A method for testing the saturation of low-permeability sandstone cores for CO2 flooding

Abstract

The application belongs to the technical field of CO2 flooding, and discloses a method for testing low-permeability sandstone core saturation for CO2 flooding, which comprises the following steps: selecting a rock sample; treating the rock sample; measuring the effective porosity and density of the rock sample; selecting divinylbenzene and styrene as a carrier; using phthalate as a stationary phase, coating the stationary phase on the surface of the carrier to prepare a special saturation analysis chromatographic column, and selecting a chromatographic column with an inner diameter of 4 mm and a length of 2.2 m made of stainless steel; using an organic solvent cleaning method + a hot cleaning method to treat and maintain the contaminated detector; and using a combination of a standard curve method and a normalization method to calculate the instantaneous peak area and the total peak area. After the application of the new method, the measurement accuracy is higher, the various deviation calculations and mathematical statistics values are smaller, the relative standard deviation of the new method is less than or equal to 2.5%, the recovery rate is more than 97.5%, the technical quality and the measurement accuracy are doubled, the dosage of the medicament and the emission of toxic substances are reduced, and the work efficiency and the analysis efficiency are improved.

Description

Technical Field

[0001] This invention belongs to the field of CO2 flooding technology and relates to a method for testing the saturation of low-permeability sandstone cores for CO2 flooding. The invention aims to determine whether the saturation measured by this invention can achieve the true saturation in CO2 flooding experiments on ultra-low permeability long cores. Background Technology

[0002] CO2 enhanced oil recovery technology has entered the industrialization and promotion stage in Jilin Oilfield, becoming the on-site basis for the company's major science and technology projects, and leading and promoting the progress of CNPC's CCUS work.

[0003] The CO2 flooding experiment with ultra-low permeability long cores is one of the important experiments for evaluating the feasibility of CO2 flooding technology. Through the experiment, characteristic parameters such as the recovery rate and displacement law of CO2 flooding in natural cores under formation temperature and pressure conditions can be obtained. However, the formation water saturation measured in the experiment is mainly achieved through the oil-water displacement method. The measurement results deviate from the original formation saturation. In actual operation, the obtained saturation values ​​need to be corrected to determine the rationality of the saturation values.

[0004] Existing methods for testing saturation have many problems, such as interference from inorganic salts and low-molecular-weight hydrocarbons, low separation efficiency between components, column contamination and decreased column efficiency, and insufficient sensitivity and accuracy of the detection response. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, the new method of this invention makes the preparation of standard solutions more accurate and convenient, with a wide linear measurement range, strong adaptability, good reproducibility, and high efficiency and practicality. It greatly improves the separation effect and analytical efficiency of components, significantly enhancing the accuracy and sensitivity of detection. By simulating the saturation measured in real reservoirs under experimental conditions, it can be used to determine whether the saturation calculated for CO2 flooding experiments on ultra-low permeability long cores can reach the true saturation.

[0006] Based on existing conditions, this invention establishes an accurate method for determining core saturation using chromatographic integration. It accurately grasps and controls the key points and details of the entire testing process. Through analysis of the method's principles, detection conditions, and influencing factors, improvements and refinements are made to sample selection, operating procedures, analytical steps, and testing stages. Simultaneously, experimental detection methods are optimized, and quality control is strengthened, effectively improving the accuracy and reliability of analytical test data and final results. The chromatographic integration method provides more accurate and convenient standard preparation, with a smaller working curve intercept, lower detection limit, wider linear range, reliable principle, good reproducibility, and increased adaptability. The preparation and use of a dedicated high-molecular-weight copolymer nonpolar chromatographic packed column, along with effective detector cleaning and maintenance, eliminates interference from inorganic salts and low-molecular-weight hydrocarbons, solving the two major problems of decreased separation capacity and reduced response signal. This improves the separation efficiency between components, reduces column contamination and decreased column efficiency, minimizes fluctuations in carrier gas flow rate and peak shape, and increases noise and drift, thereby enhancing the sensitivity of the detection response. This innovative approach, combining the standard curve method with the normalization method, ensures the accuracy of the measurement results. It provides a new method and approach for the accurate and rapid determination of oil and water saturation in large-scale core samples, and offers a reliable basis for selecting key reservoir layers in oilfield exploration and development. The innovative results reduce the influence of various physicochemical factors during the actual measurement process, and further reduce errors through simulation correction under formation environmental conditions. This makes the saturation test data closer to the actual formation values, reflecting the true state of underground oil, gas, and water more objectively and reasonably. This lays the foundation for subsequent comprehensive research and evaluation of reserves, fluid distribution, and production capacity. The innovative results also offer significant economic and social benefits in reducing experimental workload, improving testing and analysis efficiency, reducing costs and increasing efficiency, and saving energy and reducing emissions.

