Method for determining favorable lithofacies combination of continental facies mixed shale

Abstract

The invention provides a method for determining favorable lithofacies combination of continental facies mixed-volume shale. The method comprises the following steps: S1, subdividing small layers according to logging curve characteristics and stratum thickness; s2, dividing lithology types by using X-diffraction total rock test analysis data; s3, utilizing a special sedimentary structure to divide lithofacies combination types; s4, analyzing three-dimensional reservoir features and two-dimensional reservoir features of different lithofacies combinations; and S5, combining the static geological parameters with the dynamic development parameters, and determining favorable lithofacies combination. According to the method, a special sedimentary structure is used as a main division basis, and an X-diffraction total rock experiment is used for testing and analyzing total rock mineral components to divide lithofacies combination; three-dimensional and two-dimensional means are combined to carry out reservoir multi-dimensional full-scale evaluation, and favorable lithofacies combinations of the reservoir are divided; and the favorable lithofacies combination is finally defined by combining the static geological parameters and the dynamic development parameters, so that the accuracy, effectiveness and comprehensiveness of determining the favorable lithofacies combination of the continental facies mixed shale are improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of unconventional shale oil and gas exploration and development, and particularly relates to a method for determining a favorable lithofacies combination of continental mixed accumulation shale. BACKGROUND

[0002] The lithofacies of continental mixed accumulation shale is complex, and the vertical heterogeneity is strong. It is difficult to carry out evaluation simply from lithofacies, and the practicability is not strong. Taking the lithofacies combination as an evaluation unit is beneficial to overall systematic evaluation. While relying on shale parameter analysis, it is necessary to strengthen the evaluation of three-dimensional and two-dimensional characteristics of the reservoir, and finally determine the favorable lithofacies combination in combination with the actual development and production effect, which has effective guiding significance for target window optimization, fracturing scheme design, optimal development interval optimization and shale oil enrichment prediction.

[0003] The paper "Shale lithofacies combination division standard and its influence on the formation of fracture network: Taking the shale of the Silurian Longmaxi Formation in the Sichuan Basin as an example" published by Shen K et al. in Petroleum and Natural Gas Geology, Vol. 42, No. 1, 2021, records that shale gas reservoirs need to achieve economic productivity through hydraulic fracturing, but different shale lithofacies combination types have different fracturing modification effects. Considering the influence of mineral composition, reservoir properties, bedding joints and bedding on the formation of fracture network, and combining outcrop, core development characteristics and fracturing modification characteristics, the paper takes the shale of the Silurian Longmaxi Formation in the Sichuan Basin as the research object, and establishes division standards for four types of shale lithofacies combination, i.e. type I (FA1), type II (FA2), type III (FA3) and type IV (FA4). The research shows that FA1 is obviously affected by diagenetic modification, and the cemented and filled fractures are extremely developed, which can be preferentially activated to form a fracture network before fracturing, but fracturing operation anomalies are prone to occur, which limits the expansion of the fractures; FA2 is obviously controlled by sedimentation, and is prone to form a high-density interaction of dominant reservoir and dominant fracturing layer; FA3 and FA4 are greatly affected by terrigenous material, and have poor modification ability, and are not obvious in promoting the formation of fracture network. Overall, FA1 and FA2 lithofacies combination are the sweet spots for fracturing operation. The research results have theoretical support and field guidance significance for reservoir fracturing modification well selection and layer selection and fracturing scheme design.

[0004] In the paper "Rock facies combination characteristics and their influence on shale gas content" published in Fault-Block Oil and Gas Field, Vol. 30, No. 1, 2023, Liu Miaomiao et al. recorded that the continental shale has strong heterogeneity. In order to find out the influence of different rock facies combinations of Lianggaoshan Formation in Fuling area on shale gas content, the paper carried out rock facies evaluation based on core photos, ordinary thin sections, X-ray diffraction, organic matter abundance and other analysis and test data. Through scanning electron microscopy, isothermal adsorption, field gas content test and other experiments, the pore structure and gas content of six kinds of rock facies combinations were analyzed. The research shows that Lianggaoshan Formation develops six kinds of rock facies combination types, including high-carbon banded shale interbedded with siltstone, medium-carbon banded-laminated shale interbedded with siltstone, medium-carbon laminated shale interbedded with siltstone, carbon-containing massive mudstone interbedded with siltstone, medium-low carbon laminated mudstone and siltstone interbedded with siltstone, and low-carbon laminated siltstone interbedded with mudstone. The porosity and pore size distribution characteristics of different rock facies are mainly affected by bedding joints and organic matter abundance, while the specific surface area is jointly affected by clay mineral composition, organic matter abundance and microfractures. It is clear that high-carbon banded shale interbedded with siltstone is the dominant rock facies combination in the study area and is widely distributed in the study area. The research results can provide technical support for shale oil and gas enrichment prediction and indicate the direction for the next step exploration of shale oil and gas in Lianggaoshan Formation in Fuling area.

[0005] Liu Zhongbao et al. published in the Natural Gas Industry 2019 Vol. 39 No. 12 on the "Continental shale facies types, combination characteristics and their significance for oil and gas exploration" article recorded: the fine identification and division of shale facies types is an important basis for shale gas exploration and development potential evaluation, but the identification and classification standards and classification scheme of shale facies have not yet reached a consensus. Therefore, taking the middle and lower Jurassic continental shale series in Sichuan Basin as the research object, using core observation, whole rock mineral X-ray diffraction analysis, thin section identification, total organic carbon content (TOC) and helium porosity test and other means, on the basis of shale whole rock mineral composition and characteristic analysis, the facies division method is established, the shale facies type identification and division are carried out, the facies combination characteristics under different scales are studied, and its significance for shale gas exploration is discussed. The research results show that: ①Using the newly established whole rock mineral zoning-TOC classification-mineral structure and sedimentary structure correction and improvement of 3-step facies division method, 6 types of 20 kinds of shale facies types are identified in the continental shale series in this area, among which the medium-high carbon clay shale facies, laminated-thin layered clay shale facies and low-medium carbon silty shale facies are the main ones, followed by low-medium carbon clay shell gray shale facies, low-carbon silty clay shale facies; ②The average TOC and average porosity of clay shale facies and shell gray clay shale facies are higher than those of silty shale facies and silty clay shale facies, and shale mineral composition and facies type have certain influence on shale gas source and reservoir performance; ③The continental shale series in this area can identify 3 types of combination of marl deposition, mud sand deposition and marl sand mixed deposition, which reflect the sedimentary characteristics of far source area, near source area and transition area in lacustrine environment, and the description of different facies combinations helps to identify the differences of shale sedimentary environment; ④The identification and statistics of the number and frequency of gray shell laminated and thin layers in continental organic-rich shale with high clay mineral content can provide basis for reservoir transformability evaluation of gas-rich layer and selection of best exploration and development layer.

