Method and system for determining lower limit of shale oil movable pore throat

Abstract

The invention discloses a method and system for determining the lower limit of a shale oil movable pore throat, and belongs to the technical field of oil-gas exploration. The method comprises the following steps: performing slice observation, pyrolysis treatment and X-ray diffraction test on a first rock core sample, determining the first rock core sample meeting requirements based on a test result, and obtaining a second rock core sample based on the position of the first rock core sample meeting requirements in a target area, and determining the lower limit of the shale oil movable pore throat based on the oil saturation index and the average pore diameter corresponding to the second rock core sample. Therefore, according to the method, the rock core samples meeting the requirements are screened based on test results of slice observation, pyrolysis treatment and X-ray diffraction test, and the influence of the difference of shale components, structures and organic characteristics on the lower limit of the shale oil movable pore throat is fully considered, so that the shale oil movable pore throat lower limit can be determined based on the oil saturation index and the average pore diameter subsequently. And accurately determining the lower limit of the shale oil movable pore throat.

Description

Technical Field

[0001] The present application relates to the technical field of oil and gas exploration, and in particular to a method and system for determining the lower limit of movable pore throats of shale oil. Background Art

[0002] Shale oil is a hot spot and frontier in the current unconventional oil and gas exploration. Among them, the mobility of shale oil is the key content of sweet spot evaluation, especially the study of the lower limit of shale movable pore throats. The pore throats of shale determine the productivity of the reservoir and control the storage and migration of oil and gas. Systematically and scientifically determining the lower limit of shale oil movable pore throats is crucial for scientifically evaluating shale oil reserves and improving oil and gas recovery. Therefore, how to determine the lower limit of shale oil movable pore throats has become an urgent problem to be solved. Summary of the invention

[0003] The embodiment of the present application provides a method and system for determining the lower limit of movable pore throats of shale oil, which can reduce the influence of differences in shale composition, structure and organic characteristics on the lower limit of movable pore throats of shale oil, thereby accurately determining the lower limit of movable pore throats of shale oil. The technical solution is as follows:

[0004] On the one hand, a method for determining the lower limit of movable pore throats of shale oil is provided, the method comprising:

[0005] obtaining a plurality of first core samples in the target area;

[0006] For each first core sample, performing thin section observation, pyrolysis treatment, and X-ray diffraction test on the first core sample, and determining a first core sample that meets the requirements from the plurality of first core samples based on the test results;

[0007] Based on the position of the first core sample that meets the requirements in the target area, obtaining a second core sample;

[0008] determining the oil saturation index of the second core sample;

[0009] The second core sample is subjected to extraction treatment by using a weak polarity combination solvent and a strong polarity combination solvent to obtain a third core sample; wherein the weak polarity combination solvent is used to remove free shale oil in the shale pores, and the strong polarity combination solvent is used to remove adsorbed and mutually soluble shale oil in the shale pores;

[0010] Performing a N2 isothermal adsorption-desorption experiment on the third core sample to obtain an average pore diameter;

[0011] Based on the oil saturation index and the average pore diameter corresponding to the second core sample, the lower limit of the movable pore throat of shale oil in the target area is determined.

[0012] In a possible implementation, extracting the second core sample using a weak polarity combined solvent and a strong polarity combined solvent to obtain a third core sample includes:

[0013] In a weak polar combined solvent, the second core sample is extracted by ultrasonic extraction, and the extracted second core sample is rinsed and dried to obtain a fourth core sample; wherein the weak polar combined solvent includes dichloromethane and methanol, and the mass ratio of the dichloromethane to the methanol is 93:7;

[0014] In a strong polar combination solvent, the fourth core sample is extracted by ultrasonic extraction, and the fourth core sample after extraction is rinsed and dried to obtain the third core sample; wherein the strong polar combination solvent includes tetrahydrofuran, acetone and methanol, and the mass ratio of the tetrahydrofuran, the acetone and the methanol is 50:25:25.

[0015] In another possible implementation, the movable pore throat lower limit of shale oil includes: the theoretical movable pore throat lower limit of shale oil and the effective movable pore throat lower limit of shale oil, and the number of the second core samples is multiple;

[0016] Determining the lower limit of movable pore throats of shale oil in the target area based on the oil saturation index and the average pore diameter corresponding to the second core sample includes:

[0017] Based on the oil saturation index and the average pore diameter corresponding to each second core sample, a scatter plot is drawn with the average pore diameter as the abscissa and the oil saturation index as the ordinate;

[0018] The average pore diameter corresponding to the oil saturation index of 0 in the scatter plot is determined as the lower limit of the theoretical movable pore throat of the shale oil;

[0019] The average pore diameter corresponding to the oil saturation index of 100 in the scatter plot is determined as the lower limit of the effective movable pore throat of the shale oil.

[0020] In another possible implementation, performing a N2 isothermal adsorption-desorption experiment on the third core sample to obtain an average pore diameter includes:

[0021] Under the condition that the temperature is less than or equal to the first temperature and the vacuum state, degassing the third core sample for more than a first time period;

[0022] Under the condition that the temperature is less than or equal to the second temperature and the pressure is less than or equal to the first pressure, a N2 isothermal adsorption-desorption experiment is performed on the degassed third core sample to obtain experimental data;

[0023] Based on the experimental data, the average pore diameter is determined.

