A gas source burial depth prediction method and a coal-derived gas maturity prediction method

Abstract

This invention relates to a method for predicting the burial depth of coalbed methane and a method for predicting the maturity of coalbed methane, belonging to the field of oil and gas exploration and development technology. This method accurately characterizes the relationship between the composition ratio of coalbed methane and the methane carbon isotopes in coalbed methane through a two-segment linear relationship. By combining the relationship between methane carbon isotopes and coalbed methane maturity, the intermediate variable of methane carbon isotopes can be eliminated, resulting in a two-segment linear relationship between coalbed methane maturity and its composition ratio. In the actual exploration and production process of coalbed methane, since the natural gas composition content is a routine analytical item tested by general grassroots units, data is relatively easy to obtain. By determining the composition ratio of coalbed methane in the region, and utilizing the two-segment linear relationship between coalbed methane maturity and its composition ratio, the maturity value of coalbed methane in the region can be quickly calculated. Combined with the relationship between coalbed methane maturity and the burial depth of the gas source, the burial depth of the gas source can then be determined with high accuracy.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas exploration and development technology, specifically relating to a method for predicting the burial depth of gas sources and a method for predicting the maturity of coalbed methane. Background Technology

[0002] In recent years, exploration targeting coal-bearing source rocks has become a hot topic in the exploration community. With increasing exploration depth, the gas burial depth of coal-derived gas reservoirs has become a key focus. For oil and gas explorers, determining the gas source of coal-derived gas reservoirs is crucial. Identifying the gas source allows for the tracing of the source and reservoir pathways, enabling the discovery of a series of coal-derived gas reservoirs. Conversely, incorrectly identifying the gas source can lead to a series of exploration failures, wasting significant human and material resources.

[0003] Regarding the prediction of the burial depth of coalbed methane sources, existing methods mainly rely on methane carbon isotopes (δ¹⁸O₁⁻). 13 C1) can be used to infer the maturity Ro of coal-derived gas. Based on the correspondence between the maturity Ro of coal-derived gas and the burial depth of oil and gas basins, the approximate burial depth of the gas source in coal-derived gas reservoirs can be quickly estimated, thereby identifying the approximate burial depth of the gas source.

[0004] Therefore, if the maturity level Ro of coalbed methane is known, the burial depth of the gas source can be easily determined. However, determining the maturity level Ro of coalbed methane is currently quite difficult. Existing technologies mainly employ two types of methods:

[0005] The first type of method utilizes the carbon isotopes (δ¹⁸) of methane in coalbed methane. 13 The C1 method is used to determine the burial depth of coalbed methane. Stahl, Dai Jinxing, Shen Ping, Xu Yongchang, and others studied the carbon isotopes (δ¹⁰) of methane in coalbed methane. 13 The relationship between C1) and the maturity Ro of coalbed methane was obtained, and the carbon isotopes (δ¹⁴C1) of methane in coalbed methane were determined. 13 The relationship between C1 and the maturity Ro of coalbed methane isotopes is evident; however, it can be seen that different scholars have used methane carbon isotopes (δ¹⁸O) in coalbed methane to determine the relationship. 13 The formulas for inferring the maturity Ro of coalbed methane using C1) differ significantly.

[0006] For example, Dai Jinxing proposed δ 13 C1 = 14.12LgRo - 34.39, Shen Ping proposed δ 13 C1 = 40.49 lgRo-34; Xu Yongchang proposed δ 13 C1 = 49.56LgR o - 34.48. Taking a certain gas reservoir as an example, through extensive research, it can be confirmed that the gas reservoir is a coal-derived gas reservoir, and the methane carbon isotope δ¹⁸O of this gas reservoir is... 13With a C1 value of -28.6‰, the maturity Ro of coalbed methane, calculated using the formula proposed by Dai Jinxing, is 2.57%. Combined with the thermal evolution curve of the region, the estimated burial depth of the main gas source is 6524.90m. Based on the formula proposed by Shen Ping, the maturity Ro is 1.36%, and combined with the thermal evolution curve of the region, the estimated burial depth of the main gas source is 4910.67m. However, based on the formula proposed by Xu Yongchang, the maturity Ro is 1.31%, and combined with the thermal evolution curve of the region, the estimated burial depth of the main gas source is 4824.78m. Therefore, a comparison shows that the maximum burial depth of the gas source is 6524.90m, and the minimum is 4824.78m, a difference of 1700m, which is significant. This demonstrates that, to date, the use of methane carbon isotopes (δ¹⁸O) in coalbed methane... 13 The method of using C1 to determine the burial depth of gas sources in coal-derived gas reservoirs still has significant differences and is not highly reliable.

