Method and system for determining thickness of shale oil adsorption layer

Abstract

The invention discloses a method and system for determining the thickness of a shale oil adsorption layer, and belongs to the technical field of oil-gas exploration. The method comprises the following steps: carrying out first pyrolysis treatment on a plurality of shale core samples, carrying out second pyrolysis treatment, respectively carrying out N2 isothermal adsorption-desorption experiments on the core samples subjected to two-time pyrolysis treatment to respectively obtain a first pore diameter and a second pore diameter, and calculating the diameter of the shale core on the basis of the first pore diameter and the second pore diameter. And determining the adsorption layer thickness of the shale oil. Therefore, according to the method, based on a real shale sample, the accurate measurement of the shale oil adsorption layer thickness is realized through pyrolysis treatment and an N2 isothermal adsorption-desorption experiment from the perspective of experimental actual measurement.

Description

Technical Field

[0001] The present application relates to the technical field of oil and gas exploration, and in particular to a method and system for determining the 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 exists in shale in two forms: free state and adsorption-miscible state. Among them, the main contribution to shale oil production capacity is free shale oil, while adsorption-miscible shale oil is the part that cannot be used under current mining technology conditions. Therefore, how to determine the thickness of the shale oil adsorption layer is related to the accurate assessment of shale oil resources, and is also a key issue of concern in the evaluation of shale oil sweet spots and improving oil and gas recovery in the development stage.

[0003] The relevant technology mainly uses molecular dynamics simulation method to determine the thickness of shale oil adsorption layer. However, in reality, the molecular components of shale oil are complex, and the molecular dynamics simulation method is difficult to accurately characterize the real adsorption characteristics of shale oil, resulting in the inability to accurately determine the thickness of shale oil adsorption layer. Summary of the invention

[0004] The embodiment of the present application provides a method and system for determining the thickness of a shale oil adsorption layer, which can accurately determine the thickness of a shale oil adsorption layer. The technical solution is as follows:

[0005] In one aspect, a method for determining the thickness of a shale oil adsorption layer is provided, the method comprising:

[0006] Obtain multiple shale core samples in the target area;

[0007] For each shale core sample, performing a first pyrolysis treatment on the shale core sample to obtain a first core sample; wherein the first pyrolysis treatment is used to remove free shale oil in the pores of the shale;

[0008] Performing a second pyrolysis treatment on the first core sample to obtain a second core sample; wherein the second pyrolysis treatment is used to remove the shale oil in an adsorbed-miscible state in the shale pores;

[0009] Performing a N2 isothermal adsorption-desorption experiment on the first core sample to obtain a first pore diameter;

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

[0011] Based on the first pore diameters and the second pore diameters corresponding to the multiple shale core samples, the thickness of the adsorption layer of shale oil in the target area is determined.

[0012] In a possible implementation, determining the adsorption layer thickness of shale oil in the target area based on the first pore diameter and the second pore diameter corresponding to the plurality of shale core samples includes:

[0013] Based on the first pore diameters and the second pore diameters corresponding to the plurality of shale core samples, a scatter plot is drawn with the first pore diameter as the abscissa and the second pore diameter as the ordinate;

[0014] Based on the scatter plot, determining first relationship data, the first relationship data being used to represent a relationship between the first pore diameter and the second pore diameter;

[0015] Based on the first relationship data, the second pore diameter corresponding to the first pore diameter being 0 is determined as the adsorption layer thickness of the shale oil in the target area.

[0016] In another possible implementation, performing a first pyrolysis treatment on the shale core sample to obtain a first core sample includes:

[0017] Heating the shale core sample to a first temperature and maintaining the temperature for a first period of time;

[0018] The constant heating mode is adopted, the temperature is uniformly increased to the second temperature at a first heating rate, the temperature is kept constant for a second time, and the first core sample is obtained after cooling.

[0019] In another possible implementation, performing a second pyrolysis treatment on the first core sample to obtain a second core sample includes:

[0020] The first core sample is heated uniformly to a third temperature at a second heating rate in a constant temperature heating mode, and is kept constant for a third time period, and the second core sample is obtained after cooling; wherein the third temperature is greater than the second temperature.

