An evaluation model acquisition method for coal rock gas adsorption ionization ratio by acoustic wave nuclear magnetic joint measurement

Abstract

The application provides a coal rock gas adsorption and dissociation ratio evaluation model acquisition method based on acoustic wave and nuclear magnetic resonance, and relates to the technical field of coal rock evaluation methods. In the coal rock gas adsorption and dissociation ratio evaluation model acquisition method based on acoustic wave and nuclear magnetic resonance, the adsorption and dissociation ratio of nuclear magnetic method can be acquired based on the nuclear magnetic signal fed back by a coal rock sample, the sensitivity parameter corresponding to the acoustic wave response of the reaction can be calculated based on the acoustic wave signal fed back by the coal rock sample, and then the power relationship equation can be established based on the sensitivity parameter and the adsorption and dissociation ratio of the nuclear magnetic method, so as to acquire the evaluation model for evaluating the adsorption and dissociation ratio of the coal rock. The coal rock gas adsorption and dissociation ratio evaluation model acquisition method based on acoustic wave and nuclear magnetic resonance can accurately and efficiently complete the evaluation of the adsorption and dissociation ratio of the adsorptive gas and the free gas in the coal rock, and improves the technical problems of high evaluation difficulty and high cost of the coal rock gas in the prior art.

Description

Technical Field

[0001] This invention relates to the technical field of coal and rock evaluation methods, and more specifically, to a method for obtaining an evaluation model of the adsorption-to-free ratio of coal and rock gas measured by acoustic nuclear magnetic resonance. Background Technology

[0002] As a new type of unconventional natural gas resource, coal shale gas has moved from the early theoretical exploration stage to the stage of large-scale exploration and development, but it still faces many technical and management challenges.

[0003] In the existing technology, the detection of free gas and adsorbed gas in coal and rock remains quite difficult, especially the content of free gas is difficult to quantify accurately, which makes the overall evaluation of coal and rock gas difficult and costly. Summary of the Invention

[0004] The technical problem solved by this invention is how to improve the high difficulty and high cost of coal and shale gas evaluation in the prior art.

[0005] The embodiments of the present invention can be implemented as follows:

[0006] This invention provides a method for obtaining an evaluation model of the adsorption-to-free ratio of coal rock gas using acoustic-nuclear magnetic resonance (AMR) measurement, applied to an AMR-NMR measurement device. The AMR-NMR measurement device includes a gas source, a metering pump, and an AMR-NMR measurement module. The gas source includes a first container for adsorbed gas and a second container for non-adsorbed gas. The AMR-NMR measurement module includes a reference container, a sample container, an acoustic module, and a nuclear magnetic resonance (NMR) module. The reference container and the sample container are connected by a pipeline equipped with a diffusion valve. The metering pump is connected between the gas source and the AMR-NMR measurement module, used to receive gas introduced from the gas source and to introduce the gas into the reference container. The acoustic module emits acoustic waves into the coal rock sample inside the sample container and collects the acoustic wave information reflected from the coal rock sample, including longitudinal wave information and transverse wave information. The NMR module excites NMR signals into the coal rock sample inside the sample container and receives the NMR signals fed back from the coal rock sample to obtain the NMR T2 spectrum.

[0007] The method for obtaining the evaluation model of adsorbed and free ions ratio in coal rock gas by acoustic nuclear magnetic resonance spectroscopy includes:

[0008] Non-adsorbent gas is filled into the interconnected metering pump, the reference container, and the sample container, and the container is kept under a preset temperature and pressure condition. The acoustic wave base signal and nuclear magnetic resonance base signal fed back by the coal and rock sample are measured.

[0009] Multiple adsorbed or non-adsorbed gases at different preset pressures are introduced into the reference container via the metering pump. After the adsorbed or non-adsorbed gases naturally diffuse from the reference container into the sample container and reach equilibrium, the first acoustic signal, the second acoustic signal, the first NMR T2 spectrum, and the second NMR T2 spectrum fed back by the coal and rock sample are measured. The first acoustic signal and the first NMR T2 spectrum correspond to the signals fed back by the coal and rock sample when the adsorbed gas is introduced, and the second acoustic signal and the second NMR T2 spectrum correspond to the signals fed back by the coal and rock sample when the non-adsorbed gas is introduced.

[0010] The NMR adsorption-free ratio is calculated based on the NMR substrate signal and the first and second NMR T2 spectra measured under the same preset pressure, resulting in multiple NMR adsorption-free ratio values.

[0011] Based on the acoustic wave base signal and the first and second acoustic wave signals measured under the same preset pressure, the adsorbed gas sensitivity and free gas sensitivity are calculated respectively, resulting in multiple adsorbed gas sensitivity parameters and multiple free gas sensitivity parameters.

[0012] Based on the multiple NMR adsorption-to-free ratios, multiple adsorbed gas sensitivity parameters, and multiple free gas sensitivity parameters, a power-law equation is fitted, and multiple coefficients that make the power-law equation hold true are obtained.

[0013] An evaluation model for assessing the adsorption of free gas in coal and rock is established based on multiple coefficients and the power relationship equation.

[0014] Optionally, the step of introducing multiple adsorbed or non-adsorbed gases at different preset pressures into the reference container via the metering pump, allowing the adsorbed or non-adsorbed gases to diffuse naturally from the reference container into the sample container and reach equilibrium, and then measuring the first acoustic signal, second acoustic signal, first NMR T2 spectrum, and second NMR T2 spectrum fed back by the coal and rock sample, includes:

[0015] Evacuate the metering pump, the reference container, and the sample container;

[0016] Close the diffusion valve;

[0017] The metering pump fills the reference container with an adsorbent or non-adsorbent gas at a preset pressure.

[0018] Open the diffusion valve to allow the adsorbed or non-adsorbed gas to diffuse naturally until the internal gas pressure of the reference container and the sample container is balanced.

[0019] Sound waves are emitted and nuclear magnetic resonance is excited towards the coal and rock sample;

[0020] The first acoustic signal, the second acoustic signal, the first NMR T2 spectrum, and the second NMR T2 spectrum fed back from the coal and rock sample were measured.

[0021] Repeat the above steps until multiple first acoustic signals, second acoustic signals, first NMR T2 spectra, and second NMR T2 spectra are measured.

[0022] Optionally, in the process of repeating the above steps until multiple first acoustic signals, second acoustic signals, first NMR T2 spectra and second NMR T2 spectra are measured, the preset pressure is increased successively by a preset increase value.

[0023] Optionally, the step of calculating the NMR adsorption-free ratio based on the NMR substrate signal and the first and second NMR T2 spectra measured under the same preset pressure, to obtain multiple NMR adsorption-free ratio values, includes:

[0024] Based on the NMR substrate signal, the characteristic peaks of the corresponding adsorbed gas in the first NMR T2 spectrum, the characteristic peaks of the corresponding non-adsorbed gas in the second NMR T2 spectrum, and a preset cutoff value, the area values ​​of the free gas peaks and the adsorbed gas peaks are calculated sequentially to obtain multiple adsorbed gas peak area values ​​and multiple free gas peak area values; wherein, the preset cutoff value represents the cutoff value in the NMR spectrum for dividing free peaks and adsorbed peaks;

[0025] The NMR adsorption-free ratio value at the corresponding pressure is obtained based on the ratio of the free gas peak area value to the adsorbed gas peak area value; multiple NMR adsorption-free ratio values ​​are obtained.