[0007] Furthermore, for frontline oil and gas production units, the above-mentioned utilization of methane carbon isotopes (δ¹²⁸) in coalbed methane... 13 The C1 method for determining the burial depth of coalbed methane has significant limitations and is not applicable because: the carbon isotopes of methane in coalbed methane (δ¹⁴C⁻¹)... 13 The C1 method is characterized by a long analysis cycle and high requirements for testing qualifications. Generally, oil and gas field research institutions do not have the ability to determine the carbon isotope value of methane, which makes it impossible to obtain the methane carbon isotope value quickly. If a gas layer is encountered during drilling, it is often difficult for oilfield decision-makers to quickly determine whether to drill deeper or stop drilling, which affects the smooth progress of exploration.

[0008] The second type of method: Some scholars have attempted to propose applying the component ratio CH4 / (CH4+C2H6+C3H8), or the humidity of coalbed methane (W=(C2H6+C3H8+C4H8)). 10 +C5H 10 ) / (CH4+C2H6+C3H8+C4H 10 +C5H 10 To explore the relationship between the maturity Ro of coalbed methane and its composition ratio or moisture content, this method was used in actual production. However, it was found that the Ro value determined by CH4 / (CH4+C2H6+C3H8) mostly fell between 0.85 and 1.0, which is inconsistent with actual conditions. Furthermore, the Ro value determined by coalbed methane moisture content was negative in some areas, possibly due to the complex genesis of the gas reservoirs, and thus contained considerable uncertainty. Therefore, the reliability of this method in predicting the burial depth of gas sources is also low. Summary of the Invention

[0009] The purpose of this invention is to provide a method for predicting the burial depth of gas sources to address the problem of low reliability in existing methods for predicting the burial depth of gas sources. Simultaneously, this invention proposes a method for predicting the maturity of coalbed methane to address the problem of low reliability in existing methods for predicting the maturity of coalbed methane.

[0010] Based on the above objectives, a technical solution for a gas source burial depth prediction method is as follows:

[0011] (1) Based on the geochemical data of coalbed methane, the composition of methane, ethane and propane in coalbed methane in several regions and the carbon isotope value of methane in coalbed methane are obtained. The composition of methane is divided by the sum of the composition of ethane and propane to obtain the composition ratio of coalbed methane. The relationship between the composition ratio of coalbed methane and the carbon isotope value of methane in coalbed methane is fitted to obtain the first linear relationship and the second linear relationship. When the composition ratio of coalbed methane is less than the set composition ratio threshold, it is the first linear relationship; when the composition ratio of coalbed methane is not less than the composition ratio threshold, it is the second linear relationship.

[0012] (2) Obtain the relationship between the carbon isotopes of methane in coalbed methane and the maturity of coalbed methane, and combine the relationship between the component ratio of coalbed methane and the carbon isotope value of methane in coalbed methane to determine the relationship between the component ratio of coalbed methane and the maturity of coalbed methane.

[0013] (3) Obtain the coal-derived gas component ratio of the target area, and calculate the coal-derived gas maturity value of the target area by combining the relationship between the coal-derived gas component ratio and the coal-derived gas maturity. Using this value, and combining the relationship between the coal-derived gas maturity and the gas source burial depth, calculate the gas source burial depth of the target area.

[0014] The beneficial effects of the above technical solution are:

[0015] This invention accurately characterizes the relationship between the component ratio of coalbed methane and the methane carbon isotopes in coalbed methane through a two-segment linear relationship. By combining this with the relationship between methane carbon isotopes and coalbed methane maturity, the intermediate variable of methane carbon isotopes can be eliminated, resulting in a two-segment linear relationship between coalbed methane maturity and its component ratio. Therefore, in the actual exploration and production of coalbed methane, since the composition of natural gas is a routine analytical item tested by general grassroots units and data is relatively easy to obtain, the coalbed methane component ratio of the region can be determined. Then, using the two-segment linear relationship between coalbed methane maturity and its component ratio, the maturity value of the coalbed methane in that region can be quickly calculated. Combining this with the relationship between coalbed methane maturity and the burial depth of the gas source, the burial depth of the gas source can be determined with high accuracy. Compared with existing technologies, the method of this invention is simple in principle, fast in predicting the burial depth of the gas source, and highly accurate. It can be rapidly promoted and applied in frontline oil and gas units, providing technical support for efficient exploration.

