A method for determining weathering correction coefficient of organic matter abundance in shale

Abstract

The present invention provides a method for determining the weathering correction coefficient of organic matter abundance in mudstone, comprising: step 1, selecting a key layer section and sampling a fresh section or a shallow drilling system; step 2, performing an inorganic element compound and TOC analysis; step 3, calculating weathering degree parameters such as CIA and CIW; step 4, determining the TOC value of an unweathered sample; step 5, calculating the TOC correction factor of each sample; step 6, analyzing the correlation between the weathering parameter and the correction factor; and step 7, establishing a weathering degree TOC correction quantitative model. The method for determining the weathering correction coefficient of organic matter abundance in mudstone can objectively evaluate the influence of different degrees of weathering on organic matter abundance; with the inorganic element migration and compound composition change characteristics as the core, an innovative quantitative correction model for organic matter abundance under different degrees of weathering is established.

Description

Technical Field

[0001] The invention relates to the technical field of oilfield exploration and development, and in particular to a method for determining a weathering correction coefficient of organic matter abundance in mudstone. Background Art

[0002] Domestic and foreign oil and gas exploration practices have shown that oil and gas distribution is mainly controlled by the development conditions of source rocks, among which the organic matter abundance characteristics of source rocks play a key role and become a key factor in the evaluation of oil and gas accumulation conditions. There are many basins with medium and low exploration levels in my country. The source rocks in the basins are buried at great depths and the drilling data are relatively limited, which restricts the understanding of hydrocarbon supply conditions and the progress of oil and gas exploration. The mudstone samples developed in the outcrops of the basin margin have become an important basis for studying the source rocks inside the basin.

[0003] Field outcrops are geological bodies formed after underground rock formations emerge on the surface. Their preservation conditions are significantly worse than those in the deep layers of the basin. Source rock samples in the outcrop area at the edge of the basin are exposed to the surface or near the surface due to tectonic uplift. During the long-term contact with the atmosphere, surface water, and organisms, various physical, chemical, and biological weathering processes have occurred, affecting the physical structure, chemical composition, and organic chemical characteristics of the shale and its hydrocarbon generation potential, significantly reducing the abundance of organic matter and causing distortion in the evaluation results of source rocks. Therefore, weathering correction is required in the study of organic matter abundance.

[0004] The differences between samples of the same lithology in the same layer and in the outcrop are closely related to weathering. The analysis shows that the effect of weathering on organic matter abundance is complex, and the degree of influence is related to many factors such as lithology, occurrence, structural position, weathering time, and paleoclimate in the outcrop area. At present, it is difficult to analyze the specific relationship between each influencing factor and organic matter abundance. Previous studies have been conducted on the impact of weathering on the organic matter abundance of source rocks, but they mainly focus on the depth of weathering, the degree of influence of weathering on organic matter abundance indicators such as organic carbon (TOC), and most of them are qualitative or semi-quantitative analyses. The relationship between the organic matter abundance index and the degree of weathering of outcrop samples has not been fully clarified, which is difficult to meet the needs of objective evaluation and research on the organic matter abundance of outcrop shale samples in the field.

[0005] Therefore, it is urgent to establish a method for weathering correction of organic matter abundance in field outcrops to provide support for objective evaluation of source rocks in outcrop areas and lay the foundation for scientific prediction of oil and gas potential in the zone. To this end, we invented a method to determine the weathering correction coefficient of organic matter abundance in shale, which solved the above technical problems.

[0006] During the weathering process, the active alkali metal elements (Na, Ca, Mg, etc.) in the shale are lost, and the stable elements (Al, Ti, Sc, Zr, Th, etc.) are enriched, resulting in changes in the composition of the compounds, which is manifested as an increase in components such as Al2O3. The migration of inorganic elements and changes in related compounds are often significantly correlated with changes in organic matter abundance, and can serve as a direct basis for weathering correction of organic matter abundance.

