Successive-extraction analysis method and system for thickness of shale oil adsorption layer

Abstract

The present invention belongs to the field of shale oil exploration and development. Provided are a successive-extraction analysis method and system for the thickness of a shale oil adsorption layer. The successive-extraction analysis method comprises: using a first solvent and a second solvent to perform successive extraction on the core of shale, and sequentially removing free shale oil and adsorbed-miscible shale oil; for a core sample obtained by means of extraction each time, respectively carrying out an N2 isothermal adsorption-desorption experiment, so as to determine a first pore diameter of the shale and a second pore diameter of the shale; and on the basis of a positive correlation between the first pore diameter of the shale and the second pore diameter of the shale, determining the thickness of an adsorption layer of shale oil in a target area. A determination system may comprise: a successive extraction subsystem, an N2 isothermal adsorption-desorption determination subsystem, and a positive-correlation analysis sub-system. By means of the method provided in the present invention, the realistic and accurate determination of a shale oil nano-adsorption layer under geological conditions can be implemented from the perspective of experimental measurement.

Description

Successive extraction analysis method and system for shale oil adsorption layer thickness Technical Field

[0001] The present invention relates to the technical field of shale oil exploration and development, and in particular to a method for analyzing the thickness of a shale oil adsorption layer by successive extractions and a system for analyzing the thickness of a shale oil adsorption layer by successive extractions. Background Art

[0002] Shale oil is a hot topic and a frontier in unconventional oil and gas exploration. It exists in shale primarily in two forms: free and adsorbed-miscible. Free shale oil is primarily found in fractures and pores, while adsorbed-miscible shale oil primarily occurs through mineral surface adsorption and kerogen adsorption-miscible shale oil. Kerogen adsorption-miscible shale oil includes kerogen surface adsorption, non-covalent adsorption between shale oil and kerogen, and inclusion-miscible shale oil within organic macromolecules. Free shale oil primarily contributes to shale oil production capacity, while adsorbed shale oil represents the portion of shale oil that is difficult to exploit under current extraction technologies. Determining the thickness of the shale oil adsorption layer is crucial for accurately assessing the potential for shale oil reserves and is a fundamental scientific issue of key concern, including identifying shale oil sweet spots and improving oil and gas recovery during development.

[0003] However, current methods for determining the thickness of shale oil adsorption layers primarily rely on molecular dynamics simulations. While molecular dynamics simulations can provide insights into the microscopic distribution characteristics of shale oil at the molecular scale, current simulations are limited to low-carbon-number models due to computational modeling and computational effort. However, in practice, shale oil has a complex molecular composition, and both mineral models and computational effort are severely limited, making it difficult to accurately reveal the adsorption characteristics of shale oil under real-world conditions.

[0004] For example, a Chinese non-patent document published in September 2021, titled "Molecular Dynamics Simulation of Shale Oil Occurrence Characteristics in the Dongying Depression," proposes a method for assessing shale oil resources through molecular dynamics simulation. This method uses molecular dynamics to simulate the occurrence of crude oil within nanoscale pores in organic matter in the Dongying Depression. The results show that the density of shale oil in these nanoscale pores exhibits periodic variations, with the density of the adsorption layer ranging from 1.1 to 3.2 times that of the free fluid. The density of shale oil in the pore throats is consistent with the density of crude oil under reservoir conditions. Shale oil forms four adsorption layers within these nanoscale pores. The first adsorption layer is the thickest, at 0.411 nm, while the other three adsorption layers are each 0.359 nm thick, resulting in a total adsorption layer thickness of approximately 3.0 nm within the pores.

[0005] For example, a Chinese non-patent literature published in May 2018 and entitled "Molecular Dynamics Simulation of Adsorption Characteristics of Shale Oil in Nanoscale Slits" proposed a method for analyzing the volume and density of the adsorbed phase of shale oil using molecular dynamics simulation results. This method studied the adsorption characteristics of shale oil in nanoscale organic matter slits and silica mineral slits, and found that the density distribution of hydrocarbon molecules (shale oil) in nanoscale slits was not uniform. Near the slit surface, three relatively obvious adsorption layers appeared, and the peak density of the adsorption layer gradually decreased with increasing distance from the surface. The thickness of each adsorption layer was between 0.4 and 0.5 nm, that is, the thickness of the single adsorption layer was 1.2 nm to 1.5 nm, and the total thickness was 2.5 nm to 3.0 nm. Near the center of the slit, the density curve of the mixed hydrocarbon molecules tended to be stable.