[0006] The article "Types and Characteristics of Shale Facies Assemblages in Continental Graben Basins: A Case Study of Shale in the Upper Section of Sha-4 in the Dongying Depression of Jiyang Depression" published by Liu Huimin et al. in the first issue of Volume 48 of Earth Science in 2023 states that there are currently no research results and technical methods for classifying shale facies assemblages in continental graben basins, and the basic characteristics of different shale facies assemblages need to be further clarified. Based on detailed core observation and description of the shale oil well core sections, thin section observation and X-ray whole-rock mineral diffraction analysis were used to clarify the basic lithology and lithofacies types of the shale in the core sections. Through analysis of major mineral components and trace elements, paleoenvironmental information of the Paleogene shale sediments in the Jiyang Depression was extracted. Based on the basic characteristics of the four paleoenvironments (paleoclimate, paleoprovince, paleosalinity, and paleowater depth), lithofacies assemblages of the upper sub-member of the Sha-4 formation in the Dongying Depression were classified according to principles such as similarity of sedimentary environments and homogeneity of internal structure. A shale lithofacies assemblages classification scheme based on sedimentary environment was established, and reservoir and organic geochemical analyses were combined to clarify the reservoir and oil-bearing characteristics of the main lithofacies assemblages. Results Table Ming: (1) The upper shale of Sha-4 in Dongying Depression is a typical carbonate-rich shale (carbonate shale) and mixed sedimentary shale with significant laminar features, diverse pore types, well-developed bedding and structural fractures, high organic matter abundance, medium to low degree of evolution, deep burial and high pressure coefficient. (2) Based on the location of sedimentary structures and paleoenvironment, the shale of the upper sub-section of Sha-4 in Dongying Depression can be divided into 8 lithofacies assemblages. In the center of the basin, the matrix-type carbonate shale lithofacies assemblages are the main type, supplemented by the massive dolomite interbedded shale lithofacies assemblages. In the steep slope zone in the north, the sandstone interbedded shale lithofacies assemblages are the main type. In the gentle slope zone in the south, the massive dolomite interbedded type and the laminar calcareous mudstone and dolomite interbedded shale lithofacies assemblages are the main types. (3) Generally speaking, as the main body of fine-grained sediments, the matrix-type shale strata of the upper sub-section of Sha-4 in the center of the Dongying Depression develop from bottom to top in the following order: laminated argillaceous limestone interbedded with massive dolomite facies, laminated argillaceous limestone and dolomite interbedded facies, laminated argillaceous limestone and calcareous mudstone interbedded with calcareous mudstone facies, laminated argillaceous limestone and calcareous mudstone interbedded with calcareous mudstone facies, laminated argillaceous limestone and calcareous mudstone interbedded with calcareous mudstone facies, and laminated argillaceous limestone interbedded with calcareous mudstone facies. This reveals the change of the sedimentary paleoenvironment from arid, saline, semi-deep water, and low source to semi-humid, semi-saline, deep water, and higher source. (4) The most developed assemblages are layered argillaceous limestone interbedded with calcareous mudstone, as well as interbedded assemblages of layered argillaceous limestone and calcareous mudstone. These assemblages exhibit diverse reservoir types, a high proportion of large-diameter pores, and good connectivity. The interbedded layered argillaceous limestone and calcareous mudstone have relatively high oil saturation and are a favorable lithofacies assemblages for achieving breakthroughs in shale oil in the Jiyang Depression. The layered argillaceous limestone interbedded with massive dolomite assemblages possess good oil-bearing capacity and brittleness. Further analysis of the basic geological characteristics and oil-bearing properties of different lithofacies assemblages, and determination of the development and distribution characteristics of major shale lithofacies assemblages, has practical guiding significance for shale oil exploration in continental rift basins.

[0007] The article "Geological Characteristics and Exploration Practice of Continental 'Fault-Block' Shale Oil in the Subei Basin" published by Fang Zhixiong et al. in the journal "Petroleum and Natural Gas Geology" (Vol. 44, No. 6, 2023) records that: In the Mesozoic-Cenozoic era, the continental fault-depression basin group in eastern China has developed multiple sets of thick lacustrine organic-rich shale, which contain abundant shale oil resources. However, the organic-rich shale is generally cut by faults, forming several independent fault blocks. This is quite different from the continuous and stable distribution of shale strata in North America. Whether a stable commercial oil flow can be obtained is the primary problem facing exploration. Based on the study and comprehensive evaluation of the Paleogene Fu (Funing Formation) No. 2 shale lithology, source rock quality, and reservoir quality in the Gaoyou Depression of the Subei Basin, this study concludes that the Fu No. 2 shale contains three sets of thick favorable layers, possessing the conditions for multi-layered, three-dimensional exploration and development. Based on the current geological status of the favorable layers, faults, and fault blocks in the Fu No. 2 shale, a "fault-block type" shale oil exploration strategy is proposed, involving horizontal wells traversing long distances within or across fault blocks, and within or across multiple favorable layers. According to the configuration relationship between fault displacement and favorable layer thickness, "fault-block type" shale oil is classified into three exploration target types: "continuous and stable," "micro-fault-cut," and "multi-sweet spot across fault blocks." Exploration practice has confirmed that all three exploration target types can yield stable commercial oil flows. The research results enrich the scope and types of continental shale oil exploration in China and have important reference value for shale oil exploration in continental fault basins.