[0007] In the Chinese patent application with application number: CN201310008706.8, a method for distinguishing low-abundance effective source rocks is involved, and the specific steps are: obtaining pyrolysis parameters and organic matter maturity (Ro) parameters of source rocks of the same lithology at multiple locations and multiple single wells in a certain area; screening out the pyrolysis parameters and Ro corresponding to low-abundance (TOC≤0.5%) source rocks, and calculating the hydrocarbon generation potential index corresponding to each depth or Ro based on the screened source rock parameters; drawing the evolution profile of the hydrocarbon generation potential index of TOC source rocks with the same interval and different ranges versus depth or Ro; searching for the evolution profile where the hydrocarbon expulsion threshold first appears in multiple continuous evolution profiles of the hydrocarbon generation potential index of TOC source rocks in different ranges, and the TOC value (or TOC range) corresponding to the evolution profile is the TOC lower limit value of the low-abundance effective source rock, and the source rock above this TOC value is the low-abundance effective source rock. This patent requires a large number of vitrinite reflectance measurement results, and its goal is to be applied to clarify the hydrocarbon generation and expulsion characteristics of samples with different degrees of thermal evolution in order to determine the lower limit of organic matter abundance. It cannot reflect the degree of reduction in organic matter abundance caused by the weathering process.

[0008] In the Chinese patent application with application number: CN201811511167.9, a method and device for predicting the abundance of organic matter in source rocks are involved. The method includes: obtaining the well logging curve of the target area; calculating the total organic carbon TOC value of the target area according to the well logging curve; performing well-seismic calibration based on the TOC value of the target area and combining the well logging curve with the synthetic seismic record; extracting the seismic attribute characteristics of the well bypass channel according to the result of the well-seismic calibration, establishing the relationship between TOC and the seismic attribute characteristics; and establishing the spatial distribution of TOC in the target area according to the relationship. This method requires the use of a large amount of well logging data and seismic data of drilling data. Its goal is to fit the residual organic matter abundance distribution characteristics under current geological conditions through seismic and well logging data. It cannot reflect the degree of reduction in organic matter abundance caused by weathering, and cannot perform weathering correction of organic matter abundance in field outcrops.

[0009] In the Chinese patent application with application number: CN201310652232.0, a method for calculating the original organic matter abundance recovery coefficient is involved, which includes: establishing a mathematical relationship between the hydrocarbon generation rate G of each organic matter type and the vitrinite reflectance Ro; obtaining the relationship between the residual degradation rate Dc and the hydrocarbon generation rate G; assuming that the original hydrocarbon generation rate Gy is the hydrocarbon generation rate when the vitrinite reflectance Ro is equal to 4, according to the relationship between the hydrocarbon generation rate G and the vitrinite reflectance Ro and the relationship between the residual degradation rate Dc and the hydrocarbon generation rate G, the relationship between the original organic matter abundance recovery coefficient Rc of the high-evolution source rock and the vitrinite reflectance Ro is obtained; and using the vitrinite reflectance Ro and the conversion coefficient a of the conversion of effective organic carbon to hydrocarbons, the original organic matter abundance recovery coefficient Rc of the high-evolution source rock is obtained to restore the original organic matter abundance of the high-evolution source rock. This patent requires a large number of vitrinite reflectance measurement results, and the method adopted is applied to the correction of the loss part caused by the degree of thermal evolution of organic matter abundance. There are two main reasons for the loss of organic matter abundance in shale. One is the decrease in organic matter abundance caused by the degree of thermal evolution, and the other is the decrease in organic matter abundance during weathering. This method can only reflect the impact of the first method, but cannot reflect the degree of decrease in organic matter abundance caused by the weathering process, and cannot perform weathering correction for organic matter abundance in field outcrops.

[0010] To this end, we invented a new method to determine the weathering correction coefficient of shale organic matter abundance, which solved the above technical problems. Summary of the invention

[0011] The purpose of the present invention is to provide a method for determining the weathering correction coefficient of organic matter abundance in shale, which provides technical support for source rock evaluation and zone oil and gas resource potential prediction.

[0012] The object of the present invention can be achieved by the following technical measures: a method for determining the weathering correction coefficient of organic matter abundance in mud shale, the method for determining the weathering correction coefficient of organic matter abundance in mud shale comprises:

[0013] Step 1, select the key layer section and sample the fresh section or shallow drilling system;

[0014] Step 2, conducting inorganic element compound and TOC analysis;

[0015] Step 3, calculate the weathering degree parameters such as CIA and CIW;

[0016] Step 4, determining the TOC value of the unweathered sample;

[0017] Step 5, calculating the TOC correction factor for each sample;

[0018] Step 6, analyzing the correlation between weathering parameters and correction factors;

[0019] Step 7, establish a weathering degree TOC correction quantitative model.

