An evaluation model acquisition method for coal rock gas saturation degree by acoustic wave and nuclear magnetic resonance

Abstract

The application provides a coal rock gas saturation evaluation model acquisition method based on acoustic wave and nuclear magnetic resonance, and relates to the technical field of coal rock gas evaluation. In the method, the free volumes of the reference container and the sample container of the acoustic wave and nuclear magnetic resonance combined measuring device and the equilibrium gas pressures after the adsorbed gas and the free gas are respectively injected can be obtained, and the first saturation value is calculated based on the volume method. In addition, the acoustic wave data and the nuclear magnetic data under different gas pressures are measured by the acoustic wave module and the nuclear magnetic module in the acoustic wave and nuclear magnetic resonance combined measuring device. The first saturation value and the second saturation value calculated based on the nuclear magnetic data can obtain the corrected reference saturation, and the model for evaluating the gas saturation in the coal rock can be established according to the reference saturation and the elastic sensitivity parameter calculated based on the acoustic wave data. The coal rock gas saturation evaluation model acquisition method based on acoustic wave and nuclear magnetic resonance can improve the technical problems that the evaluation of the gas saturation in the coal rock is difficult and the precision is poor in the prior art.

Description

Technical Field

[0001] This invention relates to the field of coal and rock gas evaluation technology, and more specifically, to a method for obtaining an evaluation model for coal and rock gas saturation by acoustic wave nuclear magnetic resonance spectroscopy. 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 existing technologies, it is difficult to evaluate the saturation of gases contained in deep coal and rock formations. A large amount of data needs to be collected for evaluation, and the accuracy of the evaluation is also subject to significant errors. Summary of the Invention

[0004] The technical problem solved by this invention is how to improve the difficulty and poor accuracy of evaluating gas saturation in coal and rock 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 for gas saturation in coal and rock by acoustic nuclear magnetic resonance imaging, comprising:

[0007] A coal and rock sample is loaded into an acoustic-nuclear magnetic resonance (NMR) co-metry device. This device includes a gas source, a metering pump, a reference container, a sample container, an acoustic module, and an NMR module. The gas source is used to extract free or adsorbed gas. The gas source is connected to the metering pump to introduce free or adsorbed gas into the pump. The metering pump is connected to the reference container to introduce free or adsorbed gas into the reference container. The sample container is connected to and communicates with the reference container. A switching valve is provided between the sample container and the reference container. The coal and rock sample is loaded into the sample container. Both the acoustic module and the NMR module are located in the sample container. The acoustic module emits acoustic waves to the coal and rock sample and receives the acoustic signal fed back from the sample. The NMR module excites NMR signals to the coal and rock sample and receives the NMR signals fed back from the sample to generate an NMR T2 spectrum.

[0008] Obtain the free volume value of the entire reference container and the sample container;

[0009] Under vacuum and preset temperature conditions in the sample container, the acoustic wave substrate signal and nuclear magnetic resonance substrate signal of the coal and rock sample under preset confining pressure are measured.

[0010] Multiple free gases with different preset pressures are introduced into the reference container through the metering pump. After the free gases naturally diffuse from the reference container into the sample container and reach equilibrium, multiple first measured gas pressure values ​​are obtained.

[0011] Multiple adsorption gases at different preset pressures are introduced into the reference container by the metering pump. After the adsorption gases diffuse naturally from the reference container into the sample container and reach equilibrium, multiple second measured gas pressure values, as well as multiple first acoustic signals and multiple first nuclear magnetic T2 spectra fed back by the coal and rock sample are measured.

[0012] Based on multiple first measured air pressure values, multiple second measured air pressure values, and the free volume value, the adsorption amount corresponding to each different preset pressure is calculated, and multiple first saturation values ​​corresponding to each preset pressure are calculated based on the adsorption amount corresponding to each preset pressure.

[0013] Based on the NMR substrate signal and multiple first NMR T2 spectra, the gas saturation under different preset pressures is calculated to obtain multiple second saturation values;

[0014] Based on the acoustic wave substrate signal and multiple first acoustic wave signals, the elastic mechanical sensitivity parameters under different preset pressures are calculated to obtain multiple sensitivity parameter values;

[0015] Multiple reference saturations corresponding to multiple preset pressures are obtained by fitting multiple first saturation values ​​and multiple second saturation values;

[0016] A linear evaluation model and / or a power-law evaluation model are obtained by fitting multiple reference saturation levels and multiple sensitivity parameters.

[0017] The method for obtaining a gas saturation evaluation model for coal and rock samples using acoustic-nuclear magnetic resonance (NMR) measurement provided by this invention involves placing a coal and rock sample into an acoustic-nuclear magnetic resonance (NMR) measurement device to simulate the temperature and confining pressure of the coal and rock environment. By injecting adsorbed gas at different pressures in a stepped manner, the gas saturation in the coal and rock under different pressures can be simulated. Simultaneously, a first saturation value is obtained by calculating the volume of gas in a free state and the volume of gas in an adsorbed state in the coal and rock sample; the NMR T2 spectrum fed back by the coal and rock sample under different pressures is measured using NMR to calculate the gas saturation of the coal and rock sample under different pressures, yielding a second saturation value; and the acoustic signal fed back by the coal and rock sample under different pressures is measured using acoustic measurement to calculate the elastic sensitivity of the coal and rock sample to multiple types of acoustic waves under different pressures. Finally, a linear evaluation model and / or a power-law evaluation model related to gas saturation and longitudinal and transverse waves are jointly established based on elastic sensitivity, first saturation value and second saturation value to accurately evaluate the gas saturation of coal and rock. In other words, when evaluating the gas saturation in real coal and rock, it is only necessary to collect the acoustic signal fed back by the target coal and rock to evaluate the gas saturation of the target coal and rock, thereby improving the technical problems of difficulty and poor accuracy in evaluating the gas saturation in coal and rock in the existing technology. Attached Figure Description

[0018] 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.