[0016] Furthermore, the relationship between the coalbed methane component ratio and the coalbed methane maturity is expressed as follows:

[0017] Ro=a1˙Y+b1 Y<y0

[0018] Ro=a2˙Y+b2 Y≥y0

[0019] In the formula, Ro is the maturity of coalbed methane, Y is the composition ratio of coalbed methane, a1, a2, b1, and b2 are all parameters, and each parameter is determined by calculation in step (2); y0 is the set composition ratio threshold.

[0020] Furthermore, a gold tube thermal simulation experiment was used to simulate the characteristics of oil and gas generation under underground temperature and pressure conditions, and to determine the relationship between the methane carbon isotopes in the coalbed methane and the maturity of the coalbed methane, with high accuracy.

[0021] Based on the above objectives, the technical solution for a method to predict the maturity of coalbed methane is as follows:

[0022] (1) Based on the geochemical data of coalbed methane, the composition of methane, ethane and propane in coalbed methane in several regions and the carbon isotope value of methane in coalbed methane are obtained. The composition of methane is divided by the sum of the composition of ethane and propane to obtain the composition ratio of coalbed methane. The relationship between the composition ratio of coalbed methane and the carbon isotope value of methane in coalbed methane is fitted to obtain the first linear relationship and the second linear relationship. When the composition ratio of coalbed methane is less than the set composition ratio threshold, it is the first linear relationship; when the composition ratio of coalbed methane is not less than the composition ratio threshold, it is the second linear relationship.

[0023] (2) Obtain the relationship between the carbon isotopes of methane in coalbed methane and the maturity of coalbed methane, and combine the relationship between the component ratio of coalbed methane and the carbon isotope value of methane in coalbed methane to determine the relationship between the component ratio of coalbed methane and the maturity of coalbed methane.

[0024] (3) Obtain the coal-derived gas component ratio of the target area, and calculate the coal-derived gas maturity of the target area based on the relationship between the coal-derived gas component ratio and the coal-derived gas maturity.

[0025] The beneficial effects of the above technical solution are:

[0026] This invention accurately characterizes the relationship between the component ratio of coalbed methane and the methane carbon isotopes in coalbed methane through a two-segment linear relationship. By combining this with the relationship between methane carbon isotopes and coalbed methane maturity, the intermediate variable of methane carbon isotopes can be eliminated, yielding a two-segment linear relationship between coalbed methane maturity and its component ratio. Therefore, in the actual exploration and production of coalbed methane, natural gas component content is a routine analytical item tested by general grassroots units, and data is relatively easy to obtain. Thus, by determining the component ratio of coalbed methane in a region and then utilizing the two-segment linear relationship between coalbed methane maturity and its component ratio, the maturity value of coalbed methane in that region can be quickly calculated with high accuracy and reliability. The coalbed methane maturity predicted by the method of this invention helps to accurately predict the burial depth of gas sources.

[0027] Furthermore, the relationship between the coalbed methane component ratio and the coalbed methane maturity is expressed as follows:

[0028] Ro=a1˙Y+b1 Y<y0

[0029] Ro=a2˙Y+b2 Y≥y0

[0030] In the formula, Ro is the maturity of coalbed methane, Y is the composition ratio of coalbed methane, a1, a2, b1, and b2 are all parameters, and each parameter is determined by calculation in step (2); y0 is the set composition ratio threshold.

[0031] Furthermore, a gold tube thermal simulation experiment was used to simulate the characteristics of oil and gas generation under underground temperature and pressure conditions, and to determine the relationship between the methane carbon isotopes in the coalbed methane and the maturity of the coalbed methane, with high accuracy. Attached Figure Description

[0032] Figure 1 This is a flowchart of the gas source burial depth prediction method in the embodiment of the present invention;

[0033] Figure 2 This is a graph showing the relationship between the carbon isotopes of methane and the component ratios of coalbed methane in the embodiments of the method of the present invention.

