Method for determining lost gas content of deep coal rock through pressure-maintaining coring

Abstract

The invention belongs to the technical field of core analysis, and discloses a pressure-maintaining coring deep coal rock lost gas content determination method, which comprises the following steps: carrying out pressure-maintaining gas analysis on a pressure-maintaining inner cylinder with a core, and after the pressure-maintaining gas analysis is completed, obtaining the time when the pressure-maintaining inner cylinder is opened; segmenting the rock core subjected to pressure maintaining gas analysis according to rock types to obtain single rock type analysis rock samples; the analysis rock sample is loaded into an analysis tank to be analyzed, the relation between the accumulated analysis gas volume and the total time is obtained through the sampling result in the analysis process, and the linear increasing end point of the accumulated analysis gas volume is determined; after gas analysis of the analysis rock sample is finished, the mass of the analysis rock sample is weighed; obtaining the relation between the square root of the total time before the linear growth end point moment of the cumulative analytic gas volume and the cumulative analytic gas volume, and solving the lost gas volume of the analytic rock sample by adopting a USBM method; and calculating the content of the lost gas by utilizing the mass of the analyzed rock sample and the volume of the lost gas. According to the method, more accurate and reliable deep coal rock lost gas content data can be provided.

Description

A method for determining the gas loss content in deep coal and rock layers obtained by pressure-maintaining coring Technical Field

[0001] This invention belongs to the field of core analysis technology, specifically relating to a method for determining the gas loss content in deep coal and rock during pressure-controlled core sampling. Background Technology

[0002] Deep coalbed methane is a new type of natural gas resource, falling between conventional gas and coalbed methane, characterized by the coexistence of conventional and unconventional reservoirs, and the symbiosis of free and adsorbed gas. Deep coalbed methane has become an important area for natural gas production growth, and its vigorous development is of great significance for meeting the continuously and rapidly growing energy demand and for the clean and efficient utilization of energy. Determining the gas content of deep coalbed methane is crucial for reservoir evaluation and resource calculation. Currently, gas content testing is mainly divided into two methods: closed-loop coring for free and adsorbed gas calculation and field coring for actual measurement. Field coring involves taking samples to the surface for on-site gas content testing and is currently an important evaluation method and tool in natural gas geological exploration. In field coring for actual measurement, the lost gas content is obtained through mathematical calculation. Currently, the calculation of gas loss content in the market is based on shallow coalbed methane under wireline coring conditions, where adsorbed gas dominates. The zero time is defined as the time it takes for the core to be raised halfway through the shaft, and the USBM direct method (developed and widely used by the U.S. Bureau of Mines (USBM) for determining coalbed methane content) is employed. However, deep coalbed methane has well-developed macropores and fractures, resulting in high free gas content and preferential discharge of free gas. Therefore, the USBM direct method is not suitable. Using the time it takes for the core to be raised halfway through the shaft as the zero time contradicts the gas discharge pattern of deep coalbed methane, leading to large errors in the calculated gas loss content and failing to accurately reflect the gas content of the coalbed methane. In field coring technology, pressure-holding coring ensures that gas is not lost during the core extraction process, effectively avoiding the problem of free gas loss in deep coalbed methane and making gas content testing relatively more reliable. However, currently, there is a lack of definition for the zero time in calculating gas loss content under pressure-holding coring conditions, and a lack of applicable calculation models. Therefore, there is an urgent need to establish a method for calculating gas loss content that is compatible with pressure-holding coring. Summary of the Invention

[0003] To address the problems existing in the prior art, the present invention aims to provide a method for determining the gas content loss in deep coal and rock through pressure-maintaining coring. This invention can provide more accurate and reliable data on the gas content loss in deep coal and rock, and can be applied to the evaluation of the gas content of deep coal and rock reservoirs. It provides a basis for accurately calculating the total gas content of coal and rock, delineating favorable exploration areas, and improving the success rate of natural gas exploration and development.

