuclear magnetic resonance test results before the reaction and the nuclear magnetic resonance test results after the reaction.

[0062] According to an embodiment of the present invention, the analysis results of the pore size change law include at least one of the following: the pore distribution change results of the sandstone core sample before the reaction and the sandstone core sample after the reaction; the pore structure change results of the sandstone core sample before the reaction and the sandstone core sample after the reaction.

[0063] According to an embodiment of the present invention, a nuclear magnetic resonance test is performed on a sandstone core sample before the reaction to obtain a nuclear magnetic resonance test result before the reaction, and then the formation conditions of the target area are simulated, and the sandstone core sample before the reaction is placed under the simulated formation conditions for a period of time, and then a nuclear magnetic resonance test is performed on the sandstone core sample after the reaction to obtain a nuclear magnetic resonance test result after the reaction, and finally, the law of pore size change of the acidic saltwater reservoir sandstone is analyzed in combination with the nuclear magnetic resonance test results before and after the reaction. The law of sandstone pore size change can provide an important reference for the CO2 geological storage process in the target area from the perspective of chemical reaction.

[0064] According to an embodiment of the present invention, before operation S110, the sandstone core sample may be cleaned with deionized water. Specifically, the sandstone core sample may be placed in a cleaning device, and deionized water may be used to fully clean the impurities in the pores of the sandstone core sample to remove impurities that may affect the experimental results, such as silt, organic matter, etc. During the cleaning process, the cleaning time may be appropriately increased or ultrasonic cleaning may be used to ensure the cleaning effect.

[0065] According to an embodiment of the present invention, before the sandstone is cleaned with deionized water, the sandstone having the target characteristics may be cut according to a preset size to obtain a sandstone core sample, wherein the preset size is determined according to a nuclear magnetic resonance testing device used for performing the nuclear magnetic resonance test. For example, the preset size may be a cylinder with a diameter of 25 mm and a length of 81 mm.

[0066] According to an embodiment of the present invention, step S130 may include: configuring a simulated acidic saline solution according to formation water quality conditions in the target area; and determining a simulated temperature and a simulated pressure according to formation temperature and formation pressure in the target area.

[0067] According to an embodiment of the present invention, the simulated acidic saline solution can be configured by the following steps: a NaCl solution with a mass concentration of 35 g / L is configured, and the pH value of the NaCl solution is adjusted to a preset value using the acidic solution to obtain a simulated acidic saline solution, wherein the preset value is determined according to the acidity of the formation water quality in the target area.

[0068] According to an embodiment of the present invention, the acidic solution may include a nitric acid solution or a hydrochloric acid solution.

[0069] According to an embodiment of the present invention, the concentration range of the nitric acid solution or the hydrochloric acid solution is 40-50 g / L.

[0070] In one embodiment, preparing the acidic saltwater solution may specifically include: accurately weighing 500 mL of a 35 g / L NaCl solution; adding 45 g / L nitric acid dropwise to the NaCl solution, and simultaneously using a pH meter to monitor the pH value of the solution in real time until the pH value of the NaCl solution reaches the desired acidic condition. In the process of adjusting the pH value, the nitric acid should be added slowly and the solution should be stirred continuously to ensure the uniformity of the solution.

[0071] According to an embodiment of the present invention, the chemical reactions that may occur in the sandstone core sample in the simulated acidic salt water solution mainly include the following reactions:

[0072] Calcite: CaCO3+2H + →Ca 2+ +CO2↑+H2O;

[0073] Magnesite: MgCO3+2H + →Mg 2+ +CO2↑+H2O;

[0074] Siderite: FeCO3+2H + →Fe 2+ +CO2↑+H2O;

[0075] Dolomite: CaMg(CO3)2+2H + →Ca 2+ +Mg 2+ +2HCO3 - ;

[0076] Ankerite: Ca(Fe 0.7 Mg 0.3 )(CO3)2+2H + →Ca 2+ +0.7Fe 2+ +0.3Mg 2+ +2HCO3 - ;

[0077] Potassium feldspar: KAlSi3O8+4H + →K + +Al 3+ +3SiO2↓+2H2O;

[0078] Quartz: SiO2+4H + →Si 4+ +2H2O;

[0079] Sodium feldspar: NaAlSi3O8+16H + →Al 3+ +3Si 4+ +Na + +8H2O;

[0080] Carbonate ion: HCO3 - + H + →H2O+CO2↑.

