Method and device for determining gas content in methane collector in deep coal seams and readable data media

Abstract

FIELD: mining.SUBSTANCE: group of inventions relates to means for determining gas content in a methane reservoir in deep coal seams. When implementing the method for determining the gas content in a methane reservoir in deep coal seams, a base spectrum of the transverse relaxation time of a dried sample of reservoir rock, spectra of the transverse relaxation time before the establishment of adsorption equilibrium at various pressures and spectra of the transverse relaxation time after the establishment of adsorption equilibrium at various pressures are obtained. Based on the transverse relaxation time spectra before the adsorption equilibrium is established at different pressures and the transverse relaxation time spectra after the adsorption equilibrium is established at different pressures, the free gas signals are determined at different pressures. Based on the base transverse relaxation time spectrum, transverse relaxation time spectra before adsorption equilibrium is established at different pressures, and free gas signals at different pressures, the adsorbed gas signals are determined at different pressures. Based on the base transverse relaxation time spectrum, adsorbed gas signals at different pressures, and transverse relaxation time spectra after adsorption equilibrium has been established at different pressures, corrected transverse relaxation time spectra after adsorption equilibrium has been established at different pressures are determined. Based on the free gas signals at different pressures and the corrected transverse relaxation time spectra after establishing adsorption equilibrium at different pressures, the actual free gas content at different pressures is obtained. Based on the base transverse relaxation time spectrum, free gas signals at different pressures and corrected transverse relaxation time spectra after establishing adsorption equilibrium at different pressures, the actual content of adsorbed gas at different pressures is obtained. Based on the actual content of free gas and the actual content of adsorbed gas at different pressures, a model for determining the gas content is constructed. The dried rock mass from the deep coal seam methane reservoir under test and the pressure in the deep coal seam methane reservoir are obtained. This rock mass from the deep coal seam methane reservoir under test and the pressure in the deep coal seam methane reservoir as input values for the gas content determination model are used to obtain the methane content of the deep coal seam methane reservoir under test.EFFECT: increasing the accuracy of determining gas content in a methane reservoir in deep coal seams.4 cl, 12 dwg

Description

[0001] Technical field

[0002] The present invention relates to the field of oil and gas exploration, and in particular to a method for determining the gas content in methane reservoirs in deep coal seams, to a device for determining the gas content in methane reservoirs in deep coal seams, to a system for determining the gas content in methane reservoirs in deep coal seams, and to a readable data carrier.

[0003] Prerequisites for the creation of the invention

[0004] Deep coalbed methane represents a huge resource, with broad prospects for its development and use as a substitute resource. Unlike natural gas from medium- and shallow-depth coal seams, where adsorbed gas dominates the gas content, methane in deep coal seams often occurs as a combination of adsorbed gas and free gas. Estimating both reserves and quantitative resources involves gas content, a key geological parameter. However, deep coal seam methane reservoirs are formed with multiple pore types, such as micropores, mesopores, and macropores, forming complex pore structures. Adsorbed gas and free gas occur in a "multi-pore system," necessitating quantitative assessment of the free and adsorbed gas contents.Therefore, it is necessary to explore new experimental and evaluation methods to improve the accuracy of well log-based gas content calculations, providing a basis for subsequent reserve calculation, resource quantification, and fracture spacing optimization.

[0005] Nuclear magnetic resonance (NMR) is widely used in various fields of geophysical and geological research, becoming an important method for characterizing microporous structures, fluid properties, and the physical parameters of reservoirs. Furthermore, in recent years, NMR has also been extensively used to study the formation of liquid phases in adsorbent rock samples.

[0006] As a crucial component in the development of unconventional natural gas, accurately predicting the in-situ gas content and condition of deep coalbed methane reservoirs is essential for assessing resource reserves and optimizing production strategies. However, accurate methods for differentiating between adsorbed gas and free gas in deep coalbed methane reservoirs are currently lacking. Identifying these two gas types relies primarily on conventional well logging data, which limits accuracy. Therefore, identifying gas quality and quantity based on accurate experimental calibration is particularly important. One well-known method is the Schlumberger method (Ahmed U., Johnston D., and Colson L.), which combines geochemical logging with other recording methods.Using the Elemental Logging Analysis (ELAN) program to calculate the mineral content of coal, the gas content of coal seams can be determined. Furthermore, based on the Langmuir equation for coal rank, another method is proposed that uses fixed carbon and temperature to determine the value of each parameter in the equation through a least-squares fit, thereby predicting the gas content. Researchers from Ecopetrol (Rodriguez S., Navas-Guzman G., Gomez-Prada A.) applied a nonparametric regression method based on probability statistics and optimization theory, using fixed carbon, volatile matter, and depth data to predict the gas content of a coal seam. Pan Heping et al. analyzed coal quality, experimental gas content data, and corresponding logging data for coal samples in northern China.They found that coal seam gas content is closely related to temperature, pressure, carbon content, and ash content, and developed a method for estimating coal seam gas content. Chinese Patent CN 112213234B discloses a method for determining methane content in deep coal seams. It divides the coring and in-situ desorption processes into five stages based on gas evolution characteristics and identifies two key parameters: the starting time and gas loss time at each stage. Gas desorption and leakage at each stage are then analyzed using these key parameters and reservoir characteristics, and a set of in-situ gas content values ​​for core samples is obtained by analyzing the evolved gas at each stage.However, the aforementioned methods typically rely on conventional logging data from isothermal adsorption and desorption experiments to determine the relationship between time and gas release to estimate the proportion and content of free and adsorbed gas. However, due to the sensitivity of local desorption experiments to lost gas and the difficulties of accurate recovery and correction, problems arise with the accuracy of calibration data, limiting the accuracy of identification.

[0007] Currently, the above-mentioned methods have begun to use isothermal adsorption experiments combined with nuclear magnetic resonance in water-saturated rocks to determine the proportions of free and adsorbed gas. An experimental device for the simultaneous dynamic measurement of isothermal adsorption and nuclear magnetic resonance was developed, and simultaneous dynamic isothermal adsorption and nuclear magnetic resonance experiments were conducted on reservoir rock samples containing adsorbed gas. Nuclear magnetic resonance combined with isothermal adsorption was used to determine the content of free methane and adsorbed methane gas in shale. Combined isothermal adsorption and nuclear magnetic resonance experiments in coal were used to calculate the content of free and adsorbed gas.However, when applying the above-mentioned combined isothermal adsorption and nuclear magnetic resonance experiments for the qualitative and quantitative identification of the presence of a gas phase in rock samples, it is generally assumed that the first peak corresponds to the adsorbed gas signal, while the second peak corresponds to the free gas signal. However, in actual samples, adsorbed gas and free gas coexist in nanopores. Therefore, using this method to determine the proportions of free and adsorbed gas leads to some errors, yielding inaccurate results.

