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

Abstract

The invention provides a successive extraction analysis method and system for shale oil adsorption layer thickness, and belongs to the field of shale oil exploration and developing.The successive extraction analysis method comprises the steps that a first solvent and a second solvent are adopted to conduct successive extraction on a shale core, and free shale oil and adsorbed-mutually soluble shale oil are removed in sequence; respectively carrying out an N2 isothermal adsorption-desorption experiment on the core sample extracted each time, and determining a first pore diameter of shale and a second pore diameter of shale; and based on the positive correlation between the first pore diameter of the shale and the second pore diameter of the shale, determining the adsorption layer thickness of the shale oil in the target area. The measurement system can comprise a successive extraction subsystem, an N2 isothermal adsorption-desorption measurement subsystem and a positive correlation analysis subsystem. According to the method provided by the invention, real and accurate determination of the shale oil nano adsorption layer under geological conditions can be realized from the perspective of experimental actual measurement.

Description

Technical Field

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

[0002] Shale oil is a hot spot and frontier field in the current unconventional oil and gas exploration. It mainly exists in two forms in shale: free state and adsorption-miscible state. Free shale oil is mainly found in fractures and pores, while adsorption-miscible shale oil mainly includes two types: mineral surface adsorption and kerogen adsorption-miscible state. Kerogen adsorption-miscible state includes kerogen surface adsorption, non-covalent bond adsorption of shale oil and kerogen, and envelopment-miscible state of organic macromolecules. The main contributor to shale oil production capacity is free shale oil, while adsorbed shale oil is the part of shale oil that is difficult to mobilize under current mining technology conditions. How to determine the thickness of the shale oil adsorption layer is related to the accurate assessment of the movable resources of shale oil, and is also a basic scientific issue of key concern in the evaluation of shale oil sweet spots and improving oil and gas recovery in the development stage.

[0003] However, the current method for determining the thickness of the shale oil adsorption layer is mainly to use molecular dynamics simulation. The molecular dynamics simulation method can understand the microscopic occurrence characteristics of shale oil at the molecular scale. Due to the limitations of the calculation model and the amount of calculation, the current simulation is still limited to the simulation of low carbon numbers. However, in reality, the molecular components of shale oil are complex, and the mineral model and the amount of calculation are very limited, making it difficult to accurately reveal the adsorption characteristics of shale oil under real conditions.

[0004] For example, a Chinese non-patent literature entitled Molecular Dynamics Simulation of Shale Oil Occurrence Characteristics in Dongying Depression, published in September 2021, proposed a method for evaluating shale oil resources through molecular dynamics simulation. This method uses molecular dynamics to simulate the occurrence state of crude oil in organic nanoscale pores in Dongying Depression. It is found that the density of shale oil in organic nanoscale pores shows periodic changes, and the density of the adsorption layer is 1.1 to 3.2 times the density of the free fluid, while the density of shale oil in the center of the pore throat is consistent with the density of crude oil under reservoir conditions. Shale oil will form four adsorption layers in organic nanoscale pores. The thickness of the first adsorption layer is the largest, which is 0.411nm, and the thickness of the other three adsorption layers is 0.359nm, that is, the total adsorption layer thickness in the pore is about 3.0nm.

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

[0006] Of course, there are also some methods for detecting the thickness of the shale pore adsorption layer from an experimental perspective, but they are not suitable for the determination of the thickness of the shale oil adsorption layer. For example, a Chinese patent document with a publication date of January 27, 2023 and a publication number of CN115615366A proposes a method for detecting the thickness of the shale pore adsorption layer, which is implemented by 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 includes: S1, preparing a shale sample, and placing the shale sample in an oven to dry; S2, placing the dried shale sample in step S1 in a small-angle scattering unit; S3, vacuuming the gas flow path;

[0007] S4. After the vacuum treatment, the scattering intensity data of the pores of the shale sample are detected by the small-angle scattering unit, and the radius of the pores of the shale sample when no adsorption layer is formed on the pore walls of the shale sample pores is obtained; S5. The gas source unit is turned on to transport gas to the humidification unit and the drying unit respectively, and humidified gas and dry gas are obtained respectively, and the humidified gas and the dry gas are mixed in the gas mixing unit to obtain a mixed gas with a humidity reaching a preset value; S6. The mixed gas with a humidity reaching a preset value flows into the small-angle scattering unit, so that the mixed gas forms a saturated adsorption layer on the pore walls of the shale sample pores, and the scattering intensity data of the shale sample pores at this time is detected by the small-angle scattering unit; S7. The thickness of the shale pore adsorption layer is obtained according to the scattering intensity data of the shale sample pores when no adsorption layer is formed on the pore walls of the shale sample pores and the scattering intensity data of the shale sample pores after the adsorption layer is formed on the pore walls of the shale sample pores. This method can achieve humidity control of the mixed gas and form a saturated adsorption layer on the shale pores, and further realize quantitative analysis of the thickness of the shale pore adsorption layer based on small-angle scattering technology. However, this method is only applicable to the calculation of the thickness of the adsorption layer of shale gas, but not to the calculation of the thickness of the adsorption layer of crude oil in the shale pores in the shale oil reservoir. Summary of the invention

