Method, device, equipment and medium for characterizing water occurrence state in coal rock by using frozen low-pressure nitrogen adsorption

Abstract

The present application provides a method, device, equipment and medium for characterizing water occurrence state in coal rock by using frozen low-pressure nitrogen adsorption, first, a plurality of parallel samples are respectively configured as standard samples and different humidity samples, then the above samples are sequentially subjected to first freezing and second freezing, so as to avoid the problem of water loss caused by vacuumizing in the subsequent test process, finally, the above samples are subjected to low-pressure nitrogen adsorption experiment, and after calculation and difference processing by combining BJH model, the pore diameter-occurring water volume curve of different humidity samples is drawn, so as to characterize the occurrence rule of water in the coal rock sample. The method process is more standardized, the factors are more comprehensive, the water occurrence pore distribution and proportion are accurately characterized, which provides a basis for water lock damage mechanism research and technical support for coalbed methane development.

Description

Technical Field

[0001] This invention belongs to the field of unconventional oil and gas experimental technology, and relates to a method, apparatus, equipment and medium for characterizing the water occurrence state in coal and rock by using refrigerated low-pressure nitrogen adsorption. Background Technology

[0002] Coalbed methane (CBM), as an important unconventional natural gas resource, occupies a significant position in the energy structure. However, CBM reservoirs generally possess geological characteristics such as low permeability, low porosity, and high adsorption, resulting in extremely low initial production capacity. Therefore, reservoir stimulation technologies such as hydraulic fracturing are necessary to create interconnected hydraulic fracture networks to improve reservoir permeability and achieve economical extraction of CBM. During hydraulic fracturing operations, a large amount of fracturing fluid is injected into the coal reservoir. However, due to the low pressure and high capillary force in CBM reservoirs, the fracturing fluid flowback rate is usually low, with a considerable portion of the fracturing fluid remaining trapped in the pores and fractures of the coal and rock.

[0003] The retention of fracturing fluid in coal and rock can trigger a severe water-locking effect. The water-locking effect refers to the phenomenon where external fluids, after entering the tiny pores of a coal seam, are trapped within the seam by capillary forces pointing inwards, thus occupying seepage channels and reducing gas permeability. Studies have shown that the water-locking effect not only significantly reduces reservoir permeability but also increases the water saturation of the coal seam, inhibiting the desorption of coalbed methane and fundamentally reducing coalbed methane production.

[0004] The study of water occurrence states is of great significance for a deeper understanding of the water-locking damage mechanism. Water in coal and rock exists in multiple phases, including adsorbed water (bound water), capillary water, and free water. The distribution location, occurrence mechanism, and impact on coalbed methane desorption-diffusion-seepage of different phases within the pores vary significantly. Accurately characterizing the water occurrence state in coal and rock is a crucial prerequisite for revealing the water-locking damage mechanism and formulating targeted prevention and control measures.

[0005] Currently, nuclear magnetic resonance (NMR) technology is the standard method for characterizing the occurrence of water in coal. Based on the relaxation characteristics of hydrogen nuclei in an applied magnetic field, this technique can non-destructively distinguish different phases of water (adsorbed water, capillary water, and free water) in coal by measuring the transverse relaxation time (T2) spectrum, and can simultaneously obtain pore structure information, offering advantages such as speed and intuitiveness. However, the high cost of NMR equipment and testing, along with stringent requirements for sample preparation and testing environment, limits its large-scale application in conventional laboratories and field settings.

[0006] Low-pressure gas adsorption technology (such as low-temperature nitrogen adsorption and low-pressure argon adsorption) is a classic method for characterizing the pore structure of porous materials. It has significant advantages such as low equipment price and high popularity. It is also more accurate in characterizing micropores and mesopores. However, due to the vacuuming in the initial stage of the test, low-pressure gas adsorption makes it difficult to retain internal moisture, and cannot truly reflect the pore characteristics of in-situ water-bearing coal samples.

[0007] In summary, developing a method for characterizing the water occurrence state in coal and rock using low-pressure nitrogen adsorption can leverage the advantages of low-cost and widely available low-pressure gas adsorption equipment while overcoming the technical bottleneck of water loss caused by vacuuming. This method has significant theoretical and practical value for promoting research on water-locking damage mechanisms and reducing reservoir damage in coalbed methane development. Summary of the Invention

[0008] The purpose of this invention is to provide a method, apparatus, equipment, and medium for characterizing the water occurrence state in coal and rock using low-pressure nitrogen adsorption. The method can effectively prevent water loss caused by vacuuming during low-pressure nitrogen adsorption experiments, accurately characterize the water occurrence pore distribution and proportion, provide a basis for the study of water lock damage mechanism, and provide technical support for coalbed methane development.

[0009] To achieve this objective, the present invention employs the following technical solution: In a first aspect, the present invention provides a method for characterizing the water occurrence state in coal and rock using cryogenic low-pressure nitrogen adsorption, the method comprising: Several sets of parallel samples were cut from the coal and rock samples. Then, a part of the parallel samples were subjected to standard drying treatment to obtain standard samples, and another part of the parallel samples were subjected to different humidity equilibration treatments to obtain samples with different humidity. The standard sample and the samples with different humidity were subjected to a first freezing, a second freezing and a low-pressure nitrogen adsorption experiment in sequence. The pore diameter and pore volume of the standard sample and the samples with different humidity were obtained by calculation using the BJH model. For the same pore diameter, the pore volume of samples with different humidity levels was compared with that of the standard sample, and the pore diameter-water volume curves of samples with different humidity levels were plotted.