[0020] The purpose of the present invention can also be achieved by the following technical measures:

[0021] In step 1, when selecting the key layer section, the outcrop area of ​​the source rock section is determined through field survey for the target layer section of the source rock research; fresh outcrop sections such as newly built roads and newly opened mines are given priority; or relatively vertical sections are selected to carry out shallow drilling and coring.

[0022] In step 1, systematic sampling is carried out on fresh outcrop samples or shallow borehole target layers, where the sampling interval for sections with good underground preservation conditions is 0.2m-1m, and the sampling interval close to the surface is appropriately increased to 0.1m-0.5m.

[0023] In step 1, if the target layer section has a stable planar distribution and the adjacent layer has an easily identifiable marker layer, it can be compared with the close-range drilling in the basin and the drilling samples can be used as unweathered samples for systematic sampling.

[0024] In step 2, for the samples taken from the system, the elements Al, Mg, Ca, and K are determined using X-ray fluorescence spectroscopy elemental analysis to determine the contents of compounds such as aluminum oxide Al2O3, calcium oxide CaO, sodium oxide Na2O, and potassium oxide K2O. At the same time, geochemical analysis tests related to organic carbon (TOC) and organic matter abundance are performed.

[0025] In step 3, the weathering parameters of the sample CIA, CIW, and PIA are calculated using the compound determination results. The specific formula is:

[0026] CIA=[Al2O3 / (Al2O3+CaO+Na2O+K2O)]×100

[0027] CIW=[Al2O3 / (Al2O3+CaO+Na2O)]×100

[0028] PIA=[(Al2O3-K2O) / (Al2O3+CaO+Na2O-K2O)]×100.

[0029] In the formula, the units of oxides are all moles;

[0030] The chemical alteration index CIA and chemical weathering index CIW can both evaluate the degree of transformation of feldspar into clay minerals such as kaolinite, and the plagioclase alteration index PIA can eliminate the influence of potassium metasoma.

[0031] In step 4, the TOC value of the unweathered sample or the approximate parent rock sample is determined by combining the constant and lowest values ​​of the weathering parameters and the constant and highest value of the TOC measurement results. TOC is the organic carbon content of the sample in %.

[0032] In step 5, based on the TOC and TOC i Compared with the TOC value of unweathered samples and TOC o The organic matter abundance correction factor K of each sample was calculated. i , the formula is:

[0033] K i =TOC o / TOC i ;

[0034] In the formula, TOC o is the original organic carbon content of organic matter without weathering, %; TOC i is the original organic carbon content after weathering of organic matter, %.

[0035] In step 6, the correlation between the weathering parameters of the series of samples and the organic matter abundance correction coefficient Ki is analyzed to establish a single factor regression quantitative model, namely

[0036] K i1 =f(CIA)

[0037] K i2 =f(CIW).

[0038] In step 7, a weathering degree TOC correction quantitative model is established.

[0039] The method for determining the weathering correction coefficient of shale organic matter abundance also includes, after step 7, selecting the element model with the strongest correlation to determine a quantitative formula for the weathering degree correction coefficient applicable to the area; performing multiple regression on the basis of a single element, and finally using the model correlation as the basis of the formula, and at the same time, the K value should be ≥1, and K is the weathering correction coefficient.

[0040] The method for determining the weathering correction coefficient of organic matter abundance in mudstone in the present invention is based on sampling of surface outcrops, fresh outcrops, shallow boreholes and drilling sample systems, and geochemical analysis tests such as inorganic element and compound composition, TOC, etc. are carried out on source rock samples of the same layer, and the inorganic compound composition parameters are used to characterize the weathering degree of the samples, and a quantitative relationship between the weathering degree parameters and the organic matter abundance correction coefficient index under different weathering degrees is established, so as to realize the scientific quantitative prediction of the organic matter abundance correction coefficient of field outcrops under different weathering degree conditions.