[0081] According to an embodiment of the present invention, in operation S160, the nuclear magnetic resonance test result before the reaction may include a nuclear magnetic resonance imaging image (MRI image) and a transverse relaxation time curve (T2 curve) of the sandstone core sample before the reaction. The nuclear magnetic resonance test result after the reaction may include a nuclear magnetic resonance imaging image (MRI image) and a transverse relaxation time curve (T2 curve) of the sandstone core sample after the reaction.

[0082] MRI images of sandstone core samples before and after the reaction can be used to analyze the change of the core pore structure. MRI images can provide detailed information on the pore distribution inside the core. By comparing the MRI images before and after the reaction, the change of the pore size of the sandstone core sample can be observed.

[0083] MRI images before and after the reaction also help to understand the uniformity of the pore structure of the sandstone core sample. If the MRI image after the reaction shows a more uniform color distribution, it means that the pore structure has become more uniform. If there are more discontinuous or irregular color changes, it means that the pore structure has become more complex or non-uniform.

[0084] In addition, MRI images can also provide information about fluid flow. If the post-reaction MRI images show that the fluid is more evenly distributed in the sandstone core sample, it indicates that the fluid flow has improved. If the fluid is concentrated in certain areas, it indicates that there are flow barriers or pore blockages. By analyzing the MRI images before and after the reaction, the effect of the reaction on the pore structure of the sandstone core sample can be evaluated. If the post-reaction MRI images show an increase in macropores, this indicates that the reaction is effective and helps to improve the permeability of the sandstone core sample.

[0085] T2 curves are often used to analyze changes in core pore structure. T2 relaxation time is an indicator of the movement of fluid molecules in pores, and different T2 values ​​correspond to pores of different sizes.

[0086] The peak position of the T2 curve can reflect the size of the main pores in the sandstone core sample. The closer the peak is to the left, the more small pores there are in the sandstone core sample; the closer the peak is to the right, the more large pores there are in the sandstone core sample.

[0087] The height of the peak reflects the relative abundance of the pore type corresponding to the T2 value. If the peak height increases after the reaction, it means that the pore type corresponding to the T2 value becomes more abundant after the reaction.

[0088] The width of the T2 curve can reflect the distribution range of pore size. A wider T2 curve indicates a wider pore size distribution, while a narrower T2 curve indicates a more concentrated pore size distribution.

[0089] The shape of the T2 curve can provide additional information about the changes in the pore structure. If the T2 curve after the reaction becomes more symmetrical, it means that the pore structure has become more uniform. If the T2 curve after the reaction becomes skewed or multi-peaked, it indicates that the pore structure has become more complex.

[0090] In theory, the total area under the T2 curve should remain constant, as it represents the total pore volume of the sandstone core sample. However, if the reaction results in a change in the pore volume, this will be reflected in a change in the area of ​​the T2 curve.

[0091] By comparing the T2 curves before and after the reaction, the effect of the reaction on the pore size change of the sandstone core sample can be evaluated. If the peak of the T2 curve after the reaction moves to the right, it indicates that the large pores increase and the reaction improves the permeability of the core. If the peak moves to the left, it indicates that the small pores increase and the reaction has a negative impact on the permeability of the core.

[0092] Therefore, based on the MRI images and T2 curves before and after the reaction, the pore distribution change results and pore structure change results of the sandstone core samples before and after the reaction can be obtained.

[0093] Example

[0094] Step 1: Sandstone core sample preparation.

[0095] 1. Select natural loose sandstone: Select natural loose sandstone from area A.

[0096] 2. Mechanical processing of core samples: Use rock cutting and processing equipment to process natural loose sandstone into cylindrical sandstone core samples with a diameter of 25 mm and a length of 81 mm. During the processing, pay attention to maintaining the integrity of the sandstone core samples to avoid changes in the internal structure of the sandstone core samples due to external forces during the processing.

[0097] 3. Cleaning sandstone core samples: Place the processed sandstone core samples in ultrasonic cleaning equipment and use deionized water to fully clean the impurities in the pores of the sandstone core samples to remove impurities that may affect the experimental results, such as mud, organic matter, etc.