[0006] Of course, there are some experimental methods for measuring the thickness of shale pore adsorption layers, but these methods are not suitable for measuring the thickness of shale oil adsorption layers. For example, a Chinese patent application, published on January 27, 2023, with publication number CN115615366A, proposes a method for measuring the thickness of shale pore adsorption layers. This method is implemented using a shale pore adsorption layer thickness detection device. The detection device includes a gas source unit, a humidification unit, a drying unit, a gas mixing unit, and a small-angle scattering unit. The detection method comprises the following steps: S1, preparing a shale sample and placing the shale sample in an oven for drying; S2, placing the dried shale sample in step S1 in a small-angle scattering unit; S3, vacuuming the gas flow path; S4, after the vacuuming, detecting the scattering intensity data of the pores of the shale sample through the small-angle scattering unit, and obtaining the radius of the pores of the shale sample when no adsorption layer is formed on the pore wall of the shale sample; S5, turning on the gas source unit to respectively transport gas to the humidifying unit and the drying unit to obtain humidified gas and dry gas, and the humidified gas The liquid gas and dry gas are mixed in the gas mixing unit to obtain a mixed gas with a preset humidity. S6: The mixed gas with the preset humidity flows into the small-angle scattering unit, causing the mixed gas to form a saturated adsorption layer on the pore walls of the shale sample. The scattering intensity data of the shale sample pores at this time is detected by the small-angle scattering unit. S7: The shale pore adsorption layer thickness is obtained based on the scattering intensity data of the shale sample pores before the adsorption layer is formed on the pore walls of the shale sample and the scattering intensity data of the shale sample pores after the adsorption layer is formed on the pore walls of the shale sample. This method can control the humidity of the mixed gas and form a saturated adsorption layer on the shale pores. It can further quantitatively analyze the shale pore adsorption layer thickness based on small-angle scattering technology. However, this method is only applicable to the calculation of the adsorption layer thickness of shale gas and is not applicable to the calculation of the adsorption layer thickness of crude oil in shale pores in shale oil reservoirs.

[0007] Summary of the Invention

[0008] The purpose of the embodiment of the present invention is to provide a method for successive extraction analysis of the thickness of the shale oil adsorption layer, at least to solve the technical problem in the prior art of lacking experimental analysis to determine the thickness of the shale oil adsorption layer on the surface of the pore structure.

[0009] In order to achieve the above-mentioned objectives, the first aspect of the present invention provides a method for successive extraction analysis of the thickness of a shale oil adsorption layer, the method comprising the following steps: performing a primary extraction on a shale core using a first solvent to obtain a first shale sample after removing free shale oil; performing a secondary extraction on the first shale sample using a second solvent to obtain a second shale sample after removing adsorbed shale oil and miscible shale oil; conducting N2 isothermal adsorption-desorption experiments on the first shale sample and the second shale sample, respectively, to determine the first pore diameter of the shale and the second pore diameter of the shale; and determining the thickness of the shale adsorption layer of the target area based on the positive correlation between the first pore diameter of the shale and the second pore diameter of the shale.

[0010] In an exemplary embodiment of the present invention, the polarity of the second solvent may be greater than the polarity of the first solvent.

[0011] In an exemplary embodiment of the present invention, the first solvent may be a mixed solvent composed of dichloromethane and methanol in a first mixing ratio.

[0012] In an exemplary embodiment of the present invention, the second solvent may be a mixed solvent composed of tetrahydrofuran, acetone, and methanol in a second mixing ratio.

[0013] In an exemplary embodiment of the present invention, conducting N2 isothermal adsorption-desorption experiments on the first shale sample and the second shale sample respectively to determine the first pore diameter of the shale and the second pore diameter of the shale may include: determining the average pore diameter of the first shale sample based on the N2 isothermal adsorption-desorption experimental results of the first shale sample; determining the average pore diameter of the second shale sample based on the N2 isothermal adsorption-desorption experimental results of the second shale sample; determining the average pore diameter of the first shale sample as the first pore diameter, and determining the average pore diameter of the second shale sample as the second pore diameter.

[0014] In an exemplary embodiment of the present invention, the calculation formula of the average pore diameter may be:

[0015] Among them, r k is the average pore diameter of shale; r is the surface tension at the boiling point of nitrogen; V m is the molar volume of nitrogen; R is the gas constant; T is the absolute temperature of the boiling point of N2; p / p0 is the relative pressure of nitrogen.

[0016] In an exemplary embodiment of the present invention, determining the adsorption layer thickness of shale oil in the target area based on the positive correlation between the first pore diameter of shale and the second pore diameter of shale may include: drawing a scatter plot of the first pore diameter of shale and the second pore diameter of shale, and determining a calculation formula for the positive correlation between the first pore diameter of shale and the second pore diameter of shale; based on the positive correlation calculation formula, determining the value of the second pore diameter of shale corresponding to the value of 0 of the first pore diameter of shale as the adsorption layer thickness of shale oil in the target area.

[0017] In an exemplary embodiment of the present invention, the positive correlation calculation formula between the first pore diameter of shale and the second pore diameter of shale may be a linear function.