[0004] To achieve the above objectives, the technical solution adopted by this invention is as follows: A method for determining the gas loss content of deep coal and rock samples obtained through pressure-holding core sampling, comprising the following steps: performing pressure-holding gas analysis on a pressure-holding inner cylinder containing the core sample; obtaining the time when the pressure-holding inner cylinder is opened after the pressure-holding gas analysis is completed; dividing the core sample after pressure-holding gas analysis according to rock type to obtain analysis samples of a single rock type; loading the analysis samples into an analysis tank for analysis; using the gas sampling results during the analysis process to obtain the relationship between the cumulative analysis gas volume and the total time; determining the endpoint of the linear increase in the cumulative analysis gas volume based on this relationship; the total... The time is the sum of the loss time and the resolution time. The loss time is the duration between the opening of the pressure-holding inner cylinder and the sealing of the resolution vessel, and the resolution time is the duration between the sealing of the resolution vessel and the sampling time. After the gas resolution of the rock sample is completed, the mass of the rock sample is weighed. The relationship between the square root of the total time before the linear growth endpoint of the cumulative resolution gas volume and the cumulative resolution gas volume is obtained. Based on this relationship, the loss gas volume of the rock sample is calculated using the USBM method. The loss gas content of the rock sample is calculated using the mass of the rock sample and the loss gas volume V.

[0005] Preferably, the method for determining the loss gas content of deep coal and rock in pressure-holding coring of the present invention further includes the following process: after pressure-holding coring is completed, the pressure-holding status of the pressure-holding coring cylinder used to install the pressure-holding inner cylinder is checked. When the pressure-holding status is qualified, the pressure-holding gas of the pressure-holding inner cylinder is analyzed.

[0006] Preferably, when performing pressure-holding gas analysis on the pressure-holding inner cylinder, the gas analysis of the pressure-holding inner cylinder is considered to be completed when the volume of the pressure-holding gas no longer increases. Then, the pressure-holding inner cylinder is opened, the core is taken out, and the time when the pressure-holding inner cylinder is opened is recorded.

[0007] Preferably, when the rock sample is loaded into the analysis vessel for analysis, the analysis vessel is heated to the formation temperature.

[0008] Preferably, when the rock sample is loaded into the analysis vessel for analysis, the analysis vessel is heated to the formation temperature by means of a water bath.

[0009] Preferably, when the rock sample is loaded into the analysis vessel for analysis, the volume of the analysis gas no longer increases, and the analysis of the rock sample and analysis gas ends.

[0010] Preferably, during the analysis of rock samples, interval sampling is performed to obtain the volume of desorbed gas and the sampling time at each sampling time; based on the time of each sampling and the volume of desorbed gas, a graph showing the relationship between the cumulative volume of desorbed gas and the total time is obtained.

[0011] Preferably, the relationship between the cumulative desorbed gas volume and the total time is a fitted curve of the cumulative desorbed gas volume and the total time. The endpoint of the linear increase of the cumulative desorbed gas volume is determined by this fitted curve.

[0012] Preferably, the relationship between the cumulative desorbed gas volume and the total time is a discrete graph of the cumulative desorbed gas volume and the total time. Based on this discrete graph, the last sampling point of the linear growth of the cumulative desorbed gas volume is determined, and the sampling point before this sampling point is taken as the endpoint of the linear growth of the cumulative desorbed gas volume.

[0013] Preferably, the loss gas content of the analytical rock sample is obtained by dividing the loss gas volume of the analytical rock sample by the mass of the analytical rock sample.