[0098] 4. Drying the sandstone core sample: Put the cleaned sandstone core sample into the dryer and dry it at 100°C until the sandstone core sample is completely dry. After drying, take out the sandstone core sample and wait for it to cool naturally to room temperature. At this time, the sandstone core sample is considered to be in a dry state and ready for subsequent experiments.

[0099] Step 2: One-time saturation treatment of sandstone core samples.

[0100] 1. Install the sandstone core sample obtained in step 1 in a vacuum pressurized saturation device, and then evacuate the device to remove the air in the device to ensure that deionized water can fully enter the core pores during the saturation process, and set the pressure of the vacuum pressurized saturation device to 21 MPa.

[0101] 2. Inject deionized water into the vacuum pressurized saturation device to saturate the sandstone core sample at a pressure of 21 MPa for 12 hours. After saturation, close the device and take out the sandstone core sample.

[0102] Step 3: NMR test before reaction.

[0103] 1. Adjust the parameters of the nuclear magnetic resonance test equipment, where the nuclear magnetic resonance test equipment is the MesoMR12-060H-I multiphase flow displacement nuclear magnetic resonance analysis and imaging system. The T2 curve test parameter settings include: main frequency (MHz): 12, frequency offset (Hz): 335661.87, 90-degree pulse width (us): 14, waiting time (ms): 50000, 180-degree pulse width (us): 28.00, fixed wave time (ms): 0.2, number of fixed waves: 18000, RF delay (ms): 0.002, analog gain (dB) 20, data radius 1, cumulative times 16. The MRI imaging test parameter settings include: Gx Offset: -10, Gy Offset: 19, Gz Offset: 130, RFA90%: 3.2, RFA180%: 6.1, where Gx Offset, Gy Offset, and Gz Offset are the offsets of the adjustment gradient fields of the X, Y, and Z axes, respectively, to compensate for the inhomogeneity of the main magnetic field; RFA90% and RFA180% are used to control the amplitude of the radio frequency (RF) pulse, and RFA 90% and RFA 180% refer to different radio frequency powers.

[0104] 2. Install the sandstone core sample: Install the sandstone core sample obtained in step 2 on the sample rack of the nuclear magnetic resonance test equipment, ensuring that the sandstone core sample is installed in the correct position and can cooperate well with the magnetic field and detector components of the equipment.

[0105] 3. Perform NMR test: Start the NMR test equipment, which will automatically collect the NMR signal of the sandstone core sample and generate the T2 curve and MRI image. After the test is completed, save the test results, conduct a preliminary analysis of the T2 curve and MRI image, and record the pore size distribution characteristics and pore structure information of the sandstone core sample before the reaction.

[0106] Step 4: Prepare simulated acidic salt water solution.

[0107] 1. Prepare chemical reagents: accurately weigh 500 ml of 35 g / L NaCl solution; and prepare 45 g / L nitric acid solution.

[0108] 2. Adjust the pH value of the NaCl solution: Add the nitric acid solution dropwise into the NaCl solution, and use a pH meter to monitor the pH value of the solution in real time until the pH value of the solution reaches the required acidic condition to obtain a simulated acidic saline solution.

[0109] Step 5: High temperature and high pressure reactor to simulate reaction.

[0110] Figure 2Schematic diagram of the structure of a high-temperature and high-pressure reactor according to an embodiment of the present invention.

[0111] like Figure 2 As shown, the reactor includes a gas control system, a power and stirring system, a reaction chamber and a temperature control system, and a sampling and analysis unit.

[0112] The gas control system includes an inlet valve 211, an outlet valve 212, a gas pressurizing system 213 and a gas tank 214. The inlet valve 211 is located at the top or side of the reactor, and is used to accurately control the flow and pressure of the gases required for the reaction, such as CO2 and nitrogen, into the reactor; the outlet valve 212 is usually linked with a safety device to release excess pressure in the reactor or discharge reaction waste gas to ensure that the system pressure is within a safe range; the gas pressurizing system 213 is used to increase the gas pressure by mechanical or hydraulic means, and cooperates with the gas tank 214 to provide a stable high-pressure environment for the reaction.