[0019] Figure 1 This is a flowchart of the method for obtaining the evaluation model of coal and rock gas saturation by acoustic nuclear magnetic resonance (NMR) measurement provided in the embodiments of this application;

[0020] Figure 2 This is a schematic diagram of the acoustic nuclear magnetic resonance imaging (NMR) device provided in the embodiments of this application;

[0021] Figure 3 This is a flowchart of step S4 in the method for obtaining the evaluation model of coal and rock gas saturation by acoustic nuclear magnetic resonance spectroscopy provided in the embodiments of this application;

[0022] Figure 4 This is a flowchart of step S5 in the method for obtaining the evaluation model of gas saturation in coal and rock by acoustic nuclear magnetic resonance spectroscopy provided in the embodiments of this application;

[0023] Figure 5 This is a flowchart of step S6 in the method for obtaining the evaluation model of gas saturation in coal and rock by acoustic nuclear magnetic resonance spectroscopy provided in the embodiments of this application;

[0024] Figure 6 This is a flowchart of step S8 in the method for obtaining the evaluation model of gas saturation in coal and rock by acoustic nuclear magnetic resonance spectroscopy provided in the embodiments of this application.

[0025] Icons: Acoustic wave NMR combined measurement device 10, gas source 100, metering pump 200, reference container 310, switch valve 311, sample container 320, acoustic wave module 330, NMR module 340. Detailed Implementation

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] Furthermore, the terms "first" and "second" are used only to distinguish descriptions and should not be interpreted as indicating or implying relative importance.

[0031] 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.

[0032] This embodiment provides a method for obtaining an evaluation model for gas saturation in coal and rock using acoustic nuclear magnetic resonance (NMR) measurement (hereinafter referred to as the method). This method can obtain an evaluation model for evaluating the gas saturation in coal and rock. In other words, the model obtained by this method can be applied to evaluate the gas saturation of target coal and rock, and can improve the technical problems of difficulty and poor accuracy in evaluating the gas saturation in coal and rock in the prior art.

[0033] In this embodiment, the method can be executed based on the acoustic nuclear magnetic resonance (NMR) measurement device 10. In other words, the execution of this method requires the assistance of the acoustic NMR measurement device 10. The acoustic NMR measurement device 10 can be used to simulate the environment in which coal and rock are located, that is, to simulate the confining pressure and temperature of the environment in which coal and rock are located, so as to restore the real environment in which coal and rock are located and improve the evaluation accuracy of the obtained evaluation model.

[0034] The acoustic NMR spectroscopy device 10 includes a gas source 100, a metering pump 200, a reference container 310, a sample container 320, an acoustic module 330, and an NMR module 340. The gas source 100 includes at least two containers, one for free gas and one for adsorbed gas. The gas source 100 is used to extract either the free or adsorbed gas. Optionally, in this embodiment, the adsorbed gas can be methane (CH4), and the free gas can be helium (He). It should be understood that in other embodiments, other similar gases can be used for the adsorbed and free gases, which will not be elaborated here.

[0035] A gas source 100 is connected to a metering pump 200 to introduce free gas or adsorbed gas into the metering pump 200. The metering pump 200 is connected to a reference container 310 to introduce free gas or adsorbed gas into the reference container 310. The metering pump 200 can also record the amount of adsorbed gas or free gas introduced into the reference container 310. A sample container 320 is connected to and communicates with the reference container 310. A switch valve 311 is provided between the sample container 320 and the reference container 310. A coal and rock sample is loaded into the sample container 320. An acoustic module 330 and a nuclear magnetic resonance (NMR) module 340 are both located in the sample container 320. The acoustic module 330 is used to emit acoustic waves to the coal and rock sample and receive the acoustic wave signals fed back by the coal and rock sample. The NMR module 340 is used to excite NMR signals to the coal and rock sample and receive the NMR signals fed back by the coal and rock sample to generate an NMR T2 spectrum. The acoustic wave module 330 and the nuclear magnetic resonance (NMR) module 340 are located within the sample container 320. The acoustic wave module 330 has a device for generating acoustic waves connected to the sample container 320, used to excite acoustic waves into the coal and rock sample within the sample container 320. The NMR module 340 has an NMR excitation device located on the outer periphery of the sample container 320, which can excite NMR signals into the coal and rock sample within the sample container 320. Furthermore, the acoustic wave module 330 also includes a receiving device for receiving acoustic wave data fed back from the coal and rock sample; similarly, the NMR module 340 also includes a receiving device for receiving NMR signals fed back from the coal and rock sample. Of course, the arrangement of the acoustic wave module 330 and the NMR module 340 within the sample container 320, as well as their components, are existing technologies and will not be described in detail here.

[0036] In this embodiment, the method for obtaining the evaluation model of gas saturation in coal and rock by acoustic nuclear magnetic resonance includes:

[0037] S1. Load the coal and rock sample into the acoustic nuclear magnetic resonance (NMR) measurement device 10.

[0038] After placing the coal and rock sample into the sample container 320 of the acoustic nuclear magnetic resonance (AMR) device 10, the confining pressure applied to the coal and rock sample by the confining pressure device in the AMR device 10 is adjusted to reach a preset confining pressure, and the temperature inside the sample container 320 is adjusted to a preset temperature to simulate the actual environment of the coal and rock sample within the sample container 320. It is worth noting that if it is necessary to simulate the actual environment of deep coal and rock, the confining pressure can be increased and the temperature adjusted to a specified temperature; while when simulating the actual environment of shallow coal and rock, the confining pressure can be decreased and the temperature adjusted to a specified temperature.