[0014] This invention offers the following advantages: The method for determining the lost gas content in deep coal and rock core sampling using pressure-maintaining core sampling utilizes the methane carbon isotope fractionation characteristics of coal and rock gas. It determines the moment the pressure-maintaining inner cylinder is opened as zero time, and combines data such as the desorption gas volume, time, and core weight to determine the relationship between the square root of the total desorption time before the linear growth endpoint of the cumulative desorption gas volume and the desorption gas volume. Based on this relationship, the lost gas volume can be obtained using the existing USBM direct method, and the core lost gas content can be calculated. Experimental testing shows that compared to the traditional calculation method (i.e., defining the time when the core is raised to halfway through the wellbore as zero time, using the USBM direct method to obtain the lost gas volume, and calculating the core lost gas content), the method of this invention yields more accurate and less error-prone results, accurately reflecting the gas content of the coal and rock. This provides a basis for accurately calculating the total gas content of coal and rock, delineating favorable exploration areas, and improving the success rate of natural gas exploration and development. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1(a) shows the calculated gas loss volume for Q35-8-3-1 coal and rock in this embodiment of the invention; Figure 1(b) shows the calculated gas loss volume for Q35-8-3-1 coal and rock using the traditional method (i.e., defining the time when the core tube is raised to half of the shaft as zero time, using the USBM direct method to obtain the gas loss volume, and calculating the core gas loss content); Figure 2 shows the relationship between the cumulative analytical gas volume and the sampling time obtained in this embodiment of the invention; Figure 3 shows the relationship between the square root of the total analytical time before the linear growth endpoint of the cumulative analytical gas volume obtained in this embodiment of the invention and the analytical gas volume. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0018] This invention provides a method for determining the gas loss content in deep coal and rock formations using pressure-maintaining core sampling. This method is based on the methane carbon isotope fractionation characteristics of fractured free gas and matrix desorption gas, the gas occurrence state in coal and rock, and the concept of pressure-maintaining core sampling. It clarifies the changes in the natural gas occurrence state under pressure-maintaining core sampling conditions, the zero-time for calculating gas loss, and the model. This method can provide more accurate and reliable data on the gas loss content in deep coal and rock formations and can be applied to the evaluation of gas content in deep coal and rock reservoirs. It provides a basis for accurately calculating the total gas content of coal and rock, delineating favorable exploration areas, and improving the success rate of natural gas exploration and development.

[0019] Specifically, the implementation principle and process of the technical solution of the present invention are introduced as follows: The implementation principle of the technical solution of the present invention is as follows: (1) For deep coal and rock, macropores and fractures are developed, and free gas is stored in macropores and fractures; (2) In deep coal and rock, in the early stage of coal gas desorption, the free gas content in the fractures is high, and the apparent carbon isotope value δ of coal gas dominated by fracture free gas is high. 13 (3) During the drilling and ascent, as the pressure is maintained and the coal and rock gas desorption process begins, the free gas content decreases and the temperature drops, causing the adsorbed gas in the coal and rock matrix to begin to desorb, increasing the adsorbed gas content and transforming the coal and rock gas occurrence state into one dominated by adsorbed gas; (4) During the desorption process of the adsorbed gas in the coal and rock matrix, 13 CH4 ratio 12 CH4 is difficult to desorb, therefore isotopic fractionation easily occurs during desorption-diffusion, meaning that the first desorbed coal shale gas δ- 13 The C1 value is relatively low, and the methane desorbed later is relatively rich. 13 C is biased; (5) In the later stage of pressure holding and coal gas desorption, the coal gas δ is dominated by adsorbed gas. 13 Fractionation occurs at C1 value, apparent δ 13 The C1 value decreases; (6) The present invention takes the time of opening the pressure-holding inner cylinder as zero time, and the loss gas can be calculated by the USBM direct method.

