Method for dividing weathering crust structure

Abstract

The invention discloses a method for dividing a weathering crust structure, which comprises the following steps: collecting data, carrying out regional stratigraphic development characteristic analysis, and selecting a standard well in a research region; selecting a sampling sand body in the target interval according to the logging information of the standard well, and calculating the average acoustic velocity of the sampling sand body; analyzing the average sound wave velocity of the sampled sand bodies of the standard well, and determining the average sound wave velocity of the unweathered sandstone of each group of sand bodies in the target interval of the research area as the sound wave velocity value of the unweathered sandstone; a typical well is selected, the stratum development condition of the typical well is analyzed, and the numerical value of the thick-layer sand body sound wave velocity is determined; calculating the wave velocity ratio of the thick sand body of the typical well in the target interval based on the value of the sound wave velocity of the thick sand body of the typical well and the sound wave velocity value of the unweathered sandstone; performing rock core sampling on the typical well, determining the weathering degree of the rock through experimental analysis, and establishing a standard for dividing the weathering degree and the weathering structure in cooperation with a wave velocity ratio. The method is rapid, accurate and high in operability.

Description

Technical Field

[0001] The invention relates to the technical field of geological exploration, and in particular to a method for dividing a weathering crust structure. Background Art

[0002] The process of physical and chemical changes in rocks under the action of various weathering forces is called rock weathering. It includes two aspects: the weathering effect that rocks experience and the results produced. Compared with other dynamic geological actions, there are many forces that cause rock weathering, but the main ones are solar heat, aqueous solution (water on the surface, underground and in the air), air and biological organisms. The surface layer of the lithosphere that has been weathered is called the weathering crust, which is the product of the combined action of various factors of the original rock in a certain geological history period. Compared with the original rock, the weathered rock has undergone a series of changes, which are specifically reflected in the changes in structure, mineral composition and chemical composition and the deterioration of engineering properties.

[0003] Rock weathering is a common dynamic geological process during the continentalization of the earth's surface. The identification of weathering crust structure is of great significance for prospecting, studying natural environmental changes, soil occurrence and evolution, and land use. At present, qualitative classification is often used in engineering, but due to different indicators and standards for the division of weathering degree, there are often large differences due to inconsistent personal levels or difficulty in mastering the division standards, resulting in large deviations in the determination of later engineering construction plans.

[0004] Therefore, how to develop a fast, accurate and highly operable method for dividing the weathering crust structure has become a technical problem that urgently needs to be solved in this field. Summary of the invention

[0005] The present invention provides a method for dividing a weathering crust structure to solve at least one of the above-mentioned technical problems existing in the prior art.

[0006] In order to achieve the above technical objectives, the technical solution adopted by the present invention is as follows:

[0007] According to one aspect of the present invention, there is provided a method for dividing a weathering crust structure, comprising the following steps:

[0008] Step S1: Collect data and analyze the regional stratigraphic development characteristics, and select wells with complete stratigraphic development and acoustic wave data in the target layer section in the study area as standard wells;

[0009] Step S2: selecting a sand body in the target layer section that meets the predetermined lithology and thickness requirements as a sampling sand body according to the comprehensive interpretation results in the logging data of the standard well, and calculating the average acoustic wave velocity of the sampling sand body;

[0010] Step S3: analyzing the variation characteristics of the average acoustic wave velocity of the sampled sand bodies of the standard well, determining the average acoustic wave velocity of the unweathered sandstone of each group of sand bodies in the target layer of the study area, and using this velocity as the acoustic wave velocity value of each group of unweathered sandstone;

[0011] Step S4: based on the data of each well in the study area, a typical well in the weathering and erosion area is selected, the stratigraphic development of the typical well is analyzed, and the value of the acoustic wave velocity of the thick sand body is determined;

[0012] Step S5: calculating the velocity ratio of the thick sand body in the target layer of the typical well based on the acoustic velocity value of the thick sand body in the typical well and the acoustic velocity values ​​of each group of unweathered sandstones;

[0013] Step S6: core sampling is performed on the typical wells, the weathering degree of the rocks is determined through experimental analysis, and a standard for dividing the weathering degree and weathering structure of the sandstone in the study area by the wave velocity ratio is established in combination with the wave velocity ratio.

