Method and system for determining thickness of shale oil adsorption layer

Abstract

The application discloses a shale oil adsorption layer thickness determination method and system, and belongs to the technical field of oil and gas exploration. The method comprises the following steps: firstly, performing first pyrolysis treatment on a plurality of shale core samples; secondly, performing second pyrolysis treatment; thirdly, performing N2 isothermal adsorption-desorption experiments on the core samples after the two pyrolysis treatments respectively; fourthly, obtaining first pore diameters and second pore diameters respectively; and fifthly, determining the adsorption layer thickness of shale oil based on the first pore diameters and the second pore diameters. It can be seen that the method is based on real shale samples from the perspective of experimental measurement, and realizes accurate determination of the adsorption layer thickness of shale oil through pyrolysis treatment and N2 isothermal adsorption-desorption experiments.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil and gas exploration, and particularly relates to a method and system for determining thickness of a shale oil adsorption layer. BACKGROUND

[0002] Shale oil is a hot and frontier field of current unconventional oil and gas exploration, and mainly exists in two forms of free state and adsorption-miscible state in shale. The shale oil in free state mainly contributes to shale oil productivity, and the shale oil in adsorption-miscible state is a part that cannot be used under current mining technical conditions. Therefore, how to determine the thickness of the shale oil adsorption layer is related to accurate evaluation of shale oil resources, and is also a key problem that is focused on in shale oil sweet spot evaluation and development stage oil and gas recovery improvement.

[0003] In related technologies, a molecular dynamics simulation method is mainly used to determine the thickness of the shale oil adsorption layer. However, in practice, shale oil molecular components are complex, and the molecular dynamics simulation method is difficult to accurately characterize the real adsorption characteristics of shale oil, so that the thickness of the shale oil adsorption layer cannot be accurately determined. SUMMARY

[0004] Embodiments of the present application provide a method and system for determining the thickness of a shale oil adsorption layer, which can accurately determine the thickness of the 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, and the method comprises:

[0006] Obtaining a plurality of shale core samples in a target area;

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

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

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

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

[0011] Based on the first pore diameter and the second pore diameter corresponding to the plurality of shale core samples, determining the thickness of the shale oil adsorption layer in the target area.

[0012] In a possible implementation, the determining the adsorption layer thickness of the 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:

[0013] Based on the first pore diameter and the second pore diameter corresponding to the plurality of shale core samples, a scatter plot is drawn with the first pore diameter as the horizontal coordinate and the second pore diameter as the vertical coordinate.

[0014] Based on the scatter plot, first relationship data is determined, the first relationship data being used to represent the 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 of 0 is determined as the adsorption layer thickness of the shale oil in the target area.

[0016] In another possible implementation, the first pyrolysis treatment of the shale core sample to obtain a first core sample comprises:

[0017] The shale core sample is heated to a first temperature, and kept at the first temperature for a first time length.

[0018] The first core sample is uniformly heated to a second temperature at a first heating rate in a constant-rate heating mode, kept at the second temperature for a second time length, and cooled to obtain the first core sample.

[0019] In another possible implementation, the second pyrolysis treatment of the first core sample to obtain a second core sample comprises:

[0020] The first core sample is uniformly heated to a third temperature at a second heating rate in a constant-temperature heating mode, kept at the third temperature for a third time length, and cooled to obtain the second core sample; the third temperature is greater than the second temperature.

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

[0022] The first core sample is degassed for more than a fourth time length under a condition that a temperature is less than or equal to a fourth temperature and a vacuum state.

[0023] The N2 isothermal adsorption-desorption experiment of the degassed first core sample is performed to obtain experimental data under a condition that a temperature is less than or equal to a fifth temperature and a pressure is less than or equal to a first pressure.

[0024] The first pore diameter is determined based on the experimental data.

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

[0026] obtaining a plurality of shale samples in a target area which are sealed by wax or sealed coring;

[0027] for each shale sample, drilling a column sample of a target size by in-situ micro drilling;

[0028] cleaning the surface of the column sample and grinding into powder to obtain the shale core sample.

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

[0030] The raw material subsystem is configured to obtain a plurality of shale core samples in a target area;

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

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

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

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

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

[0037] In another possible implementation manner, the pyrolysis subsystem is configured to heat the shale core sample to a first temperature, keep the first temperature for a first time length, adopt a constant-speed heating mode to uniformly heat the shale core sample to a second temperature at a first heating speed, keep the second temperature for a second time length, and obtain the first core sample after cooling.

