Shale clay interlayer water content determination method based on water vapor adsorption

Abstract

The invention relates to the technical field of shale gas, aims to solve the problem that the interlayer water content of clay minerals in gas-bearing shale cannot be determined in the prior art, and provides a method for determining the interlayer water content of shale clay based on water vapor adsorption. Comprising the following steps: S1, preparing a shale particle sample; s2, performing a low-temperature nitrogen adsorption experiment and a water vapor isothermal adsorption experiment on the shale particle sample, and drawing a low-temperature nitrogen adsorption curve and a water vapor isothermal adsorption curve; s3, performing pore volume-pore size distribution analysis on the low-temperature nitrogen adsorption curve and the water vapor isothermal adsorption curve; s4, comparing the accumulated pore volume, and judging whether the interlayer water content needs to be calculated or not; s5, when it is judged that the interlayer water content needs to be calculated in the step S4, calculation is conducted; by adopting the method disclosed by the invention, the difference between water vapor adsorption and low-temperature nitrogen adsorption characterization pore size distribution of the shale with the high clay content can be effectively reduced, the interlayer water content characteristic is obtained, and the accuracy of evaluating the gas saturation of the shale with the high clay content is improved.

Description

Technical Field

[0001] This invention relates to the field of petroleum engineering technology, and to a test technology for the water content of rock samples. Specifically, it relates to a method for determining the interlayer water content of shale clay based on water vapor adsorption. Background Technology

[0002] Shale gas is characterized by its self-generation and self-storage, integrating source and reservoir functions. Its storage space is primarily composed of micro- and nano-pores, including internal pores in organic matter, intragranular pores in organic minerals, intergranular pores, and microfractures. These well-developed nano-sized pores possess a high specific surface area, providing ample sites for gas adsorption. This results in adsorbed gas accounting for a significant proportion of the total gas content in shale reservoirs, ranging from 20% to 80%. Reservoir evaluations have shown that shale generally contains a certain amount of primary water, with water saturation ranging from below 10% to 70% or 80%. Water partially occupies pore space and pore surface, reducing the space and surface area available for gas containment and adsorption, directly affecting gas reserves. Furthermore, it also affects the flow capacity of gas within the pore space. Therefore, accurate assessment of shale water content is crucial for various aspects of shale gas exploration and development, including reserve assessment and mobility evaluation.

[0003] For determining the total water content of shale samples, the drying method is currently the most common approach. This involves measuring the decrease in mass of the rock sample after drying at a specific temperature for a certain period, which represents the corresponding water content. Combined with the density of water, the volume of pore space occupied by water can be determined, thus obtaining the water saturation level. Although other experimental methods, such as nuclear magnetic resonance (NMR), are used to evaluate water content—for example, NMR can measure the hydrogen signal of fluids in the rock, and the T2 spectrum can obtain the signal intensity corresponding to different relaxation times, summing these to obtain the overall fluid signal intensity—the calibration of the signal with water content still requires the mass difference between the dried sample and the actual dried sample. Therefore, the drying method is the most fundamental and direct means of determining the water content of shale samples.

[0004] Previous research has summarized the occurrence of water in shale reservoirs as follows: From the perspective of occurrence state, it mainly includes adsorbed water and free water; from the perspective of occurrence location, it mainly includes the pores inside organic matter and inorganic minerals. Among them, organic pores are generally generated by hydrocarbon generation and expulsion processes and have almost no residual water. Only a small amount of water molecules in an adsorbed state are attached to the oxygen-containing functional groups inside the kerogen. The water in the minerals mainly includes capillary bound water inside the pores and adsorbed water on the pore surface, as well as interlayer water between clay mineral crystal layers, crystallization water that requires a high temperature (above 200℃) to be removed and participate in the formation of mineral lattices, and structural water that participates in the formation of crystal structure in the form of OH-, etc.

[0005] Among them, the water that can be removed by drying under conventional temperature conditions of 65℃ or 110℃ mainly includes capillary bound water, pore surface adsorbed water, and interlayer water of clay minerals.