[0018] According to a second aspect of the present invention, a system for analyzing the thickness of a shale oil adsorption layer by sequential extraction is provided. The system may include a sequential extraction subsystem, an N2 isothermal adsorption-desorption measurement subsystem, and a positive correlation analysis subsystem. The sequential extraction subsystem is used to perform sequential extraction on a shale core to obtain a first shale sample after removing free shale oil and a second shale sample after removing adsorbed shale oil and miscible shale oil. The N2 isothermal adsorption-desorption measurement subsystem is connected to the sequential extraction subsystem to perform N2 isothermal adsorption-desorption experiments on the first shale sample and the second shale sample, respectively, to determine a first pore diameter and a second pore diameter of the shale. The positive correlation analysis subsystem is connected to the N2 isothermal adsorption-desorption measurement subsystem to determine the thickness of the shale oil adsorption layer in the target area based on the positive correlation between the first pore diameter and the second pore diameter of the shale.

[0019] In another exemplary embodiment of the present invention, the successive extraction analysis system may further include: a raw material preparation subsystem; the raw material preparation subsystem is used to grind the columnar shale core into powder.

[0020] Through the above technical solution, the beneficial effects of the present invention are as follows:

[0021] (1) The method for analyzing the thickness of the shale oil adsorption layer provided by the present invention is based on experimental measurements and realizes the true and accurate determination of the shale oil nano-adsorption layer under geological conditions;

[0022] (2) The method for analyzing the thickness of the shale oil adsorption layer by successive extraction provided by the present invention has a scientific principle, strong operability, and is easy to promote;

[0023] (3) The shale oil adsorption layer thickness measured by the present invention helps to deepen the understanding of the shale oil occurrence mechanism and further optimize the sweet spot evaluation index;

[0024] (4) The shale oil adsorption layer thickness measured by the present invention has universal guidance for the quantitative evaluation of shale oil movable resources in major oil fields;

[0025] (5) The thickness of the shale oil adsorption layer measured by the present invention provides a solid theoretical basis for further improving the shale oil microscopic seepage model and optimizing the technology for improving oil and gas recovery rate.

[0026] Other features and advantages of the embodiments of the present invention will be described in detail in the subsequent detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings are used to provide a further understanding of the embodiments of the present invention and constitute a part of the specification. Together with the following detailed description, they are used to explain the embodiments of the present invention, but do not constitute a limitation of the embodiments of the present invention. In the accompanying drawings:

[0028] FIG1 is a flow chart of a method for successive extraction analysis of shale oil adsorption layer thickness according to an embodiment of the present invention;

[0029] FIG2 is a specific flow chart of a sequential extraction experiment provided by an embodiment of the present invention;

[0030] FIG3 is a pore size distribution curve of shale after weak polarity extraction provided by an embodiment of the present invention;

[0031] FIG4 is a pore size distribution curve of shale after strong polarity extraction provided by an embodiment of the present invention;

[0032] FIG5 is a diagram of a theoretical calculation model for the thickness of a shale oil adsorption layer provided by an embodiment of the present invention;

[0033] FIG6 is a scatter plot of the first pore diameter and the second pore diameter of shale provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0034] The following describes the specific implementation of the embodiment of the present invention in detail with reference to the accompanying drawings. It should be understood that the specific implementation described herein is only used to illustrate and explain the embodiment of the present invention and is not used to limit the embodiment of the present invention.

[0035] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0036] In the present invention, unless otherwise indicated, directional terms such as "upper, lower, top, and bottom" are generally used to describe the relative positions of components with respect to the directions shown in the drawings, or with respect to the vertical, perpendicular, or gravitational directions. Terms such as "first" and "second" are merely used for convenience of description and distinction and should not be construed as indicating or implying relative importance.

[0037] It should also be noted that, in the description of the present invention, unless otherwise expressly specified or limited, the terms "installation" and "connection" should be understood in a broad sense. For example, they may refer to fixed connection, detachable connection, or integrated connection; direct connection, indirect connection, wired connection, or wireless connection. Those skilled in the art will understand the specific meanings of the above terms in the present invention depending on the specific circumstances.

[0038] Prior art has yet to publicly report a method for quantitatively determining the thickness of the adsorption layer of shale oil on the pore surface of shale samples using experimental analysis. Therefore, the present invention provides a method for analyzing and determining the thickness of the shale oil adsorption layer based on sequential extraction experiments to address this technical problem.

[0039] The overall technical concept of the present invention is: for the core samples sampled by micro-drilling, the free shale oil and adsorbed / miscible shale oil in the shale pores are removed successively by a successive extraction method, and low-temperature N2 adsorption physical experiments are carried out on the shale samples after two extractions, respectively, to obtain the pore size distribution characteristics and average pore diameter of the shale samples after the two extractions, that is, the first pore diameter and the second pore diameter of the shale, and then a scatter plot of the first pore diameter and the second pore diameter of the shale is drawn, and the thickness of the shale oil adsorption layer is determined based on the positive correlation between the two in the scatter plot.

