Method for calculating storage coefficient and loss amount of shale gas

Abstract

The invention provides a method for calculating a shale gas preservation coefficient and loss amount. The method comprises the following steps: determining geological structure characteristics, shale thickness, organic geochemical characteristics and shale gas content of a research area; according to organic geochemical characteristics of shale in a research area, establishing a hydrocarbon generation evolution profile and designing hydrocarbon generation thermal simulation experiment verification; according to the hydrocarbon generation evolution profile, a residual hydrocarbon yield calculation model is established, and the total residual hydrocarbon amount in the geological historical period is recovered; based on the shale gas content, the shale area and the shale thickness in the research area, the total quantity of current shale gas resources is calculated through a volumetric method; dividing the total amount of current shale gas resources by the total residual amount in the geological historical period to obtain a shale gas preservation coefficient; and subtracting the total amount of the current geological resources from the total residual amount in the geological historical period to obtain the shale gas loss amount in the research area. The accuracy of the obtained preservation coefficient is far higher than that of an analogy method, and the method expands the application range of a hydrocarbon generation potential method and a cause method.

Description

Technical Field

[0001] The present invention relates to the technical field of shale gas migration, accumulation and resource potential evaluation, and in particular to a method for calculating shale gas preservation coefficient and loss. Background Art

[0002] Shale gas is a self-generating, self-storing unconventional natural gas primarily found in the pores and fractures of shale. Shale gas resource evaluation is fundamental to shale gas exploration and development, encompassing multiple areas such as shale sweet spot prediction and production area selection. Numerous resource calculation methods exist, including volumetric methods, genetic methods, scale zone methods, analogy methods, and expert assignment methods. Each of these methods has varying scopes of application. The scale zone and analogy methods, being the most widely used, are typically used in less-explored oil and gas basins, while the scale zone method is used in medium- to high-exploration oil and gas basins. The genetic method, as a method for evaluating resource potential, is currently less widely used. The reasons for this are summarized as follows: first, the method includes the chloroform asphalt "A" method and the simulated generation method. The chloroform asphalt "A" method suffers from poor reliability due to its simple parameters and susceptibility to interference from human factors and experimental errors. The simulated generation method is limited by sample quality and cannot recover resources at lower maturity stages, resulting in a narrower scope of application. Second, the genetic method requires a preservation coefficient or accumulation parameter to characterize the amount of oil and gas preserved and lost during geological history. Currently, this parameter is mainly obtained through analogy, which has large errors in application and is difficult to accurately represent the amount of gas lost and preserved during geological history. Therefore, based on the hydrocarbon generation potential method and combined with hydrocarbon generation thermal simulation experiments, a new resource calculation method and preservation coefficient calculation method are proposed. This method is derived from the hydrocarbon generation potential method, but is different from the hydrocarbon generation potential method after being verified by hydrocarbon generation thermal simulation experiments. The preservation coefficient obtained by this method is much more accurate than the analogy method, and this method expands the application scope of both the hydrocarbon generation potential method and the genetic method. Summary of the Invention

[0003] The present invention aims to provide a method for calculating the preservation coefficient and loss amount of shale gas, so as to solve the problem of difficulty in obtaining the preservation coefficient in the process of calculating the shale gas resource amount in the genetic method.

[0004] The present invention provides a method for calculating shale gas conservation coefficient and loss, comprising the following steps:

[0005] S1, determine the geological structural characteristics, shale thickness, shale organic geochemical characteristics and average gas content of shale gas migration and accumulation units in the study area;

[0006] S2: Based on the organic geochemical characteristics of shales in the study area, establish a hydrocarbon generation evolution profile and design a hydrocarbon generation thermal simulation experiment for verification;

[0007] S3, based on the hydrocarbon generation evolution profile, establish a residual hydrocarbon yield calculation model to restore the total residual hydrocarbon amount in the geological history period;

[0008] S4, based on the average gas content, shale area and shale thickness of the shale gas migration and accumulation units in the study area, the total amount of shale gas resources today is calculated using the volume method;

[0009] S5, the shale gas preservation coefficient is obtained by dividing the total amount of shale gas resources today by the total residual amount in the geological history period;

[0010] S6, the amount of shale gas lost in the study area is obtained by subtracting the total amount of geological resources today from the total residual amount in the geological history.