[0008] Essence of the invention

[0009] The aim of the embodiments of the invention is a method and device for determining the gas content in methane reservoirs in deep coal seams and a readable data carrier, designed to at least solve the problem that the proportion of free gas and adsorbed gas determined by known methods has certain errors due to the coexistence of adsorbed gas and free gas in nanopores, which leads to inaccurate results.

[0010] In order to achieve the above object, in the first aspect of the present invention, a method for determining the gas content in a deep coal seam methane reservoir is disclosed, comprising:

[0011] obtaining the base transverse relaxation time spectrum of the dried reservoir rock sample, transverse relaxation time spectra before adsorption equilibrium is established at different pressures, and transverse relaxation time spectra after adsorption equilibrium is established at different pressures;

[0012] based on the transverse relaxation time spectra before adsorption equilibrium is established at different pressures and the transverse relaxation time spectra after adsorption equilibrium is established at different pressures, determining free gas signals at different pressures;

[0013] Based on the base transverse relaxation time spectrum, transverse relaxation time spectra before adsorption equilibrium is established at different pressures and free gas signals at different pressures, determining the adsorbed gas signals at different pressures;

[0014] Based on the base transverse relaxation time spectrum, adsorbed gas signals at different pressures and transverse relaxation time spectra after adsorption equilibrium is established at different pressures, determine the adjusted transverse relaxation time spectra after adsorption equilibrium is established at different pressures;

[0015] Based on the free gas signals at different pressures and the adjusted transverse relaxation time spectra after establishing adsorption equilibrium at different pressures, obtaining the actual free gas content at different pressures;

[0016] Based on the base transverse relaxation time spectrum, free gas signals at different pressures and the adjusted transverse relaxation time spectra after establishing adsorption equilibrium at different pressures, obtaining the actual content of adsorbed gas at different pressures;

[0017] Based on the actual free gas content and the actual adsorbed gas content at different pressures, construct a model for determining the gas content;

[0018] obtaining the mass of dried rock from the deep coal bed methane reservoir under test and the pressure in the deep coal bed methane reservoir; and

[0019] Using this rock mass from the deep coal bed methane reservoir under test and the pressure in the deep coal bed methane reservoir as input values ​​for the gas content determination model to obtain the methane content of the deep coal bed methane reservoir under test.

[0020] As an option, the determination of free gas signals at different pressures based on the transverse relaxation time spectra before adsorption equilibrium is established at different pressures and the transverse relaxation time spectra after adsorption equilibrium is established at different pressures includes:

[0021] for each pressure point:

[0022] taking the difference between the area of ​​the first peak of the transverse relaxation time spectrum before the adsorption equilibrium is established at the n-th pressure point and the area of ​​the first peak of the transverse relaxation time spectrum after the adsorption equilibrium is established at the (n-1)-th pressure point as the increase in the area of ​​the first peak of the free gas at the n-th pressure point; and

[0023] Taking the sum of the increases in the area of ​​the first free gas peak from the first pressure point to the n-th pressure point as the free gas signal at the n-th pressure point.

[0024] As an option, the determination of free gas signals at different pressures based on the transverse relaxation time spectra before adsorption equilibrium is established at different pressures and the transverse relaxation time spectra after adsorption equilibrium is established at different pressures includes:

[0025] Calculate the free throttle signal using the following formula:

[0026]

[0027] where is FTSƒ n - free gas signal at the n-th pressure point; FTSI t - the area of ​​the first peak of the transverse relaxation time spectrum before the establishment of adsorption equilibrium at the i-th pressure point; FTSA i-l - the area of ​​the first peak of the transverse relaxation time spectrum after establishing adsorption equilibrium at the (il)-th pressure point.

[0028] As an option, the determination of adsorbed gas signals at different pressures based on the baseline transverse relaxation time spectrum, transverse relaxation time spectra before adsorption equilibrium is established at different pressures and free gas signals at different pressures includes:

[0029] for each pressure point:

[0030] Subtract the area of ​​the first peak of the base transverse relaxation time spectrum and the free gas signal at the n-th pressure point from the first area of ​​the peak of the transverse relaxation time spectrum before establishing adsorption equilibrium at the n-th pressure point to obtain the adsorbed gas signal at the n-th pressure point.

[0031] As an option, determining the corrected transverse relaxation time spectra after adsorption equilibrium at different pressures based on the base transverse relaxation time spectrum, adsorbed gas signals at different pressures, and transverse relaxation time spectra after adsorption equilibrium at different pressures includes:

[0032] for each pressure point:

[0033] calculating the sum of the adsorbed gas signal and the area of ​​the first peak of the base spectrum of the transverse relaxation time at the n-th pressure point, and constructing the first curve for the n-th pressure point based on the sum of the areas of the adsorbed gas signal and the area of ​​the first peak of the base spectrum of the transverse relaxation time;

[0034] calculating the sum of the areas of the first peak of the transverse relaxation time spectra after establishing adsorption equilibrium from the first pressure point to the n-th pressure point and constructing the second curve for the n-th pressure point based on the sum of the areas of the first peaks of the transverse relaxation time spectra after establishing adsorption equilibrium;

[0035] determining the transverse relaxation time corresponding to the intersection point of the first curve and the second curve for the n-th pressure point; and

[0036] taking the transverse relaxation time as the cutoff value of the transverse relaxation time of the adsorption peak and the free peak in the transverse relaxation time spectrum after establishing adsorption equilibrium for the n-th pressure point to obtain a corrected transverse relaxation time spectrum after establishing adsorption equilibrium at the n-th pressure point; wherein the cutoff value of the transverse relaxation time is configured to separate the area of ​​the first peak and the area of ​​the second peak of the transverse relaxation time spectrum after establishing adsorption equilibrium.