[0038] In another possible implementation manner, the pyrolysis subsystem is further configured to adopt a constant-speed heating mode to uniformly heat the first core sample to a third temperature at a second heating speed, keep the third temperature for a third time length, and obtain the second core sample after cooling; and the third temperature is greater than the second temperature.

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

[0040] In another possible implementation manner, the raw material subsystem is configured to obtain a plurality of shale samples that are treated by wax sealing or sealed coring in the target area, drill a column sample of a target size by an in-situ micro-drilling method for each shale sample, clean the surface of the column sample, and grind the column sample into a powder to obtain the shale core sample.

[0041] The embodiment of the present application provides a method for determining the thickness of an adsorption layer of shale oil. The method is performed on a plurality of shale core samples, which are first subjected to a first pyrolysis treatment and then subjected to a second pyrolysis treatment. Then, N2 isothermal adsorption-desorption experiments are performed on the core samples after the two pyrolysis treatments, respectively, to obtain a first pore diameter and a second pore diameter, respectively. Based on the first pore diameter and the second pore diameter, the thickness of the adsorption layer of shale oil is determined. As can be seen, the method is based on real shale samples from the experimental measurement point of view, and through pyrolysis treatment and N2 isothermal adsorption-desorption experiments, the accurate determination of the thickness of the adsorption layer of shale oil is realized.

[0042] It should be understood that the foregoing general description and the following detailed description are only exemplary and do not limit the present disclosure. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 is a flowchart of a method for determining the thickness of an adsorption layer of shale oil provided by the embodiment of the present application;

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

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

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

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

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

[0051] The terms "first", "second", "third", and "fourth" and the like in the specification of the present application, the claims, and the drawings are used to distinguish different objects, and are not used to describe a particular order. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the listed steps or units, but can optionally include steps or units not listed, or can optionally include other steps or units inherent to the process, method, product, or device.

[0052] Figure 1 is a flowchart of a shale oil adsorption layer thickness determination method provided by an embodiment of the present application, referring to Figure 1 The method comprises the following steps:

[0053] Step 101: Obtain a plurality of shale core samples in a target area.

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

[0055] (1) Obtain a plurality of shale samples in the target area that are treated with wax sealing or sealed coring.

[0056] The target area is an oil and gas exploration area.

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

[0058] For each shale sample, a column sample can be drilled according to the depositional structure of the shale sample. For example, for laminated shale, drilling along the lamina, and for massive shale, drilling perpendicular to the core direction, to ensure the uniformity of the sample.

[0059] The target size can be set and changed as needed, and no specific limitation is made 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 the shale core sample.

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

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

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

[0064] The first temperature, the first time length, the first heating rate, the second temperature and the second time length can be set and changed as needed, and no specific limitation is made thereto. For example, the first temperature is 75℃, the first time length is 3 minutes, the first heating rate is 25℃ / min, the second temperature is 350℃, and the second time length is the same as the first time length, both being 3 minutes. Correspondingly, the first pyrolysis treatment process is as follows: the shale core sample is heated to 75℃, kept at 75℃ for 3 minutes, uniformly heated to 350℃ at a heating rate of 25℃ / min using a constant rate heating mode, kept at 350℃ for 3 minutes, and a first core sample is obtained after cooling.

[0065] In addition, the pyrolysis instrument can be set and changed as needed, for example, the pyrolysis instrument is a Rock-Eval type pyrolysis instrument.

[0066] Step 103: The first core sample is subjected to a second pyrolysis treatment to obtain a second core sample.

[0067] The 1 / 2 first core sample obtained in step 102 is subjected to a second pyrolysis treatment by using a pyrolysis instrument, and the second pyrolysis treatment is performed by using a constant temperature heating mode, the first core sample is uniformly heated to a third temperature at a second heating rate, and the third temperature is kept constant for a third time length, so as to remove the shale oil in the adsorbed and mutual solubility state in the shale pores, and a second core sample is obtained after cooling; wherein the third temperature is greater than the second temperature.

[0068] The second heating rate, the third temperature and the third time length can be set and changed as needed, and no specific limitation is made thereto. For example, the second heating rate is the same as the first heating rate, both of which are 25℃ / min, the third temperature is 450℃, and the third time length is the same as the first time length, both of which are 3 minutes. Correspondingly, the second pyrolysis treatment process is: using a constant heating mode, uniformly heating to 450℃ at a rate of 25℃ / min, keeping constant for 3 minutes, and obtaining a second core sample after cooling.

