A five-end-member three-component division and characterization method for shale lithofacies

Abstract

The present invention discloses a five-end-member three-component classification and characterization method for shale lithofacies, comprising performing X-ray diffraction analysis on shale samples to determine the shale mineral components and contents; performing vitrinite reflectance measurement on the shale samples to determine the shale maturity; performing total organic carbon analysis on the shale samples to determine the total organic carbon content percentage; calculating the content percentages of quartz and feldspar, clay minerals, and carbonate rock; determining the shale lithofacies type based on the position of the shale maturity, total organic carbon content percentage, quartz and feldspar content percentage, clay mineral content percentage, and carbonate rock content percentage of the shale sample in a five-end-member three-group classification diagram; and characterizing the lithofacies characteristics in the form of a radar chart. The present invention can classify and intuitively represent shale lithofacies, facilitate comparison of shale lithofacies of different samples, and be used to determine the most favorable shale lithofacies, guiding the selection of favorable areas for shale gas exploration and development.

Description

Technical Field

[0001] The present invention belongs to the technical field of shale gas geological evaluation and zone selection, and particularly relates to a five-end-member three-component division and characterization method for shale lithofacies. Background Art

[0002] Shale gas is an unconventional natural gas resource that is self-generated and self-stored in shale. To effectively develop shale gas, the first step is to select favorable areas through geological evaluation. At present, breakthroughs have been made in key technologies for shale gas exploration and development, and shale gas exploration and development have further expanded to new areas and new fields. Among them, deep and complex structural areas in the transitional phase between sea and land have gradually become one of the hot spots for exploration and development.

[0003] Shale is a fine-grained sediment containing inorganic components, including quartz, feldspar, and clay minerals, as well as organic components, with a genetic connection between the two. The organic components control the hydrocarbon-generating capacity of shale, and the occurrence and coupling relationships between various inorganic components and organic matter influence the enrichment and production of shale gas. A certain proportion of inorganic and organic components forms under specific sedimentary environments, resulting in different shale facies. These different shale facies have significantly different reservoir characteristics and gas-enrichment capacities. The variations in these shale facies reflect the genetic connection between sedimentary environment, mineral composition, and organic matter.

[0004] Most of the journal articles published at home and abroad focus on the division and characterization of shale lithofacies. Che Shiqi. Use of logging data for shale lithofacies division and identification: A case study of the Wufeng Formation-Longmaxi Formation in Fuling Gas Field [J]. Lithologic Reservoirs, 2018, 30(01): 121–132. Shale lithofacies were divided using TOC+mineral content, and shale lithofacies in the vertical direction of a single well were predicted using neural networks, but the lithofacies plane distribution has not been studied. Li Zhuo, Jiang Zhenxue, Tang Xianglu, et al. Lithofacies characteristics of the Longmaxi Formation shale in the Lower Silurian in southeastern Chongqing and its control on pore structure [J]. Earth Science, 2017, 42(07): 1116–1123. Shale lithofacies were divided using organic matter content and mineral composition, but the lithofacies plane distribution has not been studied. Dong Chunmei, Ma Cunfei, Lin Chengyan, et al. A method for facies division of mudstone strata[J]. Journal of China University of Petroleum (Natural Science Edition), 2015, 39(03): 1–7. Quartz, carbonate rock, and clay minerals in shale are selected as the three end members, with 25% and 50% as the main content dividing lines. Chinese invention patents CN201610226265.2, A method for rapid identification of shale lithofacies by well logging, and CN201610724474.X, A method for continuous prediction of shale lithofacies based on well logging information, both focus on how to predict and identify shale lithofacies in a single well, and do not mention planar lithofacies prediction. Chinese invention patents CN201711170899.1, a method for compiling the planar distribution of shale lithofacies and a shale exploration system, CN202010842778.2, a shale classification method and its application and a shale lithofacies distribution construction system, CN201710910428.3, a method for fine identification of mud shale lithofacies based on triple information, and CN201810864183.X, a lithofacies division method and verification method for inter-salt mud shale formations, all failed to consider the auxiliary role of organic carbon and organic matter maturity in lithofacies division, and the classification was not comprehensive.

[0005] Currently, there are numerous issues with shale lithofacies classification methods both domestically and internationally. These issues primarily manifest themselves in three key areas. First, while organic matter is a crucial parameter in shale reservoir evaluation, the classification scheme fails to consider the organic matter content of shale. Second, shale lithofacies classification fails to consider the impact of shale evolution on shale reservoir characteristics, making it difficult to guide shale gas geological evaluation. Third, there is a lack of intuitive comparison or characterization methods for classified shale lithofacies types, hindering the effectiveness of the classification scheme.