[0037] As an option, obtaining the actual free gas content at different pressures based on the free gas signals at different pressures and the corrected transverse relaxation time spectra after adsorption equilibrium has been established at different pressures includes:

[0038] GasA n = k*(FTSƒ n + STS' n );

[0039] Where is GasA n - actual content of free gas at the n-th pressure point; k - conversion factor; FTSƒ n - free gas signal at the n-th pressure point; STS' n - the area of ​​the second peak of the corrected spectrum of transverse relaxation time after establishing adsorption equilibrium at the n-th pressure point.

[0040] As an option, obtaining the actual adsorbed gas content at different pressures based on the base transverse relaxation time spectrum, free gas signals at different pressures and the adjusted transverse relaxation time spectra after establishing adsorption equilibrium at different pressures includes:

[0041] GasF n = k* (FTSA' n - FTSD - FTSƒ n )

[0042] Where is GasF n - actual content of adsorbed gas at the n-th pressure point; k - conversion factor; FTSA ' n- the area of ​​the first peak of the corrected transverse relaxation time spectrum after establishing adsorption equilibrium at the n-th pressure point; FTSD - the total area of ​​the base transverse relaxation time spectrum; FTSƒ n - free gas signal at the n-th pressure point.

[0043] As an option, the expression for the gas content determination model is:

[0044] F gas = (a*P) / m;

[0045] A gas = [c*ln(P)+d] / m;

[0046] where F gas - the actual content of free gas in the tested reservoir rock; A gas - actual content of adsorbed gas in the tested reservoir rock; a, c, and d are fitting coefficients; P is the formation pressure in the tested reservoir rock; m is the mass of the tested reservoir rock after drying.

[0047] A second aspect of the present disclosure relates to a device for determining gas content in a deep coal bed methane reservoir, comprising:

[0048] time spectrum acquisition module, configured to acquire the base transverse relaxation time spectrum of the dried reservoir rock sample, the transverse relaxation time spectra before adsorption equilibrium is established at different pressures, and the transverse relaxation time spectra after adsorption equilibrium is established at different pressures;

[0049] free gas signal detection module, configured to detect free gas signals at different pressures based on the transverse relaxation time spectra before adsorption equilibrium is established at different pressures and the transverse relaxation time spectra after adsorption equilibrium is established at different pressures;

[0050] adsorbed gas signal detection module, configured to detect adsorbed gas signals at different pressures based on the base transverse relaxation time spectrum, transverse relaxation time spectra before adsorption equilibrium is established at different pressures, and free gas signals at different pressures;

[0051] time spectrum correction module, configured to determine corrected transverse relaxation time spectra after adsorption equilibrium is established at different pressures based on the base transverse relaxation time spectrum, adsorbed gas signals at different pressures, and transverse relaxation time spectra after adsorption equilibrium is established at different pressures;

[0052] actual free gas content determination module, configured to obtain the actual free gas content at different pressures based on the free gas signals at different pressures and the adjusted transverse relaxation time spectra after adsorption equilibrium is established at different pressures;

[0053] Actual adsorbed gas content determination module, configured to obtain the actual adsorbed gas content at different pressures based on the base transverse relaxation time spectrum, free gas signals at different pressures, and the adjusted transverse relaxation time spectra after establishing adsorption equilibrium at different pressures;

[0054] gas content determination model construction module, configured to construct a gas content determination model based on the actual free gas content and the actual adsorbed gas content under different pressures;

[0055] a data acquisition module configured to acquire the mass of dried rock from the deep coal bed methane reservoir under test and the pressure in the deep coal bed methane reservoir; and

[0056] A reservoir gas content determination module configured to use the rock mass of a deep coalbed methane reservoir under test and the pressure of the deep coalbed methane reservoir as input data to a gas content determination model to obtain the gas content of the deep coalbed methane reservoir under test.

[0057] A third aspect of the present disclosure relates to a system for determining gas content in a deep coal bed methane reservoir, comprising:

[0058] An experimental apparatus for measuring isothermal adsorption, having a cylinder for a reference sample inside;

[0059] a device for measuring nuclear magnetic resonance in a rock, having a sample cylinder with a constant temperature inside, configured to measure a baseline transverse relaxation time spectrum of a dried reservoir rock sample, transverse relaxation time spectra before adsorption equilibrium is established at different pressures, and transverse relaxation time spectra after adsorption equilibrium is established at different pressures;

[0060] a gas source connected to the experimental isothermal adsorption measuring device and the rock nuclear magnetic resonance measuring device via a pipeline and configured to supply compressed gas to the reference sample cylinder and the constant temperature sample cylinder;

[0061] a pressure sensing mechanism located in a pipeline and configured to sense a gas pressure; and

[0062] The above-mentioned device for detecting the methane content in a deep coal seam reservoir, which is connected with a device for measuring nuclear magnetic resonance in a rock.

[0063] In another aspect, the present invention relates to a readable storage medium storing instructions that cause a machine to perform the proposed method for determining the gas content of a deep coal bed methane reservoir.

[0064] Compared with the known technical solutions, the technical solutions according to the present invention achieve the following positive results:

[0065] By performing two transverse relaxation time measurements, before and after adsorption equilibrium is established following methane injection at different pressures, this technical solution enables the separation of gas signals in different states in the first peak. This allows for the redefinition of the T2 cutoff values ​​for adsorbed gas and free gas, enabling the accurate calculation of free gas and adsorbed gas contents. This solution improves the accuracy of gas content calculations in deep coalbed methane reservoirs and enhances the qualitative and quantitative identification of gas generation modes in the reservoir, providing technical support for the accurate evaluation of reservoirs and reserves in oil fields.

[0066] Other features and advantages of the embodiments of the invention will be set forth in detail below in the detailed description section.