[0010] In this invention, the low-pressure nitrogen adsorption experiment was conducted using a fully automated surface area analyzer.

[0011] This invention innovatively proposes a method for characterizing the spatial distribution of water in coal and rock using existing low-pressure nitrogen adsorption technology. First, several sets of parallel samples are configured as standard samples and samples with different humidity levels. Then, these samples undergo a first freezing and a second freezing process sequentially to avoid moisture loss caused by vacuuming during subsequent testing. Finally, low-pressure nitrogen adsorption experiments are performed on these samples. After calculation and difference processing using the BJH model, pore diameter-water volume curves for samples with different humidity levels are plotted, thus characterizing the water accumulation pattern in coal and rock samples. This method is more standardized, considers more comprehensive factors, and accurately characterizes the pore distribution and proportion of water accumulation, providing a basis for the study of water-locking damage mechanisms and technical support for coalbed methane development.

[0012] It should be noted that by placing coal and rock samples in different humidity environments, water will enter and penetrate the pores of the coal and rock under the retention effect of capillary force, and freeze at the liquid nitrogen temperature. The surface of the pores occupied by water cannot adsorb nitrogen gas. Therefore, the penetrated pores will show a lower nitrogen adsorption amount in the low-pressure nitrogen adsorption experiment, thus reducing the measurable pore volume of the pore. Therefore, the difference in pore volume between the standard sample and the sample with different humidity at the same pore diameter can be calculated as the volume of water in the pore corresponding to that pore size.

[0013] Preferably, the parallel samples are obtained by cutting adjacent positions along the bedding direction of the coal and rock samples.

[0014] In this invention, several sets of parallel samples need to be taken from adjacent positions along the bedding direction of the same coal and rock sample in order to reduce the influence of the heterogeneity of the coal and rock pore structure on the results.

[0015] Preferably, after cutting, the material is further subjected to crushing, drying, and degassing in sequence.

[0016] Preferably, the particle size of the parallel samples after crushing is ≤0.25mm, for example, it can be 0.24mm, 0.22mm, 0.2mm, 0.18mm, 0.16mm, 0.15mm or 0.12mm, etc.

[0017] In this invention, the crushing refers to crushing parallel samples to a particle size of less than 60 mesh standard sieve (0.25 mm).

[0018] Preferably, the drying temperature is 100℃-120℃, for example, it can be 102℃, 105℃, 106℃, 108℃, 110℃, 112℃, 115℃, 116℃ or 118℃, etc.

[0019] Preferably, the drying time is ≥48h, for example, it can be 49h, 50h, 51h, 52h, 53h, 54h or 55h.

[0020] Preferably, the degassing temperature is 100℃-120℃, for example, it can be 102℃, 105℃, 106℃, 108℃, 110℃, 112℃, 115℃, 116℃ or 118℃, etc.

[0021] Preferably, the degassing time is 8h-12h, for example, it can be 8.5h, 9h, 9.5h, 10h, 10.5h, 11h or 11.5h.

[0022] In this invention, the mass of each group of samples is weighed after degassing (denoted as m0).

[0023] Preferably, the temperature of the standard drying treatment is 100℃-120℃, for example, it can be 102℃, 105℃, 106℃, 108℃, 110℃, 112℃, 115℃, 116℃ or 118℃, etc.

[0024] Preferably, the standard drying time is ≥120h, for example, it can be 121h, 122h, 123h, 124h, 125h, 126h or 128h, etc.

[0025] Preferably, the different humidity balancing treatment includes: placing the pretreated parallel samples in a closed environment of saturated salt water solutions of different concentrations for at least 120 hours, and the parallel samples are not in direct contact with the saturated salt water solutions.

[0026] In this invention, the sealed environment is a constant temperature and humidity environment. After different humidity equilibrium treatments, the mass of each group of samples is weighed (denoted as m1), and the difference between the mass of the sample and the mass of the degassed sample (m0) is the pore water mass of the sample.

[0027] Preferably, the salt in the saturated salt solution includes potassium chloride and / or potassium nitrate.

[0028] Preferably, before the first freezing, the standard sample and the samples with different humidity levels are placed in glass tubes respectively.

[0029] In this invention, the purpose of loading the sample into a glass tube and then freezing it is to prevent the loss of moisture inside the sample after freezing.

[0030] Preferably, the first freezing medium is liquid nitrogen.

[0031] In this invention, liquid nitrogen is used as the quick-freezing liquid because of its ultra-low temperature properties, economy, and ease of availability, which can ensure that water can be instantly frozen in situ without flowing.

[0032] Preferably, the temperature of the first freezing is -190℃ to -200℃, for example, it can be -191℃, -192℃, -193℃, -194℃, -195℃, -196℃, -197℃, -198℃ or -199℃, etc.

[0033] Preferably, the first freezing time is ≥0.5h, for example, it can be 0.6h, 0.7h, 0.8h, 0.9h or 1h.

[0034] Preferably, the second freezing temperature is -10℃ to 0℃, for example, it can be -9℃, -8℃, -7℃, -6℃, -5℃, -4℃, -3℃, -2℃ or -1℃, etc.

[0035] Preferably, the second freezing time is ≥24h, for example, it can be 25h, 26h, 27h, 28h, 29h or 30h.

[0036] In this invention, after the second freezing, the mass of each group of samples is weighed (denoted as m2), and the difference between the mass of each sample and the mass of the sample with different humidity levels (m1) is the amount of pore water loss of the sample.

