Method and apparatus for determining gas content of deep coalbed methane reservoir, and readable storage medium

Abstract

A method and apparatus for determining the gas content of a deep coalbed methane reservoir, and a readable storage medium. The method comprises: acquiring a baseline transverse relaxation time spectrum of a dried reservoir rock sample, transverse relaxation time spectra before adsorption equilibrium at different pressure points and transverse relaxation time spectra after adsorption equilibrium at different pressure points; on the basis of the baseline transverse relaxation time spectrum, the transverse relaxation time spectra before adsorption equilibrium at different pressure points and the transverse relaxation time spectra after adsorption equilibrium at different pressure points, determining corrected transverse relaxation time spectra after adsorption equilibrium at different pressure points; obtaining actual free gas contents at different pressure points and actual adsorbed gas contents at different pressure points; and constructing a gas content determination model for outputting the gas content of a deep coalbed methane reservoir to be tested. T2 cutoff values of adsorbed gas and free gas are redefined to accurately calculate an adsorbed gas content and a free gas content, such that the precision of calculation of the gas content of a reservoir can be improved.

Description

Method, device and readable storage medium for determining gas content in deep coal-rock gas reservoirs Technical Field

[0001] The present invention relates to the field of oil and gas exploration technology, and in particular to a method for determining the gas content of a deep coal-rock gas reservoir, a device for determining the gas content of a deep coal-rock gas reservoir, a system for determining the gas content of a deep coal-rock gas reservoir, and a readable storage medium. Background Art

[0002] Deep coal-rock gas resources are enormous, and the development and utilization of deep coal-rock gas as a replacement for these resources is promising. Unlike shallow and medium-layer coal-rock gas, which is primarily composed of adsorbed gas, deep coal-rock gas exhibits a multi-state existence, with both adsorbed and free gas coexisting. Gas content is a key geological parameter that is crucial for both reserve calculations and resource evaluations. However, deep coal-rock gas reservoirs are characterized by the development of multiple pores, including micropores, mesopores, and macropores, resulting in complex pore structures. Adsorbed and free gas occur within this "multiple pore systems," making well logging quantitative calculations of free and adsorbed gas difficult. New experimental and evaluation methods are needed to improve the accuracy of well logging gas content calculations and provide a basis for subsequent reserve calculations, resource evaluation, and the optimization of fractured intervals.

[0003] Nuclear magnetic resonance (NMR) technology has been widely used in various fields of geophysics and geology, becoming a key method for characterizing reservoir micropore structure, fluid properties, and physical parameters. In recent years, NMR has also gained widespread application in the study of fluid phases in adsorbent rock samples.

[0004] Deep coal-rock gas reservoirs are an important component of unconventional natural gas development. Accurately predicting their in-situ gas content and occurrence state is very important in resource reserve assessment and mining strategy optimization. However, there is currently a lack of accurate means to distinguish between adsorbed gas and free gas in deep coal-rock gas reservoirs. The identification of adsorbed gas and free gas mostly relies on conventional logging data, and the identification accuracy is limited. Therefore, qualitative and quantitative identification of gas based on precise experimental calibration is particularly important. In the existing technology, for example, Schlumberger (Ahmed U., Johnston D. and Colson L.) developed a method that combines geochemical logging and other logging methods. The elemental logging analysis (ELAN) program is used to calculate the content of each mineral component in the coal, thereby calculating the gas content of the coal seam. Based on the Lang's coal rank equation, another method is proposed that uses fixed carbon and temperature to perform the least squares fitting of the parameter values ​​in the equation to predict the gas content; researchers from the Colombian National Oil Company (Rodriguez S., Navas-Guzman G., Gomez Prada A) A nonparametric regression technique based on probability statistics and optimization theory was proposed to predict coal seam gas content using fixed carbon, volatile matter, and depth data. Pan Heping et al. analyzed coal sample quality, gas content experimental test data, and corresponding well logging data from North China and found that coal seam gas content is closely related to coal seam temperature, pressure, and carbon and ash contents. They also established a method for estimating coal seam gas content. Chinese patent CN112213234B discloses a method for determining the gas content of deep coal gas reservoirs. This method divides the coring and field desorption processes into five stages based on gas release behavior, and determines two key parameters for each stage: the time zero point and gas loss time. Gas desorption and gas release in each stage are analyzed and calculated based on these key parameters and reservoir characteristics. The gas desorption amounts in each stage are analyzed to obtain a series of in situ gas contents of the cores. The above-mentioned method usually relies on conventional logging data. Based on isothermal adsorption and on-site pressure-maintained coring desorption experiments, the relationship between time and desorbed gas volume is established to evaluate the proportion and content of free adsorbed gas. However, since on-site desorption experiments are prone to gas loss and difficult to accurately restore and correct, the accuracy of the calibration data is questionable and the recognition accuracy is limited.

[0005] Currently, researchers have begun using isothermal adsorption experiments combined with saturated water nuclear magnetic resonance to infer the proportions of free and adsorbed gas. They have also developed a dynamic isothermal adsorption and nuclear magnetic resonance test setup and conducted simultaneous isothermal adsorption and nuclear magnetic resonance experiments on rock samples from adsorbed gas reservoirs. They have also used nuclear magnetic resonance (NMR) combined with isothermal adsorption to determine the free and adsorbed methane content in shales. Furthermore, they have used isothermal adsorption and nuclear magnetic resonance (NMR) experiments on coal to calculate its free adsorbed gas content. However, these isothermal adsorption and nuclear magnetic resonance experiments, when applied to qualitative and quantitative identification of gas phases in rock samples, generally assume that the first peak represents the adsorbed gas signal, while the second peak represents the free gas signal. However, in real samples, adsorbed and free gas coexist in nanopores. Therefore, using this method to determine the proportion of free adsorbed gas can introduce errors, resulting in inaccurate results.

[0006] Summary of the Invention

[0007] The purpose of the embodiments of the present invention is to provide a method, device and readable storage medium for determining the gas content of deep coal gas reservoirs, so as to at least solve the problem that adsorbed gas and free gas coexist in the above-mentioned nanopores, and the proportion of free adsorbed gas determined in the prior art has a certain error, resulting in inaccurate results.