[0039] In addition, the coal and rock samples need to be dried before loading, for example, by drying them to constant weight at 100°C in a constant temperature chamber. Then, the weight of the coal and rock samples is measured, and the density of the coal and rock samples is calculated based on the weight and volume of the samples.

[0040] S2. Obtain the overall free volume value of the reference container 310 and the sample container 320.

[0041] The calibration method for the free volumes of the reference container 310 and the sample container 320 is as follows: After evacuating the metering pump 200, the reference container 310, and the sample container 320, the switch valve 311 between the sample container 320 and the reference container 310 is closed. A specified amount of free gas is introduced into the reference container 310 through the metering pump 200, and the gas pressure in the reference container 310 and the gas volume recorded by the metering pump 200 are recorded. After the gas pressure reaches equilibrium, the switch valve 311 is opened, allowing the gas to diffuse naturally into the sample container 320, and the gas pressure inside the sample container 320 is obtained after the gas pressure reaches equilibrium. The overall free volume value of the reference container 310 and the sample container 320 can be calculated based on Boyle's law.

[0042] S3. Under vacuum and preset temperature conditions in sample container 320, the acoustic wave substrate signal and nuclear magnetic resonance substrate signal fed back by the coal and rock sample under preset confining pressure are measured.

[0043] S4. Multiple free gases with different preset pressures are introduced into the reference container 310 through the metering pump 200. After the free gases naturally diffuse from the reference container 310 into the sample container 320 and reach equilibrium, multiple first measured gas pressure values ​​are obtained.

[0044] Step S4 includes:

[0045] S41. With the switch valve 311 closed, free gas is introduced into the reference container 310 to make the gas pressure in the reference container 310 reach the preset pressure.

[0046] Since the reference container 310 and the sample container 320 have already been evacuated in the preceding step S3 of step S4, they are already in a vacuum state before the first execution of step S41. Therefore, no evacuation is required, and gas can be injected directly.

[0047] S42. Open the switch valve 311 to allow the free gas to diffuse naturally into the sample container 320.

[0048] It is worth noting that the purpose of filling the reference container 310 with free gas before the free gas diffuses naturally is that, since no coal or rock sample is placed in the reference container 310, the amount of gas filled can be precisely controlled, which can ensure that the amount of gas filled multiple times can be precisely controlled and ensure the consistency of multiple experiments.

[0049] S43. After the reference container 310 and the sample container 320 reach pressure equilibrium, the first measured air pressure value corresponding to the preset pressure is measured.

[0050] S44. Repeat the above steps until multiple first measured air pressure values ​​are obtained.

[0051] Step S44 refers to repeatedly executing steps S41 to S43, wherein in each subsequent execution of step S41, the preset pressure is set to be different from the preset pressure in the previous step S41. Of course, the preset pressures in the multiple repeated steps S41 are all different. Optionally, in this embodiment, in the multiple steps S41 executed multiple times in step S4, the preset pressures gradually increase according to the order of execution. Further, in one embodiment, step S41 is executed ten times, and the preset pressures can be 2MPa, 4MPa...18MPa and 20MPa. Based on this, after executing step S4, ten first measured air pressure values ​​are obtained.

[0052] Additionally, it should be noted that in some embodiments, before the next execution of step S41, the reference container 310 and the sample container 320 need to be evacuated. This ensures that the experimental conditions corresponding to each preset pressure are the same during subsequent adsorption gas filling, thus ensuring the consistency and validity of the experimental results. Of course, in other embodiments, evacuation may not be performed; simply using the metering pump 200 to precisely control the amount of gas filled each time will also ensure the same experimental conditions during subsequent adsorption gas filling, guaranteeing the consistency and validity of the experimental results.

[0053] S5. Multiple adsorption gases with different preset pressures are introduced into the reference container 310 through the metering pump 200. After the adsorption gases naturally diffuse from the reference container 310 into the sample container 320 and reach equilibrium, multiple second measured gas pressure values, as well as multiple first acoustic signals and multiple first nuclear magnetic T2 spectra fed back from the coal and rock samples, are measured.

[0054] Similarly, step S5 may include:

[0055] S51. With the switch valve 311 closed, adsorption gas is introduced into the reference container 310 to make the gas pressure in the reference container 310 reach the preset pressure.

[0056] Of course, before performing step S51 for the first time, it is necessary to evacuate the reference container 310 and the sample container 320 to prevent the free gas inside the reference container 310 and the sample container 320 from affecting the experiment.

[0057] S52. Open the switch valve 311 to allow the adsorbed gas to diffuse naturally into the sample container 320.

[0058] S53. After the reference container 310 and the sample container 320 reach pressure equilibrium, the second measured air pressure value, the first acoustic signal and the first nuclear magnetic T2 spectrum corresponding to the preset pressure are measured.

[0059] S54. Repeat the above steps until multiple second measured air pressure values, multiple first acoustic signals, and multiple first nuclear magnetic T2 spectra are obtained.

[0060] Similarly, step S54 refers to repeatedly executing steps S51 to S53, and in each subsequent execution of step S51, the preset pressure is set to be different from the preset pressure in the previous step S51. Of course, the preset pressures in the multiple repeated steps S51 are all different. Optionally, in this embodiment, in the multiple steps S51 executed multiple times in step S5, the multiple preset pressures also gradually increase according to the order of execution. Further, in one embodiment, step S51 is executed ten times, and the multiple preset pressures can be 2MPa, 4MPa...18MPa and 20MPa. Based on this, after executing step S5, ten second measured air pressure values, ten first acoustic signals and ten first nuclear magnetic resonance T2 spectra are obtained.

[0061] It is worth noting that the multiple preset pressures in step S5 correspond one-to-one with the preset pressures in step S4.