[0024] In another possible implementation, performing thin section observation, pyrolysis treatment, and X-ray diffraction testing on the first core sample, and determining a first core sample that meets the requirements from the plurality of first core samples based on the test results, includes:

[0025] Performing thin section observation on the first core sample to determine the sedimentary structure of the first core sample;

[0026] Performing an X-ray diffraction test on the first core sample to determine the whole-rock mineral composition of the first core sample;

[0027] Performing pyrolysis treatment on the first core sample to determine pyrolysis parameters of the first core sample;

[0028] Based on the sedimentary structure, whole-rock mineral composition and pyrolysis parameters of the first core sample, a first core sample that meets the requirements is determined from the multiple first core samples.

[0029] In another possible implementation, the pyrolysis parameters include: free hydrocarbon content and organic matter abundance;

[0030] Determining the oil saturation index of the second core sample includes:

[0031] Determining a ratio of free hydrocarbon content to organic matter abundance of a first core sample corresponding to the second core sample;

[0032] The ratio is expressed as a percentage to obtain the oil saturation index.

[0033] On the other hand, a system for determining the lower limit of movable pore throats of shale oil is provided, the system comprising: a raw material subsystem, an extraction subsystem, a N2 isothermal adsorption-desorption measurement subsystem and an analysis subsystem;

[0034] The raw material subsystem is used to obtain a plurality of first core samples in the target area; for each first core sample, perform thin section observation, pyrolysis treatment and X-ray diffraction test on the first core sample, and determine a first core sample that meets the requirements from the plurality of first core samples based on the test results; obtain a second core sample based on the position of the first core sample that meets the requirements in the target area; and determine the oil saturation index of the second core sample;

[0035] The extraction subsystem is used to extract the second core sample by using a weak polarity combination solvent and a strong polarity combination solvent to obtain a third core sample; wherein the weak polarity combination solvent is used to remove free shale oil in shale pores, and the strong polarity combination solvent is used to remove adsorbed and miscible shale oil in the shale pores;

[0036] The N2 isothermal adsorption-desorption measurement subsystem is used to perform a N2 isothermal adsorption-desorption experiment on the third core sample to obtain an average pore diameter;

[0037] The analysis subsystem is used to determine the lower limit of movable pore throats of shale oil in the target area based on the oil saturation index and average pore diameter corresponding to the second core sample.

[0038] In a possible implementation, the extraction subsystem is used to extract the second core sample in a weak polar combined solvent by ultrasonic extraction, and rinse and dry the extracted second core sample to obtain a fourth core sample; wherein the weak polar combined solvent includes dichloromethane and methanol, and the mass ratio of the dichloromethane to the methanol is 93:7;

[0039] In a strong polar combination solvent, the fourth core sample is extracted by ultrasonic extraction, and the fourth core sample after extraction is rinsed and dried to obtain the third core sample; wherein the strong polar combination solvent includes tetrahydrofuran, acetone and methanol, and the mass ratio of the tetrahydrofuran, the acetone and the methanol is 50:25:25.

[0040] In another possible implementation, the movable pore throat lower limit of shale oil includes: the theoretical movable pore throat lower limit of shale oil and the effective movable pore throat lower limit of shale oil, and the number of the second core samples is multiple;

[0041] The analysis subsystem is used to draw a scatter plot based on the oil saturation index and the average pore diameter corresponding to each second core sample, with the average pore diameter as the horizontal coordinate and the oil saturation index as the vertical coordinate; the average pore diameter corresponding to the oil saturation index of 0 in the scatter plot is determined as the lower limit of the theoretical movable pore throat of the shale oil; the average pore diameter corresponding to the oil saturation index of 100 in the scatter plot is determined as the lower limit of the effective movable pore throat of the shale oil.

[0042] In another possible implementation, the N2 isothermal adsorption-desorption measurement subsystem is used to degas the third core sample for more than a first time period under the conditions of a temperature less than or equal to a first temperature and a vacuum state; to perform a N2 isothermal adsorption-desorption experiment on the degassed third core sample under the conditions of a temperature less than or equal to a second temperature and a pressure less than or equal to a first pressure to obtain experimental data; and to determine the average pore diameter based on the experimental data.

[0043] In another possible implementation, the raw material subsystem is used to perform thin section observation on the first core sample to determine the sedimentary structure of the first core sample; perform X-ray diffraction test on the first core sample to determine the whole rock mineral composition of the first core sample; perform pyrolysis treatment on the first core sample to determine the pyrolysis parameters of the first core sample; and determine a first core sample that meets the requirements from the multiple first core samples based on the sedimentary structure, whole rock mineral composition and pyrolysis parameters of the first core sample.

[0044] In another possible implementation, the pyrolysis parameters include: free hydrocarbon content and organic matter abundance;

[0045] The raw material subsystem is used to determine the ratio of free hydrocarbon content to organic matter abundance of the first core sample corresponding to the second core sample; the ratio is expressed as a percentage to obtain the oil saturation index.