[0006] The above three problems affect the accuracy and reliability of shale gas geological evaluation area selection. Summary of the Invention

[0007] The purpose of the present invention is to provide a five-end-member three-component division and characterization method for shale lithofacies. Based on X-ray diffraction whole-rock analysis, organic matter content determination and total organic carbon determination, it fully considers the influence of organic matter content and total organic carbon content on shale reservoirs, and establishes a new shale lithofacies division and characterization method. It can more comprehensively and systematically reflect the types of shale lithofacies, and at the same time more intuitively reflect the differences between shale lithofacies, so as to better guide the selection of shale gas exploration and development areas.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] The present invention provides a five-end-member three-component division and characterization method for shale lithofacies, comprising:

[0010] Conduct X-ray diffraction analysis on shale samples to determine the mineral composition and content of shale;

[0011] Vitrinite reflectance is measured on shale samples, and shale maturity is determined based on the vitrinite reflectance;

[0012] Perform total organic carbon analysis on shale samples to determine the percentage of total organic carbon content in the shale;

[0013] Calculate the percentage of quartz and feldspar, clay minerals and carbonate rock based on the mineral composition and content of shale;

[0014] The shale lithofacies type is determined based on the position of the shale maturity, total organic carbon content percentage, quartz and feldspar content percentage, clay mineral content percentage, and carbonate rock content percentage of the shale sample in the drawn five-end member three-group classification diagram, and the lithofacies characteristics are characterized in the form of a radar map.

[0015] Furthermore, the shale sample is subjected to X-ray diffraction experimental analysis to determine the shale mineral components and content, which include at least one of the following shale mineral components: quartz, feldspar, carbonate rock, pyrite, and clay minerals.

[0016] Furthermore, the vitrinite reflectance measurement of the shale sample and the determination of shale maturity based on the vitrinite reflectance include:

[0017] Shale samples of 1*1cm size were collected and polished using a precision polishing instrument. The back of the sample was glued to a glass slide with paraffin wax and pressed using a tablet press to prepare an observation sample. The sample was then placed in a microphotometer to measure the vitrinite reflectance.

[0018] Select multiple sampling points for measurement and obtain the maximum vitrinite reflectance, minimum vitrinite reflectance and average vitrinite reflectance of the shale sample;

[0019] The average vitrinite reflectance is taken as the shale maturity.

[0020] Furthermore, the number of the sampling points is no less than 50.

[0021] Furthermore, the calculation of the percentages of the three components of quartz and feldspar, clay minerals, and carbonate rock includes:

[0022] According to the shale mineral composition and content obtained by X-ray diffraction experiment, the total weight of quartz, feldspar, carbonate rock and clay minerals is added together.

[0023] The quartz + feldspar content percentage is obtained by comparing the weight of quartz + feldspar with the total weight, the carbonate content percentage is obtained by comparing the weight of carbonate rock with the total weight, and the clay mineral content percentage is obtained by comparing the weight of clay mineral with the total weight.

[0024] Furthermore, it also includes drawing the classification diagram of the three groups of five end members as follows:

[0025] The percentage of quartz + feldspar content, carbonate content percentage and clay mineral content percentage were used as the three segments of the central triangle diagram, and the shale maturity and total organic carbon content percentage were used as the two wings extending outward from the central triangle diagram to draw three groups of classification diagrams with five end members.

[0026] Furthermore, it also includes,

[0027] Divide the three sides of the central triangle into three segments according to the percentages of 25, 50, and 75.

[0028] The two wings of the central triangle are divided into high maturity, medium maturity and low maturity zones according to shale maturity greater than 2%, between 1% and 2%, and less than 1%; and are divided into organic-rich, medium organic and low organic zones according to total organic carbon content greater than 2%, between 1% and 2%, and less than 1%.

[0029] Furthermore, the characterization of lithofacies characteristics in the form of radar charts includes:

[0030] The percentage of quartz + feldspar content, the percentage of carbonate content, the percentage of clay mineral content, the maturity of shale and the percentage of total organic carbon content are taken as the five vertices of the radar chart, and the center of the pentagon is taken as the zero starting point to connect the five vertices;

[0031] The lines connecting the center with the percentage of quartz + feldspar content, the percentage of carbonate content, and the percentage of clay mineral content are marked with 25, 50, and 75, respectively; the lines connecting the center with the percentage of shale maturity and total organic carbon content are marked with 1, 2, and 3, respectively;

[0032] The calculated shale maturity, total organic carbon content percentage, quartz and feldspar content percentage, clay mineral content percentage, and carbonate rock content percentage of the shale sample are projected onto corresponding connecting lines, and the data points are connected to obtain a radar map of the petrographic characteristics of the shale sample.