[0062] Alternatively, in some embodiments, before performing step S51 again, the reference container 310 and the sample container 320 need to be evacuated to ensure that the amount of gas introduced corresponds one-to-one with that in step S4 above, ensuring the consistency of experimental conditions and thus ensuring the validity of the experimental results. Of course, in other embodiments, the evacuation step may not be performed, and the amount of gas introduced each time can be precisely controlled by the metering pump 200.

[0063] After acquiring the first measured air pressure value, the second measured air pressure value, the first acoustic signal, and the first NMR T2 spectrum, the method further includes:

[0064] S6. Calculate the adsorption amount corresponding to each preset pressure based on multiple first measured air pressure values, multiple second measured air pressure values ​​and free volume values, and calculate multiple first saturation values ​​corresponding to each preset pressure based on the adsorption amount corresponding to each preset pressure.

[0065] Step S6 includes:

[0066] S61. Multiple first free quantities are calculated based on multiple first measured air pressure values ​​and free volume values.

[0067] The first free quantity represents the total amount of gas in a free state in the reference container 310 and the sample container 320.

[0068] The first measured air pressure value, free volume value, and first free quantity satisfy the following formula:

[0069] ;

[0070] Among them, P X Indicates the first measured air pressure value; V S The free volume is represented by Z, which is the compressibility coefficient. Z can be 1 or obtained experimentally based on actual conditions. The method of obtaining this Z value is existing technology and will not be elaborated here. n1 is the first free volume; R is the gas constant; and T is the thermodynamic temperature.

[0071] Based on the above formula, where, in P X and V S With the value of n1 determined, the values ​​of Z, R, and T are also determined, and thus the value of n1 can be solved, thereby obtaining multiple values ​​of n1.

[0072] S62. Multiple second free quantities are calculated based on multiple measured air pressure values ​​and free volume values.

[0073] The second free quantity represents the total amount of gas in a free state in the reference container 310 and the sample container 320.

[0074] Among them, the second measured air pressure value, the free volume value, and the second free quantity satisfy the following formula:

[0075] ;

[0076] Among them, P Y This represents the second measured air pressure value, and n2 is the second free quantity.

[0077] Based on the above formula, multiple values ​​of n² can be calculated.

[0078] S63. Based on the differences between multiple first free quantities and multiple second free quantities, obtain multiple adsorption quantities corresponding to multiple preset pressures.

[0079] The difference between the first and second free amounts under the same preset pressure is the amount of gas adsorbed in the coal sample. In other words, the amount of adsorption under the corresponding preset pressure can be obtained by subtracting n2 from n1.

[0080] S64. Calculate multiple first saturation values ​​based on multiple adsorption amounts.

[0081] The formula for calculating multiple first saturation values ​​in step S64 is as follows:

[0082] ;

[0083] S R S represents the first saturation value, S represents the adsorption amount corresponding to any preset pressure, and S1 represents the adsorption amount corresponding to the maximum preset pressure.

[0084] It should be noted that the higher the gas pressure, the closer the gas adsorption in the coal and rock sample is to saturation. In other words, when the gas pressure reaches a certain level, the coal and rock sample reaches gas adsorption saturation, at which point the saturation degree is 1. In this embodiment, since the saturation degree corresponding to the highest preset pressure among multiple preset pressures is relatively closer to 1, the saturation degree corresponding to the highest preset pressure among multiple preset pressures is used as 1 for relevant calculations.

[0085] Through the calculation in step S64, multiple S values ​​corresponding to each preset pressure can be obtained. R value.

[0086] S7. Calculate the gas saturation at different preset pressures based on the NMR substrate signal and multiple first NMR T2 spectra to obtain multiple second saturation values.

[0087] Optionally, the formula for calculating the gas saturation at different preset pressures based on the NMR substrate signal and multiple first NMR T2 spectra is as follows:

[0088] ;

[0089] Among them, S NMR Indicates the second saturation value, A i A represents the peak area of ​​the NMR signal in the first NMR T2 spectrum under the corresponding preset pressure. sat A0 represents the peak area of ​​the NMR signal in the first NMR T2 spectrum corresponding to the largest preset pressure among multiple preset pressures, and A0 represents the peak area of ​​the NMR signal in the NMR T2 spectrum corresponding to the NMR substrate signal.

[0090] Based on the calculation in step S7, multiple second saturation values ​​corresponding to different preset pressures can be obtained, that is, multiple S values. NMR value.

[0091] S8. Calculate the elastic mechanical sensitivity parameters under different preset pressures based on the acoustic wave base signal and multiple first acoustic wave signals to obtain multiple sensitivity parameter values.

[0092] It should be noted that, in this embodiment, each first acoustic wave signal includes first transverse wave data and first longitudinal wave data, wherein the first transverse wave data includes at least transverse wave velocity and the first longitudinal wave data includes at least longitudinal wave velocity; similarly, the acoustic wave substrate signal includes second transverse wave data and second longitudinal wave data, wherein the second transverse wave data includes at least substrate transverse wave velocity and the second longitudinal wave data includes at least substrate longitudinal wave velocity.

[0093] Step S8 includes:

[0094] S81. Calculate the corresponding transverse wave velocity ratio, Poisson's ratio, Young's modulus, bulk modulus, and shear modulus based on the first transverse wave data and the first longitudinal wave data corresponding to any preset pressure.

[0095] Among them, V Z Let V be the longitudinal wave velocity. H The velocity is the transverse wave velocity.

[0096] The formula for calculating the P-wave to S-wave velocity ratio is as follows:

[0097] ;

[0098] in, This represents the ratio of longitudinal to transverse wave velocities.

[0099] The formula for calculating Poisson's ratio is as follows:

[0100] ;

[0101] Where v represents the Poisson ratio.

[0102] The formula for calculating Young's modulus is as follows:

[0103] ;

[0104] Where E represents Young's modulus and ρ represents the density of the coal and rock sample.