[0021] In another possible implementation, performing a N2 isothermal adsorption-desorption experiment on the first core sample to obtain a first pore diameter includes:

[0022] Degassing the first core sample for a fourth period of time under a vacuum state at a temperature less than or equal to a fourth temperature;

[0023] Under the condition that the temperature is less than or equal to the fifth temperature and the pressure is less than or equal to the first pressure, a N2 isothermal adsorption-desorption experiment is performed on the first core sample after degassing to obtain experimental data;

[0024] Based on the experimental data, the first pore diameter is determined.

[0025] In another possible implementation, obtaining a plurality of shale core samples in the target area includes:

[0026] Obtaining a plurality of shale samples in the target area by wax sealing or closed coring;

[0027] For each shale sample, a core sample of target size was drilled by in-situ micro-drilling;

[0028] The surface of the column sample is cleaned and ground into powder to obtain the shale core sample.

[0029] On the other hand, a system for determining the thickness of a shale oil adsorption layer is provided, the system comprising: a raw material subsystem, a pyrolysis subsystem, a N2 isothermal adsorption-desorption measurement subsystem, and an analysis subsystem;

[0030] The raw material subsystem is used to obtain multiple shale core samples in the target area;

[0031] The pyrolysis subsystem is used to perform a first pyrolysis treatment on each shale core sample to obtain a first core sample; wherein the first pyrolysis treatment is used to remove free shale oil in shale pores;

[0032] The pyrolysis subsystem is further used to perform a second pyrolysis treatment on the first core sample to obtain a second core sample; wherein the second pyrolysis treatment is used to remove the shale oil in an adsorbed-miscible state in the shale pores;

[0033] The N2 isothermal adsorption-desorption measurement subsystem is used to perform a N2 isothermal adsorption-desorption experiment on the first core sample to obtain a first pore diameter;

[0034] The N2 isothermal adsorption-desorption measurement subsystem is also used to perform a N2 isothermal adsorption-desorption experiment on the second core sample to obtain a second pore diameter;

[0035] The analysis subsystem is used to determine the thickness of the adsorption layer of shale oil in the target area based on the first pore diameter and the second pore diameter corresponding to the multiple shale core samples.

[0036] In one possible implementation, the analysis subsystem is used to draw a scatter plot based on the first pore diameter and the second pore diameter corresponding to the multiple shale core samples, with the first pore diameter as the horizontal coordinate and the second pore diameter as the vertical coordinate; based on the scatter plot, determine first relationship data, the first relationship data is used to represent the relationship between the first pore diameter and the second pore diameter; based on the first relationship data, determine the second pore diameter corresponding to when the first pore diameter is 0 as the adsorption layer thickness of the shale oil in the target area.

[0037] In another possible implementation, the pyrolysis subsystem is used to heat the shale core sample to a first temperature and keep the temperature constant for a first period of time; adopt a constant heating rate mode to uniformly heat the temperature to a second temperature at a first heating rate and keep the temperature constant for a second period of time, and obtain the first core sample after cooling.

[0038] In another possible implementation, the pyrolysis subsystem is also used to adopt a constant temperature heating mode to uniformly heat the first core sample to a third temperature at a second heating rate, keep the temperature constant for a third time, and obtain the second core sample after cooling; wherein the third temperature is greater than the second temperature.

[0039] In another possible implementation, the N2 isothermal adsorption-desorption measurement subsystem is used to degas the first core sample for more than a fourth time period under a vacuum state at a temperature less than or equal to a fourth temperature; to perform a N2 isothermal adsorption-desorption experiment on the degassed first core sample under the conditions of a temperature less than or equal to a fifth temperature and a pressure less than or equal to the first pressure to obtain experimental data; and to determine the first pore diameter based on the experimental data.

[0040] In another possible implementation, the raw material subsystem is used to obtain multiple shale samples that have been wax-sealed or sealed in the target area; for each shale sample, a column sample of a target size is drilled by an in-situ micro-drilling method; the surface of the column sample is cleaned and ground into powder to obtain the shale core sample.

