A method for high evolution shale organic matter type classification

Abstract

The application discloses a method for high-evolution shale organic matter type division, which comprises the following steps: S1, collecting conventional logging data and core sampling data of shale gas wells in a research area; S2, selecting typical shale gas wells to perform systematic sampling on small layers of the high-evolution shale, performing ordinary thin section production, cheese root analysis and light thin section production on the samples, and then obtaining organic matter different microcomponent contents through cheese root microcomponent identification experiments; S3, on the basis of the organic matter different microcomponent contents, calculating TI values of the shale samples according to a TI index method formula; S4, performing comparative observation on the ordinary thin sections and cheese roots by using a scanning electron microscope, and identifying and counting shale hydrocarbon source rock types and contents; S5, establishing a coupling relationship among the TI values, GR values and hydrocarbon source rocks; and S6, further subdividing shale organic matter types according to the coupling relationship and combining the TI values and GR values.

Description

Technical Field

[0001] This invention belongs to the field of geological exploration technology, specifically relating to a method for classifying organic matter types in highly evolved shale. Background Technology

[0002] The Ordovician Wufeng Formation-Lower Silurian Longmaxi Formation, Section 1 (referred to as Longyi 1 Section) shale in the Sichuan Basin is one of the main stratigraphic units for unconventional gas exploration and development in my country. It possesses advantages such as abundant organic matter, high content of brittle minerals, moderate burial conditions, and good gas content. Organic matter is the most important material basis of shale; shale with industrial development value contains a high abundance of organic matter (generally greater than 2%). Furthermore, organic matter acts as a carrier for gas adsorption, and organic matter pores are the most prevalent pore type in shale reservoirs. The hydrocarbon generation process in shale is complex, and its hydrocarbon generation capacity is mainly controlled by the type of organic matter. Organic matter is generally classified into Type I, Type II, and Type III organic matter, with varying abilities in hydrocarbon generation and pore formation. Type I and Type II organic matter are more prone to pyrolysis and hydrocarbon generation and the formation of organic matter pores than Type III organic matter. Organic matter type is one of the important indicators when evaluating the quality of source rocks. The organic matter in the black shale of the Wufeng-Longmaxi Formation in the Sichuan Basin mainly comes from lower aquatic organisms, primarily of type I and II, with a high proportion of sapropelic content. It is a typical sapropelic kerogen and has excellent gas generation conditions.

[0003] Currently, organic matter types are classified by calculating the Ti value: a Ti value greater than 80 is Type I, a Ti value between 40 and 80 is Type II1, a Ti value between 0 and 40 is Type II2, and a Ti value less than 0 is Type III. Based on existing methods for classifying organic matter types, the organic matter in the Wufeng Formation-Longyi 1 sub-member shale of the Sichuan Basin is classified as Type I and Type II1, with Type I primarily developed in the Longyi 1 sub-member. 1 Xiaofeng Formation and local strata of Wufeng Formation, Wufeng Formation and Longyi 1 2 Small floor ~ Dragon 1 4 The sublayers mostly develop type II1 organic matter, but for the Wufeng group and Longyi 1, which develop type II1 organic matter, 2 Small floor ~ Dragon 1 4 For smaller layers, the sedimentary environments, source materials for hydrocarbon generation, and reservoir quality vary significantly. Under existing classification methods, the results are not ideal, as the organic matter type, a crucial evaluation indicator, fails to effectively reflect the differences in source rocks. Therefore, for the Wufeng Formation-Longyi 1 sub-member shale in the Sichuan Basin, the classification method for type II1 organic matter needs to be re-developed and refined. Furthermore, currently, the classification of organic matter types primarily relies on microscopic component identification experiments of shale samples, using formulas to calculate the kerogen type from the obtained components.

[0004] Furthermore, given the sheer number of shale gas wells, it's currently impossible to cor the samples from every single well. For wells without core samples where organic matter microstructure identification experiments cannot be performed, it's impossible to evaluate the source rock based on organic matter type. Therefore, it's crucial to establish a relationship between conventional logging curves common to all shale gas wells and organic matter type to further evaluate the source rock. Natural gamma-ray spectroscopy (GR) logging, as the most common conventional logging method, reflects the natural radioactivity intensity and elemental types of the formation, playing a vital role in identifying complex lithologies, fractures, sequence stratigraphy, and reconstructing sedimentary environments. Summary of the Invention

[0005] To address the aforementioned shortcomings in existing technologies, this invention provides a method for classifying organic matter types in highly evolved shale, which solves the problem of poor performance of existing classification methods.