[0008] The article "Breakthrough and Significance in Paleogene Continental Shale Oil Exploration in Gaoyou Depression, Subei Basin" published by Zhu Xiangyu et al. in the 2023 issue of *Acta Petrolei Sinica* (Vol. 44, No. 8) records that in 2022, two key shale oil exploration wells—HY1HF and H2CHF—were drilled in the second member (Fu'er Member) of the Paleogene Funing Formation in the Gaoyou Depression of the Subei Basin. After fracturing, industrial oil flows of 29.7 t / d and 50.5 t / d were obtained respectively during the production stage, achieving a major breakthrough in shale oil exploration in the Fu'er Member of the Gaoyou Depression. Based on core and thin-section observations from wells such as HY1, as well as experimental data including X-ray diffraction of whole-rock minerals, nitrogen adsorption, nuclear magnetic resonance, and frozen core organic geochemical analysis, combined with production dynamic data from wells such as HY1HF and H2CHF, the geological characteristics of the Fu'er Member shale in the Gaoyou Depression were systematically analyzed, further revealing the enrichment patterns and controlling factors of shale oil in the Fu'er Member of the Subei Basin. The Fu'er Member of the Gaoyou Depression is characterized by semi-deep to deep lacustrine shale formations, featuring significant vertical thickness and wide planar distribution, forming the basis for its shale oil enrichment. The lithofacies of the shale control the planar and vertical distribution of "source sweet spots" and "reservoir sweet spots." Lithofacies with relatively high clay mineral content exhibit good hydrocarbon generation potential, while those with higher felsic and carbonate mineral content demonstrate better physical properties and pore-throat structure. Based on lithological assemblage characteristics, the Fu'er Member shale reservoirs can be classified into three types: "self-generated and self-reservoir," "mud-generated ash / cloud-reservoir," and "mud-generated sand-textured reservoir." "Mud-generated ash / cloud-reservoir" type shale reservoirs develop high-quality pore-fracture systems in their source-reservoir assemblage, exhibiting good oil-bearing capacity and high fluidity. Existing production dynamics data indicate that this type of shale reservoir has good shale oil production capacity. Favorable preservation conditions and shale maturation and hydrocarbon generation pressurization are key to high and stable shale oil production. The breakthrough in shale oil exploration in the Fu-2 Member of the Gaoyou Depression demonstrates the promising exploration prospects of Paleogene shale oil in the Subei Basin, making the Gaoyou Depression a key area for increasing reserves and production. This research provides important reference and guidance for the exploration and development of shale oil in continental rift basins in eastern China.

[0009] Chinese patent CN115542420A discloses a method for determining the lithofacies classification scheme of continental mixed sedimentary mudstone and shale, comprising: 1. Core observation: Observing the cores according to the sedimentary principles of the strata, following a depth-to-shallow sequence; 2. Stratigraphic division: Using the results of core observations and combining them with well logging curve characteristics, stratigraphic division is performed; 3. Sub-layer evaluation: Sampling is conducted on each sub-layer, and pyrolysis and irregular sample property analysis are performed. Sub-layer evaluation is then performed based on the analysis results; 4. Composition determination: X-ray diffraction whole-rock analysis is performed on the cores corresponding to each sub-layer to analyze the rock mineral composition; 5. Scheme determination: Based on the above analysis results, the target classification scheme is determined. This invention improves the accuracy and effectiveness of lithofacies classification schemes, accurately and efficiently classifying lithofacies types, laying the foundation for further evaluation of favorable lithofacies, and providing a basis for selecting "sweet spot" layers and target windows.

[0010] Chinese patent CN117169083A discloses a method for characterizing the pore size of shale reservoirs. The method includes: measuring micropores with a main pore size of 2–100 nm using nitrogen adsorption-desorption; measuring mesopores with a main pore size of 100–1000 nm using scanning electron microscopy; calibrating the P1 and P2 peaks of the nuclear magnetic resonance T2 spectrum of shale using the pore sizes of micropores and mesopores respectively, and obtaining the correspondence between the T2 relaxation time and pore size of shale; and using function fitting to calibrate the T-2 relaxation time of micropores and mesopores with the corresponding pore size to obtain the full-scale pore size distribution curve of shale reservoirs.

[0011] In the "Classification and Nomenclature Scheme for Sedimentary Rocks" (GB / T17412.2-1998), rocks containing more than 50% endogenous minerals or terrigenous clastic material, or those reflecting the basic characteristics and properties of the rock, serve as the basis for determining its basic name. Minor minerals containing less than 5% are not included in the naming. When a rock has special geological significance, "slightly contains XX minerals" is used as an additional modifier; when the minor mineral content is 5% or less than 25%, "contains XX minerals" is used as an additional modifier; when the minor mineral content is 25% to 50%, "XX minerals" is used as an additional modifier.

[0012] Chinese patent CN116973987A discloses a comprehensive characterization method for predicting the distribution of lithofacies assemblages in four paleoenvironments of terrestrial lacustrine basins. The method includes: Step 1, collecting core samples from sedimentary basins and relevant laboratory analytical data; Step 2, classifying and summarizing lithofacies assemblages under different sedimentary backgrounds within the basin; Step 3, conducting quantitative reconstructions of paleoclimate, paleowater depth, paleosalinity, and paleosource input in the paleolake basin; Step 4, establishing discriminant relationships between the quantitatively reconstructed paleoclimate, paleowater depth, paleosalinity, and paleosource input and various lithofacies assemblages; and Step 5, predicting the vertical and horizontal distribution patterns of lithofacies assemblages. This comprehensive characterization method for predicting the distribution of lithofacies assemblages in four paleoenvironments of terrestrial lacustrine basins realizes a predictive method for the vertical and horizontal distribution of lithofacies assemblages using paleoenvironments, providing new research ideas and technical means for the study of the distribution of high-quality lithofacies in paleolakes.

[0013] Chinese patent CN115047538A discloses a classification method for lithofacies assemblages of continental shale, comprising: preliminarily identifying the basic lithofacies types of shale strata through shale core logging analysis and core observation description; selecting samples and completing tests such as mineral composition and major and trace element analysis; extracting paleoenvironmental information and analyzing the shale depositional environment based on mineral content and elements; classifying lithofacies assemblages of shale with similar depositional environments and performing primary lithofacies assemblages; determining the brittle mineral content characteristics of different lithofacies and combining them with well logging response characteristics to perform secondary lithofacies assemblages; and classifying shale lithofacies assemblages by combining primary and secondary classifications based on the clear lithofacies types and characteristics. This classification method for lithofacies assemblages of continental shale satisfies both shale oil geological evaluation and drilling engineering practice requirements, is highly operable, and provides a solution for determining the target stratigraphic group for shale oil exploration and development.

[0014] Chinese patent CN104914482A discloses a method for quantitatively identifying complex sandstone and conglomerate lithofacies assemblages. This method includes the following steps: classifying lithofacies assemblages and quantitatively describing them; using core data to calibrate imaging logging response characteristics; using core and imaging logging data to constrain conventional logging response characteristics; selecting sensitive conventional logging curves; constructing sandstone and conglomerate lithofacies identification curves; and establishing a lithofacies assemblage type identification template to identify the lithofacies assemblages. This method overcomes the problem of unclear logging response characteristics in sandstone and conglomerate by selecting sensitive conventional logging curves to construct lithofacies assemblages.