[0034] Figure 3 This is a diagram showing the relationship between methane carbon isotopes and coalbed methane maturity in the embodiments of the method of the present invention.

[0035] Figure 4 This is a graph showing the relationship between coalbed methane maturity and coalbed methane component ratio in the embodiments of the method of the present invention. Detailed Implementation

[0036] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0037] Example of a depth prediction method:

[0038] This embodiment proposes a method for predicting the burial depth of gas sources. The basic principle is as follows: Based on geochemical data of coalbed methane, the composition of methane, ethane, and propane in coalbed methane from several regions is obtained, along with the carbon isotopes of methane in the coalbed methane. The methane composition is then divided by the sum of the ethane and propane compositions to obtain the coalbed methane composition ratio. The relationship between the coalbed methane composition ratio and the carbon isotopes of methane in the coalbed methane is fitted to obtain a first linear relationship and a second linear relationship. When the coalbed methane composition ratio is less than a set composition ratio threshold, it is considered the first linear relationship; when the coalbed methane composition ratio is not less than the threshold, it is considered the second linear relationship. The slope of the first linear relationship is greater than the slope of the second linear relationship.

[0039] Then, coal-bearing source rock samples were obtained, and gold tube thermal simulation experiments were conducted on the samples to simulate the relationship between methane carbon isotopes and coal-bearing gas maturity in the generated coal-bearing source rock under different thermal evolution conditions. Using this relationship, combined with the first and second linear relationships obtained above, the relationship between coal-bearing gas component ratio and coal-bearing gas maturity was determined.

[0040] Finally, by utilizing the relationship between the coalbed methane composition ratio and coalbed methane maturity, and substituting the coalbed methane composition ratio of a specific region, the coalbed methane maturity of that region can be accurately calculated. Using this coalbed methane maturity, and combining it with the relationship between coalbed methane maturity and gas source burial depth, the gas source burial depth of that region can be predicted with relatively high accuracy. The overall process is as follows: Figure 1 As shown.

[0041] The implementation steps of this method are described below:

[0042] Step 1: Based on geochemical data of coalbed methane, obtain the composition of methane, ethane, and propane in coalbed methane from 150 regions (target areas), as well as the carbon isotope (δ¹⁸) of methane in the coalbed methane. 13 C1), see Table 1 for details.

[0043] Table 1. Composition of coalbed methane and methane isotopes in the target area

[0044]

[0045]

[0046]

[0047]

[0048] Step 2: Fit the relationship between the composition ratio of coalbed methane and the carbon isotopes of methane in coalbed methane.

[0049] Specifically, the composition ratio of coalbed methane (CH4) in Table 1 is calculated by adding the composition ratios of ethane (C2H6) and propane (C3H8), i.e., Y = CH4 / (C2H6 + C3H8). The calculated ratios are shown in Table 2.

[0050] Table 2. Composition ratio of coalbed methane Y and maturity of coalbed methane Ro

[0051]

[0052]

[0053]

[0054] After determining the coalbed methane composition ratio, based on the coalbed methane composition ratio in Table 2 and the methane carbon isotopes in Table 1, the coalbed methane composition ratio Y was fitted to the relationship between the methane carbon isotopes (δ¹⁸O) in the coalbed methane. 13 The relationship between C1), such as Figure 2 As shown, the first linear relationship and the second linear relationship are expressed as follows:

[0055] δ 13 C1=0.2659Y-38.284 Y<40 (1)

[0056] δ 13 C1=0.0135Y-28.657 Y≥40 (2)

[0057] Equation (1) represents the first linear relationship, and Equation (2) represents the second linear relationship. When the coalbed methane component ratio Y < 40, the two show a linear correlation in the first linear relationship with a steep slope. This is because in the low-temperature evolution stage, the content of ethane and propane is already high, and they can be cracked into methane, so the content changes greatly, which may cause instability and result in a steep slope. When the coalbed methane component ratio Y ≥ 40, as the value of Y increases, the carbon isotope (δ¹⁰) of methane in the coalbed methane increases. 13 The C1) change is relatively weak, and the two show a second linear relationship with a relatively gentle slope. This is because in the high-temperature evolution stage, the content of ethane and propane is already low, and the difficulty of cracking into methane gradually increases. The composition of natural gas is relatively stable, so the slope is relatively gentle.