[0046] The embodiment of the present application provides a method for determining the lower limit of movable pore throats of shale oil, which method determines the first core sample that meets the requirements based on the test results by thin section observation, pyrolysis treatment and X-ray diffraction test of the first core sample, obtains the second core sample based on the position of the first core sample that meets the requirements in the target area, and determines the lower limit of movable pore throats of shale oil based on the oil saturation index and average pore diameter corresponding to the second core sample. It can be seen that the method screens core samples that meet the requirements based on the test results of thin section observation, pyrolysis treatment and X-ray diffraction test, and fully considers the influence of differences in shale composition, structure and organic characteristics on the lower limit of movable pore throats of shale oil, so that the lower limit of movable pore throats of shale oil can be accurately determined based on the oil saturation index and average pore diameter in the future.

[0047] It is to be understood that the foregoing general description and the following detailed description are exemplary only and are not restrictive of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a flow chart of a method for determining the lower limit of movable pore throats of shale oil provided in an embodiment of the present application;

[0049] Figure 2 is a schematic diagram of a system for determining the lower limit of movable pore throats of shale oil provided in an embodiment of the present application;

[0050] Figure 3 It is a schematic diagram of a theoretical calculation model of the lower limit of movable pore throats of shale oil provided in an embodiment of the present application;

[0051] Figure 4It is a schematic diagram of an embodiment of the present application providing a method for extracting a second core sample by sequentially using a weak polarity combined solvent and a strong polarity combined solvent;

[0052] Figure 5 is a schematic diagram of a pore size distribution curve obtained after a N2 isothermal adsorption-desorption experiment is performed on a third core sample provided in an embodiment of the present application;

[0053] Figure 6 It is a scatter plot based on the oil saturation index and the average pore diameter provided in an embodiment of the present application. DETAILED DESCRIPTION

[0054] In order to make the technical solutions and advantages of the present application clearer, the implementation methods of the present application are described in further detail below.

[0055] The terms "first", "second", "third" and "fourth" etc. in the specification and claims of the present application and the drawings are used to distinguish different objects, rather than to describe a specific order. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but optionally includes steps or units that are not listed, or optionally includes other steps or units inherent to these processes, methods, products or devices.

[0056] There are many methods to determine the lower limit of movable pore throats of shale oil, mainly including comprehensive characterization by multi-technical means, geochemical methods and molecular material simulation methods. However, these methods all ignore the influence of shale composition, structure and organic characteristics on the lower limit of movable pore throats of shale oil in the process of determining the lower limit of movable pore throats of shale oil. The lower limit of movable pore throats of shale oil with different composition, structure and organic characteristics is different. It lacks scientific significance to conduct research on the lower limit of movable pore throats of shale oil without considering these factors.

[0057] To this end, the present application provides a method for determining the lower limit of movable pore throats of shale oil. This method fully considers the impact of differences in shale composition, structure and organic characteristics on the lower limit of movable pore throats of shale oil, thereby accurately determining the lower limit of movable pore throats of shale oil.

[0058] Figure 1 is a flow chart of a method for determining the lower limit of movable pore throats of shale oil provided in an embodiment of the present application, see Figure 1 , the method comprising:

[0059] Step 101: Acquire a plurality of first core samples in a target area.

[0060] Combined with the geological data and exploration results of the target area, the area where the sweet spot section of the target area is located is determined, and multiple shale core samples with a diameter of 2.5 cm are drilled in the area after wax sealing or closed coring to obtain multiple first core samples, and the depth of the location is recorded. Among them, the target area is the oil and gas exploration area.

[0061] Step 102: For each first core sample, perform thin section observation, pyrolysis treatment, and X-ray diffraction test on the first core sample, and determine a first core sample that meets the requirements from a plurality of first core samples based on the test results.

[0062] This step can be achieved by following the steps (1) to (4), including:

[0063] (1) Conduct thin section observation on the first core sample to determine the sedimentary structure of the first core sample.

[0064] Based on ordinary thin section observations, the sedimentary structures of the first core sample were determined, such as laminar, layered and massive.

[0065] (2) Performing an X-ray diffraction test on the first core sample to determine the whole-rock mineral composition of the first core sample.

[0066] An XRD (X-Ray Diffraction) experimental analysis is performed on the first core sample to determine the main mineral components of the first core sample.

[0067] (3) Performing pyrolysis treatment on the first core sample to determine the pyrolysis parameters of the first core sample.

[0068] The first core sample is pyrolyzed to determine the organic matter abundance (TOC, Total Organic Carbon), free hydrocarbon content S1, hydrogen index HI, Tmax and other parameters of the first core sample, and obtain the pyrolysis parameters of the first core sample. Among them, Tmax refers to the temperature point corresponding to the maximum content of hydrocarbons.

[0069] Among them, ordinary thin section observation follows the standard SY / T 6414 (identification and statistical methods of whole rock optical section microscopic components), pyrolysis treatment follows GB / T 18602-2012 (pyrolysis analysis of rocks), and X-ray diffraction test follows SY / T5163 (X-ray diffraction analysis method of clay minerals and common non-clay minerals in sedimentary rocks).

[0070] (4) Based on the sedimentary structure, whole-rock mineral composition and pyrolysis parameters of the first core sample, a first core sample that meets the requirements is determined from multiple first core samples.