[0007] The above-mentioned objective of this invention is achieved through the following technical solution:

[0008] A method for testing the saturation of low-permeability sandstone cores for CO2 flooding includes the following steps:

[0009] Step (1), rock sample selection;

[0010] Step (2), rock sample processing;

[0011] Step (3): Determination of effective porosity and density of rock samples;

[0012] Step (4), selection of support: divinylbenzene and styrene are selected as supports;

[0013] Step (5): Using phthalate as the stationary phase, the stationary phase is coated on the surface of the support to prepare a special chromatographic column for saturation analysis. A stainless steel column with an inner diameter of 4 mm and a length of 2.2 m is selected.

[0014] Step (6): Clean and maintain the contaminated detector using organic solvent cleaning and thermal cleaning methods;

[0015] Step (7) uses a combination of standard curve method and normalization method to calculate instantaneous peak area and total peak area.

[0016] Furthermore, the specific steps for weighing the rock sample in step (1) are as follows:

[0017] ① To make the saturation measurement value closer to the actual value of the formation, the saturation sample should be sorted and packed within 40 minutes after the core is brought to the surface from the well.

[0018] ②The saturation sample taken is representative. Remove the mud immersion ring at the edge of the rock core and take two small cubic rock samples, each weighing 10-15g.

[0019] ③ Place the sample into a numbered, pre-dried, constant-weight cloth bag, weigh it, and calculate and record the mass M of the rock sample using the difference method. 岩样 .

[0020] Furthermore, the specific steps of rock sample treatment in step (2) are as follows:

[0021] ① Dry the sample bag and steel can at 105℃ for 4 hours, and use them after cooling in the desiccator. After sealing and weighing the rock sample, put it into a dry and clean stainless steel sealed can in an orderly manner, add 25mL±0.25mL of anhydrous ethanol, and tighten the top cover to seal the can.

[0022] ② Place it in a constant temperature chamber at a temperature ≤140℃ and a constant temperature vaporization time ≥4h to ensure that at least 98% of the water in the rock sample is extracted by ethanol.

[0023] ③ After cooling, open the stainless steel sealed container at room temperature and immediately perform chromatographic water content analysis on the ethanol solution inside the container;

[0024] ④ Take the rock sample bag out of the steel can, wait for the residual ethanol to evaporate, wrap it with clean filter paper, and put it into the oil washing instrument for oil washing.

[0025] ⑤ Ensure that the original structure of the rock sample is not damaged or altered. Use a benzene:ethanol = 3:1 (v / v) mixture to heat and distill, then condense and impregnate the sample. Repeat this process for 60-72 hours to thoroughly wash away the crude oil contained in the rock sample.