[0058] In this step, since the coalbed methane component ratio in Table 2 is generally between 5 and 60, the range is large and the discrimination is high, so the fitted two-segment linear relationship is more in line with the actual situation.

[0059] Step 3: Fit the maturity Ro of coalbed methane with the carbon isotope (δ¹⁸) of methane in the coalbed methane. 13 The relationship between C1).

[0060] Specifically, coal-bearing source rock samples were obtained, and gold tube thermal simulation experiments were conducted on these samples to simulate the methane carbon isotopes (δ¹⁸O) in coal-bearing gas under different thermal evolution conditions. 13 The relationship between C1) and the maturity Ro of coalbed methane, and the carbon isotope (δ¹⁴) of methane in the generated coalbed methane. 13 Table 3 shows the relationship between C1 and coalbed methane maturity Ro:

[0061] Table 3. Carbon isotope values ​​of methane generated by coal and rock under different thermal evolution degrees (Ro).

[0062]

[0063] Based on the experimental data in Table 3 above, the carbon isotopes of methane in coalbed methane (δ¹⁸O₁⁻¹) were obtained by fitting the data. 13 The relationship between C1 and coalbed methane maturity Ro, such as Figure 3 As shown, the mathematical expression is as follows:

[0064] δ 13 C1 = 7.9602Ln(Ro) - 39.074R 2 =0.9574 (3)

[0065] In the formula, Ln represents an exponential function with base e, and R... 2 Represents (δ) 13 The correlation between C1 and Ro was 95.74%.

[0066] Rearranging the above formula, we obtain the following expression for the coalbed methane maturity Ro:

[0067] Ro=exp(δ 13 C1+39.074) / 7.9602 (4)

[0068] In this step, a gold tube thermal simulation experiment is used, which can accurately simulate the characteristics of oil and gas generation under underground temperature and pressure conditions. It can accurately determine the methane carbon isotopes in coalbed methane at different thermal evolution levels. Alternatively, without conducting experiments, the existing coalbed methane maturity Ro and methane carbon isotope (δ¹⁸O) data can be directly used. 13 The relational expression for C1) is replaced.

[0069] Step four: Determine the relationship between the coalbed methane component ratio Y and the coalbed methane maturity Ro, and calculate the coalbed methane maturity Ro.

[0070] Specifically, by combining the first relation (1) and the second relation (2) in step two, and the expression (4) for the maturity of coalbed methane in step three, the relationship between the coalbed methane component ratio Y and the maturity of coalbed methane Ro can be obtained, such as... Figure 4As shown, the expression is as follows:

[0071] Ro=0.0719Y+0.8624 Y<40 (5)

[0072] Ro=0.008Y+3.6388 Y≥40 (6)

[0073] After determining the relationship between the coalbed methane component ratio Y and the coalbed methane maturity Ro, the coalbed methane maturity Ro of a certain region can be calculated based on the coalbed methane component ratio value of that region.

[0074] Step 5: Obtain the relationship between the coalbed methane maturity Ro and the gas source burial depth (D) in this region. Substitute the coalbed methane maturity Ro obtained in Step 4 into this relationship to calculate the gas source burial depth in this region, thus achieving accurate prediction of the gas source burial depth.

[0075] Taking the q131-q150 area in Table 2 as an example, q131-q150 are all located in the Dongpu Depression of the Bohai Bay Basin. Although the tectonic locations of the samples are different, they all belong to the same depression and have a consistent thermal history evolution pattern. Through extensive measurements of the maturity Ro of the coal-bearing source rocks in this depression, the following relationship was found between the maturity Ro of the coal-bearing source rocks and the burial depth (D):

[0076] D = 2533.7Ln(Ro) + 4132.6 (7)

[0077] Using a natural gas composition ratio of 40 as the boundary, and following the relationships in Equations 5 and 6, the coal-derived gas maturity Ro of samples q131-q150 was calculated, as shown in the fourth column of Table 4. Based on the geological principle that the coal-derived gas maturity of the same gas reservoir is consistent with that of the coal-bearing source rocks, and according to the thermal history evolution relationship in Equation 7, the source depth of the natural gas reservoir in the aforementioned area was obtained (Table 4). This conclusion is also consistent with the burial depth of the coal-bearing source rocks in this area, which is mainly between 5000-9000m, further confirming the reliability of this method.