[0037] In this invention, if This indicates that the method of characterizing the water occurrence state in coal and rock using low-pressure nitrogen adsorption in this invention has high accuracy. If the calculated value is ≥5%, the sample should be subjected to different humidity equilibration treatments again.

[0038] Preferably, during the low-pressure nitrogen adsorption experiment, when the Dewar flask is not raised, an insulation component is wrapped around the outer surface of the glass tube.

[0039] In this invention, the heat preservation component includes an ice pack; since the low-pressure gas adsorption will undergo a free volume test before the test, the Dewar flask does not rise during this process. In order to prevent water from melting in the sample pores, an ice pack needs to be wrapped around the glass tube during this process, and then the ice pack is removed before the Dewar flask rises.

[0040] Preferably, the relative pressure of the low-pressure nitrogen adsorption experiment is 0-0.995, for example, it can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9, etc.

[0041] In this invention, the equilibrium time of the low-pressure nitrogen adsorption experiment is 8s-12s, for example, it can be 8.5s, 9s, 9.5s, 10s, 10.5s, 11s or 11.5s, etc.

[0042] In this invention, after the low-pressure nitrogen adsorption experiment, the nitrogen adsorption-desorption curve of each group of samples is obtained, and the corresponding BJH pore volume and pore diameter-pore volume curve are calculated by software.

[0043] Preferably, the method for calculating the pore diameter includes: substituting the nitrogen adsorption equilibrium pressure into the Kelvin equation to calculate the Kelvin radius; calculating the adsorption layer thickness corresponding to the nitrogen adsorption equilibrium pressure according to the Halsey empirical film thickness formula; and calculating the pore diameter based on the Kelvin radius and the adsorption layer thickness.

[0044] Preferably, the formula for calculating the Kelvin radius is as shown in equation (1): (1) In formula (1): Kelvin radius (nm); The surface tension of the liquid condensate is taken as 8.85 × 10⁻⁶. -3 N / m; The molar volume of the liquid condensate is 3.468 × 10⁻⁶. -5 m 3 / mol; R is the ideal gas constant, with a value of 8.3144 J / (mol·K); The analysis temperature was set at 77 K, the temperature of liquid nitrogen. The adsorption equilibrium pressure of nitrogen (kPa); is the saturated vapor pressure of nitrogen at liquid nitrogen temperature, with a value of 101.325 kPa.

[0045] In this invention, nitrogen gas will be adsorbed on the surface of porous materials under low pressure and liquid nitrogen temperature (77K). The amount of adsorbed gas can be recorded as a function of the relative pressure of the adsorbed substance. The relationship between the relative pressure and the radius of curvature of the adsorbed gas condensed in the pores can be described by the Kelvin equation.

[0046] Preferably, the formula for calculating the thickness of the adsorption layer is as shown in equation (2): (2) In formula (2): The average thickness of the monomolecular adsorption layer is 0.43 nm when the adsorbate is nitrogen.

[0047] Preferably, the formula for calculating the pore diameter is as shown in equation (3): (3) In formula (3): The diameter of the cylindrical hole is in nm. The thickness of the adsorption layer is in nm.

[0048] In this invention, all pore throats are cylindrical. When capillary condensation occurs, the diameter of the cylindrical pore is calculated taking into account the thickness of the adsorption layer.

[0049] Preferably, the pore volume is calculated according to the BJH model, and the calculation formula is shown in equation (4) below: (4) In equation (4): Pore ​​volume (cm³) 3 / g); This is the volume correction factor; The volume of gas desorbed when the pressure decreases, expressed as liquid volume (cm³). 3 / g); The change in adsorption layer thickness (nm) is the amount of change in the thickness of the adsorption layer when the pressure decreases. It is the ratio (nm) of the average capillary radius to the average pore size of the desorption pores during the pressure drop process. The surface area of ​​the pores (m 2 / g).

[0050] In this invention, the pore size distribution is calculated by software based on the BJH model, and the pore volume under the pore size is equivalent to the amount of liquid nitrogen filling the pore.

[0051] Preferably, the pore diameter-water volume curves of the samples with different humidity levels are used to characterize the water occurrence characteristics in the pores of coal and rock.

[0052] Secondly, the present invention provides an apparatus for characterizing the water occurrence state in coal and rock using refrigerated low-pressure nitrogen adsorption, the apparatus comprising: The standard sample and sample preparation module for different humidity levels is used to cut several sets of parallel samples from coal and rock samples, then perform standard drying treatment on a portion of the parallel samples to obtain standard samples, and perform different humidity equilibration treatment on another portion of the parallel samples to obtain samples with different humidity levels. The pore diameter and pore volume determination module is used to perform a first freezing, a second freezing, and a low-pressure nitrogen adsorption experiment on the standard sample and the samples with different humidity levels in sequence, and calculate the pore diameter and pore volume of the standard sample and the samples with different humidity levels by combining the BJH model. The pore diameter-water volume plotting module is used to calculate the difference between the pore volume of samples with different humidity levels and a standard sample under the same pore diameter, and plot the pore diameter-water volume curve for samples with different humidity levels.

[0053] Thirdly, the present invention provides an electronic device, the electronic device comprising: At least one processor; and A memory communicatively connected to the at least one processor; wherein, The memory stores a computer program that can be executed by the at least one processor, such that the at least one processor can perform the method described in the first aspect for characterizing the water occurrence state in coal and rock by adsorption of frozen low-pressure nitrogen.

