A method for calculating total gas content of deep coal rock gas reservoir

Abstract

The present application relates to the technical field of deep coal rock gas reservoir resource evaluation, and particularly relates to a method for calculating total gas content of deep coal rock gas reservoir. The method comprises the following steps: determining a target research area, obtaining a first adsorbed gas content relationship and a second adsorbed gas content relationship of the target research area, constructing a coal rock total gas content calculation formula of the target research area from the two adsorbed gas content relationships, determining a verification test area, actually measuring actual coal rock total gas content of the verification test area, calculating predicted coal rock total gas content of the verification test area through the coal rock total gas content calculation formula, obtaining a relative error of the actual coal rock total gas content and the predicted coal rock total gas content, determining a discriminant of the coal rock total gas content calculation formula, when the relative error satisfies the discriminant, determining a test area to be tested, and calculating coal rock adsorbed gas content, free gas content and total gas content of the test area to be tested. The method provided by the present application can efficiently calculate coal rock adsorbed gas content, free gas content and total gas content of the test area to be tested by using the coal rock total gas content calculation formula.

Description

Technical Field

[0001] This invention relates to the technical field of deep coal-rock gas reservoir resource evaluation, and in particular to a method for calculating the total gas content of deep coal-rock gas reservoirs. Background Technology

[0002] Currently, methods for calculating the gas content of coal seams are mainly divided into two categories. The first category is the direct method and its modified direct method, which involves direct measurement according to the relevant standards of the U.S. Bureau of Mines. This method yields accurate results but is extremely resource-intensive. The second category is the indirect method. One is the isothermal adsorption method, mainly for shallow coalbed methane reservoirs without free gas. The isothermal adsorption method is well-developed and mainly uses the Langevin equation or the relationship between gas content and depth, as well as numerical simulations, to obtain information on gas content. The other is the volumetric method, which mainly calculates free gas content by relying on characteristic parameters such as coal porosity, gas saturation, and gas compressibility coefficient, combined with parameters such as formation depth and coal seam density.

[0003] Currently, the isothermal adsorption method has three main shortcomings: it requires complex isothermal adsorption experiments on specific strata, resulting in high costs; with increasing burial depth, the results are subject to error due to changes in the geological environment and the lack of consideration for the destructive effects of later development; existing studies have modified the Langevin equation to improve its accuracy by considering factors such as coal rank, ash content, and fixed carbon, but these multiple variables also introduce error risks. The volumetric method ignores the difficulty in calculating porosity and gas saturation caused by the strong heterogeneity of coal and rock, making its operational feasibility and error control difficult. Therefore, to address these shortcomings, a new method for calculating the total gas content of deep coal-rock gas reservoirs is proposed. Summary of the Invention

[0004] (a) Technical problems to be solved

[0005] This invention provides a method for calculating the total gas content of deep coalbed methane reservoirs, overcoming the shortcomings of existing technologies where deep coalbed methane reservoirs contain both adsorbed and free gas, with a higher proportion of free gas, which differs significantly from traditional coalbed methane reservoirs containing only adsorbed gas. Traditional gas content calculation methods are inefficient and highly dependent on reservoir characteristic parameters, leading to large errors.

[0006] (II) Technical Solution

[0007] To address the above problems, this invention provides a method for calculating the total gas content of deep coal-rock gas reservoirs, comprising:

[0008] Step S1: Determine the target study area, collect formation isothermal adsorption data of the target study area and obtain the organic matter maturity of each formation, obtain the first relationship based on the formation isothermal adsorption data, obtain the second relationship based on the organic matter maturity, substitute both the first and second relationships into the Langmuir equation to obtain the first adsorbed gas quantity relationship of the target study area.

[0009] Step S2: Conduct a dynamic experiment of methane adsorption and desorption in coal and rock using nuclear magnetic resonance in the target study area determined in Step S1. The proportion of adsorbed gas and free gas in coal and rock under different formation pressures in the target study area is determined by the experiment. The second adsorbed gas quantity relationship formula in the target study area is obtained by considering the relationship between formation pressure and the proportion of adsorbed gas and free gas in coal and rock.