[0006] Interlayer water refers to neutral water molecules existing between the structural units of layered silicate minerals, such as the interlayer water in montmorillonite. Its content is variable; water loss does not destroy the structure, only reducing the interlayer spacing between adjacent structural units. When water is present, it is reabsorbed and expands. A significant difference between interlayer water and capillary-bound water or surface-adsorbed water is that the pore space occupied by water in the latter two remains after water loss and can be measured by helium expansion. However, after the loss of interlayer water, the interlayer space between adjacent structural units shrinks, and this pore space is not included in the pore volume measured by helium expansion. When the content of capillary-bound water and adsorbed water is high, the superposition of a certain amount of interlayer water may lead to a water saturation (the ratio of water volume to pore volume) measurement exceeding 100%, a result that has no physical meaning. For example, when saturating water vapor adsorption in shale samples from the Longmaxi Formation in the southern Sichuan Basin, we found that the maximum water saturation at saturation equilibrium in high-clay-content shale samples exceeded 100% (e.g., ...). Figure 1 (As shown).

[0007] The pore size distribution of shale with different clay contents was analyzed by conducting low-temperature nitrogen adsorption and gravimetric water vapor adsorption tests. The results are as follows: Figure 2 and Figure 3 As shown. Figure 2 The cumulative pore volume versus pore size curves obtained by low-temperature nitrogen adsorption and water vapor adsorption tests are shown for RS5-61JX sample with a clay content of 51%. Figure 3 The cumulative pore volume versus pore size curves are shown for RS5-61JX samples with a clay content of 2%, obtained by low-temperature nitrogen adsorption and water vapor adsorption tests.

[0008] A comparison of the cumulative pore volume characterized by low-temperature nitrogen adsorption and the relative pore volume characterized by water vapor adsorption clearly shows that the pore volume characterized by water vapor adsorption in the RS-61JX shale sample with high clay content is significantly larger than that characterized by low-temperature nitrogen adsorption. However, for the RS5-66JX shale with extremely low clay content, the pore volumes characterized by these two methods are quite similar. Based on existing understanding of the forms of water in clay, for shale with high clay content, the increase in pore volume characterized by water vapor adsorption is mainly due to the increase in interlayer water, which increases the interlayer distance between clay minerals.

[0009] Figure 4A schematic diagram illustrating the differences in pore volume characterization using two different methods—water vapor adsorption and low-temperature nitrogen adsorption—is presented. The incremental volume characterized by water vapor adsorption primarily stems from the increased interlayer spacing due to the increased interlayer water content in clay minerals. This incremental volume is undetectable during helium porosity testing of dried samples. However, during the drying process of extracted core samples, some interlayer water escapes and is included in the water content calculation. Therefore, when calculating water saturation, the water volume (numerator) includes a portion of the interlayer water, while the pore volume (denominator) does not include the pore space occupied by this interlayer water, potentially leading to an overestimation of water saturation. Therefore, accurately evaluating the interlayer water content is crucial for obtaining accurate gas saturation (1 - water saturation).

[0010] Currently, the main method for determining the moisture content of clay is thermogravimetric analysis (TGA). TGA analysis shows that water molecules in hydrated montmorillonite exist in three main states: free water, loosely adsorbed water, and tightly adsorbed water, corresponding to the temperature ranges of 25–75℃, 75–120℃, and 120–230℃, respectively (Wang Pingquan & Chen Dikui, 2006). Figure 5 The weight loss curve of montmorillonite as a function of temperature is shown. The determination of these three stages is based on the different rates of weight loss with increasing temperature in different temperature ranges of the thermogravimetric method.

[0011] In addition, there is the method of analyzing water content by isothermal adsorption of water vapor, which divides the area into zones based on the difference in the rate of increase of water absorption in different pressure ranges. Figure 6 The adsorption and desorption isotherms of montmorillonite are shown.