[0008] In view of the technical problem that the prior art lacks experimental analysis to determine the thickness of the adsorption layer of shale oil on the surface of the pore structure, the present invention provides a method for successive extraction analysis of the thickness of the shale oil adsorption layer. This method can quantitatively measure the thickness of the shale oil adsorption layer, thereby realizing the true and accurate determination of the shale oil nano-adsorption layer under geological conditions.

[0009] To achieve the above-mentioned purpose, 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: using a first solvent to perform an initial extraction on a shale core to obtain a first shale sample after removing free shale oil; using a second solvent to perform a secondary extraction on the first shale sample 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; based on the positive correlation between the first pore diameter of the shale and the second pore diameter of the shale, determining the thickness of the adsorption layer of shale oil in the target area.

[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 results of the N2 isothermal adsorption-desorption experiment of the first shale sample; determining the average pore diameter of the second shale sample based on the results of the N2 isothermal adsorption-desorption experiment 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]

[0016] Among them, r k is the average pore diameter of shale; r is the surface tension at the boiling point of nitrogen; Vm 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.

[0017] In an exemplary embodiment of the present invention, 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 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.

[0018] 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.

[0019] According to a second aspect of the present invention, there is provided a successive extraction analysis system for the thickness of a shale oil adsorption layer, and the successive extraction analysis system may include: a successive extraction subsystem, a N2 isothermal adsorption-desorption measurement subsystem and a positive correlation analysis subsystem; the successive extraction subsystem is used to perform successive 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, respectively; the N2 isothermal adsorption-desorption measurement subsystem is connected to the successive extraction subsystem to carry out N2 isothermal adsorption-desorption experiments on the first shale sample and the second shale sample, respectively, to determine a first pore diameter of the shale 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 of the shale and the second pore diameter of the shale.

[0020] 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 column-like shale core into powder.

[0021] Through the technical solution provided by the present invention, the present invention has at least the following technical effects:

[0022] (1) The method for successive extraction analysis of the thickness of the shale oil adsorption layer provided by the present invention realizes the true and accurate determination of the shale oil nano-adsorption layer under geological conditions from the perspective of experimental measurement;

[0023] (2) The successive extraction analysis method for the thickness of the shale oil adsorption layer provided by the present invention has a scientific principle, strong operability, and is easy to promote;

[0024] (3) The thickness of the shale oil adsorption layer measured by the present invention helps to deepen the understanding of the shale oil storage mechanism and further optimize the sweet spot evaluation index;

[0025] (4) The thickness of the shale oil adsorption layer measured by the present invention has general guidance for the quantitative evaluation of shale oil movable resources in major oil fields;

[0026] (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.

[0027] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] 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 specific embodiments, they are used to explain the embodiments of the present invention, but do not constitute a limitation on the embodiments of the present invention. In the accompanying drawings:

[0029] Figure 1 A flow chart of a method for successive extraction analysis of shale oil adsorption layer thickness provided in an embodiment of the present invention;

[0030] Figure 2 A specific flow chart of the successive extraction experiment provided by the embodiment of the present invention;

[0031] Figure 3 The pore size distribution curve of shale after weak polarity extraction provided by an embodiment of the present invention;

[0032] Figure 4 The pore size distribution curve of shale after strong polarity extraction provided by the embodiment of the present invention;

[0033] Figure 5 A theoretical calculation model diagram of the thickness of the shale oil adsorption layer provided in an embodiment of the present invention;

[0034] Figure 6 A scatter plot of the first pore diameter of shale and the second pore diameter of shale provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0035] The specific implementation of the embodiment of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here 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.

[0036] 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.

[0037] In the present invention, unless otherwise specified, the directional words used, such as "upper, lower, top, bottom", are usually used to describe the relative positional relationship of the components in terms of the directions shown in the drawings or in terms of the vertical, perpendicular or gravity directions. "First", "second", etc. are only used for the convenience of description and distinction, and cannot be understood as indicating or implying relative importance.