[0067] Brief description of drawings

[0068] The accompanying drawings are included to provide a better understanding of the embodiments of the invention and form a part of this description, and together with the detailed description below serve to explain, but not limit, the embodiments of the invention. In the drawings:

[0069] Fig. 1 shows a flow chart of the method for determining the gas content in a deep coal seam methane reservoir according to the present invention;

[0070] Fig. 2 shows a T2 nuclear magnetic resonance spectrum for a dried reservoir rock sample measured according to the present invention;

[0071] Fig. 3 shows a T2 nuclear magnetic resonance spectrum measured immediately after gas injection at different pressures according to the present invention;

[0072] Fig. 4 shows a T2 nuclear magnetic resonance spectrum measured after establishing adsorption equilibrium at different pressures according to the present invention;

[0073] Fig. 5 shows the envelope of the areas of the T2 spectrum between a direct measurement at a certain pressure point and an adsorption equilibrium measurement at a previous pressure point, according to the present invention;

[0074] Fig. 6 shows a diagram of separating the first peak signal according to the present invention;

[0075] Fig. 7 shows a T2 cutoff separation diagram for free gas and adsorbed gas signals according to the present invention;

[0076] Fig. 8 shows a diagram of the relationship between the cutoff values ​​T2 for the adsorbed gas and free gas peaks and the pressure according to the present invention;

[0077] Fig. 9 shows a diagram of the relationship between the adsorbed gas content and the pressure according to the present invention;

[0078] Fig. 10 shows a diagram of the relationship between the free gas content and the pressure according to the present invention;

[0079] Fig. 11 shows a diagram of the calculation result, in application to well A, for the method according to the present invention; and

[0080] Fig. 12 shows a block diagram of an apparatus for determining the gas content in a deep coal seam methane reservoir according to the present invention.

[0081] The positions indicate:

[0082] 10 - time spectrum receiving module;

[0083] 20 - free gas signal detection module;

[0084] 30 - Adsorbed gas signal detection module;

[0085] 40 - time spectrum correction module;

[0086] 50 - module for determining the actual content of free gas;

[0087] 60 - module for determining the actual content of adsorbed gas;

[0088] 70 - module for constructing a model for determining gas content;

[0089] 80 - data receiving module; and

[0090] 90 - module for determining the gas content in the reservoir. Detailed description of embodiments of the invention

[0091] Below, specific embodiments of the invention are described in detail with reference to the drawings. It is understood that the specific embodiments of the invention described herein are merely illustrative and are not intended to limit the present invention.

[0092] Fig. 1 is a flow chart showing a method for determining the gas content in a deep coal bed methane reservoir according to the present invention; Fig. 2 is a T2 nuclear magnetic resonance spectrum for a dried reservoir rock sample measured according to the present invention; Fig. 3 is a T2 nuclear magnetic resonance spectrum measured immediately after gas injection at different pressures according to the present invention; Fig. 4 is a T2 nuclear magnetic resonance spectrum measured after adsorption equilibrium has been established at different pressures according to the present invention; Fig. 3 is a T2 spectrum area envelope between a direct measurement at a certain pressure point and an adsorption equilibrium measurement at the previous pressure point according to the present invention; Fig. 6 is a first peak signal separation diagram according to the present invention; Fig.7 shows a diagram of the separation of T2 cutoffs for free gas and adsorbed gas signals according to the present invention; Fig. 8 shows a diagram of the relationships between the T2 cutoff values ​​for the adsorbed gas and free gas peaks as a function of pressure.

[0093] according to the present invention; Fig. 9 is a diagram showing the relationship between the adsorbed gas content and the pressure according to the present invention; Fig. 10 is a diagram showing the relationship between the free gas content and the pressure according to the present invention; Fig. 11 is a diagram showing the calculation result of the method applied to the well A according to the present invention; and Fig. 12 is a block diagram of the apparatus for determining the gas content in a deep coal bed methane reservoir according to the present invention;

[0094] As shown in Fig. 1, embodiments of the invention relate to a method for determining gas content in a deep coal bed methane reservoir, comprising the following:

[0095] In step 1, the base transverse relaxation time spectrum of the dried reservoir rock sample, the transverse relaxation time spectra before adsorption equilibrium is established at different pressures, and the transverse relaxation time spectra after adsorption equilibrium is established at different pressures are obtained;

[0096] In particular, in this embodiment of the invention, a reservoir rock sample is selected. This reservoir rock sample is a deep coal-bearing rock sample capable of adsorbing methane gas and having practical value for exploitation. The sample is cut into uniform pieces without distortion of shape and without impacts, damage, or cracks. The reservoir rock sample is dried at a drying temperature determined based on the conditions in the reservoir from which the rock sample is collected. The temperature should be adjusted to ensure the removal of free water and adsorbed water from the rock sample, thereby preventing water molecules from occupying adsorption sites, and also ensuring that substances such as structured water and kerogen in the rock sample do not denature or separate.The dried rock sample is placed in a special holder and the baseline transverse relaxation time (T2) is measured to obtain a baseline transverse relaxation time spectrum for the reservoir rock sample, as shown in Fig. 2, where the abscissa represents time and the ordinate represents amplitude.

[0097] Additionally, measure the transverse relaxation time (T2) immediately after methane injection at each designated pressure point. After checking the external pressure with the instrument, from the moment the injection pressure reaches equilibrium and the gas source is disconnected, measure the transverse relaxation time (T2) for two minutes, ensuring there is no change in the pressure gauge reading during this process.

[0098] Therefore, the increase in the adsorbed gas signal due to its adsorption can be neglected, and the transverse relaxation time spectra are obtained before the adsorption equilibrium is established and at different pressures, as shown in Fig. 3, where the time is plotted on the abscissa and the amplitude on the ordinate. Subsequent measurements of the transverse relaxation time (T2) are performed after the adsorption equilibrium is established, obtaining the transverse relaxation time spectra after the adsorption equilibrium is established at each pressure point, as shown in Fig. 4, where the time is plotted on the abscissa and the amplitude on the ordinate. In particular, the experiment can be carried out at a sequence of pressures increasing from low to high to simulate the actual conditions in the reservoir.

[0099] In step 2, the free gas signals are determined at different pressures based on the transverse relaxation time spectra before adsorption equilibrium is established at different pressures and the transverse relaxation time spectra after adsorption equilibrium is established at different pressures;

[0100] In this embodiment of the invention, the following steps are performed to determine free gas signals at different pressures, including:

[0101] for each pressure:

[0102] taking the difference between the area of ​​the first peak of the transverse relaxation time spectrum before the adsorption equilibrium is established at the n-th pressure point and the area of ​​the first peak of the transverse relaxation time spectrum after the adsorption equilibrium is established at the (n-1)-th pressure point as the increase in the area of ​​the first peak of the free gas at the n-th pressure point; and

[0103] Taking the sum of the increases in the area of ​​the first free gas peak from the first pressure point to the n-th pressure point as the free gas signal at the n-th pressure point.