[0033] The beneficial effects of the present invention are:

[0034] The present invention provides a five-end-member three-component division and characterization method for shale lithofacies, and draws a five-end-member three-group classification diagram based on shale maturity, total organic carbon content percentage, quartz and feldspar content percentage, clay mineral content percentage, and carbonate rock content percentage. This method can fully consider the shale organic matter maturity and total organic carbon content, make the shale lithofacies division more detailed and accurate, and more intuitively display the differences between different shale lithofacies, thereby improving the accuracy of shale gas favorable area prediction and enhancing the geological exploration evaluation effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A flow chart of a method for five-end-member three-component division and characterization of shale lithofacies provided by the present invention;

[0036] Figure 2 A classification diagram of five-end-member and three-component shale lithofacies in a certain region according to an embodiment of the present invention;

[0037] Figure 3 A five-endmember radar display of shale lithofacies of a DH-1 sample in a certain area according to an embodiment of the present invention. DETAILED DESCRIPTION

[0038] The present invention will be further described below. The following examples are only used to more clearly illustrate the technical solution of the present invention and are not intended to limit the scope of protection of the present invention.

[0039] The present invention provides a method for dividing and characterizing shale facies into five end members and three components, see Figure 1 , including the following steps:

[0040] S110, performing X-ray diffraction analysis on the shale sample to determine the shale mineral composition and content;

[0041] S120, measuring the vitrinite reflectance (Ro) of the shale sample to determine the shale maturity;

[0042] S130, performing a total organic carbon (TOC) analysis on the shale sample to determine the percentage of total organic carbon content in the shale;

[0043] S140, taking the content of quartz and feldspar, clay minerals, and carbonate rock as 100, calculate the percentage content of the three components;

[0044] S150, draw a five-end member three-group classification diagram based on shale maturity, total organic carbon content percentage, quartz and feldspar content percentage, clay mineral content percentage, and carbonate rock content percentage, and determine the shale lithofacies type based on the position of the sample point on the diagram;

[0045] S160, shale maturity, total organic carbon content percentage, quartz and feldspar content percentage, clay mineral content percentage and carbonate rock content percentage are used to characterize the lithofacies characteristics in the form of radar charts.

[0046] As a preferred embodiment, X-ray diffraction analysis is performed on shale samples to determine the mineral components and contents of the shale, including the weight percentages of major components such as quartz, feldspar, carbonate rock, pyrite, and clay minerals.

[0047] As a preferred embodiment, vitrinite reflectance (Ro) is measured on shale samples using a microphotometer. Analysis results include maximum vitrinite reflectance, minimum vitrinite reflectance, and average vitrinite reflectance according to the industry standard SY / T 5124-2012, Determination of Vitrinite Reflectance in Sedimentary Rocks. In oil and gas exploration, vitrinite reflectance is the most accurate indicator of shale maturity. In this method, average vitrinite reflectance is used to characterize shale maturity. Maturity can be differentiated based on the average vitrinite reflectance, with 1% and 2% as the boundaries.

[0048] As a preferred embodiment, calculating the percentage content of the three components means adding quartz, feldspar, carbonate rock and clay minerals as the total weight, the ratio of quartz + feldspar to the total weight is the percentage content of quartz + feldspar, the ratio of carbonate rock to the total weight is the percentage content of carbonate rock, and the percentage of clay mineral to the total weight is the percentage content of clay mineral.

[0049] As a preferred embodiment, drawing a five-end-member three-group classification diagram means using the percentage of quartz + feldspar content, the percentage of carbonate rock content, and the percentage of clay mineral content as the three segments of the central triangle diagram, and using shale maturity and total organic carbon content percentage as the two wings extending outward from the central triangle diagram to draw a five-end-member three-group classification diagram.

[0050] Among them, the three sides of the central triangle are divided into three sections according to the percentages of 25, 50 and 75. The two wings of the central triangle are divided into high maturity zone, medium maturity zone and low maturity zone according to the average vitrinite reflectance greater than 2%, between 1% and 2%, and less than 1%. They are divided into organic matter-rich zone, medium organic matter zone and low organic matter zone according to the total organic carbon content greater than 2%, between 1% and 2%, and less than 1%.