[0011] Furthermore, in step S1, the geological structural characteristics of the study area include the degree of fault development, fold type and stratum dip.

[0012] Furthermore, in step S1, the organic geochemical characteristics of the shale include total organic carbon, pyrolysis peak temperature, vitrinite reflectance, hydrocarbon generation potential and residual hydrocarbon content.

[0013] Furthermore, in step S1, the organic geochemical characteristics of the shale include total organic carbon, pyrolysis peak temperature, burial depth, hydrocarbon generation potential and residual hydrocarbon content.

[0014] Furthermore, step S3 includes the following sub-steps:

[0015] Recovering residual hydrocarbons;

[0016] The residual hydrocarbon amount per unit organic carbon and the yield per unit residual hydrocarbon amount are established based on the recovered residual hydrocarbon amount;

[0017] The residual hydrocarbon intensity and total residual hydrocarbon content were calculated by analyzing the relationship between the residual hydrocarbon content per unit organic carbon and the vitrinite reflectance.

[0018] Furthermore, the residual hydrocarbon amount is recovered by the following formula:

[0019]

[0020] Among them, S1 is the amount of residual hydrocarbons after recovery, S1 * is the measured residual hydrocarbon amount S1, R o is the vitrinite reflectance.

[0021] Furthermore, the residual hydrocarbon content per unit organic carbon is established by the following formula:

[0022] q r =S1 / TOC;

[0023] Among them, q r is the residual hydrocarbon per unit organic carbon, and TOC is the total organic carbon.

[0024] Furthermore, the unit residual hydrocarbon yield is established by the following formula:

[0025]

[0026] Among them, V r is the unit residual hydrocarbon yield.

[0027] Furthermore, the residual hydrocarbon intensity and the total residual hydrocarbon amount are calculated by the following formula:

[0028]

[0029]

[0030] Among them, I r is the residual hydrocarbon intensity, Q r is the total residual hydrocarbon volume, HGT is the hydrocarbon expulsion threshold, ρ is the density of source rock, and S is the shale area.

[0031] Furthermore, in step S4, the total amount of current shale gas resources is calculated using the following formula:

[0032] Q=H×S×ρ average

[0033] Where Q is the total amount of shale gas resources today; H is the thickness of shale; S is the area of ​​shale; ρ average is the average gas content of shale gas migration and accumulation units.

[0034] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0035] 1. To address the difficulty in obtaining the preservation coefficient during the calculation of shale gas resources using the genetic method, the present invention proposes a method for calculating the shale gas preservation coefficient and loss amount, which is derived from the hydrocarbon generation potential method. However, after verification through a hydrocarbon generation thermal simulation experiment, the present invention differs from the hydrocarbon generation potential method. The accuracy of the preservation coefficient obtained by the present invention is far higher than that obtained using the analogy method, and this method expands the application scope of both the hydrocarbon generation potential method and the genetic method.

[0036] 2. This invention focuses on the entire process of shale gas generation, migration, accumulation and reservoir formation, and has important reference value and constructive suggestions for the calculation of shale gas resources, resource potential evaluation and demarcation of shale gas geological sweet spots in the study area. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings in the embodiments will be briefly introduced below. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0038] Figure 1 The present invention is a flow chart of the method for calculating the shale gas preservation coefficient and loss amount. DETAILED DESCRIPTION

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0040] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are intended to fall within the scope of protection of the present invention.