[0071] The organic matter type of shale can be determined by drawing a scatter plot based on the hydrogen index HI and Tmax of the first core sample.

[0072] Based on the sedimentary structure, whole-rock mineral composition, organic matter type and other pyrolysis parameters of the first core sample, combined with the sweet spot evaluation criteria of the target area, the first core sample corresponding to the lithology of the sweet spot segment of the target area is screened from multiple first core samples to obtain the first core sample that meets the requirements, and the depth of the location is recorded.

[0073] One point that needs to be explained is that the order of thin section observation, pyrolysis treatment and X-ray diffraction test can be set and changed as needed. For example, thin section observation is performed first, then pyrolysis treatment is performed, and finally X-ray diffraction test is performed; or, thin section observation is performed first, then X-ray diffraction test is performed, and finally pyrolysis treatment is performed. There is no specific limitation on this order.

[0074] Step 103: Based on the position of the first core sample that meets the requirements in the target area, a second core sample is obtained.

[0075] Based on the position of the first core sample that meets the requirements in the target area, a column sample with a diameter of 3 mm and a length of not less than 13 mm is drilled at this position by in-situ micro-drilling. For laminated shale, the drilling is carried out along the laminae, and for massive shale, the drilling is carried out vertically to the core direction to ensure the uniformity of sampling; the surface of the column sample is cleaned and ground into 100 mesh powder to obtain the second core sample.

[0076] Step 104: Determine the oil saturation index of the second core sample.

[0077] Determine the ratio of the free hydrocarbon content S1 to the organic matter abundance TOC of the first core sample corresponding to the second core sample; express the ratio as a percentage to obtain the oil saturation index.

[0078] Step 105: extracting the second core sample using a weak polarity combined solvent and a strong polarity combined solvent to obtain a third core sample.

[0079] This step can be achieved by following the steps (1) to (2), including:

[0080] (1) In a weak polar combined solvent, the second core sample is extracted by ultrasonic extraction, and the extracted second core sample is rinsed and dried to obtain a fourth core sample.

[0081] Among them, the weak polar combination solvent is used to remove free shale oil in the shale pores. The weak polar combination solvent includes dichloromethane and methanol, and the mass ratio of dichloromethane to methanol is 93:7.

[0082] Weigh about 10g of the second core sample and place it in a beaker or other container. Use ultrasonic extraction at room temperature in a weak polar combination solvent. The amount of weak polar combination solvent is 0.4mL / g. The frequency of ultrasonic extraction is 4000r / min, the centrifugation time is 15min, and the extraction is considered to be completed until the color does not change after adding fresh solvent. The second core sample after extraction is rinsed 3 times and dried naturally to obtain the fourth core sample.

[0083] (2) In a highly polar combined solvent, the fourth core sample is extracted by ultrasonic extraction, and the extracted fourth core sample is rinsed and dried to obtain a third core sample.

[0084] Among them, the highly polar combined solvent is used to remove adsorbed and miscible shale oil in shale pores, and the highly polar combined solvent includes tetrahydrofuran, acetone and methanol, and the mass ratio of the tetrahydrofuran, the acetone and the methanol is 50:25:25.

[0085] The fourth core sample was placed in a beaker or other container, and polar extraction was performed by ultrasonic extraction at room temperature in a strong polar combination solvent, and the amount of the strong polar combination solvent was 0.4 mL / g. The frequency of ultrasonic extraction was 4000 r / min, and the centrifugation time was 15 min. The extraction was considered to be completed until the color did not change after adding fresh solvent. The second core sample after extraction was rinsed 3 times and dried naturally to obtain the third core sample.

[0086] Step 106: Perform a N2 isothermal adsorption-desorption experiment on the third core sample to obtain an average pore diameter.

[0087] Under the conditions that the temperature is less than or equal to the first temperature and the vacuum state, the third core sample is degassed for more than a first time period; under the conditions that the temperature is less than or equal to the second temperature and the pressure is less than or equal to the first pressure, a N2 isothermal adsorption-desorption experiment is performed on the degassed third core sample to obtain experimental data; based on the experimental data, the average pore diameter is determined.

[0088] Among them, the first temperature, the first duration, the second temperature and the first pressure can be set and changed as needed. For example, the first temperature is 70°C, the first duration is 8 hours, the second temperature is -195°C, and the first pressure is 101.3KPa. Correspondingly, the process of the N2 isothermal adsorption-desorption experiment is: at a temperature of ≤70°C and a vacuum state, the third core sample is degassed for more than 8 hours, and then the degassed third core sample is subjected to a N2 isothermal adsorption-desorption experiment under the conditions of a temperature of ≤-195°C and a pressure of ≤101.3KPa to obtain experimental data.

[0089] After obtaining the experimental data, the BJH theory is used to process the experimental data through the following formula 1 to obtain the average pore diameter.

[0090] Formula 1:

[0091] Among them, r k represents the average pore diameter, γ represents the surface tension at the boiling point of nitrogen, and υ m represents the molar volume of nitrogen, R represents the gas constant, T represents the absolute temperature of the boiling point of nitrogen (77K), and p / p0 represents the relative pressure of nitrogen. m , R, T and p / p0 are constants or obtained from experimental data.