[0038] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "installation", "connection", etc. should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integrated connection; it can be a direct connection, or an indirect connection; it can be a wired connection, or a wireless connection. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances.

[0039] In the prior art, there is no public report on a method for quantitatively determining the thickness of the adsorption layer of shale oil on the surface of the pore structure for real shale samples from the perspective of experimental analysis. To this end, the present invention provides a method for analyzing and determining the thickness of the shale oil adsorption layer based on successive extraction experiments to solve the above technical problems.

[0040] 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 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 according to the positive correlation between the two in the scatter plot.

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

[0042] Embodiment 1

[0043] Please refer to Figure 1 The first embodiment 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:

[0044] Step S101: using a first solvent to perform initial extraction on a shale core to obtain a first shale sample after free shale oil is removed.

[0045] Step S102: using a second solvent to perform secondary extraction on the first shale sample to obtain a second shale sample after removing the adsorbed shale oil and the miscible shale oil.

[0046] 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.

[0047] Exemplarily, N2 isothermal adsorption-desorption experiments are carried out 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.

[0048] 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.

[0049] The calculation formula for the average pore diameter is:

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] Exemplarily, 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.

[0055] 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.

[0056] 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.

[0057] It should be noted that the sequential extraction method is one of the effective means to separate shale oil in different occurrence states. Its principle is to use the differences in the occurrence space and molecular polarity of shale oil in different occurrence states, and use appropriate solvents to extract shale oil in different occurrence states. Generally speaking, free shale oil has a relatively large occurrence space, so it has a strong contact ability with the first solvent and is easy to be extracted; while shale oil adsorbed in micropores and shale oil encapsulated by kerogen macromolecules are difficult to be extracted due to their limited contact ability with the second solvent.

[0058] Furthermore, in this embodiment, the polarity of the second solvent can be greater than the polarity of the first solvent. This is because the free shale oil generally has a smaller molecular polarity and is easy to be extracted, while the adsorbed shale oil generally has a larger molecular polarity and is relatively difficult to be extracted. Therefore, solvents of different polarities can be selected successively to extract and remove the free and adsorbed-miscible shale oils.

[0059] Preferably, the first solvent can be a weak polarity combination solvent that is combined and matched in a predetermined ratio by utilizing the difference in polarity of the washing oil solvents; the second solvent can be a strong polarity combination solvent that is combined and matched in a predetermined ratio by utilizing the difference in polarity of the washing oil solvents. Compared with a single type of washing oil solvent, a mixed solvent has better dissolving performance.

[0060] For example, the first solvent may be a weak polarity 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 strong polarity 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).

[0061] Furthermore, in this embodiment, the positive correlation calculation formula of the first shale pore diameter and the second shale pore diameter can be a linear function. In this case, the intercept value of the linear straight line of the linear function and the X-axis (when the second shale pore diameter is the X-axis) is the thickness of the shale oil adsorption layer.

[0062] Embodiment 2

[0063] The second embodiment 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:

[0064] Step S201: A microdrill is used to obtain a plurality of wax-sealed or sealed coring shale core samples, and the samples are ground into 100-mesh powder samples.

[0065] Step S202: subjecting the processed powder sample to a first solvent extraction treatment to remove free shale oil in the pores of the shale to obtain a first shale sample, and then drying the first shale sample for later use.

[0066] 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.

[0067] Step S204: Take 1 / 2 of the first shale sample reserved in step S202, and then subject it to a second solvent extraction treatment 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.

[0068] 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.

[0069] Step S206: draw a scatter plot of the first pore diameter and the second pore diameter of the shale, obtain a positive correlation curve between the two, and determine the thickness of the shale oil adsorption layer in the target area.

[0070] In this embodiment, the specific implementation method of step S201 is as follows: select multiple shale core samples that have been wax-sealed or sealed, and drill column samples with a diameter of 3 mm and a length of not less than 13 mm by in-situ micro-drilling (laminated shale is drilled along the laminae, and blocky shale is drilled perpendicular to the core direction) to ensure the uniformity of sampling; clean the surface of each shale core sample and grind it into a 100-mesh powder sample.

[0071] 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 the first solvent to remove the free shale oil in the pores of the shale, and obtain the first shale sample. Among them, 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 dried naturally for use.