[0040] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0041] Example 1

[0042] Referring to FIG1 , a first embodiment of the present invention provides a method for analyzing the thickness of a shale oil adsorption layer by sequential extraction, the method comprising the following steps:

[0043] Step S101: performing a primary extraction on a shale core using a first solvent to obtain a first shale sample after free shale oil is removed.

[0044] Step S102: performing secondary extraction on the first shale sample using a second solvent to obtain a second shale sample after removing the adsorbed shale oil and the miscible shale oil.

[0045] Step S103: conducting N2 isothermal adsorption-desorption experiments on the first shale sample and the second shale sample respectively to determine the first pore diameter of the shale and the second pore diameter of the shale.

[0046] For example, N2 isothermal adsorption-desorption experiments are conducted on the first shale sample and the second shale sample respectively, and the process of determining the first pore diameter of the shale and the second pore diameter of the shale includes but is not limited to the following sub-steps S1031 to S1033.

[0047] Sub-step S1031: Determine the average pore diameter of the first shale sample based on the N2 isothermal adsorption-desorption experimental results of the first shale sample.

[0048] The calculation formula for the average pore diameter is:

[0049] Among them, r k is the average pore diameter of shale; r is the surface tension at the boiling point of nitrogen; V m is the molar volume of nitrogen; R is the gas constant; T is the absolute temperature of the boiling point of N2 (77K); p / p0 is the relative pressure of nitrogen.

[0050] Sub-step S1032: Determine the average pore diameter of the second shale sample based on the N2 isothermal adsorption-desorption experimental results of the second shale sample.

[0051] Sub-step S1033: determining the average pore diameter of the first shale sample as the first pore diameter, and determining the average pore diameter of the second shale sample as the second pore diameter.

[0052] Step S104: Based on the positive correlation between the first pore diameter of the shale and the second pore diameter of the shale, the thickness of the adsorption layer of the shale oil in the target area is determined.

[0053] For example, based on the positive correlation between the first pore diameter of shale and the second pore diameter of shale, the process of determining the thickness of the adsorption layer of shale oil in the target area includes but is not limited to the following sub-steps S1041 to S1042.

[0054] Sub-step S1041: draw a scatter plot of the first pore diameter of shale and the second pore diameter of shale, and determine a calculation formula for the positive correlation between the first pore diameter of shale and the second pore diameter of shale.

[0055] Sub-step S1042: Based on the positive correlation calculation formula, the value of the second pore diameter of the shale corresponding to the value of the first pore diameter of the shale is 0 is determined as the adsorption layer thickness of the shale oil in the target area.

[0056] It should be noted that the sequential extraction method is an effective means of separating shale oils of different occurrence states. Its principle is to exploit the differences in the distribution space and molecular polarity of shale oils of different occurrence states and extract them with appropriate solvents to obtain shale oils of different occurrence states. Generally speaking, free shale oil, due to its relatively large distribution space, has a strong contact with the first solvent and is easily extracted. However, shale oil adsorbed in micropores and shale oil encapsulated by kerogen macromolecules are difficult to extract due to their limited contact with the second solvent.

[0057] Furthermore, in this embodiment, the polarity of the second solvent can be greater than that of the first solvent. This is because free shale oil generally has a lower molecular polarity and is easily extracted, while adsorbed shale oil generally has a higher molecular polarity and is relatively difficult to extract. Therefore, solvents of different polarities can be selected sequentially to extract and remove free and adsorbed-miscible shale oil.

[0058] Preferably, the first solvent can be a combination of weakly polar solvents, using the differences in polarity of the wash oil solvents to create a predetermined ratio; the second solvent can be a combination of strongly polar solvents, using the differences in polarity of the wash oil solvents to create a predetermined ratio. Compared to a single type of wash oil solvent, a mixed solvent has better solubility.

[0059] For example, the first solvent may be a weakly polar solvent combination of dichloromethane and methanol in a first mixing ratio, and the first mixing ratio (volume ratio) may be (90-95):(5-10). The second solvent may be a strongly polar solvent combination of tetrahydrofuran, acetone, and methanol in a second mixing ratio, and the second mixing ratio (volume ratio) may be (48-52):(24-26):(24-26).

[0060] Furthermore, in this embodiment, the positive correlation formula between the first shale pore diameter and the second shale pore diameter can be a linear function. In this case, the intercept value between the linear line of the linear function and the x-axis (with the second shale pore diameter as the x-axis) is the thickness of the shale oil adsorption layer.

[0061] Example 2

[0062] A second embodiment of the present invention provides a method for analyzing the thickness of a shale oil adsorption layer by successive extractions, the method comprising the following steps:

[0063] Step S201: a micro-drill is used to obtain multiple wax-sealed or sealed coring shale core samples, and the samples are ground into 100-mesh powder samples.