[0026] Optionally, the formula for calculating the peak area of ​​the adsorbed gas based on the NMR substrate signal, the characteristic peak of the corresponding adsorbed gas in the first NMR T2 spectrum, and the preset cutoff value is as follows:

[0027] ;

[0028] Among them, A AG T represents the area of ​​the adsorbed gas peak. 2，cutoff A0 represents the preset cutoff value, and A0 represents the T2 spectrum intensity characterized by the NMR substrate signal.

[0029] The formula for calculating the free gas peak area value based on the NMR substrate signal, the characteristic peaks of the corresponding non-adsorbed gas in the second NMR T2 spectrum, and the preset cutoff value is as follows:

[0030] ;

[0031] Among them, A AF This represents the area of ​​the free gas peak.

[0032] Optionally, the step of calculating the adsorbed gas sensitivity and free gas sensitivity based on the acoustic wave substrate signal and the first and second acoustic wave signals measured under the same preset pressure, to obtain multiple adsorbed gas sensitivity parameters and multiple free gas sensitivity parameters, includes:

[0033] The Poisson's ratio, bulk modulus, and longitudinal impedance of the substrate are calculated based on the transverse and longitudinal wave signals in the acoustic substrate signal.

[0034] Based on the transverse wave signal and longitudinal wave signal in the multiple first acoustic wave signals, calculate the corresponding multiple first longitudinal wave impedance values ​​and multiple first bulk modulus values ​​respectively;

[0035] Based on the transverse wave signal and longitudinal wave signal in the multiple second acoustic signals, calculate the corresponding multiple second longitudinal wave impedance values, multiple Poisson ratio values ​​and multiple second bulk modulus values ​​respectively;

[0036] Based on the first longitudinal wave impedance value, the second longitudinal wave impedance value, the second bulk modulus value, and the first bulk modulus value under each preset pressure, a plurality of longitudinal wave impedance sensitivity parameters and first bulk modulus sensitivity parameters corresponding to the adsorbent gas are calculated.

[0037] Based on the substrate Poisson's ratio value, the substrate bulk modulus value, and the Poisson's ratio value and the second bulk modulus value under each preset pressure, a plurality of corresponding non-adsorbent gas Poisson's ratio sensitivity parameters and second bulk modulus sensitivity parameters are calculated.

[0038] A quantitative formula for the adsorbed gas sensitivity parameters is obtained by fitting multiple longitudinal wave impedance sensitivity parameters and multiple first bulk modulus sensitivity parameters.

[0039] The quantification formula for the free gas sensitivity parameter is obtained by fitting multiple Poisson's ratio sensitivity parameters and multiple second bulk modulus sensitivity parameters.

[0040] Optionally, the formulas for calculating the longitudinal wave impedance sensitivity parameters and the first bulk modulus sensitivity parameters of multiple corresponding adsorbent gases based on the first longitudinal wave impedance value, the second longitudinal wave impedance value, the second bulk modulus value, and the first bulk modulus value under each preset pressure are as follows:

[0041] ;

[0042] Where S1 represents the longitudinal wave impedance sensitivity parameter or the first bulk modulus sensitivity parameter, M i_AG M represents the first longitudinal wave impedance value or the first bulk modulus value corresponding to the preset pressure. sat_AGM represents the first longitudinal wave impedance value or the first bulk modulus value corresponding to the maximum preset pressure. i_AF M represents the second longitudinal wave impedance value or the second bulk modulus value corresponding to the preset pressure. sat_AF The second longitudinal wave impedance value or the second bulk modulus value corresponding to the maximum preset pressure;

[0043] The formulas for calculating the Poisson's ratio sensitivity parameter and the second bulk modulus sensitivity parameter for multiple corresponding non-adsorbent gases based on the substrate Poisson's ratio value, the substrate bulk modulus value, and the Poisson's ratio value and the second bulk modulus value at each preset pressure are as follows:

[0044] ;

[0045] Where S2 represents the Poisson's ratio sensitivity parameter or the second bulk modulus sensitivity parameter, M i_AF M represents the Poisson's ratio or the second bulk modulus value corresponding to the preset pressure. sat_AF M represents the Poisson's ratio or second bulk modulus value corresponding to the maximum preset pressure. 0_AF This indicates the Poisson's ratio or bulk modulus of the substrate.

[0046] Optionally, the quantification formula for the adsorbed gas sensitivity parameter is obtained by fitting the longitudinal wave impedance sensitivity parameter and the first bulk modulus sensitivity parameter as follows:

[0047] ,

[0048] Where I1 represents the adsorption gas sensitivity parameter, S zp S represents the longitudinal wave impedance sensitivity parameter. k1 The first bulk modulus sensitivity parameter is represented by a and b, where a and b are two of the plurality of coefficients.

[0049] The quantification formula for the free gas sensitivity parameter, obtained by fitting the Poisson's ratio sensitivity parameter and the second bulk modulus sensitivity parameter, is as follows:

[0050] ,

[0051] Where I2 represents the free gas sensitivity parameter, S v S represents the Poisson's ratio sensitivity parameter. k2 The second bulk modulus sensitivity parameter is represented by m and n, which represent the other two coefficients.

[0052] Optionally, the following equation is fitted based on the multiple NMR adsorption-to-free ratios, the multiple adsorbed gas sensitivity parameters, and the multiple free gas sensitivity parameters:

[0053] ;

[0054] Where K represents the NMR adsorption-to-free ratio, and a, b, m, n, α, β, and γ represent multiple coefficients obtained through fitting that make the above equations true.

[0055] Optionally, an evaluation model for assessing the adsorption of free gas in coal and rock is established based on multiple coefficients and the power-law equation as follows:

[0056] ;

[0057] Where K0 represents the adsorbed-to-free ratio to be calculated.

[0058] The advantages of the method for obtaining the evaluation model of adsorption-to-free ratio of coal rock gas by acoustic nuclear magnetic resonance spectroscopy provided by this invention compared with the prior art include:

[0059] In this method for obtaining the evaluation model of adsorption-to-free gas ratio in coal and rock samples using acoustic-nuclear magnetic resonance (NMR) measurement, the method involves filling the coal and rock sample with free or adsorbed gas at a specified pressure. Once the gas pressure within the space containing the coal and rock sample reaches equilibrium, it indicates that the gas adsorption within the pores of the coal and rock sample has reached equilibrium. During this equilibrium stage, the adsorption status of adsorbed and free gas is accurately obtained by detecting the NMR T2 spectrum, allowing for precise calculation of the adsorption-to-free gas ratio at the corresponding pressure. Simultaneously, acoustic waves are emitted from the coal and rock sample. Based on the attenuation of the transverse and longitudinal wave signals in the acoustic signal returned by the coal and rock sample, the elastic sensitivity parameter based on the acoustic signal can be calculated. Finally, a physical correlation can be established between the elastic sensitivity and the adsorption-to-free gas ratio to form a power-law equation relating the adsorption-to-free gas ratio and the acoustic signal, thus forming the evaluation model. In the subsequent evaluation of the adsorption-to-free ratio, the adsorption-to-free ratio of adsorbed and free gases in the coal can be directly and efficiently determined by taking the acoustic signal fed back by the coal to be evaluated and based on the above evaluation model. The required data collection is simple and the evaluation accuracy is high, which can improve the technical problems of high difficulty and high cost in coal gas evaluation in the existing technology. Attached Figure Description