[0105] The formula for calculating the bulk modulus is as follows:

[0106] ;

[0107] Where K represents the bulk modulus value.

[0108] The formula for calculating the shear modulus is as follows:

[0109] ;

[0110] Where G represents the shear modulus value.

[0111] Based on the above formula, the longitudinal and transverse wave velocity ratio, Poisson's ratio, Young's modulus, bulk modulus, and shear modulus corresponding to any preset pressure can be calculated respectively; thus, multiple longitudinal and transverse wave velocity ratios, multiple Poisson's ratios, multiple Young's modulus values, multiple bulk modulus values, and multiple shear modulus values ​​corresponding to multiple preset pressures can be obtained.

[0112] S82. Calculate the ratio of longitudinal to transverse wave velocities of the substrate, the Poisson's ratio of the substrate, the Young's modulus of the substrate, the bulk modulus of the substrate, and the shear modulus of the substrate based on the second transverse wave data and the second longitudinal wave data.

[0113] Similarly, based on the above formula, the ratio of longitudinal to transverse wave velocities of the substrate, the Poisson's ratio of the substrate, the Young's modulus of the substrate, the bulk modulus of the substrate, and the shear modulus of the substrate are calculated using the transverse wave velocity in the second transverse wave data and the longitudinal wave velocity in the second longitudinal wave data.

[0114] S83. Based on the longitudinal and transverse wave velocity ratio, Poisson's ratio, Young's modulus, bulk modulus, and shear modulus of the substrate, as well as the longitudinal and transverse wave velocity ratio, Poisson's ratio, Young's modulus, bulk modulus, and shear modulus corresponding to any preset pressure, calculate the corresponding elastic sensitivity of the longitudinal and transverse wave velocity ratio, Poisson's ratio, Young's modulus, bulk modulus, and shear modulus.

[0115] The formulas for calculating the elastic sensitivity of the longitudinal and transverse wave velocity ratio, Poisson's ratio, Young's modulus, bulk modulus, and shear modulus in step S83 are as follows:

[0116] ;

[0117] Among them, S 敏感度 M represents any one of the following elastic sensitivity parameters: longitudinal and transverse wave velocity ratio, Poisson's ratio, Young's modulus, bulk modulus, and shear modulus; M represents the elastic sensitivity relative to S. 敏感度 The corresponding ratio of longitudinal to transverse wave velocity, Poisson's ratio, Young's modulus, bulk modulus, and shear modulus; in other words, in S 敏感度 When M is the elastic sensitivity to the ratio of longitudinal to transverse wave velocities, then M is the ratio of longitudinal to transverse wave velocities; similarly, when S... 敏感度 When the elasticity sensitivity is Poisson's ratio, M is the Poisson's ratio value. M0 represents the sensitivity to S. 敏感度 The corresponding substrate longitudinal and transverse wave velocity ratio, substrate Poisson's ratio, substrate Young's modulus, substrate bulk modulus, and substrate shear modulus; similarly, in S 敏感度 When representing the elastic sensitivity of the longitudinal and transverse wave velocity ratio, M0 represents the longitudinal and transverse wave velocity ratio of the substrate. satThis indicates that among the multiple preset pressures, the maximum preset pressure corresponds to the ratio of longitudinal to transverse wave velocities, Poisson's ratio, Young's modulus, bulk modulus, and shear modulus values, and is related to S. 敏感度 One corresponding to; in other words, in S 敏感度 When M is the elastic sensitivity of the ratio of longitudinal to transverse wave velocity, sat This represents the maximum P-wave velocity ratio among multiple preset pressures.

[0118] Based on the above calculations, for each preset pressure condition, a corresponding elastic sensitivity of longitudinal and transverse wave velocity ratio, Poisson's ratio, Young's modulus, bulk modulus, and shear modulus can be calculated. After the calculation in step S83, multiple elastic sensitivities of longitudinal and transverse wave velocity ratio, multiple elastic sensitivities of Poisson's ratio, multiple elastic sensitivities of Young's modulus, multiple elastic sensitivities of bulk modulus, and multiple elastic sensitivities of shear modulus can be obtained for multiple preset pressure conditions.

[0119] S84. Based on any preset pressure, construct the corresponding sensitivity parameter values ​​through linear and / or exponential relationships for the elastic sensitivity of longitudinal and transverse wave velocity ratio, Poisson's ratio, Young's modulus, bulk modulus, and shear modulus.

[0120] Here, "and / or" means that you can construct only one sensitivity parameter value for a linear relationship, or only one sensitivity parameter value for an exponential relationship; or you can construct both a sensitivity parameter value for a linear relationship and a sensitivity parameter value for an exponential relationship.

[0121] After constructing the sensitivity parameter values, the method provided in this embodiment further includes:

[0122] S9. Based on multiple first saturation values ​​and multiple second saturation values, multiple reference saturations corresponding to multiple preset pressures are obtained.

[0123] The following formula is established using the first and second saturation values ​​corresponding to the preset pressure:

[0124] Among them, S R S represents the first saturation value. NMR Let S represent the second saturation value, and a and b be constants that make the above equation true. It is worth noting that in this step, a and b can be expressed as unknowns; in other words, through S... NMR and S R Constructing a linear function can be done through S R To correct S NMR To improve S NMR The accuracy.

[0125] Then, the values ​​of a and b are obtained by fitting multiple formulas corresponding to multiple preset pressures. A reference saturation formula is established based on the values ​​of a and b, as follows:

[0126] Among them, S 参考 This represents the reference saturation. The obtained reference saturation is then a more accurate saturation reference value, accurately reflecting the gas saturation of the coal sample under the corresponding preset pressure. Specifically, S corresponds to each preset pressure. NMR By substituting the value into the above formula, a more accurate gas saturation can be obtained under the corresponding preset pressure conditions. Thus, multiple more accurate gas saturations can be obtained under multiple preset pressure conditions.