[0113] The power and stirring system includes a motor 221 and a rotating blade 222. The motor 221 drives the rotating blade 222 to rotate at a high speed, providing strong stirring for the solution in the kettle, ensuring uniform mixing of the reactants and accelerating the heat transfer process. The rotating blade 222: is usually a turbine or paddle structure, directly immersed in the solution in the kettle, and improves the reaction efficiency through mechanical stirring.

[0114] The reaction chamber and temperature control system include a reaction kettle chamber 231: made of high temperature and high pressure resistant materials such as stainless steel and Hastelloy, which can hold reaction solutions and samples; a constant temperature heating layer 232: wrapped around the outside of the reaction kettle chamber 231, and realizing precise temperature control through electric heating or circulating heat conduction to ensure that the reaction is carried out at the set temperature; a cup holder 233: a bracket for fixing the sample 234, usually designed as an adjustable structure to facilitate the placement of samples of different specifications.

[0115] The sampling and analysis unit includes a sampling valve 241: located on the side wall of the reactor, connected to the interior of the reactor chamber 231 through a slender pipe, and can collect trace samples without interrupting the reaction. A sampling beaker 242: used to receive liquid or gas samples discharged from the sampling valve 241 for subsequent analysis such as chromatography and mass spectrometry.

[0116] The workflow of the high temperature and high pressure reactor includes:

[0117] 1. Place the reaction solution and install the sandstone core sample: Pour the simulated acidic salt water solution prepared in step 4 into the high temperature and high pressure reactor, and then place the sandstone core sample on the cup holder 233 in the reactor to ensure that the sandstone core sample is completely immersed in the simulated acidic salt water solution. After installing the sandstone core sample, seal the reactor to ensure that its sealing performance is good.

[0118] 2. Set the reaction conditions: According to the formation temperature and pressure conditions in area A, determine the simulated temperature and simulated pressure, and set the temperature and pressure parameters of the reactor. After setting the reaction conditions, start the reactor, inject gas into the reactor through the air inlet valve 211 and the gas booster system 213 and increase the pressure to the simulated pressure; the constant temperature heating layer 323 is started to increase the temperature to the simulated temperature, and then the motor 221 drives the rotating plate 222 to stir the solution to promote the reaction.

[0119] 3. Reaction process monitoring: The reaction time is 400 hours. During the reaction, sandstone core samples can be collected through the sampling valve 241 to analyze the reaction progress.

[0120] 4. End of reaction and sample removal: After the reaction is finished, the pressure is slowly released through the air release valve 212 to safely remove the sandstone core sample after the reaction.

[0121] Step 6: Secondary saturation and NMR testing.

[0122] 1. Drying the core sample: Place the reacted sandstone core sample obtained in step 5 into a dryer and dry it at 100°C until the reacted sandstone core sample is completely dry. After drying, take out the reacted sandstone core sample and wait for it to cool naturally to room temperature.

[0123] 2. Secondary saturation treatment: Repeat the operation of step 2, install the dried and reacted sandstone core sample in the vacuum pressure saturation device again, and fully saturate it with deionized water at a pressure of 21 MPa for 12 hours. After saturation, take out the sandstone core sample.

[0124] 3. Secondary NMR test: Install the sandstone core sample obtained in step 6 on the NMR test equipment, and test it according to the equipment's operating procedures to obtain the T2 curve and MRI image of the sandstone core sample after the reaction. After the test is completed, save the test results, compare the T2 curves and MRI images of the sandstone core sample before the reaction and the sandstone core sample after the reaction, and analyze the pore size change law of loose sandstone under acidic conditions.

[0125] Figure 3 1 is a magnetic resonance imaging image (MRI imaging image) according to an embodiment of the present invention, wherein (a) represents the MRI imaging image before the reaction, and (b) represents the MRI imaging image after the reaction.

[0126] like Figure 3 As shown, Figure 3The significant increase in the red and yellow areas in (b) of the figure compared to those in (b) indicates that the number of macropores in the sandstone core samples after the reaction has increased significantly. The increase in these macropores provides more space for the flow of CO2 and improves the permeability of the sandstone core samples. Macropores usually correspond to larger pores or cracks in sandstone core samples and are the main space for CO2 storage and flow. The increase in their number means that the storage capacity of sandstone core samples and the mobility of CO2 have been significantly improved.