[0014] According to one embodiment of the present invention, the method further comprises:

[0015] Step S7: Divide the weathering degree and weathering structure of multiple wells in the weathering and erosion area according to the established standard.

[0016] According to one embodiment of the present invention, the method further comprises:

[0017] Step S8: Produce a cross-sectional view of the weathering structure of connected wells according to the weathering degrees of multiple wells and the division results of the weathering structures, and determine the spatial distribution characteristics of the weathering crust structure.

[0018] According to an embodiment of the present invention, the data collected in step S1 includes geological data and well logging data.

[0019] According to an embodiment of the present invention, in step S2, the predetermined lithology requirement is fine sandstone, the thickness requirement is that the sand body thickness is greater than 2 m, and the average acoustic wave velocity of the sand body is calculated based on the acoustic logging data.

[0020] According to one embodiment of the present invention, step S3 analyzes the variation characteristics of the average acoustic wave velocity of the sampled sand bodies of the standard well, and determines the average acoustic wave velocity of the unweathered sandstone of each group of sand bodies in the target layer section of the study area, including:

[0021] The calculated average acoustic wave velocity of the sand body is fitted into a velocity curve, and the intersection of the velocity curve and the bottom boundary of each group of sand bodies is taken as the average acoustic wave velocity of the unweathered sandstone of the corresponding group of sand bodies.

[0022] According to one embodiment of the present invention, the well data in step S4 includes at least one of well logging, well logging and seismic data.

[0023] According to one embodiment of the present invention, in step S4, wells with formation thickness as low as a predetermined value, incomplete development, and obvious truncation characteristics on the seismic section are taken as typical wells.

[0024] According to an embodiment of the present invention, the predetermined value is 300 meters.

[0025] According to one embodiment of the present invention, in step S5, the wave velocity ratio is equal to the ratio of the value of the acoustic wave velocity of the thick layer sand body of the typical well determined in step S4 to the value of the acoustic wave velocity of the unweathered sandstone of the corresponding group of sand bodies of the standard well determined in step S3.

[0026] According to one embodiment of the present invention, the experimental analysis in step S6 includes measuring the major elements of the core and calculating the chemical alteration index.

[0027] According to one embodiment of the present invention, when the chemical alteration index is 50-60, it corresponds to weak weathering, when the chemical alteration index is 60-80, it corresponds to moderate weathering, and when the chemical alteration index is 80-100, it corresponds to strong weathering.

[0028] According to one embodiment of the present invention, the experimental analysis in step S6 also includes calculating a chemical weathering index, a Parker weathering index, and a plagioclase alteration index.

[0029] According to one embodiment of the present invention, the chemical alteration index is used to determine the weathering degree, and the chemical weathering index, the Parker weathering index, and the plagioclase alteration index are used as references to adjust the weathering degree.

[0030] According to one embodiment of the present invention, the standard for dividing the weathering degree and weathering structure of sandstone in the study area based on the wave velocity ratio in step S6 includes associating the weathering conditions and wave velocity ratios at the corresponding core sampling positions, and determining the wave velocity ratio ranges corresponding to different weathering degrees as the standard for dividing the weathering degree and weathering structure.

[0031] Due to the adoption of the above technical scheme, the method for dividing the weathering crust structure provided by the present invention has the following beneficial effects compared with the prior art: the method of the present invention divides the weathering crust structure by using the wave velocity ratio combined with core experimental analysis, which is fast, accurate and highly operable. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present invention but do not constitute a limitation of the present invention. In the accompanying drawings:

[0033] Figure 1 A sonic logging data diagram of an example well in which the method for dividing the weathering crust structure according to the present invention is implemented is shown;

[0034] Figure 2 A diagram showing the average acoustic wave velocity of a sand body calculated according to a specific example of the method for dividing a weathering crust structure according to the present invention;

[0035] Figure 3 A composite histogram showing an example well implementing the method of partitioning a weathering crust structure according to the present invention;

[0036] Figure 4 The figure shows the weathering crust structure of the connected wells obtained by using the method for dividing the weathering crust structure according to the present invention. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0038] The present invention provides a method for dividing a weathering crust structure. The method generally comprises the following steps:

[0039] Step S1: Collect data and analyze the regional stratigraphic development characteristics, and select wells with complete stratigraphic development and acoustic wave data in the target layer section in the study area as standard wells;

[0040] Step S2: selecting a sand body in the target layer section that meets the predetermined lithology and thickness requirements as a sampling sand body according to the comprehensive interpretation results in the logging data of the standard well, and calculating the average acoustic wave velocity of the sampling sand body;

[0041] Step S3: analyzing the variation characteristics of the average acoustic wave velocity of the sand bodies sampled in the standard well, determining the average acoustic wave velocity of the unweathered sandstone of each group of sand bodies in the target layer of the study area, and using this velocity as the acoustic wave velocity value of each group of unweathered sandstone;

[0042] Step S4: Based on the data of each well in the study area, a typical well in the weathering and erosion area is selected, the stratigraphic development of the typical well is analyzed, and the value of the acoustic wave velocity of the thick sand body is determined;

[0043] Step S5: Calculate the velocity ratio of the thick sand body in the target layer of the typical well based on the acoustic velocity value of the thick sand body in the typical well and the acoustic velocity value of each group of unweathered sandstone;

[0044] Step S6: core sampling is performed on typical wells, and the weathering degree of the rock is determined through experimental analysis. The standard of weathering degree and weathering structure classification of sandstone wave velocity ratio in the study area is established in combination with the wave velocity ratio.

[0045] The following is an exemplary description of each step in the method.

[0046] In step S1, data is collected and regional stratigraphic development characteristics are analyzed, and wells with complete stratigraphic development and acoustic wave data in the target layer section in the study area are selected as standard wells. The collected data may include geological data, such as core data and seismic data, and may also include well logging data, such as natural gamma curve GR, density curve DEN, neutron porosity curve CN, acoustic wave time difference curve AC, and deep lateral resistivity curve RD. The regional stratigraphic development characteristics analysis may include, for example, the type, age, and structure of the rock.

[0047] In step S2, according to the comprehensive interpretation results in the logging data of the standard well, the sand body in the target layer section that meets the predetermined lithology and thickness requirements is selected as the sampling sand body, and the average acoustic wave velocity of the sampling sand body is calculated. There are many factors that affect the acoustic wave velocity of the sand body, among which the thickness of the sand body and the mud content have a greater influence. The thinner the sand body, the greater the acoustic wave velocity, and the higher the mud content, the smaller the acoustic wave velocity. In order to reduce the influence of these factors on the acoustic wave velocity, it is necessary to select a sand body that meets the predetermined lithology and thickness requirements as the sampling sand body. For example, a sand body with a lithology of fine sandstone and a thickness greater than 2m can be selected as the sampling sand body. The average acoustic wave velocity of each group of sand bodies can be calculated based on the acoustic logging data.

[0048] In step S3, the variation characteristics of the average acoustic wave velocity of the sand bodies sampled in the standard well are analyzed to determine the average acoustic wave velocity of the unweathered sandstone of each group of sand bodies in the target layer of the study area, and this velocity is used as the acoustic wave velocity value of each group of unweathered sandstone. Specifically, the calculated average acoustic wave velocity of the sand bodies can be fitted into a velocity curve, and the intersection of the velocity curve and the bottom boundary of each group of sand bodies is used as the average acoustic wave velocity of the unweathered sandstone of the corresponding group of sand bodies.

[0049] In step S4, based on the data of each well in the study area, a typical well in the weathering and erosion area is selected, the stratigraphic development of the typical well is analyzed, and the value of the acoustic velocity of the thick sand body is determined. For example, the logging, well logging, seismic data, etc. of each well can be analyzed to find wells with obvious weathering and erosion characteristics as typical wells. The characteristics of typical wells include, for example, thin stratigraphic thickness, incomplete development, and obvious truncation characteristics on the seismic profile. The acoustic velocity of the thick sand body is calculated based on the acoustic logging data of the typical well. Since the sand body of the typical well is obviously weathered, the acoustic velocity of its sand body is significantly lower than the acoustic velocity of the sand body in the corresponding group of the standard well.