[0041] Example

[0042] like Figure 1 As shown, this embodiment proposes a method for calculating shale gas preservation coefficient and loss, including the following steps:

[0043] S1, determine the geological structure characteristics, shale thickness, shale organic geochemical characteristics and average gas content of shale gas migration and accumulation units in the study area; the geological structure characteristics of the study area include the degree of fault development, fold type, formation dip, etc.; the organic geochemical characteristics of shale include total organic carbon (TOC), pyrolysis peak temperature (Tmax), vitrinite reflectance (R o ), hydrocarbon generation potential (S1+S2), residual hydrocarbon content (S1), where Ro can be replaced by burial depth;

[0044] S2. Based on the organic geochemical characteristics of the shales in the study area, a hydrocarbon generation evolution profile was constructed and validated with a thermal simulation experiment. The principles underlying this profile are the material balance theory and the hydrocarbon generation and expulsion theory. According to the material balance theory, the hydrocarbon generation potential of shale remains constant throughout geological history and can be divided into three components: kerogen or residual organic matter that has not yet generated hydrocarbons, hydrocarbons generated and remaining in the source rock, and hydrocarbons that have been expelled. Furthermore, once the shale's hydrocarbon generation capacity meets its own residual capacity, it begins to expel hydrocarbons. The thermal simulation experiment validation was designed for two reasons: first, the hydrocarbon generation potential method requires extensive basic data support, resulting in a limited number of data points and prone to errors; second, it aims to clarify the type of shale gas remaining in the shale interval. Finally, both the hydrocarbon generation potential method and the thermal simulation experiment are methods for characterizing the hydrocarbon generation potential and expulsion characteristics of source rocks, each with its own advantages and disadvantages. Only by validating and coordinating the two methods can the hydrocarbon generation and expulsion capacity of the primary source rock interval be more accurately characterized.

[0045] S3, based on the hydrocarbon generation evolution profile, establish a residual hydrocarbon yield calculation model to restore the total residual hydrocarbon amount in the geological history period;

[0046] It should be noted that during the geological history, factors such as temperature and pressure may cause some of the liquid hydrocarbons remaining in the source rocks to dissipate, resulting in a lower value for the measured residual hydrocarbon amount. Therefore, the residual hydrocarbon amount can be restored using the following formula:

[0047]

[0048] Among them, S1 is the amount of residual hydrocarbons after recovery, S1 * is the measured residual hydrocarbon amount S1.

[0049] After recovery, the residual hydrocarbon per unit organic carbon q r and unit residual hydrocarbon yield V r ;

[0050] q r =S1 / TOC;

[0051]

[0052] By analyzing the residual hydrocarbon amount per unit organic carbon q r and vitrinite reflectance R o The relationship between the residual hydrocarbon intensity I r and the total residual hydrocarbon amount Q r , the calculation formula is as follows:

[0053]

[0054]

[0055] Among them, I ris the residual hydrocarbon intensity, Q r is the total residual hydrocarbon volume, HGT is the hydrocarbon expulsion threshold, ρ is the density of source rock, and S is the shale area.

[0056] S4. Based on the average gas content, shale area, and shale thickness of the shale gas migration and accumulation units in the study area, the total amount of shale gas resources today is calculated using the volumetric method:

[0057] Q=H×S×ρ average

[0058] Where Q is the total amount of shale gas resources today, m 3 ; H is the shale thickness, m; S is the shale area, km 2 ρ average is the average gas content of shale gas migration and accumulation units.

[0059] S5, the shale gas preservation coefficient is obtained by dividing the total amount of shale gas resources today by the total residual amount in the geological history period;

[0060] It should be noted that during the generation of oil and gas from source rocks, hydrocarbons are expelled only after the amount of hydrocarbons generated by the source rocks meets their own residual capacity. In addition, due to factors such as structural and hydrogeological conditions, the generated oil and gas escape and cannot be completely preserved in the reservoir. Only a small amount of oil and gas can be preserved. Considering the "source-reservoir integration" characteristics of shale, the preservation coefficient K is used to characterize the proportion of hydrocarbon gases that can actually be preserved in the shale reservoir, that is:

[0061]

[0062] Where K is the preservation coefficient, dimensionless.

[0063] S6, the amount of shale gas lost in the study area is obtained by subtracting the total amount of geological resources today from the total residual amount in the geological history.

