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

Abstract

The application discloses a shale oil movable pore throat lower limit determination method and system, and belongs to the technical field of oil and gas exploration. The method performs slice observation, pyrolysis treatment and X-ray diffraction testing on a first core sample, determines a required first core sample based on the test results, obtains a second core sample based on the position of the required first core sample in a target area, and determines a shale oil movable pore throat lower limit based on the oil saturation index and the average pore diameter corresponding to the second core sample. As can be seen, the method screens the required core sample based on the test results of slice observation, pyrolysis treatment and X-ray diffraction testing, fully considers the influence of the differences of shale composition, structure and organic characteristics on the shale oil movable pore throat lower limit, and thus the shale oil movable pore throat lower limit can be accurately determined based on the oil saturation index and the average pore diameter.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil and gas exploration, and particularly relates to a shale oil movable pore throat lower limit determination method and system. BACKGROUND

[0002] Shale oil is a hot spot and frontier field in 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 shale movable pore throat lower limit. The pore throat of shale determines the productivity of the reservoir and controls the storage and migration of oil and gas, and scientifically determining the shale oil movable pore throat lower limit is crucial for scientific evaluation of shale oil reserves and improvement of oil and gas recovery. Therefore, how to determine the shale oil movable pore throat lower limit has become a problem to be solved. SUMMARY

[0003] The shale oil movable pore throat lower limit determination method and system provided by the embodiments of the present application can reduce the influence of the differences in shale composition, structure and organic characteristics on the shale oil movable pore throat lower limit, so as to accurately determine the shale oil movable pore throat lower limit. The technical solution is as follows:

[0004] In one aspect, a shale oil movable pore throat lower limit determination method is provided, and the method comprises the following steps:

[0005] Obtaining a plurality of first core samples in a 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 required first core sample from the plurality of first core samples based on the test results;

[0007] Based on the location of the required first core sample in the target area, obtaining a second core sample;

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

[0009] Performing extraction treatment on the second core sample by using a weak polar combined solvent and a strong polar combined solvent to obtain a third core sample; wherein the weak polar combined solvent is used to remove free-state shale oil in shale pores, and the strong polar combined solvent is used to remove adsorbed-state and mutual-solvent-state shale oil in the shale pores;

[0010] Performing 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, determining the shale oil movable pore throat lower limit in the target area.

[0012] In a possible implementation, the extracting the second core sample by using a weakly polar combined solvent and a strongly polar combined solvent to obtain a third core sample comprises the following steps.

[0013] The second core sample is extracted by using an ultrasonic extraction method in a weakly polar combined solvent, and the extracted second core sample is rinsed and dried to obtain a fourth core sample; the weakly polar combined solvent comprises dichloromethane and methanol, and the mass ratio of the dichloromethane to the methanol is 93:7.

[0014] The fourth core sample is extracted by using an ultrasonic extraction method in a strongly polar combined solvent, and the extracted fourth core sample is rinsed and dried to obtain the third core sample; the strongly polar combined solvent comprises tetrahydrofuran, acetone and methanol, and the mass ratio of the tetrahydrofuran to the acetone to the methanol is 50:25:25.

[0015] In another possible implementation, the lower limit of the shale oil movable pore throat comprises a theoretical lower limit of shale oil movable pore throat and an effective lower limit of shale oil movable pore throat, and the second core sample is multiple in number.

[0016] The lower limit of the shale oil movable pore throat in the target area is determined based on the oil saturation index and the average pore diameter corresponding to the second core sample, comprising:

[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 theoretical lower limit of the shale oil movable pore throat.

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

[0020] In another possible implementation, the N2 isothermal adsorption-desorption experiment on the third core sample is performed to obtain the average pore diameter, comprising:

[0021] The third core sample is degassed for more than a first time length under the condition that the temperature is less than or equal to a first temperature and the vacuum state.