[0064] Step S202: subjecting the processed powder sample to a first solvent extraction process to remove free shale oil in the shale pores to obtain a first shale sample, and then drying the first shale sample for later use.

[0065] Step S203: Perform a N2 isothermal adsorption-desorption experiment on the first shale sample processed in step S202, obtain test data of the N2 isothermal adsorption-desorption experiment, draw a pore size distribution curve of the first shale sample, and calculate the first pore diameter of the shale.

[0066] Step S204: Take 1 / 2 of the first shale sample reserved in step S202, and subject it to a second solvent extraction process to remove the adsorbed shale oil and the miscible shale oil in the shale pores to obtain a second shale sample, and dry the second shale sample for later use.

[0067] Step S205: Perform a N2 isothermal adsorption-desorption experiment on the second shale sample processed in step S204, obtain test data of the N2 isothermal adsorption-desorption experiment, draw a pore size distribution curve of the second shale sample, and calculate the second pore diameter of the shale.

[0068] Step S206: draw a scatter plot of the first pore diameter and the second pore diameter of the shale to obtain a positive correlation curve between the two, and determine the thickness of the shale oil adsorption layer in the target area.

[0069] In this embodiment, step S201 is specifically implemented as follows: multiple wax-sealed or sealed cored shale samples are selected, and columnar samples with a diameter of 3 mm and a length of not less than 13 mm are drilled using an in-situ micro-drilling method (laminated shale is drilled along the laminae, and massive shale is drilled perpendicular to the core direction) to ensure sampling uniformity; the surface of each shale core sample is cleaned and ground into a 100-mesh powder sample.

[0070] In this embodiment, the specific implementation method of step S202 is as follows: weigh about 20g of powder sample, use ultrasonic extraction at room temperature in a first solvent to remove the free shale oil in the shale pores, and obtain a first shale sample. The first solvent used is a weak polar combination solvent in which dichloromethane and methanol are combined in a volume ratio of 93:7, and the amount of the first solvent is 0.4mL / g. The frequency selected for ultrasonic extraction 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. After the extraction is completed, the powdered first shale sample is rinsed with clean water 3 times and then naturally dried for use.

[0071] In this embodiment, step S203 is implemented as follows: 1 g of the first shale sample treated in step S202 is weighed and degassed at low temperature (≤70°C) under vacuum for over 8 hours. A nitrogen isothermal adsorption-desorption experiment is then performed on the degassed powdered first shale sample under experimental conditions of a temperature ≤-195°C and a pressure ≤101.3 kPa. After the experiment, the nitrogen isothermal adsorption-desorption experimental data of the first shale sample is processed using the BJH theory to obtain the pore size distribution curve and the first pore diameter after free shale oil is removed from the shale.

[0072] In this embodiment, the specific implementation method of step S204 is as follows: 10 g of the first shale sample naturally dried in step S202 is weighed and placed in a beaker, and ultrasonic extraction is performed in a second solvent at room temperature to remove the adsorbed and mutually soluble shale oil in the pores of the shale to obtain a second shale sample. The second solvent used is a highly polar combination solvent in which tetrahydrofuran, acetone, and methanol are combined in a volume ratio of 50:25:25, and the amount of the second solvent is 0.4 mL / g. The frequency selected for ultrasonic extraction is 4000 r / min, the centrifugation time is 15 min, and the extraction is completed until the color of the added fresh solvent no longer changes. After the extraction is completed, the powdered second shale sample is rinsed with clean water 3 times and then naturally dried for use.

[0073] In this embodiment, step S205 is implemented as follows: 1 g of the second shale sample treated in step S204 is weighed and degassed at low temperature (≤70°C) under vacuum for over 8 hours. A N2 isothermal adsorption-desorption experiment is then performed on the degassed powdered second shale sample under experimental conditions of a temperature ≤-195°C and a pressure ≤101.3 kPa. After the experiment, the N2 isothermal adsorption-desorption experimental data of the second shale sample is processed using the BJH theory to obtain the pore size distribution curve and second pore diameter after the adsorbed and miscible shale oil is removed from the shale.

[0074] In this embodiment, step S206 is specifically implemented as follows: the first pore diameter of the shale obtained through the N2 physical adsorption experiment after the extraction treatment in step S202 (i.e., after removing the free shale oil) is used as the Y-axis, and the second pore diameter of the shale obtained through the N2 physical adsorption experiment after the extraction treatment in step S204 (i.e., after removing the adsorbed / miscible shale oil) is used as the X-axis to form a scatter plot of the two; based on the positive correlation function relationship between the first pore diameter of the shale and the second pore diameter of the shale in the scatter plot, the X value (i.e., the value of the second pore diameter of the shale) corresponding to Y=0 (i.e., the value of the first pore diameter of the shale is 0) is determined as the adsorption layer thickness of the shale oil in the target area.