[0069] Pyrolysis is one of the effective means for separating shale oil in different states, and its principle lies in that shale oil in different states has different molecular thermal volatilization capacity, shale oil in free state is more easily released than shale oil in adsorbed state, and shale oil with small molecules is more easily released than shale oil with large molecules. In the embodiments of the present application, the shale oil in different states is removed step by step from the shale pores by setting reasonable heating conditions, so as to facilitate subsequent determination of the thickness of the shale oil adsorption layer.

[0070] Step 104: performing 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 degassed for more than a fourth time length under the condition that the temperature is less than or equal to a fourth temperature and the vacuum state; then, the N2 isothermal adsorption-desorption experiment is performed on the degassed first core sample under the condition that the temperature is less than or equal to a fifth temperature and the pressure is less than or equal to a first pressure, and experimental data is obtained; and based on the experimental data, the first pore diameter is determined.

[0072] The fourth temperature, the fourth time length, the fifth temperature and the first pressure can be set and changed as needed, and no specific limitation is made thereto. For example, the fourth temperature is 70℃, the fourth time length is 8 hours, the fifth temperature is 195℃, and the first pressure is 101.3KPa. Correspondingly, the process of performing the N2 isothermal adsorption-desorption experiment on the first core sample is: degassing the first core sample for more than 8 hours under the condition that the temperature is ≤70℃ and the vacuum state; then, the N2 isothermal adsorption-desorption experiment is performed on the degassed first core sample under the condition that the temperature is ≤-195℃ and the pressure is ≤101.3KPa, and experimental data is obtained.

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

[0074] Formula one:

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

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

[0077] In this step, the N2 isothermal adsorption-desorption experiment is performed on the second core sample to obtain the second pore diameter. The process is the same as that in step 104, and the experimental conditions are the same as those for the first core sample. Therefore, no further description is given here.

[0078] It should be noted that when determining the thickness of the shale oil adsorption layer, steps 102-103 can be performed first, and then steps 104-105 can be performed. Alternatively, steps 102 and 104 can be performed first, and then steps 103 and 105 can be performed. No specific limitation is made in this regard.

[0079] Step 106: determining the thickness of the shale oil adsorption layer 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 implemented through the following steps (1) to (3), comprising:

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

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

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

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

[0086] It should be noted that the second pore diameter can also be used as the horizontal coordinate, and the first pore diameter can be used as the vertical coordinate to draw a scatter plot. Based on the scatter plot, the second relationship data is determined, and then the intercept of the straight line corresponding to the second relationship data on the X axis is determined as the adsorption layer thickness of shale oil.

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

[0088] The present application releases and removes the free shale oil and the adsorbed-miscible shale oil in the shale pores in turn by the distributed pyrolysis method, carries out low-temperature N2 adsorption physical experiments on the shale samples after two pyrolysis respectively, and then compares the average pore diameters of the shale samples after two pyrolysis, that is, the first pore diameter and the second pore diameter, draws a scatter plot, obtains a linear relationship straight line of the two, and determines the intercept of the linear straight line with the Y axis as the shale oil adsorption layer thickness.

[0089] The embodiment of the present application provides a method for determining the shale oil adsorption layer thickness. The method first performs a first pyrolysis treatment on a plurality of shale core samples, then performs a second pyrolysis treatment, and then performs N2 isothermal adsorption-desorption experiments on the core samples after two pyrolysis respectively to obtain the first pore diameter and the second pore diameter. Based on the first pore diameter and the second pore diameter, the adsorption layer thickness of shale oil is determined. As can be seen, the method is based on the actual shale sample from the experimental measurement point of view, and realizes the accurate determination of the shale oil adsorption layer thickness through pyrolysis treatment and N2 isothermal adsorption-desorption experiments.

[0090] Moreover, the method provided by the present application helps to deepen the understanding of the shale oil occurrence mechanism, further optimizes the sweet spot evaluation index, has universal guidance for the quantitative evaluation of movable resources of shale oil in each oilfield, provides a solid theoretical basis for the improvement of the shale oil micro-flow model and the optimization of the oil and gas recovery technology. In addition, the distributed pyrolysis technology+N2 adsorption physical experiment is adopted to realize the joint research of the advantageous technologies.

[0091] Figure 3 is a system for determining the shale oil adsorption layer thickness provided by the embodiment of the present application, referring toFigure 3 The system comprises a raw material subsystem 301, a pyrolysis subsystem 302, an N2 isothermal adsorption-desorption measurement subsystem 303, and an analysis subsystem 304.

[0092] The raw material subsystem 301 is configured to obtain a plurality of shale core samples in a target area.

[0093] The pyrolysis subsystem 302 is configured to perform a first pyrolysis process on each shale core sample to obtain a first core sample; wherein the first pyrolysis process is configured to remove free-state shale oil in shale pores.