[0072] In this embodiment, the specific implementation of step S203 is as follows: weigh 1g of the first shale sample processed in step S202, and degas it for more than 8 hours at low temperature (≤70°C) and vacuum state; then, perform N2 isothermal adsorption-desorption experiment on the degassed powdered first shale sample under experimental conditions of temperature ≤-195°C and pressure ≤101.3kPa. After the experiment, the N2 isothermal adsorption-desorption experimental data of the first shale sample are processed using the BJH theory to obtain the pore size distribution curve and the first pore diameter after the free shale oil is removed from the shale.

[0073] In this embodiment, the specific implementation method of step S204 is as follows: weigh 10g of the first shale sample naturally dried in step S202 and place it in a beaker, and use ultrasonic extraction at room temperature in the second solvent to remove the adsorbed and mutually soluble shale oil in the pores of the shale to obtain a second shale sample. Among them, the second solvent used is a strong 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 0.4mL / g. The frequency selected for ultrasonic extraction is 4000r / min, the centrifugation time is 15min, and the extraction is performed until the color of the added fresh solvent no longer changes, which is considered to be the end of the entire extraction process. After the extraction is completed, the powdered second shale sample is rinsed with clean water 3 times and then dried naturally for use.

[0074] In this embodiment, the specific implementation of step S205 is as follows: weigh 1g of the second shale sample processed in step S204, and degas it for more than 8 hours at low temperature (≤70°C) and vacuum state; then, perform N2 isothermal adsorption-desorption experiment on the degassed powdered second shale sample under experimental conditions of temperature ≤-195°C and pressure ≤101.3kPa. After the experiment, the N2 isothermal adsorption-desorption experimental data of the second shale sample are processed using the BJH theory to obtain the pore size distribution curve and the second pore diameter after the shale removes the adsorbed-miscible shale oil.

[0075] In this embodiment, the specific implementation method of step S206 is as follows: the first pore diameter of the shale obtained by 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 by 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.

[0076] Embodiment 3

[0077] The Cangdong Sag is located in the southern part of the basin. It was developed under the regional tension background and is sandwiched between the Cangxian Uplift, Xuhei Uplift and Kongdian Uplift. The sag is composed of Mesozoic and Cenozoic basin filling strata. The Paleogene strata develop the Kongdian Formation, Shahejie Formation and Dongying Formation from bottom to top. The Kongdian Formation is further subdivided into three sections from bottom to top, Ek3, Ek2 and Ek1, with a sedimentary stratum thickness of 400-600m. During the Ek2 deposition period, the Cangdong Sag experienced the largest marine transgression period and subtropical humid climate, and developed freshwater-semi-brackish water closed depression lake basin sediments, which are characterized by a strong reduction environment of the sedimentary water body and high organic matter paleoproductivity. The Ek2 lithology is mainly composed of three major rock types: felsic, mixed and carbonate rocks. Laminated felsic shale is regarded as the key object of shale oil exploration in the second section of Kong in the Cangdong Sag, and the main production wells are vertically buried at a depth of 3800m to 4100m.

[0078] 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 successive extraction analysis of the thickness of a shale oil adsorption layer, the method comprising the following steps:

[0079] Step S301: obtaining a plurality of shale core samples, and grinding the shale core samples into 100-mesh powder samples.

[0080] Specifically, 12 wax-sealed or closed-cored shale samples from the second sweet spot layer 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.

[0081] Step S302: weigh about 20 g of powder sample for each sample, and use two combined solvents of different polarities to extract the powder sample successively to remove free shale oil and adsorbed / miscible shale oil in the shale pores.

[0082] For example, Figure 2 As shown, the specific implementation of step S302 is as follows:

[0083] 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.

[0084] Specifically, weigh about 20g of powder sample, and use a weak polar combination solvent as the first solvent to perform ultrasonic extraction on the powder sample at room temperature. Among them, 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. Here, dichloromethane is a non-polar solvent, and 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.

[0085] The frequency of ultrasonic extraction was 4000r / min, the centrifugal time was 15min, and the extraction was considered complete until the color of the added fresh solvent no longer changed. After one extraction was completed, the powdered first shale sample was rinsed with clean water for 3 times and then dried naturally for later use.

[0086] Sub-step S3022: performing 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 in the shale pores.

[0087] Specifically, about 20 g of the first shale sample in powder form was weighed, and the first shale sample was subjected to ultrasonic extraction at room temperature using a strongly polar combined solvent as the second solvent. The second solvent used was a strongly polar combined solvent in which tetrahydrofuran, acetone and methanol were combined in a volume ratio of 50:25:25, and the amount of the second solvent was 0.4 mL / g.