[0041] The innovations of the present invention lie in the following two points: first, the influence of different degrees of weathering on the abundance of organic matter can be objectively evaluated; second, the method takes the characteristics of inorganic element migration and compound composition changes as the core, and innovatively establishes a quantitative correction model for organic matter abundance under different degrees of weathering. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 A flowchart of a specific embodiment of the method for determining the weathering correction coefficient of organic matter abundance in shale according to the present invention;

[0043] Figure 2 It is a correlation diagram between sample burial depth and organic matter abundance (TOC) in a specific embodiment of the present invention;

[0044] Figure 3 It is a correlation diagram between sample burial depth and weathering degree parameter 1 (CIA) in a specific embodiment of the present invention;

[0045] Figure 4 It is a correlation diagram between sample burial depth and weathering degree parameter 2 (CIW) in a specific embodiment of the present invention;

[0046] Figure 5 It is a correlation diagram between sample burial depth and TOC weathering correction coefficient (K) in a specific embodiment of the present invention;

[0047] Figure 6 It is a correlation diagram between the TOC weathering correction coefficient (K) and the weathering degree parameter (CIA) in a specific embodiment of the present invention;

[0048] Figure 7 1 is a correlation diagram between the TOC weathering correction coefficient (K) and the weathering degree parameter (CIW) in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0049] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0050] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations and / or combinations thereof.

[0051] like Figure 1 As shown, Figure 1The present invention is a flow chart of a method for determining weathering correction coefficient of organic matter abundance in shale using inorganic element composition.

[0052] Step 1: For the target layer of source rock to be studied, determine the exposed area of ​​the source rock layer through field survey; give priority to selecting fresh outcrop sections such as newly built roads and newly opened mines; or select relatively vertical sections with shallow drilling and coring. The recommended drilling depth is 20-100m, and the specific depth is determined by factors such as stratum lithology, age, occurrence and weathering time; combined with actual geological conditions, excavation equipment can also be rented for assistance.

[0053] Step 2: systematically sample the above-mentioned fresh outcrop samples or shallow borehole target layer sections, wherein the sampling interval for sections with better underground preservation conditions can be 0.2m-1m, and the sampling interval close to the surface can be appropriately increased to 0.1m-0.5m.

[0054] Step 3: If the target layer segment has a stable planar distribution and the adjacent layer has an easily identifiable marker layer, it can be compared with the close-range drilling in the basin and the drilling samples can be used as unweathered samples for systematic sampling.

[0055] Step 4: For the samples taken from the system, use the X-ray fluorescence spectroscopy elemental analysis method to determine the elements such as Al, Mg, Ca, K, determine the composition of compounds such as Al2O3, CaO, N2O, K2O, and perform geochemical analysis tests related to the abundance of organic matter such as organic carbon (TOC).

[0056] Step 5: Calculate the weathering parameters of the sample such as CIA, CIW, and PIA using the compound determination results. The calculation methods are based on Nesbitt and Young (1982), Harnois (1988), and Fedo (1995). The specific formula is:

[0057] CIA=[Al2O3 / (Al2O3+CaO+N2O+K2O)]×100

[0058] CIW=[Al2O3 / (Al2O3+CaO+Na2O)]×100

[0059] PIA=[(Al2O3-K2O) / (Al2O3+CaO+Na2O-K2O)]×100

[0060] Step 6, combining the constant and lowest values ​​of the weathering parameters and the constant and highest values ​​in the organic carbon (TOC) measurement results, determine the unweathered sample or the similar parent rock sample.

[0061] Step 7: Based on the TOC (TOC i ) and the TOC value of the unweathered sample (TOC o), calculate the organic matter abundance correction factor K for each sample i , the formula is:

[0062] K i =TOC o / TOC i

[0063] Step 8: Analyze the correlation between the weathering parameters of the series of samples and the organic matter abundance correction coefficient Ki, and establish a single factor regression quantitative model, namely

[0064] K i1 =f(CIA)

[0065] K i2 =f(CIW)

[0066] Step 9, select the element model with the strongest correlation and determine the quantitative formula of the weathering degree correction coefficient applicable to the area; multiple regression can be performed on the basis of a single element, and finally the model correlation is used as the basis of the formula, and the K value should be ≥1.