[0092] Step 107: Based on the oil saturation index and average pore diameter corresponding to the second core sample, determine the lower limit of the movable pore throats of shale oil in the target area.

[0093] The lower limit of movable pore throats of shale oil includes: the lower limit of theoretical movable pore throats of shale oil and the lower limit of effective movable pore throats of shale oil. The lower limit of theoretical movable pore throats of shale oil is the pore throat value corresponding to the initial flow of shale oil, and the lower limit of effective movable pore throats of shale oil is the minimum value of movable pore throats in the sweet spot section with development value. Both belong to the research scope of the lower limit of movable pore throats. And the number of the second core samples is multiple.

[0094] The process may be: based on the oil saturation index and the average pore diameter corresponding to each second core sample, a scatter plot is drawn with the average pore diameter as the abscissa and the oil saturation index as the ordinate. The average pore diameter corresponding to the oil saturation index of 0 in the scatter plot is determined as the lower limit of the theoretical movable pore throat of shale oil; the average pore diameter corresponding to the oil saturation index of 100 in the scatter plot is determined as the lower limit of the effective movable pore throat of shale oil.

[0095] It should be noted that a scatter plot can also be drawn with the oil saturation index as the horizontal axis and the average pore diameter as the vertical axis, without specific limitation. Moreover, in practical applications, the minimum value of the average pore diameter that meets the conditions near the oil saturation index of 0 in the scatter plot can be determined as the lower limit of the theoretical movable pore throat of shale oil; similarly, the minimum value of the average pore diameter that meets the conditions near the oil saturation index of 100 in the scatter plot can be determined as the lower limit of the effective movable pore throat of shale oil.

[0096] This application targets the shale in the same sweet spot section of the target area, conducts thin section observation, rock pyrolysis data and X-ray diffraction test, and screens the shale in the sweet spot section with the same sedimentary structure, similar mineral composition and organic matter type; obtains the average pore diameter of the shale by extracting and washing the shale oil in the shale sample, and then conducts a low-temperature nitrogen adsorption experiment; draws a relationship diagram between the shale oil saturation index OSI (Oil Saturation Index) and the average pore diameter of the shale after extraction and washing; uses OSI=0 and OSI=100 as the basis for identification, thereby determining the theoretical movable pore throat lower limit and the effective movable pore throat lower limit of shale oil.

[0097] The embodiment of the present application provides a method for determining the lower limit of movable pore throats of shale oil, which method determines the first core sample that meets the requirements based on the test results by thin section observation, pyrolysis treatment and X-ray diffraction test of the first core sample, obtains the second core sample based on the position of the first core sample that meets the requirements in the target area, and determines the lower limit of movable pore throats of shale oil based on the oil saturation index and average pore diameter corresponding to the second core sample. It can be seen that the method screens core samples that meet the requirements based on the test results of thin section observation, pyrolysis treatment and X-ray diffraction test, and fully considers the influence of differences in shale composition, structure and organic characteristics on the lower limit of movable pore throats of shale oil, so that the lower limit of movable pore throats of shale oil can be accurately determined based on the oil saturation index and average pore diameter in the future.

[0098] Moreover, this application is based on the sweet spot evaluation parameters, and provides the theoretical movable pore throat lower limit and effective movable pore throat lower limit of shale oil, which is more direct, comprehensive and scientific in guiding the exploration and development of shale oil, and has general guidance for the evaluation of shale oil mobility, resource calculation and sweet spot prediction in various oil fields. In addition, from the perspective of technology advancement and energy conservation and emission reduction, this application can be completed only by using N2 gas adsorption-desorption experiments, without the need for the combination of multiple other technologies, such as mercury injection, nuclear magnetic resonance, small angle scattering and CO2 adsorption, etc., which significantly reduces the experimental cost and potential environmental pollution problems.

[0099] Figure 2 is a schematic diagram of a system for determining the lower limit of movable pore throats of shale oil provided in an embodiment of the present application, see Figure 2 The system includes: a raw material subsystem 201, an extraction subsystem 202, a N2 isothermal adsorption-desorption measurement subsystem 203 and an analysis subsystem 204;

[0100] The raw material subsystem 201 is used to obtain a plurality of first core samples in the target area; for each first core sample, perform thin section observation, pyrolysis treatment and X-ray diffraction test on the first core sample, and determine a first core sample that meets the requirements from the plurality of first core samples based on the test results; obtain a second core sample based on the position of the first core sample that meets the requirements in the target area; and determine the oil saturation index of the second core sample;

[0101] The extraction subsystem 202 is used to extract the second core sample using a weak polarity combination solvent and a strong polarity combination solvent to obtain a third core sample; wherein the weak polarity combination solvent is used to remove free shale oil in the shale pores, and the strong polarity combination solvent is used to remove adsorbed and miscible shale oil in the shale pores;

[0102] N2 isothermal adsorption-desorption measurement subsystem 203, used to perform N2 isothermal adsorption-desorption experiment on the third core sample to obtain an average pore diameter;

[0103] The analysis subsystem 204 is used to determine the lower limit of movable pore throats of shale oil in the target area based on the oil saturation index and the average pore diameter corresponding to the second core sample.