[0010] Step S3: Based on the first adsorbed gas quantity relationship determined in step S1 and the second adsorbed gas quantity relationship determined in step S2, construct the formula for calculating the total gas content of coal and rock in the target study area;

[0011] Step S4: Determine the verification test area, actually measure the total gas content of coal and rock in the verification test area, calculate the predicted total gas content of coal and rock in the verification test area using the formula for calculating the total gas content of coal and rock in step S3, and obtain the relative error between the actual total gas content of coal and rock and the predicted total gas content of coal and rock obtained in step S3.

[0012] Step S5: Determine the discriminant of the formula for calculating the total gas content of coal and rock determined in step S3. When the relative error determined in step S4 satisfies the discriminant, determine the test area to be tested, and calculate the adsorbed gas content, free gas content, and total gas content of the coal and rock in the test area using the formula for calculating the total gas content of coal and rock.

[0013] Preferably, in step S1, the first adsorbed gas quantity relationship is a formula for the adsorbed gas content in coal and rock, and its calculation formula is as follows:

[0014]

[0015] Among them, V s m represents the adsorbed gas content. 3 / t; P is the formation pressure, MPa; C P C is the pressure coefficient. P =P / gD; P L The pressure is represented by the Landau pressure in MPa and V. L For the Langevin volume, m 3 / t; D is the formation depth, in meters.

[0016] Preferably, in step S1, the formation isothermal adsorption data includes temperature, formation depth, formation pressure, Langmuir volume, and Langmuir pressure.

[0017] Preferably, in step S1, isothermal adsorption curves are obtained based on formation isothermal adsorption data, and a first relationship is obtained by fitting coal and rock data of each layer in the target study area based on the isothermal adsorption curves. The first relationship is the calculation relationship between the Langmuir volume and the Langmuir pressure, and its calculation formula is as follows:

[0018] P L = -0.1205·V L +7.0421 (3)

[0019] Among them, P L The pressure is represented by the Landau pressure in MPa and V. L For the Langevin volume, m 3 / t.

[0020] Preferably, in step S1, the second relationship is the Langmuir volume of the reservoir. The Langmuir volume of the reservoir is obtained based on the organic matter maturity of each stratum in the target study area, and its calculation formula is as follows:

[0021] V L =(94.3R0-43.72)e -0.0049t (4)

[0022] Among them, V L For the Langevin volume, m 3 / t; R0 is the organic matter maturity, %; t is the formation temperature, t = 0.0593D, K.

[0023] Preferably, in step S1, the formula for calculating the organic matter maturity of each stratum is:

[0024] R0 = (D - 658.39) / 1712.8 (5);

[0025] Where R0 is the organic matter maturity (%), and D is the formation depth (m).

[0026] Preferably, in step S2, the second adsorbed gas quantity relationship is the relationship between the proportion of coal and rock adsorbed gas and the formation pressure, and its calculation formula is as follows:

[0027] r s =-1.2198P+97.985 (6)

[0028] Where, r s P represents the percentage of adsorbed gas (%); P represents the formation pressure (MPa).

[0029] Preferably, in step S3, the formula for calculating the total gas content of coal and rock is:

[0030]

[0031] Among them, V总 For total gas content, m 3 / t; D is the formation depth, m; C P C is the pressure coefficient. P =P / gD; P is the formation pressure, MPa.

[0032] Preferably, in step S4, the formula for calculating the relative error is:

[0033] L=| (V1-V2) / V2|*100% (8)

[0034] Where L is the relative error, %; V1 is the predicted total gas content of coal and rock, m 3 / t; V2 is the actual total gas content of coal and rock, m 3 / t.

[0035] Preferably, in step S5, the discriminant is L≤10%. When the relative error satisfies the discriminant, it proves that the formula for calculating the total gas content of coal and rock is feasible.

[0036] (III) Beneficial Effects

[0037] The method for calculating the total gas content of deep coal-rock gas reservoirs provided by this invention fits the calculation formula of the total gas content of coal-rock using nuclear magnetic resonance experimental data and isothermal adsorption experimental data. The calculation formula of the total gas content of coal-rock can be used to calculate the adsorbed gas content, free gas content and total gas content of coal-rock in the test area more efficiently, effectively solving the problem of high error caused by indirect calculation in existing calculation methods. Attached Figure Description

[0038] Figure 1 This is a flowchart illustrating the method for calculating the total gas content of deep coal-rock gas reservoirs according to an embodiment of the present invention;

[0039] Figure 2 This is an isothermal adsorption curve for calculating the amount of gas adsorbed by coal and rock in an embodiment of the present invention;

[0040] Figure 3 This is a T2 spectrum distribution characteristic diagram of a coal and rock sample at a depth of 2053.0m from well HX20, according to an embodiment of the present invention.