[0020] Specifically, the method for determining the gas loss content in deep coal and rock using pressure-holding coring provided in this embodiment includes the following steps: Step ①, performing pressure-holding coring. After the pressure-holding coring cylinder reaches the surface, check whether the pressure holding of the pressure-holding coring cylinder is successful. If the pressure holding is successful, proceed to Step ②; Step ②, remove the pressure-holding inner cylinder from the pressure-holding coring cylinder and connect the pressure-holding inner cylinder to the analysis equipment; Step ③, open the gas outlet valve of the pressure-holding inner cylinder and start the pressure-holding gas analysis; Step ④, take gas samples during the pressure-holding gas analysis process and number the gas samples. The gas sample obtained from the i-th sampling is recorded as the pressure-holding gas sample QB. iStep 5: During the pressure-holding gas analysis process, when the volume of the pressure-holding gas no longer increases, it is determined that the pressure-holding gas analysis in the inner cylinder has ended. Step 6: Then, open the inner cylinder and record the opening time T0. Step 7: Remove the rock core from the inner cylinder and divide the rock core according to different rock types to obtain single-type analytical rock samples. The analytical rock sample corresponding to each type of rock is denoted as analytical rock sample SY. j Specifically, the j-th analytical rock sample is denoted as analytical rock sample SY. j For any type of rock, the corresponding analytical rock sample SY j The following steps are performed; Step ⑧, the rock sample SY is analyzed. j The sample was placed into the analysis container, and the sealing time T1 was recorded; the analysis rock sample SY was then placed into the analysis container. j When loading the analysis vessel, simply load the sample according to the vessel's requirements for the rock sample; step 9, load the rock sample containing the analysis vessel SY j The analytical container is connected to the analytical equipment, and the analytical container is placed in a water bath that maintains the formation temperature for analytical purposes, so as to simulate the temperature environment of the analytical rock sample in the actual formation; step 10, the analytical rock sample SY is analyzed through the analytical container. j During the analysis process, analysis gas samples (QG) are obtained from the analysis tank at multiple intervals. k Let the desorption gas sample obtained from the desorption vessel in the kth iteration be denoted as desorption gas sample QG. k Simultaneously record the time T of the k-th sampling. k The analytical gas volume V obtained from the kth sampling k Where k = 1, 2, 3…n, and n is the total number of times the gas sample is obtained; step 11, the rock sample SY is analyzed using an analytical vessel. j During the analysis process, the rock sample analysis ends when the cumulative analysis gas volume no longer increases; step 12, then open the analysis vessel and take the analysis rock sample SY. j After being removed, the sample was weighed to obtain the analytical rock sample SY. j weight M j Step 13: The pressure-holding gas sample QB obtained in step 4... i Carbon isotope analysis was performed to obtain the pressurized gas sample QB. i carbon isotope value δ 13 C 1i Step 14: Analyze the pressure-holding gas sample QB. i Carbon isotope value δ 13 C 1i If the carbon isotope value δ 13 C 1i A decrease indicates an increase in the adsorbed gas content of the coal matrix, further indicating that the coal gas occurrence state has changed to be dominated by adsorbed gas; step ⑮, based on the desorbed gas volume V k Total time t 总 Obtain the cumulative analysis volume and total time t 总Referring to Figure 2, the endpoint of the linear growth of the cumulative analytical volume can be obtained from this relationship diagram; where the total time t 总 The total time t is obtained as follows: 总 The sum of the loss time and the resolution time is calculated, where the loss time is the duration between the sealing time T1 and the opening time of the pressure-holding inner cylinder T0; and the resolution time is the duration between each sampling time during resolution through the resolution tank and the sealing time T1. If the graph of the cumulative resolution gas volume versus total time is a fitted curve of the cumulative resolution gas volume versus total time, then on this fitted curve, find the endpoint of the linear growth of the cumulative resolution gas volume (also called the inflection point; after this inflection point, the cumulative resolution volume generally exhibits obvious nonlinearity), and determine the time of this endpoint; if the graph of the cumulative resolution gas volume versus total time is a discrete graph of the cumulative resolution gas volume versus total time, as shown in Figure 2, then based on this discrete graph, determine the last sampling point T of the linear growth of the cumulative resolution gas volume. k Sampling point T k The previous sampling point T k-1 As the endpoint of the linear increase in the cumulative desorbed gas volume, this ensures that sampling point T... k-1 Previously, the cumulative desorbed gas volume showed a relatively good linear growth trend. In this case, the total time t mentioned above... 总 The calculation formula is: t 总 = (T1-T0)+(T k-1 -T1) = T k-1 -T0; Referring to Figure 2, in the above scheme, the linear growth segment of the cumulative desorbed gas volume refers to the segment where the cumulative desorbed gas volume roughly increases linearly. This linear growth generally appears at the beginning of the fitted curve y in Figure 2, and is not strictly linear. Those skilled in the art can make a rough judgment based on the actual situation. This invention does not make specific limitations. If the sampling time interval is short enough during the analysis of the rock sample in the analysis vessel, then in the above scheme, the last sampling point T that determines the linear growth of the cumulative desorbed gas volume is determined. k If this point is taken as the endpoint of linear growth, it is closer to the inflection point obtained by fitting the curve, so no further points are taken; step 16, then plot the total time t before the inflection point. 总 The relationship between the square root and the cumulative analytical gas volume (denoted as the square root relationship diagram) is shown in Figure 3; Step 17: Using the square root relationship diagram, the USBM method is used to determine the analytical rock sample SY. j Loss of gas volume V: Step 18, calculate the analytical rock sample SY using the following formula. j Loss gas content: Q j损 = V / M j .