[0012] Besides this, there is also the volumetric flask method for determining bound water. The basic principle is to place clay into a water-containing volumetric flask; the clay absorbs water, causing the water level in the flask to drop, and the volume of bound water is calculated based on this drop. Its accuracy is lower than the previous two methods, making it suitable for qualitative analysis. It only provides an overall water content, which may include water that has entered the pore space, water adsorbed on the pore surface, and water that has entered the clay mineral layers, making further subdivision difficult.

[0013] The methods described above have several limitations in determining the interlayer water content in shale. First, shale samples contain not only clay but also organic matter and other inorganic minerals. Their water vapor isothermal adsorption characteristics differ from those of standard clay. Therefore, the temperature range for thermogravimetric analysis and the pressure range for isothermal adsorption analysis determined based on clay samples may not be applicable to shale. Furthermore, the water adsorption and loss characteristics in the pores of other organic and inorganic minerals must also be considered. In addition, existing analytical methods primarily classify water based on its adsorption and loss characteristics, defining different states as distinct components. While water adsorption and loss characteristics are related to their location within the environment, this relationship may not be entirely accurate and is also influenced by pore structure and other factors. Therefore, determining the portion of water belonging to the interlayer from the water content at different stages remains unclear. Summary of the Invention

[0014] Primary shale generally contains a certain amount of primary water. However, the interlayer water and pore water in clay minerals are difficult to distinguish in drying tests, affecting the accuracy of gas saturation determination. To address the problem of determining the interlayer water content of clay minerals in gas-bearing shale, this invention proposes a novel analytical method: a method for determining the interlayer water content of shale clay based on water vapor adsorption. This method compares the differences in pore volume-pore size distribution curves characterized by low-temperature nitrogen adsorption and water vapor adsorption, and then corrects the pore volume-pore size distribution curve obtained from water vapor adsorption to determine the interlayer water content characteristics. This method helps to gain a deeper understanding of the interlayer water content characteristics of clay in shale, reduces the uncertainty in evaluating the gas saturation of shale with high clay content, and provides more comprehensive and accurate parameters for reservoir evaluation.

[0015] This invention is achieved using the following technical solution:

[0016] This invention provides a method for determining the interlayer water content of shale clay based on water vapor adsorption, comprising the following steps:

[0017] S1: Shale particle sample preparation;

[0018] S2: Low-temperature nitrogen adsorption experiment and water vapor isotherm adsorption experiment were carried out on shale particle samples. The amount of nitrogen adsorbed by the sample under low temperature conditions and the amount of water vapor adsorbed at a specified temperature were measured as a function of relative pressure. Low-temperature nitrogen adsorption curve and water vapor isotherm adsorption curve were plotted.

[0019] S3: Perform pore volume-pore size distribution analysis on the low-temperature nitrogen adsorption curve and the water vapor isotherm adsorption curve to obtain the cumulative pore volume-pore size distribution curves for the low-temperature nitrogen adsorption and water vapor adsorption characterization.

[0020] S4: Compare the cumulative pore volume characterized by low-temperature nitrogen adsorption and water vapor adsorption within the specified pore size range to determine whether it is necessary to calculate the interlayer water content;

[0021] When the cumulative pore volume of the low-temperature nitrogen adsorption characterization is greater than that of the water vapor adsorption characterization, the interlayer water content is low, and no analysis or calculation of the interlayer water content is required; when the cumulative pore volume of the low-temperature nitrogen adsorption characterization is less than that of the water vapor adsorption characterization, the interlayer water content is high, and analysis and calculation of the interlayer water content are required.

[0022] S5: When step S4 determines that it is necessary to calculate the interlayer water content, the following steps are performed:

[0023] S501: Plot a semi-logarithmic plot of cumulative pore volume-pore size distribution for water vapor adsorption characterization. The horizontal axis, pore size, is displayed on a logarithmic scale with base 10, and the vertical axis, cumulative pore volume, is displayed on a linear scale. The curve in the plot is denoted as psd1.

[0024] S502: In the semi-logarithmic plot, the point with the largest partial pressure and its adjacent left point are linearly fitted to obtain the fitted line. The fitted line is extended to the measured minimum partial pressure point, and the ordinate of the intersection point of the fitted line and the line x = 1nm is calculated and denoted as the intercept.