[0054] Fourthly, the present invention provides a computer-readable storage medium storing computer instructions that, when executed by a processor, implement the method described in the first aspect for characterizing the water occurrence state in coal and rock by adsorption of frozen low-pressure nitrogen.

[0055] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0056] Compared with the prior art, the present invention has the following beneficial effects: This invention innovatively proposes a method for characterizing the spatial distribution of water in coal and rock using existing low-pressure nitrogen adsorption technology. First, several sets of parallel samples are configured as standard samples and samples with different humidity levels. Then, these samples undergo a first freezing and a second freezing process sequentially to avoid moisture loss caused by vacuuming during subsequent testing. Finally, low-pressure nitrogen adsorption experiments are performed on these samples. After calculation and difference processing using the BJH model, pore diameter-water volume curves for samples with different humidity levels are plotted, thus characterizing the water accumulation pattern in coal and rock samples. This method is more standardized, considers more comprehensive factors, and accurately characterizes the pore distribution and proportion of water accumulation, providing a basis for the study of water-locking damage mechanisms and technical support for coalbed methane development. Attached Figure Description

[0057] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0058] Figure 1 This is a flowchart of the method for characterizing the water occurrence state in coal and rock using low-pressure nitrogen adsorption in Example 1.

[0059] Figure 2 This is the nitrogen adsorption-desorption curve of sample A in Example 2.

[0060] Figure 3 This is the nitrogen adsorption-desorption curve of sample B in Example 2.

[0061] Figure 4 This is the nitrogen adsorption-desorption curve of sample C in Example 2.

[0062] Figure 5 This is a graph showing the pore diameter versus pore volume of samples A and B in Example 2.

[0063] Figure 6 This is a graph showing the pore diameter versus pore volume of samples A and C in Example 2.

[0064] Figure 7 This is a curve showing the pore diameter versus the volume of water contained in sample B, as plotted in Example 2.

[0065] Figure 8 This is a curve showing the pore diameter versus the volume of water contained in sample C, as plotted in Example 2.

[0066] Figure 9 This is a schematic diagram of the device structure for characterizing the water occurrence state in coal and rock using low-pressure nitrogen adsorption in a specific embodiment of the present invention. Figure 10 This is a schematic diagram of an electronic device structure provided by a specific embodiment of the present invention for characterizing the water occurrence state in coal and rock by adsorption of frozen low-pressure nitrogen. Detailed Implementation

[0067] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of the present application.

[0068] It should be noted that the terms "first," "second," "candidate," "target," etc., used in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0069] Example 1 This embodiment provides a method for characterizing the water occurrence state in coal and rock by adsorption of frozen low-pressure nitrogen. The method can be executed by a device for characterizing the water occurrence state in coal and rock by adsorption of frozen low-pressure nitrogen. The device can be implemented in hardware and / or software and can be configured in an electronic device that has the ability to characterize the water occurrence state in coal and rock by adsorption of frozen low-pressure nitrogen.

[0070] like Figure 1 As shown, the method provided in this embodiment includes: S110. Several sets of parallel samples are cut from the coal and rock samples. Then, a part of the parallel samples are subjected to standard drying treatment to obtain standard samples, and another part of the parallel samples are subjected to different humidity balancing treatments to obtain samples with different humidity.

[0071] In step S110, the parallel samples are obtained by cutting adjacent positions along the bedding direction of the coal and rock samples; after cutting, they are further subjected to crushing, drying and degassing in sequence.

[0072] Specifically, the particle size of the parallel samples after crushing is ≤0.25mm; the drying temperature is 100℃-120℃ and the time is ≥48h; the degassing temperature is 100℃-120℃ and the time is 8h-12h.

[0073] In step S110, the temperature of the standard drying treatment is 100℃-120℃, and the time is ≥120h.

[0074] In step S110, the different humidity balancing treatment includes: placing the pretreated parallel samples in a closed environment of saturated salt water solutions of different concentrations for at least 120 hours, and the parallel samples are not in direct contact with the saturated salt water solutions; the salts in the saturated salt water solutions include potassium chloride and / or potassium nitrate.

[0075] In step S110, the mass m0 of the degassed sample, the mass m1 of the standard sample and the samples with different humidity levels are weighed respectively.

[0076] S120. The standard sample and the samples with different humidity levels are subjected to a first freezing, a second freezing, and a low-pressure nitrogen adsorption experiment in sequence. The pore diameter and pore volume of the standard sample and the samples with different humidity levels are obtained by calculation using the BJH model.

[0077] In step S120, prior to the first freezing, the standard sample and the samples with different humidity levels were placed in glass tubes respectively. The medium for the first freezing was liquid nitrogen; the temperature for the first freezing was -190℃ to -200℃, and the time was ≥0.5h; the temperature for the second freezing was -10℃ to 0℃, and the time was ≥24h.

[0078] In step S120, the mass m2 of each group of samples after the second freezing is weighed.

[0079] Specifically, if This indicates that the method of characterizing the water occurrence state in coal and rock using low-pressure nitrogen adsorption in this invention has high accuracy. If the calculated value is ≥5%, the sample should be subjected to different humidity equilibration treatments again.

[0080] In step S120, during the low-pressure nitrogen adsorption experiment, an insulation component is wrapped around the outer surface of the glass tube before the Dewar flask is raised, and then the insulation component is removed before the Dewar flask is raised. The relative pressure of the low-pressure nitrogen adsorption experiment is 0-0.995.