[0051] As a preferred embodiment, characterizing the lithofacies characteristics in the form of a radar chart means using the percentage of quartz + feldspar content, the percentage of carbonate rock content, the percentage of clay mineral content, the shale maturity and the percentage of total organic carbon content as the five vertices of the radar chart, and using the center of the pentagon as the zero starting point, connecting the five vertices with lines, and marking the percentage content values ​​on the connecting lines.

[0052] The implementation process of a specific embodiment of the five-end-member three-component division and characterization method of shale lithofacies according to the present invention is as follows:

[0053] In step S110, a representative Longmaxi Formation shale sample from a region of the Sichuan Basin is selected, the shale is finely crushed, and then ground, precipitated, and smeared using an agate grinder to prepare an X-ray diffraction analysis sample. The shale mineral component content is analyzed according to the standard SY / T 5163-2010 X-ray Diffraction Analysis Method for Clay Minerals and Common Non-Clay Minerals in Sedimentary Rocks. The analysis results include the weight percentages of major components such as quartz, feldspar, carbonate rock, pyrite, and clay minerals.

[0054] Step S120: Collect a representative sample of 1 cm by 1 cm in size, polish the surface using a precision polishing instrument, adhere the back of the sample to a glass slide with paraffin wax, use a tablet press to press the sample into an observation sample, and place it in a microphotometer for observation. The observation method is based on the industry standard SY / T 5124-2012 for the determination of vitrinite reflectance in sedimentary rocks. The analysis results include the maximum vitrinite reflectance, the minimum vitrinite reflectance, and the average value. The number of sampling points is generally no less than 50, as shown in Table 1.

[0055] Table 1 Vitrinite reflectance determination of Longmaxi Formation shale in a certain area of ​​Sichuan Basin

[0056]

[0057] In step S130, a representative shale sample is collected, finely crushed, and then ground using an agate grinder. After screening, 5-10 g is taken for organic carbon content testing. The testing method is based on the national standard GB / T 19145-2003 for the determination of total organic carbon in sedimentary rocks, as shown in Table 2.

[0058] Table 2 Total organic carbon content of Longmaxi Formation shale in a certain area of ​​Sichuan Basin

[0059] Serial number Sample number Lithologic description Total organic carbon TOC (%) 1 DH-1 shale 0.57 2 DH-2 shale 2.05 3 DH-3 shale 0.85 4 DH-4 shale 0.38 5 DH-5 shale 0.79 6 DH-6 shale 0.78 7 DH-7 shale 1.77 8 DH-8 shale 1.49 9 DH-9 shale 1.80 10 DH-10 shale 2.25

[0060] In step S140, the quartz, feldspar, carbonate rock and clay mineral are added together as the total weight, the ratio of quartz + feldspar to the total weight is the percentage of quartz + feldspar, the ratio of carbonate rock to the total weight is the percentage of carbonate rock, and the percentage of clay mineral to the total weight is the percentage of clay mineral, as shown in Table 3.

[0061] Table 3 X-ray diffraction whole-rock analysis and three-end-member content percentages of Longmaxi Formation shale in a certain area of ​​the Sichuan Basin

[0062]

[0063]

[0064] In the table, the chemical formula of siderite is FeCO3, which belongs to carbonate rock.

[0065] Step S150: The percentage of quartz + feldspar content, the percentage of carbonate content and the percentage of clay mineral content are respectively used as the three segments of the central triangle graph. Figure 3 The edge values ​​25, 50, and 75 represent percentages. With shale maturity and total organic carbon content percentage as the two wings, a five-end member three-group classification diagram is drawn, as shown in Figure 2 According to the location of the sample points in the figure, it can be judged that the shale samples in this area are mainly highly mature and low-organic siliceous shale.

[0066] Step S160: The percentage of quartz + feldspar content, carbonate content, clay mineral content, shale maturity, and total organic carbon content are used as the five vertices of the radar chart. With the center of the pentagon as the zero starting point, lines are connected to the five vertices, and the percentage content values ​​are marked on the lines. Taking sample DH-1 as an example, the measured data of each sample in Table 1, Table 2, and Table 3 are projected on the radar chart, and the data points are connected to obtain the radar chart, as shown in FIG. Figure 3 Other samples can be projected using the same method to obtain corresponding radar charts.