[0104] In a possible implementation, the extraction subsystem 202 is used to extract the second core sample in a weak polar combined solvent by ultrasonic extraction, and rinse and dry the extracted second core sample to obtain a fourth core sample; wherein the weak polar combined solvent includes dichloromethane and methanol, and the mass ratio of dichloromethane to methanol is 93:7;

[0105] The fourth core sample is extracted by ultrasonic extraction in a strong polar combination solvent, and the extracted fourth core sample is rinsed and dried to obtain a third core sample; wherein the strong polar combination solvent includes tetrahydrofuran, acetone and methanol, and the mass ratio of tetrahydrofuran, acetone and methanol is 50:25:25.

[0106] In another possible implementation, the lower limit of movable pore throats of shale oil includes: the lower limit of theoretical movable pore throats of shale oil and the lower limit of effective movable pore throats of shale oil, and the number of the second core samples is multiple;

[0107] The analysis subsystem 204 is used to draw a scatter plot based on the oil saturation index and the average pore diameter corresponding to each second core sample, with the average pore diameter as the horizontal coordinate and the oil saturation index as the vertical coordinate; the average pore diameter corresponding to the oil saturation index of 0 in the scatter plot is determined as the lower limit of the theoretical movable pore throat of shale oil; the average pore diameter corresponding to the oil saturation index of 100 in the scatter plot is determined as the lower limit of the effective movable pore throat of shale oil.

[0108] In another possible implementation, the N2 isothermal adsorption-desorption measurement subsystem 203 is used to degas the third core sample for more than a first time period under the conditions of a temperature less than or equal to the first temperature and a vacuum state; to perform a N2 isothermal adsorption-desorption experiment on the degassed third core sample under the conditions of a temperature less than or equal to the second temperature and a pressure less than or equal to the first pressure to obtain experimental data; and to determine the average pore diameter based on the experimental data.

[0109] In another possible implementation, the raw material subsystem 201 is used to perform thin section observation on the first core sample to determine the sedimentary structure of the first core sample; perform X-ray diffraction test on the first core sample to determine the whole rock mineral composition of the first core sample; perform pyrolysis treatment on the first core sample to determine the pyrolysis parameters of the first core sample; and determine a first core sample that meets the requirements from multiple first core samples based on the sedimentary structure, whole rock mineral composition and pyrolysis parameters of the first core sample.

[0110] In another possible implementation, the pyrolysis parameters include: free hydrocarbon content and organic matter abundance;

[0111] The raw material subsystem 201 is used to determine the ratio of the free hydrocarbon content to the organic matter abundance of the first core sample corresponding to the second core sample; the ratio is expressed as a percentage to obtain the oil saturation index.

[0112] In an embodiment of the present application, the output of the raw material subsystem is connected to the input of the extraction subsystem, the output of the extraction subsystem is connected to the input of the N2 isothermal adsorption-desorption measurement subsystem, and the output of the N2 isothermal adsorption-desorption measurement subsystem is connected to the input of the analysis subsystem.

[0113] The embodiment of the present application provides a system for determining the lower limit of movable pore throats of shale oil, which determines the first core sample that meets the requirements based on the test results by performing thin section observation, pyrolysis treatment and X-ray diffraction test on the first core sample, obtains the second core sample based on the position of the first core sample that meets the requirements in the target area, and determines the lower limit of movable pore throats of shale oil based on the oil saturation index and average pore diameter corresponding to the second core sample. It can be seen that the system screens core samples that meet the requirements based on the test results of thin section observation, pyrolysis treatment and X-ray diffraction test, and fully considers the influence of differences in shale composition, structure and organic characteristics on the lower limit of movable pore throats of shale oil, so that the lower limit of movable pore throats of shale oil can be accurately determined based on the oil saturation index and average pore diameter in the future.

[0114] The present application will be described below through specific embodiments.

[0115] The Cangdong Sag is located in the southern part of the basin. It was developed under the regional tension background and is sandwiched between the Cangxian Uplift, Xuhei Uplift and Kongdian Uplift. The sag is composed of Mesozoic and Cenozoic basin filling strata. The Paleogene strata develop the Kongdian Formation, Shahejie Formation and Dongying Formation from bottom to top. The Kongdian Formation is further subdivided into three sections from bottom to top, Ek3, Ek2 and Ek1, with a sedimentary stratum thickness of 400-600m. During the Ek2 deposition period, the Cangdong Sag experienced the largest marine transgression period and subtropical humid climate, and developed freshwater-semi-brackish water closed depression lake basin sediments, which are characterized by a strong reduction environment of the sedimentary water body and high organic matter paleoproductivity. The Ek2 lithology is mainly composed of three major rock types: felsic, mixed and carbonate rocks. Laminated felsic shale is regarded as the key object of shale oil exploration in the second section of Kong in the Cangdong Sag, and the main production wells are vertically buried at a depth of 3800m to 4100m.