[0127] S10. Obtain a linear evaluation model and / or a power-law evaluation model by fitting multiple reference saturation and multiple sensitivity parameters.

[0128] The linear evaluation model is as follows:

[0129] ;

[0130] Among them, S 待测 The gas saturation of the target coal and rock. k1, k2, k3, k4 and k5 represent multiple coefficients obtained by fitting multiple reference saturation and multiple sensitivity parameters to make the above equation true. Indicates the ratio of longitudinal to transverse wave velocity to elastic sensitivity; Indicates Poisson's ratio elasticity sensitivity; Indicates the elastic sensitivity of Young's modulus; Indicates the elastic sensitivity of bulk modulus; This indicates the elastic sensitivity of the shear modulus.

[0131] It is worth noting that the above This can be viewed as a sensitivity parameter value representing a linear relationship constructed from the elastic sensitivity of longitudinal and transverse wave velocity ratio, Poisson's ratio, Young's modulus, bulk modulus, and shear modulus. Based on this, the reference saturation S under multiple preset pressure conditions is used. 参考 The sensitivity parameter values ​​for multiple linear relationships can be used to construct multiple corresponding equations as described above. By fitting these equations together, a set of values ​​that makes the above equations true can be obtained. Multiple coefficients, k1, k2, k3, k4, and k5, are used to obtain a linear evaluation model for assessing the gas saturation of coal and rock.

[0132] After obtaining After selecting multiple coefficients k1, k2, k3, k4, and k5, the following linear evaluation model is obtained. Among them, S 待测 The gas saturation of the target coal and rock; and , , , as well as This can be replaced by relevant formulas, which can be found in the calculation formulas in step S81. When evaluating the gas saturation of the target coal and rock, it is only necessary to measure the acoustic signal fed back by the target coal and rock, and substitute the longitudinal wave velocity and transverse wave velocity from the acoustic signal into the above formula to calculate S. 待测 Therefore, the gas saturation of the target coal and rock can be evaluated based on this linear evaluation model.

[0133] In addition, the power-law evaluation model is as follows:

[0134] ;

[0135] Among them, k6, k7, k8, k9, k 10 l1, l2, l3, l4 and l5 represent multiple coefficients obtained by fitting multiple reference saturation and multiple sensitivity parameters, which make the above equation true.

[0136] in, This can be viewed as a sensitivity parameter value constructed from a power-law relationship of elastic sensitivity based on the ratio of longitudinal and transverse wave velocities, Poisson's ratio, Young's modulus, bulk modulus, and shear modulus. Based on this, the reference saturation S under multiple preset pressure conditions is used... 参考 The sensitivity parameter values ​​for multiple exponential relationships can be used to construct multiple corresponding equations as described above. By fitting these equations, we can obtain k6, k7, k8, k9, and k... that make the above equations true. 10 Multiple coefficients, l1, l2, l3, l4 and l5, are used to obtain a power-law evaluation model for evaluating the gas saturation of coal and rock.

[0137] After obtaining k6, k7, k8, k9, k 10 After adding multiple coefficients l1, l2, l3, l4, and l5, the following power-law evaluation model is obtained. Among them, S 待测 The gas saturation of the target coal and rock; and , , , as well as This can be replaced by relevant formulas, which can be found in the calculation formulas in step S81. When evaluating the gas saturation of the target coal and rock, it is only necessary to measure the acoustic signal fed back by the target coal and rock, and substitute the longitudinal wave velocity and transverse wave velocity from the acoustic signal into the above formula to calculate S. 待测 Therefore, the gas saturation of the target coal and rock can be evaluated based on this power-law evaluation model.

[0138] In summary, the method for obtaining the evaluation model of gas saturation in coal and rock using acoustic-nuclear magnetic resonance (NMR) measurement provided in this embodiment allows coal and rock samples to be placed in the acoustic-nuclear magnetic resonance (NMR) measurement device 10 to simulate the temperature and confining pressure of the coal and rock environment. By injecting adsorbed gas at different pressures in a stepped manner, the gas saturation in coal and rock under different pressures can be simulated. Simultaneously, a first saturation value is obtained by calculating the volume of gas in a free state and the volume of gas in an adsorbed state in the coal and rock sample; the NMR T2 spectrum fed back by the coal and rock sample under different pressures is measured by NMR to calculate the gas saturation of the coal and rock sample under different pressures, thus obtaining a second saturation value; and the acoustic signal fed back by the coal and rock sample under different pressures is measured by acoustic measurement to calculate the elastic sensitivity of the coal and rock sample to multiple types of acoustic waves under different pressures. Finally, a linear evaluation model and / or a power-law evaluation model related to gas saturation and longitudinal and transverse waves are established based on elastic sensitivity, the first saturation value, and the second saturation value. This model is used to accurately evaluate the gas saturation of coal and rock. In other words, when evaluating the gas saturation in real coal and rock, only the acoustic signal fed back by the target coal and rock needs to be collected to evaluate the gas saturation, thus improving the technical problems of difficulty and poor accuracy in evaluating gas saturation in coal and rock in existing technologies. Furthermore, since the reference saturation value is obtained by jointly correcting the first saturation value measured by the volumetric method and the second saturation value measured by the nuclear magnetic resonance method, it can more accurately express the saturation under the corresponding preset pressure conditions. This makes the evaluation model constructed using the reference saturation value and the corresponding sensitivity parameters more accurate, thereby enabling the obtained linear evaluation model and / or power-law evaluation model to more accurately evaluate the gas saturation of the target coal and rock, improving the evaluation accuracy.