[0026] ⑥ After cooling to room temperature, remove the rock sample bag, evaporate the solvent inside the rock sample, dry it in a constant temperature oven at ≤105℃ for 8 hours, and then weigh it (M) after cooling to room temperature in a desiccator. 干样 The difference in mass between the rock sample and its contents before and after washing and drying is the sum of the masses of crude oil and water contained in the rock sample, i.e., M. 岩样 -M 干样 =M原油 +M 含水 After obtaining the water content of the rock sample through chromatographic analysis, the crude oil content in the rock sample is obtained by subtraction. This crude oil content is then divided by the formation water density and crude oil density at the sampling stratum to obtain the formation water volume V in the rock sample. 水 =M 含水 / ρ 水 Volume of crude oil contained (V) 油 =M 原油 / ρ crude oil.

[0027] Furthermore, the specific steps for determining the effective porosity and density of the rock sample in step (3) are as follows:

[0028] ① Under vacuum conditions, the rock sample is first saturated with kerosene of known accurate density. The kerosene is then absorbing the colloids with activated carbon or white clay, and the water is absorbed with calcium chloride or silica gel. It is then filtered through filter paper before use. Excess kerosene is wiped off the surface of the rock sample, and it is weighed on a balance with an accuracy exceeding one-thousandth to determine the mass M of the kerosene-saturated rock sample. 油湿 Subtract the mass of the dry rock sample M 干样 Divide by the density of kerosene ρ 煤油 The pore volume V of the rock sample was obtained. 孔隙 =(M 油湿 -M 干样 ) / ρ 煤油 ;

[0029] ②The rock sample saturated with kerosene is suspended in a beaker containing saturated kerosene using a copper wire loop, and its suspended mass M, which is submerged in the kerosene, is weighed using a balance. 悬吊 The mass M of the saturated kerosene rock sample in air 油湿 Subtract the mass M measured in kerosene 悬吊 Divide by the density ρ of kerosene 煤油 The apparent total volume V of the rock sample was obtained. 总 =(M 油湿 -M 悬吊 ) / ρ 煤油 rock sample grain skeleton volume V 骨架 =(M 干样 -M 悬吊 ) / ρ 煤油 The total volume of the rock sample minus the volume of the grain skeleton equals the pore volume V. 孔隙 =V 总 -V 骨架 They can calculate and determine the measurement error and deviation between each other;

[0030] ③ Calculate the porosity Particle skeleton density ρ 岩样 =M 干样 / V 骨架 And from this, the oil saturation of the measured core was obtained. water saturation

[0031] Furthermore, in step (4), the mass ratio of divinylbenzene to styrene in the support is 6:4, forming spherical GDX series nonpolar copolymer particles with a surface area of ​​1.5 cm². 2 / g.

[0032] Furthermore, in step (5), the mass ratio of the fixative to the support is 1:9.

[0033] Further, the specific steps of step (6) are as follows: using a constant mobile phase, increasing the bridge current to 180A, increasing the temperature difference between the hot wire and the tank to 360℃, using activated copper for deoxygenation, using molecular sieves and activated carbon adsorbents to remove organic impurities, using silica gel and molecular sieve adsorbents to remove water, reducing the TCD tank pressure by 60%, reducing the tail gas flow rate to 5mL / min, and increasing the TCD detection to 10. -5 mg / L.

[0034] Furthermore, the specific steps of step (7) are as follows: based on the gas chromatograph detection data results, the relevant data are converted using Excel to filter out the sampling interval and subtract the peak value of the baseline data to obtain the continuous values ​​within the peak time period. The instantaneous peak area is calculated using normalized interpolation.

[0035] μ (t) =∑σ(t-nλ)

[0036] The total peak area is obtained by spectral summation.

[0037]

[0038] Where t is the retention time, a and b are constants, x is the retention exponent, and L is the flow length.