[0104] In particular, n is a positive integer, and the calculation is performed repeatedly for each pressure point from 1 to N, with the maximum value of n being N. The free gas signals from the first to the nth pressure point are obtained and combined to form free gas signals at different pressures.

[0105] In another embodiment of the invention, free gas signals at different pressures may also be determined in the following manner, including:

[0106] Calculate the free throttle signal using the following formula: where is FTSƒ n - free gas signal at the n-th pressure point; FTSI t - the area of ​​the first peak of the transverse relaxation time spectrum before the establishment of adsorption equilibrium at the i-th pressure point; FTSA i-l- the area of ​​the first peak of the transverse relaxation time spectrum after establishing adsorption equilibrium at the (il)-th pressure point.

[0107] Fig. 5 schematically shows the signal diagram of free gas at a pressure of 11.703 MPa and 13.825 MPa.

[0108] In step 3, the adsorbed gas signals are determined at different pressures based on the baseline transverse relaxation time spectrum, the transverse relaxation time spectra before adsorption equilibrium is established at different pressures, and the free gas signals at different pressures,

[0109] in this embodiment of the invention, for each pressure point:

[0110] To obtain the signal of the adsorbed gas at the n-th pressure point, subtract the area of ​​the first peak in the base spectrum of the transverse relaxation time and the signal of the free gas at the n-th pressure point from the area of ​​the first peak of the spectrum of the transverse relaxation time until adsorption equilibrium is established at the n-th pressure point.

[0111] In particular, n is a positive integer, and the calculations are performed repeatedly for each pressure point from 1 to N. The free gas signals at the first to nth pressure points are obtained and combined to form adsorbed gas signals at different pressures.

[0112] As shown in Fig. 6, a first peak signal separation diagram is obtained, from which the area composition of the first peak can be clearly identified.

[0113] In step 4, the adjusted transverse relaxation time spectra after adsorption equilibrium is established at different pressures are determined based on the base transverse relaxation time spectrum, the adsorbed gas signals at different pressures, and the transverse relaxation time spectra after adsorption equilibrium is established at different pressures;

[0114] in this embodiment of the invention, the step of determining the corrected transverse relaxation time spectra after establishing adsorption equilibrium at different pressures includes:

[0115] for each pressure point:

[0116] calculating the sum of the adsorbed gas signal and the area of ​​the first peak of the base spectrum of the transverse relaxation time at the n-th pressure point, and constructing the first curve for the n-th pressure point based on the sum of the areas of the adsorbed gas signal and the area of ​​the first peak of the base spectrum of the transverse relaxation time;

[0117] calculating the sum of the areas of the first peak of the transverse relaxation time spectra after establishing adsorption equilibrium from the first pressure point to the n-th pressure point and constructing the second curve for the n-th pressure point based on the sum of the areas of the first peaks of the transverse relaxation time spectra after establishing adsorption equilibrium;

[0118] determining the transverse relaxation time corresponding to the intersection point of the first curve and the second curve for the n-th pressure point; and

[0119] taking this transverse relaxation time as the cutoff value of the transverse relaxation time of the adsorption peak and the free peak in the transverse relaxation time spectrum after establishing adsorption equilibrium at the n-th pressure point to obtain a corrected transverse relaxation time spectrum after establishing adsorption equilibrium at the n-th pressure point; wherein the cutoff value of the transverse relaxation time is configured to separate the area of ​​the first peak and the area of ​​the second peak of the transverse relaxation time spectrum after establishing adsorption equilibrium.

[0120] In particular, here n is a positive integer, and the calculations are performed repeatedly for each pressure point from 1 to N, obtaining the first and second curves under pressures with indices from 1 to n. The transverse relaxation time corresponding to the intersection of the first and second curves in the same coordinate system is taken as the transverse relaxation time cutoff value for the adsorbed and free gas peaks in the transverse relaxation time spectra after equilibrium is established. This enables accurate separation of the areas of the new first and second peaks, effectively separating the adsorbed gas signal regions from the free gas signal regions in the T2 spectra at different pressure points. As shown in Fig. 7, the newly determined transverse relaxation time cutoff value is more shifted toward the first peak of the transverse relaxation time spectrum after adsorption equilibrium is established.

[0121] In prior art, it is generally assumed by default that the lowest point between the first and second peaks is used to separate the area of ​​the first peak from the area of ​​the second peak. However, this approach results in less accurate calculations of these areas. Therefore, in this embodiment, by redefining the T2 cutoff value for adsorbed gas and free gas to accurately separate the adsorbed gas signal region from the free gas signal region in the T2 spectrum at each pressure point, the method ensures accurate calculation of the free gas and adsorbed gas contents. This improves the accuracy of gas content calculations in deep coalbed methane reservoirs and improves the accuracy of the qualitative and quantitative identification of gas occurrence conditions in the reservoir, facilitating accurate reservoir evaluation and reserve assessment in deposits.

[0122] In another embodiment of the invention, by approximating the transverse relaxation time cutoff values ​​at different pressures, it can be determined that the relationship between the transverse relaxation time cutoff value (T2) and the pressure at each pressure point is linear, as shown by the following formula:

[0123] T2cutoƒƒ = j*P + s

[0124] where T2cutoƒƒ is the transverse relaxation time cutoff value (T2); P is the pressure; j and s are dimensionless coefficients obtained by fitting. Fig. 8 illustrates the variation pattern of the transverse relaxation time cutoff value (T2) at a pressure of 13.825 MPa.

[0125] In step 5, the actual free gas content at different pressures is obtained based on the free gas signals at different pressures and the adjusted transverse relaxation time spectra after adsorption equilibrium is established at different pressures;

[0126] In particular, in this embodiment of the invention, the proportion of free gas can first be calculated using the following formula:

[0127]

[0128] Then the proportion of free gas is converted into the actual content of free and adsorbed gas:

[0129] GasA n = k* RFp n * (FTSA' n - FTSD + STS' n );

[0130] and the following formula can be obtained:

[0131] GasA n = k* (FTSƒ n +STS' n )

[0132] Where is GasA n - the actual free gas content at the n-th pressure point; k is the conversion factor; and, in particular, k=h*Vm / 100, k is the conversion factor between the peak area and the methane content and is dimensionless; h is a constant obtained by fitting the nuclear magnetic resonance signal to the amount of methane; FTSA ' n- the area of ​​the first peak of the corrected transverse relaxation time spectrum after establishing adsorption equilibrium at the n-th pressure point; FTSD - the total area of ​​the base transverse relaxation time spectrum; FTSƒ n - free gas signal at the n-th pressure point; STS' n - the area of ​​the second peak of the corrected spectrum of transverse relaxation time after establishing adsorption equilibrium at the n-th pressure point.