[0050] In step S5, the velocity ratio of the thick sand body in the target layer of the typical well is calculated based on the acoustic velocity value of the thick sand body in the typical well and the acoustic velocity value of each group of unweathered sandstone. For example, the velocity ratio can be equal to the ratio of the acoustic velocity value of the thick sand body in the typical well determined in step S4 to the acoustic velocity value of the unweathered sandstone in the corresponding group of sand bodies in the standard well determined in step S3.

[0051] In step S6, core sampling is performed on typical wells, the degree of weathering of the rock is determined through experimental analysis, and the standard for dividing the degree of weathering and weathering structure of sandstone in the study area by the wave velocity ratio is established in conjunction with the wave velocity ratio. Specifically, core sampling and analysis can be performed on typical wells, the major elements of the core can be measured, and CIA (chemical alteration index), CIW (chemical weathering index), WIP (Parker weathering index), and PIA (plagioclase alteration index) can be calculated. The calculation method of each index is as follows:

[0052]

[0053] The chemical alteration index CIA is used to quantitatively evaluate the chemical weathering intensity of feldspar. It is the ratio of Al2O3 to unstable oxides, reflecting the degree of weathering of feldspar into clay minerals. The higher the CIA value, the more K, Na and Ca elements in silicate minerals are leached from the parent rock, and the stronger the chemical weathering of feldspar. CIA = 50-60 reflects a weak degree of weathering, CIA = 60-80 is a moderate degree of weathering, and CIA = 80-100 reflects a strong degree of weathering.

[0054] Optionally, when using the above-mentioned weathering indicators to evaluate the weathering conditions of the study area, in order to avoid distortion of the evaluation results caused by the use of a single indicator, multiple indicators such as WIP, CIA, PIA, etc. are often combined to jointly indicate the weathering conditions of the study area, with the chemical alteration index CIA as the main one, supplemented by multiple indicators such as WIP, CIA, PIA, etc.

[0055] The weathering conditions and wave velocity ratios at the corresponding core sampling locations can be correlated to determine the range of wave velocity ratios corresponding to different weathering degrees, which can be used as a standard for dividing weathering degrees and weathering structures.

[0056] Optionally, in some embodiments, the method further includes: step S7: dividing the weathering degree and weathering structure of the remaining wells in the denudation zone according to the established standard. For example, the acoustic velocity of the thick sand body of each well can be calculated based on the acoustic logging data of each well, and the acoustic velocity of the thick sand body is divided by the acoustic velocity of the unweathered sandstone of the corresponding group of sand bodies in the standard well to obtain a velocity ratio. The weathering degree of the sand body is determined by comparing the velocity ratio with the velocity ratio range in the established standard.

[0057] Optionally, in some embodiments, the method further comprises: step S8: producing a well-connected weathering structure profile according to the weathering degrees and weathering structure division results of the multiple wells, and determining the spatial distribution characteristics of the weathering crust structure. According to the distribution amplitude of the weathering crust structure in each well, a fitting algorithm can be used to connect the weathering zones with the same weathering degree in the multiple wells to obtain the spatial distribution characteristics of the weathering crust structure.

[0058] In some embodiments, the standard for dividing the weathering crust structure is: dividing the weathering crust into a strong weathering zone, a medium weathering zone and a weak weathering zone, wherein the wave velocity ratio of the strong weathering zone is 0.70-0.82, the wave velocity ratio of the medium weathering zone is 0.82-0.87, and the wave velocity ratio of the weak weathering zone is 0.87-0.95.

[0059] The method for dividing the weathering crust structure of the present invention is described below with a specific application example.

[0060] It is widely distributed in the weathering crust area of ​​the Mesozoic-Paleozoic clastic rock in the Dagang exploration area and has become an important buried hill oil-bearing stratum in the Dagang exploration area. Industrial oil and gas flows have been obtained in the clastic rock weathering crust reservoirs of the Shihezi Formation in the Ganggu 1505, Zhong 1502 wells in the Gangbei buried hill and Kou 11 and Kou 24 wells in the Koucun buried hill. High-yield oil and gas flows have been obtained in the Jurassic system in the Zhanghai 11 and Zhanghai 4 wells in the Zhangdongdong buried hill, and reserves have all been reported.