[0041] The embodiment of the present application provides a method for determining the thickness of a shale oil adsorption layer, which first performs a first pyrolysis treatment on multiple shale core samples, then performs a second pyrolysis treatment, and then performs N2 isothermal adsorption-desorption experiments on the core samples after the two pyrolysis treatments, respectively, to obtain a first pore diameter and a second pore diameter, and based on the first pore diameter and the second pore diameter, the thickness of the shale oil adsorption layer is determined. It can be seen that the method is based on real shale samples from the perspective of experimental measurement, and through pyrolysis treatment and N2 isothermal adsorption-desorption experiments, the thickness of the shale oil adsorption layer is accurately determined.

[0042] It is to be understood that the foregoing general description and the following detailed description are exemplary only and are not restrictive of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a flow chart of a method for determining the thickness of a shale oil adsorption layer provided in an embodiment of the present application;

[0044] Figure 2 It is a schematic diagram of a theoretical calculation model of shale oil adsorption layer thickness provided in an embodiment of the present application;

[0045] Figure 3 is a schematic diagram of a system for determining the thickness of a shale oil adsorption layer provided in an embodiment of the present application;

[0046] Figure 4 is a schematic diagram of a first pyrolysis treatment process and a second pyrolysis treatment process provided in an embodiment of the present application;

[0047] Figure 5 is a schematic diagram of a pore size distribution curve corresponding to a first core sample provided in an embodiment of the present application;

[0048] Figure 6 is a schematic diagram of a pore size distribution curve corresponding to a second core sample provided in an embodiment of the present application;

[0049] Figure 7 It is a scatter plot based on the first pore diameter and the second pore diameter provided in an embodiment of the present application. DETAILED DESCRIPTION

[0050] In order to make the technical solutions and advantages of the present application clearer, the implementation methods of the present application are described in further detail below.

[0051] The terms "first", "second", "third" and "fourth" etc. in the specification and claims of the present application and the drawings are used to distinguish different objects, rather than to describe a specific order. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but optionally includes steps or units that are not listed, or optionally includes other steps or units inherent to these processes, methods, products or devices.

[0052] Figure 1 is a flow chart of a method for determining the thickness of a shale oil adsorption layer provided in an embodiment of the present application, see Figure 1 , the method comprising:

[0053] Step 101: Acquire multiple shale core samples in a target area.

[0054] This step can be achieved by following the steps (1) to (3), including:

[0055] (1) Obtain multiple shale samples in the target area by wax sealing or sealed core sampling.

[0056] Among them, the target area is the oil and gas exploration area.

[0057] (2) For each shale sample, a column sample of target size is drilled by in-situ micro-drilling.

[0058] For each shale sample, a core sample can be drilled according to the sedimentary structure of the shale sample. For example, for laminated shale, the sample is drilled along the laminae, and for massive shale, the sample is drilled perpendicular to the core direction to ensure the uniformity of the sampling.

[0059] The target size can be set and changed as needed, and is not specifically limited thereto. For example, the target size is 3 mm in diameter and not less than 13 mm in length.

[0060] (3) The surface of the column sample is cleaned and ground into powder to obtain a shale core sample.

[0061] The surface of the column sample was cleaned and ground into 100 mesh powder to obtain a shale core sample.

[0062] Step 102: For each shale core sample, perform a first pyrolysis treatment on the shale core sample to obtain a first core sample.

[0063] About 10 g of a shale core sample was weighed and subjected to a first pyrolysis treatment through a pyrolyzer. The process of the first pyrolysis treatment was as follows: the shale core sample was heated to a first temperature and kept at a constant temperature for a first time to release gaseous hydrocarbons in the shale pores; a constant heating mode was adopted to uniformly heat the sample to a second temperature at a first heating rate and kept at a constant temperature for a second time to remove free shale oil in the shale pores, and the first core sample was obtained after cooling.