[0067] Step 10, determine the weathering parameter related elements and TOC of other surface outcrop source rock samples in the area, and substitute them into the formula determined in step 10 to determine the unweathered TOC value (TOC o ).

[0068] TOC o '=TOC i ×K i

[0069] In the embodiment 1 of the present invention, the following steps are included:

[0070] (1) A vertical section of the stratigraphic occurrence near the Liwaxia Reservoir in the Liupanshan Basin in the Hexi Corridor was selected. The measured stratigraphic dip was 90°, and the studied stratum was the Madongshan Formation (K1m) of the Lower Cretaceous.

[0071] (2) In the section where source rocks of the Madongshan Formation are concentrated, shallow drilling to a depth of 35 m was carried out and coring was performed in the entire section.

[0072] (3) Intensive sampling is carried out near the surface, with sample intervals of 0.1m-0.5m. The sampling intervals of core sections with better underground preservation conditions are 0.2m-1m.

[0073] (4) Conduct geochemical analysis and testing related to organic matter abundance such as organic carbon (TOC), and compile a correlation diagram between the burial depth and TOC of K1m samples ( Figure 2 ).

[0074] (5) Use X-ray fluorescence spectroscopy to determine the content of elements such as Al, Mg, Ca, K and related compounds in the sample. According to the element determination results, calculate the weathering degree characterization parameters (CIA, CIW, PIA, etc.) of the sample. Prepare a correlation diagram between the sample burial depth and key weathering parameters (CIA, CIW). Figure 3 , Figure 4 ).

[0075] (6) Combined with the fact that the weathering parameters tend to be constant and the lowest value, and the TOC determination results are constant and the highest value, it is considered to be an unweathered sample or a sample similar to the parent rock. Figure 3 , Figure 4 It can be seen that the weathering depth of this profile is about 5m-10m. The weathering parameters of the layers with significant surface weathering are relatively large, with CIA of 50-82 and CIW up to 90. In the samples buried at a depth of 10m-25m, TOC is close to 1.34%, CIA is 44-46, and CIW is about 60. Therefore, the TOC value of the unweathered sample (TOC o ) was determined to be 1.34%.

[0076] (7) Based on the TOC (TOC) of each sample i ) and the determined TOC value of the unweathered sample (TOC o ), calculate the organic matter abundance correction factor K for each sample i , the formula is:

[0077] K i =TOC o / TOC i

[0078] On this basis, a correlation diagram between sample burial depth and TOC correction coefficient was compiled ( Figure 5 ),Depend on Figure 5 It can be seen that the maximum TOC correction factor of the sample can reach 2.85.

[0079] (8) Analysis of the correlation between various weathering parameters of the series of samples and the organic matter abundance correction factor Ki ( Figure 6 , Figure 7 ), and establish a single factor regression quantitative model of weathering parameters and abundance correction factors. Among them:

[0080] K i1 =2.9097×ln(CIA)-9.8625(R 2 =0.8504)

[0081] K i2 =5.323×ln(CIW)-20.627(R 2 =0.8491)

[0082] Since the evaluation of weathering by parameters such as CIA, CIW, and PIA has different understandings on the potassium replacement, the evaluation results are different. In the early weathering stage, the weathering of plagioclase is the main one. After the disappearance of plagioclase, minerals such as potassium feldspar and illite are weathered, and the release and replacement of K element occur. In the application of this method, a typical weathering parameter can be selected for fitting according to the outcrop strata, weathering time, and the characteristics of typical compound components.

[0083] (9) Based on the single factor, multivariate regression was performed to establish a quantitative model for organic matter abundance correction constrained by multiple weathering degree parameters.

[0084] K=f(CIA,CIW)

[0085] Through multiple regression, the quantitative prediction formula of organic matter abundance weathering correction coefficient under multi-factor constraints is obtained as follows:

[0086] K=1.512×ln(CIA)+2.645×ln(CIW)-15.407(R 2 =0.864)

[0087] In the embodiment 2 of the present invention, the following steps are included:

[0088] (1) A vertical section of the stratigraphic occurrence near the Xidalongkou Reservoir in the southern margin of the Junggar Basin was selected. The measured stratigraphic dip was 80°, and the studied stratum was the Middle Permian Lucaogou Formation (P2l).