[0061] The study area is located in the middle of Huanghua Depression, with Koucun buried hill in the south, Beidagang buried hill in the north, and Chenghai buried hill in the east. Through the analysis of geological data and well logging data, it is known that the Permian system in the Haigu 1 well in the study area is well developed, with Shiqianfeng Formation, Upper Shihezi Formation, Lower Shihezi Formation and Shanxi Formation developed. In addition, the acoustic logging data of this well is good. Therefore, this well is selected as the standard well for dividing the weathering crust structure of this area. Figure 1 Shown is the acoustic logging data of the Haigu 1 well.

[0062] After determining the standard well, it is necessary to further determine the acoustic velocity values ​​of the unweathered sandstone of each group of sand bodies. There are many factors that affect the acoustic velocity of sand bodies, among which the thickness of the sand body and the mud content have a greater impact. The thinner the sand body, the greater the acoustic velocity, and the higher the mud content, the smaller the acoustic velocity. In order to reduce these effects, a sand body with a thickness greater than 2m and a lithology of fine sandstone is selected as the sampling analysis sand body (reference Figure 1 Comprehensive explanation). At the same time, the average acoustic velocity of the sand body at each location is calculated based on the acoustic logging data. Figure 2 It can be seen that in the Permian strata, the average acoustic velocity of the sand body has a strong regularity and changes basically linearly with the increase of depth. The average acoustic velocity curve of the sand body is fitted according to the calculated average acoustic velocity of the sand body at each position, and then the average acoustic velocity of each group of unweathered sandstone is inferred according to the intersection of the average acoustic velocity curve of the sand body and the bottom boundary of each group. Figure 2 As shown, the average acoustic wave velocity of each group of unweathered sandstone is selected as follows: Shiqianfeng Group 4090m / s; Upper Shihezi Group 4270m / s; Lower Shihezi Group 4505m / s; Shanxi Group 5300m / s.

[0063] After determining the average acoustic velocity of the unweathered sandstone in the standard well, a typical weathered well was selected to further determine the wave velocity ratio. Well Kou 24 is located on the Kou Village buried hill uplift in the Qikou area. The Permian has obvious weathering and erosion characteristics. Its stratum thickness is relatively thin, only 278.5m. The Lower Shihezi Formation and Shanxi Formation are developed, and the Shiqianfeng Formation and Upper Shihezi Formation are missing. There are two sets of bauxite at the top of the Permian. On the seismic profile, the truncation characteristics are obvious. The acoustic velocity of the thick sand body in the Permian is calculated based on the acoustic wave data, such as Figure 2 As shown in the figure, it can be seen that the acoustic wave velocity of the top sand body of the Permian in Well Kou-24 is significantly smaller than the acoustic wave velocity of the top sand body of the Lower Shihezi Formation in Well Haigu-1, which indicates the existence of Permian weathering and erosion in Well Kou-24.

[0064] Based on the calculation of the average acoustic wave velocity of the Permian thick sand body in the Kou 24 well, the average acoustic wave velocity of the unweathered sand body of the Shihezi Formation (4505m / s) was divided to obtain the velocity ratio of the Permian thick sand body in the Kou 24 well ( Figure 3 wave speed ratio).

[0065] Based on the core sampling analysis of Kou 24 well, the measurement of the major elements of the core and the calculation of CIA, CIW, WIP and PIA ( Figure 3 ), the corresponding relationship between the wave velocity ratio and the weathering degree in Qikou area was established, and the weathering structure was divided. The weathering crust in the area can be divided into strong weathering zone, medium weathering zone and weak weathering zone. The wave velocity ratio of the strong weathering zone is 0.70-0.82, the wave velocity ratio of the medium weathering zone is 0.82-0.87, and the wave velocity ratio of the weak weathering zone is 0.87-0.95.

[0066] The above method was used to perform similar analysis on Well Zhong 1502, Well Ganggu 16102, Well Qigu 8, and Well Qigu 1601. The weathering zones with the same weathering degree in the comprehensive column charts of these wells were fitted and connected together to obtain the spatial distribution diagram of the weathering crust structure in the area, as shown in Figure 2. Figure 4 shown.