[0064] Among them, the first temperature, the first duration, the first heating rate, the second temperature and the second duration can be set and changed as needed, and there is no specific limitation on this. For example, the first temperature is 75°C, the first duration is 3 minutes, the first heating rate is 25°C / min, the second temperature is 350°C, and the second duration is the same as the first duration, both of which are 3 minutes. Correspondingly, the first pyrolysis treatment process is: heat the shale core sample to 75°C, keep the temperature constant for 3 minutes, use the constant heating mode, uniformly heat to 350°C at 25°C / min, keep the temperature constant for 3 minutes, and obtain the first core sample after cooling.

[0065] In addition, the pyrolyzer can be set up and changed as needed, for example, the pyrolyzer is a Rock-Eval model pyrolyzer.

[0066] Step 103: Perform a second pyrolysis treatment on the first core sample to obtain a second core sample.

[0067] Weigh 1 / 2 of the first core sample obtained in step 102, and perform a second pyrolysis treatment on the shale core sample through a pyrolyzer. The process of the second pyrolysis treatment is: adopt a constant temperature heating mode, and uniformly heat the first core sample to a third temperature at a second heating rate, and keep the temperature constant for a third time to remove the shale oil adsorbed and miscible in the shale pores, and obtain a second core sample after cooling; wherein the third temperature is greater than the second temperature.

[0068] Among them, the second heating rate, the third temperature and the third duration can be set and changed as needed, and there is no specific limitation on this. For example, the second heating rate is the same as the first heating rate, both are 25°C / min, the third temperature is 450°C, and the third duration is the same as the first duration, both are 3 minutes. Correspondingly, the second pyrolysis treatment process is: using a constant heating mode, heating at a constant speed of 25°C / min to 450°C, keeping the temperature constant for 3 minutes, and cooling to obtain the second core sample.

[0069] Pyrolysis is one of the effective means to separate shale oil in different occurrence states. The principle is that shale oil in different occurrence states has different molecular thermal volatility. Free shale oil is easier to release by thermal than adsorbed shale oil, and small molecule shale oil is easier to release by thermal than large molecule shale oil. In the embodiment of the present application, shale oil in different occurrence states is removed from the shale pores step by step by setting reasonable heating conditions, so as to facilitate the subsequent determination of the thickness of the shale oil adsorption layer.

[0070] Step 104: Perform a N2 isothermal adsorption-desorption experiment on the first core sample to obtain a first pore diameter.

[0071] In this step, the first core sample is first degassed for more than a fourth time period under a vacuum state at a temperature less than or equal to a fourth temperature; then, a N2 isothermal adsorption-desorption experiment is performed on the degassed first core sample under the conditions that the temperature is less than or equal to a fifth temperature and the pressure is less than or equal to the first pressure to obtain experimental data; based on the experimental data, the first pore diameter is determined.

[0072] Among them, the fourth temperature, the fourth duration, the fifth temperature and the first pressure can be set and changed as needed, and there is no specific limitation on this. For example, the fourth temperature is 70°C, the fourth duration is 8 hours, the fifth temperature is 195°C, and the first pressure is 101.3KPa. Correspondingly, the process of conducting a N2 isothermal adsorption-desorption experiment on the first core sample is: degas the first core sample for more than 8 hours at a temperature of ≤70°C and a vacuum state; then, at a temperature of ≤-195°C and a pressure of ≤101.3KPa, conduct a N2 isothermal adsorption-desorption experiment on the degassed first core sample to obtain experimental data.

[0073] In the embodiment of the present application, after the experimental data are obtained, the BJH (Barrett-Joyner-Halenda) theory is used to process the experimental data through the following formula 1 to obtain the first pore diameter.

[0074] Formula 1:

[0075] Among them, r k represents the first pore diameter, γ represents the surface tension at the boiling point of nitrogen, and v m represents the molar volume of nitrogen, R represents the gas constant, T represents the absolute temperature of the boiling point of nitrogen (77K), and p / p0 represents the relative pressure of nitrogen. m , R, T and p / p0 are constants or obtained from experimental data.

[0076] Step 105: Perform a N2 isothermal adsorption-desorption experiment on the second core sample to obtain a second pore diameter.