[0081] In step S120, after the low-pressure nitrogen adsorption experiment, the nitrogen adsorption-desorption curve of each group of samples is obtained. The corresponding pore diameter and BJH pore volume are calculated by software, and then the pore diameter-pore volume curve is plotted.

[0082] In step S120, the method for calculating the pore diameter includes: substituting the nitrogen adsorption equilibrium pressure into the Kelvin equation to calculate the Kelvin radius; calculating the adsorption layer thickness corresponding to the nitrogen adsorption equilibrium pressure according to the Halsey empirical film thickness formula; and calculating the pore diameter based on the Kelvin radius and the adsorption layer thickness.

[0083] Specifically, the formula for calculating the Kelvin radius is shown in equation (1) below: (1) In formula (1): Kelvin radius (nm); The surface tension of the liquid condensate is taken as 8.85 × 10⁻⁶.-3 N / m; The molar volume of the liquid condensate is 3.468 × 10⁻⁶. -5 m 3 / mol; R is the ideal gas constant, with a value of 8.3144 J / (mol·K); The analysis temperature was set at 77 K, the temperature of liquid nitrogen. The adsorption equilibrium pressure of nitrogen (kPa); is the saturated vapor pressure of nitrogen at liquid nitrogen temperature, with a value of 101.325 kPa.

[0084] Specifically, the formula for calculating the thickness of the adsorption layer is shown in equation (2) below: (2) In formula (2): The average thickness of the monomolecular adsorption layer is 0.43 nm when the adsorbate is nitrogen.

[0085] Specifically, the formula for calculating the pore diameter is shown in equation (3) below: (3) In formula (3): The diameter of the cylindrical hole is in nm. The thickness of the adsorption layer is in nm.

[0086] In step S120, the pore volume is calculated according to the BJH model, and the calculation formula is shown in the following formula (4): (4) In equation (4): Pore ​​volume (cm³) 3 / g); This is the volume correction factor; The volume of gas desorbed when the pressure decreases, expressed as liquid volume (cm³). 3 / g); The change in adsorption layer thickness (nm) is the amount of change in the thickness of the adsorption layer when the pressure decreases. It is the ratio (nm) of the average capillary radius to the average pore size of the desorption pores during the pressure drop process. The surface area of ​​the pores (m 2 / g).

[0087] S130. Under the same pore diameter, the pore volume of samples with different humidity levels is subtracted from that of the standard sample, and the pore diameter-water volume curve of samples with different humidity levels is plotted.

[0088] In step S130, the pore diameter-water volume curve of the samples with different humidity levels is used to characterize the water occurrence characteristics in the pores of coal and rock.

[0089] The method provided in this embodiment first configures several groups of parallel samples as standard samples and samples with different humidity levels. Then, these samples undergo a first freezing and a second freezing process sequentially to avoid moisture loss during subsequent vacuuming tests. Finally, a low-pressure nitrogen adsorption experiment is performed on the samples. After calculation and difference processing using the BJH model, pore diameter-water volume curves for samples with different humidity levels are plotted, thus characterizing the water accumulation pattern in coal and rock samples. This method is more standardized, considers more comprehensive factors, and accurately characterizes the distribution and proportion of water accumulation in pores, providing a basis for the study of water-locking damage mechanisms and technical support for coalbed methane development.

[0090] Example 2 This embodiment takes anthracite from Zhaozhuang Mine in the Qinshui Basin as the research object in order to further explain the composition of the specific technical solution.

[0091] like Figure 1 As shown, the method provided in this embodiment includes: First, based on step S110, three sets of parallel samples are cut from the selected coal and rock samples and pre-treated. Then, the mass m0 of the three sets of samples is weighed. Then, one set of parallel samples is subjected to standard drying treatment to obtain standard samples. Two sets of parallel samples are subjected to different humidity equilibration treatments to obtain samples with different humidity. Then, the mass m1 of the three sets of samples is weighed. Specifically, the pretreatment includes crushing, drying, and degassing performed sequentially; the crushing is done through a 60-mesh standard sieve; the drying temperature is 110℃ and the time is 48 hours; the degassing temperature is 110℃ and the time is 10 hours. Specifically, parallel sample (A) was subjected to standard drying treatment at 110℃ for 120h; parallel sample (B) was equilibrated at 84% constant humidity for 120h; and parallel sample (C) was equilibrated at 97% constant humidity for 120h. Different humidity conditions were created by using 84% KCl solution and 97% K2SO4 solution in combination with sealed desiccators. Then, based on step S120, the standard sample and the samples with different humidity levels are subjected to a first freezing, a second freezing, and a low-pressure nitrogen adsorption experiment in sequence; and then, using the BJH model, the pore diameter and pore volume of the standard sample and the samples with different humidity levels are calculated by software. Specifically, the first freezing temperature was -196℃ and the time was 0.5h; the second freezing temperature was -5℃ and the time was 24h; the mass m2 of the three groups of samples after the second freezing was weighed respectively. Specifically, the relative pressure of the low-pressure nitrogen adsorption experiment was 0-0.995 and the equilibrium time was 10s; Among them, nitrogen adsorption-desorption curves of three groups of samples were obtained after the low-pressure nitrogen adsorption experiment (e.g. Figure 2-4 As shown), after calculation, pore diameter-pore volume curves for three groups of samples were plotted (e.g. Figure 5-6 (As shown).