[0041] Figure 4 This is a fitted curve of the proportion of adsorbed gas and free gas in deep coal and rock gas versus pressure in an embodiment of the present invention. Detailed Implementation

[0042] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] Figure 1 This is a flowchart illustrating the method for calculating the total gas content of deep coal-rock gas reservoirs according to an embodiment of the present invention, as shown below. Figure 1 As shown, this invention provides a method for calculating the total gas content of deep coal-rock gas reservoirs, including:

[0044] Step S1: Determine the target study area, collect formation isothermal adsorption data of the target study area and obtain the organic matter maturity of each formation, obtain the first relationship based on the formation isothermal adsorption data, obtain the second relationship based on the organic matter maturity, substitute both the first and second relationships into the Langmuir equation to obtain the first adsorbed gas quantity relationship of the target study area.

[0045] Step S2: Conduct a dynamic experiment of methane adsorption and desorption in coal and rock using nuclear magnetic resonance in the target study area determined in Step S1. The proportion of adsorbed gas and free gas in coal and rock under different formation pressures in the target study area is determined by the experiment. The second adsorbed gas quantity relationship formula in the target study area is obtained by considering the relationship between formation pressure and the proportion of adsorbed gas and free gas in coal and rock.

[0046] Step S3: Based on the first adsorbed gas quantity relationship determined in step S1 and the second adsorbed gas quantity relationship determined in step S2, construct the formula for calculating the total gas content of coal and rock in the target study area;

[0047] Step S4: Determine the verification test area, actually measure the total gas content of coal and rock in the verification test area, calculate the predicted total gas content of coal and rock in the verification test area using the formula for calculating the total gas content of coal and rock in step S3, and obtain the relative error between the actual total gas content of coal and rock and the predicted total gas content of coal and rock obtained in step S3.

[0048] Step S5: Determine the discriminant of the formula for calculating the total gas content of coal and rock determined in step S3. When the relative error determined in step S4 satisfies the discriminant, determine the test area to be tested, and calculate the adsorbed gas content, free gas content, and total gas content of the coal and rock in the test area using the formula for calculating the total gas content of coal and rock.

[0049] In this calculation method, in step S1, the first adsorbed gas quantity relationship is the coal and rock adsorbed gas content formula, and its calculation formula is as follows:

[0050]

[0051]

[0052] Among them, V s m represents the adsorbed gas content. 3 / t; P is the formation pressure, MPa; C P C is the pressure coefficient. P =P / gD; P L The pressure is represented by the Landau pressure in MPa and V. L For the Langevin volume, m 3 / t; D is the formation depth, in meters.

[0053] In practical applications, in step S1, the formation isothermal adsorption data includes temperature, formation depth, formation pressure, Langmuir volume, and Langmuir pressure. Based on the formation isothermal adsorption data, isothermal adsorption curves are obtained. Based on these isothermal adsorption curves, the coal and rock data of each layer in the target study area are fitted to obtain the first relationship. The first relationship is the calculation relationship between Langmuir volume and Langmuir pressure, and its calculation formula is:

[0054] P L = -0.1205·V L +7.0421 (3)

[0055] Among them, P L The pressure is represented by the Landau pressure in MPa and V. L For the Langevin volume, m 3 / t.

[0056] It should be noted that the role of the first relation is to build a basic framework for calculating the gas content of coal seams, and the data used is easy to obtain and the calculation process is simple.

[0057] In this calculation method, in step S1, the second relationship is the Lanthal volume of the reservoir. The Lanthal volume of the reservoir is obtained based on the organic matter maturity of each stratum in the target study area, and its calculation formula is as follows:

[0058] V L =(94.3R0-43.72)e -0.0049t (4)

[0059] Among them, V L For the Langevin volume, m 3 / t; R0 is the organic matter maturity, %; t is the formation temperature, t = 0.0593D, K.

[0060] In step S1, the formula for calculating the organic matter maturity of each stratum is as follows:

[0061] R0 = (D - 658.39) / 1712.8 (5);

[0062] Where R0 is the organic matter maturity (%), and D is the formation depth (m).