[0067] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0068] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0069] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for dividing weathering crust structure, characterized in that: The following steps are involved: Step S1: Collect data and analyze the regional stratigraphic development characteristics, and select wells with complete stratigraphic development and acoustic wave data in the target layer section in the study area as standard wells; Step S2: selecting a sand body in the target layer section that meets the predetermined lithology and thickness requirements as a sampling sand body according to the comprehensive interpretation results in the logging data of the standard well, and calculating the average acoustic wave velocity of the sampling sand body; Step S3: analyzing the variation characteristics of the average acoustic wave velocity of the sampled sand bodies of the standard well, determining the average acoustic wave velocity of the unweathered sandstone of each group of sand bodies in the target layer of the study area, and using this velocity as the acoustic wave velocity value of each group of unweathered sandstone; Step S4: based on the data of each well in the study area, a typical well in the weathering and erosion area is selected, the stratigraphic development of the typical well is analyzed, and the value of the acoustic wave velocity of the thick sand body is determined; Step S5: calculating the velocity ratio of the thick sand body in the target layer of the typical well based on the acoustic velocity value of the thick sand body in the typical well and the acoustic velocity values ​​of each group of unweathered sandstones; Step S6: core sampling is performed on the typical wells, the weathering degree of the rocks is determined through experimental analysis, and a standard for dividing the weathering degree and weathering structure of the sandstone in the study area by the wave velocity ratio is established in combination with the wave velocity ratio.

2. The method according to claim 1, characterized in that: Also includes: Step S7: Divide the weathering degree and weathering structure of multiple wells in the weathering and erosion area according to the established standard.

3. The method according to claim 2, characterized in that Also includes: Step S8: Produce a cross-sectional view of the weathering structure of connected wells according to the weathering degrees of multiple wells and the division results of the weathering structures, and determine the spatial distribution characteristics of the weathering crust structure.

4. The method according to claim 1, characterized in that The data collected in step S1 include geological data and well logging data.

5. The method according to claim 1, characterized in that: In step S2, the predetermined lithology requirement is fine sandstone, the thickness requirement is that the sand body thickness is greater than 2 m, and the average acoustic wave velocity of the sand body is calculated based on the acoustic logging data.

6. The method according to claim 1, characterized in that Step S3 analyzes the variation characteristics of the average acoustic wave velocity of the sampled sand bodies of the standard well, and determines the average acoustic wave velocity of the unweathered sandstone of each group of sand bodies in the target layer section of the study area, including: The calculated average acoustic wave velocity of the sand body is fitted into a velocity curve, and the intersection of the velocity curve and the bottom boundary of each group of sand bodies is taken as the average acoustic wave velocity of the unweathered sandstone of the corresponding group of sand bodies.

7. The method according to claim 1, characterized in that The well data in step S4 includes at least one of well logging, well logging and seismic data.

8. The method according to claim 1, characterized in that: In step S4, wells with formation thickness as low as a predetermined value, incomplete development and obvious truncation characteristics on the seismic section are taken as typical wells.

9. The method according to claim 8, characterized in that The predetermined value is 300 meters.

10. The method according to claim 1, characterized in that In step S5, the wave velocity ratio is equal to the ratio of the value of the acoustic wave velocity of the thick layer sand body of the typical well determined in step S4 to the value of the acoustic wave velocity of the unweathered sandstone of the corresponding group of sand bodies of the standard well determined in step S3.

11. The method according to claim 1, characterized in that The experimental analysis in step S6 includes measuring the major elements of the core and calculating the chemical alteration index.

12. The method according to claim 11, characterized in that When the chemical alteration index is 50-60, it corresponds to weak weathering, when the chemical alteration index is 60-80, it corresponds to moderate weathering, and when the chemical alteration index is 80-100, it corresponds to strong weathering.

13. The method according to claim 12, characterized in that The experimental analysis in step S6 also includes calculating the chemical weathering index, Parker weathering index, and plagioclase alteration index.

14. The method according to claim 13, characterized in that The chemical alteration index is used to judge the weathering degree, and the chemical weathering index, the Parker weathering index, and the plagioclase alteration index are used as references to adjust the weathering degree.

15. The method according to claim 12, characterized in that The standard for dividing the weathering degree and weathering structure of the sandstone in the study area by the wave velocity ratio in step S6 includes associating the weathering conditions and wave velocity ratios at the corresponding core sampling positions, and determining the wave velocity ratio ranges corresponding to different weathering degrees as the standard for dividing the weathering degree and weathering structure.

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