[0060] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0061] Figure 1 This is a schematic diagram of the acoustic-nuclear magnetic resonance imaging (NMR) device provided in the embodiments of this application;

[0062] Figure 2 This is a flowchart of the preparatory steps before obtaining the evaluation model for the adsorption-to-free ratio of coal rock gas provided in the embodiments of this application;

[0063] Figure 3 This is a flowchart of the method for obtaining the evaluation model of adsorption-to-free ratio of coal rock gas by acoustic nuclear magnetic resonance spectroscopy provided in the embodiments of this application;

[0064] Figure 4 This is a flowchart of step S20 in the method for obtaining the evaluation model of adsorption-free ratio of coal rock gas by acoustic nuclear magnetic resonance spectroscopy provided in the embodiments of this application.

[0065] Figure 5 This is a flowchart of step S30 in the method for obtaining the evaluation model of adsorption-free ratio of coal rock gas by acoustic nuclear magnetic resonance spectroscopy provided in the embodiments of this application.

[0066] Figure 6 This is a flowchart of step S40 in the method for obtaining the evaluation model of adsorption-free ratio of coal rock gas by acoustic nuclear magnetic resonance spectroscopy provided in the embodiments of this application.

[0067] Icons: Acoustic-NMR co-measurement device 10, gas source 100, first container 110, second container 120, metering pump 200, acoustic-NMR co-measurement module 300, reference container 310, diffusion valve 311, sample container 320, acoustic module 330, NMR module 340. Detailed Implementation

[0068] 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, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0069] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0070] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0071] In the description of this invention, it should be noted that if terms such as "upper," "lower," "inner," or "outer" are used to indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of this invention is usually placed, they are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0072] Furthermore, the terms "first" and "second" are used only to distinguish descriptions and should not be interpreted as indicating or implying relative importance.

[0073] It should be noted that, where there is no conflict, the features in the embodiments of the present invention can be combined with each other.

[0074] This embodiment provides a method for obtaining an evaluation model for the adsorption-to-free ratio of coal and rock gas using acoustic nuclear magnetic resonance (NMR) measurement. This method can obtain an evaluation model for assessing the adsorption-to-free ratio of adsorbed and free gases in coal and rock. In other words, this evaluation model can be used to quickly and accurately calculate the adsorption-to-free ratio of adsorbed and free gases in coal and rock, thereby achieving a simple and efficient evaluation of the distribution of adsorbed and free gases in coal and rock, and improving the technical problems of high difficulty and high cost in coal and rock gas evaluation in existing technologies.

[0075] It should be noted that this acquisition method can be applied to the acoustic-nuclear magnetic resonance imaging (NMR) device 10. In other words, the acoustic-nuclear magnetic resonance imaging (NMR) device 10 can be used to execute the above method to obtain the corresponding data parameters, thereby assisting in the acquisition of the evaluation model.

[0076] In this embodiment, please refer to the following: Figure 1The acoustic-nuclear magnetic resonance (AMMR) co-detection device 10 includes a gas source 100, a metering pump 200, and an AMMR co-detection module 300. The gas source 100 includes a first container 110 for containing adsorbed gases and a second container 120 for containing non-adsorbed gases, wherein the non-adsorbed gases are free gases. The AMMR co-detection module 300 includes a reference container 310, a sample container 320, an acoustic module 330, and a nuclear magnetic resonance (NMR) module 340. The reference container 310 and the sample container 320 are connected by a pipeline, and a diffusion valve 311 is installed on the pipeline. The metering pump 200 is connected between the gas source 100 and the AMMR co-detection module 300. The metering pump 200 receives the gas introduced by the gas source 100 and introduces the gas into the reference container 310. The acoustic module 330 emits acoustic waves into the coal and rock sample inside the sample container 320 and collects the acoustic wave information reflected from the coal and rock sample, including longitudinal wave information and transverse wave information. The NMR module 340 is used to excite NMR signals to the coal and rock sample in the sample container 320 and receive the NMR signals fed back by the coal and rock sample to obtain the NMR T2 spectrum.

[0077] In this embodiment, CH4 is used as the adsorbent gas, and He is used as the non-adsorbent gas. Of course, in other embodiments, other types of gases can be used for both the adsorbent and non-adsorbent gases, which will not be elaborated here.

[0078] Of course, the acoustic-nuclear magnetic resonance imaging device 10 may also include a confining pressure-temperature control device, a clamp, a magnet box, a data transmission line, a data acquisition system, a pressure relief valve, a gas recovery pipeline, and other equipment. The use and installation of these devices are existing technologies and will not be described in detail here.

[0079] Before implementing the method for obtaining the evaluation model of adsorption-free ratio of coal and rock gas by acoustic nuclear magnetic resonance spectroscopy provided in this embodiment, some preparatory steps are required. Of course, in some embodiments, these preparatory steps can also be incorporated into the method for obtaining the evaluation model of adsorption-free ratio of coal and rock gas by acoustic nuclear magnetic resonance spectroscopy alone.

[0080] Please refer to Figure 2 The preparation steps include:

[0081] S1, Rock sample preparation.

[0082] Coal and rock samples are obtained by drilling a plunger, and the end face is cut and ground flat. After cleaning, the coal and rock samples are placed in a constant temperature oven to dry to constant weight. The temperature inside the constant temperature oven can be controlled at 100℃.

[0083] After the coal and rock samples are dried to constant weight, their basic parameters are measured. For example, the mass m of the coal and rock sample is measured. sample Furthermore, the volume V of the coal sample was obtained by placing the coal sample in a liquid of known density and observing the volume change of the coal sample immersed in the liquid.m The density ρ of the coal and rock sample is obtained by calculating its mass and volume.

[0084] S2. Load the sample and perform an airtightness test on the reference container 310 and the sample container 320.

[0085] The coal and rock sample is loaded into the sample container 320, ensuring good contact with the acoustic transducer in the acoustic module 330. A low initial confining pressure (e.g., 2 MPa) is applied using a clamp to fix the sample. After fixing the sample, the entire system (gas source 100, metering pump 200, reference container 310, sample container 320, and corresponding pipelines, etc.) is tested for air tightness using a staged pressurization valve air tightness test method.

[0086] After completing the above preparation steps, the method for obtaining the evaluation model of coal rock gas adsorption-free ratio by acoustic nuclear magnetic resonance measurement in this embodiment can be executed.

[0087] Please refer to Figure 3 The methods for obtaining the evaluation model of adsorption-to-free ratio in coal rock gas by acoustic nuclear magnetic resonance spectroscopy include:

[0088] S10. Non-adsorbent gas is introduced into the interconnected metering pump 200, reference container 310 and sample container 320, and the gas is kept under a preset temperature and pressure condition. The acoustic wave base signal and nuclear magnetic resonance base signal fed back by the coal and rock sample are measured.