[0092] Finally, based on step S130, under the same pore diameter, the pore volume of samples with different humidity levels is subtracted from that of the standard sample, and the pore diameter-water volume curves of samples with different humidity levels are plotted (e.g., Figure 7-8 As shown in the figure, it is used to characterize the occurrence characteristics of water in coal and rock pores.

[0093] In this embodiment, the measured values ​​of the degassed mass m0, equilibrium mass m1, and initial mass m2 of each sample group are as follows: The calculated values ​​are shown in Table 1.

[0094] Table 1 As shown in Table 1: The accuracy of the results is ≤5%, indicating that the method provided by this invention for characterizing the water occurrence state in coal and rock using frozen low-pressure nitrogen adsorption has high precision.

[0095] Figure 7-8 In the pore diameter-pore water volume curve, each data point represents the volume of pore water in the pores corresponding to a specific pore diameter in the coal or rock. Therefore, the pore diameter-pore water volume curve of a sample can represent the pore water occurrence characteristics of that sample with different pore diameters. Figure 7-8 It can be seen that the water content in both parallel samples (B) and (C) is mainly mesopores (pore size > 100 nm, according to the Hordott classification). Among them, the pore volumes of micropores, mesopores, and mesopores in parallel sample (B) are 0.000158 cm³. 3 / g, 0.000612cm 3 / g and 0.000762cm 3 / g, accounting for 10.34%, 39.94%, and 49.72% respectively, and the pore volumes of micropores, mesopores, and intermediate pores in parallel samples (C) were 0.000163 cm³. 3 / g, 0.001001cm 3 / g and 0.000762cm 3 / g, accounting for 8.97%, 36.08% and 54.93% respectively.

[0096] Example 3 This embodiment provides a method for characterizing the water occurrence state in coal and rock by using refrigerated low-pressure nitrogen adsorption. Except for the absence of degassing, all other conditions are the same as in Example 2.

[0097] In this embodiment, because the sample was not degassed, there will be residual impurity gases in the sample, which will cause the results of different humidity balance treatments to be distorted.

[0098] Comparative Example 1 This comparative example provides a method for characterizing the water occurrence state in coal and rock using low-pressure nitrogen adsorption under freezing conditions. Except for the absence of a first freezing, all other conditions are the same as in Example 2.

[0099] In this comparative example, because the sample was not subjected to a first freezing treatment, the moisture in the sample was difficult to retain in the indoor environment, resulting in a lower calculated result for the water-bearing pore volume.

[0100] Comparative Example 2 This comparative example provides a method for characterizing the water occurrence state in coal and rock using low-pressure nitrogen adsorption under freezing conditions. Except for the absence of a second freezing, all other conditions are the same as in Example 2.

[0101] In this comparative example, because the sample was not subjected to a second freezing treatment, there was a risk of water loss during the vacuuming step of the free volume test after the sample was mounted on the equipment, resulting in a lower calculated water-bearing pore volume.

[0102] The present invention also provides a device for characterizing the water occurrence state in coal and rock by adsorption of refrigerated low-pressure nitrogen gas, such as... Figure 9 As shown, the device includes: a standard sample and sample preparation module 201 with different humidity levels, a pore diameter and pore volume determination module 202, and a pore diameter-occupied water volume plotting module 203. Wherein: The standard sample and sample preparation module 201 is used to cut several sets of parallel samples from the coal and rock sample, and then perform standard drying treatment on a part of the parallel samples to obtain standard samples, and perform different humidity balancing treatment on another part of the parallel samples to obtain samples with different humidity. The pore diameter and pore volume determination module 202 is used to perform a first freezing, a second freezing and low-pressure nitrogen adsorption experiment on the standard sample and the samples with different humidity in sequence, and calculate the pore diameter and pore volume of the standard sample and the samples with different humidity in combination with the BJH model. The pore diameter-water volume plotting module 203 is used to calculate the difference between the pore volume of samples with different humidity levels and the standard sample under the same pore diameter, and plot the pore diameter-water volume curve of samples with different humidity levels.

[0103] The apparatus provided in the specific embodiments of the present invention can execute the method for characterizing the water occurrence state in coal and rock by adsorption of frozen low-pressure nitrogen provided in any embodiment of the present invention, and has the corresponding functional modules and beneficial effects of the method.

[0104] The present invention also provides an electronic device for implementing a method of characterizing the water occurrence state in coal and rock using refrigerated low-pressure nitrogen adsorption, such as... Figure 10 As shown, this electronic device is intended to represent various forms of digital computers, such as laptop computers, desktop computers, workstations, personal digital assistants, servers, blade servers, mainframe computers, and other suitable computers. This electronic device can also represent various forms of mobile devices, such as personal digital processors, cellular phones, smartphones, wearable devices (such as helmets, glasses, watches, etc.), and other similar computing devices. The components shown herein, their connections and relationships, and their functions are merely illustrative and are not intended to limit the implementation of the present application described and / or claimed herein.

[0105] like Figure 10 As shown, the electronic device 10 includes at least one processor 11 and a memory, such as a read-only memory (ROM) 12 or a random access memory (RAM) 13, communicatively connected to the at least one processor 11. The memory stores computer programs executable by the at least one processor. The processor 11 can perform various appropriate actions and processes based on the computer program stored in the ROM 12 or loaded from storage unit 18 into the RAM 13. The RAM 13 can also store various programs and data required for the operation of the electronic device 10. The processor 11, ROM 12, and RAM 13 are interconnected via a bus 14. An input / output (I / O) interface 15 is also connected to the bus 14.