[0127] Figure 3 Figure (b) shows a more uniform color distribution, which means that the pore structure of the sandstone core sample after the reaction has become more uniform compared to before the reaction. This improvement in uniformity not only optimizes the flow path of CO2, but also reduces the resistance of CO2 flowing in the sandstone core sample, allowing CO2 to flow more smoothly in the sandstone core sample. The uniform pore structure helps to improve the overall performance of the sandstone core sample, making it more stable during the geological storage process.

[0128] The T2 curve is a spectrum obtained by measuring T2 in a nuclear magnetic resonance instrument. It can accurately reflect the internal pore size distribution of sandstone core samples and is an important parameter for characterizing the pore structure of rocks. During the analysis process, the T2 distribution can be divided into different intervals such as micropores (T2<10ms), mesopores (10ms≤T2≤100ms) and macropores (>100 ms), and then the contribution of each interval to the total porosity is analyzed. Then the signal amplitude of each interval is integrated to obtain the porosity contribution corresponding to each interval.

[0129] Micropores usually correspond to small pores in rocks or bound water in clay minerals. By integrating the signal amplitude in this interval, the porosity contribution of micropores can be obtained. Assume that the integral result is , the integral formula is as follows (1):

[0130] (1);

[0131] Among them, A(T2) represents the quadratic function of T2; d(T2) represents the integration of T2. During the integration process, the small change of T2 is expressed as d(T2).

[0132] Mesopores usually correspond to medium-sized pores in rocks and are the main channels for CO2 flow. By integrating the signal amplitude in this interval, the porosity contribution of mesopores can be obtained. Assume that the integral result is , the integral formula is as follows (2):

[0133] (2).

[0134] Macropores usually correspond to larger pores in rocks and are the main space for CO2 storage and flow. By integrating the signal amplitude in this interval, the porosity contribution of macropores can be obtained. Assume that the integral result is , the integral formula is as follows (3):

[0135] (3).

[0136] Figure 4 is a transverse relaxation time curve (T2 curve) according to an embodiment of the present invention. Wherein, au represents dimensionless, indicating that the amplitude is a signal quantity without unit.

[0137] like Figure 4 As shown, according to the T2 curve combined with the above formula (1), it can be concluded that before the reaction It is 4154.553, which is significantly higher than the reaction is 3852.521. This indicates that there are more clay minerals in the sandstone core samples before the reaction, and these clay minerals fill part of the pores, resulting in more micropores and affecting the permeability of the reservoir. After the reaction, as the clay minerals dissolve or the structure changes, some micropores are transformed into medium-sized pores, and the number of micropores decreases, thereby improving the permeability of the sandstone core samples.

[0138] According to the T2 curve combined with the above formula (2), it can be concluded that after the reaction is 1428.924 relative to that before the reaction The average porosity of the sandstone core sample increased from 759.047 to 759.047. This shows that the development of medium-sized pores in the sandstone core sample after the reaction has increased significantly. The increase in mesopores means that the flow path of CO2 in the sandstone core sample is more unobstructed, and the fluidity of CO2 has been significantly improved. This change directly leads to an increase in the permeability of the sandstone core sample, thereby improving the transmission capacity of the reservoir. The increase in mesopores is also related to the dissolution and recrystallization of minerals during the reaction process. These processes change the morphology and connectivity of the pores, which increases the number of mesopores.

[0139] According to the T2 curve combined with the above formula (3), it can be concluded that after the reaction 335.841 relative to the pre-reaction The increase in macropores has an important impact on the storage capacity and production capacity of the reservoir. The macropores not only provide more storage space, but also provide channels for the rapid flow of CO2, thereby significantly improving the gas storage capacity and transmission efficiency of the sandstone core samples. The increase in macropores after the reaction is related to the dissolution of minerals under acidic conditions, especially the dissolution of carbonate minerals, which leads to the expansion of pores and cracks. This change not only improves the storage capacity of the sandstone core samples, but also improves the flow characteristics of CO2, making the sandstone core samples perform better in the process of CO2 geological storage.