[0008] In order to achieve the above-mentioned object, the first aspect of the present invention provides a method for determining the gas content of a deep coal-rock gas reservoir, the method comprising:

[0009] Obtaining the base transverse relaxation time spectrum of the dried reservoir rock sample, the transverse relaxation time spectrum before adsorption equilibrium at different pressure points, and the transverse relaxation time spectrum after adsorption equilibrium at different pressure points;

[0010] Based on the transverse relaxation time spectra before and after adsorption equilibrium at different pressure points, the free gas signals at different pressure points are determined;

[0011] Based on the transverse relaxation time spectrum of the substrate, the transverse relaxation time spectrum before adsorption equilibrium at different pressure points and the free gas signal at different pressure points, the adsorbed gas signal at different pressure points is determined;

[0012] Determining a corrected transverse relaxation time spectrum after adsorption equilibrium at different pressure points based on the substrate transverse relaxation time spectrum, the adsorbed gas signal at different pressure points, and the transverse relaxation time spectrum after adsorption equilibrium at different pressure points;

[0013] Based on the free gas signal at different pressure points and the transverse relaxation time correction spectrum after adsorption equilibrium at different pressure points, the actual free gas amount at different pressure points is obtained;

[0014] The actual adsorbed gas amount at different pressure points is obtained based on the substrate transverse relaxation time spectrum, the free gas signal at different pressure points, and the transverse relaxation time correction spectrum after adsorption equilibrium at different pressure points.

[0015] Based on the actual free gas volume and the actual adsorbed gas volume at different pressure points, a gas content determination model is constructed;

[0016] Obtain the rock quality and deep coal-rock gas reservoir pressure of the deep coal-rock gas reservoir to be tested after drying;

[0017] The rock quality and deep coal-rock gas reservoir pressure of the deep coal-rock gas reservoir to be detected are used as inputs of a gas content determination model to obtain the gas content of the deep coal-rock gas reservoir to be detected.

[0018] Optionally, based on the transverse relaxation time spectra before adsorption equilibrium and the transverse relaxation time spectra after adsorption equilibrium at different pressure points, the free gas signals at different pressure points are determined, including:

[0019] For each pressure point:

[0020] The difference between the first peak area of ​​the transverse relaxation time spectrum before adsorption equilibrium at the nth pressure point and the first peak area of ​​the transverse relaxation time spectrum after adsorption equilibrium at the n-1th pressure point is taken as the increase in the first peak free gas area at the nth pressure point;

[0021] The sum of the increase in the first peak free gas area from the first pressure point to the nth pressure point is taken as the free gas signal at the nth pressure point.

[0022] Optionally, based on the transverse relaxation time spectra before adsorption equilibrium and the transverse relaxation time spectra after adsorption equilibrium at different pressure points, the free gas signals at different pressure points are determined, including:

[0023] The free gas signal is calculated using the following formula:

[0024] Among them, FTSf n is the free gas signal at the nth pressure point; FTSI i is the first peak area of ​​the transverse relaxation time spectrum before adsorption equilibrium at the i-th pressure point; FTSA i-1 is the first peak area of ​​the transverse relaxation time spectrum after adsorption equilibrium at the i-1th pressure point.

[0025] Optionally, determining the adsorbed gas signal at different pressure points based on the substrate transverse relaxation time spectrum, the transverse relaxation time spectrum before adsorption equilibrium at different pressure points, and the free gas signal at different pressure points includes:

[0026] For each pressure point:

[0027] The first peak area of ​​the transverse relaxation time spectrum before adsorption equilibrium at the nth pressure point minus the first peak area of ​​the substrate transverse relaxation time spectrum and the free gas signal at the nth pressure point is taken as the adsorbed gas signal at the nth pressure point.

[0028] Optionally, determining a corrected transverse relaxation time spectrum after adsorption equilibrium at different pressure points based on the substrate transverse relaxation time spectrum, the adsorbed gas signal at different pressure points, and the transverse relaxation time spectrum after adsorption equilibrium at different pressure points includes:

[0029] For each pressure point:

[0030] Calculating the sum of the first peak areas of the adsorbed gas signal and the substrate transverse relaxation time spectrum at the n-th pressure point, and constructing a first curve at the n-th pressure point based on the sum of the first peak areas of the adsorbed gas signal and the substrate transverse relaxation time spectrum;

[0031] Calculating the sum of the first peak areas of the transverse relaxation time spectra after adsorption equilibrium from the first pressure point to the nth pressure point, and constructing a second curve at the nth pressure point based on the sum of the first peak areas of the transverse relaxation time spectra after adsorption equilibrium;

[0032] Determine the transverse relaxation time corresponding to the intersection of the first curve and the second curve at the nth pressure point;

[0033] The transverse relaxation time is used as the transverse relaxation time cutoff value of the adsorption peak and the free peak of the transverse relaxation time spectrum after adsorption equilibrium at the nth pressure point to obtain the transverse relaxation time correction spectrum after adsorption equilibrium at the nth pressure point; the transverse relaxation time cutoff value is used to divide the first peak area and the secondary peak area of ​​the transverse relaxation time spectrum after adsorption equilibrium.

[0034] Optionally, the actual free gas amount at different pressure points is obtained based on the free gas signal at different pressure points and the transverse relaxation time correction spectrum after adsorption equilibrium at different pressure points, including:

[0035] GasA n =k*(FTSf n +STS′ n );

[0036] Among them, GasA n is the actual free gas volume at the nth pressure point; k is the conversion coefficient; FTSf n is the free gas signal at the nth pressure point; STS′ n is the secondary peak area of ​​the spectrum corrected for the transverse relaxation time after the nth adsorption equilibrium.

[0037] Optionally, the actual adsorbed gas amount at different pressure points is obtained based on the substrate transverse relaxation time spectrum, the free gas signal at different pressure points, and the transverse relaxation time correction spectrum after adsorption equilibrium at different pressure points, including:

[0038] GasF n =k*(FTSA′ n -FTSD-FTSfn );

[0039] Among them, GasF n is the actual adsorbed gas volume at the nth pressure point; k is the conversion coefficient; FTSA n ′ is the first peak area of ​​the transverse relaxation time correction spectrum after adsorption equilibrium at the nth pressure point; FTSD is the total area of ​​the base transverse relaxation time spectrum; FTSf n is the free gas signal at the nth pressure point.