[0063] It is important to note that by calculating the organic matter maturity at the location of the coal seam, the condition of the coal seam can be interpreted, making the calculation results more accurately close to the actual strata and improving the accuracy of the equations. This eliminates the need to consider cumbersome additional factors such as coal rank, ash content, and fixed carbon.

[0064] In practical applications, in step S2, the second adsorbed gas quantity relationship is the relationship between the proportion of adsorbed gas in coal and formation pressure. Based on the dynamic experiment of methane adsorption and desorption in coal using nuclear magnetic resonance, the proportions of adsorbed and free gas in coal under different formation pressures are determined. According to the fitting data of the relationship between formation pressure and the proportions of adsorbed and free gas in coal, the formula between the proportion of adsorbed gas in coal and formation pressure is obtained. The calculation formula is as follows:

[0065] r s =-1.2198P+97.985 (6)

[0066] Where, r s P represents the percentage of adsorbed gas (%); P represents the formation pressure (MPa).

[0067] It is important to note that nuclear magnetic resonance (NMR) technology can be used to conveniently and accurately measure the proportion of adsorbed gas and free gas in coal seams and establish the relationship between the proportion of adsorbed gas and formation pressure without considering other formation parameters, thus simplifying the calculation process while ensuring accuracy.

[0068] In this calculation method, the formula for calculating the total gas content of coal and rock in step S3 is as follows:

[0069]

[0070] Among them, V 总 For total gas content, m 3 / t; D is the formation depth, m; C P C is the pressure coefficient. P =P / gD; P is the formation pressure, MPa.

[0071] In practical applications, by using the formula for the amount of gas adsorbed in coal and rock obtained from the isothermal adsorption curve and the formula for the proportion of adsorbed gas obtained by fitting nuclear magnetic resonance data, a formula for calculating the total gas content of coal and rock that is only related to the formation depth can be constructed.

[0072] In this calculation method, the formula for calculating the relative error in step S4 is:

[0073] L=| (V1-V2) / V2|*100% (8)

[0074] Where L is the relative error, %; V1 is the predicted total gas content of coal and rock, m3 / t; V2 is the actual total gas content of coal and rock, m 3 / t.

[0075] In practical applications, in step S5, the discriminant is L≤10%. When the relative error satisfies the discriminant, it proves that the formula for calculating the total gas content of coal and rock is feasible.

[0076] This invention provides a method for calculating the total gas content of deep coal-rock gas reservoirs, taking into account the characteristics of traditional methods that are cumbersome, have large errors, and are inaccurate. The specific advantages are as follows:

[0077] First, addressing the problem that traditional methods require tedious isothermal adsorption experiments on specific formations for each gas content calculation, wasting time and costs, this approach obtains the basic framework of the Langmuir equation and then uses nuclear magnetic resonance technology to measure and predict the gas content of adsorbed and free gas in coal and rock under various formation pressures. This technology not only ensures the reliability of the data but also avoids multiple tedious isothermal adsorption experiments, shortening the experimental cycle and saving costs.

[0078] Secondly, in addressing the issues of lengthy formulas and large calculation errors caused by considering stratigraphic variations and formula improvements in traditional methods, organic matter maturity reflects the gas reservoir abundance characteristics in a region. Using it as a variable yields more accurate final results and a simpler calculation process.

[0079] Third, addressing the error issues arising from the indirect calculation of free gas content using parameters such as coal porosity, moisture content, ash yield, and methane adsorption volume in existing methods, the final formula for calculating the total gas content of coal and rock only includes formation depth and formation pressure, eliminating high-error factors such as porosity and ash yield that are difficult to measure, thus making the final calculation results more accurate and reliable.

[0080] The working principle of this method for calculating the total gas content of deep coal-rock gas reservoirs is described in detail below:

[0081] Step 1: Determine the target study area, collect formation isothermal adsorption data for the target study area and obtain the organic matter maturity of each formation, obtain the first relationship based on the formation isothermal adsorption data, obtain the second relationship based on the organic matter maturity, substitute both the first and second relationships into the Langmuir equation to obtain the first adsorbed gas quantity relationship for the target study area.