[0077] In this step, a N2 isothermal adsorption-desorption experiment is performed on the second core sample to obtain the second pore diameter in the same manner as step 104, and the experimental conditions are the same as those for the first core sample, which will not be repeated here.

[0078] It should be noted that when determining the thickness of the shale oil adsorption layer, steps 102-103 may be performed first, and then steps 104-105, or steps 102 and 104 may be performed first, and then steps 103 and 105, and there is no specific limitation on this.

[0079] Step 106: Determine the adsorption layer thickness of shale oil in the target area based on the first pore diameter and the second pore diameter corresponding to the plurality of shale core samples.

[0080] This step can be achieved by following the steps (1) to (3), including:

[0081] (1) Based on the first pore diameters and the second pore diameters corresponding to the plurality of shale core samples, a scatter plot is drawn with the first pore diameter as the abscissa and the second pore diameter as the ordinate.

[0082] (2) Based on the scatter plot, first relationship data is determined, where the first relationship data is used to represent the relationship between the first pore diameter and the second pore diameter.

[0083] The first relationship data is obtained by performing linear fitting on the points in the scatter plot.

[0084] (3) Based on the first relationship data, the second pore diameter corresponding to the first pore diameter being 0 is determined as the adsorption layer thickness of the shale oil in the target area.

[0085] In this step, based on the linear relationship between the first pore diameter and the second pore diameter, the intercept of the straight line corresponding to the first relationship data on the Y-axis, that is, the second pore diameter corresponding to the first pore diameter being 0, is determined as the thickness of the shale oil adsorption layer.

[0086] One point that needs to be explained is that a scatter plot can be drawn with the second pore diameter as the horizontal coordinate and the first pore diameter as the vertical coordinate. Based on the scatter plot, the second relationship data can be determined, and then the intercept of the straight line corresponding to the second relationship data on the X-axis can be determined as the thickness of the adsorption layer of shale oil.

[0087] See also Figure 2 , Figure 2 This is a schematic diagram of the theoretical calculation model for the thickness of the shale oil adsorption layer. It can be seen from the figure that the pore diameter corresponding to the free shale oil is the first pore diameter, and the adsorbed-miscible shale oil is adsorbed on the surface of the inorganic mineral or organic matter layer, and the corresponding pore diameter is the second pore diameter. Therefore, when the first pore diameter is 0, the corresponding second pore diameter is the thickness of the shale oil adsorption layer.

[0088] In this application, free shale oil and adsorbed-miscible shale oil in shale pores are released and removed successively by distributed pyrolysis method, and low-temperature N2 adsorption physical experiments are carried out on shale samples after two pyrolysis. Then, the average pore diameters of the shale samples after the two pyrolysis, i.e., the first pore diameter and the second pore diameter, are compared, and a scatter plot is drawn to obtain a linear relationship line between the two. The intercept of the linear line with the Y-axis is determined to be the thickness of the shale oil adsorption layer.

[0089] The embodiment of the present application provides a method for determining the thickness of a shale oil adsorption layer, which first performs a first pyrolysis treatment on multiple shale core samples, then performs a second pyrolysis treatment, and then performs N2 isothermal adsorption-desorption experiments on the core samples after the two pyrolysis treatments, respectively, to obtain a first pore diameter and a second pore diameter, and based on the first pore diameter and the second pore diameter, the thickness of the shale oil adsorption layer is determined. It can be seen that the method is based on real shale samples from the perspective of experimental measurement, and through pyrolysis treatment and N2 isothermal adsorption-desorption experiments, the thickness of the shale oil adsorption layer is accurately determined.

[0090] Moreover, the method provided in this application helps to deepen the understanding of the occurrence mechanism of shale oil, further optimize the sweet spot evaluation index, and has a general guiding role in the quantitative evaluation of movable resources of shale oil in various oil fields, providing a solid theoretical basis for the further improvement of shale oil microscopic seepage model and the further optimization of oil and gas recovery technology. In addition, the distributed pyrolysis technology + N2 adsorption physical experiment is used to achieve the joint research of superior technologies.