[0075] Example 3

[0076] The Cangdong Sag, located in the southern part of the basin, developed under a regional extensional setting, sandwiched between the Cangxian Uplift, the Xuhei Uplift, and the Kongdian Uplift. The sag is composed of Mesozoic and Cenozoic basin-fill strata. The Paleogene strata comprise, from bottom to top, the Kongdian, Shahejie, and Dongying Formations. The Kongdian Formation is further subdivided into three members, Ek3, Ek2, and Ek1, with sedimentary thicknesses ranging from 400 to 600 meters. During the deposition of the Ek2, the Cangdong Sag experienced a period of maximum marine transgression and a subtropical humid climate, resulting in the development of freshwater-brackish closed depression-lake basin sediments characterized by a highly reducing environment of the sedimentary waters and high organic paleoproductivity. The Ek2 lithology is primarily composed of felsic, mixed, and carbonate rocks. Laminated felsic shale is the primary target for shale oil exploration in the Kong2 Member of the Cangdong Sag, with the main producing wells located at vertical depths of 3,800 to 4,100 meters.

[0077] Taking some core samples of shale oil in the Cangdong Depression as an example, the third embodiment of the present invention provides a method for sequential extraction analysis of the thickness of the shale oil adsorption layer, which includes the following steps:

[0078] Step S301: obtaining a plurality of shale core samples, and grinding the shale core samples into 100-mesh powder samples.

[0079] Specifically, 12 wax-sealed or sealed cored shale samples from the sweet spot layer of the second section of the hole were selected, and column samples with a diameter of 3 mm and a length of not less than 13 mm were drilled along the laminae of the felsic laminar shale to ensure the uniformity of sampling; the surface of each shale sample was cleaned and ground into a 100-mesh powder sample.

[0080] Step S302: About 20 g of powder sample is weighed for each sample, and the powder sample is extracted successively using a combination of two solvents of different polarities to successively remove free shale oil and adsorbed / miscible shale oil in the shale pores.

[0081] For example, as shown in FIG2 , the specific implementation of step S302 is as follows:

[0082] Sub-step S3021: extracting the powder sample once with a first solvent to obtain a first shale sample after removing free shale oil in the shale pores.

[0083] Specifically, about 20g of powder sample was weighed, and the powder sample was ultrasonically extracted at room temperature using a weak polarity combination solvent as the first solvent. Among them, the first solvent used is a weak polarity combination solvent in which dichloromethane and methanol are combined in a volume ratio of 93:7, and the amount of the first solvent is 0.4mL / g. Here, dichloromethane is a non-polar solvent, while methanol is a polar solvent. In some reactions, it is necessary to increase the polarity without affecting the reaction to promote the reaction. Therefore, adding a small amount of methanol can increase the polarity of the entire mixed solvent. In addition, the addition of methanol can also speed up the oil washing efficiency.

[0084] Ultrasonic extraction was performed at a frequency of 4000 r / min and a centrifugation time of 15 min. Extraction was considered complete when the color of the added fresh solvent ceased to change. After one extraction, the powdered first shale sample was rinsed three times with clean water and then air-dried for later use.

[0085] Sub-step S3022: performing secondary extraction on the first shale sample using a second solvent to obtain a second shale sample after removing the adsorbed shale oil and the miscible shale oil in the shale pores.

[0086] Specifically, approximately 20g of a powdered first shale sample was ultrasonically extracted at room temperature using a highly polar solvent combination as the second solvent. The second solvent used was a highly polar solvent combination of tetrahydrofuran, acetone, and methanol in a volume ratio of 50:25:25, with a dosage of 0.4mL / g.

[0087] The ultrasonic extraction frequency was 4000 r / min, the centrifugation time was 15 min, and the extraction was considered complete when the color of the added fresh solvent no longer changed. After the secondary extraction, the powdered first shale sample was rinsed three times with clean water and then naturally dried for later use.

[0088] Step S303: performing N2 isothermal adsorption-desorption experiments on the first shale sample and the second shale sample after extraction and drying, respectively, to determine the first pore diameter of the shale and the second pore diameter of the shale.

[0089] Each time the N2 isothermal adsorption-desorption experiment was conducted, 1 g of sample was taken and degassed at low temperature (≤70°C) and vacuum state for more than 8 hours; then, the degassed powdered shale sample was subjected to a N2 isothermal adsorption-desorption experiment under the experimental conditions of temperature ≤-195°C and pressure ≤101.3 kPa.

[0090] According to the BJH theory and related calculation formulas, the pore size distribution curve and average pore diameter of the shale oil obtained after two extractions were obtained, namely the first pore diameter of shale (as shown in Figure 3) and the second pore diameter of shale (as shown in Figure 4).