[0139] 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 gas saturation in coal and rock measured by acoustic nuclear magnetic resonance, characterized in that, include: A coal and rock sample is loaded into an acoustic nuclear magnetic resonance (NMR) co-detection device (10); wherein the acoustic NMR co-detection device (10) includes a gas source (100), a metering pump (200), a reference container (310), a sample container (320), an acoustic module (330), and an NMR module (340); the gas source (100) is used to extract free gas or adsorbed gas; the gas source (100) is connected to the metering pump (200) to introduce free gas or adsorbed gas into the metering pump (200); the metering pump (200) is connected to the reference container (310) to introduce free gas or adsorbed gas into the reference container (310), and so on. The sample container (320) is connected to and communicates with the reference container (310), and a switch valve (311) is provided between the sample container (320) and the reference container (310); the coal and rock sample is loaded into the sample container (320); the acoustic module (330) and the nuclear magnetic resonance module (340) are both located in the sample container (320), the acoustic module (330) is used to emit acoustic waves to the coal and rock sample and receive the acoustic wave signal fed back by the coal and rock sample, and the nuclear magnetic resonance module (340) is used to excite nuclear magnetic resonance signals to the coal and rock sample and receive the nuclear magnetic resonance signals fed back by the coal and rock sample to generate a nuclear magnetic resonance T2 spectrum; Obtain the free volume value of the entire reference container (310) and the sample container (320); In the sample container (320) under vacuum and preset temperature conditions, the acoustic wave substrate signal and nuclear magnetic resonance substrate signal fed back by the coal and rock sample under preset confining pressure conditions are measured. Multiple free gases with different preset pressures are introduced into the reference container (310) by the metering pump (200). After the free gases naturally diffuse from the reference container (310) into the sample container (320) and reach equilibrium, multiple first measured gas pressure values ​​are obtained. Multiple adsorption gases with different preset pressures are introduced into the reference container (310) by the metering pump (200). After the adsorption gases naturally diffuse from the reference container (310) into the sample container (320) and reach equilibrium, multiple second measured gas pressure values, as well as multiple first acoustic signals and multiple first nuclear magnetic T2 spectra fed back by the coal and rock sample are measured. Based on multiple first measured air pressure values, multiple second measured air pressure values, and the free volume value, the adsorption amount corresponding to each different preset pressure is calculated, and multiple first saturation values ​​corresponding to each preset pressure are calculated based on the adsorption amount corresponding to each preset pressure. Based on the NMR substrate signal and multiple first NMR T2 spectra, the gas saturation under different preset pressures is calculated to obtain multiple second saturation values; Based on the acoustic wave substrate signal and multiple first acoustic wave signals, the elastic mechanical sensitivity parameters under different preset pressures are calculated to obtain multiple sensitivity parameter values; Multiple reference saturations corresponding to multiple preset pressures are obtained by fitting multiple first saturation values ​​and multiple second saturation values; A linear evaluation model and / or a power-law evaluation model are obtained by fitting multiple reference saturations and multiple sensitivity parameters; Each of the first acoustic wave signals includes first transverse wave data and first longitudinal wave data, and the acoustic wave substrate signal includes second transverse wave data and second longitudinal wave data. The step of calculating elastic mechanical sensitivity parameters under different preset pressures based on the acoustic wave substrate signal and multiple first acoustic wave signals to obtain multiple sensitivity parameter values ​​includes: Calculate the corresponding longitudinal and transverse wave velocity ratio, Poisson's ratio, Young's modulus, bulk modulus, and shear modulus based on the first transverse wave data and the first longitudinal wave data corresponding to any of the preset pressures. The substrate longitudinal-transverse wave velocity ratio, substrate Poisson's ratio, substrate Young's modulus, substrate bulk modulus, and substrate shear modulus are calculated based on the second transverse wave data and the second longitudinal wave data. Based on the longitudinal and transverse wave velocity ratio of the substrate, the Poisson's ratio of the substrate, the Young's modulus of the substrate, the bulk modulus of the substrate, and the shear modulus of the substrate, as well as the longitudinal and transverse wave velocity ratio, the Poisson's ratio, the Young's modulus, the bulk modulus, and the shear modulus corresponding to any preset pressure, the corresponding elastic sensitivity of the longitudinal and transverse wave velocity ratio, the Poisson's ratio, the Young's modulus, and the shear modulus is calculated. Based on any of the preset pressures, the elastic sensitivity of the longitudinal and transverse wave velocity ratio, the elastic sensitivity of Poisson's ratio, the elastic sensitivity of Young's modulus, the elastic sensitivity of the bulk modulus, and the elastic sensitivity of the shear modulus are constructed through linear and / or exponential relationships to obtain corresponding sensitivity parameter values. Based on the substrate's longitudinal and transverse wave velocity ratio, substrate Poisson's ratio, substrate Young's modulus, substrate bulk modulus, and substrate shear modulus, and for any preset pressure, the corresponding elastic sensitivity of the longitudinal and transverse wave velocity ratio, Poisson's ratio, Young's modulus, bulk modulus, and shear modulus are calculated using the following formulas: ； Among them, S 敏感度 M represents any one of the following: the elastic sensitivity of the longitudinal and transverse wave velocity ratio, the elastic sensitivity of Poisson's ratio, the elastic sensitivity of Young's modulus, the elastic sensitivity of the bulk modulus, and the elastic sensitivity of the shear modulus; M represents the relationship between S and 敏感度 The corresponding values ​​are one of the following: the longitudinal and transverse wave velocity ratio, the Poisson's ratio, the Young's modulus, the bulk modulus, and the shear modulus; M0 represents the value related to S. 敏感度 The corresponding value is one of the following: the ratio of longitudinal to transverse wave velocities of the substrate, the Poisson's ratio of the substrate, the Young's modulus of the substrate, the bulk modulus of the substrate, and the shear modulus of the substrate; M sat This refers to the ratio of longitudinal to transverse wave velocities, the Poisson's ratio, the Young's modulus, the bulk modulus, and the shear modulus corresponding to the largest of the multiple preset pressures, and is related to S. 敏感度 One corresponding to; The linear evaluation model is as follows: ； Among them, S 待测 The gas saturation of the target coal and rock. k1, k2, k3, k4, and k5 represent multiple coefficients obtained by fitting multiple reference saturation and multiple sensitivity parameters to make the above equation true; Indicates the ratio of longitudinal to transverse wave velocity to elastic sensitivity; Indicates Poisson's ratio elasticity sensitivity; Indicates the elastic sensitivity of Young's modulus; Indicates the elastic sensitivity of bulk modulus; Indicates shear modulus elastic sensitivity; The power-law evaluation model is as follows: ； Among them, k6, k7, k8, k9, k 10 l1, l2, l3, l4 and l5 represent multiple coefficients obtained by fitting multiple reference saturation and multiple sensitivity parameters, which make the above equation true.