[0039] The advantages of this invention compared to the prior art are:

[0040] The original method for saturation determination typically had an error greater than 10%, while the new method can control it to within 5%. The new method has higher measurement accuracy than the original method, with smaller deviations and statistical values. The new method has a relative standard deviation of ≤2.5% and a recovery rate of over 97.5%. The technical quality and measurement accuracy have been improved exponentially, reducing the amount of reagents used and the emission of toxic substances, while improving work efficiency and analytical efficiency. Compared with similar technologies in China, its main performance has reached an advanced level, and it has also generated certain benefits in terms of cost reduction, efficiency improvement, energy conservation, and emission reduction. Attached Figure Description

[0041] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0042] Appendix Figure 1 This is a standard working curve of peak height method for saturation chromatographic analysis;

[0043] Appendix Figure 2 This is a standard working curve of peak area integration method for saturation chromatographic analysis;

[0044] Appendix Figure 3 It is a working curve for component qualitative analysis by increasing peak height in saturation chromatography;

[0045] Appendix Figure 4 This is a comparison curve of the SNB well core saturation measurement data before and after simulation correction. Detailed Implementation

[0046] To provide a clearer understanding of the technical features, objectives, and beneficial effects of this invention, the technical solution of this invention will now be described in detail with reference to the following specific embodiments. However, this should not be construed as limiting the scope of implementation of this invention. Unless otherwise specified, the experimental methods used in this invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used are all commercially available.

[0047] Example 1

[0048] Step 1. Rock Sample Selection: ① To ensure the measured saturation value is closer to the actual formation value, the saturation samples should be sorted and containerized within 40 minutes of the core reaching the surface from the well. ② The selected saturation samples should be representative. Remove the mud-impregnated ring at the edge of the core and carve out two cubic rock sample pieces, each weighing 10-15g. Based on existing formation data or experience, preliminarily determine the core porosity and water content, and adjust the size of the saturation rock samples to ensure the total water content of the two samples is within the range of 0.2-2.0g for optimal measurement linearity and minimal error. ③ Place the samples into numbered, pre-dried, constant-weight, and dry cloth bags. Weigh them (the weighing error of any balance must be <0.005g), and use the difference method to obtain and record the sample mass M. 岩样 .

[0049] Step 2. Rock Sample Preparation: ① Dry the sample bag and steel container at 105℃ for 4 hours. After cooling in a desiccator, seal the bag tightly, weigh the rock sample, and orderly pack it into a clean, dry stainless steel sealed container. Add 25 mL (error ±0.25 mL, or accurately weigh the mass) of anhydrous ethanol, then tighten the top cover and seal the container. The operation should be quick and compact to minimize oil and water loss. ② Place the container in a constant temperature oven at below 140℃ for at least 4 hours to ensure complete extraction of all water from the rock sample (>98%). ③ After cooling to room temperature, open the stainless steel sealed container. Immediately perform chromatographic water content analysis on the ethanol solution inside the container to avoid concentration changes caused by evaporation. ④ Remove the sample bag from the steel container, allow residual ethanol to evaporate, wrap it with clean filter paper, and place it in an oil washing apparatus for oil washing, avoiding damage or dissolution of the sample bag. ⑤ Ensure the original structure of the rock sample is not damaged or altered. Use a 3:1 mixture of benzene and ethanol for heating, distillation, condensation, and immersion, repeating this process for 60–72 hours to thoroughly wash away the crude oil contained within the sample. During the washing process, ensure the washing apparatus is leak-proof, the fume hood is well-ventilated, and take precautions to prevent poisoning from solvent evaporation. After washing, ensure the sample bag is clean and free of oil stains or contaminants, and that any remaining solvent in the core chamber of the washing apparatus is colorless or has a fluorescence color lighter than that of the grade III standard solution. ⑥ After cooling to room temperature, remove the sample bag. After evaporating the solvent from the sample, dry it at 105°C for 8 hours in a constant temperature oven. After cooling to room temperature in a desiccator, weigh it (M). 干样 The difference in quality between the rock sample inside the bag before and after washing and drying is the sum of the masses of crude oil and water contained in the rock sample (M). 岩样 -M 干样 =M 原油 +M 含水 After determining the water content of the rock sample through chromatographic analysis, the crude oil content in the rock sample is obtained by subtraction. This subtraction is then divided by the formation water density and crude oil density at the sampling stratum to obtain the formation water volume V in the rock sample. 水 =M 含水 / ρ 水 Volume of crude oil contained (V) 油 =M 原油 / ρ 原油 .