[0088] The frequency of ultrasonic extraction was 4000r / min, the centrifugal time was 15min, and the extraction was considered complete until the color of the added fresh solvent no longer changed. After the second extraction, the powdered first shale sample was rinsed with clean water for 3 times and then dried naturally for later use.

[0089] Step S303: conducting 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.

[0090] Each time the N2 isothermal adsorption-desorption experiment was carried out, 1 g of the sample was taken and degassed for more than 8 hours at low temperature (≤70°C) and vacuum state; then, the N2 isothermal adsorption-desorption experiment was carried out on the degassed powdered shale sample under the experimental conditions of temperature ≤-195°C and pressure ≤101.3 kPa.

[0091] 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 are obtained, that is, the first pore diameter of the shale (such as Figure 3) and the second pore diameter of shale (as shown Figure 4 shown).

[0092] 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.

[0093] Figure 5 This is a theoretical calculation model diagram of the thickness of the shale oil adsorption layer in this embodiment, such as Figure 5 As shown, the first pore diameter of free shale oil superimposed on the oil layer thickness of adsorbed / miscible shale oil is the second pore diameter of adsorbed / miscible shale oil. In other words, the positive correlation between the first pore diameter and the second pore diameter satisfies a linear relationship.

[0094] With the first pore diameter of shale as the Y axis and the second pore diameter of shale as the X axis, a scatter plot of the first pore diameter of shale and the second pore diameter of shale is drawn. Based on the fitting of the scatter plot, it is determined that the positive correlation between the first pore diameter of shale and the second pore diameter of shale is a linear relationship. The intercept value of the linear relationship line between the first pore diameter and the second pore diameter on the X axis can be determined as the thickness of the shale oil adsorption layer. Figure 6 As shown, the final adsorption layer thickness of shale oil in the target area is about 10 nm.

[0095] Embodiment 4

[0096] 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, a N2 isothermal adsorption-desorption measurement subsystem, and a positive correlation analysis subsystem.

[0097] 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.

[0098] 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 primary extraction on the shale core using a weak polarity combination solvent as an extraction solvent to remove free shale oil in the shale pores. The secondary extraction unit is used to perform secondary extraction on the shale core after the primary extraction treatment using a strong polarity combination solvent as an extraction solvent to remove adsorbed shale oil and miscible shale oil in the shale pores.

[0099] 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.

[0100] 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.

[0101] Embodiment 5

[0102] The fifth embodiment of the present invention provides another successive extraction analysis system for the thickness of the shale oil adsorption layer, which may include a raw material preparation subsystem, a successive extraction subsystem, a N2 isothermal adsorption-desorption measurement subsystem and a linear analysis subsystem.

[0103] The raw material preparation subsystem is used to grind the shale core of the column 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 a column sample with a diameter of 3 mm and a length of not less than 13 mm by an in-situ micro-drilling method (laminated shale is drilled along the laminae, and blocky shale is drilled perpendicular to the core direction) to ensure the uniformity of sampling. The grinding unit is used to grind the shale sample with a clean surface into a 100-mesh powder.

[0104] The successive extraction subsystem can be extracted successively by ultrasonic extraction at room temperature, and the two solvent combinations used successively are extracted until the color of the added fresh solvent no longer changes, which serves as the end mark of each extraction; its input is connected to the output of the raw material preparation subsystem. The two solvent combinations are respectively a weak polarity combination solvent and a strong polarity combination solvent, the weak polarity combination solvent is used to remove free oil in the shale pores, and the strong polarity combination solvent is used for adsorbed / miscible shale oil in the shale pores.

[0105] 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.

[0106] The input of the linear analysis subsystem is connected to the output of the N2 isothermal adsorption-desorption measurement subsystem, and 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.

[0107] In summary, the beneficial effects of the present invention may include:

[0108] (1) From the perspective of experimental measurement, the real and accurate determination of the shale oil nano-adsorption layer under geological conditions was achieved;

[0109] (2) Sweet spot evaluation: It helps to deepen the understanding of the storage mechanism of shale oil and further optimize the sweet spot evaluation indicators;

[0110] (3) Resource calculation: It has general guidance for the quantitative evaluation of movable resources of shale oil in major oil fields;

[0111] (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;

[0112] (5) The present invention adopts the successive extraction technology + N2 physical adsorption experiment to achieve the joint research of advantageous technologies.

[0113] 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, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0114] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0115] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by 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.

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