[0094] The pyrolysis subsystem 302 is further configured to perform a second pyrolysis process on the first core sample to obtain a second core sample; wherein the second pyrolysis process is configured to remove adsorbed-solvent-state shale oil in shale pores.

[0095] The N2 isothermal adsorption-desorption measurement subsystem 303 is configured to perform an 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 further configured to perform an N2 isothermal adsorption-desorption experiment on the second core sample to obtain a second pore diameter.

[0097] The analysis subsystem 304 is configured to determine an 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.

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

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

[0100] In another possible implementation, the pyrolysis subsystem 302 is further configured 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 length, and obtain the 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 configured to: degas the first core sample under a condition of a temperature less than or equal to a fourth temperature and a vacuum state for more than a fourth time length; and perform an N2 isothermal adsorption-desorption experiment on the degassed first core sample under a condition of a temperature less than or equal to a fifth temperature and a pressure less than or equal to a 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 configured to: obtain a plurality of shale samples subjected to wax sealing or sealed coring in a target area; for each shale sample, drill a column sample of a target size by using an in-situ micro-drilling method; clean a surface of the column sample, and grind the column sample into a powder to obtain a shale core sample.

[0103] In the 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 an adsorption layer of shale oil. The system performs first pyrolysis processing and second pyrolysis processing on a plurality of shale core samples, and then performs N2 isothermal adsorption-desorption experiments on the core samples after the two pyrolysis processes, respectively, to obtain a first pore diameter and a second pore diameter, respectively. Based on the first pore diameter and the second pore diameter, the thickness of the adsorption layer of shale oil is determined. As can be seen, the system starts from the actual measurement of the shale sample, and realizes accurate determination of the thickness of the adsorption layer of shale oil through pyrolysis processing and N2 isothermal adsorption-desorption experiments.

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

[0106] Cangdong Sag is located in the southern part of the basin and developed in a regional extensional setting, sandwiched between Cangxian Uplift, Xuhai Uplift and Kongdian Salient. The sag is composed of Mesozoic and Cenozoic basin filling strata. Paleogene strata develop Kongdian Formation, Shahejie Formation and Dongying Formation from bottom to top. Kongdian Formation is further divided into three sections from bottom to top, namely Ek3, Ek2 and Ek1, with a sedimentary strata thickness of 400-600 m. During the Ek2 deposition period, Cangdong Sag experienced the maximum transgression period and a subtropical humid climate, developing a fresh water-semi-salt water closed type depression lake basin deposition, showing a relatively strong reducing environment of the sedimentary water body and a relatively high organic matter paleo-productivity. Ek2 lithology is mainly composed of felsic, mixed and carbonate rocks, and laminated felsic shale is regarded as the key object for shale oil exploration of Ek2 in Cangdong Sag. The main production well is vertically buried at a depth of 3800 m-4100 m.

[0107] The shale sample is selected from the multi-piece wax sealing treatment or sealed coring of the second dessert layer of the hole, a column sample with a diameter of 3 mm and a length of not less than 13 mm is drilled by an in-situ micro-drilling method, the column sample is drilled along the layer of the long and English layer shale to ensure the uniformity of the sample, the surface of each shale sample is cleaned, and the shale sample is ground into a 100-mesh powder to obtain a shale core sample.

[0108] About 10 g of the shale core sample is taken, and the shale core sample is subjected to twice pyrolysis treatment by a pyrolysis instrument. The first pyrolysis treatment process is as follows: first, the shale core sample is heated to 75 ℃, and kept at 75 ℃ for 3 minutes to release gaseous hydrocarbons in the shale pores; then, the temperature is uniformly increased to 350 ℃ at a constant rate of 25 ℃ / min, and kept at 350 ℃ for 3 minutes to remove free shale oil in the shale pores; and then, the shale core sample is cooled for standby. The second pyrolysis treatment process is as follows: 1 / 2 of the sample obtained by the first pyrolysis treatment is uniformly heated to 450 ℃ at a constant rate of 25 ℃ / min, and kept at 450 ℃ for 3 minutes to remove adsorbed-intermolecular shale oil in the shale pores; and then, the shale core sample is cooled for standby. See Figure 4 , Figure 4 FIG. 1 is a schematic diagram of the first pyrolysis treatment process and the second pyrolysis treatment process.

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

[0110] In the embodiments of the present application, the pore size distribution curve can also be obtained by processing the experimental data. See Figure 5 and Figure 6 , Figure 5 FIG. 2 is a pore size distribution curve corresponding to the first core sample, Figure 6 FIG. 3 is a pore size distribution curve corresponding to the second core sample.