[0050] Step 3. Determination of effective porosity and density of rock sample: ① Under vacuum conditions, the rock sample is first saturated with kerosene of known accurate density (the colloids in the kerosene are absorbed by activated carbon or white clay, the water in the kerosene is absorbed by calcium chloride or silica gel, and it is filtered through filter paper before use). Then, the excess kerosene on the surface of the rock sample is wiped off, and it is weighed on a balance with an accuracy of more than one-thousandth to obtain the mass M of the kerosene-saturated rock sample. 油湿 Subtract the mass M of the dry rock sample. 干样 Divide by the density of kerosene ρ 煤油 The pore volume V of the rock sample was obtained. 孔隙 =(M 油湿 -M 干样) / ρ 煤油 ② A rock sample saturated with kerosene is suspended in a beaker containing saturated kerosene using a copper wire loop. The suspended mass M, submerged in the kerosene, is weighed using a balance. 悬吊 The mass M of the saturated kerosene rock sample in air. 油湿 Subtract the mass M measured in kerosene 悬吊 Divide by the density ρ of kerosene 煤油 The apparent total volume V of the rock sample was obtained. 总 =(M 油湿 -M 悬吊 ) / ρ 煤油 The volume V of the rock sample grain framework 骨架 =(M 干样 -M 悬吊 ) / ρ 煤油 The total volume of the rock sample minus the volume of the grain skeleton equals the pore volume V. 孔隙 =V 总 -V 骨架 They can mutually calculate and determine measurement errors and deviations. The volume of the rock sample grain framework, V, is among them. 骨架 With density ρ 岩样 The easiest to measure accurately, and also the benchmark value for all calculations. ③ Calculate the porosity. Particle skeleton density ρ 岩样 =M 干样 / V 骨架 And from this, the oil saturation of the measured core was obtained. water saturation To ensure measurement accuracy, the absolute error porosity value must be ≤0.5% and the saturation value must be ≤0.1%.

[0051] Step 4. Selection of Support: Based on literature review and considering the characteristics of Jilin Oilfield, the main raw material used is a GDX series nonpolar copolymer with a divinylbenzene:styrene mass ratio of 6:4, forming spherical particles with a surface area of ​​1.5 cm². 2 Using / g as a support, the stationary phase has high mechanical strength, large surface area, good wettability, is easy to uniformly coat with the fixative, has good filling and permeability, good chemical inertness and thermal stability, low adsorption, and corrosion resistance.

[0052] Step 5. Using phthalate as the stationary phase, coat the stationary phase onto the support surface to prepare a special chromatographic packed column for saturation analysis. The mass ratio of stationary phase to support is 1:9. The stationary phase, formed by the chemical reaction and bonding between the stationary phase and support, offers high column efficiency, good thermal stability, and symmetrical peak shapes for analyzing polar or non-polar compounds, avoiding peak broadening or tailing, effectively shortening analysis time, and achieving the best separation effect. Based on the premise that the net van der Waals forces on molecules attached to the support surface and within the pores of the gas phase are zero, under constant temperature, constant pressure, and a certain vapor composition, according to the Kelvin equation:

[0053]

[0054] Where Pr is the actual vapor pressure; Po is the saturated vapor pressure; γ is the interfacial tension; R is the universal gas constant; T is the temperature; and r is the radius of the tiny droplet.

[0055] According to the Gibbs-Duhem equation:

[0056] n1μ1+n2μ2=0

[0057] At adsorption equilibrium, the instantaneous separation rate is:

[0058]

[0059] Peak time:

[0060]

[0061] Based on the peak elution time and considering factors such as connectors, filters, and pressure caps, a stainless steel chromatographic column with an inner diameter of 4 mm and a length of 2.2 m was calculated to have the highest column efficiency and stability, making it suitable for sandstone reservoirs in the Jilin Oilfield.