[0040] Optionally, the expression of the gas content determination model is:

[0041] F gas =(a*P) / m;

[0042] A gas =[c*ln(P)+d] / m;

[0043] Among them, F gas is the actual free gas content of the reservoir rock to be tested; A gas is the actual adsorbed gas content of the reservoir rock to be tested; a, c, and d are all fitting coefficients; P is the formation pressure of the reservoir rock to be tested; and m is the mass of the reservoir rock to be tested after drying.

[0044] A second aspect of the present invention provides a device for determining the gas content of a deep coal-rock gas reservoir, the device comprising:

[0045] A time spectrum acquisition module is used to obtain the base transverse relaxation time spectrum of the dried reservoir rock sample, the transverse relaxation time spectrum before adsorption equilibrium at different pressure points, and the transverse relaxation time spectrum after adsorption equilibrium at different pressure points;

[0046] A free gas signal determination module is used to determine the free gas signal at different pressure points based on the transverse relaxation time spectra before adsorption equilibrium at different pressure points and the transverse relaxation time spectra after adsorption equilibrium at different pressure points;

[0047] An adsorbed gas signal determination module is used to determine the adsorbed gas signal at different pressure points based on the substrate transverse relaxation time spectrum, the transverse relaxation time spectrum before adsorption equilibrium at different pressure points, and the free gas signal at different pressure points;

[0048] A time spectrum correction module is used to determine a corrected transverse relaxation time spectrum after adsorption equilibrium at different pressure points based on the substrate transverse relaxation time spectrum, the adsorbed gas signal at different pressure points, and the transverse relaxation time spectrum after adsorption equilibrium at different pressure points;

[0049] The actual free gas volume determination module is used to obtain the actual free gas volume at different pressure points based on the free gas signal at different pressure points and the transverse relaxation time correction spectrum after adsorption equilibrium at different pressure points;

[0050] The actual adsorbed gas amount determination module is used to obtain the actual adsorbed gas amount at different pressure points based on the substrate transverse relaxation time spectrum, the free gas signal at different pressure points, and the transverse relaxation time correction spectrum after adsorption equilibrium at different pressure points;

[0051] A gas content determination model building module is used to build a gas content determination model based on the actual adsorbed gas content and the actual free gas content at different pressure points;

[0052] A data acquisition module is used to obtain the rock quality and deep coal-rock gas reservoir pressure of the deep coal-rock gas reservoir to be detected after drying;

[0053] The reservoir gas content determination module is used to take the rock quality and deep coal-rock gas reservoir pressure of the deep coal-rock gas reservoir to be detected as inputs of the gas content determination model to obtain the gas content of the deep coal-rock gas reservoir to be detected.

[0054] A third aspect of the present invention provides a system for determining the gas content of a deep coal-rock gas reservoir, the system comprising:

[0055] Isothermal adsorption experimental device, with a sample reference cylinder inside;

[0056] A rock physics nuclear magnetic resonance measurement device is provided with a constant temperature sample cylinder inside, which is used to measure the base transverse relaxation time spectrum of the dried reservoir rock sample, the transverse relaxation time spectrum before adsorption equilibrium at different pressure points, and the transverse relaxation time spectrum after adsorption equilibrium at different pressure points;

[0057] A gas source, connected to the isothermal adsorption experimental device and the rock physics nuclear magnetic measurement device through a pipeline, is used to supply compressed gas to the sample reference cylinder and the constant temperature sample cylinder;

[0058] An air pressure detection mechanism is provided on the pipeline and is used to detect the gas pressure;

[0059] The above-mentioned deep coal-rock gas reservoir gas content determination device is connected to the rock physical nuclear magnetic measurement device.

[0060] On the other hand, the present invention provides a readable storage medium having instructions stored thereon, the instructions being used to enable a machine to execute the above-mentioned method for determining the gas content of a deep coal-rock gas reservoir.

[0061] Compared with the prior art, the above technical solution of the present invention has the following beneficial effects:

[0062] This technical solution conducts two measurements of the transverse relaxation time before and after adsorption equilibrium after filling with methane gas at different pressure points, realizing the separation of gas signals of different occurrence states of the first peak, redefining the T2 cutoff value of adsorbed gas and free gas, accurately calculating the amount of free gas and adsorbed gas, improving the calculation accuracy of the gas content of deep coal reservoirs, and improving the accuracy of quantitative and qualitative definition of reservoir gas occurrence mode, providing technical support for detailed evaluation of oilfield reservoirs and reserve declaration.

[0063] Other features and advantages of the embodiments of the present invention will be described in detail in the subsequent detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] The accompanying drawings are used to provide a further understanding of the embodiments of the present invention and constitute a part of the specification. Together with the following detailed description, they are used to explain the embodiments of the present invention, but do not constitute a limitation of the embodiments of the present invention. In the accompanying drawings:

[0065] The accompanying drawings are used to provide a further understanding of the embodiments of the present invention and constitute a part of the specification. Together with the following detailed description, they are used to explain the embodiments of the present invention, but do not constitute a limitation of the embodiments of the present invention. In the accompanying drawings:

[0066] FIG1 is a flow chart of a method for determining gas content in a deep coal-rock gas reservoir provided by the present invention;

[0067] FIG2 is a nuclear magnetic T2 spectrum of a dried reservoir rock sample obtained by nuclear magnetic resonance measurement according to the present invention;

[0068] FIG3 is a nuclear magnetic resonance T2 spectrum measured immediately after inflation to various pressures provided by the present invention;

[0069] FIG4 is a NMR T2 spectrum measured after adsorption equilibrium at each pressure point provided by the present invention;

[0070] FIG5 is an envelope diagram of the adsorption equilibrium T2 spectrum area at a certain pressure point measured immediately and at the previous pressure point provided by the present invention;

[0071] FIG6 is a diagram of first peak signal separation provided by the present invention;

[0072] FIG7 is a diagram showing the T2 cutoff value division of the free adsorption signal provided by the present invention;

[0073] FIG8 is a diagram showing the relationship between the adsorption free peak T2 cutoff value and pressure provided by the present invention;

[0074] FIG9 is a graph showing the relationship between adsorbed gas content and pressure provided by the present invention;

[0075] FIG10 is a diagram showing the relationship between free gas content and pressure provided by the present invention;

[0076] FIG11 is a diagram showing calculation results of the method for Well A provided by the present invention;

[0077] FIG12 is a schematic structural diagram of a device for determining gas content in a deep coal-rock gas reservoir provided by the present invention.