[0015] Although the above classification scheme solves some problems, its application to the determination of favorable lithofacies assemblages in terrestrial mixed sedimentary shale still has certain limitations as described in the background technology. Summary of the Invention

[0016] This application provides a method for determining favorable lithofacies assemblages of terrestrial mixed sedimentary shale, which improves the accuracy, effectiveness, and comprehensiveness of determining favorable lithofacies assemblages of terrestrial mixed sedimentary shale.

[0017] This application provides a method for determining favorable lithofacies assemblages in terrestrial mixed sedimentary shale, including:

[0018] S1, subdivided into smaller layers based on well logging curve characteristics and formation thickness;

[0019] S2, using X-ray diffraction whole-rock test data to classify lithology;

[0020] S3, using special sedimentary structures to classify lithofacies assemblage types;

[0021] S4, analyze the three-dimensional and two-dimensional reservoir characteristics of different lithofacies combinations;

[0022] S5, by combining static geological parameters and dynamic development parameters, identifies favorable lithofacies combinations.

[0023] In step S1, the rock stratigraphic units include groups, sections, and layers. The Subei Basin has 6 groups developed from bottom to top: Taizhou Group K2t, Funing Group E1f, Dainan Group E2d, Sanduo Group E2s, Yancheng Group N1y-N2y, and Dongtai Group Qd. The E1f strata are divided into 4 sections from bottom to top: Fuyi Section 1 E1f1, Fuyi Section 2 E1f2, Fuyi Section 3 E1f3, and Fuyi Section 4 E1f4.

[0024] In step S1, the Fu'er section E1f2 is divided into five sub-segments from bottom to top: I, II, III, IV, and V. The resistivity curve of sub-segment V ranges from 1.9 to 14 Ω, with a flat upper curve and five high-resistivity peaks in the middle and lower parts. The resistivity of sub-segment IV ranges from 1.2 to 13 Ω, with four sets of high-resistivity peaks within the curve. The resistivity of sub-segment III ranges from 0.5 to 3 Ω, with a sawtooth curve and 7-8 sawtooth cycles. The resistivity of sub-segment II ranges from 1.8 to 4.3 Ω, with a low-amplitude arc curve. The resistivity of sub-segment I ranges from 0.6 to 1.5 Ω. Two or more wells on the sub-segment division plane can be compared.

[0025] Among them, subsegments IV and V are divided into 18 sub-layers from bottom to top, based on the characteristics of resistivity RT and gamma GR curves, respectively: IV-8 to IV-1 and V-10 to V-1.

[0026] Specifically, for sublayers V-4 to V-8 and IV-2 to IV-7, based on the resistivity RT and gamma GR curve characteristics, they are divided into 15 sublayers from bottom to top. V-4 to V-8 have 4 sets of GR and RT layers with electrical characteristics of GR: 81-92 API, RT: 27-92 Ω, and a thickness of 2.5-5 μm, and 2 sets of GR and RT layers with electrical characteristics of GR: 107-115 API, RT: 6-7 Ω, and a thickness of 1.3-1.9 μm. IV-2 to IV-7 have 5 sets of GR and RT layers with electrical characteristics of GR: 77-93 API, RT: 8-99 Ω, and a thickness of 1.5-6 μm, and GR and RT layers with electrical characteristics of GR: 95-105 API, RT: 5-8 Ω, and a thickness of 3.5 μm.

[0027] In step S2, the lithological types are classified according to the mineral composition triangle plate based on the differences in the contents of feldspar, quartz, carbonate, and clay minerals. The lithological types include: dolomitic shale, clay-bearing felsic dolomitic shale, felsic dolomitic mixed sedimentary shale, felsic clay mixed sedimentary shale, clay-bearing dolomitic felsic shale, dolomitic clay felsic shale, and felsic shale.

[0028] In step S3, core observation and thin section identification are used to describe the special sedimentary structures developed in the mixed shale, including sandy laminae or bands, dolomitic laminae, calcite veins, and dolomite bands. The dolomitic laminae, calcite veins, and dolomite bands are collectively referred to as carbonate laminae or bands. They are divided into three lithofacies combinations: mixed shale, mixed shale with carbonate laminae or bands, and mixed shale with sandy laminae or bands. The thickness of the sublayers and the top and bottom depths of the sublayers in step S2 are combined to constrain the top and bottom ranges of different lithofacies combinations.

[0029] In step S4, the three-dimensional reservoir characteristic analysis includes: using a 10cm diameter core sample to test dual-energy CT to analyze the number and thickness of different properties of laminae, bands and fractures; using a 3mm diameter plunger sample to test μmCT to analyze micron-level pore radius, throat radius, pore-throat coordination number and shape factor; and using sheet-like samples with a diameter less than 25mm to test focused ion beam scanning electron microscopy (FIB-SEM) to analyze nano-level pore radius, throat radius, pore-throat coordination number and shape factor.

[0030] In step S4, the two-dimensional reservoir characteristic analysis includes:

[0031] MAPS scanning electron microscopy mapping and QEMSCAN mineral quantitative analysis were performed on samples with a field of view of 400-450μm*400-450μm to analyze porosity, inorganic pore ratio, and organic pore ratio. Low-temperature nitrogen adsorption, argon ion polishing scanning electron microscopy, high-pressure mercury intrusion porosimetry, and nuclear magnetic resonance were used to analyze the full-scale pore structure characteristics. Thin sections were used to identify and analyze laminar or banded types.

[0032] In step S5, static geological parameters of different lithofacies combinations, including total organic carbon (TOC) content, liquid nitrogen cryogenic pyrolysis (S1) content, oil saturation index (OSI), porosity (φ), and reservoir characteristics, are compared. Dynamic parameters are developed by combining the water cut and oil production contribution rate corresponding to different lithofacies combinations, and favorable lithofacies combinations are identified in both directions.