[0089] It should be noted that before measuring the base signal, the entire system consisting of metering pump 200, reference container 310, and sample container 320 needs to be evacuated. After evacuation, a non-adsorbent gas, such as He, is introduced into the system to bring the temperature inside sample container 320 to 40°C, the confining pressure to 22 MPa, and the pore pressure of the coal sample to 20 MPa. After the temperature and pore pressure stabilize, the acoustic velocity and attenuation of the coal sample are measured and recorded as the acoustic background value of the coal sample under stress; simultaneously, the nuclear magnetic resonance T2 spectrum is scanned to obtain the nuclear magnetic base signal A0 of the coal sample.

[0090] After acquiring the substrate signal, an experiment was conducted to separate the adsorbed gas from the non-adsorbed gas. In other words, the experiment was carried out by separately filling the substrate with the adsorbed gas and the non-adsorbed gas.

[0091] S20. Multiple adsorbed or non-adsorbed gases with different preset pressures are introduced into the reference container 310 through the metering pump 200. After the adsorbed or non-adsorbed gases naturally diffuse from the reference container 310 into the sample container 320 and reach equilibrium, the first acoustic signal, the second acoustic signal, the first NMR T2 spectrum, and the second NMR T2 spectrum fed back by the coal and rock sample are measured.

[0092] The first acoustic signal and the first NMR T2 spectrum correspond to the signals fed back by the coal and rock samples when the adsorbent gas is introduced, while the second acoustic signal and the second NMR T2 spectrum correspond to the signals fed back by the coal and rock samples when the non-adsorbent gas is introduced.

[0093] It is worth noting that step S20 refers to obtaining multiple first acoustic signals, multiple second acoustic signals, multiple first NMR T2 spectra, and multiple second NMR T2 spectra by repeatedly filling the gas. Specifically, for example, firstly, gas at 2 MPa is introduced into the reference container 310 via metering pump 200. After free diffusion to pressure equilibrium, sound waves are emitted and nuclear magnetic resonance (NMR) is excited to obtain the first sound wave signal, the second sound wave signal, the first NMR T2 spectrum, and the second NMR T2 spectrum corresponding to that pressure. Then, after evacuation, gas at 4 MPa is introduced into the reference container 310 again via metering pump 200. After free diffusion to pressure equilibrium, sound waves are emitted and NMR is excited to obtain the first sound wave signal, the second sound wave signal, the first NMR T2 spectrum, and the second NMR T2 spectrum corresponding to that pressure. This process is repeated until the acquisition of the first sound wave signal, the second sound wave signal, the first NMR T2 spectrum, and the second NMR T2 spectrum corresponding to multiple preset pressures is completed, resulting in multiple first sound wave signals, multiple second sound wave signals, multiple first NMR T2 spectra, and multiple second NMR T2 spectra.

[0094] It should be noted that in step S20, while the metering pump 200 is filling the reference container 310 with gas at a specified pressure, the diffusion valve 311 is closed to prevent the gas from diffusing into the sample container 320 prematurely. After the gas pressure inside the reference container 310 reaches the specified pressure, the diffusion valve 311 is opened until the gas pressure inside the reference container 310 and the sample container 320 reaches equilibrium, and then the sound wave is emitted and the nuclear magnetic resonance is excited.

[0095] In addition, in step S20, after acquiring the data on sound velocity and attenuation and the NMR data under the first specified pressure, it is necessary to first evacuate the reference container 310 and the sample container 320, and then fill the reference container 310 with a gas at another specified pressure.

[0096] For details, please refer to Figure 4 Step S20 may include:

[0097] S21. Evacuate the metering pump 200, reference container 310 and sample container 320.

[0098] S22, Close diffusion valve 311.

[0099] The purpose of closing the diffusion valve 311 is to prevent gas from diffusing into the sample container 320 before the gas pressure inside the reference container 310 reaches the preset pressure, thus ensuring that the gas is quantitatively filled.

[0100] S23. The reference container 310 is filled with an adsorbent gas or a non-adsorbent gas at a preset pressure through the metering pump 200.

[0101] It is worth noting that in step S20, a separation experiment of adsorbed gas and non-adsorbed gas is used, that is, the experiments for adsorbed gas and non-adsorbed gas are performed separately. Specifically, adsorbed gas is first introduced into reference container 310 to measure and obtain the first acoustic signal and the first NMR T2 spectrum corresponding to the adsorbed gas; after completing the experiment of adsorbed gas, non-adsorbed gas is then introduced into reference container 310 to measure and obtain the second acoustic signal and the second NMR T2 spectrum corresponding to the non-adsorbed gas.

[0102] S24. Open the diffusion valve 311 to allow the adsorbed or non-adsorbed gas to diffuse naturally until the internal gas pressure of the reference container 310 and the sample container 320 is balanced.

[0103] S25. Emit sound waves and excite nuclear magnetic resonance to the coal and rock samples.

[0104] S26. The first acoustic signal, the second acoustic signal, the first NMR T2 spectrum, and the second NMR T2 spectrum were measured from the coal and rock sample.

[0105] S27. Repeat the above steps until multiple first acoustic signals, second acoustic signals, first NMR T2 spectra, and second NMR T2 spectra are measured.

[0106] Step S27 means repeating steps S21-S26 above, and when executing step S21 for the second time, adjusting the preset pressure to be different from the preset pressure in the previous cycle.

[0107] Optionally, in some embodiments of this application, the preset pressure is increased sequentially by a preset increase value. For example, in the first execution of steps S21-S26, the preset pressure is 2 MPa, while in the second execution of steps S21-S26, the preset pressure is 4 MPa, that is, the preset increase pressure is 2 MPa, and so on, with the preset pressure in the third execution being 6 MPa. In some embodiments, the above steps can be performed sequentially with preset pressures of 2 MPa, 4 MPa, 6 MPa, 8 MPa, 10 MPa, 12 MPa, 14 MPa, 16 MPa, 18 MPa, and 20 MPa.

[0108] Step S20 can also be viewed as follows: The following steps are performed sequentially: the reference container 310 and sample container 320 are evacuated; the diffusion valve 311 is closed; an adsorbent or non-adsorbent gas at a specified pressure is introduced into the reference container 310 via the metering pump 200; the diffusion valve 311 is opened to allow the gas to diffuse freely into the sample container 320, until the reference container 310 and sample container 320 reach pressure equilibrium. Pressure equilibrium can be achieved by detecting whether the pressure at the connection point between the reference container 310 and sample container 320 is balanced. If they are balanced, it indicates that the reference container 310 and sample container 320 have reached pressure equilibrium. For example, if the pressure at the outlet of the reference container 310 and the pressure at the inlet of the sample container 320 are consistent, and the pressure change is less than 0.1% of the initial pressure over two consecutive hours, then the adsorption of gas by the coal sample can be considered to have reached dynamic equilibrium, meaning that the gas pressure in the reference container 310 and sample container 320 has reached dynamic equilibrium. After pressure equilibrium is achieved, sound waves can be emitted into the coal and rock sample to excite nuclear magnetic resonance (NMR) signals. After obtaining the corresponding sound wave data and NMR data, the above operation is repeated, that is, vacuuming and gas filling at a specified pressure are performed again until the sound wave data and NMR data of adsorbed and non-adsorbed gases under various pressure environments are collected.