[0022] The degassed third core sample is subjected to an N2 isothermal adsorption-desorption experiment under the condition that the temperature is less than or equal to a second temperature and the pressure is less than or equal to a first pressure to obtain experimental data.

[0023] The average pore diameter is determined based on the experimental data.

[0024] In another possible implementation, the slice observation, pyrolysis treatment and X-ray diffraction test are performed on the first core samples, and a required first core sample is determined from the plurality of first core samples based on test results, including:

[0025] The slice observation is performed on the first core sample to determine a sedimentary structure of the first core sample;

[0026] The X-ray diffraction test is performed on the first core sample to determine a whole-rock mineral composition of the first core sample;

[0027] The pyrolysis treatment is performed on the first core sample to determine a pyrolysis parameter of the first core sample;

[0028] The required first core sample is determined from the plurality of first core samples based on the sedimentary structure, the whole-rock mineral composition and the pyrolysis parameter of the first core sample.

[0029] In another possible implementation, the pyrolysis parameter includes a free hydrocarbon content and an organic matter abundance;

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

[0031] The ratio of the free hydrocarbon content to the organic matter abundance of the first core sample corresponding to the second core sample is determined;

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

[0033] In another aspect, a system for determining a lower limit of movable pore throat of shale oil is provided, and the system includes a raw material subsystem, an extraction subsystem, an N2 isothermal adsorption-desorption determination subsystem and an analysis subsystem;

[0034] The raw material subsystem is configured to obtain a plurality of first core samples in a target area; for each first core sample, slice observation, pyrolysis treatment and X-ray diffraction test are performed on the first core sample, and a required first core sample is determined from the plurality of first core samples based on test results; based on the position of the required first core sample in the target area, a second core sample is obtained; and an oil saturation index of the second core sample is determined;

[0035] The extraction subsystem is configured to perform extraction treatment on the second core sample by using a weakly polar combined solvent and a strongly polar combined solvent to obtain a third core sample; wherein the weakly polar combined solvent is used to remove free-state shale oil in shale pores, and the strongly polar combined solvent is used to remove adsorbed-state and mutually soluble-state shale oil in the shale pores;

[0036] The N2 isothermal adsorption-desorption measurement subsystem is configured to perform N2 isothermal adsorption-desorption experiments on the third core sample to obtain an average pore diameter.

[0037] The analysis subsystem is configured to determine a shale oil movable pore throat lower limit in the target zone based on the oil saturation index and the average pore diameter corresponding to the second core sample.

[0038] In a possible implementation, the extraction subsystem is configured to perform extraction processing on the second core sample in a weakly polar combined solvent by using an ultrasonic extraction method, and to rinse and dry the second core sample after the extraction processing to obtain a fourth core sample; the weakly polar combined solvent includes dichloromethane and methanol, and the mass ratio of the dichloromethane to the methanol is 93:7.

[0039] The fourth core sample is extracted in a strongly polar combined solvent by using an ultrasonic extraction method, and the fourth core sample after the extraction processing is rinsed and dried to obtain the third core sample; the strongly polar combined 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 shale oil movable pore throat lower limit includes a shale oil theoretical movable pore throat lower limit and a shale oil effective movable pore throat lower limit, and the number of the second core samples is a plurality.

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

[0042] In another possible implementation, the N2 isothermal adsorption-desorption measurement subsystem is configured to degas the third core sample for more than a first time length under the condition that the temperature is less than or equal to a first temperature and the vacuum state, to perform N2 isothermal adsorption-desorption experiments on the degassed third core sample under the condition that the temperature is less than or equal to a second temperature and the pressure is 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 a possible implementation, the raw material subsystem is configured to: perform thin section observation on the first core sample to determine a sedimentary structure of the first core sample; perform X-ray diffraction testing on the first core sample to determine a whole-rock mineral composition of the first core sample; and perform pyrolysis processing on the first core sample to determine a pyrolysis parameter of the first core sample; and determine a required first core sample from the plurality of first core samples based on the sedimentary structure, the whole-rock mineral composition, and the pyrolysis parameter of the first core sample.