[0082] In this embodiment, isothermal adsorption data of the South Second Member coal and rock formation were collected, including temperature, formation depth, formation pressure, Langmuir volume, and Langmuir pressure, to obtain isothermal adsorption curves. Figure 2As shown, the curves relating adsorption equilibrium pressure to absolute adsorption capacity are presented for three coal and rock samples from well HX20. Based on the isothermal adsorption curves, the data from each coal and rock layer were fitted to obtain the calculated relationship between the Langmuir volume and the Langmuir pressure.

[0083] P L = -0.1205·V L +7.0421 (3)

[0084] Among them, P L The pressure is represented by the Landau pressure in MPa and V. L For the Langevin volume, m 3 / t.

[0085] In practical applications, the organic matter maturity of each layer is obtained based on stratigraphic data, and the formula for calculating the reservoir's Langmuir volume is derived from this:

[0086] R0 = (D - 658.39) / 1712.8 (5)

[0087] V L =(94.3R0-43.72)e -0.0049t (4)

[0088] Among them, V L For the Langevin volume, m 3 / t; R0 is the organic matter maturity, %; D is the formation depth, m; t is the formation temperature, t = 0.0593D, K.

[0089] In this embodiment, formulas (3), (4), and (5) are substituted into the Langmuir equation to calculate the formula for coal rock adsorbed gas content:

[0090]

[0091] Among them, V s m represents the adsorbed gas content. 3 / t; P is the formation pressure, MPa; C P C is the pressure coefficient. P =P / gD; P L The pressure is represented by the Landau pressure in MPa and V. L For the Langevin volume, m 3 / t; D is the formation depth, in meters.

[0092] Step 2: Conduct dynamic experiments on methane adsorption and desorption in coal and rock using nuclear magnetic resonance in the target study area. Determine the proportion of adsorbed gas and free gas in coal and rock under different formation pressures in the target study area. Obtain the second adsorbed gas quantity relationship formula in the target study area based on the relationship between formation pressure and the proportion of adsorbed gas and free gas in coal and rock.

[0093] In this embodiment, a dynamic experiment based on nuclear magnetic resonance (NMR) was conducted to determine the proportions of adsorbed and free gas in coal under different formation pressures using methane adsorption and desorption. The specific steps are as follows: The experimental apparatus was connected, and an airtightness check was performed. The free space volume of each part of the experimental apparatus was measured using an AJP-100 helium porosimeter. After evacuating the sample cylinder, methane gas was injected, and the methane signal was measured at different pressures. The methane signal was calibrated based on the actual methane volume. After thoroughly drying the coal core, it was placed in a specially designed core holder and placed under the NMR spectroscopy system. In the resonance detection system, the confining pressure was applied to the set value, and after sealing, a vacuum was applied for more than 24 hours. Nuclear magnetic resonance measurements were performed on the coal core using a CPMG pulse sequence to obtain the T2 spectrum of the dried coal sample, which was then used as the base signal. Methane gas was injected into the core and pressurized to 20 MPa, allowing it to fully saturate for 24 days to simulate the original state of adsorbed methane gas. During saturation, changes in the methane gas signal in the core were monitored in real time. The outlet of the core holder was opened to conduct a coal gas depletion development simulation experiment, recording the inlet pressure and outlet flow rate. Throughout the entire experiment, real-time monitoring of changes in the methane gas signal in the coal core was necessary.

[0094] In practical applications, such as Figure 3 The figure shows the T2 spectral characteristics of adsorbed and free methane gas in HX20 well coal samples under eleven test pressures. Methane gas was injected into the coal core under constant pressure. The T2 NMR spectrum of methane-saturated coal showed a distinct bimodal characteristic. Adsorbed methane mainly resided on the surface of the coal nanopores. Due to surface relaxation control, its relaxation time was short, corresponding to the left peak in the T2 spectrum, with relaxation times ranging from 0.01 to 1.0 ms and the main peak at 0.2 ms. Free methane, on the other hand, resided in larger coal pores, unconstrained by the pore walls, resulting in a longer relaxation time, corresponding to the right peak in the T2 spectrum, with relaxation times ranging from 1 to 10 ms and the main peak at 5 ms. The T2 spectrum can be used to determine the signal quantities of adsorbed / free methane gas in the coal core.