[0078] Description of Reference Numerals

[0079] 10-time spectrum acquisition module; 20-free gas signal determination module;

[0080] 30-adsorbed gas signal determination module; 40-time spectrum correction module;

[0081] 50-actual free gas volume determination module; 60-actual adsorbed gas volume determination module;

[0082] 70-Gas content determination model establishment module; 80-Data acquisition module;

[0083] 90-Reservoir gas content determination module. DETAILED DESCRIPTION

[0084] The following describes the specific embodiments of the present invention in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0085] Figure 1 is a flow chart of the method for determining the gas content of deep coal-rock gas reservoirs provided by the present invention; Figure 2 is the nuclear magnetic T2 spectrum of the nuclear magnetic measurement of the dried reservoir rock sample provided by the present invention; Figure 3 is the nuclear magnetic T2 spectrum measured immediately after being inflated to various pressures provided by the present invention; Figure 4 is the nuclear magnetic T2 spectrum measured after adsorption equilibrium at each pressure point provided by the present invention; Figure 5 is the T2 spectrum area envelope diagram of the instant measurement at a certain pressure point and the adsorption equilibrium at the previous pressure point provided by the present invention; Figure 6 is the first peak signal separation diagram provided by the present invention; Figure 7 is the free adsorption signal T2 cutoff value division diagram provided by the present invention; Figure 8 is the adsorption free peak T2 cutoff value and pressure relationship diagram provided by the present invention; Figure 9 is the adsorbed gas content and pressure relationship diagram provided by the present invention; Figure 10 is the free gas content and pressure relationship diagram provided by the present invention; Figure 11 is the calculation result diagram of the method of Well A provided by the present invention; Figure 12 is a structural schematic diagram of the device for determining the gas content of deep coal-rock gas reservoirs provided by the present invention.

[0086] As shown in FIG1 , an embodiment of the present invention provides a method for determining the gas content of a deep coal-rock gas reservoir, the method comprising:

[0087] Step 1: Obtaining a base transverse relaxation time spectrum of the dried reservoir rock sample, a transverse relaxation time spectrum before adsorption equilibrium at different pressure points, and a transverse relaxation time spectrum after adsorption equilibrium at different pressure points;

[0088] Specifically, in this embodiment, a reservoir rock sample is selected, which is a deep coal rock that can adsorb methane gas and has actual mining value. It is ensured that the plunger sample is cut regularly, has a complete shape, and is free of bumps, damage, cracks, etc.; the reservoir rock sample is dried, and the temperature during the drying treatment is determined according to the reservoir conditions of the rock sample. It needs to be controlled to ensure that free water and adsorbed water in the rock sample are removed to ensure that no water molecules occupy the adsorption sites, and at the same time ensure that structural water kerogen in the rock sample does not denature or detach. The dried rock sample is placed in a special clamp, and the transverse relaxation time (T2) of the substrate is measured to obtain the transverse relaxation time spectrum of the substrate of the reservoir rock sample, as shown in Figure 2, where the horizontal axis is time and the vertical axis is amplitude.

[0089] In addition, the transverse relaxation time (T2) was measured immediately after the methane was filled at each designed pressure node. The external pressure gauge verified that the instant transverse relaxation time (T2) measurement was completed within two minutes from the time the filling pressure was balanced and the gas source was disconnected. During this process, the pressure gauge did not change. Therefore, the adsorbed gas signal increment generated by adsorption during this time was negligible. The transverse relaxation time spectrum before adsorption equilibrium at different pressure points was obtained, as shown in Figure 3, with the horizontal axis being time and the vertical axis being amplitude. The transverse relaxation time (T2) was measured again after adsorption equilibrium, and the transverse relaxation time spectrum after adsorption equilibrium at each pressure point was obtained, as shown in Figure 4, with the horizontal axis being time and the vertical axis being amplitude. Specifically, the test can be carried out in order of pressure from small to large to simulate the actual reservoir conditions.

[0090] Step 2: determining the free gas signals at different pressure points based on the transverse relaxation time spectra before adsorption equilibrium and the transverse relaxation time spectra after adsorption equilibrium at different pressure points;

[0091] In this embodiment, the following steps are taken to determine the free gas signals at different pressure points, including:

[0092] For each pressure point:

[0093] The difference between the first peak area of ​​the transverse relaxation time spectrum before adsorption equilibrium at the nth pressure point and the first peak area of ​​the transverse relaxation time spectrum after adsorption equilibrium at the n-1th pressure point is taken as the increase in the first peak free gas area at the nth pressure point;

[0094] The sum of the increase in the first peak free gas area from the first pressure point to the nth pressure point is taken as the free gas signal at the nth pressure point.

[0095] Specifically, the value of n here is a positive integer, and calculation is performed on each of the 1-N pressure points, where the maximum value of n is N, and the free gas signals under the 1-n pressure points are obtained and merged as the free gas signals under different pressure points.

[0096] In another embodiment, the free gas signal at different pressure points may be determined in the following manner, including:

[0097] The free gas signal is calculated using the following formula:

[0098] Among them, FTSf n is the free gas signal at the nth pressure point; FTSI i is the first peak area of ​​the transverse relaxation time spectrum before adsorption equilibrium at the i-th pressure point; FTSA i-1 is the first peak area of ​​the transverse relaxation time spectrum after adsorption equilibrium at the i-1th pressure point.