[0033] The method for determining favorable lithofacies assemblages of terrestrial mixed sedimentary shale in this application has the following beneficial effects:

[0034] This application method primarily uses special sedimentary structures as the basis for classification, supplemented by X-ray diffraction whole-rock experiments to analyze whole-rock mineral composition and classify lithofacies assemblages; it combines three-dimensional and two-dimensional methods to conduct multi-dimensional, full-scale reservoir evaluation and classify favorable lithofacies assemblages; and it combines static geological parameters and dynamic development parameters to ultimately identify favorable lithofacies assemblages, thus improving the accuracy, effectiveness, and comprehensiveness of determining favorable lithofacies assemblages in continental mixed sedimentary shale. Attached Figure Description

[0035] Figure 1This is a schematic flowchart illustrating the method for determining favorable lithofacies assemblages of terrestrial mixed sedimentary shale according to an embodiment of this application;

[0036] Figure 2 This is a comparison diagram of the interconnected well layers of wells H2C, HY1, and H101 in this application;

[0037] Figure 3 This is a triangular diagram of the mineral composition of well HY1 in this application;

[0038] Figure 4 Photographs of different lithofacies assemblages from well HY1 in this application;

[0039] Figure 5 This is a columnar section of the lithofacies assemblage of sub-members IV and V of well HY1 in this application;

[0040] Figure 6 This is a comparison diagram of the three-dimensional reservoir characteristics of different lithofacies combinations in well HY1 of this application;

[0041] Figure 7 This is a comparison diagram of two-dimensional reservoir characteristics of different lithofacies combinations in well HY1 of this application;

[0042] Figure 8 This is a comparison diagram of the full-scale pore-throat structure characteristics of two-dimensional reservoirs with different lithofacies combinations in well HY1 of this application. Detailed Implementation

[0043] The present application will be further described below with reference to the accompanying drawings and embodiments.

[0044] The following description provides several embodiments of the present invention. Different embodiments can be substituted or combined. Therefore, this application can also be considered to include all possible combinations of the same and / or different embodiments described. Thus, if one embodiment includes features A, B, and C, and another embodiment includes features B and D, then this application should also be considered to include embodiments containing one or more other possible combinations of features A, B, C, and D, even if such embodiments are not explicitly described in the following text.

[0045] Example 1

[0046] like Figure 1 As shown, the method for determining favorable lithofacies assemblages in terrestrial mixed sedimentary shale of this application includes: S1, subdividing into smaller layers based on well logging curve characteristics and formation thickness; S2, classifying lithological types using X-ray diffraction whole-rock experimental test data; S3, classifying lithofacies assemblages using special sedimentary structures; S4, analyzing the three-dimensional and two-dimensional reservoir characteristics of different lithofacies assemblages; and S5, identifying favorable lithofacies assemblages by combining static geological parameters and dynamic development parameters.

[0047] The method employed in this application improves the accuracy, effectiveness, and comprehensiveness of determining favorable lithofacies assemblages in continental mixed sedimentary shale. It combines special structural lithofacies assemblages classification schemes with two-dimensional and three-dimensional reservoir evaluation methods, as well as dynamic and static comprehensive analysis, thereby improving the accuracy of identifying favorable lithofacies assemblages.

[0048] Example 2

[0049] This application provides a method for determining favorable lithofacies assemblages of terrestrial mixed sedimentary shale, taking well HY1 or H101 in the XX Depression of the XX Basin as an example, including:

[0050] Step 1: Subdivide the formation into smaller layers based on the characteristics of the well logging curves and the formation thickness.

[0051] The stratigraphic units of well HY1 or H101 include groups, sections, and layers. From bottom to top, there are six groups: Taizhou Group (K2t), Funing Group (E1f), Dainan Group (E2d), Sanduo Group (E2s), Yancheng Group (N1y-N2y), and Dongtai Group (Qd). The E1f strata are further divided into four sections from bottom to top: Fuyi Section 1 (E1f1), Fuyi Section 2 (E1f2), Fuyi Section 3 (E1f3), and Fuyi Section 4 (E1f4). The division of these groups and sections follows the State Administration of Science, Technology and Industry for National Exploration Agency Standard Q / SHJS 0117-2006, which is well-known to researchers in this basin.

[0052] The E1f strata are divided into four segments from bottom to top: Fuyi 1 (E1f1), Fuyi 2 (E1f2), Fuyi 3 (E1f3), and Fuyi 4 (E1f4). The boundary between E1f1 and K2t is the end of the highstand reverse cycle at the end of the Cretaceous and the beginning of the Paleocene lowstand positive cycle. The boundary between E1f2 and E1f1 is the bottom of the "mountain-shaped segment" of the first lacustrine flooding surface during the first Paleocene regional transgression. The boundary between E1f3 and E1f2 is the end of the maximum lacustrine flooding surface during the first Paleocene regional transgression and the beginning of the reverse cycle. The boundary between E1f4 and E1f3 is the bottom of the "spring segment" of the first lacustrine flooding surface during the second Paleocene regional transgression. The boundary between E2d and E1f4 is the regional unconformity surface formed by the Wubu event. The stratigraphic division follows the State Administration of Science, Technology and Industry for National Geophysics Agency standard Q / SHJS 0117-2006.

[0053] Based on the research needs of this area, the rock stratigraphic units are further divided into sub-units, small layers, and sub-sublayers, in addition to the division of groups, sections, and layers.

[0054] The second section of HY1 well (E1f2) is divided into five sub-segments from bottom to top: I, II, III, IV, and V. The resistivity curve of sub-segment V ranges from 1.9 to 14 Ω, with a flat upper curve and five high-resistivity peaks in the middle and lower parts, commonly known as the "mountain shape". The resistivity of sub-segment IV ranges from 1.2 to 13 Ω, with four sets of high-resistivity peaks within the curve, commonly known as the "four peaks". The resistivity of sub-segment III ranges from 0.5 to 3 Ω, with a sawtooth curve and 7-8 sawtooth cycles, commonly known as the "seven peaks". The resistivity of sub-segment II ranges from 1.8 to 4.3 Ω, with a low-amplitude arc-shaped curve, commonly known as the "turtle cover". The resistivity of sub-segment I ranges from 0.6 to 1.5 Ω, with a flat curve and little variation, commonly known as the "mud neck".