[0006] To achieve the aforementioned objectives, the present invention employs the following technical solution: a method for classifying organic matter types in highly evolved shale, comprising the following steps:

[0007] S1. Collect conventional logging data and core sampling data of shale gas wells in the study area;

[0008] S2. Select typical shale gas wells to systematically sample the sub-layers of highly evolved shale, and perform ordinary thin section preparation, kerogen analysis and optical thin section preparation on the samples. Then, obtain the content of different micro-components of organic matter through kerogen micro-component identification experiments.

[0009] S3. Based on the clear content of different micro-components of organic matter, calculate the TI value of each shale sample according to the TI index method formula;

[0010] S4. Using scanning electron microscopy to compare and observe ordinary thin sections and kerogen, identify and statistically analyze the types and contents of shale hydrocarbon-generating parent materials;

[0011] S5. Establish the coupling relationship between TI value, GR value and hydrocarbon-generating parent material;

[0012] S6. Based on the coupling relationship and combined with TI and GR values, further subdivide the shale organic matter types.

[0013] Furthermore, the ordinary thin sections must be made parallel to the rock strata and have a thickness of less than 20 μm.

[0014] Furthermore: during the preparation of the thin section, the rock sample needs to be ground into particles with a diameter greater than 2 mm, and the carbonate rock and silicate minerals are removed by acidification. The remaining organic matter is washed with distilled water until neutral and then allowed to settle freely.

[0015] Furthermore, the ordinary thin sections, kerogen and optical thin sections were observed under a scanning electron microscope (SEM). The SEM was set to high vacuum mode, with an accelerating voltage of 1–5 kV and a maximum resolution of 1 nm.

[0016] Furthermore, the contents of saprophytic, chitinous, vitrinous, and inertinous groups in the sample were determined through microscopic component identification experiments of kerogen.

[0017] Furthermore: the formula for calculating the TI value is as follows:

[0018] TI = (100a + 50b - 75c - 100d) / 100

[0019] In the above formula, a, b, c, and d represent the contents of saprophytic group, chitinous group, vitrinite group, and inertinite group, respectively.

[0020] Furthermore, the hydrocarbon-generating parent material includes benthic algae and planktonic algae.

[0021] Further, the subdivision method is as follows: GR with high value characteristics, saprophytic content greater than 90%, and TI index greater than 80 is classified as Type I kerogen; GR with medium-high value characteristics, saprophytic content between 80-90%, and TI index between 60-80 is classified as Type II kerogen. 1a Type II kerogen; GR is low, humic content is between 60-80%, and TI index is between 40-60. 1b Type II kerogen; a TI index below 40 indicates Type II kerogen; a TI index below 0 indicates Type III kerogen.

[0022] Furthermore: the high value characteristic of GR is above 250 API, the medium-high value characteristic of GR is 200-250 API, and the low value characteristic of GR is below 200 API.

[0023] The beneficial effects of this invention are as follows: This invention establishes a method for further subdividing the organic matter types of highly mature shale, which has promotional value for the subdivision of organic matter types and the evaluation and prediction of gas content in marine shale in southern China. Furthermore, given the large number of shale gas wells, this invention solves the problem of the inability to classify the organic matter types of shale gas wells without core sampling. Based on the coupling relationship between the electrical characteristics of the logging curves and the organic matter types established in this invention, the organic matter types of shale gas wells without core sampling can be preliminarily classified quickly through electrical characteristics. Attached Figure Description

[0024] Figure 1 This is a flowchart of the present invention;

[0025] Figure 2 This is a comprehensive columnar section of the shale formation from Wufeng Formation to Longyi 1 Member in well Ning 201, as described in this embodiment of the invention.

[0026] Figure 3This invention illustrates the relationship between the Ti index and GR content in the Wufeng Formation-Longyi 1 sub-member shale of the Changning area in southern Sichuan.

[0027] Figure 4 Longitudinal profile of organic matter type in the shale of the Wufeng Formation to Longyi 1 sub-section of Well Ning 213. Detailed Implementation

[0028] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0029] like Figure 1 As shown, a method for classifying organic matter types in highly evolved shale includes the following steps:

[0030] S1. Collect conventional logging data and core sampling data of shale gas wells in the study area;

[0031] S2. Select typical shale gas wells to systematically sample the sub-layers of highly evolved shale, and perform ordinary thin section preparation, kerogen analysis and optical thin section preparation on the samples. Then, obtain the content of different micro-components of organic matter through kerogen micro-component identification experiments.