[0091] Step S304: Based on the positive correlation between the first pore diameter of the shale and the second pore diameter of the shale, the thickness of the adsorption layer of the shale oil in the target area is determined.

[0092] Figure 5 shows a theoretical calculation model for the thickness of the shale oil adsorption layer according to this embodiment. As shown in Figure 5 , the second pore diameter of the adsorbed / miscible shale oil is calculated by adding the first pore diameter of the free shale oil to the oil layer thickness of the adsorbed / miscible shale oil. In other words, the positive correlation between the first pore diameter and the second pore diameter satisfies a linear relationship.

[0093] A scatter plot of the first and second pore diameters of the shale was plotted, with the first pore diameter of the shale as the Y-axis and the second pore diameter of the shale as the X-axis. Fitting this scatter plot confirmed that the positive correlation between the first and second pore diameters is a linear relationship. The intercept of the linear relationship between the first and second pore diameters on the X-axis can be used to determine the thickness of the shale oil adsorption layer. As shown in Figure 6, the final thickness of the shale oil adsorption layer in the target area is approximately 10 nm.

[0094] Example 4

[0095] The fourth embodiment of the present invention provides a successive extraction analysis system for the thickness of a shale oil adsorption layer. The successive extraction analysis system may include a successive extraction subsystem, an N2 isothermal adsorption-desorption measurement subsystem, and a positive correlation analysis subsystem.

[0096] Among them, the successive extraction subsystem is used to extract the shale core successively, and obtain the first shale sample after removing the free shale oil and the second shale sample after removing the adsorbed shale oil and the miscible shale oil.

[0097] Specifically, the sequential extraction subsystem can be composed of a primary extraction unit and a secondary extraction unit. The primary extraction unit is used to perform a primary extraction on the shale core using a weakly polar solvent combination as the extraction solvent to remove free shale oil from the shale pores. The secondary extraction unit is used to perform a secondary extraction on the shale core after the primary extraction using a strong polar solvent combination as the extraction solvent to remove adsorbed shale oil and miscible shale oil from the shale pores.

[0098] The N2 isothermal adsorption-desorption measurement subsystem is connected to the successive extraction subsystem and is used to carry out N2 isothermal adsorption-desorption experiments on the first shale sample and the second shale sample, respectively, to determine the first pore diameter of the shale and the second pore diameter of the shale.

[0099] The positive correlation analysis subsystem is connected to the N2 isothermal adsorption-desorption measurement subsystem and is used to determine the adsorption layer thickness of shale oil in the target area based on the positive correlation between the first pore diameter of the shale and the second pore diameter of the shale.

[0100] Example 5

[0101] The fifth embodiment of the present invention provides another successive extraction analysis system for the thickness of the shale oil adsorption layer. The successive extraction analysis system may include a raw material preparation subsystem, a successive extraction subsystem, an N2 isothermal adsorption-desorption measurement subsystem and a linear analysis subsystem.

[0102] The raw material preparation subsystem is used to grind the shale core sample into powder. Specifically, the raw material preparation subsystem can be composed of a drilling unit and a grinding unit. The drilling unit is used to drill in-situ micro-drilling to produce a core sample with a diameter of 3 mm and a length of at least 13 mm (laminated shale is drilled along the laminae; massive shale is drilled perpendicular to the core) to ensure sampling uniformity. The grinding unit is used to grind the cleaned shale sample into a 100-mesh powder.

[0103] The sequential extraction subsystem can perform sequential extractions using ultrasonic extraction at room temperature, using two solvent combinations, and extracting until the color of the fresh solvent no longer changes, marking the end of each extraction. Its input is connected to the output of the raw material preparation subsystem. The two solvent combinations are a weakly polar solvent combination and a strongly polar solvent combination. The weakly polar solvent combination is used to remove free oil from shale pores, while the strongly polar solvent combination is used to absorb / dissolve shale oil in the shale pores.

[0104] The N2 isothermal adsorption-desorption measurement subsystem is used to perform N2 isothermal adsorption-desorption measurement on each shale raw material sample to obtain the pore size distribution curve and average pore diameter of the shale raw material sample. Its input is connected to the output of the successive extraction subsystem.

[0105] The input of the linear analysis subsystem is connected to the output of the N2 isothermal adsorption-desorption measurement subsystem, which is used to draw a scatter plot of the first pore diameter and the second pore diameter of the shale, perform correlation analysis, and obtain a linear relationship line between the two; and determine the thickness of the shale oil adsorption layer based on the intercept value of the linear line in the relationship diagram and the X-axis.