[0021] The example analysis examines the carbon isotope fractionation characteristics of methane in the pressure-holding gas of coal and rock in well Q35-8-3-1 of well Q35. The time when the pressure-holding inner cylinder is opened is determined as the zero time. Combined with the analysis of gas volume, time, and core weight data, the loss gas volume is obtained using the USBM direct method, and the core loss gas content is calculated.

[0022] This embodiment of the method for determining the gas loss content in deep coal and rock through pressure-holding coring includes the following steps: Step ①, performing pressure-holding coring; after the pressure-holding coring cylinder reaches the surface, check that the pressure-holding effect of the pressure-holding coring cylinder is good, then proceed to Step ②; Step ②, removing the pressure-holding inner cylinder from the pressure-holding coring cylinder and connecting the pressure-holding inner cylinder to the analysis equipment; Step ③, opening the gas outlet valve of the pressure-holding inner cylinder to start pressure-holding gas analysis; Step ④, taking gas samples during the pressure-holding gas analysis process, and numbering the gas samples accordingly; the i-th gas sample is registered as pressure-holding gas sample QB. i In this embodiment, a total of 14 gas samples were taken, and the gas sample obtained from the i-th sample was recorded as Q35-B. i Where i = 1, 2, ..., 14; Step ⑤, during the pressure-holding gas analysis process, when the volume of the pressure-holding gas no longer increases, it is determined that the pressure-holding gas analysis of the inner cylinder has ended; Step ⑥, then open the inner cylinder and record the opening time T0 (i.e., time T0 = 14:08); Step ⑦, take out the rock core from the inner cylinder, divide the rock core according to different rock types, and obtain single-type analytical rock samples. In this embodiment, the analytical rock sample corresponding to coal and rock is denoted as analytical rock sample SY. j The j-th analytical rock sample is denoted as analytical rock sample SY. j (Q35-8-3-1, j=1); Step ⑧, load the analysis rock sample SY1 (Q35-8-3-1) into the analysis container and record the sealing time T1 (i.e., time T1=14:18); Step ⑨, connect the analysis container containing the analysis rock sample SY1 (Q35-8-3-1) to the analysis equipment, and place the analysis container in a water bath that maintains the formation temperature (e.g., 70℃) for analysis; Step ⑩, analyze the analysis rock sample SY1 through the analysis container. j During the analysis process, analysis gas samples (QG) are obtained from the analysis tank at multiple intervals. k In this embodiment, a total of 10 samples were taken. The desorption gas sample obtained from the desorption vessel in the kth sample is denoted as desorption gas sample QG. k Record the time T of the kth sampling. k and the volume V of the gas in the kth analysis k Where k = 1, 2, 3, ..., 10, 10 represents the total number of times the gas sample was obtained; step 11, the rock sample SY was analyzed using an analytical vessel. j During the analysis process, after the 10th sampling, it was found that the cumulative desorption gas volume no longer increased, and no further sampling was performed, indicating that the core gas analysis was completed; Step 12, open the analysis vessel and take the analysis rock sample SY j(Q35-8-3-1) After being taken out, it was weighed to obtain the analytical rock sample SY. j The weight is M j (i.e. M) j =1575g); Step 13, take the pressurized gas sample QB obtained in step 4. i Carbon isotope analysis was performed to obtain the pressurized gas sample QB. i carbon isotope value δ 13 C 1i (i=14, where QB1, QB2, QB3, ..., QB 14 The corresponding carbon isotope value δ 13 C 1i The values ​​are, in sequence: -32.0‰, -31.5‰, -31.2‰, -32.0‰, -31.6‰, -32.1‰, -32.4‰, -32.2‰, -32.5‰, -32.5‰, -33.2‰, -34.0‰, -34.1‰, -34.1‰); step 14, analyze the pressure-holding gas sample QB obtained in step 13. i Carbon isotope value δ 13 C 1i It can be determined by the carbon isotope value δ. 13 C 1i The decrease (-32.0‰→-34.1‰) indicates an increase in the adsorbed gas content of the coal matrix, suggesting that adsorbed gas is the dominant form of coal gas. Step ⑮ involves determining the gas volume V... k Total time t 总 Compile cumulative analytical volume and total time t 总 The relationship diagram (discrete diagram as shown in Figure 2) is used to obtain the inflection point on the discrete diagram. This inflection point occurs in the sixth sampling in step 11, i.e., k=6. At this time, the fifth sampling time (i.e., k-1=5) in step 11 is taken as the endpoint of the linear growth of the cumulative analytical volume. The time T at this time is... k-1 =20:48; Therefore, in this embodiment, based on the opening time of the pressure-holding inner cylinder T0 (14:08), the sealing time T1 (14:18), and the inflection point sampling time T k-1 (20:48), total time t 总 = (T1-T0)+(T k-1 -T1) = T k-1 -T0 = (20:48) - (14:08) = 400 min; Step 16, use the total time t corresponding to each of the first five samplings in step 11. 总 The square root and the cumulative analytical volume corresponding to each sampling are used to obtain the cumulative analytical volume and the total time t. 总And the relationship diagram (denoted as the square root relationship diagram); Step 17, using the square root relationship diagram in Step 16, the loss gas volume V = 6726.8 ml of the analytical rock sample is obtained by the USBM method, as shown in Figure 1(a); Step 18, based on the loss gas volume of the analytical rock sample calculated in Step 17 and the weight of the analytical rock sample obtained in Step 12, M is... j Calculate the loss gas content Q j损 = V / M j = 6726.8ml / 1575g = 4.3ml / g.