[0025] The fitted straight line is then shifted down by the intercept distance, and the shifted straight line is denoted as psd2, which is the cumulative pore volume-pore size distribution characterized by water vapor adsorption after removing interlayer water.

[0026] S503: Calculate the interlayer water content distribution with pore size, i.e., psd1-psd2.

[0027] As a preferred technical solution:

[0028] Step S1 includes:

[0029] Shale samples were prepared into particles of a certain mesh size, ranging from 20 to 40 mesh.

[0030] As a preferred technical solution:

[0031] In step S2:

[0032] Low temperature conditions refer to a temperature of 77.3K, with a specified temperature of 30℃.

[0033] As a preferred technical solution:

[0034] In step S3:

[0035] In the cumulative pore volume-pore size distribution curve characterized by low-temperature nitrogen adsorption, the cumulative pore volume is denoted as vd1; in the cumulative pore volume-pore size distribution curve characterized by water vapor adsorption, the cumulative pore volume is denoted as vd2.

[0036] As a preferred technical solution:

[0037] If vd1 is greater than vd2, it indicates that the interlayer water content is low and there is no need to calculate the interlayer water content; otherwise, the interlayer water content needs to be analyzed and calculated.

[0038] As a preferred technical solution:

[0039] Step S3 includes:

[0040] The low-temperature nitrogen adsorption curve was analyzed using a pore size analysis model to obtain the cumulative pore volume-pore size distribution curve.

[0041] The water vapor isothermal adsorption curve was analyzed using a pore size analysis model to obtain the cumulative pore volume-pore size distribution curve.

[0042] As a preferred technical solution:

[0043] The low-temperature nitrogen adsorption curves were analyzed using BJH, NLDFT, or QSDFT pore size distribution analysis models.

[0044] The BJH pore size distribution analysis model was used to analyze the isothermal adsorption curves of water vapor.

[0045] As a preferred technical solution:

[0046] In step S4:

[0047] The specified aperture range refers to an aperture of 0-50 nm.

[0048] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0049] This invention, through low-temperature nitrogen adsorption and water vapor adsorption experiments on the same shale sample, reveals that for shale with relatively uniform micro- and nano-pore development, the semi-logarithmic curve of cumulative pore volume versus pore size, characterized by nitrogen adsorption, exhibits a near-linear distribution in the meso- and macro-pore regions. However, the corresponding curve obtained from water vapor adsorption shows a faster rate of increase with pore size in the small pore size range and a slower rate of increase with pore size in the large pore size range, with the trend in the large pore size range being more consistent with the trend characterized by nitrogen adsorption. Analysis suggests that the increased rate of increase in cumulative pore volume characterized by water vapor adsorption in the small pore size range is due to the adsorption of a large amount of interlayer water. Therefore, based on these characteristics, the method of this invention is proposed, which uses linear fitting to extrapolate the trend of water vapor adsorption in the large pore size range to the small pore size range to distinguish the contribution of interlayer water.

[0050] The intercept determined by the method of this invention can indicate the content of interlayer water. For different shale samples, the corresponding intercept values ​​were calculated using the above method, and it was found that there is a good positive correlation between the intercept and the clay mineral content, further demonstrating the effectiveness of the method.

[0051] The above method can effectively reduce the differences in pore size distribution characterized by water vapor adsorption and low-temperature nitrogen adsorption in shale with high clay content, obtain the interlayer water content characteristics, and improve the accuracy of gas saturation evaluation in shale with high clay content. Attached Figure Description

[0052] Figure 1 The graph shows the change in water saturation over time for eight shale samples after long-term water vapor adsorption saturation, based on the adsorption amount.

[0053] Figure 2 The cumulative pore volume versus pore size curve is obtained by low-temperature nitrogen adsorption and water vapor adsorption tests on RS5-61JX sample with clay content of 51%.

[0054] Figure 3 The cumulative pore volume versus pore size curve is obtained by low-temperature nitrogen adsorption and water vapor adsorption tests on RS5-61JX sample with 2% clay content.