[0099] As shown in Figure 5, a schematic diagram of the free gas signal at 11.703 MPa and 13.825 MPa.

[0100] Step 3: Determine the adsorbed gas signal at different pressure points based on the substrate transverse relaxation time spectrum, the transverse relaxation time spectrum before adsorption equilibrium at different pressure points, and the free gas signal at different pressure points;

[0101] In this embodiment, for each pressure point:

[0102] The first peak area of ​​the transverse relaxation time spectrum before adsorption equilibrium at the nth pressure point minus the first peak area of ​​the substrate transverse relaxation time spectrum and the free gas signal at the nth pressure point is taken as the adsorbed gas signal at the nth pressure point.

[0103] Specifically, the value of n here is a positive integer, and calculation is performed on each pressure point from 1 to N to obtain the free gas signals under the 1st to nth pressure points, which are combined as the adsorbed gas signals under different pressure points.

[0104] As shown in FIG6 , a first peak signal separation diagram is obtained, in which the composition of the first peak area can be clearly obtained.

[0105] Step 4: determining a corrected transverse relaxation time spectrum after adsorption equilibrium at different pressure points based on the substrate transverse relaxation time spectrum, the adsorbed gas signal at different pressure points, and the transverse relaxation time spectrum after adsorption equilibrium at different pressure points;

[0106] In this embodiment, the following steps are used to determine the corrected transverse relaxation time spectra after adsorption equilibrium at different pressure points, including:

[0107] For each pressure point:

[0108] Calculating the sum of the first peak areas of the adsorbed gas signal and the substrate transverse relaxation time spectrum at the n-th pressure point, and constructing a first curve at the n-th pressure point based on the sum of the first peak areas of the adsorbed gas signal and the substrate transverse relaxation time spectrum;

[0109] Calculating the sum of the first peak areas of the transverse relaxation time spectra after adsorption equilibrium from the first pressure point to the nth pressure point, and constructing a second curve at the nth pressure point based on the sum of the first peak areas of the transverse relaxation time spectra after adsorption equilibrium;

[0110] Determine the transverse relaxation time corresponding to the intersection of the first curve and the second curve at the nth pressure point;

[0111] The transverse relaxation time is used as the transverse relaxation time cutoff value of the adsorption peak and the free peak of the transverse relaxation time spectrum after adsorption equilibrium at the nth pressure point to obtain the transverse relaxation time correction spectrum after adsorption equilibrium at the nth pressure point; the transverse relaxation time cutoff value is used to divide the first peak area and the secondary peak area of ​​the transverse relaxation time spectrum after adsorption equilibrium.

[0112] Specifically, n is a positive integer, and calculations are performed at each pressure point from 1 to N, obtaining the first and second curves at each pressure point from 1 to n. The transverse relaxation time corresponding to the intersection of the first and second curves is then determined within the same coordinate system. This is used as the transverse relaxation time cutoff for the adsorption peak and free peak of the transverse relaxation time spectrum after adsorption equilibrium. New first and second peak areas are then delineated, accurately separating the adsorbed gas signal region from the free gas signal region in the T2 spectrum at each pressure point. As shown in Figure 7, the newly determined transverse relaxation time cutoff is more biased towards the first peak of the transverse relaxation time spectrum after adsorption equilibrium.

[0113] In the prior art, the lowest point between the first peak and the secondary peak is usually taken as the dividing point to obtain the first peak area and the secondary peak area. However, the calculated first peak area and the secondary peak area using this method are not accurate enough. Therefore, in this embodiment, by redefining the T2 cutoff value of adsorbed gas and free gas, the adsorbed gas signal area and the free gas signal area in the T2 spectrum at each pressure point are accurately divided, and the free gas volume and the adsorbed gas volume can be accurately calculated, thereby improving the calculation accuracy of the gas content in deep coal reservoirs, and improving the accuracy of quantitatively and qualitatively defining the gas occurrence mode of the reservoir, providing technical support for the detailed evaluation of oilfield reservoirs and reserve declaration.

[0114] In another embodiment, by fitting and analyzing the transverse relaxation time cutoff values ​​at different pressure points, it can be obtained that the relationship between the transverse relaxation time (T2) cutoff value and pressure at each pressure point is a linear relationship, such as the following formula:

[0115] T2cutoff=j*P+s;

[0116] Where T2cutoff is the cutoff value of the transverse relaxation time (T2); P is the pressure; j and s are dimensionless fitting coefficients. As shown in Figure 8, the change law of the cutoff value of the transverse relaxation time (T2) under 13.825 MPa is shown.

[0117] Step 5: Based on the free gas signal at different pressure points and the transverse relaxation time correction spectrum after adsorption equilibrium at different pressure points, the actual free gas amount at different pressure points is obtained;

[0118] Specifically, in this embodiment, the free gas ratio can be calculated using the following formula:

[0119] Then, convert the free gas percentage into the actual free adsorbed gas amount:

[0120] GasA n =k*RFp n *(FTSA′ n -FTSD+STS′ n );

[0121] This results in the following calculation formula:

[0122] GasA n =k*(FTSf n +STS′ n );

[0123] Among them, GasA n is the actual free gas volume at the nth pressure point; k is the conversion coefficient, and k = h*Vm / 1000, k is the conversion coefficient between peak area and methane gas volume, dimensionless; h is a constant obtained by fitting the NMR signal with the amount of methane substance; FTSA n ′ is the first peak area of ​​the transverse relaxation time correction spectrum after adsorption equilibrium at the nth pressure point; FTSD is the total area of ​​the base transverse relaxation time spectrum; FTSf n is the free gas signal at the nth pressure point; STS′ n is the secondary peak area of ​​the spectrum corrected for the transverse relaxation time after the nth adsorption equilibrium.