[0044] In a possible implementation, the pyrolysis parameter includes: free hydrocarbon content and organic matter abundance.

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

[0046] The embodiment of the present application provides a method for determining a lower limit of movable pore throat of shale oil. The method performs thin section observation, pyrolysis processing, and X-ray diffraction testing on a first core sample, determines a required first core sample based on the test results, obtains a second core sample based on the position of the required first core sample in a target area, and determines a lower limit of movable pore throat of shale oil based on the oil saturation index and the average pore diameter corresponding to the second core sample. It can be seen that the method screens a required core sample based on the test results of thin section observation, pyrolysis processing, and X-ray diffraction testing, fully considers the influence of the differences in shale composition, structure, and organic characteristics on the lower limit of movable pore throat of shale oil, and thus can accurately determine the lower limit of movable pore throat of shale oil based on the oil saturation index and the average pore diameter.

[0047] It should be understood that the general description above and the detailed description below are only examples and cannot limit the present disclosure. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 FIG. 1 is a flowchart of a method for determining a lower limit of movable pore throat of shale oil according to an embodiment of the present application;

[0049] Figure 2 FIG. 2 is a schematic diagram of a system for determining a lower limit of movable pore throat of shale oil according to an embodiment of the present application;

[0050] Figure 3 FIG. 3 is a schematic diagram of a theoretical calculation model of a lower limit of movable pore throat of shale oil according to an embodiment of the present application;

[0051] Figure 4is a schematic view of the first core sample being extracted by a weak polar combined solvent and a strong polar combined solvent in sequence provided by an embodiment of the present application.

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

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

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

[0055] The terms "first", "second", "third", and "fourth" and the like in the specification and claims of the present application and the drawings are used to distinguish different objects, and are not used to describe a particular order. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion. 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 can optionally include steps or units not listed, or can optionally include other steps or units inherent to the process, method, product, or device.

[0056] There are many methods for determining the lower limit of movable pore throat of shale oil, mainly including multi-technical means comprehensive characterization method, geochemical method, and molecular material simulation method, but these methods all ignore the influence of shale composition, structure, and organic characteristics on the lower limit of movable pore throat of shale oil. The lower limit of movable pore throat of shale oil is different for different compositions, structures, and organic characteristics, and the research on the lower limit of movable pore throat of shale oil without considering these factors lacks scientific significance.

[0057] Therefore, the present application provides a method for determining the lower limit of movable pore throat of shale oil, which fully considers the influence of the differences in shale composition, structure, and organic characteristics on the lower limit of movable pore throat of shale oil, so that the lower limit of movable pore throat of shale oil can be accurately determined.

[0058] Figure 1 is a flowchart of a method for determining the lower limit of movable pore throat of shale oil provided by an embodiment of the present application, referring to Figure 1 The method comprises the following steps.

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

[0060] In combination with geological data and exploration results of the target area, a region where a favorable drilling sweet spot of the target area is located is determined, a plurality of shale core samples with a diameter of 2.5 cm are drilled in the region by wax sealing treatment or sealed coring, a plurality of first core samples are obtained, and the depth of the position is recorded. The target area is an oil and gas exploration area.

[0061] Step 102: For each first core sample, slice observation, pyrolysis treatment and X-ray diffraction test are performed on the first core sample, and based on the test results, a required first core sample is determined from the plurality of first core samples.

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

[0063] (1) Slice observation is performed on the first core sample to determine the sedimentary structure of the first core sample.

[0064] According to ordinary slice observation, the sedimentary structure of the first core sample is determined, such as lamination, layering and blockiness.

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

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

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

[0068] Pyrolysis treatment is performed on the first core sample to determine parameters such as total organic carbon (TOC), free hydrocarbon content S1, hydrogen index HI and Tmax of the first core sample, and pyrolysis parameters of the first core sample are obtained. Tmax refers to the temperature point size corresponding to the largest amount of hydrocarbons.