[0055] Figure 4 This is a schematic diagram illustrating the differences in pore volume between two different pore size distribution characterization methods: water vapor adsorption and low-temperature nitrogen adsorption.

[0056] Figure 5 This is a graph showing the weight loss of montmorillonite as a function of temperature.

[0057] Figure 6 This is an isotherm diagram of montmorillonite adsorption and desorption.

[0058] Figure 7 This is a flowchart of the method for determining the interlayer water content of shale clay based on water vapor adsorption, as described in this invention.

[0059] Figure 8 This is a schematic diagram of a shale particle sample.

[0060] Figure 9 The graphs show the low-temperature nitrogen adsorption curve and the water vapor isothermal adsorption curve.

[0061] Figure 10 The cumulative pore volume-pore size distribution curves characterizing low-temperature nitrogen adsorption and water vapor adsorption are shown.

[0062] Figure 11 This is a semi-logarithmic plot of the cumulative pore volume-pore size distribution for water vapor adsorption characterization.

[0063] Figure 12 This is a correlation analysis diagram between intercept and clay mineral content. Detailed Implementation

[0064] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0065] Example 1

[0066] like Figure 7 As shown in the figure, this embodiment proposes a method for determining the interlayer water content of shale clay based on water vapor adsorption, including the following steps:

[0067] S1: Shale particle sample preparation;

[0068] Shale samples are prepared into particles of a certain mesh size, generally recommended to be between 20-40 mesh, with a mass of approximately 10g. Figure 8 This is a schematic diagram of a shale particle sample.

[0069] S2: Low-temperature nitrogen adsorption experiment and water vapor isotherm adsorption experiment were carried out on shale particle samples. The amount of nitrogen adsorbed by the sample under low temperature conditions and the amount of water vapor adsorbed at a specified temperature were measured as a function of relative pressure. Low-temperature nitrogen adsorption curve and water vapor isotherm adsorption curve were plotted.

[0070] Specifically, the amount of nitrogen adsorbed by the sample at a low temperature of 77.3 K is measured as a function of relative pressure (between 0 and 1), denoted as Iso1. Figure 9As shown by the blue dotted line;

[0071] The amount of water vapor adsorbed by a sample at a certain temperature (generally 30℃, but not limited to this temperature) changes with relative pressure (between 0 and 1), and is denoted as Iso2. Figure 9 As shown by the orange dotted line in the middle;

[0072] Figure 9 The low-temperature nitrogen adsorption curve and water vapor isothermal adsorption curve are shown. In the figure, the horizontal axis represents the relative pressure P / P0, where P is the absolute pressure of the gas and P0 is the saturated vapor pressure of the gas at the test temperature. The vertical axis represents the adsorption amount Q.

[0073] S3: Perform pore volume-pore size distribution analysis on the low-temperature nitrogen adsorption curve and the water vapor isotherm adsorption curve to obtain the cumulative pore volume-pore size distribution curves for the low-temperature nitrogen adsorption and water vapor adsorption characterization.

[0074] Specifically, a pore size analysis model was used to analyze the low-temperature nitrogen adsorption curves to obtain the cumulative pore volume-pore size distribution curves. The cumulative pore volume characterized by low-temperature nitrogen adsorption was denoted as vd1. Figure 10 As shown by the blue dotted line; pore size distribution analysis models include BJH, NLDFT, or QSDFT, etc.

[0075] The isothermal adsorption curves of water vapor were analyzed using a pore size analysis model to obtain the cumulative pore volume-pore size distribution curves. The cumulative pore volume characterized by water vapor adsorption is denoted as vd2. Figure 10 As shown by the orange dotted line, the BJH model is generally used for analysis;

[0076] Figure 10 The cumulative pore volume-pore size distribution curves for low-temperature nitrogen adsorption and water vapor adsorption are shown. In the figure, the horizontal axis represents the pore size and the vertical axis represents the cumulative pore volume.