[0124] Step 6: Based on the substrate transverse relaxation time spectrum, the free gas signal at different pressure points, and the transverse relaxation time correction spectrum after adsorption equilibrium at different pressure points, the actual adsorbed gas amount at different pressure points is obtained;

[0125] Specifically, in this embodiment, the free gas ratio can be calculated using the following formula:

[0126] Then, convert the free gas percentage into the actual free adsorbed gas amount:

[0127] GasF n =k*RAp n *(FTSA′ n -FTSD+STS′n );

[0128] This results in the following calculation formula:

[0129] GasF n =k*(FTSA′ n -FTSD-FTSf n );

[0130] Among them, GasF n is the actual adsorbed gas volume at the nth pressure point; k is the conversion coefficient, and k = h*Vm / 1000, k is the conversion coefficient between the peak area and the methane gas volume, dimensionless; h is a constant obtained by fitting the NMR signal with the amount of methane substance; FTSA n ′ is the first peak area of ​​the transverse relaxation time correction spectrum after adsorption equilibrium at the nth pressure point; FTSD is the total area of ​​the base transverse relaxation time spectrum; FTSf n is the free gas signal at the nth pressure point.

[0131] Step 7: Based on the actual adsorbed gas volume and the actual free gas volume at different pressure points, a gas content determination model is constructed;

[0132] In this embodiment, the expression of the gas content determination model is:

[0133] F gas =(a*P) / m;

[0134] A gas =[c*ln(P)+d] / m;

[0135] Among them, F gas is the actual free gas content of the reservoir rock to be tested; A gas is the actual adsorbed gas content of the reservoir rock to be tested; a, c, and d are all fitting coefficients; P is the formation pressure of the reservoir rock to be tested; and m is the mass of the reservoir rock to be tested after drying.

[0136] As shown in FIG9 and FIG10 , the gas content determination model can be represented by the curves shown in the figures, so that the actual free gas content and the actual adsorbed gas content at different pressure points can be obtained.

[0137] Step 8: Obtain the rock quality and deep coal-rock gas reservoir pressure of the deep coal-rock gas reservoir to be tested after drying;

[0138] Step nine: Using the rock quality and deep coal-rock gas reservoir pressure of the deep coal-rock gas reservoir to be detected as inputs to a gas content determination model to obtain the gas content of the deep coal-rock gas reservoir to be detected.

[0139] As shown in Figure 11, the gas content determination model in this scheme is used for actual application to obtain the calculation result diagram of Well A in a certain oil field. In the figure, from left to right, the following are lithologic indicator data; depth data; resistivity curve data; CNL, DEN, and DT are three-porosity curve data; SW and POR are porosity and saturation data; T2_CUT and CMR are nuclear magnetic logging data; the actual free gas volume and adsorbed gas volume calculated by the nuclear magnetic method, among which the yellow area in the track is the calculated actual adsorbed gas volume, and the green area is the calculated actual free gas volume; lithologic profile data: from left to right in the track, SH represents mudstone, SAND represents sandstone, COAL represents coal seam, SILT represents siltstone, LIME represents limestone, DOLO represents dolomite, and TZNY represents carbonaceous mudstone.

[0140] As shown in FIG12 , the second aspect of the present invention provides a device for determining the gas content of a deep coal-rock gas reservoir, the device comprising:

[0141] The time spectrum acquisition module 10 is used to obtain the base transverse relaxation time spectrum of the dried reservoir rock sample, the transverse relaxation time spectrum before adsorption equilibrium at different pressure points, and the transverse relaxation time spectrum after adsorption equilibrium at different pressure points;

[0142] A free gas signal determination module 20 is configured to determine free gas signals at different pressure points based on transverse relaxation time spectra before adsorption equilibrium and transverse relaxation time spectra after adsorption equilibrium at different pressure points;

[0143] an adsorbed gas signal determination module 30 for determining the adsorbed gas signal at different pressure points based on the substrate transverse relaxation time spectrum, the transverse relaxation time spectrum before adsorption equilibrium at different pressure points, and the free gas signal at different pressure points;

[0144] A time spectrum correction module 40 is configured to determine a corrected transverse relaxation time spectrum after adsorption equilibrium at different pressure points based on the substrate transverse relaxation time spectrum, the adsorbed gas signal at different pressure points, and the transverse relaxation time spectrum after adsorption equilibrium at different pressure points;

[0145] The actual free gas volume determination module 50 is used to obtain the actual free gas volume at different pressure points based on the free gas signal at different pressure points and the transverse relaxation time correction spectrum after adsorption equilibrium at different pressure points;

[0146] The actual adsorbed gas amount determination module 60 is used to obtain the actual adsorbed gas amount at different pressure points based on the substrate transverse relaxation time spectrum, the free gas signal at different pressure points, and the transverse relaxation time correction spectrum after adsorption equilibrium at different pressure points;

[0147] A gas content determination model building module 70 is used to build a gas content determination model based on the actual adsorbed gas content and the actual free gas content at different pressure points;

[0148] The data acquisition module 80 is used to obtain the rock quality and deep coal-rock gas reservoir pressure of the deep coal-rock gas reservoir to be detected after drying;

[0149] The reservoir gas content determination module 90 is used to use the rock quality and deep coal-rock gas reservoir pressure of the deep coal-rock gas reservoir to be detected as inputs of the gas content determination model to obtain the gas content of the deep coal-rock gas reservoir to be detected.

[0150] Furthermore, the present invention also provides a system for determining the gas content of a deep coal-rock gas reservoir, the system comprising:

[0151] Isothermal adsorption experimental device, with a sample reference cylinder inside;

[0152] A rock physics nuclear magnetic resonance measurement device is provided with a constant temperature sample cylinder inside, which is used to measure the base transverse relaxation time spectrum of the dried reservoir rock sample, the transverse relaxation time spectrum before adsorption equilibrium at different pressure points, and the transverse relaxation time spectrum after adsorption equilibrium at different pressure points;

[0153] A gas source, connected to the isothermal adsorption experimental device and the rock physics nuclear magnetic measurement device through a pipeline, is used to supply compressed gas to the sample reference cylinder and the constant temperature sample cylinder;

[0154] An air pressure detection mechanism is provided on the pipeline and is used to detect the gas pressure;

[0155] The above-mentioned deep coal-rock gas reservoir gas content determination device is connected to the rock physical nuclear magnetic measurement device.