[0055] Based on the resistivity RT and gamma GR curve characteristics, subsections IV and V of well HY1 are divided into 18 sub-layers from bottom to top: IV-8 to IV-1 and V-10 to V-1, respectively. Among them, sub-layer IV-3 has a slightly lower overall GR value, with the upper part slightly higher than the lower part, corresponding to a higher RT at the bottom and a higher RT at the top, forming the second peak of the "four peaks"; sub-layer IV-4 has a generally higher GR value, gradually increasing from top to bottom, corresponding to a low RT segment, with the lowest RT at the bottom; sub-layer IV-5 has a generally lower GR value, with two low GR segments at the top and bottom, the top GR value being relatively lower, corresponding to two high RT peaks, and a low RT value region in the middle; sub-layer IV-6 has a generally higher GR value, relatively increasing from top to bottom, corresponding to an overall low RT segment; sub-layer IV-7 has a generally higher GR value, comparable to the bottom baseline of IV-6, with a slightly lower GR value from top to bottom, corresponding to... The resistivity (RT) gradually increases from top to bottom, with the highest RT at the bottom, corresponding to the fourth peak of the "four peaks". The GR value of sublayer V-5 is generally low, with the lowest GR value in the middle, which is also the lowest segment of sublayer V, corresponding to a higher RT, though lower than that of sublayer V-4. Sublayer V-6 has the highest GR baseline in sublayer V, exhibiting two low-to-high variation patterns from top to bottom. The resistivity on the RT curve has two slightly higher segments in the middle. Sublayer V-7 has a lower GR value, with an overall baseline slightly higher than V-5, and GR decreases slightly from top to bottom. The RT curve shows two high values ​​at the top and bottom, with even higher resistivity at the bottom. Sublayer V-8 has a higher GR value, with a baseline similar to sublayer V-6; the resistivity curve exhibits low-value characteristics. Figure 2 As shown, the sub-segments and sub-layers can be compared on the dividing plane.

[0056] Based on the resistivity (RT) and gamma ray (GR) curve characteristics, the sublayers V-4 to V-8 and IV-2 to IV-7 of well HY1 are further divided into 15 sublayers from bottom to top, for a total of 30 sublayers. V-4 to V-8 contain four sets of low GR, high RT layers with electrical characteristics of 81-92 API, 27-92 Ω, and a thickness of 2.5-5 m; and two sets of high GR, low RT layers with electrical characteristics of 107-115 API, 6-7 Ω, and a thickness of 1.3-1.9 m. IV-2 to IV-7 contain five sets of low GR, high RT layers with electrical characteristics of 77-93 API, 8-99 Ω, and a thickness of 1.5-6 m; and a high GR, low RT layer with electrical characteristics of 95-105 API, 5-8 Ω, and a thickness of 3.5 m.

[0057] Table 1. Stratigraphic stratification and lithofacies assemblage of the Fu'er Member in Well HY1

[0058]

[0059]

[0060] Step 2 involves classifying lithology using X-ray diffraction whole-rock analysis data. X-ray diffraction whole-rock analysis is a method well-known to professionals in this field, capable of testing the types and percentages of minerals in shale and mudstone, including quartz, potassium feldspar, plagioclase, calcite, dolomite, ferrodolithite, siderite, pyrite, halite, anhydrite, gypsum, gypsum, anhydrous mirabilite, barite, calcium mirabilite, zeolite, analcime, and clay minerals, as well as their content. Quartz, potassium feldspar, and plagioclase belong to feldspar quartz minerals, while calcite, dolomite, and ferrodolithite belong to carbonate minerals. The differences in the content of feldspar quartz minerals, carbonate minerals, and clay minerals are used to classify lithology on a triangular plot. For example... Figure 3 As shown, well HY1 exhibits seven lithological types: dolomitic shale, clay-bearing felsic dolomitic shale, felsic dolomitic mixed shale, felsic clay mixed shale, clay-bearing dolomitic felsic shale, dolomitic clay felsic shale, and felsic shale. Among these, mixed shale (felsic dolomitic mixed shale and felsic clay mixed shale) is dominant, accounting for 85%.

[0061] The lithological naming principles refer to the "Classification and Naming Scheme for Sedimentary Rocks" [Source: GB / T17412.2-1998].

[0062] Ⅰ 1 Grey dolomite shale (carbonate mineral content >50%, feldspar and quartz mineral content <25%, clay mineral content <25%)

[0063] Ⅰ 2 Clay-bearing felsic shale (carbonate mineral content >50%, feldspar and quartz mineral content <50%, clay mineral content <25%)

[0064] Ⅰ 3 : Felsic clayey shale (carbonate mineral content >50%, clay mineral content <50%, feldspar and quartz mineral content <25%)

[0065] II 1 Felsite shale (feldspar and quartz mineral content >50%, carbonate mineral content <25%, clay mineral content <25%)

[0066] II 2 : Contains gray-cloudy clayey felsic shale (feldspar and quartz mineral content >50%, clay mineral content <50%, carbonate mineral content <25%)

[0067] II 3 Clay-bearing dolomitic felsic shale (feldspar and quartz mineral content >50%, carbonate mineral content <50%, clay mineral content <25%)

[0068] III 1 Clay shale (clay mineral content >50%, carbonate mineral content <25%, feldspar and quartz mineral content <25%)

[0069] III 2 : Grey dolomitic felsic claystone (clay mineral content >50%, feldspar and quartz mineral content <50%, carbonate mineral content <25%)

[0070] III 3 : Feldspar-bearing dolomitic claystone (clay mineral content >50%, carbonate mineral content <50%, feldspar-quartz mineral content <25%)

[0071] IV 1 Felsic clayey shale (feldspar, quartz, carbonate, and clay mineral content are all less than 50%, with feldspar > clay > carbonate or clay > feldspar > quartz > carbonate)

[0072] IV 2 Felsic dolomitic mixed sedimentary shale (feldspar, quartz, carbonate, and clay mineral content are all less than 50%, with feldspar > carbonate > clay mineral content or carbonate > feldspar > quartz > clay mineral content)

[0073] IV 3 Clayey-dus-rich mixed shale (feldspar and quartz mineral content, carbonate mineral content, and clay mineral content are all less than 50%, with clay mineral content > carbonate mineral content > feldspar and quartz mineral content or carbonate mineral content > clay mineral content > feldspar and quartz mineral content).

[0074] In this invention, the specific composition of felsic clayey mixed shale, felsic dolomitic mixed shale, and clayey dolomitic mixed shale is no longer distinguished, and they are all classified as mixed shale.