[0116] Select the first core samples of multiple wax-sealed or sealed cores in the same sweet spot section of the target area, clean the first surface, and conduct thin section observation, pyrolysis treatment and X-ray diffraction test. Among them, based on thin section observation, identify the shale sedimentary structure, such as laminar, layered and massive; based on XRD experimental analysis, determine the main mineral components of shale; based on pyrolysis data, obtain the organic matter abundance, free hydrocarbon content, hydrogen index, Tmax and other parameters of shale, and then identify the organic matter type of shale based on the scatter plot of hydrogen index and Tmax; based on the target area sweet spot evaluation criteria, screen the lithology of concern in the target area sweet spot section and record the depth of the location.

[0117] After the sampling position is determined, multiple column samples with a diameter of 3 mm and a length of not less than 13 mm are drilled by in-situ micro-drilling along the laminae to ensure the uniformity of sampling. The surface of each column sample is cleaned and ground into 100 mesh powder to obtain the second core sample.

[0118] For each second core sample, the oil saturation index of the shale core sample, that is, the oil saturation index of the second core sample, is determined according to the pyrolysis parameters of the shale core sample corresponding to the second core sample.

[0119] Take 10g of the second core sample, and successively extract it with a weak polar solvent combination and a strong polar solvent combination to remove the free, adsorbed and mutually soluble shale oil in the shale pores, dry it for later use, and obtain the third core sample. Among them, the weak polar combination solvent is dichloromethane and methanol, the mass ratio of the two is 93:7, and the amount of the weak polar combination solvent is 0.4mL / g; the strong polar combination solvent is tetrahydrofuran, acetone and methanol, the mass ratio of the three is 50:25:25, and the amount of solvent is 0.4mL / g. Ultrasonic extraction is adopted at room temperature, the ultrasonic frequency is 4000r / min, the centrifugation time is 15min, and the extraction is considered to be completed until the color of the added fresh solvent no longer changes. Rinse it with clean water 3 times and dry it naturally.

[0120] Among them, see Figure 3 , Figure 3 Schematic diagram of the theoretical calculation model of the lower limit of the movable pore throat of shale oil, in which the adsorbed and miscible shale oil is adsorbed on the surface of inorganic minerals or organic matter layers. Figure 4 , Figure 4 This is a schematic diagram of the extraction treatment of the second core sample by a weak polar combination solvent and a strong polar combination solvent in sequence.

[0121] Take 1g of the third core sample and conduct N2 isothermal adsorption-desorption experiment. The experimental process is: degassing for more than 8 hours at low temperature (≤70℃) and vacuum state, and N2 isothermal adsorption-desorption experiment is conducted on the degassed third core sample under the conditions of temperature ≤-195℃ and pressure ≤101.3KPa. By processing the experimental data, the pore size distribution curve and average pore diameter are obtained. Figure 5 , Figure 5 Schematic diagram of the pore size distribution curve obtained after N2 isothermal adsorption-desorption experiment on the third core sample.

[0122] Draw a scatter plot based on the average pore diameter and oil saturation index, see Figure 6 The minimum value of the average pore diameter that meets the conditions near the oil saturation index OSI of 0 in the scatter plot is 10nm, which is determined as the lower limit of the theoretical movable pore throat of shale oil, and the minimum value of the average pore diameter that meets the conditions near the oil saturation index OSI of 100 is 20nm, which is determined as the lower limit of the effective movable pore throat of shale oil.

[0123] The above description is only for the purpose of facilitating those skilled in the art to understand the technical solution of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for determining the lower limit of movable pore throats of shale oil, characterized in that: The method comprises: obtaining a plurality of first core samples in the target area; For each first core sample, performing thin section observation, pyrolysis treatment, and X-ray diffraction test on the first core sample, and determining a first core sample that meets the requirements from the plurality of first core samples based on the test results; Based on the position of the first core sample that meets the requirements in the target area, obtaining a second core sample; determining the oil saturation index of the second core sample; The second core sample is subjected to extraction treatment by using a weak polarity combination solvent and a strong polarity combination solvent to obtain a third core sample; wherein the weak polarity combination solvent is used to remove free shale oil in the shale pores, and the strong polarity combination solvent is used to remove adsorbed and mutually soluble shale oil in the shale pores; Performing a N2 isothermal adsorption-desorption experiment on the third core sample to obtain an average pore diameter; Based on the oil saturation index and the average pore diameter corresponding to the second core sample, the lower limit of the movable pore throat of shale oil in the target area is determined.

2. The method according to claim 1, characterized in that The step of extracting the second core sample by using a weak polarity combined solvent and a strong polarity combined solvent to obtain a third core sample comprises: In a weak polar combined solvent, the second core sample is extracted by ultrasonic extraction, and the extracted second core sample is rinsed and dried to obtain a fourth core sample; wherein the weak polar combined solvent includes dichloromethane and methanol, and the mass ratio of the dichloromethane to the methanol is 93:7; In a strong polar combination solvent, the fourth core sample is extracted by ultrasonic extraction, and the fourth core sample after extraction is rinsed and dried to obtain the third core sample; wherein the strong polar combination solvent includes tetrahydrofuran, acetone and methanol, and the mass ratio of the tetrahydrofuran, the acetone and the methanol is 50:25:

25.