[0089] (2) In the concentrated section of source rock development in the Lucaogou Formation, a shallow hole with a depth of 10 m was drilled at a fresh outcrop of about 20 m above the ground, and coring was performed in the entire section.

[0090] (3) Intensive sampling is carried out near the surface, with sample intervals of 0.1m-0.5m. The sampling intervals of core sections with better underground preservation conditions are 0.2m-1m.

[0091] (4) Conduct geochemical analysis and testing related to the abundance of organic matter such as organic carbon (TOC), and compile a correlation diagram between the burial depth and TOC of the P2l shale sample.

[0092] (5) X-ray fluorescence elemental analysis is used to determine the content of Al, Mg, Ca, K and other elements and related compounds in the samples. Based on the elemental determination results, the weathering degree characterization parameters (CIA, CIW, PIA, etc.) of the samples are calculated. A correlation diagram between the sample burial depth and key weathering parameters (PIA, CIA, CIW) is compiled.

[0093] (6) Combined with the fact that each weathering parameter tends to be constant and at the lowest value, and the organic carbon (TOC) measurement result has a constant and highest value, it is considered as an unweathered sample or a similar parent rock sample. From the correlation diagram between the sample burial depth and the key weathering parameters (PIA, CIA, CIW), it can be seen that the weathering influence depth of this profile is about 8m-12m. The weathering parameters of the layer with significant surface weathering are relatively large, with CIA of 60-89, CIW of 81-92, and PIA of 75-96. For samples 5m-10m below the surface, TOC approaches 2.15%, CIA is 50-52, CIW is around 55, and PIA is 70. Therefore, the TOC value of the unweathered sample (TOC o ) is determined to be 2.15%.

[0094] (7) Based on the TOC (TOC) of each sample i ) and the determined TOC value of the unweathered sample (TOC o ), calculate the organic matter abundance correction factor K for each sample i , the formula is:

[0095] K i =TOC o / TOC i

[0096] On this basis, a correlation diagram between sample burial depth and TOC correction coefficient was compiled. Figure 6 It can be seen that the maximum sample TOC correction factor can reach 3.62.

[0097] (8) Analyze the correlation between the weathering parameters of the series of samples and the organic matter abundance correction factor Ki, and establish a single factor regression quantitative model of weathering parameters and abundance correction factor.

[0098] K i1 =3.8221×ln(CIA)-6.2075(R 2 =0.8329)

[0099] K i2 =3.5912×ln(CIW)-15.3744(R 2 =0.8656)

[0100] K i3 =6.2508×ln(PIA)-8.6679(R 2 =0.8530)

[0101] (9) Perform multiple regression on the basis of single factors to establish a quantitative model for organic matter abundance correction constrained by multiple weathering degree parameters. Since the correlation of CIW and PIA parameters in step 8 is slightly higher, CIW and PIA parameters are selected for dual-factor fitting.

[0102] K=f(PIA,CIW)

[0103] Through multiple regression, the quantitative prediction formula of organic matter abundance weathering correction coefficient under multi-factor constraints is obtained as follows:

[0104] K=3.3701×ln(PIA)+4.9323×ln(CIW)-12.8260(R 2 =0.872)

[0105] The method for determining the correction coefficient of organic matter abundance under the weathering degree in the present invention involves theoretical methods such as elemental geochemistry and organic geochemistry, and aims to provide technical support and theoretical basis for the objective evaluation of organic matter abundance in outcrop source rocks in low-exploration areas. Based on systematic sampling and analysis tests of fresh outcrops or shallow borehole samples in the field, for the first time, with the migration of inorganic elements and the characteristics of compound changes as the core, an innovative quantitative correction model for organic matter abundance under different degrees of weathering was established, realizing the scientific evaluation of original organic matter abundance under different weathering effects.

[0106] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions recorded in the aforementioned embodiments or replace some of the technical features therein with equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

[0107] Except for the technical features described in the specification, all other technical features are known technologies to those skilled in the art.