[0023] The results of calculating the lost gas volume of Q35-8-3-1 coal using the traditional method (i.e., defining the time when the core tube is raised to half of the shaft as zero time, using the USBM direct method to obtain the lost gas volume, and calculating the core lost gas content) are shown in Figure 1(b). The lost gas content is 21998 ml.

[0024] The experimental results of the embodiments of the present invention and the above-described conventional methods are shown in Table 1: Table 1

[0025] As can be seen from the results in Table 1, the calculation results of this invention show that the gas volume loss is 6726.8 ml and the gas content loss is 4.3 m³. 3 / t, with a gas loss ratio of 15.3% and a free gas ratio of 22.8%. Method ②, using the time to reach halfway up the wellbore as zero time, calculated a gas loss volume of 21998 ml and a gas loss content of 14.0 m³. 3 / t, with a gas loss ratio of 37.1% and a free gas ratio of 42.7%. The reason for the difference in the above calculations is that due to the development of macropores and fractures in deep coal and rock, the free gas content is high, and the free gas is preferentially discharged. Using the time when the core tube is raised to half of the shaft as the zero time contradicts the gas discharge law of deep coal and rock, resulting in a large error in the calculated gas loss content, which cannot accurately reflect the gas content of coal and rock.

[0026] As can be seen from the above scheme, this invention, by analyzing the carbon isotope fractionation characteristics of methane in coalbed methane, determines that the opening time of the pressure-holding inner cylinder is zero. Combining the data of gas volume, time, and core weight, the loss gas volume is obtained using the USBM direct method, and the loss gas content in the core is calculated. The calculation results are more accurate. Because this invention accurately calculates the loss gas content under pressure-holding core sampling conditions, it provides a strong basis for accurately calculating the total gas content and resource volume of deep coalbed methane, evaluating favorable exploration areas, and improving the success rate of deep coalbed methane exploration and development.