[0075] Step 3: Utilizing unique sedimentary structures to classify lithofacies assemblages. Core observation and thin section identification are used to describe the unique structures developed in the mixed-sedimentary shale. Well HY1 includes sandy laminae or bands, dolomitic laminae, calcite veins, and dolomite bands. Further, the dolomitic laminae, calcite veins, and dolomite bands are collectively referred to as carbonate laminae or bands. The dolomitic laminae, calcite veins, and dolomite bands are lithologically classified as dolomitic shale, clayey felsic dolomitic shale, or felsic clayey dolomitic shale. The sandy laminae or bands are lithologically classified as felsic shale, clayey dolomitic felsic shale, or dolomitic clayey felsic shale. The remaining lithology is mixed-sedimentary shale. For example... Figure 4 As shown, combining sedimentary structures and lithology, the Fu-2 member of Well HY1 is divided into three lithofacies assemblages: mixed shale, mixed shale interbedded with carbonate laminar or banded rocks, and mixed shale interbedded with sandy laminar or banded rocks. Based on the sublayer thickness and top and bottom depths in step 2, the top and bottom ranges of different lithofacies assemblages are constrained. Sublayers I and II are mixed shale assemblages, and sublayer III is a mixed shale interbedded with carbonate banded or laminar rocks. Figure 5 As shown, Ⅳ-1 to Ⅳ-4-1 are mixed shale assemblages; Ⅳ-4-2 is a mixed shale interbedded with siltstone with bedding or banding; Ⅳ-5 is a mixed shale interbedded with carbonate rocks with banding or bedding; Ⅳ-6-1 is a mixed shale interbedded with siltstone with bedding or banding; Ⅳ-6-2 to Ⅳ-7 are mixed shale interbedded with carbonate rocks with banding or bedding; Ⅳ-8 to Ⅴ-5-1 are mixed shale assemblages; Ⅴ-5-3 to Ⅴ-6-1 are mixed shale interbedded with siltstone with bedding or banding; Ⅴ-6-2 to Ⅴ-7-3 are mixed shale interbedded with carbonate rocks. The rock bands or lamellar combinations are as follows: V-7-4 is a combination of lamellar or banded shale interbedded with siltstone and a combination of lamellar or banded carbonate rocks; V-8-1 is a combination of lamellar or banded shale interbedded with siltstone; V-8-2 is a combination of lamellar or banded carbonate rocks; V-9-1 is a combination of lamellar or banded shale interbedded with siltstone; V-9-2 is a combination of lamellar or banded shale interbedded with siltstone and a combination of lamellar or banded carbonate rocks; V-10 is a combination of lamellar or banded shale interbedded with siltstone.

[0076] Step 4: Analyze the three-dimensional and two-dimensional reservoir characteristics of three different lithofacies combinations: mixed shale, mixed shale with carbonate laminae or bands, and mixed shale with sandy laminae or bands.

[0077] Three-dimensional reservoir characteristic analysis includes:

[0078] Dual-energy CT was used to test full-diameter core samples (10cm) to analyze the number and thickness of laminae, bands, and fractures of different properties. Here, "laminates, bands, and fractures of different properties" refers to the "special sedimentary structures" in step 3. The mixed-sedimentary shale facies assemblage contained 32 fractures with an average thickness of 3.98mm; the mixed-sedimentary shale interbedded with carbonate bands or laminae contained 7 carbonate laminae with an average thickness of 17cm and 88 fractures with an average thickness of 2.25mm; the mixed-sedimentary shale interbedded with sandy laminae or bands contained 7 sandy laminae with an average thickness of 21mm and 56 fractures with an average thickness of 1.91mm.

[0079] μm CT (micron CT) was performed using 3mm diameter plunger samples to analyze the micron-level average pore radius, average throat radius, average pore-throat coordination number, and average shape factor. The mixed-sedimentary shale facies assemblage showed an average pore radius of 3.2 μm, an average throat radius of 1.9 μm, an average coordination number of 2.23, and an average shape factor of 0.054. The mixed-sedimentary shale interbedded with carbonate bands or lamellar lithology showed an average pore radius of 3.40 μm, an average throat radius of 1.60 μm, an average coordination number of 2.36, and an average shape factor of 0.054. The mixed-sedimentary shale interbedded with sandy lamellar or banded lithology showed an average pore radius of 1.93 μm, an average throat radius of 1.28 μm, an average coordination number of 3.6, and an average shape factor of 0.057.

[0080] FIB-SEM (Focused Ion Beam Scanning Electron Microscopy) was used to analyze nanoscale pore radius, throat radius, pore-throat coordination number, and shape factor using sheet-like samples with a diameter less than 25 mm. The average nanoscale pore radius of the mixed-sedimentary shale facies assemblage was 40.7 nm, the average throat radius was 25.0 nm, the average coordination number was 2.21, and the average shape factor was 0.055. The average nanoscale pore radius of the mixed-sedimentary shale interbedded with carbonate bands or lamellar lithology was 76.5 nm, the average throat radius was 41.9 nm, the average coordination number was 3.45, and the average shape factor was 0.057. The average nanoscale pore radius of the mixed-sedimentary shale interbedded with sandy lamellar or banded lithology was 55.7 nm, the average throat radius was 26.8 nm, the average coordination number was 4.06, and the average shape factor was 0.055.

[0081] like Figure 6 As shown, the lithological assemblage of mixed shale interbedded with dolomite bands has relatively large number and thickness of laminations and fractures, relatively good average pore radius, average throat radius, average coordination number and average shape factor at the micron and nanometer scales, and the best three-dimensional reservoir pore-throat characteristics.

[0082] Two-dimensional reservoir characteristic analysis includes:

[0083] Thin sections are used to identify and analyze the type of laminae or bands. In mixed-sedimentary shale facies combinations, laminae are either underdeveloped or weakly developed with clayey and felsic laminae; in mixed-sedimentary shale interbedded with carbonate bands or laminae, dolomite bands or gray-dolomite laminae are developed; in mixed-sedimentary shale interbedded with sandy laminae or bands, felsic laminae are developed.

[0084] MAPS scanning electron microscopy mapping and QEMSCAN mineral quantification were performed on samples with a field of view of 400-450μm*400-450μm (width range 400-450μm, length range 400-450μm) to analyze porosity, inorganic pore ratio and organic pore ratio. The mixed-sedimentary shale lithological assemblage has a porosity of 0.82%, organic matter pores and fissures of 0.085%, inorganic pores and fissures of 0.73%, illite 31.7%, plagioclase 24.2%, and quartz 22.3%; the mixed-sedimentary shale interbedded with carbonate bands or lamellar lithology has a porosity of 1.79%, organic matter pores and fissures of 0.97%, inorganic pores and fissures of 0.83%, dolomite 54.0%, plagioclase 24.8%, and quartz 10.4%; the mixed-sedimentary shale interbedded with sandy lamellar or banded lithology has a porosity of 3.48%, organic matter pores and fissures of 0%, inorganic pores and fissures of 3.48%, quartz 46.0%, feldspar 23.2%, dolomite 13.6%, and ferrodolithite 2.8%.