[0069] The ordinary slice observation follows the standard SY / T 6414 (Whole Rock Optical Microscopic Component Identification and Statistical Method), the pyrolysis treatment follows GB / T 18602-2012 (Rock Pyrolysis Analysis), and the 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 required first core sample is determined from the plurality of first core samples.

[0071] Based on the hydrogen index HI and Tmax of the first core sample, a scatter plot can be drawn to determine the organic matter type of the shale.

[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 target area sweet spot evaluation standard, the first core sample corresponding to the lithology of the target area sweet spot segment concerned is screened from a plurality of first core samples, to obtain a first core sample meeting the requirements, and the position depth is recorded.

[0073] It should be noted that the order of thin section observation, pyrolysis treatment and X-ray diffraction test can be set and changed as needed, for example, first thin section observation, then pyrolysis treatment, and finally X-ray diffraction test; or, first thin section observation, then X-ray diffraction test, and finally pyrolysis treatment, and the order is not specifically limited.

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

[0075] Based on the position of the first core sample meeting the requirements in the target area, a column sample with a diameter of 3mm and a length of not less than 13mm is drilled by in-situ micro-drilling at the position. Among them, for laminated shale, drilling along the lamina, for massive shale, drilling perpendicular to the core direction, to ensure the uniformity of the sample; 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: Extract the second core sample by using weak polar combined solvent and strong polar combined solvent to obtain a third core sample.

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

[0080] (1) In the 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] The weak polar combined solvent is used to remove free shale oil in the shale pores, and the weak polar combined solvent includes dichloromethane and methanol, and the mass ratio of dichloromethane to methanol is 93:7.

[0082] A second core sample of about 10 g is placed in a beaker or other container, and is extracted in a weakly polar combined solvent at room temperature by ultrasonic extraction. The amount of weakly polar combined solvent used is 0.4 mL / g. The ultrasonic extraction is performed at a frequency of 4000 r / min, and the centrifugation time is 15 min. The extraction is continued until the color of the sample does not change after the addition of fresh solvent, and is considered to be complete. The second core sample after extraction is washed three times with clean water and is naturally dried to obtain a fourth core sample.

[0083] (2) The fourth core sample is extracted in a strongly polar combined solvent by ultrasonic extraction, and the fourth core sample after extraction is washed and dried to obtain a third core sample.

[0084] The strongly polar combined solvent is used to remove the adsorbed and mutually soluble shale oil in the pores of the shale. The strongly 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 is placed in a beaker or other container, and is extracted in a strongly polar combined solvent at room temperature by ultrasonic extraction. The amount of strongly polar combined solvent used is 0.4 mL / g. The ultrasonic extraction is performed at a frequency of 4000 r / min, and the centrifugation time is 15 min. The extraction is continued until the color of the sample does not change after the addition of fresh solvent, and is considered to be complete. The second core sample after extraction is washed three times with clean water and is naturally dried to obtain a third core sample.

[0086] Step 106: The third core sample is subjected to N2 isothermal adsorption-desorption experiment to obtain the average pore diameter.

[0087] The third core sample is degassed for more than a first time length under the condition of a temperature less than or equal to a first temperature and a vacuum state. The degassed third core sample is subjected to N2 isothermal adsorption-desorption experiment under the condition 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. The average pore diameter is determined based on the experimental data.

[0088] The first temperature, the first time length, the second temperature and the first pressure can be set and changed as needed. For example, the first temperature is 70℃, the first time length is 8 hours, the second temperature is -195℃, and the first pressure is 101.3 KPa. Accordingly, the process of the N2 isothermal adsorption-desorption experiment is as follows: the third core sample is degassed for more than 8 hours under the condition of a temperature ≤70℃ and a vacuum state, and then the degassed third core sample is subjected to N2 isothermal adsorption-desorption experiment under the condition of a temperature ≤-195℃ and a pressure ≤101.3 KPa to obtain experimental data.