[0156] Among them, the isothermal adsorption experimental device adopts the conventional isothermal adsorption experimental device, removes its constant temperature water bath (oil bath) sample cylinder part, and replaces it with a special sample cylinder without nuclear magnetic resonance signal. Its constant temperature process is guaranteed by the internal constant temperature module of the nuclear magnetic resonance instrument;

[0157] The rock physics nuclear magnetic resonance (NMR) measurement setup includes a nuclear magnetic resonance (NMR) instrument (this experiment used an NMR instrument). The holder was modified to a custom-sized holder to accommodate the newly prepared NMR-free sample cylinder used in the isothermal adsorption experiment. The sample cylinder was placed in the custom-made NMR holder via an extended pipeline for combined measurements. A T-joint was used at the sample cylinder's gas interface, connected to an external high-precision pressure gauge to monitor internal cylinder pressure changes. Pretreatment included core drying and airtightness testing of the experimental apparatus.

[0158] Among them, the classification and implementation methods of the data analysis and processing module include subordinate modules; the gas sources include: CH4 gas cylinders and H2 gas cylinders; in addition, a booster pump and a vacuum pump are also installed on the pipeline. The booster pump is used to increase the pressure in the pipeline, and the vacuum pump is used to keep the pipeline vacuum. Secondly, valves are installed at the gas outlet and gas inlet of each component to achieve opening and closing control and flow regulation.

[0159] On the other hand, the present invention provides a readable storage medium having instructions stored thereon, the instructions being used to enable a machine to execute the above-mentioned method for determining the gas content of a deep coal-rock gas reservoir.

[0160] The above describes in detail the optional embodiments of the present invention in conjunction with the accompanying drawings. However, the embodiments of the present invention are not limited to the specific details in the above embodiments. Within the technical concept of the embodiments of the present invention, a variety of simple modifications can be made to the technical solutions of the embodiments of the present invention, and these simple modifications all fall within the scope of protection of the embodiments of the present invention. It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner unless there is any contradiction. In order to avoid unnecessary repetition, the embodiments of the present invention will no longer describe the various possible combinations separately.

[0161] In addition, the various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the embodiments of the present invention, they should also be regarded as the contents disclosed in the embodiments of the present invention.

Claims

1. A method for determining the gas content of a deep coal-rock gas reservoir, characterized in that: The method comprises: Obtaining the base transverse relaxation time spectrum of the dried reservoir rock sample, the transverse relaxation time spectrum before adsorption equilibrium at different pressure points, and the transverse relaxation time spectrum after adsorption equilibrium at different pressure points; Based on the transverse relaxation time spectra before and after adsorption equilibrium at different pressure points, the free gas signals at different pressure points are determined; Based on the transverse relaxation time spectrum of the substrate, the transverse relaxation time spectrum before adsorption equilibrium at different pressure points and the free gas signal at different pressure points, the adsorbed gas signal at different pressure points is determined; Based on the transverse relaxation time spectrum of the substrate, the adsorbed gas signal at different pressure points and the transverse relaxation time spectrum after adsorption equilibrium at different pressure points, the corrected transverse relaxation time spectrum after adsorption equilibrium at different pressure points is determined; Based on the free gas signal at different pressure points and the transverse relaxation time correction spectrum after adsorption equilibrium at different pressure points, the actual free gas volume at different pressure points is obtained; Based on the substrate transverse relaxation time spectrum, the free gas signal at different pressure points and the transverse relaxation time correction spectrum after adsorption equilibrium at different pressure points, the actual adsorbed gas amount at different pressure points is obtained; Based on the actual free gas volume at different pressure points and the actual adsorbed gas volume at different pressure points, a gas content determination model is constructed; Obtain the rock quality and deep coal-rock gas reservoir pressure of the deep coal-rock gas reservoir to be tested after drying; The rock quality and deep coal-rock gas reservoir pressure of the deep coal-rock gas reservoir to be detected are used as inputs of a gas content determination model to obtain the gas content of the deep coal-rock gas reservoir to be detected.

2. The method for determining the gas content of a deep coal-rock gas reservoir according to claim 1, characterized in that: Based on the transverse relaxation time spectra before adsorption equilibrium at different pressure points and the transverse relaxation time spectra after adsorption equilibrium at different pressure points, the free gas signals at different pressure points are determined, including: For each pressure point: The difference between the first peak area of ​​the transverse relaxation time spectrum before adsorption equilibrium at the nth pressure point and the first peak area of ​​the transverse relaxation time spectrum after adsorption equilibrium at the n-1th pressure point is taken as the increase in the first peak free gas area at the nth pressure point; The sum of the increase in the first peak free gas area from the 1st pressure point to the nth pressure point is taken as the free gas signal at the nth pressure point.

3. The method for determining the gas content of a deep coal-rock gas reservoir according to claim 1, characterized in that: Based on the transverse relaxation time spectra before adsorption equilibrium at different pressure points and the transverse relaxation time spectra after adsorption equilibrium at different pressure points, the free gas signals at different pressure points are determined, including: The free gas signal is calculated using the following formula: Among them, FTSf n is the free gas signal at the nth pressure point; FTSI i is the first peak area of ​​the transverse relaxation time spectrum before adsorption equilibrium at the i-th pressure point; FTSA i-1 is the first peak area of ​​the transverse relaxation time spectrum after adsorption equilibrium at the i-1th pressure point.

4. The method for determining the gas content of a deep coal-rock gas reservoir according to claim 1, characterized in that: Based on the substrate transverse relaxation time spectrum, the transverse relaxation time spectrum before adsorption equilibrium at different pressure points and the free gas signal at different pressure points, the adsorbed gas signal at different pressure points is determined, including: For each pressure point: The first peak area of ​​the transverse relaxation time spectrum before adsorption equilibrium at the nth pressure point minus the first peak area of ​​the substrate transverse relaxation time spectrum and the free gas signal at the nth pressure point is taken as the adsorbed gas signal at the nth pressure point.