[0077] S4: Compare the cumulative pore volume characterized by low-temperature nitrogen adsorption and water vapor adsorption within the specified pore size range to determine whether it is necessary to calculate the interlayer water content;

[0078] When the cumulative pore volume of the low-temperature nitrogen adsorption characterization is greater than that of the water vapor adsorption characterization, the interlayer water content is low, and no analysis or calculation of the interlayer water content is required; when the cumulative pore volume of the low-temperature nitrogen adsorption characterization is less than that of the water vapor adsorption characterization, the interlayer water content is high, and analysis and calculation of the interlayer water content are required.

[0079] Specifically, compare the cumulative pore volumes characterized by low-temperature nitrogen adsorption and water vapor adsorption within the pore size range of 0-50 nm; if vd1 is greater than vd2 overall, it indicates that the interlayer water content is low and there is no need to calculate the interlayer water content; otherwise, the interlayer water content needs to be analyzed and calculated.

[0080] S5: When step S4 determines that it is necessary to calculate the interlayer water content, the following steps are performed:

[0081] S501: Plot a semi-logarithmic diagram of the cumulative pore volume-pore size distribution for water vapor adsorption characterization, such as... Figure 11 As shown in the figure, the horizontal axis represents the pore diameter, displayed on a logarithmic scale with a base of 10, and the vertical axis represents the cumulative pore volume, displayed on a linear scale. The curve is denoted as psd1. Figure 11 As shown by the blue dotted line in the image;

[0082] S502: In the semi-logarithmic plot, the point with the largest partial pressure and its adjacent left point are linearly fitted to obtain the fitted line. The fitted line is extended to the measured minimum partial pressure point, and the ordinate of the intersection point of the fitted line and the line x = 1nm is calculated and denoted as the intercept.

[0083] The fitted straight line is then shifted down by the intercept distance, and the shifted line is denoted as psd2. This represents the cumulative pore volume-pore size distribution characterized by water vapor adsorption after removing interlayer water. Figure 11 The orange dotted line in the image is shown. Figure 11 The yellow dotted line represents the cumulative pore volume-pore size distribution curve obtained by analyzing the low-temperature nitrogen adsorption curve using the BJH method.

[0084] The point with the highest partial pressure is the water vapor isothermal adsorption curve. Figure 9 The point located on the far right of the graph is the point with the largest P / P0 (partial voltage) value.

[0085] S503: Calculate the interlayer water content distribution with pore size, i.e., psd1-psd2, which is... Figure 11 The difference between the blue dotted line and the orange dotted line.

[0086] Analysis of low-temperature nitrogen adsorption and water vapor adsorption experiments on the same shale sample revealed that for shale with relatively uniform micro-nano pore development, the semi-logarithmic curve of cumulative pore volume versus pore size, characterized by nitrogen adsorption, exhibits a near-linear distribution in the meso-macropore region. However, the corresponding curve obtained from water vapor adsorption shows a faster rate of increase with pore size in the small pore size range and a slower rate of increase with pore size in the large pore size range, with the trend in the large pore size range being more consistent with the trend characterized by nitrogen adsorption. Analysis suggests that the increased rate of increase in cumulative pore volume characterized by water vapor adsorption in the small pore size range is due to the adsorption of a large amount of interlayer water. Therefore, based on these characteristics, the method of this invention is proposed, which uses linear fitting to extrapolate the trend of water vapor adsorption in the large pore size range to the small pore size range to distinguish the contribution of interlayer water.

[0087] The intercept determined using the method of this invention can indicate the content of interlayer water. For different shale samples, the corresponding intercept values ​​were calculated using the above method, and a good positive correlation was found between the intercept and the clay mineral content. Figure 12 As shown, this further illustrates the effectiveness of the method.

[0088] The above method was used to effectively reduce the differences in pore size distribution characterized by water vapor adsorption and low-temperature nitrogen adsorption in shale with high clay content, and obtained the interlayer water content characteristics, thereby improving the accuracy of gas saturation evaluation in shale with high clay content.