[0067] The present invention has been described above in conjunction with specific features and embodiments thereof. It is obvious that various modifications and combinations may be made thereto without departing from the spirit and scope of the present invention. Accordingly, this specification and the drawings are merely illustrative of the present invention as defined by the appended claims and are deemed to have covered any and all modifications, variations, combinations or equivalents within the scope of the present invention. Obviously, those skilled in the art may make various changes and modifications to the present invention, and these modifications and variations that do not depart from the spirit and scope of the present invention also fall within the scope of the claims of the present invention and their equivalents.

Claims

1. A method for the five-end-member three-component division and characterization of shale lithofacies, characterized in that: include: Conduct X-ray diffraction analysis on shale samples to determine the mineral composition and content of shale; Vitrinite reflectance is measured on shale samples, and shale maturity is determined based on the vitrinite reflectance; Perform total organic carbon analysis on shale samples to determine the percentage of total organic carbon content in the shale; Calculate the percentage of quartz and feldspar, clay minerals and carbonate rock based on the mineral composition and content of shale; According to the position of shale maturity, total organic carbon content percentage, quartz and feldspar content percentage, clay mineral content percentage and carbonate content percentage of the shale sample in the drawn five-end member three-group classification diagram, the shale lithofacies type is determined, and the lithofacies characteristics are characterized in the form of radar diagram; The five-end member three-group classification diagram is drawn as follows: The percentage of quartz + feldspar content, the percentage of carbonate content and the percentage of clay mineral content were used as the three segments of the central triangle diagram, and the shale maturity and the percentage of total organic carbon content were used as the two wings extending outward from the central triangle diagram to draw the five-end-member three-group classification diagram; The characterization of lithofacies characteristics in the form of radar charts includes: The percentage of quartz + feldspar content, the percentage of carbonate content, the percentage of clay mineral content, the maturity of shale and the percentage of total organic carbon content are taken as the five vertices of the radar chart, and the center of the pentagon is taken as the zero starting point to connect the five vertices; The lines connecting the center with the percentage of quartz + feldspar content, the percentage of carbonate content, and the percentage of clay mineral content are marked with 25, 50, and 75, respectively; the lines connecting the center with the percentage of shale maturity and total organic carbon content are marked with 1, 2, and 3, respectively; The calculated shale maturity, total organic carbon content percentage, quartz and feldspar content percentage, clay mineral content percentage, and carbonate rock content percentage of the shale sample are projected onto corresponding connecting lines, and the data points are connected to obtain a radar map of the petrographic characteristics of the shale sample.

2. The five-end-member three-component division and characterization method of shale lithofacies according to claim 1 is characterized in that: The X-ray diffraction analysis of the shale sample is performed to determine the shale mineral components and content, which include at least one of the following shale mineral components: quartz, feldspar, carbonate rock, pyrite, and clay minerals.

3. The five-end-member three-component division and characterization method of shale lithofacies according to claim 1 is characterized in that: The method of measuring the vitrinite reflectance of the shale sample and determining the shale maturity based on the vitrinite reflectance includes: Shale samples of 1*1cm size were collected and polished using a precision polishing instrument. The back of the sample was glued to a glass slide with paraffin wax and pressed using a tablet press to prepare an observation sample. The sample was then placed in a microphotometer to measure the vitrinite reflectance. Multiple sampling points were selected for measurement to obtain the maximum vitrinite reflectance, minimum vitrinite reflectance and average vitrinite reflectance of the shale samples. The average vitrinite reflectance is taken as the shale maturity.

4. The method for five-end-member three-component division and characterization of shale lithofacies according to claim 3, characterized in that: The number of the sampling points is no less than 50.

5. The five-end-member three-component division and characterization method of shale lithofacies according to claim 1 is characterized in that: The calculation of the percentage of the three components of quartz and feldspar, clay minerals, and carbonate rocks includes: According to the shale mineral composition and content obtained by X-ray diffraction experiment, the total weight of quartz, feldspar, carbonate rock and clay minerals is added together. The quartz + feldspar content percentage is obtained by comparing the weight of quartz + feldspar with the total weight, the carbonate content percentage is obtained by comparing the weight of carbonate rock with the total weight, and the clay mineral content percentage is obtained by comparing the weight of clay mineral with the total weight.

6. The method for five-end-member three-component division and characterization of shale lithofacies according to claim 1, characterized in that: Also includes, Divide the three sides of the central triangle into three segments according to the percentages of 25, 50, and 75. The two wings of the central triangle are divided into high maturity, medium maturity and low maturity zones according to shale maturity greater than 2%, between 1% and 2%, and less than 1%; and are divided into organic-rich, medium organic matter and low organic matter zones according to total organic carbon content greater than 2%, between 1% and 2%, and less than 1%.

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