[0109] It is worth noting that after each time the gas pressure in the reference container 310 and the sample container 320 reaches dynamic equilibrium, acoustic data and NMR data can be acquired simultaneously. Of course, in some other embodiments, the acquisition of acoustic data and NMR data can also be performed separately. For example, acoustic waves can be emitted to the coal sample first to obtain the acoustic data fed back by the coal sample; after obtaining the acoustic data, an NMR signal can be excited to obtain NMR data.

[0110] Of course, in this embodiment, the simultaneous acquisition of acoustic and nuclear magnetic resonance signals can significantly improve data acquisition efficiency and reduce the cost of acquiring the evaluation model. Furthermore, since both acoustic and nuclear magnetic resonance data can be acquired simultaneously, while improving efficiency, sufficient time is available to collect more data, thereby increasing the data volume and ultimately improving the accuracy of the evaluation model.

[0111] Furthermore, after acquiring multiple first acoustic signals, multiple second acoustic signals, multiple first NMR T2 spectra, and multiple second NMR T2 spectra, please continue reading. Figure 3 The methods also include:

[0112] S30. Calculate the NMR adsorption-free ratio based on the NMR substrate signal and the first and second NMR T2 spectra measured under the same preset pressure, and obtain multiple NMR adsorption-free ratio values.

[0113] Please refer to Figure 5 Step S30 includes:

[0114] S31. Based on the NMR base signal, the characteristic peaks of the corresponding adsorbed gas in the first NMR T2 spectrum, the characteristic peaks of the corresponding non-adsorbed gas in the second NMR T2 spectrum, and the preset cutoff value, calculate the area values ​​of the free gas peaks and the adsorbed gas peaks to obtain multiple adsorbed gas peak area values ​​and multiple free gas peak area values.

[0115] The preset cutoff value represents the cutoff value for distinguishing between free peaks and adsorption peaks in the NMR spectrum.

[0116] In step S31, the formula for calculating the adsorption gas peak area is as follows:

[0117] ;

[0118] Among them, A AG T represents the area of ​​the adsorbed gas peak. 2，cutoff This represents the preset cutoff value, and A0 represents the T2 spectral intensity characterized by the NMR substrate signal. Of course, T... 2，min This represents the minimum value of the nuclear magnetic resonance intensity in the T2 spectrum; correspondingly, T... 2，max This represents the maximum value of the nuclear magnetic resonance intensity in the T2 spectrum; generally, T 2，cutoff Greater than T 2，min And less than T 2，max .

[0119] In addition, the formula for calculating the area of ​​the free gas peak is as follows:

[0120] ;

[0121] Among them, A AF This represents the area of ​​the free gas peak.

[0122] S32. Obtain the NMR adsorption-free ratio at the corresponding pressure based on the ratio of the corresponding free gas peak area to the adsorbed gas peak area; obtain multiple NMR adsorption-free ratios.

[0123] The formula for calculating the adsorption-to-free ratio by NMR is as follows:

[0124] .

[0125] Please continue reading. Figure 3 The method for obtaining the evaluation model of adsorption-to-free ratio in coal rock gas by acoustic nuclear magnetic resonance also includes:

[0126] S40. Calculate the adsorbed gas sensitivity and free gas sensitivity based on the acoustic wave base signal and the first and second acoustic wave signals measured under the same preset pressure, respectively, to obtain multiple adsorbed gas sensitivity parameters and multiple free gas sensitivity parameters.

[0127] It is worth noting that the acoustic wave measurement values ​​obtained when the adsorption of adsorbed gases in coal and rock samples reaches dynamic equilibrium, minus the acoustic wave measurement values ​​obtained after injecting non-adsorbed gases under the same pressure, can effectively eliminate the influence of pore free gas and confining pressure stress on the acoustic wave response. The resulting net response can be attributed to the adsorption effect of adsorbed gases.

[0128] Additionally, it should be noted that the acoustic signal acquired in step S40 includes longitudinal wave signals and transverse wave signals, including at least the propagation speed of the longitudinal wave and the propagation speed of the transverse wave.

[0129] Please refer to Figure 6 Step S40 includes:

[0130] S41. Calculate the Poisson's ratio, bulk modulus, and longitudinal impedance of the substrate based on the transverse and longitudinal wave signals in the acoustic substrate signal.

[0131] The formula for calculating Poisson's ratio is as follows:

[0132] ;

[0133] Among them, V p V represents the propagation speed of longitudinal waves. s The value represents the propagation speed of the transverse wave, and v represents Poisson's ratio.

[0134] The formula for calculating the bulk modulus is as follows:

[0135] ;

[0136] Among them, K 体积模量This represents the bulk modulus value.

[0137] The formula for calculating the longitudinal wave impedance is as follows:

[0138] ;

[0139] Where Zp represents the longitudinal wave impedance value.

[0140] In step S41, the propagation velocities of the transverse wave in the acoustic substrate signal and the longitudinal wave in the longitudinal wave in the acoustic substrate signal are substituted into the above calculation formula, and the substrate Poisson's ratio, substrate bulk modulus, and substrate longitudinal wave impedance can be calculated.

[0141] S42. Calculate the corresponding first longitudinal wave impedance values ​​and first bulk modulus values ​​based on the transverse wave signal and longitudinal wave signal in the multiple first acoustic wave signals.

[0142] Similarly, when calculating the first longitudinal wave impedance value and the bulk modulus value corresponding to the first acoustic signal, the transverse wave propagation velocity in the transverse wave signal and the longitudinal wave propagation velocity in the longitudinal wave signal in the first acoustic signal are substituted into the corresponding formulas mentioned above, and multiple first longitudinal wave impedance values ​​and multiple first bulk modulus values ​​can be calculated.

[0143] S43. Calculate the corresponding second longitudinal wave impedance values, multiple Poisson ratio values, and multiple second bulk modulus values ​​based on the transverse wave signal and longitudinal wave signal in the multiple second acoustic wave signals.

[0144] Similarly, when calculating the Poisson's ratio and bulk modulus value corresponding to the second acoustic signal, by substituting the transverse wave propagation velocity in the transverse wave signal and the longitudinal wave propagation velocity in the longitudinal wave signal in the second acoustic signal into the corresponding formulas mentioned above, multiple second longitudinal wave impedance values, multiple Poisson's ratio values, and multiple second bulk modulus values ​​can be calculated.

[0145] S44. Based on the first longitudinal wave impedance value, the second longitudinal wave impedance value, the second bulk modulus value, and the first bulk modulus value under each preset pressure, calculate the longitudinal wave impedance sensitivity parameter and the first bulk modulus sensitivity parameter of multiple corresponding adsorbent gases.