[0091] Figure 3 This is a system for determining the thickness of a shale oil adsorption layer provided in an embodiment of the present application, see Figure 3 The system includes: a raw material subsystem 301, a pyrolysis subsystem 302, a N2 isothermal adsorption-desorption measurement subsystem 303 and an analysis subsystem 304;

[0092] The raw material subsystem 301 is used to obtain multiple shale core samples in the target area;

[0093] The pyrolysis subsystem 302 is used for performing a first pyrolysis treatment on each shale core sample to obtain a first core sample; wherein the first pyrolysis treatment is used to remove free shale oil in the pores of the shale;

[0094] The pyrolysis subsystem 302 is also used to perform a second pyrolysis treatment on the first core sample to obtain a second core sample; wherein the second pyrolysis treatment is used to remove the shale oil in an adsorbed-miscible state in the pores of the shale;

[0095] N2 isothermal adsorption-desorption measurement subsystem 303, used to perform N2 isothermal adsorption-desorption experiment on the first core sample to obtain a first pore diameter;

[0096] The N2 isothermal adsorption-desorption measurement subsystem 303 is also used to perform a N2 isothermal adsorption-desorption experiment on the second core sample to obtain a second pore diameter;

[0097] The analysis subsystem 304 is used to determine the thickness of the adsorption layer of shale oil in the target area based on the first pore diameter and the second pore diameter corresponding to the plurality of shale core samples.

[0098] In one possible implementation, the analysis subsystem 304 is used to draw a scatter plot based on the first pore diameters and the second pore diameters corresponding to multiple shale core samples, with the first pore diameter as the horizontal coordinate and the second pore diameter as the vertical coordinate; based on the scatter plot, determine first relationship data, the first relationship data is used to represent the relationship between the first pore diameter and the second pore diameter; based on the first relationship data, determine the second pore diameter corresponding to the first pore diameter being 0 as the adsorption layer thickness of the shale oil in the target area.

[0099] In another possible implementation, the pyrolysis subsystem 302 is used to heat the shale core sample to a first temperature and keep the temperature constant for a first period of time; adopt a constant heating rate mode to uniformly heat the temperature to a second temperature at a first heating rate and keep the temperature constant for a second period of time, and obtain a first core sample after cooling.

[0100] In another possible implementation, the pyrolysis subsystem 302 is also used to adopt a constant temperature heating mode to uniformly heat the first core sample to a third temperature at a second heating rate, keep the temperature constant for a third time, and obtain a second core sample after cooling; wherein the third temperature is greater than the second temperature.

[0101] In another possible implementation, the N2 isothermal adsorption-desorption measurement subsystem 303 is used to degas the first core sample for more than a fourth time period under a vacuum state at a temperature less than or equal to a fourth temperature; perform a N2 isothermal adsorption-desorption experiment on the degassed first core sample under the conditions of a temperature less than or equal to a fifth temperature and a pressure less than or equal to the first pressure to obtain experimental data; and determine the first pore diameter based on the experimental data.

[0102] In another possible implementation, the raw material subsystem 301 is used to obtain multiple shale samples that have been wax-sealed or sealed in the target area; for each shale sample, a column sample of a target size is drilled by an in-situ micro-drilling method; the surface of the column sample is cleaned and ground into powder to obtain a shale core sample.

[0103] In an embodiment of the present application, the output of the raw material subsystem is connected to the input of the pyrolysis subsystem, the output of the pyrolysis subsystem is connected to the input of the N2 isothermal adsorption-desorption measurement subsystem, and the output of the N2 isothermal adsorption-desorption measurement subsystem is connected to the input of the analysis subsystem.

[0104] The embodiment of the present application provides a system for determining the thickness of a shale oil adsorption layer. The system first performs a first pyrolysis treatment on multiple shale core samples, then performs a second pyrolysis treatment, and then performs N2 isothermal adsorption-desorption experiments on the core samples after the two pyrolysis treatments, respectively, to obtain a first pore diameter and a second pore diameter, and determines the thickness of the shale oil adsorption layer based on the first pore diameter and the second pore diameter. It can be seen that the system is based on real shale samples from the perspective of experimental measurement, and through pyrolysis treatment and N2 isothermal adsorption-desorption experiments, the thickness of the shale oil adsorption layer is accurately determined.