[0027] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for determining the gas content of deep coal and rock loss during pressure-maintaining coring, characterized in that, The process includes the following steps: performing pressure-holding gas analysis on the pressure-holding inner cylinder containing the core sample; obtaining the time when the pressure-holding inner cylinder was opened after the pressure-holding gas analysis was completed; and dividing the core sample after the pressure-holding gas analysis was completed according to rock type to obtain analytical rock samples of single rock type. The rock sample is placed in an analytical vessel for analysis. Using the gas sampling results during the analysis process, the relationship between the cumulative analytical gas volume and the total time is obtained. Based on this relationship, the endpoint of the linear increase in the cumulative analytical gas volume is determined. The total time is the sum of the loss time and the analysis time. The loss time is the duration between the opening of the pressure-holding inner cylinder and the sealing of the analytical vessel, and the analysis time is the duration between the sealing of the analytical vessel and the sampling time. After the gas analysis of the rock sample is completed, the mass of the rock sample is weighed. The relationship between the square root of the total time before the endpoint of the linear increase in the cumulative analytical gas volume and the cumulative analytical gas volume is obtained. Based on this relationship, the loss gas volume of the rock sample is calculated using the USBM method. Using the mass of the rock sample and the loss gas volume, the loss gas content of the rock sample is calculated.

2. The method for determining the gas content of deep coal and rock loss during pressure-maintaining coring according to claim 1, characterized in that, The process also includes the following steps: After the pressure-holding core sampling is completed, check the pressure-holding status of the pressure-holding core sampling cylinder used to install the pressure-holding inner cylinder. Once the pressure-holding status is qualified, perform pressure-holding gas analysis on the pressure-holding inner cylinder.

3. The method for determining the gas loss content in deep coal and rock formations using pressure-maintaining coring according to claim 1, characterized in that, When performing pressure-holding gas analysis on the pressure-holding inner cylinder, the gas analysis of the pressure-holding inner cylinder is considered to be completed when the volume of the pressure-holding gas no longer increases. Then, the pressure-holding inner cylinder is opened, the core is taken out, and the time of opening the pressure-holding inner cylinder is recorded.

4. The method for determining the gas content of deep coal and rock loss in pressure-maintaining coring according to claim 1, characterized in that, When the rock sample is loaded into the analysis vessel for analysis, the analysis vessel is heated to the formation temperature.

5. The method for determining the gas loss content in deep coal and rock formations using pressure-maintaining coring according to claim 4, characterized in that, When the rock samples are loaded into the analysis vessel for analysis, the analysis vessel is heated to the formation temperature by means of a water bath.

6. The method for determining the gas content of deep coal and rock loss in pressure-maintaining coring according to claim 1, characterized in that, When the rock sample is loaded into the analysis vessel for analysis, the volume of the analysis gas no longer increases, and the analysis of the analysis gas in the rock sample is completed.

7. The method for determining the gas content of deep coal and rock loss in pressure-maintaining coring according to claim 1, characterized in that, During the analysis of rock samples, interval sampling was performed to obtain the volume of desorbed gas and the sampling time for each sampling. Based on the sampling time and the volume of desorbed gas for each sampling, a graph showing the relationship between the cumulative volume of desorbed gas and the total time was obtained.

8. The method for determining the gas loss content in deep coal and rock formations using pressure-maintaining coring according to claim 7, characterized in that, The relationship between the cumulative desorbed gas volume and the total time is a fitted curve of the cumulative desorbed gas volume and the total time. The endpoint of the linear increase of the cumulative desorbed gas volume is determined by this fitted curve.

9. The method for determining the gas loss content in deep coal and rock formations using pressure-maintaining coring according to claim 7, characterized in that, The relationship between the cumulative desorbed gas volume and the total time is a discrete graph of the cumulative desorbed gas volume and the total time. Based on this discrete graph, the last sampling point of the linear growth of the cumulative desorbed gas volume is determined, and the sampling point before this sampling point is taken as the endpoint of the linear growth of the cumulative desorbed gas volume.

10. The method for determining the gas loss content in deep coal and rock formations using pressure-maintaining coring according to claim 1, characterized in that, The loss gas content of the analytical rock sample is obtained by dividing the volume of gas lost from the analytical rock sample by the mass of the analytical rock sample.

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