[0095] In this embodiment, as Figure 4 As shown, based on the fitting data of the relationship between formation pressure and the proportions of adsorbed gas and free gas in coal and rock, the formula for the relationship between the proportion of adsorbed gas in coal and rock and formation pressure is obtained:

[0096] r s =-1.2198P+97.985 (6)

[0097] Where, r s P represents the percentage of adsorbed gas (%); P represents the formation pressure (MPa).

[0098] Step 3: Based on the first and second adsorbed gas volume relationship formulas, construct the formula for calculating the total gas content of coal and rock in the target study area.

[0099] In this embodiment, the formula for the amount of gas adsorbed in coal and rock obtained by using the isothermal adsorption curve is used to calculate the proportion of adsorbed gas obtained by fitting nuclear magnetic resonance data, so that a formula for calculating the total gas content of coal and rock that is close to the formation depth can be constructed.

[0100]

[0101] Among them, V 总 For total gas content, m 3 / t; D is the formation depth, m; C P C is the pressure coefficient. P =P / gD; P is the formation pressure, MPa.

[0102] Step 4: Determine the verification test area, measure the actual total gas content of coal and rock in the verification test area, calculate the predicted total gas content of coal and rock in the verification test area using the formula for calculating the total gas content of coal and rock, and obtain the relative error between the actual total gas content of coal and rock and the predicted total gas content of coal and rock.

[0103] In this embodiment, the HT1H well in the Huhehu Depression of the Hailar Basin is used as the verification test area. That is, the coal and rock samples of the South Second Section of the HT1H well in the Hailar Basin are used as verification materials. The actual total gas content of the coal and rock is measured, and the predicted total gas content of the coal and rock is calculated by the formula for calculating the total gas content of the coal and rock. The relative error between the actual total gas content of the coal and rock and the predicted total gas content of the coal and rock is obtained.

[0104] The formula for calculating the relative error is as follows:

[0105] L=| (V1-V2) / V2|*100% (8)

[0106] Where L is the relative error, %; V1 is the predicted total gas content of coal and rock, m 3 / t; V2 is the actual total gas content of coal and rock, m 3 / t.

[0107] Step 5: Determine the discriminant for calculating the total gas content of coal and rock. When the relative error satisfies the discriminant, determine the test area to be tested, and calculate the adsorbed gas content, free gas content, and total gas content of the coal and rock in the test area using the formula for calculating the total gas content of coal and rock.

[0108] In this embodiment, the discriminant is L≤10%. When the relative error satisfies the discriminant, it proves that the formula for calculating the total gas content of coal and rock is feasible. The calculation in step four shows that the relative error between the proportions of free gas and adsorbed gas measured by NMR and the measured proportions is less than 10%, indicating that the formula for calculating the total gas content of coal and rock is feasible. Therefore, the test area can be determined, and the adsorbed gas content, free gas content, and total gas content of the coal and rock in the test area can be further calculated using the formula for calculating the total gas content of coal and rock.

[0109] The method for calculating the total gas content of deep coal-rock gas reservoirs provided by this invention fits the calculation formula of the total gas content of coal-rock using nuclear magnetic resonance experimental data and isothermal adsorption experimental data. The calculation formula of the total gas content of coal-rock can be used to calculate the adsorbed gas content, free gas content and total gas content of coal-rock in the test area more efficiently, effectively solving the problem of high error caused by indirect calculation in existing calculation methods.

[0110] The above embodiments are only used to illustrate the present invention and are not intended to limit the present invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions also fall within the scope of the present invention, and the patent protection scope of the present invention should be defined by the claims.

Claims

1. A method for calculating the total gas content of a deep coal-rock gas reservoir, characterized in that, include: Step S1: Determine the target study area, collect formation isothermal adsorption data of the target study area and obtain the organic matter maturity of each formation, obtain the first relationship based on the formation isothermal adsorption data, obtain the second relationship based on the organic matter maturity, substitute both the first and second relationships into the Langmuir equation to obtain the first adsorbed gas quantity relationship of the target study area. Step S2: Conduct a dynamic experiment of methane adsorption and desorption in coal and rock using nuclear magnetic resonance in the target study area determined in Step S1. The proportion of adsorbed gas and free gas in coal and rock under different formation pressures in the target study area is determined by the experiment. The second adsorbed gas quantity relationship formula in the target study area is obtained by considering the relationship between formation pressure and the proportion of adsorbed gas and free gas in coal and rock. Step S3: Based on the first adsorbed gas quantity relationship determined in step S1 and the second adsorbed gas quantity relationship determined in step S2, construct the formula for calculating the total gas content of coal and rock in the target study area; Step S4: Determine the verification test area, actually measure the total gas content of coal and rock in the verification test area, calculate the predicted total gas content of coal and rock in the verification test area using the formula for calculating the total gas content of coal and rock in step S3, and obtain the relative error between the actual total gas content of coal and rock and the predicted total gas content of coal and rock obtained in step S3. Step S5: Determine the discriminant of the formula for calculating the total gas content of coal and rock determined in step S3. When the relative error determined in step S4 satisfies the discriminant, determine the test area to be tested, and calculate the adsorbed gas content, free gas content, and total gas content of the coal and rock in the test area using the formula for calculating the total gas content of coal and rock.