[0062] Step 6. Clean and maintain the contaminated detector using organic solvents and thermal cleaning to increase separation selectivity, improve component separation, enhance column stability, and extend column lifespan. Maintaining a constant mobile phase, increasing the bridge current to 180A, and increasing the temperature difference between the hot filament and the cell to 360℃ lays the foundation for improved separation and analytical efficiency. Activated copper is used for oxygen removal, molecular sieves and activated carbon adsorbents for organic impurities removal, and silica gel and molecular sieve adsorbents for water removal. This results in high detection sensitivity, smooth and symmetrical peak shapes, stable response factors, easy quantification, and a wide linear range. Reducing the TCD cell pressure by 60% and decreasing the tail gas flow rate to 5mL / min achieves optimal TCD response conditions, improving peak shape and increasing TCD detection efficiency by 10%. - 5 mg / L, improving accuracy by more than 80%.

[0063] Step 7. In the establishment and practical application of the chromatographic integral method for saturation determination, the method of directly increasing peak height by adding pure substances is used for qualitative analysis of the separated components, which is simple and intuitive. A combination of the standard curve method and the normalization method is used to eliminate interference from inorganic salts, low-molecular-weight hydrocarbons, and other components, ensuring the precision and accuracy of the determination results.

[0064] Based on the gas chromatograph detection data, the relevant data were converted using Excel, and the peak values ​​of the sampling interval and baseline data were subtracted to obtain continuous values ​​within the peak time period. Then, using normalized interpolation, the instantaneous peak area was calculated.

[0065] μ (t) =∑σ(t-nλ)

[0066] The total peak area is obtained by accumulating the spectrum.

[0067]

[0068] Where t is the retention time, a and b are constants, x is the retention exponent, and L is the flow length.

[0069] The combination of standard curve method and normalization method is used to ensure the accuracy of the measurement results, providing a new method and approach for the accurate determination of core saturation, and also providing an accurate basis for the selection of the main stratigraphic position in CO2 flooding exploration and development.

[0070] Chromatographic peak height is highly susceptible to fluctuations due to changes in analytical conditions and various physicochemical factors, resulting in poor data reproducibility. The traditional peak height method is only suitable for quantitative analysis under specific ideal conditions such as no interference, rapid elution, sharp peak shape, smooth and symmetrical peaks, and constant half-width. The saturation determination results obtained using the peak height method typically have an error >10%. Figure 1 As shown in the standard working curve of the peak height method for saturation chromatography analysis, the present invention controls the relative standard deviation to be ≤5% and the recovery rate to be above 95%.

[0071] The integral method is advantageous in overcoming interference from factors such as excessively low or high sample concentrations, intermittent or excessively large injection volumes, fluctuations in injection pressure or carrier gas flow rate, loss of bonded phase or low carrier gas purity, insensitive temperature control or parameter fluctuations, large noise or drift, and the appearance of broad peaks, shoulder peaks, flat-topped peaks, forward-protruding peaks, or tailed peaks. Figure 2 As shown in the standard working curve of the peak area integration method for saturation chromatographic analysis, the error of the saturation determination result by the chromatographic integration method of this invention can be controlled within < 5%, the precision and accuracy are greatly improved, the various deviation calculations and mathematical statistics values ​​are significantly reduced, the relative standard deviation is ≤ 2.5%, and the recovery rate is above 97.5%, ensuring the technical quality and accuracy and reliability of the core saturation test results.

[0072] The sophistication of the instrument and the magnitude of changes in operating conditions significantly affect peak height determination and are prone to errors, while having little impact on integral chromatographic methods, which are relatively more accurate for qualitative and quantitative analysis. Even minute differences in mobile phase flow rate can cause fluctuations in retention time in peak height determination, while retention volume remains unchanged in integral chromatographic methods. Adding pure substances directly increases peak height, making qualitative analysis of separated components simpler and more intuitive. The results of this invention are as follows... Figure 3 The working curve for component qualitative analysis using saturation chromatography with the addition of peak height method is shown.