[0032] Systematic sampling was conducted on the shale formations of the Wufeng Formation to Longyi-1 sub-member from typical shale gas wells. The samples underwent ordinary thin section preparation, kerogen analysis, and polished thin section preparation, as well as kerogen microstructure identification experiments. Ordinary thin sections were ground parallel to the rock bedding planes, with a thickness generally less than 20 μm. Polished thin sections required grinding the rock samples to a particle size greater than 2 mm, removing carbonate rocks and silicate minerals using acidification, and washing the remaining organic matter with distilled water until neutral, followed by free settling. Ordinary thin sections, kerogen samples, and polished thin sections were observed under a Leica DM4P microscope. Scanning electron microscopy (SEM) of the rock samples was performed in high vacuum mode with an accelerating voltage of 1–5 kV and a maximum resolution of 1 nm. The contents of sapropelic, chrysinic, vitrinic, and inertinic groups in the samples were determined through kerogen microstructure identification experiments, as shown in Table 1.

[0033] Table 1. Microscopic component data of kerogen in Longmaxi Formation shale of Changning area.

[0034] W-1 Longma Creek Group 79 21 0 0 W-2 Longma Creek Group 79 17 0 4 W-3 Longma Creek Group 79 21 0 0 W-4 Longma Creek Group 78 20 0 2 W-5 Longma Creek Group 80 20 0 0 W-6 Longma Creek Group 79 21 0 0 W-7 Longma Creek Group 78 21 0 1 W-8 Longma Creek Group 78 16 0 6 W-9 Wufeng Group 78 20 0 2 W10 Longma Creek Group 80 16 0 4 W-11 Longma Creek Group 81 18 0 1 W-12 Longma Creek Group 76 21 0 3 W-13 Longma Creek Group 79 21 0 0 W-14 Longma Creek Group 77 22 0 1 W-15 Longma Creek Group 86 12 0 2 W-16 Wufeng Group 79 21 0 0 W-17 Longma Creek Group 87 11 0 2 W-18 Longma Creek Group 77 22 0 1 W-19 Longma Creek Group 90 10 0 0 W-20 Longma Creek Group 90 10 0 0 W-21 Longma Creek Group 89 11 0 0 W-22 Longma Creek Group 83 14 0 0

[0035] S3. Based on the clear content of different microscopic components of organic matter, calculate the TI value of each shale sample according to the TI index method formula; the calculation formula is TI=(100a+50b-75c-100d) / 100, where a, b, c, and d are the contents of sapropelic group, chrysinic group, vitrinic group, and inertinic group, respectively.

[0036] S4. Using scanning electron microscopy to compare and observe ordinary thin sections and kerogen, identify and statistically analyze the types and contents of shale hydrocarbon-generating parent materials;

[0037] The biota in the Wufeng Formation-Longyi 1 sub-member shale mainly consists of benthic algae and phytoplankton. Benthic algae generally appear as reticulate, granular, or filamentous structures, while phytoplankton mostly occur as monomers or aggregates. The results of statistical analysis of benthic and phytoplankton content are shown in Table 2.

[0038] Table 2. Data on phytoplankton content in the Longmaxi Formation shale of Changning area.

[0039] SH-09 78.0 214.9 38.2 SH-08 48.0 162.2 10.4 SH-07 72.0 227.0 29.8 SH-06 82.0 359.2 51.2 SH-05 54.0 132.3 16.2 SH-04 77.5 192.0 22.7 SH-03 60.0 195.2 12.3 SH-02 66.0 198.2 15.5 SH-01 82.0 300.1 45.6

[0040] When the GR value is high (>250 API), the TI value is greater than 80, the phytoplankton content is the highest (up to 51.2%), indicating the strongest hydrocarbon generation capacity of shale; when the GR value is medium to high (between 180 and 250 API), the TI value is between 60 and 80, the phytoplankton content is relatively high (about 20%), and the hydrocarbon generation capacity is relatively strong; when the GR value is low and box-shaped (<180 API), the TI value is generally below 60, the phytoplankton content is low (about 13.6%), and the hydrocarbon generation capacity is weak.

[0041] S5. Establish the coupling relationship between TI value, GR value, and hydrocarbon-generating parent material, and analyze the correspondence between kerogen microcomponents and GR value. For example... Figure 2 As shown, the vertical trend of the GR curve is basically consistent with that of the TI value, exhibiting a phenomenon of "both high and low". This is particularly evident in the five-peak group and Longyi 1. 1 He Longyi 1 3 The lower layers show high-value characteristics, at the top of the Wufeng Group (Guanyinqiao section) and Longyi 1. 2 He Longyi 1 4 The lower layer displays low-value characteristics; by plotting all its data, we can discover, for example... Figure 3 As shown, the GR curve and the TI value have a very good positive correlation (correlation coefficient R). 2 =0.68), which can be expressed by the formula y = 0.07x. 2 -5.87x+277.41 means that x and y represent the TI value and GR value, respectively. When the TI value is 80, the GR value is 255.81 API, and when the TI value is 60, the GR value is 177.21 API.