[0146] The formulas for calculating the longitudinal wave impedance sensitivity parameters and the first bulk modulus sensitivity parameters of multiple corresponding adsorbed gases based on the first longitudinal wave impedance value, the second longitudinal wave impedance value, the second bulk modulus value, and the first bulk modulus value under various preset pressures are as follows:

[0147] ;

[0148] Where S1 represents the longitudinal wave impedance sensitivity parameter or the first bulk modulus sensitivity parameter, M i_AGM represents the first longitudinal wave impedance value or the first bulk modulus value under the corresponding preset pressure. sat_AG M represents the first longitudinal wave impedance value or the first bulk modulus value corresponding to the maximum preset pressure. i_AF M represents the second longitudinal wave impedance value or the second bulk modulus value corresponding to the preset pressure. sat_AF This represents the second longitudinal wave impedance value or the second bulk modulus value corresponding to the maximum preset pressure. In other words, when calculating the longitudinal wave impedance sensitivity parameter, the first longitudinal wave impedance value at the corresponding pressure is used to replace the aforementioned M. i_AG Instead, the M value mentioned above is replaced by the first longitudinal wave impedance value corresponding to the maximum preset pressure among the multiple first longitudinal wave impedance values ​​that have been obtained. sat_AG The M value mentioned above is replaced with the second longitudinal wave impedance value under the corresponding pressure. i_AF The M value mentioned above is replaced with the second longitudinal wave impedance value corresponding to the maximum preset pressure from among the multiple acquired second longitudinal wave impedance values. sat_AF The longitudinal wave impedance sensitivity parameter can then be calculated. Correspondingly, when calculating the first bulk modulus sensitivity parameter, the first bulk modulus value under the corresponding pressure is used to replace the aforementioned M. i_AG Instead, the first volume modulus value corresponding to the maximum preset pressure among the multiple first volume modulus values ​​obtained is used to replace the aforementioned M. sat_AG The M value mentioned above is replaced with the second bulk modulus value under the corresponding pressure. i_AF The M value mentioned above is replaced with the second bulk modulus value corresponding to the maximum preset pressure from among the multiple acquired second bulk modulus values. sat_AF The first bulk modulus sensitivity parameter can then be calculated.

[0149] S45. Based on the substrate Poisson's ratio, substrate bulk modulus, and Poisson's ratio and second bulk modulus at various preset pressures, calculate the Poisson's ratio sensitivity parameters and second bulk modulus sensitivity parameters for multiple corresponding non-adsorbent gases.

[0150] The formulas for calculating the Poisson's ratio sensitivity parameters and the second bulk modulus sensitivity parameters for multiple corresponding non-adsorbent gases based on the substrate Poisson's ratio, substrate bulk modulus, and Poisson's ratio and second bulk modulus values ​​at various preset pressures are as follows:

[0151] ;

[0152] Where S2 represents the Poisson's ratio sensitivity parameter or the second bulk modulus sensitivity parameter, M i_AF M represents the Poisson's ratio or second bulk modulus value under the corresponding preset pressure. sat_AF M represents the Poisson's ratio or second bulk modulus value corresponding to the maximum preset pressure. 0_AFThis represents the base Poisson's ratio or base bulk modulus. In other words, when calculating the Poisson's ratio sensitivity parameter, the Poisson's ratio at the corresponding pressure is used to replace the aforementioned M. i_AF Instead, the Poisson's ratio corresponding to the maximum preset pressure among the multiple obtained Poisson's ratio values ​​is used to replace the aforementioned M. sat_AF Replace M with the base Poisson's ratio value calculated above. 0_AF The Poisson's ratio sensitivity parameter can then be calculated. Correspondingly, when calculating the second bulk modulus sensitivity parameter, the second bulk modulus value at the corresponding pressure is used to replace the aforementioned M. i_AF Instead, the M value obtained from multiple second volumetric modulus values ​​corresponds to the second volumetric modulus value with the maximum preset pressure and is used to replace the M value mentioned above. sat_AF The matrix bulk modulus value calculated above is used to replace M. 0_AF The second bulk modulus sensitivity parameter can then be calculated.

[0153] S46. Based on the fitting of multiple longitudinal wave impedance sensitivity parameters and multiple first bulk modulus sensitivity parameters, the quantitative formulas of multiple adsorbed gas sensitivity parameters are obtained.

[0154] The quantitative formula for the adsorbed gas sensitivity parameter, obtained by fitting the longitudinal wave impedance sensitivity parameter and the first bulk modulus sensitivity parameter, is as follows:

[0155] ,

[0156] Where I1 represents the adsorption gas sensitivity parameter, S zp S represents the longitudinal wave impedance sensitivity parameter. k1 Let represent the first bulk modulus sensitivity parameter, and a and b are two coefficients for fitting.

[0157] It should be noted that when fitting the formula for I1 in step S46, the coefficients a and b are unknowns, while S... zp and S k1 These are the known values ​​obtained through the above steps. Since the above calculations for each preset pressure yield multiple longitudinal wave impedance sensitivity parameters and multiple first bulk modulus sensitivity parameters, multiple quantization formulas corresponding to I1 can then be fitted and obtained.

[0158] S47. The quantitative formula for the free gas sensitivity parameter is obtained by fitting multiple Poisson's ratio sensitivity parameters and multiple second bulk modulus sensitivity parameters.

[0159] The quantification formula for the free gas sensitivity parameter, obtained by fitting the Poisson's ratio sensitivity parameter and the second bulk modulus sensitivity parameter, is as follows:

[0160] ,

[0161] Where I2 represents the free gas sensitivity parameter, S v S represents the Poisson's ratio sensitivity parameter. k2 This represents the second bulk modulus sensitivity parameter, where m and n are two coefficients used for fitting.

[0162] Similarly, when fitting the formula for I2 in step S47, the coefficients m and n are unknowns, while S... v and S k2 These are the known values ​​obtained through the above steps. Since the above calculations for each preset pressure yield multiple Poisson's ratio sensitivity parameters and multiple second bulk modulus sensitivity parameters, multiple quantization formulas corresponding to I2 can then be fitted and obtained.

[0163] After obtaining the sensitivity parameters of the adsorbed gas and the free gas, the relationship between the adsorption-to-free gas ratio and the acoustic response can be derived based on the NMR adsorption-to-free gas ratio calculated above. That is, please refer to [further details omitted]. Figure 3 The method also includes:

[0164] S50. Fit a power-law equation based on multiple NMR adsorption-to-free ratios, multiple adsorbed gas sensitivity parameters, and multiple free gas sensitivity parameters, and obtain multiple coefficients that make the power-law equation true.

[0165] The following equation is derived by fitting a power relationship based on multiple NMR adsorption-to-free gas ratios, multiple adsorbed gas sensitivity parameters, and multiple free gas sensitivity parameters:

[0166] ;

[0167] Where K represents the ratio of adsorption to free ionization by NMR, and a, b, m, n, α, β and γ represent multiple coefficients obtained by fitting that make the above equation true.

[0168] It is worth noting that in this equation, K, I1, and I2 are the values ​​and quantification formulas obtained under various preset pressures. In other words, when the preset pressure is 2 MPa, the K value is the NMR adsorption-free ratio calculated at the preset pressure of 2 MPa, while I1 and I2 are the quantification formulas calculated based on the first and second acoustic signals at the preset pressure of 2 MPa. Therefore, under various preset pressure settings, multiple power-law equations can be obtained. By fitting these multiple power-law equations, the specific values ​​of a, b, m, n, α, β, and γ that make these multiple power-law equations true can be obtained.