[0064] It should be noted that the total amount of hydrocarbon generated by source rocks remains unchanged during the process of generating oil and gas. The source rocks begin to expel hydrocarbons only after the amount of hydrocarbon generated by the source rocks meets their own residual amount. Therefore, the total residual hydrocarbon amount minus the hydrocarbons currently preserved is the lost amount, that is:

[0065] Q s =Q r -Q

[0066] Among them, Q s is the amount of shale gas lost during the geological history, m 3 .

[0067] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for calculating shale gas conservation coefficient and loss, characterized in that: The steps include: S1, determine the geological structural characteristics, shale thickness, shale organic geochemical characteristics and average gas content of shale gas migration and accumulation units in the study area; S2, based on the organic geochemical characteristics of shales in the study area, establish hydrocarbon generation evolution profiles and design hydrocarbon generation thermal simulation experiments for verification; S3, based on the hydrocarbon generation evolution profile, establish a residual hydrocarbon yield calculation model to restore the total residual hydrocarbon amount in the geological history period; S4, based on the average gas content, shale area and shale thickness of the shale gas migration and accumulation units in the study area, the total amount of shale gas resources today is calculated using the volume method; S5, the shale gas preservation coefficient is obtained by dividing the total amount of shale gas resources today by the total residual amount in the geological history period; S6, the amount of shale gas lost in the study area is obtained by subtracting the total amount of geological resources today from the total residual amount in the geological history.

2. The method for calculating shale gas preservation coefficient and loss according to claim 1, characterized in that: In step S1, the geological structural characteristics of the study area include the degree of fault development, fold type and stratum dip.

3. The method for calculating shale gas conservation coefficient and loss according to claim 1, characterized in that: In step S1, the organic geochemical characteristics of the shale include total organic carbon, pyrolysis peak temperature, vitrinite reflectance, hydrocarbon generation potential and residual hydrocarbon content.

4. The method for calculating shale gas preservation coefficient and loss according to claim 1, characterized in that: In step S1, the organic geochemical characteristics of the shale include total organic carbon, pyrolysis peak temperature, burial depth, hydrocarbon generation potential and residual hydrocarbon content.

5. The method for calculating shale gas preservation coefficient and loss according to claim 1, characterized in that: Step S3 includes the following sub-steps: Recovering residual hydrocarbons; The residual hydrocarbon amount per unit organic carbon and the yield per unit residual hydrocarbon amount are established based on the recovered residual hydrocarbon amount; The residual hydrocarbon intensity and total residual hydrocarbon content were calculated by analyzing the relationship between the residual hydrocarbon content per unit organic carbon and the vitrinite reflectance.

6. The method for calculating shale gas conservation coefficient and loss according to claim 5, characterized in that: The residual hydrocarbon amount is recovered by the following formula: Among them, S1 is the amount of residual hydrocarbons after recovery, is the measured residual hydrocarbon amount S1, R o is the vitrinite reflectance.

7. The method for calculating shale gas preservation coefficient and loss according to claim 6, characterized in that: The residual hydrocarbon content per unit organic carbon is established by the following formula: what r =S1 / TOC; Among them, q r is the residual hydrocarbon per unit organic carbon, and TOC is the total organic carbon.

8. The method for calculating shale gas preservation coefficient and loss according to claim 7, characterized in that: The unit residual hydrocarbon yield is established by the following formula: Among them, V r is the unit residual hydrocarbon yield.

9. The method for calculating shale gas preservation coefficient and loss according to claim 8, characterized in that: The residual hydrocarbon intensity and total residual hydrocarbon content are calculated using the following formula: Among them, I r is the residual hydrocarbon intensity, Q r is the total residual hydrocarbon volume, HGT is the hydrocarbon expulsion threshold, ρ is the density of source rock, and S is the shale area.

10. The method for calculating shale gas preservation coefficient and loss according to claim 9, characterized in that: In step S4, the total amount of shale gas resources today is calculated using the following formula: Q=H×S×ρ average Where Q is the total amount of shale gas resources today; H is the thickness of shale; S is the area of ​​shale; ρ average is the average gas content of shale gas migration and accumulation units.

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