[0106] In summary, the beneficial effects of the present invention may include:

[0107] (1) From the perspective of experimental measurement, the true and accurate determination of the shale oil nano-adsorption layer under geological conditions was achieved;

[0108] (2) Sweet spot evaluation: This helps deepen the understanding of shale oil occurrence mechanism and further optimize the sweet spot evaluation indicators;

[0109] (3) Resource calculation: It provides general guidance for the quantitative evaluation of movable shale oil resources in major oil fields;

[0110] (4) Improve oil and gas recovery: Provide a solid theoretical basis for further improvement of shale oil microscopic seepage model and optimization of oil and gas recovery technology;

[0111] (5) The present invention adopts the successive extraction technology + N2 physical adsorption experiment to achieve the joint research of advantageous technologies.

[0112] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the scope of protection of the present invention.

[0113] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0114] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. A method for successive extraction analysis of shale oil adsorption layer thickness, characterized in that: The successive extraction analysis method comprises: Performing primary extraction on the shale core using a first solvent to obtain a first shale sample after free shale oil is removed; Performing secondary extraction on the first shale sample using a second solvent to obtain a second shale sample after removing the adsorbed shale oil and the miscible shale oil; N2 isothermal adsorption-desorption experiments were carried out on the first shale sample and the second shale sample to determine the first pore diameter of the shale and the second pore diameter of the shale; Based on the positive correlation between the first pore diameter of shale and the second pore diameter of shale, the thickness of the adsorption layer of shale oil in the target area is determined.

2. The method for successive extraction analysis of shale oil adsorption layer thickness according to claim 1, characterized in that: The polarity of the second solvent is greater than the polarity of the first solvent.

3. The method for successive extraction analysis of shale oil adsorption layer thickness according to claim 1, characterized in that: The first solvent is a mixed solvent composed of dichloromethane and methanol in a first mixing ratio.

4. The method for successive extraction analysis of shale oil adsorption layer thickness according to claim 1, characterized in that: The second solvent is a mixed solvent composed of tetrahydrofuran, acetone and methanol in a second mixing ratio.

5. The method for successive extraction analysis of shale oil adsorption layer thickness according to claim 1, characterized in that: The N2 isothermal adsorption-desorption experiment is carried out on the first shale sample and the second shale sample respectively to determine the first pore diameter of the shale and the second pore diameter of the shale, including: Based on the N2 isothermal adsorption-desorption experimental results of the first shale sample, an average pore diameter of the first shale sample is determined; Based on the N2 isothermal adsorption-desorption experimental results of the second shale sample, an average pore diameter of the second shale sample is determined; The average pore diameter of the first shale sample is determined as a first pore diameter, and the average pore diameter of the second shale sample is determined as a second pore diameter.

6. The method for successive extraction analysis of shale oil adsorption layer thickness according to claim 5, characterized in that: The calculation formula of the average pore diameter is: Among them, r k is the average pore diameter of shale; r is the surface tension at the boiling point of nitrogen; V m is the molar volume of nitrogen; R is the gas constant; T is the absolute temperature of the boiling point of N2; p / p0 is the relative pressure of nitrogen.

7. The method for successive extraction analysis of shale oil adsorption layer thickness according to claim 1, characterized in that: The method of determining the adsorption layer thickness of shale oil in the target area based on the positive correlation between the first pore diameter of shale and the second pore diameter of shale includes: Draw a scatter plot of the first pore diameter of shale and the second pore diameter of shale, and determine a calculation formula for the positive correlation between the first pore diameter of shale and the second pore diameter of shale; Based on the positive correlation calculation formula, the value of the second pore diameter of the shale corresponding to the value of the first pore diameter of the shale is 0 is determined as the adsorption layer thickness of the shale oil in the target area.

8. The method for successive extraction analysis of shale oil adsorption layer thickness according to claim 7, characterized in that: The calculation formula for the positive correlation between the first pore diameter of shale and the second pore diameter of shale is a linear function.

9. A sequential extraction analysis system for shale oil adsorption layer thickness, characterized in that: The successive extraction analysis system comprises: a successive extraction subsystem, a N2 isothermal adsorption-desorption measurement subsystem and a positive correlation analysis subsystem; The successive extraction subsystem is used to extract the shale core successively, and obtain the first shale sample after removing the free shale oil and the second shale sample after removing the adsorbed shale oil and the miscible shale oil respectively; The N2 isothermal adsorption-desorption determination subsystem is connected to the successive extraction subsystem, and is used to carry out N2 isothermal adsorption-desorption experiments on the first shale sample and the second shale sample, respectively, to determine the first pore diameter of the shale and the second pore diameter of the shale; The positive correlation analysis subsystem is connected to the N2 isothermal adsorption-desorption measurement subsystem, and is used to determine the adsorption layer thickness of shale oil in the target area based on the positive correlation between the first pore diameter of the shale and the second pore diameter of the shale.

10. The successive extraction analysis system for shale oil adsorption layer thickness according to claim 9, characterized in that: The sequential extraction analysis system further comprises: a raw material preparation subsystem; the raw material preparation subsystem is used to grind the columnar shale core into powder.

Images