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

[0090] Formula one:

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

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

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

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

[0095] It should be noted that the oil saturation index can also be used as the horizontal coordinate and the average pore diameter as the vertical coordinate to draw a scatter plot, which is not specifically limited. In actual application, the minimum value of the average pore diameter near the oil saturation index of 0 in the scatter plot that meets the conditions can be determined as the lower limit of theoretical movable pore throat of shale oil; and similarly, the minimum value of the average pore diameter near the oil saturation index of 100 in the scatter plot that meets the conditions can be determined as the lower limit of effective movable pore throat of shale oil.

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

[0097] The present application provides a shale oil movable pore throat lower limit determination method, which carries out thin section observation, pyrolysis treatment and X-ray diffraction test on the first core sample, determines the required first core sample based on the test results, obtains the second core sample based on the position of the required first core sample in the target area, and determines the shale oil movable pore throat lower limit based on the oil saturation index and average pore diameter corresponding to the second core sample. As can be seen, the method screens the required core sample based on the test results of thin section observation, pyrolysis treatment and X-ray diffraction test, fully considers the influence of the difference of shale composition, structure and organic characteristics on the shale oil movable pore throat lower limit, and thus can accurately determine the shale oil movable pore throat lower limit based on the oil saturation index and average pore diameter.

[0098] In addition, the present application provides shale oil theoretical movable pore throat lower limit and effective movable pore throat lower limit based on the sweet spot section evaluation parameters, which is more direct, comprehensive and scientific in guiding shale oil exploration and development, and has universal guidance for shale oil mobility evaluation, resource quantity calculation and sweet spot prediction of various oilfields. In addition, from the perspective of technical advancement and energy saving and emission reduction, the present application only uses N2 gas adsorption-desorption experiment, without other multiple technologies such as mercury injection, nuclear magnetic resonance, small angle scattering and CO2 adsorption, which significantly reduces the experimental cost and potential environmental pollution problems.

[0099] Figure 2 is a schematic diagram of a shale oil movable pore throat lower limit determination system provided by the present application, referring to Figure 2 The system comprises a raw material subsystem 201, an extraction subsystem 202, an N2 isothermal adsorption-desorption determination subsystem 203 and an analysis subsystem 204.

[0100] The raw material subsystem 201 is configured 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 testing on the first core sample, determine a qualified first core sample from the plurality of first core samples based on the testing results; obtain a second core sample based on the position of the qualified first core sample in the target area; and determine the oil saturation index of the second core sample;

[0101] The extraction subsystem 202 is configured to perform extraction treatment on the second core sample by using a weak-polarity combined solvent and a strong-polarity combined solvent to obtain a third core sample; wherein the weak-polarity combined solvent is used to remove free-state shale oil in shale pores, and the strong-polarity combined solvent is used to remove adsorbed-state and mutual-solubility-state shale oil in shale pores.

[0102] The N2 isothermal adsorption-desorption measurement subsystem 203 is configured to perform N2 isothermal adsorption-desorption experiments on the third core sample to obtain the average pore diameter.

[0103] The analysis subsystem 204 is configured 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 configured to perform extraction treatment on the second core sample in a weak-polarity combined solvent by using an ultrasonic extraction method, rinse and air-dry the second core sample after the extraction treatment to obtain a fourth core sample; wherein the weak-polarity combined solvent includes dichloromethane and methanol, and the mass ratio of dichloromethane to methanol is 93:7.

[0105] In a strong-polarity combined solvent, perform extraction treatment on the fourth core sample by using an ultrasonic extraction method, rinse and air-dry the fourth core sample after the extraction treatment to obtain the third core sample; wherein the strong-polarity combined solvent includes tetrahydrofuran, acetone and methanol, and the mass ratio of tetrahydrofuran to acetone to methanol is 50:25:25.

[0106] In another possible implementation, the lower limit of movable pore throats of shale oil includes a theoretical lower limit of movable pore throats of shale oil and an effective lower limit of movable pore throats of shale oil, and the number of second core samples is a plurality.