[0133] In step 6, the actual content of adsorbed gas at different pressures is obtained based on the base transverse relaxation time spectrum, free gas signals at different pressures, and the adjusted transverse relaxation time spectra after adsorption equilibrium is established at different pressures;

[0134] In particular, in this embodiment of the invention, the proportion of free gas can be first calculated using the following formula:

[0135]

[0136] Then the proportion of free gas is converted into the actual content of free and adsorbed gas:

[0137] GasF n = k *RAp n * (FTSA' n -FTSD+STS' n )

[0138] and the following calculation formula is obtained:

[0139] GasF n = k * (FTSA' n -FTSD-FTSƒ n )

[0140] where is GasF n - the actual free gas content at the n-th pressure point; k is the conversion factor; and, in particular, k=h*Vm / 100 k is the conversion factor between the peak area and the methane content and is dimensionless; h is a constant obtained by fitting the nuclear magnetic resonance signal to the amount of methane; FTSA' n and is the area of ​​the first peak of the corrected transverse relaxation time spectrum after establishing adsorption equilibrium at the n-th pressure point; FTSD is the total area of ​​the base transverse relaxation time spectrum; FTSƒn - free gas signal at the n-th pressure point.

[0141] In step 7, a gas content determination model is constructed based on the actual adsorbed gas content and the actual free gas content at different pressures;

[0142] In this embodiment of the invention, the expression for the gas content determination model is:

[0143] F gas = (a*P) / m;

[0144] A gas = [c*ln(P) + d] / m;

[0145] where F gas - the actual content of free gas in the tested reservoir rock; A gas - actual content of adsorbed gas in the tested reservoir rock; a, c, and d are fitting coefficients; P is the formation pressure in the tested reservoir rock; m is the mass of the tested reservoir rock after drying.

[0146] As shown in Fig. 9 and 10, the gas content determination model can be represented by the curves shown in the drawings so that the actual free gas content and the actual adsorbed gas content can be obtained under different pressures.

[0147] In step 8, the dried rock mass of the deep coal bed methane reservoir to be tested and the pressure in the deep coal bed methane reservoir are obtained; and

[0148] In step 9, use the rock mass of the deep coal bed methane reservoir under test and the pressure in the deep coal bed methane reservoir as input values ​​for the gas content determination model to obtain the methane content of the deep coal bed methane reservoir under test.

[0149] As shown in Fig. 11, the calculation results for well A in a certain oilfield are obtained by applying the gas content determination model proposed in the invention. The figure, from left to right, shows lithology data, depth data, resistivity curve data, CNL, DEN and DT (three groups of porosity curve data), SW and POR (porosity and saturation data), T2_CUT and CMR (nuclear magnetic resonance logging data), actual free gas content, and adsorbed gas content calculated based on nuclear magnetic resonance. Specifically, the yellow area in the graph represents the calculated actual adsorbed gas content, and the green area represents the calculated actual free gas content.Lithology Profile Data: The data on the graph from left to right are: SH represents shale, SAND represents sandstone, COAL represents coal seam, SILT represents siltstone, LIME represents limestone, DOLO represents dolomite, and TZNY represents carboniferous mudstone.

[0150] As shown in Fig. 12, the second aspect of the present invention relates to a device for determining the methane content in a deep coal seam reservoir, comprising:

[0151] time spectrum obtaining module 10, configured to obtain a base transverse relaxation time spectrum of the dried reservoir rock sample, transverse relaxation time spectra before adsorption equilibrium is established at different pressures, and transverse relaxation time spectra after adsorption equilibrium is established at different pressures;

[0152] a free gas signal detection module 20, configured to detect free gas signals at different pressures based on the transverse relaxation time spectra before adsorption equilibrium is established at different pressures and the transverse relaxation time spectra after adsorption equilibrium is established at different pressures;

[0153] an adsorbed gas signal detection module 30, configured to detect adsorbed gas signals at different pressures based on a base transverse relaxation time spectrum, transverse relaxation time spectra before adsorption equilibrium is established at different pressures, and free gas signals at different pressures;

[0154] time spectrum correction module 40, configured to determine corrected transverse relaxation time spectra after adsorption equilibrium is established at different pressures based on the base transverse relaxation time spectrum, adsorbed gas signals at different pressures, and transverse relaxation time spectra after adsorption equilibrium is established at different pressures;

[0155] an actual free gas content determination module 50, configured to obtain an actual free gas content at different pressures based on free gas signals at different pressures and adjusted transverse relaxation time spectra after establishing adsorption equilibrium at different pressures;

[0156] an actual adsorbed gas content determination module 60, configured to obtain an actual adsorbed gas content at different pressures based on a base transverse relaxation time spectrum, free gas signals at different pressures, and adjusted transverse relaxation time spectra after establishing adsorption equilibrium at different pressures;

[0157] gas content determination model construction module 70, configured to construct a gas content determination model based on the actual free gas content and the actual adsorbed gas content at different pressures;

[0158] a data acquisition module 80 configured to acquire a mass of dried rock from a deep coal bed methane reservoir under test and a pressure in the deep coal bed methane reservoir; and

[0159] a reservoir gas content determination module 90 configured to use a rock mass from a deep coal bed methane reservoir under test and a pressure in the deep coal bed methane reservoir as input values ​​for a gas content determination model to obtain a methane content in the deep coal bed methane reservoir under test.

[0160] Furthermore, the present invention relates to a system for determining the gas content in a deep coal seam methane reservoir, comprising:

[0161] An experimental apparatus for measuring isothermal adsorption, having a cylinder for a reference sample inside;

[0162] a device for measuring nuclear magnetic resonance in a rock, having a sample cylinder with a constant temperature inside, configured to measure a baseline transverse relaxation time spectrum of a dried reservoir rock sample, transverse relaxation time spectra before adsorption equilibrium is established at different pressures, and transverse relaxation time spectra after adsorption equilibrium is established at different pressures;

[0163] a gas source connected to an experimental apparatus for measuring isothermal adsorption and a nuclear magnetic resonance measurement apparatus in a rock via a pipeline, configured to supply compressed gas to a reference sample cylinder and a constant temperature sample cylinder;

[0164] a pressure sensing mechanism located in the pipeline and configured to sense the gas pressure; and

[0165] Device for detecting the methane content in a deep coal seam reservoir, which is connected with a device for measuring nuclear magnetic resonance in a rock.