[0073] Example 2

[0074] according to Figure 4 A comparison of the SNB well core saturation measurement data before and after simulation correction shows that, without correction, the average oil saturation was 23.5%, ranging from 10% to 30%. After correction, the average oil saturation was 43.5%, ranging from 40% to 50%. Chromatographic integration was used to reduce interference from various physicochemical factors, and simulation correction further reduced errors. A combination of standard curve and normalization methods ensured the accuracy of the results, providing a new method and approach for the accurate and rapid determination of oil-water saturation in large batches of core samples.

[0075] The embodiments described above are merely preferred embodiments of the present invention, and not all feasible embodiments of the present invention. Any obvious modifications made by those skilled in the art without departing from the principles and spirit of the present invention should be considered to be included within the scope of protection of the claims of the present invention.

Claims

1. A method for testing the saturation of low-permeability sandstone cores for CO2 flooding, characterized in that, Includes the following steps: Step (1), rock sample selection; Step (2), rock sample processing; Step (3), determination of effective porosity and density of rock sample; Step (4), selection of support: divinylbenzene and styrene are selected as supports; Step (5): Using phthalate as the stationary phase, the stationary phase is coated on the surface of the support to prepare a special chromatographic column for saturation analysis. A stainless steel column with an inner diameter of 4 mm and a length of 2.2 m is selected. Step (6): Clean and maintain the contaminated detector using organic solvent cleaning and thermal cleaning methods; Step (7) uses a combination of the standard curve method and the normalization method to calculate the instantaneous peak area and the total peak area; Step (3) The specific steps for determining the effective porosity and density of the rock sample are as follows: ① Under vacuum conditions, the rock sample is first saturated with kerosene of known accurate density. The kerosene is then absorbing the colloids with activated carbon or white clay, and the water is absorbed with calcium chloride or silica gel. It is then filtered through filter paper before use. Excess kerosene is wiped off the surface of the rock sample, and it is weighed on a balance with an accuracy exceeding one-thousandth to determine the mass M of the kerosene-saturated rock sample. 油湿 Subtract the mass of the dry rock sample M 干样 Divide by the density of kerosene ρ 煤油 The pore volume V of the rock sample was obtained. 孔隙 =(M 油湿 -M 干样 ) / ρ 煤油 ; ②The rock sample saturated with kerosene is suspended in a beaker containing saturated kerosene using a copper wire loop, and its suspended mass M, which is submerged in the kerosene, is weighed using a balance. 悬吊 The mass M of the saturated kerosene rock sample in air 油湿 Subtract the mass M measured in kerosene 悬吊 Divide by the density ρ of kerosene 煤油 The apparent total volume V of the rock sample was obtained. 总 =(M 油湿 -M 悬吊 ) / ρ 煤油 rock sample grain skeleton volume V 骨架 =( M 干样 -M 悬吊 ) / ρ 煤油 The total volume of the rock sample minus the volume of the grain skeleton equals the pore volume V. 孔隙 =V 总 -V 骨架 They can calculate and determine the measurement error and deviation between each other; ③ The porosity φ = V was calculated. 孔隙 / V 总 ·100, particle skeleton density ρ 岩样 =M 干样 / V 骨架 And from this, the oil saturation S of the measured core was obtained. 油 =V 油 / V 孔隙 ·100=(V 油 ·ρ 岩样 ) / (M 干样 ·φ )·100、Water saturation S 水 =V 水 / V 孔隙 ·100= (V) 水 ·ρ 岩样 ) / (M 干样 ·φ)·100; The specific steps of step (7) are as follows: Based on the gas chromatograph detection data, the relevant data were converted using Excel, and the peak values ​​of the sampling interval and baseline data were subtracted to obtain continuous values ​​within the peak time period. Then, using normalized interpolation, the instantaneous peak area was calculated. The total peak area is obtained by spectral summation. Where t is the retention time, a and b are constants, x is the retention exponent, and L is the flow length.