[0107] The analysis subsystem 204 is configured to plot a scatter plot by taking the average pore diameter as the horizontal coordinate and the oil saturation index as the vertical coordinate based on the oil saturation index and the average pore diameter corresponding to each second core sample; determine the average pore diameter corresponding to the oil saturation index of 0 in the scatter plot as the theoretical lower limit of movable pore throats of shale oil; and determine the average pore diameter corresponding to the oil saturation index of 100 in the scatter plot as the effective lower limit of movable pore throats of shale oil.

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

[0109] In another possible implementation, the raw material subsystem 201 is configured to: perform slice observation on the first core sample to determine a sedimentary structure of the first core sample; perform X-ray diffraction testing on the first core sample to determine a whole-rock mineral composition of the first core sample; perform pyrolysis processing on the first core sample to determine a pyrolysis parameter of the first core sample; and determine a required first core sample from the plurality of first core samples based on the sedimentary structure, the whole-rock mineral composition, and the pyrolysis parameter of the first core sample.

[0110] In another possible implementation, the pyrolysis parameter includes: free hydrocarbon content and organic matter abundance.

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

[0112] In the embodiments 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 embodiments of the present application provide a system for determining a lower limit of movable pore throat of shale oil. The system performs slice observation, pyrolysis processing, and X-ray diffraction testing on a first core sample, determines a required first core sample based on the test results, obtains a second core sample based on the location of the required first core sample in a target area, and determines a lower limit of movable pore throat of shale oil based on an oil saturation index and an average pore diameter corresponding to the second core sample. As can be seen, the system screens a required core sample based on the test results of slice observation, pyrolysis processing, and X-ray diffraction testing, fully considers the influence of differences in shale composition, structure, and organic characteristics on the lower limit of movable pore throat of shale oil, and thus can accurately determine the lower limit of movable pore throat of shale oil based on the oil saturation index and the average pore diameter.

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

[0115] Cangdong Sag is located in the southern part of the basin, developed in the regional extensional setting, sandwiched between Cangxian uplift, Xuhei uplift and Kongdian salient. The sag is composed of the Mesozoic and Cenozoic basin filling strata, and the Paleogene strata are developed from bottom to top as Kongdian Formation, Shahejie Formation and Dongying Formation. Kongdian Formation is further divided into three sections from bottom to top, Ek3, Ek2 and Ek1, and the sedimentary strata thickness is 400-600m. During the Ek2 deposition period, Cangdong Sag experienced the maximum transgression period and subtropical humid climate, and developed fresh water-semi-salt water closed type depression lake basin deposition, showing strong reducing environment of the sedimentary water body and high organic matter paleo-productivity. Ek2 lithology is mainly composed of felsic, mixed and carbonate rocks, and laminated felsic shale is considered as the key object for shale oil exploration in the second member of Kongdian Formation in Cangdong Sag, and the main production well is vertically buried at a depth of 3800m-4100m.

[0116] Select first core samples from multiple wax sealing treatments or sealed coring of the same sweet spot section in the target area, clean the first surface, and carry out thin section observation, pyrolysis treatment and X-ray diffraction test. Among them, according to the thin section observation, the shale sedimentary structure is identified, such as laminated, layered and massive; according to the XRD experimental analysis, the main mineral components of the shale are determined; according to the pyrolysis treatment data, the parameters of the shale such as organic matter abundance, free hydrocarbon content, hydrogen index and Tmax are obtained, and then the organic matter type of the shale is identified according to the scatter plot of hydrogen index and Tmax; according to the sweet spot evaluation standard of the target area, the lithology of the sweet spot section in the target area is selected, and the depth of the position is recorded.