[0166] The experimental apparatus for measuring isothermal adsorption is modified from a conventional apparatus by removing part of the sample cylinder with a constant-temperature water bath (oil bath) and replacing it with a custom-made sample cylinder without a nuclear magnetic resonance signal. The constant-temperature process is ensured by the internal constant-temperature module of the nuclear magnetic resonance measuring apparatus.

[0167] The nuclear magnetic resonance measurement apparatus in rock contains a nuclear magnetic resonance measurement apparatus (the nuclear magnetic resonance apparatus is used in this experiment). The holder is modified to user-specified dimensions to fit a custom-made non-magnetic sample cylinder used in the isothermal adsorption experiment. An extended tube is used to place the sample cylinder into the custom-made nuclear magnetic resonance measurement holder for combined measurements. Specifically, a T-connector is used to supply gas to the sample cylinder, and an external high-precision pressure gauge is connected to observe changes in the internal pressure of the sample cylinder. Pre-treatment includes core drying and leak testing of the experimental apparatus.

[0168] The classification and implementation methods of the data analysis and processing module include dependent modules. The gas sources consist of a methane (CH4) cylinder and a hydrogen (H2) cylinder. Additionally, a booster pump and a vacuum pump are installed in the pipeline. The booster pump is used to increase the pressure in the pipeline, while the vacuum pump is used to maintain a vacuum in the pipeline. Furthermore, valves are installed in the gas inlet and outlet ports of each component to enable on / off control and flow rate adjustment.

[0169] In another aspect, the present invention relates to a readable storage medium storing instructions for causing a computer to perform the method for determining the gas content of a deep coal bed methane reservoir described above.

[0170] Alternative embodiments of the invention are described above in detail in conjunction with the drawings. However, the embodiments of the invention are not limited to the specific details of the above embodiments. Many simple changes can be made to the technical solutions described in the embodiments within the technical concept of the embodiments, all of which are within the scope of the present invention. Furthermore, it should be noted that the specific technical functions described above in the detailed description can be combined in any suitable manner without any contradiction. To avoid unnecessary repetition, various possible combinations of the embodiments of the invention have not been separately described.

[0171] Furthermore, various embodiments of the invention can be arbitrarily combined, and as long as they do not violate the essence of the embodiments of the invention, they should be regarded as the content disclosed in the embodiments of the invention.

Claims

1. A method for determining the gas content of a methane reservoir in deep coal seams, comprising: obtaining a base spectrum of transverse relaxation time of a dried sample of reservoir rock, spectra of transverse relaxation time before the establishment of adsorption equilibrium at different pressures and spectra of transverse relaxation time after the establishment of adsorption equilibrium at different pressures; based on the transverse relaxation time spectra before the establishment of adsorption equilibrium at different pressures and the transverse relaxation time spectra after the establishment of adsorption equilibrium at different pressures, determination of free gas signals at different pressures; based on the base transverse relaxation time spectrum, transverse relaxation time spectra before adsorption equilibrium is established at different pressures and free gas signals at different pressures, determination of adsorbed gas signals at different pressures; based on the base transverse relaxation time spectrum, adsorbed gas signals at different pressures and transverse relaxation time spectra after establishing adsorption equilibrium at different pressures, determining the corrected transverse relaxation time spectra after establishing adsorption equilibrium at different pressures; based on free gas signals at different pressures and corrected transverse relaxation time spectra after establishing adsorption equilibrium at different pressures, obtaining the actual content of free gas at different pressures; based on the base transverse relaxation time spectrum, free gas signals at different pressures and adjusted transverse relaxation time spectra after establishing adsorption equilibrium at different pressures, obtaining the actual content of adsorbed gas at different pressures; based on the actual content of free gas and the actual content of adsorbed gas at different pressures, construction of a model for determining the gas content; obtaining a dried rock mass from a test deep coal bed methane reservoir and a pressure in the deep coal bed methane reservoir; and using this rock mass from the test deep coal seam methane reservoir and the pressure in the deep coal seam methane reservoir as input values ​​for the gas content determination model to obtain the methane content in the test deep coal seam methane reservoir.

2. The method according to claim 1, in which the determination of free gas signals at different pressures based on the transverse relaxation time spectra before the establishment of adsorption equilibrium at different pressures and the transverse relaxation time spectra after the establishment of adsorption equilibrium at different pressures includes for each pressure point: taking the difference between the area of ​​the first peak of the transverse relaxation time spectrum before the establishment of adsorption equilibrium at the n-th pressure point and the area of ​​the first peak of the transverse relaxation time spectrum after the establishment of adsorption equilibrium at the (n-1)-th pressure point as the increase in the area of ​​the first peak of free gas at the n-th pressure point; and taking the sum of the increases in the area of ​​the first free gas peak from the first pressure point to the n-th pressure point as the free gas signal at the n-th pressure point.

3. The method according to claim 1, wherein determining free gas signals at different pressures based on transverse relaxation time spectra before adsorption equilibrium is established at different pressures and transverse relaxation time spectra after adsorption equilibrium is established at different pressures includes: Calculate the free gas signal using the following formula: , where is FTSƒ n - free gas signal at the n-th pressure point; FTSI i - the area of ​​the first peak of the transverse relaxation time spectrum before the establishment of adsorption equilibrium at the i-th pressure point; FTSA i-l - the area of ​​the first peak of the transverse relaxation time spectrum after establishing adsorption equilibrium at the (i-1)-th pressure point.

4. The method according to claim 1, in which the determination of adsorbed gas signals at different pressures based on the base transverse relaxation time spectrum, transverse relaxation time spectra before adsorption equilibrium is established at different pressures and free gas signals at different pressures includes for each pressure point: subtracting the area of ​​the first peak of the base transverse relaxation time spectrum and the free gas signal at the n-th pressure point from the first area of ​​the peak of the transverse relaxation time spectrum before establishing adsorption equilibrium at the n-th pressure point to obtain the adsorbed gas signal at the n-th pressure point.