[0140] Through , and From the comprehensive analysis, we can draw the following conclusions:

[0141] Micropores in the core before reaction ( ) indicates the presence of more clay minerals, which fill part of the pores, resulting in more micropores and reducing the permeability and CO2 mobility of the sandstone core samples. ) and macropores ( ) are less developed, limiting the ability of sandstone core samples to transport CO2.

[0142] Micropores in sandstone core samples after reaction ( ) is reduced, and the mesopores ( ) and macropores ( ) has increased significantly. This change has optimized the pore structure of the sandstone core samples, significantly improved the permeability, and made the CO2 flow smoother. The increase in macropores has also enhanced the gas storage capacity of the core, providing a more favorable micro-environment for CO2 geological storage.

[0143] These changes indicate that the reaction under acidic conditions has significantly optimized the pore structure of loose sandstone, thereby improving the storage capacity and transmission capacity of the core. This optimization effect is of great significance for the successful implementation of CO2 geological storage technology and provides an important scientific basis for future research and application in related fields.

[0144] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for analyzing pore size changes in acidic saline reservoir sandstone based on nuclear magnetic resonance technology, characterized in that: The method comprises: After drying the sandstone core sample with target characteristics in the target area, saturating it with deionized water to obtain a first saturated sandstone core sample; Performing a nuclear magnetic resonance test on the first saturated sandstone core sample to obtain a nuclear magnetic resonance test result before the reaction; After drying the first saturated sandstone core sample, placing it under simulated formation conditions for the target area to react for a preset time to obtain a reacted sandstone core sample, wherein the simulated formation conditions include simulated acidic saline solution, simulated temperature and simulated pressure; The reacted sandstone core sample is dried and then saturated with deionized water to obtain a second saturated sandstone core sample; Performing a nuclear magnetic resonance test on the second saturated sandstone core sample to obtain a nuclear magnetic resonance test result after the reaction; The nuclear magnetic resonance test results before the reaction and the nuclear magnetic resonance test results after the reaction are used to generate analysis results of the pore size variation law of the sandstone core sample under the simulated formation conditions.

2. The method according to claim 1, characterized in that The method further comprises: preparing the simulated acidic saline solution according to the formation water quality conditions of the target area; The simulated temperature and the simulated pressure are determined according to the formation temperature and the formation pressure of the target area.

3. The method according to claim 2, characterized in that The simulated acidic salt water solution is determined by the following steps: A NaCl solution with a mass concentration of 35 g / L is prepared, and the pH value of the NaCl solution is adjusted to a preset value using an acidic solution to obtain the simulated acidic saline solution, wherein the preset value is determined according to the acidity of the formation water quality in the target area.

4. The method according to claim 3, characterized in that The acidic solution includes a nitric acid solution or a hydrochloric acid solution.

5. The method according to claim 4, characterized in that The concentration range of the nitric acid solution or the hydrochloric acid solution is 40-50 g / L.

6. The method according to claim 1, characterized in that The nuclear magnetic resonance test results before the reaction include a nuclear magnetic resonance imaging image and a transverse relaxation time curve of the sandstone core sample before the reaction; The nuclear magnetic resonance test results after the reaction include a nuclear magnetic resonance imaging image and a transverse relaxation time curve of the sandstone core sample after the reaction.

7. The method according to claim 1, characterized in that The analysis result of the pore size variation law includes at least one of the following: The pore distribution change results of the sandstone core samples before and after the reaction; The pore structure change results of sandstone core samples before and after reaction.

8. The method according to claim 1, characterized in that The method further comprises: After the sandstone core sample with the target characteristics in the target area is dried, it is saturated with deionized water. Before obtaining the first saturated sandstone core sample, the sandstone core sample is cleaned with deionized water.

9. The method according to claim 8, characterized in that The method further comprises: Before the sandstone core sample is cleaned with deionized water, the sandstone having the target characteristics is cut according to a preset size to obtain the sandstone core sample, wherein the preset size is determined according to a nuclear magnetic resonance testing device used for nuclear magnetic resonance testing.

10. The method according to claim 1, characterized in that The target characteristics include at least one of the following: rock strength is lower than a first value, mud content is greater than a second value, and cement content is less than a third value.

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