[0106] Multiple components in electronic device 10 are connected to I / O interface 15, including: input unit 16, such as keyboard, mouse, etc.; output unit 17, such as various types of displays, speakers, etc.; storage unit 18, such as secondary storage area, optical disc, etc.; and communication unit 19, such as network card, modem, wireless transceiver, etc. Communication unit 19 allows electronic device 10 to exchange information / data with other devices through computer networks such as the Internet and / or various telecommunications networks.

[0107] Processor 11 can be a variety of general-purpose and / or special-purpose processing components with processing and computing capabilities. Some examples of processor 11 include, but are not limited to, central processing unit (CPU), graphics processing unit (GPU), various special-purpose artificial intelligence (AI) computing chips, various processors running machine learning model algorithms, digital signal processors (DSPs), and any suitable processor, controller, microcontroller, etc. Processor 11 performs the various methods and processes described above, such as the method of characterizing the water occurrence state in coal and rock using cryogenic low-pressure nitrogen adsorption.

[0108] In some embodiments, the method for characterizing the water state in coal and rock using cryogenic low-pressure nitrogen adsorption can be implemented as a computer program tangibly contained in a computer-readable storage medium, such as storage unit 18. In some embodiments, part or all of the computer program can be loaded and / or installed on electronic device 10 via ROM 12 and / or communication unit 19. When the computer program is loaded into RAM 13 and executed by processor 11, one or more steps of the method for characterizing the water state in coal and rock using cryogenic low-pressure nitrogen adsorption described above can be performed. Alternatively, in other embodiments, processor 11 can be configured by any other suitable means (e.g., by means of firmware) to perform the method for characterizing the water state in coal and rock using cryogenic low-pressure nitrogen adsorption.

[0109] Various embodiments of the systems and techniques described above herein can be implemented in digital electronic circuit systems, integrated circuit systems, field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), application-specific standard products (ASSPs), systems-on-a-chip (SoCs), payload-programmable logic devices (CPLDs), computer hardware, firmware, software, and / or combinations thereof. These various embodiments may include implementations in one or more computer programs that can be executed and / or interpreted on a programmable system including at least one programmable processor, which may be a dedicated or general-purpose programmable processor, capable of receiving data and instructions from a storage system, at least one input device, and at least one output device, and transmitting data and instructions to the storage system, the at least one input device, and the at least one output device.

[0110] Computer programs used to implement the methods of this application may be written in any combination of one or more programming languages. These computer programs may be provided to the processor of a general-purpose computer, a special-purpose computer, or other programmable target-determining device, such that when executed by the processor, the computer programs cause the functions / operations specified in the flowcharts and / or block diagrams to be implemented. The computer programs may be executed entirely on a machine, partially on a machine, or as a standalone software package, partially on a machine and partially on a remote machine, or entirely on a remote machine or server.

[0111] In the context of this application, a computer-readable storage medium can be a tangible medium that may contain or store a computer program for use by or in conjunction with an instruction execution system, apparatus, or device. A computer-readable storage medium can be, but is not limited to, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems, apparatus, or devices, or any suitable combination of the foregoing. Alternatively, a computer-readable storage medium can be a machine-readable signal medium. More specific examples of machine-readable storage media include electrical connections based on one or more wires, portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber, portable compact disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination of the foregoing.

[0112] To provide interaction with a user, the systems and techniques described herein can be implemented on an electronic device having: a display device (e.g., a CRT (cathode ray tube) or LCD (liquid crystal display) monitor) for displaying information to the user; and a keyboard and pointing device (e.g., a mouse or trackball) through which the user provides input to the electronic device. Other types of devices can also be used to provide interaction with the user; for example, feedback provided to the user can be any form of sensory feedback (e.g., visual feedback, auditory feedback, or tactile feedback); and input from the user can be received in any form (including sound input, voice input, or tactile input).

[0113] The systems and technologies described herein can be implemented in computing systems that include backend components (e.g., as data servers), or middleware components (e.g., application servers), or frontend components (e.g., user computers with graphical user interfaces or web browsers through which users can interact with implementations of the systems and technologies described herein), or any combination of such backend, middleware, or frontend components. The components of the system can be interconnected via digital data communication of any form or medium (e.g., communication networks). Examples of communication networks include local area networks (LANs), wide area networks (WANs), blockchain networks, and the Internet.

[0114] A computing system can include clients and servers. Clients and servers are generally located far apart and typically interact through communication networks. The client-server relationship is created by computer programs running on the respective computers and having a client-server relationship with each other. The server can be a cloud server, also known as a cloud computing server or cloud host, which is a hosting product within the cloud computing service system to address the shortcomings of traditional physical hosts and VPS services, such as high management difficulty and weak business scalability.

[0115] It should be understood that the various forms of processes shown above can be used to rearrange, add, or delete steps. For example, the steps described in this application can be executed in parallel, sequentially, or in different orders, as long as the desired information of the technical solution of this application can be achieved, and this is not limited herein.