2. The method for testing the saturation of low-permeability sandstone cores for CO2 flooding as described in claim 1, characterized in that, The specific steps for weighing the rock sample in step (1) are as follows: ① To make the saturation measurement value closer to the actual value of the formation, the saturation sample should be sorted and packed within 40 minutes after the core is brought to the surface from the well. ②The saturation sample taken is representative. Remove the mud immersion ring at the edge of the rock core and take two small cubic rock samples, each weighing 10~15g. ③ Place the sample into a numbered, pre-dried, constant-weight cloth bag, weigh it, and calculate and record the mass M of the rock sample using the difference method. 岩样 .

3. The method for testing the saturation of low-permeability sandstone cores for CO2 flooding as described in claim 1, characterized in that, The specific steps for rock sample processing in step (2) are as follows: ① Dry the sample bag and steel can at 105℃ for 4 hours, and use them after cooling in the desiccator. After sealing and weighing the rock sample, pack it into a dry and clean stainless steel sealed can in an orderly manner. Add 25mL±0.25mL of anhydrous ethanol and tighten the top cover to seal the can. ② Place it in a constant temperature chamber at a temperature ≤140℃ and a constant temperature vaporization time ≥4h to ensure that at least 98% of the water in the rock sample is extracted by ethanol. ③ After cooling, open the stainless steel sealed container at room temperature and immediately perform chromatographic water content analysis on the ethanol solution inside the container; ④ Take the rock sample bag out of the steel can, wait for the residual ethanol to evaporate, wrap it with clean filter paper, and put it into the oil washing instrument for oil washing. ⑤ Ensure that the original structure of the rock sample is not damaged or altered. Use a benzene:ethanol = 3:1 (v / v) mixture to heat and distill, then condense and impregnate the sample. Repeat this process for 60-72 hours to thoroughly wash away the crude oil contained in the rock sample. ⑥ After cooling to room temperature, remove the rock sample bag, evaporate the solvent inside the rock sample, dry it in a constant temperature oven at ≤105℃ for 8 hours, and then weigh it (M) after cooling to room temperature in a desiccator. 干样 The difference in mass between the rock sample and its contents before and after washing and drying is the sum of the masses of crude oil and water contained in the rock sample, i.e., M. 岩样 -M 干样 =M 原油 +M 含水 After obtaining the water content of the rock sample through chromatographic analysis, the crude oil content in the rock sample is obtained by subtraction. This crude oil content is then divided by the formation water density and crude oil density at the sampling stratum to obtain the formation water volume V in the rock sample. 水 = M 含水 / ρ 水 Volume of crude oil contained (V) 油 = M 原油 / ρ 原油 .

4. The method for testing the saturation of low-permeability sandstone cores for CO2 flooding as described in claim 1, characterized in that, In step (4), the mass ratio of divinylbenzene to styrene in the support is 6:4, forming spherical GDX series nonpolar copolymer particles with a surface area of ​​1.5 cm². 2 / g.

5. The method for testing the saturation of low-permeability sandstone cores for CO2 flooding as described in claim 1, characterized in that, The mass ratio of the fixative to the support in step (5) is 1:

9.

6. The method for testing the saturation of low-permeability sandstone cores for CO2 flooding as described in claim 1, characterized in that, The specific steps of step (6) are as follows: using a constant mobile phase, increasing the bridge current to 180A, increasing the temperature difference between the hot wire and the tank to 360℃, using activated copper for deoxygenation, using molecular sieves and activated carbon adsorbents to remove organic impurities, using silica gel and molecular sieve adsorbents to remove water, reducing the TCD tank pressure by 60%, reducing the tail gas flow rate to 5mL / min, and increasing the TCD detection to 10. -5 mg / L.

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