[0111] The first pore diameter is taken as the horizontal coordinate, and the second pore diameter is taken as the vertical coordinate, to draw a scatter plot, and the intercept of the linear relationship straight line between the first pore diameter and the second pore diameter on the Y axis in the scatter plot is determined as the adsorbed layer thickness of the shale oil.

[0112] See Figure 7 , Figure 7For the scatter diagram based on the first pore diameter and the second pore diameter, it is determined that the intercept of the linear relation line between the first pore diameter and the second pore diameter on the Y axis is about 10 nm, that is, the shale oil adsorption layer thickness is about 10 nm.

[0113] The above description is only for facilitating the understanding of the technical solution of the present application by those skilled in the art, and is not used 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 an adsorbed layer of shale oil, characterized in that, The method comprises: acquiring a plurality of shale core samples in a 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-state shale oil in shale pores; 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 adsorption-miscible-state shale oil in the shale pores; performing an N2 isothermal adsorption-desorption experiment on the first core sample to obtain a first pore diameter; performing an 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 plurality of shale core samples, determining an adsorption layer thickness of shale oil in the target area.

2. The method of claim 1, wherein, The determination of the adsorption layer thickness of the shale oil in the target area based on the first pore diameters and the second pore diameters 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, drawing a scatter plot with the first pore diameters as the horizontal coordinates and the second pore diameters as the vertical coordinates; based on the scatter plot, determining first relationship data representing the relationship between the first pore diameters and the second pore diameters; based on the first relationship data, determining the second pore diameter corresponding to the first pore diameter of 0 as the adsorption layer thickness of the shale oil in the target area.

3. The method of claim 1, wherein, The first pyrolysis treatment on the shale core sample to obtain the first core sample comprises: heating the shale core sample to a first temperature and keeping the temperature constant for a first time length; using a constant heating rate mode, uniformly heating the shale core sample to a second temperature at a first heating rate, keeping the temperature constant for a second time length, and cooling to obtain the first core sample.

4. The method of claim 3, wherein, The second pyrolysis treatment on the first core sample to obtain the second core sample comprises: using a constant heating rate mode, uniformly heating the first core sample to a third temperature at a second heating rate, keeping the temperature constant for a third time length, and cooling to obtain the second core sample; wherein the third temperature is greater than the second temperature.

5. The method of claim 1, wherein, The N2 isothermal adsorption-desorption experiment on the first core sample to obtain the first pore diameter comprises: degassing the first core sample for more than a fourth time length under a vacuum state at a temperature less than or equal to a fourth temperature; performing an N2 isothermal adsorption-desorption experiment on the degassed first core sample under the condition of a temperature less than or equal to a fifth temperature and a pressure less than or equal to a first pressure to obtain experimental data; determining the first pore diameter based on the experimental data.

6. The method of claim 1, wherein, The acquisition of the plurality of shale core samples in the target area comprises: acquiring a plurality of shale samples in the target area that are treated by wax sealing or sealed coring; for each shale sample, drilling a column sample of a target size by an in-situ micro-drilling method; cleaning the surface of the column sample and grinding it into a powder to obtain the shale core sample.

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

8. The system of claim 7, wherein, The analysis subsystem is configured to plot 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 diameters as the horizontal coordinates and the second pore diameters as the vertical coordinates. Based on the scatter plot, first relationship data is determined, wherein the first relationship data is configured to represent a relationship between the first pore diameters and the second pore diameters; and based on the first relationship data, a second pore diameter corresponding to a first pore diameter of 0 is determined as the adsorption layer thickness of shale oil in the target area.

9. The system of claim 7, wherein, The pyrolysis subsystem is configured to heat the shale core sample to a first temperature and maintain the temperature for a first duration; use a constant heating rate mode to uniformly heat the shale core sample to a second temperature at a first heating rate, maintain the temperature for a second duration, and cool the shale core sample to obtain the first core sample.

10. The system of claim 7, wherein, The N2 isothermal adsorption-desorption measurement subsystem is configured to degas the first core sample for more than a fourth duration under a condition that a temperature is less than or equal to a fourth temperature and a vacuum state. The N2 isothermal adsorption-desorption measurement subsystem is configured to perform an N2 isothermal adsorption-desorption experiment on the degassed first core sample under a condition that a temperature is less than or equal to a fifth temperature and a pressure is less than or equal to a first pressure to obtain experimental data; and determine the first pore diameter based on the experimental data.

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