[0169] Specifically, making the aforementioned power relationship equation hold can be seen as substituting the determined K value, Poisson's ratio sensitivity parameter, longitudinal wave impedance sensitivity parameter, first bulk modulus sensitivity parameter, and second bulk modulus sensitivity parameter into a multidimensional coordinate system to form a coordinate point. The multiple coordinate points corresponding to multiple power relationship equations form a linear function, and the aforementioned a, b, m, n, α, β, and γ are multiple coefficients of the multiple coordinate points converging to this function. Thus, the definite values ​​of multiple coefficients a, b, m, n, α, β, and γ can be obtained in reverse.

[0170] S60. An evaluation model for assessing the adsorption of free gas in coal and rock is established based on multiple coefficients and power-law equations.

[0171] In this embodiment, an evaluation model for assessing the adsorption of free gas in coal and rock is established based on multiple coefficients and power-law equations as follows:

[0172] ;

[0173] Where K0 represents the adsorbed-to-free ratio to be calculated.

[0174] In other words, after determining the values ​​of the coefficients a, b, m, n, α, β, and γ in step S50, these coefficients are substituted into the above equation to form the adsorption-to-free ratio K0 and the transverse wave propagation velocity V to be calculated. s and longitudinal wave propagation speed V p The function is used to form an evaluation model. When evaluating the adsorption-to-free ratio of adsorbed and free gases in coal and rock, it is only necessary to emit sound waves to the target coal and rock, obtain the sound wave signal fed back by the target coal and rock, and substitute the longitudinal wave propagation velocity and transverse wave propagation velocity contained in the obtained sound wave signal into the above function to calculate the adsorption-to-free ratio of the target coal and rock, so as to accurately and quickly complete the evaluation of the adsorption-to-free ratio of the coal and rock.

[0175] In summary, this method for obtaining the evaluation model of adsorption-to-free gas ratio in coal and rock samples using acoustic-nuclear magnetic resonance (NMR) measurement is based on the introduction of free or adsorbed gas into the coal and rock sample at a specified pressure. Once the gas pressure within the space containing the coal and rock sample reaches equilibrium, it indicates that the gas adsorption within the pores of the coal and rock sample has reached equilibrium. During this equilibrium stage, the adsorption status of adsorbed and free gas can be accurately obtained by detecting the NMR T2 spectrum, thus allowing for precise calculation of the adsorption-to-free gas ratio at the corresponding pressure. Simultaneously, acoustic waves are emitted from the coal and rock sample. Based on the attenuation of the transverse and longitudinal wave signals in the acoustic signal returned by the coal and rock sample, the elastic sensitivity parameter based on the acoustic signal can be calculated. Finally, a physical correlation can be established between the elastic sensitivity and the adsorption-to-free gas ratio to form a power-law equation relating the adsorption-to-free gas ratio and the acoustic signal, thereby forming the evaluation model. In the subsequent evaluation of the adsorption-to-free ratio, the adsorption-to-free ratio of adsorbed and free gases in the coal can be directly and efficiently determined by taking the acoustic signal fed back by the coal to be evaluated and based on the above evaluation model. The required data collection is simple and the evaluation accuracy is high, which can improve the technical problems of high difficulty and high cost in coal gas evaluation in the existing technology.

[0176] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for obtaining an evaluation model for the adsorption-to-free ratio of coal rock gas measured by acoustic nuclear magnetic resonance, characterized in that, An acoustic-nuclear magnetic resonance (NMR) co-measurement device (10) is applied, comprising a gas source (100), a metering pump (200), and an acoustic-nuclear magnetic resonance (NMR) co-measurement module (300). The gas source (100) includes a first container (110) for containing adsorbed gases and a second container (120) for containing non-adsorbed gases. The acoustic-nuclear magnetic resonance (NMR) co-measurement module (300) includes a reference container (310), a sample container (320), an acoustic module (330), and a nuclear magnetic resonance (NMR) module (340). The reference container (310) and the sample container (320) are connected by a pipeline, and a diffusion valve (311) is provided on the pipeline. A metering pump (200) is connected between the gas source (100) and the acoustic-nuclear magnetic resonance (NMR) co-measurement module (300). The metering pump (200) is used to receive the gas introduced by the gas source (100) and to introduce the gas into the reference container (310). The acoustic module (330) is used to emit acoustic waves into the coal and rock sample inside the sample container (320) and to collect the acoustic wave information reflected by the coal and rock sample. The acoustic wave information includes longitudinal wave information and transverse wave information. The NMR module (340) is used to excite NMR signals into the coal and rock sample inside the sample container (320) and to receive the NMR signals fed back by the coal and rock sample to obtain the NMR T2 spectrum. The method for obtaining the evaluation model of adsorbed and free ions ratio in coal rock gas by acoustic nuclear magnetic resonance spectroscopy includes: Non-adsorbent gas is filled into the interconnected metering pump (200), the reference container (310), and the sample container (320), and the sample is kept under a preset temperature and pressure condition. The acoustic wave base signal and nuclear magnetic resonance base signal fed back by the coal and rock sample are measured. Multiple adsorbent or non-adsorbent gases at different preset pressures are introduced into the reference container (310) via the metering pump (200). After the adsorbent or non-adsorbent gases naturally diffuse from the reference container (310) into the sample container (320) and reach equilibrium, the first acoustic signal, the second acoustic signal, the first NMR T2 spectrum, and the second NMR T2 spectrum fed back by the coal and rock sample are measured. The first acoustic signal and the first NMR T2 spectrum correspond to the signals fed back by the coal and rock sample when the adsorbent gas is introduced, and the second acoustic signal and the second NMR T2 spectrum correspond to the signals fed back by the coal and rock sample when the non-adsorbent gas is introduced. The NMR adsorption-free ratio is calculated based on the NMR substrate signal and the first and second NMR T2 spectra measured under the same preset pressure, resulting in multiple NMR adsorption-free ratio values. Based on the acoustic wave base signal and the first and second acoustic wave signals measured under the same preset pressure, the adsorbed gas sensitivity and free gas sensitivity are calculated respectively, resulting in multiple adsorbed gas sensitivity parameters and multiple free gas sensitivity parameters. Based on the multiple NMR adsorption-to-free ratios, multiple adsorbed gas sensitivity parameters, and multiple free gas sensitivity parameters, a power-law equation is fitted, and multiple coefficients that make the power-law equation hold true are obtained. An evaluation model for assessing the adsorption of free gas in coal and rock is established based on multiple coefficients and the power relationship equation. The steps for calculating the adsorbed gas sensitivity and free gas sensitivity based on the acoustic wave substrate signal and the first and second acoustic wave signals measured under the same preset pressure, and obtaining multiple adsorbed gas sensitivity parameters and multiple free gas sensitivity parameters, include: The Poisson's ratio, bulk modulus, and longitudinal impedance of the substrate are calculated based on the transverse and longitudinal wave signals in the acoustic substrate signal. Based on the transverse wave signal and longitudinal wave signal in the multiple first acoustic wave signals, calculate the corresponding multiple first longitudinal wave impedance values ​​and multiple first bulk modulus values ​​respectively; Based on the transverse wave signal and longitudinal wave signal in the multiple second acoustic signals, calculate the corresponding multiple second longitudinal wave impedance values, multiple Poisson ratio values ​​and multiple second bulk modulus values ​​respectively; Based on the first longitudinal wave impedance value, the second longitudinal wave impedance value, the second bulk modulus value, and the first bulk modulus value under each preset pressure, a plurality of longitudinal wave impedance sensitivity parameters and first bulk modulus sensitivity parameters corresponding to the adsorbent gas are calculated. Based on the substrate Poisson's ratio value, the substrate bulk modulus value, and the Poisson's ratio value and the second bulk modulus value under each preset pressure, a plurality of corresponding non-adsorbent gas Poisson's ratio sensitivity parameters and second bulk modulus sensitivity parameters are calculated. A quantitative formula for the adsorbed gas sensitivity parameters is obtained by fitting multiple longitudinal wave impedance sensitivity parameters and multiple first bulk modulus sensitivity parameters. The quantification formula for the free gas sensitivity parameter is obtained by fitting multiple Poisson's ratio sensitivity parameters and multiple second bulk modulus sensitivity parameters; The quantification formula for the adsorbed gas sensitivity parameter, obtained by fitting the longitudinal wave impedance sensitivity parameter and the first bulk modulus sensitivity parameter, is as follows: ； Where I1 represents the adsorption gas sensitivity parameter, S zp S represents the longitudinal wave impedance sensitivity parameter. k1 This represents the first bulk modulus sensitivity parameter, where the two coefficients a and b are unknowns. The quantification formula for the free gas sensitivity parameter, obtained by fitting the Poisson's ratio sensitivity parameter and the second bulk modulus sensitivity parameter, is as follows: ； Where I2 represents the free gas sensitivity parameter, S v S represents the Poisson's ratio sensitivity parameter. k2 This represents the second bulk modulus sensitivity parameter, where the coefficients m and n are unknowns. Based on the NMR adsorption-to-free ratio, the adsorbed gas sensitivity parameters, and the free gas sensitivity parameters, the power-law relationship is fitted as follows: ； Where K represents the adsorption-to-free ratio by NMR, and a, b, m, n, α, β and γ represent the specific values ​​of the multiple coefficients obtained by fitting that make the above equations true; Based on the aforementioned coefficients and the power-law equation, the following evaluation model is established to assess the adsorption of free gas in coal and rock: ； Where K0 represents the adsorbed-to-free ratio to be calculated.