[0089] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1.A method for determining interlayer water content of shale clay based on water vapor adsorption, comprising the following steps: S1: shale particle sample preparation; S2: low-temperature nitrogen adsorption experiment and water vapor isothermal adsorption experiment are performed on the shale particle sample to determine the adsorption amount of nitrogen at low temperature and the adsorption amount of water vapor at a specified temperature with respect to the change of relative pressure, and low-temperature nitrogen adsorption curve and water vapor isothermal adsorption curve are drawn; S3: pore volume-pore size distribution analysis is performed on the low-temperature nitrogen adsorption curve and the water vapor isothermal adsorption curve to obtain cumulative pore volume-pore size distribution curves characterized by low-temperature nitrogen adsorption and water vapor adsorption; S4: cumulative pore volumes characterized by low-temperature nitrogen adsorption and water vapor adsorption in a specified pore size range are compared to determine whether interlayer water content needs to be calculated; when the cumulative pore volume characterized by low-temperature nitrogen adsorption is greater than the cumulative pore volume characterized by water vapor adsorption, the interlayer water content is low, and no analysis and calculation of the interlayer water content are needed; when the cumulative pore volume characterized by low-temperature nitrogen adsorption is less than the cumulative pore volume characterized by water vapor adsorption, the interlayer water content is high, and the interlayer water content needs to be analyzed and calculated; S5: when it is determined in step S4 that the interlayer water content needs to be calculated, the following steps are performed: S501: a semi-logarithmic graph of the cumulative pore volume-pore size distribution characterized by water vapor adsorption is drawn, the pore size is displayed on the logarithmic coordinate with a base of 10, and the cumulative pore volume is displayed on the linear coordinate, and the curve in the graph is denoted as psd1; S502: in the semi-logarithmic graph, the point with the maximum partial pressure and its adjacent left point are linearly fitted to obtain a fitting straight line, the fitting straight line is extended to the measured minimum partial pressure point, and the vertical coordinate of the intersection point of the fitting straight line and the straight line x=1 nm is calculated and denoted as intercept; then the fitting straight line is moved downward by the distance of intercept, and the moved straight line is denoted as psd2, which is the cumulative pore volume-pore size distribution characterized by water vapor adsorption after removing the interlayer water; S503: the interlayer water content with respect to the pore size distribution is calculated, which is psd1-psd2. 2.The method for determining interlayer water content of shale clay based on water vapor adsorption according to claim 1, wherein step S1 comprises: preparing the shale sample into particles with a certain mesh size, and the mesh size is 20-40 mesh. 3.The method for determining interlayer water content of shale clay based on water vapor adsorption according to claim 1, wherein in step S2: the low-temperature condition refers to a temperature of 77.3 K, and the specified temperature is 30℃. 4.The method for determining interlayer water content of shale clay based on water vapor adsorption according to claim 1, wherein in step S3: in the cumulative pore volume-pore size distribution curve characterized by low-temperature nitrogen adsorption, the cumulative pore volume characterized by low-temperature nitrogen adsorption is denoted as vd1; and in the cumulative pore volume-pore size distribution curve characterized by water vapor adsorption, the cumulative pore volume characterized by water vapor adsorption is denoted as vd2. 5.The method for determining interlayer water content of shale clay based on water vapor adsorption according to claim 4, wherein: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ If vd1 is greater than vd2 as a whole, it indicates that the interlayer water content is low, and there is no need to calculate the interlayer water content; otherwise, the interlayer water content needs to be analyzed and calculated. 6.The method of claim 1, wherein the method is characterized in that: Step S3 comprises: The low-temperature nitrogen adsorption curve is analyzed by using a pore size analysis model to obtain a cumulative pore volume-pore size distribution curve. The water vapor isotherm adsorption curve is analyzed by using a pore size analysis model to obtain a cumulative pore volume-pore size distribution curve. 7.The method of claim 6, wherein the method is characterized in that: The low-temperature nitrogen adsorption curve is analyzed by using a BJH, NLDFT or QSDFT pore size distribution analysis model. The water vapor isotherm adsorption curve is analyzed by using a BJH pore size distribution analysis model. 8.The method of claim 1, wherein the method is characterized in that: In step S4: The specified pore size range refers to a pore size of 0-50 nm.

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