Claims

1. A method for determining weathering correction coefficient of organic matter abundance in shale, characterized in that: The method for determining the weathering correction coefficient of shale organic matter abundance includes: Step 1, select the key layer section and sample the fresh section or shallow drilling system; Step 2, conducting inorganic element compound and TOC analysis; Step 3, calculate the weathering degree parameters such as CIA and CIW; Step 4, determining the TOC value of the unweathered sample; Step 5, calculating the TOC correction factor for each sample; Step 6, analyzing the correlation between weathering parameters and correction factors; Step 7, establishing a weathering degree TOC correction quantitative model; In step 5, based on the TOC and TOC i Compared with the TOC value of unweathered samples and TOC o The organic matter abundance correction factor K of each sample was calculated. i , the formula is: K i =TOC o / TOC i ; In the formula, TOC o is the original organic carbon content of organic matter without weathering, %; TOC i is the original organic carbon content after weathering of organic matter, %; In step 6, the correlation between the weathering parameters of the series of samples and the organic matter abundance correction coefficient Ki is analyzed to establish a single factor regression quantitative model, namely K i1 =f(CIA) K i2 =f(CIW); Select the element model with the strongest correlation to determine the quantitative formula of the weathering degree correction coefficient applicable to the area; perform multiple regression based on the single element, and finally use the model correlation as the basis of the formula. At the same time, the K value should be ≥1, where K is the weathering correction coefficient; Determine the weathering parameter related elements and TOC of other surface outcrop source rock samples in the area, and substitute them into the formula determined in step 10 to determine the unweathered TOC value (TOC o ), TOC o '=TOC i ×K i .

2. The method for determining weathering correction coefficient of shale organic matter abundance according to claim 1, characterized in that: In step 1, when selecting the key layer section, the outcrop area of ​​the source rock section is determined through field survey for the target layer section of the source rock research; fresh outcrop sections such as newly built roads and newly opened mines are given priority; or relatively vertical sections are selected to carry out shallow drilling and coring.

3. The method for determining weathering correction coefficient of shale organic matter abundance according to claim 2, characterized in that: In step 1, systematic sampling is carried out on fresh outcrop samples or shallow borehole target layers, where the sampling interval for sections with good underground preservation conditions is 0.2m-1m, and the sampling interval close to the surface is appropriately increased to 0.1m-0.5m.

4. The method for determining weathering correction coefficient of shale organic matter abundance according to claim 3, characterized in that: In step 1, if the target layer section has a stable planar distribution and the adjacent layer has an easily identifiable marker layer, it can be compared with the close-range drilling in the basin and the drilling samples can be used as unweathered samples for systematic sampling.

5. The method for determining weathering correction coefficient of shale organic matter abundance according to claim 1, characterized in that: In step 2, for the samples taken from the system, the elements Al, Mg, Ca, and K are determined using X-ray fluorescence spectroscopy elemental analysis to determine the contents of compounds such as aluminum oxide Al2O3, calcium oxide CaO, sodium oxide Na2O, and potassium oxide K2O. At the same time, geochemical analysis tests related to organic carbon (TOC) and organic matter abundance are performed.

6. The method for determining weathering correction coefficient of shale organic matter abundance according to claim 1, characterized in that: In step 3, the weathering parameters of the sample CIA, CIW, and PIA are calculated using the compound determination results. The specific formula is: CIA=[Al2O3 / (Al2O3+CaO+Na2O+K2O)]×100 CIW=[Al2O3 / (Al2O3+CaO+Na2O)]×100 PIA=[(Al2O3-K2O) / (Al2O3+CaO+Na2O-K2O)]×100 In the formula, the units of oxides are all moles; The chemical alteration index CIA and chemical weathering index CIW can both evaluate the degree of transformation of feldspar into kaolinite clay minerals, and the plagioclase alteration index PIA can eliminate the influence of potassium metasoma.

7. The method for determining weathering correction coefficient of shale organic matter abundance according to claim 1, characterized in that: In step 4, the TOC value of the unweathered sample or the approximate parent rock sample is determined by combining the constant and lowest values ​​of the weathering parameters and the constant and highest value of the TOC measurement results. TOC is the organic carbon content of the sample in %.

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