2. The method for obtaining the evaluation model of gas saturation in coal and rock by acoustic nuclear magnetic resonance imaging according to claim 1, characterized in that, The steps of introducing multiple free gases at different preset pressures into the reference container (310) via the metering pump (200), allowing the free gases to diffuse naturally from the reference container (310) into the sample container (320) and reach equilibrium, and then measuring multiple first measured gas pressure values ​​include: With the switch valve (311) closed, free gas is introduced into the reference container (310) to make the gas pressure inside the reference container (310) reach the preset pressure; Open the switch valve (311) to allow the free gas to diffuse naturally into the sample container (320); After the reference container (310) and the sample container (320) reach pressure equilibrium, the first measured air pressure value corresponding to the preset pressure is measured. Repeat the above steps until multiple first measured air pressure values ​​are obtained.

3. The method for obtaining the evaluation model of gas saturation in coal and rock by acoustic nuclear magnetic resonance imaging according to claim 1, characterized in that, The steps of introducing multiple adsorbed gases at different preset pressures into the reference container (310) via the metering pump (200), allowing the adsorbed gases to diffuse naturally from the reference container (310) into the sample container (320) and reach equilibrium, and then measuring multiple second measured gas pressure values, as well as multiple first acoustic signals and multiple first nuclear magnetic resonance T2 spectra fed back by the coal and rock sample, include: With the switch valve (311) closed, adsorption gas is introduced into the reference container (310) to make the gas pressure inside the reference container (310) reach the preset pressure; Open the switch valve (311) to allow the adsorbed gas to diffuse naturally into the sample container (320). After the reference container (310) and the sample container (320) reach pressure equilibrium, the second measured air pressure value, the first acoustic signal and the first nuclear magnetic T2 spectrum corresponding to the preset pressure are measured. Repeat the above steps until multiple second measured air pressure values, multiple first acoustic signals, and multiple first nuclear magnetic T2 spectra are obtained; In the step of repeatedly filling the reference container (310) with the pre-set pressure of adsorbed gas, the multiple pre-set pressures increase sequentially according to the step order.

4. The method for obtaining the evaluation model of gas saturation in coal and rock by acoustic nuclear magnetic resonance imaging according to claim 1, characterized in that, The steps of calculating the adsorption amount corresponding to each different preset pressure based on multiple first measured air pressure values, multiple second measured air pressure values, and the free volume value, and calculating multiple first saturation values ​​corresponding to each preset pressure based on the adsorption amount corresponding to each preset pressure, include: Multiple first free quantities are calculated based on multiple first measured gas pressure values ​​and the free volume values. The first free quantities represent the total amount of gas in a free state in the reference container (310) and the sample container (320). Multiple second free quantities are calculated based on multiple second measured gas pressure values ​​and the free volume value. The second free quantities represent the total amount of gas in a free state in the reference container (310) and the sample container (320). Multiple adsorption amounts corresponding to multiple preset pressures are obtained based on the differences between multiple first free amounts and multiple second free amounts; Multiple first saturation values ​​are calculated based on multiple adsorption amounts.

5. The method for obtaining the evaluation model of gas saturation in coal and rock by acoustic nuclear magnetic resonance imaging according to claim 4, characterized in that, The formula for calculating multiple first saturation values ​​based on multiple adsorption amounts is as follows: ； S R S represents the first saturation value, S represents the adsorption amount corresponding to any preset pressure, and S1 represents the adsorption amount corresponding to the maximum preset pressure.

6. The method for obtaining the evaluation model of coal and rock gas saturation by acoustic nuclear magnetic resonance according to claim 1, characterized in that, The formula for calculating the gas saturation at different preset pressures based on the NMR substrate signal and multiple first NMR T2 spectra is as follows: ； Among them, S NMR A represents the second saturation value. i A represents the peak area of ​​the NMR signal in the first NMR T2 spectrum corresponding to the preset pressure. sat A0 represents the area of ​​the NMR signal peak in the first NMR T2 spectrum corresponding to the largest preset pressure among the multiple preset pressures, and A0 represents the area of ​​the NMR signal peak in the NMR T2 spectrum corresponding to the NMR substrate signal.

7. The method for obtaining the evaluation model of gas saturation in coal and rock by acoustic nuclear magnetic resonance imaging according to claim 1, characterized in that, The step of fitting multiple reference saturations corresponding to multiple preset pressures based on multiple first saturation values ​​and multiple second saturation values ​​includes: The following formula is established based on the first saturation value and the second saturation value corresponding to the preset pressure: Among them, S R S represents the first saturation value. NMR Let a and b represent the second saturation value, where a and b are constants that make the above equation true; The values ​​of a and b are obtained by fitting the above formulas corresponding to multiple preset pressures, and a reference saturation formula is established based on the values ​​of a and b. The reference saturation formula is as follows: Among them, S 参考 This represents the reference saturation.

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