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

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

[0119] Take 10g of the second core sample, and then extract it with a weak polar solvent combination and a strong polar solvent combination to remove the shale oil in the free state, adsorbed state and mutual state in the shale pores, and dry it for standby to obtain a third core sample. Among them, the weak polar solvent combination is dichloromethane and methanol, and the mass ratio of the two is 93:7, and the amount of the weak polar solvent combination is 0.4mL / g; the strong polar solvent combination is tetrahydrofuran, acetone and methanol, and the mass ratio of the three is 50:25:25, and the solvent amount is 0.4mL / g. The extraction is carried out by ultrasonic extraction at room temperature, the ultrasonic frequency is 4000r / min, the centrifugation time is 15min, and the extraction is considered to be completed when the color of the fresh solvent added does not change any more. After washing with clean water for 3 times, it is naturally dried.

[0120] wherein, referring to Figure 3 , Figure 3 is a schematic diagram of a theoretical calculation model of the lower limit of movable pore throat of shale oil, wherein the shale oil in adsorbed state and mutual solubility state is adsorbed on the surface of inorganic mineral or organic matter layer. Referring to Figure 4 , Figure 4 is a schematic diagram of extracting the second core sample by weak polar combined solvent and strong polar combined solvent in sequence.

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

[0122] Based on the average pore diameter and the oil saturation index, a scatter plot is drawn, referring to Figure 6 . The minimum value of the average pore diameter of 10nm in the scatter plot around the oil saturation index OSI of 0 is determined as the theoretical lower limit of movable pore throat of shale oil, and the minimum value of the average pore diameter of 20nm in the scatter plot around the oil saturation index OSI of 100 is determined as the effective lower limit of movable pore throat of shale oil.

[0123] The above only serves to facilitate the understanding of the technical solution of the present application by those skilled in the art, and does not limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles 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 mobile pore throat in shale oil, characterized in that, The method comprises: obtaining a plurality of first core samples in a 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 qualified first core sample from the plurality of first core samples based on the test results; based on the location of the qualified first core sample in the target area, obtaining a second core sample; determining the oil saturation index of the second core sample; extracting the second core sample by a weakly polar combined solvent and a strongly polar combined solvent to obtain a third core sample; wherein the weakly polar combined solvent is used to remove free-state shale oil in shale pores, and the strongly polar combined solvent is used to remove adsorbed-state and mutually soluble-state shale oil in the shale pores; performing N2 isothermal adsorption-desorption experiment on the third core sample to obtain the average pore diameter; based on the oil saturation index and the average pore diameter corresponding to the second core sample, determining the lower limit of shale oil movable pore throat in the target area.

2. The method of claim 1, wherein, The extraction of the second core sample by a weakly polar combined solvent and a strongly polar combined solvent to obtain a third core sample comprises: in a weakly 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 weakly polar combined solvent comprises dichloromethane and methanol, and the mass ratio of dichloromethane to methanol is 93:7; in a strongly polar combined solvent, the fourth core sample is extracted by ultrasonic extraction, and the extracted fourth core sample is rinsed and dried to obtain the third core sample; wherein the strongly polar combined solvent comprises tetrahydrofuran, acetone and methanol, and the mass ratio of tetrahydrofuran, acetone and methanol is 50:25:

25.

3. The method of claim 1, wherein, The lower limit of shale oil movable pore throat comprises a shale oil theoretical movable pore throat lower limit and a shale oil effective movable pore throat lower limit, and the number of the second core sample is multiple; Based on the oil saturation index and the average pore diameter corresponding to the second core sample, the lower limit of shale oil movable pore throat in the target area is determined, comprising: based on the oil saturation index and the average pore diameter corresponding to each second core sample, an average pore diameter is taken as the abscissa, and an oil saturation index is taken as the ordinate to draw a scatter plot; the average pore diameter corresponding to the oil saturation index of 0 in the scatter plot is determined as the shale oil theoretical movable pore throat lower limit; the average pore diameter corresponding to the oil saturation index of 100 in the scatter plot is determined as the shale oil effective movable pore throat lower limit.