[0078] Table 4. Identification of Coalbed Gas Source Depth in Q131-Q150 Region

[0079]

[0080] This embodiment accurately characterizes the relationship between the composition ratio of coalbed methane (CH4 / (C2H6+C3H8)) and the carbon isotope (δ¹⁸C) of methane in coalbed methane through a two-segment linear relationship. 13The relationship between C1) is defined by taking CH4 / (C2H6+C3H8) = 40 as the dividing point. When CH4 / (C2H6+C3H8) < 40, there is a linear correspondence between the coalbed methane component ratio and the methane carbon isotope value. When CH4 / (C2H6+C3H8) ≥ 40, there is another linear correspondence between the coalbed methane component ratio and the methane carbon isotope value. By using this two-segment linear relationship and combining it with the relationship between methane carbon isotopes and coalbed methane maturity, the intermediate variable methane carbon isotopes can be eliminated, and the relationship between coalbed methane maturity and coalbed methane component ratio can also be obtained as a two-segment linear relationship. Therefore, in the actual exploration and production process of coalbed methane, the coalbed methane component ratio of the region can be determined (the natural gas component content is a routine analysis item tested by general grassroots units, and the data is relatively easy to obtain). Then, by using the two-segment linear relationship between the coalbed methane maturity and the coalbed methane component ratio, the coalbed methane maturity value of the region can be quickly calculated, and the gas source burial depth can be determined with high accuracy.

[0081] In this embodiment, the order of steps one through five is not mandatory. For example, step three can be performed first to determine the maturity Ro of the coalbed methane and the carbon isotope (δ¹⁸) of methane in the coalbed methane. 13 The relationship between C1) is then performed, followed by steps one and two, to determine the relationship between the coalbed methane component ratio Y and the methane carbon isotopes (δ¹⁰) in the coalbed methane. 13 The relationship between C1); or performing step three while simultaneously performing the content of steps one and two.

[0082] In this embodiment, when the data in the geochemical data of coalbed methane are different, the parameters and component ratio thresholds in the determined linear relationship expressions (5) and (6) may change, but the overall relationship still shows a two-segment linear relationship, as shown in the following expression:

[0083] Ro=a1˙Y+b1 Y<y0

[0084] Ro=a2˙Y+b2 Y≥y0

[0085] In the formula, Ro is the maturity of coalbed methane, Y is the composition ratio of coalbed methane, a1, a2, b1, and b2 are all parameters, and a1>a2, and y0 is the composition ratio threshold.

[0086] Compared with existing technologies, the method of this invention is simple in principle, can predict the burial depth of gas sources quickly and accurately, and can be rapidly promoted and applied in front-line oil and gas units, providing technical support for efficient exploration.

[0087] Example of a method for predicting the maturity of coalbed methane:

[0088] This embodiment proposes a method for predicting the maturity of coalbed methane, which includes:

[0089] Based on geochemical data of coalbed methane, the components of methane, ethane, and propane in coalbed methane from several regions, as well as the carbon isotopes of methane in coalbed methane, were obtained. The composition ratio of methane was calculated by dividing it by the sum of the compositions of ethane and propane. The relationship between the composition ratio of coalbed methane and the carbon isotopes of methane in coalbed methane was fitted to obtain a first linear relationship and a second linear relationship. When the composition ratio of coalbed methane is less than a set composition ratio threshold, the first linear relationship is obtained; when the composition ratio of coalbed methane is not less than the set composition ratio threshold, the second linear relationship is obtained. The slope of the first linear relationship is greater than the slope of the second linear relationship.

[0090] Then, using the gold tube thermal simulation experiment, the relationship between the carbon isotopes of methane in coalbed methane and the maturity of coalbed methane is determined, or the relationship provided by the existing technology is used as a substitute; using this relationship, combined with the first linear relationship and the second linear relationship obtained above, the relationship between the component ratio of coalbed methane and the maturity of coalbed methane is determined.

[0091] Finally, by using the relationship between the coalbed methane composition ratio and the coalbed methane maturity, and substituting the coalbed methane composition ratio of a certain region, the coalbed methane maturity of that region can be accurately calculated.