[0116] The present invention has been illustrated with the above embodiments to illustrate its detailed structural features. However, the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the components used in the present invention, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for characterizing the water occurrence state in coal and rock using low-pressure nitrogen adsorption at freezing temperatures, characterized in that, The method includes: Several sets of parallel samples were cut from the coal and rock samples. Then, a part of the parallel samples were subjected to standard drying treatment to obtain standard samples, and another part of the parallel samples were subjected to different humidity equilibration treatments to obtain samples with different humidity. The standard sample and the samples with different humidity levels were subjected to a first freezing, a second freezing, and a low-pressure nitrogen adsorption experiment in sequence. The pore diameter and pore volume of the standard sample and the samples with different humidity levels were obtained by calculation using the BJH model. For the same pore diameter, the pore volume of samples with different humidity levels was compared with that of the standard sample, and the pore diameter-water volume curves of samples with different humidity levels were plotted.

2. The method according to claim 1, characterized in that, The parallel samples in several groups are obtained by cutting adjacent positions along the bedding direction of the coal and rock samples; Preferably, after cutting, the material is further subjected to crushing, drying, and degassing in sequence; Preferably, the particle size of the parallel samples after crushing is ≤0.25mm; Preferably, the drying temperature is 100℃-120℃; Preferably, the drying time is ≥48 hours; Preferably, the degassing temperature is 100℃-120℃; Preferably, the degassing time is 8h-12h.

3. The method according to claim 1 or 2, characterized in that, The temperature for the standard drying process is 100℃-120℃; Preferably, the standard drying time is ≥120 hours; Preferably, the different humidity balancing treatment includes: placing the pretreated parallel samples in a closed environment of saturated salt water solutions of different concentrations for at least 120 hours, and the parallel samples are not in direct contact with the saturated salt water solutions; Preferably, the salt in the saturated salt solution includes potassium chloride and / or potassium nitrate.

4. The method according to any one of claims 1-3, characterized in that, Before the first freezing, the standard sample and the samples with different humidity levels were placed in glass tubes respectively; Preferably, the first freezing medium is liquid nitrogen; Preferably, the temperature of the first freezing is -190℃ to -200℃; Preferably, the first freezing time is ≥0.5h; Preferably, the temperature of the second freezing is -10℃ to 0℃; Preferably, the second freezing time is ≥24h.

5. The method according to any one of claims 1-4, characterized in that, During the low-pressure nitrogen adsorption experiment, when the Dewar flask is not raised, a heat-insulating component is wrapped around the outer surface of the glass tube. Preferably, the relative pressure of the low-pressure nitrogen adsorption experiment is 0-0.995; Preferably, the method for calculating the pore diameter includes: substituting the nitrogen adsorption equilibrium pressure into the Kelvin equation to calculate the Kelvin radius; calculating the adsorption layer thickness corresponding to the nitrogen adsorption equilibrium pressure according to the Halsey empirical film thickness formula; and calculating the pore diameter based on the Kelvin radius and the adsorption layer thickness. Preferably, the formula for calculating the Kelvin radius is as shown in equation (1): （1） In formula (1): Kelvin radius; The surface tension of liquid condensates; The molar volume of the liquid condensate; R is the ideal gas constant; For temperature analysis; This is the adsorption equilibrium pressure of nitrogen. This is the saturated vapor pressure of nitrogen at liquid nitrogen temperature; Preferably, the formula for calculating the thickness of the adsorption layer is as shown in equation (2): （2） In formula (2): The average thickness of the monomolecular adsorption layer is 0.43 nm when the adsorbate is nitrogen. Preferably, the formula for calculating the pore diameter is as shown in equation (3): （3） In formula (3): The diameter of the cylindrical hole; The thickness is the adsorption layer.

6. The method according to any one of claims 1-5, characterized in that, The pore volume is calculated according to the BJH model, and the calculation formula is shown in equation (4) below: （4） In equation (4): Pore ​​volume; This is the volume correction factor; The volume of gas desorbed when the pressure decreases, expressed as liquid volume; This represents the change in the thickness of the adsorbed layer as the pressure decreases. This is the ratio of the average capillary tube radius to the average pore diameter of the desorption pores during the pressure drop process. It represents the surface area of ​​the pores.

7. The method according to any one of claims 1-6, characterized in that, The pore diameter-water volume curves of the samples with different humidity levels are used to characterize the water occurrence characteristics in the pores of coal and rock.

8. A device for characterizing the water occurrence state in coal and rock using refrigerated low-pressure nitrogen adsorption, characterized in that, The device includes: The standard sample and sample preparation module for different humidity levels is used to cut several sets of parallel samples from coal and rock samples, then perform standard drying treatment on a portion of the parallel samples to obtain standard samples, and perform different humidity equilibration treatment on another portion of the parallel samples to obtain samples with different humidity levels. The pore diameter and pore volume determination module is used to perform a first freezing, a second freezing, and a low-pressure nitrogen adsorption experiment on the standard sample and the samples with different humidity levels in sequence, and calculate the pore diameter and pore volume of the standard sample and the samples with different humidity levels by combining the BJH model. The pore diameter-water volume plotting module is used to calculate the difference between the pore volume of samples with different humidity levels and a standard sample under the same pore diameter, and plot the pore diameter-water volume curve for samples with different humidity levels.

9. An electronic device, characterized in that, The electronic device includes: At least one processor; and A memory communicatively connected to the at least one processor; wherein, The memory stores a computer program that can be executed by the at least one processor, the computer program being executed by the at least one processor to enable the at least one processor to perform the method for characterizing the water occurrence state in coal and rock using the adsorption of frozen low-pressure nitrogen as described in any one of claims 1-7.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores computer instructions that cause a processor to execute the method for characterizing the water occurrence state in coal and rock using the adsorption of frozen low-pressure nitrogen as described in any one of claims 1-7.

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