[0105] The present application will be described below through specific embodiments.

[0106] 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.

[0107] Several wax-sealed or sealed cored shale samples were selected from the sweet spot layer of the second section of the hole, and column samples with a diameter of 3 mm and a length of not less than 13 mm were drilled by in-situ micro-drilling. The samples 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 100 mesh powder to obtain shale core samples.

[0108] Take about 10g of shale core sample and perform two pyrolysis treatments on the shale core sample through a pyrolyzer. The first pyrolysis treatment process is: first heat the shale core sample to 75℃, keep the temperature constant for 3 minutes, release the gaseous hydrocarbons in the shale pores, and then use a constant heating mode of 25℃ / min to uniformly heat it to 350℃, keep the temperature constant for 3 minutes, remove the free shale oil in the shale pores, and cool it for use. The second pyrolysis treatment process is: use a constant heating mode of 25℃ / min to uniformly heat it to 450℃, keep the temperature constant for 3 minutes, remove the adsorbed-miscible shale oil in the shale pores, and cool it for use. See Figure 4 , Figure 4 Schematic diagram of the first pyrolysis treatment process and the second pyrolysis treatment process.

[0109] The first core sample obtained by the first pyrolysis treatment was subjected to a N2 isothermal adsorption-desorption experiment, and the second core sample obtained by the second pyrolysis treatment was subjected to a N2 isothermal adsorption-desorption experiment, to obtain the first pore diameter and the second pore diameter, respectively. The process of the N2 isothermal adsorption-desorption experiment is as follows: weigh 1 g of the first core sample or the second core sample, degas for more than 8 hours at low temperature (≤70°C) and vacuum state, and then perform a N2 isothermal adsorption-desorption experiment on the degassed core sample at a temperature of ≤-195°C and a pressure of ≤101.3KPa.

[0110] In the examples of the present application, the pore size distribution curve can also be obtained by processing the experimental data. Figure 5 and Figure 6 , Figure 5 is the pore size distribution curve corresponding to the first core sample, Figure 6 is the pore size distribution curve corresponding to the second core sample.

[0111] A scatter plot is drawn with the first pore diameter as the horizontal coordinate and the second pore diameter as the vertical coordinate, and the intercept of the linear relationship line between the first pore diameter and the second pore diameter in the scatter plot on the Y-axis is determined as the thickness of the shale oil adsorption layer.

[0112] See also Figure 7 , Figure 7It is a scatter plot based on the first pore diameter and the second pore diameter. According to the scatter plot, it is determined that the intercept of the linear relationship line between the first pore diameter and the second pore diameter on the Y-axis is about 10 nm, that is, the thickness of the shale oil adsorption layer is about 10 nm.

[0113] The above description is only for the purpose of facilitating those skilled in the art to understand the technical solution of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for determining the thickness of a shale oil adsorption layer, characterized in that: The method comprises: Obtain multiple shale core samples in the target area; For each shale core sample, performing a first pyrolysis treatment on the shale core sample to obtain a first core sample; wherein the first pyrolysis treatment is used to remove free shale oil in the pores of the shale; Performing a second pyrolysis treatment on the first core sample to obtain a second core sample; wherein the second pyrolysis treatment is used to remove the shale oil in an adsorbed-miscible state in the shale pores; Performing a N2 isothermal adsorption-desorption experiment on the first core sample to obtain a first pore diameter; Performing a N2 isothermal adsorption-desorption experiment on the second core sample to obtain a second pore diameter; Based on the first pore diameters and the second pore diameters corresponding to the multiple shale core samples, the thickness of the adsorption layer of shale oil in the target area is determined.