[0042] S6, such as Figure 4As shown, based on the coupling relationship and combined with TI and GR values, the shale organic matter types are further subdivided. The classification method is as follows: The classification method for Type I kerogen remains unchanged, with a TI index greater than 80 and a high GR value (above 250 API); Type II kerogen is further subdivided, where GR is a medium-to-high value characteristic (between 180 and 250 API) and a TI index between 60 and 80 is classified as Type II. 1a Type II kerogen; GR is a low value characteristic (below 180 API), and TI index is between 40-60. 1b Type II kerogen; the classification method for Type II and Type III kerogen remains unchanged, with a TI index below 40 being Type II kerogen; and a TI index less than 0 being Type III kerogen.

[0043] This invention establishes a method for further subdividing the organic matter types of highly mature shale, which has promotional value for the subdivision of organic matter types and the evaluation and prediction of gas bearing capacity in marine shale in southern China. Furthermore, given the large number of shale gas wells, this invention solves the problem of the inability to classify the organic matter types of shale gas wells without core sampling. Based on the coupling relationship between the electrical characteristics of logging curves and organic matter types established in this invention, preliminary classification of organic matter types in shale gas wells without core sampling can be quickly performed using electrical characteristics.

Claims

1. A method for classifying organic matter types in highly evolved shale, characterized in that, Includes the following steps: S1. Collect conventional logging data and core sampling data of shale gas wells in the study area; S2. Select typical shale gas wells to systematically sample the sub-layers of highly evolved shale, and perform ordinary thin section preparation, kerogen analysis and optical thin section preparation on the samples. Then, obtain the content of different micro-components of organic matter through kerogen micro-component identification experiments. S3. Based on the clear content of different micro-components of organic matter, calculate the TI value of each shale sample according to the TI index method formula; S4. Using scanning electron microscopy to compare and observe ordinary thin sections and kerogen, identify and statistically analyze the type and content of shale hydrocarbon-generating parent material; S5. Establish the coupling relationship between TI value, GR value and hydrocarbon-generating parent material; S6. Based on the coupling relationship and combined with TI and GR values, further subdivide the shale organic matter types; the subdivision method is as follows: GR with high value characteristics, sapropelic content greater than 90% and TI index greater than 80 is Type I kerogen; GR with medium to high value characteristics, sapropelic content between 80-90% and TI index between 60-80 is Type II. 1a Type II kerogen; GR is low, humic content is between 60-80%, and TI index is between 40-60. 1b Type II kerogen; a TI index below 40 indicates Type II kerogen; a TI index below 0 indicates Type III kerogen.

2. The method for classifying organic matter types in highly evolved shale according to claim 1, characterized in that, The ordinary thin sections must be made parallel to the rock strata and have a thickness of less than 20 μm.

3. The method for classifying organic matter types in highly evolved shale according to claim 1, characterized in that, The thin section preparation process requires grinding the rock sample into particles larger than 2 mm, using acidification to remove carbonate rocks and silicate minerals, washing the remaining organic matter with distilled water until neutral, and allowing it to settle freely.

4. The method for classifying organic matter types in highly evolved shale according to claim 1, characterized in that, The ordinary thin sections, kerogen sections, and optical thin sections were observed under a scanning electron microscope (SEM). The SEM was set to high vacuum mode, with an accelerating voltage of 1-5 kV and a maximum resolution of 1 nm.

5. The method for classifying organic matter types in highly evolved shale according to claim 1, characterized in that, The contents of saprophytic, chitinous, vitrinous, and inertinous groups in the sample were determined by microscopic component identification experiments of kerogen.

6. The method for classifying organic matter types in highly evolved shale according to claim 1, characterized in that, The formula for calculating the TI value is as follows: TI=(100a+50b-75c-100d) / 100 In the above formula, a, b, c, and d represent the contents of saprophytic group, chitinous group, vitrinite group, and inertinite group, respectively.

7. The method for classifying organic matter types in highly evolved shale according to claim 1, characterized in that, The hydrocarbon-generating parent material includes benthic algae and planktonic algae.

8. The method for classifying organic matter types in highly evolved shale according to claim 1, characterized in that, The high value characteristic of GR is above 250 API, the medium-high value characteristic of GR is 180~250 API, and the low value characteristic of GR is below 180 API.

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