4. The method of claim 1, wherein, The N2 isothermal adsorption-desorption experiment on the third core sample to obtain the average pore diameter comprises: degassing the third core sample for more than a first time under the condition of a temperature less than or equal to a first temperature and a vacuum state; performing N2 isothermal adsorption-desorption experiment on the degassed third core sample under the condition 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; Based on the experimental data, the average pore diameter is determined.

5. The method of claim 1, wherein, The slice observation, pyrolysis treatment and X-ray diffraction test are performed on the first core sample, and based on the test results, a qualified first core sample is determined from the plurality of first core samples, including: The slice observation is performed on the first core sample to determine the sedimentary structure of the first core sample; The X-ray diffraction test is performed on the first core sample to determine the whole rock mineral composition of the first core sample; The pyrolysis treatment is performed on the first core sample to determine the pyrolysis parameters of the first core sample; Based on the sedimentary structure, the whole rock mineral composition and the pyrolysis parameters of the first core sample, a qualified first core sample is determined from the plurality of first core samples.

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

7. A system for determining the lower limit of mobile pore throat in shale oil, characterized in that, The system includes: a raw material subsystem, an extraction subsystem, an 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 a target area; for each first core sample, slice observation, pyrolysis treatment and X-ray diffraction test are performed on the first core sample, and based on the test results, a qualified first core sample is determined from the plurality of first core samples; based on the location of the qualified first core sample in the target area, a second core sample is obtained; the oil saturation index of the second core sample is determined; The extraction subsystem is used to perform extraction treatment on the second core sample by using a weakly polar combined solvent and a strongly polar combined solvent to obtain a third core sample; wherein the weakly polar combined solvent is used to remove free-state shale oil in shale pores, and the strongly polar combined solvent is used to remove adsorbed-state and mutually soluble-state shale oil in the shale pores; The N2 isothermal adsorption-desorption measurement subsystem is used to perform N2 isothermal adsorption-desorption experiments on the third core sample to obtain an average pore diameter; The analysis subsystem is used to determine the lower limit of movable pore throat of shale oil in the target area based on the corresponding oil saturation index and the average pore diameter of the second core sample.

8. The system of claim 7, wherein, The extraction subsystem is used to perform extraction treatment on the second core sample in a weakly polar combined solvent by using an ultrasonic extraction method, and the second core sample after extraction treatment is rinsed and dried to obtain a fourth core sample; wherein the weakly polar combined solvent includes dichloromethane and methanol, and the mass ratio of the dichloromethane to the methanol is 93:7; In a strongly polar combined solvent, the fourth core sample is extracted by using an ultrasonic extraction method, and the fourth core sample after extraction treatment is rinsed and dried to obtain the third core sample; wherein the strongly polar combined 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 of claim 7, wherein, The shale oil movable pore throat lower limit comprises a shale oil theoretical movable pore throat lower limit and a shale oil effective movable pore throat lower limit, and the number of the second core samples is multiple; The analysis subsystem is configured to: plot a scatter plot based on the oil saturation index and the average pore diameter of each second core sample, with the average pore diameter as the horizontal coordinate and the oil saturation index as the vertical coordinate; determine the average pore diameter corresponding to the oil saturation index of 0 in the scatter plot as the shale oil theoretical movable pore throat lower limit; and determine the average pore diameter corresponding to the oil saturation index of 100 in the scatter plot as the shale oil effective movable pore throat lower limit.

10. The system of claim 7, wherein, The N2 isothermal adsorption-desorption measurement subsystem is configured to: deaerate the third core sample for more than a first time length under the condition that the temperature is less than or equal to a first temperature and the vacuum state; The N2 isothermal adsorption-desorption measurement subsystem is configured to: deaerate the third core sample for more than a first time length under the condition that the temperature is less than or equal to a first temperature and the vacuum state; The N2 isothermal adsorption-desorption measurement subsystem is configured to: deaerate the third core sample for more than a first time length under the condition that the temperature is less than or equal to a first temperature and the vacuum state;

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