2. The method for calculating the total gas content of deep coal-rock gas reservoirs according to claim 1, characterized in that, In step S1, the first adsorbed gas quantity relationship is the coal and rock adsorbed gas content formula, and its calculation formula is: Among them, V s For the adsorbed gas content, m 3 / t; P is the formation pressure, MPa; C P C is the pressure coefficient. P =P / gD; P L The pressure is represented by the Landau pressure in MPa and V. L For the Langevin volume, m 3 / t; D is the formation depth, in meters.

3. The method for calculating the total gas content of deep coal-rock gas reservoirs according to claim 1, characterized in that, In step S1, the formation isothermal adsorption data includes temperature, formation depth, formation pressure, Langmuir volume, and Langmuir pressure.

4. The method for calculating the total gas content of deep coal-rock gas reservoirs according to claim 3, characterized in that, In step S1, isothermal adsorption curves are obtained based on formation isothermal adsorption data. Based on these isothermal adsorption curves, the coal and rock data of each layer in the target study area are fitted to obtain the first relationship. This first relationship is the calculated relationship between the Langmuir volume and Langmuir pressure, and its calculation formula is as follows: P L =-0.1205 V L +7.0421 (3) Among them, P L The pressure is represented by the Landau pressure in MPa and V. L For the Langevin volume, m 3 / t.

5. The method for calculating the total gas content of deep coal-rock gas reservoirs according to claim 1, characterized in that, In step S1, the second relationship is the Langmuir volume of the reservoir. The Langmuir volume of the reservoir is obtained based on the organic matter maturity of each stratum in the target study area, and its calculation formula is as follows: V L =(94.3R0-43.72)e -0.0049t (4) Among them, V L For the Langevin volume, m 3 / t; R0 is the organic matter maturity, %; t is the formation temperature, t = 0.0593D, K.

6. The method for calculating the total gas content of deep coal-rock gas reservoirs according to claim 5, characterized in that, In step S1, the formula for calculating the organic matter maturity of each stratum is as follows: R0 = (D - 658.39) / 1712.8 (5); Where R0 is the organic matter maturity (%), and D is the formation depth (m).

7. The method for calculating the total gas content of deep coal-rock gas reservoirs according to claim 1, characterized in that, In step S2, the second adsorbed gas quantity relationship is the relationship between the proportion of coal and rock adsorbed gas and the formation pressure, and its calculation formula is as follows: r s ＝-1.2198P+97.985 (6) Where, r s P represents the percentage of adsorbed gas (%); P represents the formation pressure (MPa).

8. The method for calculating the total gas content of deep coal-rock gas reservoirs according to claim 1, characterized in that, In step S3, the formula for calculating the total gas content of coal and rock is: Among them, V 总 For total gas content, m 3 / t; D is the formation depth, m; C P C is the pressure coefficient. P =P / gD; P is the formation pressure, MPa.

9. The method for calculating the total gas content of deep coal-rock gas reservoirs according to claim 1, characterized in that, In step S4, the formula for calculating the relative error is: L=| (V1-V2) / V2|*100% (8) Where L is the relative error, %; V1 is the predicted total gas content of coal and rock, m 3 / t; V2 is the actual total gas content of coal and rock, m 3 / t.

10. The method for calculating the total gas content of deep coal-rock gas reservoirs according to claim 1, characterized in that, In step S5, the discriminant is L≤10%. When the relative error satisfies the discriminant, it proves that the formula for calculating the total gas content of coal and rock is feasible.

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