5. The method according to claim 1, in which the determination of the corrected transverse relaxation time spectra after establishing adsorption equilibrium at different pressures based on the base transverse relaxation time spectrum, adsorbed gas signals at different pressures and transverse relaxation time spectra after establishing adsorption equilibrium at different pressures includes for each pressure point: calculating the sum of the adsorbed gas signal and the area of ​​the first peak of the base spectrum of transverse relaxation time at the n-th pressure point and constructing the first curve at the n-th pressure point based on the sum of the areas of the adsorbed gas signal and the area of ​​the first peak of the base spectrum of transverse relaxation time; calculating the sum of the areas of the first peak of the transverse relaxation time spectra after establishing adsorption equilibrium from the first pressure point to the n-th pressure point and constructing a second curve at the n-th pressure point based on the sum of the areas of the first peaks of the transverse relaxation time spectra after establishing adsorption equilibrium; determining the transverse relaxation time corresponding to the point of intersection of the first curve and the second curve at the n-th pressure point; and taking the transverse relaxation time as the cutoff value of the transverse relaxation time of the adsorption peak and the free peak in the transverse relaxation time spectrum after establishing adsorption equilibrium at the n-th pressure point to obtain the corrected transverse relaxation time spectrum after establishing adsorption equilibrium at the n-th pressure point; wherein the cutoff value of the transverse relaxation time is configured to separate the area of ​​the first peak and the area of ​​the second peak of the transverse relaxation time spectrum after the adsorption equilibrium is established.

6. The method according to claim 1, wherein obtaining the actual free gas content at different pressures based on free gas signals at different pressures and corrected transverse relaxation time spectra after establishing adsorption equilibrium at different pressures includes: GasA n = k⋅(FTSƒ n + STS' n ), where is GasA n - actual content of free gas at the n-th pressure point; k - conversion factor; FTSƒ n - free gas signal at the n-th pressure point; STS' n - the area of ​​the second peak of the corrected spectrum of the transverse relaxation time after establishing adsorption equilibrium at the n-th pressure point.

7. The method according to claim 1, wherein obtaining the actual content of adsorbed gas at different pressures based on the base transverse relaxation time spectrum, free gas signals at different pressures and corrected transverse relaxation time spectra after establishing adsorption equilibrium at different pressures includes: GasF n = k⋅(FTSA' n - FTSD - FTSƒ n ), where is GasF n - actual content of adsorbed gas at the n-th pressure point; k - conversion factor; FTSA' n - the area of ​​the first peak of the corrected transverse relaxation time spectrum after establishing adsorption equilibrium at the n-th pressure point; FTSD - the total area of ​​the base transverse relaxation time spectrum; FTSƒ n - free gas signal at the n-th pressure point.

8. The method according to claim 1, wherein the expression for the gas content determination model is: F gas= (a⋅P) / m; A gas = [c⋅ln(P) + d] / m; where F gas - the actual content of free gas in the tested reservoir rock; A gas - actual content of adsorbed gas in the tested reservoir rock; a, c and d are fitting coefficients; P is formation pressure in the tested reservoir rock; m is the mass of the tested reservoir rock after drying.

9. A device for determining the gas content in a deep coal seam methane reservoir, comprising: a time spectrum obtaining module configured to obtain a base transverse relaxation time spectrum of a dried reservoir rock sample, transverse relaxation time spectra before adsorption equilibrium is established at different pressures, and transverse relaxation time spectra after adsorption equilibrium is established at different pressures; a free gas signal detection module configured to detect free gas signals at different pressures based on transverse relaxation time spectra before adsorption equilibrium is established at different pressures and transverse relaxation time spectra after adsorption equilibrium is established at different pressures; an adsorbed gas signal detection module configured to detect adsorbed gas signals at different pressures based on a base transverse relaxation time spectrum, transverse relaxation time spectra before adsorption equilibrium is established at different pressures, and free gas signals at different pressures; a time spectrum correction module configured to determine corrected transverse relaxation time spectra after establishing adsorption equilibrium at different pressures based on the base transverse relaxation time spectrum, adsorbed gas signals at different pressures, and transverse relaxation time spectra after establishing adsorption equilibrium at different pressures; an actual free gas content determination module configured to obtain the actual free gas content at different pressures based on free gas signals at different pressures and corrected transverse relaxation time spectra after establishing adsorption equilibrium at different pressures; a module for determining the actual content of adsorbed gas, configured to obtain the actual content of adsorbed gas at different pressures based on the base transverse relaxation time spectrum, free gas signals at different pressures and corrected transverse relaxation time spectra after establishing adsorption equilibrium at different pressures; a gas content determination model building module configured to build a gas content determination model based on the actual free gas content and the actual adsorbed gas content at different pressures; a data acquisition module configured to obtain a mass of dried rock from a test deep coal bed methane reservoir and a pressure in the deep coal bed methane reservoir; and a reservoir gas content determination module configured to use a rock mass from a test deep coal bed methane reservoir and a pressure in the deep coal bed methane reservoir as input values ​​for a gas content determination model to obtain a gas content in the test deep coal bed methane reservoir.

10. A system for determining the gas content of a deep coal seam methane reservoir, comprising: an experimental device for measuring isothermal adsorption, having a cylinder for a reference sample inside; a device for measuring nuclear magnetic resonance in a rock, inside which there is a sample cylinder with a constant temperature, configured to measure a baseline spectrum of transverse relaxation time of a dried sample of a reservoir rock, transverse relaxation time spectra before the establishment of adsorption equilibrium at different pressures and transverse relaxation time spectra after the establishment of adsorption equilibrium at different pressures; a gas source connected via a pipeline to an experimental apparatus for measuring isothermal adsorption and an apparatus for measuring nuclear magnetic resonance in a rock and configured to supply compressed gas to the reference sample cylinder and the constant temperature sample cylinder; a pressure sensing mechanism located in the pipeline and configured to sense the gas pressure; and a device for determining the gas content in a deep coal seam methane reservoir according to claim 9, which is connected to a device for measuring nuclear magnetic resonance in a rock.

11. A readable storage medium storing instructions for causing a computer to perform the method for determining gas content in a deep coal bed methane reservoir according to any one of claims 1 to 8.

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