[0092] Since the calculation process of coalbed methane maturity in this embodiment has been clearly and completely described in the deep prediction method embodiment, it will not be repeated in this embodiment.

[0093] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method of predicting the burial depth of a gas source, characterized by, Includes the following steps: (1) Based on the geochemical data of coalbed methane, the composition of methane, ethane and propane in coalbed methane in several regions and the carbon isotope value of methane in coalbed methane are obtained. The composition of methane is divided by the sum of the composition of ethane and propane to obtain the composition ratio of coalbed methane. The relationship between the composition ratio of coalbed methane and the carbon isotope value of methane in coalbed methane is fitted to obtain the first linear relationship and the second linear relationship. When the composition ratio of coalbed methane is less than the set composition ratio threshold, it is the first linear relationship; when the composition ratio of coalbed methane is not less than the composition ratio threshold, it is the second linear relationship. (2) Obtain the relationship between the carbon isotopes of methane in coalbed methane and the maturity of coalbed methane, and combine the relationship between the composition ratio of coalbed methane and the carbon isotope value of methane in coalbed methane to determine the relationship between the composition ratio of coalbed methane and the maturity of coalbed methane. (3) Obtain the coal-derived gas component ratio of the target area, and calculate the coal-derived gas maturity value of the target area by combining the relationship between the coal-derived gas component ratio and the coal-derived gas maturity. Using this value, and combining the relationship between the coal-derived gas maturity and the gas source burial depth, calculate the gas source burial depth of the target area.

2. The method for predicting the burial depth of a gas source according to claim 1, characterized in that, The relationship between the proportion of coalbed methane components and the maturity of coalbed methane is expressed as follows: Ro = a 1˙Y + b 1Y<y0 Ro = a 2˙Y+ b 2Y≥y0 In the formula, Ro represents the maturity of coalbed methane, and Y represents the composition ratio of coalbed methane. a 1. a 2. b 1. b 2 are all parameters, and each parameter is determined by calculation in step (2); y0 is the set component ratio threshold.

3. The method for predicting the burial depth of a gas source according to claim 1, characterized in that, A gold tube thermal simulation experiment was used to simulate the characteristics of oil and gas generation under underground temperature and pressure conditions, and to determine the relationship between the methane carbon isotopes in the coalbed methane and the maturity of the coalbed methane.

4. A method for predicting the maturity of coalbed methane, characterized in that, Includes the following steps: (1) Based on the geochemical data of coalbed methane, the composition of methane, ethane and propane in coalbed methane in several regions and the carbon isotope value of methane in coalbed methane are obtained. The composition of methane is divided by the sum of the composition of ethane and propane to obtain the composition ratio of coalbed methane. The relationship between the composition ratio of coalbed methane and the carbon isotope value of methane in coalbed methane is fitted to obtain the first linear relationship and the second linear relationship. When the composition ratio of coalbed methane is less than the set composition ratio threshold, it is the first linear relationship; when the composition ratio of coalbed methane is not less than the composition ratio threshold, it is the second linear relationship. (2) Obtain the relationship between the carbon isotopes of methane in coalbed methane and the maturity of coalbed methane, and combine the relationship between the composition ratio of coalbed methane and the carbon isotope value of methane in coalbed methane to determine the relationship between the composition ratio of coalbed methane and the maturity of coalbed methane. (3) Obtain the coal-derived gas component ratio of the target area, and calculate the coal-derived gas maturity of the target area by combining the relationship between the coal-derived gas component ratio and the coal-derived gas maturity.

5. The method for predicting coalbed methane maturity according to claim 4, characterized in that, The relationship between the proportion of coalbed methane components and the maturity of coalbed methane is expressed as follows: Ro = a 1˙Y + b 1Y<y0 Ro = a 2˙Y+ b 2 Y≥y0 In the formula, Ro represents the maturity of coalbed methane, and Y represents the composition ratio of coalbed methane. a 1. a 2. b 1. b 2 are all parameters, and each parameter is determined by calculation in step (2); y0 is the set component ratio threshold.

6. The method for predicting coalbed methane maturity according to claim 4, characterized in that, A gold tube thermal simulation experiment was used to simulate the characteristics of oil and gas generation under underground temperature and pressure conditions, and to determine the relationship between the methane carbon isotopes in the coalbed methane and the maturity of the coalbed methane.

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