5. The method for determining the gas content of a deep coal-rock gas reservoir according to claim 1, characterized in that: Based on the substrate transverse relaxation time spectrum, the adsorbed gas signal at different pressure points and the transverse relaxation time spectrum after adsorption equilibrium at different pressure points, a corrected transverse relaxation time spectrum after adsorption equilibrium at different pressure points is determined, including: For each pressure point: Calculating the sum of the first peak areas of the adsorbed gas signal and the substrate transverse relaxation time spectrum at the nth pressure point, and constructing a first curve at the nth pressure point based on the sum of the first peak areas of the adsorbed gas signal and the substrate transverse relaxation time spectrum; Calculating the sum of the first peak areas of the transverse relaxation time spectra after adsorption equilibrium from the first pressure point to the nth pressure point, and constructing a second curve at the nth pressure point based on the sum of the first peak areas of the transverse relaxation time spectra after adsorption equilibrium; Determine the transverse relaxation time corresponding to the intersection of the first curve and the second curve at the nth pressure point; The transverse relaxation time is used as the transverse relaxation time cutoff value of the adsorption peak and the free peak of the transverse relaxation time spectrum after adsorption equilibrium at the nth pressure point to obtain a transverse relaxation time correction spectrum after adsorption equilibrium at the nth pressure point; The transverse relaxation time cutoff value is used to divide the first peak area and the second peak area of ​​the transverse relaxation time spectrum after adsorption equilibrium.

6. The method for determining the gas content of a deep coal-rock gas reservoir according to claim 1, characterized in that: Based on the free gas signal at different pressure points and the transverse relaxation time correction spectrum after adsorption equilibrium at different pressure points, the actual free gas volume at different pressure points is obtained, including: GasA n = k*(FTSf n +STS′ n ); Among them, GasA n is the actual free gas volume at the nth pressure point; k is the conversion coefficient; FTSf n is the free gas signal at the nth pressure point; STS′ n is the secondary peak area of ​​the transverse relaxation time corrected spectrum after the nth adsorption equilibrium.

7. The method for determining the gas content of a deep coal-rock gas reservoir according to claim 1, characterized in that: Based on the substrate transverse relaxation time spectrum, the free gas signal at different pressure points and the transverse relaxation time correction spectrum after adsorption equilibrium at different pressure points, the actual adsorbed gas amount at different pressure points is obtained, including: GasF n = k*(FTSA′ n -FTSD-FTSf n ); Among them, GasF n is the actual adsorbed gas volume at the nth pressure point; k is the conversion coefficient; FTSA′ n is the first peak area of ​​the transverse relaxation time correction spectrum after adsorption equilibrium at the nth pressure point; FTSD is the total area of ​​the base transverse relaxation time spectrum; FTSf n is the free gas signal at the nth pressure point.

8. The method for determining the gas content of a deep coal-rock gas reservoir according to claim 1, characterized in that: The expression of the gas content determination model is: gas =(a*P) / m; A gas =[c*ln(P)+d] / m; Among them, F gas A is the actual free gas content of the reservoir rock to be tested; gas is the actual adsorbed gas content of the reservoir rock to be tested; a, c, d are all fitting coefficients; P is the formation pressure of the reservoir rock to be tested; m is the mass of the reservoir rock to be tested after drying.

9. A device for determining the gas content of a deep coal-rock gas reservoir, characterized in that: The device comprises: A time spectrum acquisition module is used to obtain the base transverse relaxation time spectrum of the dried reservoir rock sample, the transverse relaxation time spectrum before adsorption equilibrium at different pressure points, and the transverse relaxation time spectrum after adsorption equilibrium at different pressure points; A free gas signal determination module, used to determine the free gas signals at different pressure points based on the transverse relaxation time spectra before adsorption equilibrium at different pressure points and the transverse relaxation time spectra after adsorption equilibrium at different pressure points; An adsorbed gas signal determination module, used to determine the adsorbed gas signal at different pressure points based on the substrate transverse relaxation time spectrum, the transverse relaxation time spectrum before adsorption equilibrium at different pressure points, and the free gas signal at different pressure points; A time spectrum correction module is used to determine the transverse relaxation time correction spectrum after adsorption equilibrium at different pressure points based on the substrate transverse relaxation time spectrum, the adsorbed gas signal at different pressure points and the transverse relaxation time spectrum after adsorption equilibrium at different pressure points; An actual free gas volume determination module is used to obtain the actual free gas volume at different pressure points based on the free gas signal at different pressure points and the transverse relaxation time correction spectrum after adsorption equilibrium at different pressure points; The actual adsorbed gas volume determination module is used to obtain the actual adsorbed gas volume at different pressure points based on the substrate transverse relaxation time spectrum, the free gas signal at different pressure points and the transverse relaxation time correction spectrum after adsorption equilibrium at different pressure points; A gas content determination model building module is used to build a gas content determination model based on the actual free gas content and the actual adsorbed gas content at different pressure points; A data acquisition module, used to obtain the rock quality and deep coal-rock gas reservoir pressure of the deep coal-rock gas reservoir to be detected after drying; The reservoir gas content determination module is used to take the rock quality and deep coal-rock gas reservoir pressure of the deep coal-rock gas reservoir to be detected as inputs of the gas content determination model to obtain the gas content of the deep coal-rock gas reservoir to be detected.

10. A system for determining the gas content of a deep coal-rock gas reservoir, characterized in that: The system comprises: Isothermal adsorption experimental device, with a sample reference cylinder inside; A rock physics nuclear magnetic resonance measuring device is provided with a constant temperature sample cylinder inside, which is used to measure the base transverse relaxation time spectrum of the dried reservoir rock sample, the transverse relaxation time spectrum before adsorption equilibrium at different pressure points, and the transverse relaxation time spectrum after adsorption equilibrium at different pressure points; A gas source, connected to the isothermal adsorption experimental device and the rock physics nuclear magnetic measurement device through a pipeline, is used to supply compressed gas to the sample reference cylinder and the constant temperature sample cylinder; A gas pressure detection mechanism, arranged on the pipeline, for detecting gas pressure; The deep coal-rock gas reservoir gas content determination device described in claim 9 is connected to the rock physical nuclear magnetic resonance measurement device.

11. A readable storage medium having instructions stored thereon, the instructions being used to enable a machine to execute the method for determining the gas content of a deep coal-rock gas reservoir as described in any one of claims 1 to 8.

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