3. The method according to claim 1, characterized in that The movable pore throat lower limit of shale oil includes: the theoretical movable pore throat lower limit of shale oil and the effective movable pore throat lower limit of shale oil, and the number of the second core samples is multiple; Determining the lower limit of movable pore throats of shale oil in the target area based on the oil saturation index and the average pore diameter corresponding to the second core sample includes: Based on the oil saturation index and the average pore diameter corresponding to each second core sample, a scatter plot is drawn with the average pore diameter as the abscissa and the oil saturation index as the ordinate; The average pore diameter corresponding to the oil saturation index of 0 in the scatter plot is determined as the lower limit of the theoretical movable pore throat of the shale oil; The average pore diameter corresponding to the oil saturation index of 100 in the scatter plot is determined as the lower limit of the effective movable pore throat of the shale oil.

4. The method according to claim 1, characterized in that: The N2 isothermal adsorption-desorption experiment is performed on the third core sample to obtain an average pore diameter, including: Under the condition that the temperature is less than or equal to the first temperature and the vacuum state, degassing the third core sample for more than a first time period; Under the condition that the temperature is less than or equal to the second temperature and the pressure is less than or equal to the first pressure, a N2 isothermal adsorption-desorption experiment is performed on the degassed third core sample to obtain experimental data; Based on the experimental data, the average pore diameter is determined.

5. The method according to claim 1, characterized in that The step of performing thin section observation, pyrolysis treatment, and X-ray diffraction testing on the first core sample, and determining a first core sample that meets the requirements from the plurality of first core samples based on the test results, comprises: Performing thin section observation on the first core sample to determine the sedimentary structure of the first core sample; Performing an X-ray diffraction test on the first core sample to determine the whole-rock mineral composition of the first core sample; Performing pyrolysis treatment on the first core sample to determine pyrolysis parameters of the first core sample; Based on the sedimentary structure, whole-rock mineral composition and pyrolysis parameters of the first core sample, a first core sample that meets the requirements is determined from the multiple first core samples.

6. The method according to claim 5, characterized in that The pyrolysis parameters include: free hydrocarbon content and organic matter abundance; Determining the oil saturation index of the second core sample includes: Determining a ratio of free hydrocarbon content to organic matter abundance of a first core sample corresponding to the second core sample; The ratio is expressed as a percentage to obtain the oil saturation index.

7. A system for determining the lower limit of movable pore throats of shale oil, characterized in that: The system comprises: a raw material subsystem, an extraction subsystem, a N2 isothermal adsorption-desorption measurement subsystem and an analysis subsystem; The raw material subsystem is used to obtain a plurality of first core samples in the target area; for each first core sample, perform thin section observation, pyrolysis treatment and X-ray diffraction test on the first core sample, and determine a first core sample that meets the requirements from the plurality of first core samples based on the test results; obtain a second core sample based on the position of the first core sample that meets the requirements in the target area; and determine the oil saturation index of the second core sample; The extraction subsystem is used to extract the second core sample by using a weak polarity combination solvent and a strong polarity combination solvent to obtain a third core sample; wherein the weak polarity combination solvent is used to remove free shale oil in shale pores, and the strong polarity combination solvent is used to remove adsorbed and miscible shale oil in the shale pores; The N2 isothermal adsorption-desorption measurement subsystem is used to perform a N2 isothermal adsorption-desorption experiment on the third core sample to obtain an average pore diameter; The analysis subsystem is used to determine the lower limit of movable pore throats of shale oil in the target area based on the oil saturation index and average pore diameter corresponding to the second core sample.

8. The system according to claim 7, characterized in that The extraction subsystem is used to extract the second core sample in a weak polar combined solvent by ultrasonic extraction, and rinse and dry the extracted second core sample to obtain a fourth core sample; wherein the weak polar combined solvent includes dichloromethane and methanol, and the mass ratio of the dichloromethane to the methanol is 93:7; In a strong polar combination solvent, the fourth core sample is extracted by ultrasonic extraction, and the fourth core sample after extraction is rinsed and dried to obtain the third core sample; wherein the strong polar combination solvent includes tetrahydrofuran, acetone and methanol, and the mass ratio of the tetrahydrofuran, the acetone and the methanol is 50:25:

25.

9. The system according to claim 7, characterized in that The movable pore throat lower limit of shale oil includes: the theoretical movable pore throat lower limit of shale oil and the effective movable pore throat lower limit of shale oil, and the number of the second core samples is multiple; The analysis subsystem is used to draw a scatter plot based on the oil saturation index and the average pore diameter corresponding to each second core sample, with the average pore diameter as the horizontal coordinate and the oil saturation index as the vertical coordinate; the average pore diameter corresponding to the oil saturation index of 0 in the scatter plot is determined as the lower limit of the theoretical movable pore throat of the shale oil; the average pore diameter corresponding to the oil saturation index of 100 in the scatter plot is determined as the lower limit of the effective movable pore throat of the shale oil.

10. The system according to claim 7, characterized in that The N2 isothermal adsorption-desorption measurement subsystem is used to degas the third core sample for a first period of time under the condition that the temperature is less than or equal to the first temperature and the vacuum state; Under the conditions that the temperature is less than or equal to the second temperature and the pressure is less than or equal to the first pressure, a N2 isothermal adsorption-desorption experiment is performed on the degassed third core sample to obtain experimental data; based on the experimental data, the average pore diameter is determined.

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