2. The method for obtaining the evaluation model of the adsorption-to-free ratio of coal gas by acoustic nuclear magnetic resonance spectroscopy according to claim 1, characterized in that, The steps of introducing multiple adsorbed or non-adsorbed gases at different preset pressures into the reference container (310) via the metering pump (200), allowing the adsorbed or non-adsorbed gases to naturally diffuse from the reference container (310) into the sample container (320) and reach equilibrium, and then measuring the first acoustic signal, second acoustic signal, first NMR T2 spectrum, and second NMR T2 spectrum fed back from the coal and rock sample, include: The metering pump (200), the reference container (310), and the sample container (320) are evacuated; Close the diffusion valve (311); The metering pump (200) fills the reference container (310) with an adsorbent or non-adsorbent gas at a preset pressure. Open the diffusion valve (311) to allow the adsorbed or non-adsorbed gas to diffuse naturally until the internal gas pressure of the reference container (310) and the sample container (320) is balanced. Sound waves are emitted and nuclear magnetic resonance is excited towards the coal and rock sample; The first acoustic signal, the second acoustic signal, the first NMR T2 spectrum, and the second NMR T2 spectrum fed back from the coal and rock sample were measured. Repeat the above steps until multiple first acoustic signals, second acoustic signals, first NMR T2 spectra, and second NMR T2 spectra are measured.

3. The method for obtaining the evaluation model of the adsorption-to-free ratio of coal rock gas by acoustic nuclear magnetic resonance spectroscopy according to claim 2, characterized in that, In the process of repeating the above steps until multiple first acoustic signals, second acoustic signals, first NMR T2 spectra and second NMR T2 spectra are measured, the preset pressure is increased successively by a preset increase value.

4. The method for obtaining the evaluation model of the adsorption-to-free ratio of coal rock gas by acoustic nuclear magnetic resonance spectroscopy according to claim 1, characterized in that, The step of calculating the NMR adsorption-free ratio based on the NMR substrate signal and the first and second NMR T2 spectra measured under the same preset pressure, and obtaining multiple NMR adsorption-free ratio values, includes: Based on the NMR substrate signal, the characteristic peaks of the corresponding adsorbed gas in the first NMR T2 spectrum, the characteristic peaks of the corresponding free gas in the second NMR T2 spectrum, and a preset cutoff value, the area values ​​of the free gas peaks and the adsorbed gas peaks are calculated sequentially to obtain multiple adsorbed gas peak area values ​​and multiple free gas peak area values; wherein, the preset cutoff value represents the cutoff value in the NMR spectrum for dividing the free peaks and adsorbed peaks; The NMR adsorption-free ratio at the corresponding pressure is obtained based on the ratio of the adsorbed gas peak area to the free gas peak area; multiple NMR adsorption-free ratios are obtained.

5. The method for obtaining the evaluation model of the adsorption-to-free ratio of coal rock gas by acoustic nuclear magnetic resonance spectroscopy according to claim 1, characterized in that, The formulas for calculating the longitudinal wave impedance sensitivity parameters and the first bulk modulus sensitivity parameters of multiple corresponding adsorbed gases based on the first longitudinal wave impedance value, the second longitudinal wave impedance value, the second bulk modulus value, and the first bulk modulus value under each preset pressure are as follows: ； Among them, S zp M represents the longitudinal wave impedance sensitivity parameter. i_AG_zp M represents the first longitudinal wave impedance value corresponding to the preset pressure. sat_AG_zp M represents the first longitudinal wave impedance value corresponding to the maximum preset pressure. i_AF_zp M represents the second longitudinal wave impedance value corresponding to the preset pressure. sat_AF_zp This represents the second longitudinal wave impedance value corresponding to the maximum preset pressure; ； Among them, S k1 M represents the first bulk modulus sensitivity parameter. i_AG_k1 M represents the first bulk modulus value corresponding to the preset pressure. sat_AG_k1 M represents the first bulk modulus value corresponding to the maximum preset pressure. i_AF_k1 M represents the second bulk modulus value corresponding to the preset pressure. sat_AF_k1 This represents the second bulk modulus value corresponding to the maximum preset pressure; The formulas for calculating the Poisson's ratio sensitivity parameter and the second bulk modulus sensitivity parameter for multiple corresponding non-adsorbent gases based on the substrate Poisson's ratio value, the substrate bulk modulus value, and the Poisson's ratio value and the second bulk modulus value at each preset pressure are as follows: ； Among them, S v M represents the Poisson's ratio sensitivity parameter. i_AF_v M represents the Poisson's ratio value corresponding to the preset pressure. sat_AF_v M represents the Poisson's ratio value corresponding to the maximum preset pressure. 0_AF_v Indicates the base Poisson ratio; ； Among them, S k2 M represents the second bulk modulus sensitivity parameter. i_AF_k2 M represents the second bulk modulus value corresponding to the preset pressure. sat_AF_k2 M represents the second bulk modulus value corresponding to the maximum preset pressure. 0_AF_k2 This represents the bulk modulus of the substrate.

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