2. The method according to claim 1, characterized in that The step of determining the adsorption layer thickness of shale oil in the target area based on the first pore diameter and the second pore diameter corresponding to the plurality of shale core samples comprises: Based on the first pore diameters and the second pore diameters corresponding to the plurality of shale core samples, a scatter plot is drawn with the first pore diameter as the abscissa and the second pore diameter as the ordinate; Based on the scatter plot, determining first relationship data, the first relationship data being used to represent a relationship between the first pore diameter and the second pore diameter; Based on the first relationship data, the second pore diameter corresponding to the first pore diameter being 0 is determined as the adsorption layer thickness of the shale oil in the target area.

3. The method according to claim 1, characterized in that The step of performing a first pyrolysis treatment on the shale core sample to obtain a first core sample comprises: Heating the shale core sample to a first temperature and maintaining the temperature for a first period of time; The constant heating mode is adopted, the temperature is uniformly increased to the second temperature at a first heating rate, the temperature is kept constant for a second time, and the first core sample is obtained after cooling.

4. The method according to claim 3, characterized in that The step of performing a second pyrolysis treatment on the first core sample to obtain a second core sample comprises: The first core sample is heated uniformly to a third temperature at a second heating rate in a constant temperature heating mode, and is kept constant for a third time period, and the second core sample is obtained after cooling; wherein the third temperature is greater than the second temperature.

5. The method according to claim 1, characterized in that The step of performing a N2 isothermal adsorption-desorption experiment on the first core sample to obtain a first pore diameter includes: Degassing the first core sample for a fourth period of time under a vacuum state at a temperature less than or equal to a fourth temperature; Under the condition that the temperature is less than or equal to the fifth temperature and the pressure is less than or equal to the first pressure, a N2 isothermal adsorption-desorption experiment is performed on the first core sample after degassing to obtain experimental data; Based on the experimental data, the first pore diameter is determined.

6. The method according to claim 1, characterized in that The method of obtaining a plurality of shale core samples in the target area comprises: Obtaining a plurality of shale samples in the target area by wax sealing or closed coring; For each shale sample, a core sample of target size was drilled by in-situ micro-drilling; The surface of the column sample is cleaned and ground into powder to obtain the shale core sample.

7. A system for determining the thickness of a shale oil adsorption layer, characterized in that: The system comprises: a raw material subsystem, a pyrolysis subsystem, a N2 isothermal adsorption-desorption measurement subsystem and an analysis subsystem; The raw material subsystem is used to obtain multiple shale core samples in the target area; The pyrolysis subsystem is used to perform a first pyrolysis treatment on each shale core sample to obtain a first core sample; wherein the first pyrolysis treatment is used to remove free shale oil in shale pores; The pyrolysis subsystem is further used to perform a second pyrolysis treatment on the first core sample to obtain a second core sample; wherein the second pyrolysis treatment is used to remove the shale oil in an adsorbed-miscible state in the shale pores; The N2 isothermal adsorption-desorption measurement subsystem is used to perform a N2 isothermal adsorption-desorption experiment on the first core sample to obtain a first pore diameter; The N2 isothermal adsorption-desorption measurement subsystem is also used to perform a N2 isothermal adsorption-desorption experiment on the second core sample to obtain a second pore diameter; The analysis subsystem is used to determine the thickness of the adsorption layer of shale oil in the target area based on the first pore diameter and the second pore diameter corresponding to the multiple shale core samples.

8. The system according to claim 7, characterized in that The analysis subsystem is used to draw a scatter plot based on the first pore diameters and the second pore diameters corresponding to the plurality of shale core samples, with the first pore diameter as the abscissa and the second pore diameter as the ordinate; Based on the scatter plot, first relationship data is determined, and the first relationship data is used to represent the relationship between the first pore diameter and the second pore diameter; based on the first relationship data, the second pore diameter corresponding to when the first pore diameter is 0 is determined as the adsorption layer thickness of shale oil in the target area.

9. The system according to claim 7, characterized in that The pyrolysis subsystem is used to heat the shale core sample to a first temperature and keep the temperature constant for a first period of time; adopt a constant heating mode to uniformly heat the sample to a second temperature at a first heating rate and keep the temperature constant for a second period of time, and obtain the first core sample after cooling.

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

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