[0085] The full-scale pore-throat structure characteristics were analyzed using low-temperature nitrogen adsorption, argon-ion polishing scanning electron microscopy, high-pressure mercury intrusion porosimetry, and nuclear magnetic resonance spectroscopy. The pore structure of mixed-sedimentary shale facies combinations mostly exhibits a single-peak characteristic, with pore sizes primarily ranging from 1 to 100 nm and throat sizes primarily ranging from 5 to 30 nm. The pore structure of mixed-sedimentary shale interbedded with carbonate bands or lamellar lithologies mostly exhibits a three-peak characteristic, with micron-sized pores and throat sizes primarily ranging from 10 to 30 nm. The pore structure of mixed-sedimentary shale interbedded with sandy lamellar or banded lithologies mostly exhibits a bimodal characteristic, with pore sizes primarily ranging from 100 to 1000 nm and throat sizes primarily ranging from 10 to 30 nm.

[0086] like Figure 7 As shown, the lithological assemblage of mixed shale interbedded with dolomite bands is characterized by well-developed carbonate laminae or bands, high porosity, large pore size across the entire scale, relatively large throats, and optimal two-dimensional reservoir pore-throat characteristics.

[0087] Step 5 involves combining static geological parameters and dynamic development parameters to identify favorable lithofacies assemblages. Static parameters or characteristics such as total organic carbon (TOC) content, liquid nitrogen cryogenic pyrolysis (S1) content, oil saturation index (OSI), porosity (φ), and reservoir characteristics (referring to both three-dimensional and two-dimensional reservoir characteristics) are compared across different lithofacies assemblages. Dynamic development parameters, including water cut and oil production contribution rate, are then used to identify favorable lithofacies assemblages in both directions. For example, the mixed sedimentary shale lithofacies assemblages have a TOC of 1.04%, S1 of 1.13 mg / g, φ of 2.8%, and an OSI of 108.7 mg / g. The water cut decreases slowly, remaining above 55% at the end of the second stage and above 50% for most of the time, with an oil production contribution rate of 4.1%.

[0088] Mixed shale with carbonate bands or lamellar lithological assemblage: TOC: 2.14%, S1: 2.43 mg / g, Φ: 5.7%, OSI: 120.3 mg / g. It is a rapidly decreasing water cut type, with the water cut dropping to about 23% at the end of the second stage and dropping to below 10% (9.2%) in the third stage. Its oil production contribution rate is 9%.

[0089] The mixed sedimentary shale interbedded with sandy lamellar or banded lithological assemblage has a TOC of 0.94%, S1 of 0.9 mg / g, Φ of 5.01%, and OSI of 98.7 mg / g. The water cut decreased rapidly in the first and third stages, especially in the later stage of the third stage when the water cut dropped to below 30%, with a minimum water cut of 12.53%. The oil production contribution rate was 3.9%.

[0090] like Figure 8 As shown, the lithological combination of mixed shale interbedded with dolomite bands has good oil generation, oil-bearing, mobility and reservoir properties, the best two-dimensional and three-dimensional pore throat characteristics of the reservoir, high oil-water replacement efficiency, rapid dynamic water cut decline during production, low water cut, and high oil production contribution rate, making it the most favorable lithological combination.

[0091] The following table compares the static and dynamic parameters of different lithofacies combinations in well HY1 in this application:

[0092]

[0093] The method employed in this application improves the accuracy, effectiveness, and comprehensiveness of determining favorable lithofacies assemblages in continental mixed sedimentary shale. It combines a special structural lithofacies assemblage classification scheme with two-dimensional and three-dimensional reservoir evaluation methods, as well as comprehensive analysis of dynamic and static parameters or characteristics. This enhances the accuracy of identifying favorable lithofacies assemblages, avoiding the limitations of conventional methods in comprehensively and effectively analyzing favorable lithofacies assemblages. The accuracy is improved by 75 percentage points, reaching 95%. It also improves work efficiency, avoiding repetitive work and reducing the workload from 5 people working for 20 days to 2 people working for 10 days, increasing efficiency by over 85%. The method accurately and efficiently identifies favorable lithofacies types, providing crucial information for further optimization of "honey spots" and target boxes, assisting in high-yield well drilling, and effectively meeting practical application needs. After application in 9 wells in the XX Basin depression, the total peak daily oil production exceeded 220 tons, and the cumulative oil production exceeded 100,000 tons. Eight wells achieved a peak daily oil production exceeding 20 tons, and four wells achieved a peak daily oil production exceeding 40 tons. The four wells achieved a cumulative oil production exceeding 10,000 tons, achieving a breakthrough in exploration and demonstrating promising exploration and development prospects.

[0094] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method of determining a favorable lithofacies combination of a continental mixed sediment shale, the method comprising: Comprise: ​ S1, according to the characteristics of well logging curve and formation thickness, small layer is subdivided; S2, using X-ray diffraction whole rock test analysis data to divide lithology type; S3, using special sedimentary structure to divide lithofacies assemblage type; S4, analyzing different lithofacies assemblage three-dimensional reservoir characteristics and two-dimensional reservoir characteristics; S5, using static geological parameters and dynamic development parameters to combine, clear favorable lithofacies assemblage.

2. The method of claim 1, wherein the favorable lithofacies assemblage of continental mixed-shale is characterized by, In step S1, rock formation unit includes group, section and layer, from bottom to top, 6 groups are developed in Subei Basin: Taizhou group K2t, Funing group E1f, Dainan group E2d, Sanduo group E2s, Yancheng group N1y-N2y and Dongtai group Qd; E1f formation is divided into 4 sections from bottom to top: Funing 1 section E1f1, Funing 2 section E1f2, Funing 3 section E1f3, Funing 4 section E1f4.

3. The method of claim 2, wherein the favorable lithofacies assemblage of continental mixturbidite shale is characterized by, In step S1, Funing 2 section E1f2 is divided into Ⅰ, Ⅱ, Ⅲ, Ⅳ and Ⅴ 5 sub-sections from bottom to top, the resistivity curve range of Ⅴ sub-section is 1.9-14Ω, the upper curve is flat, the middle and lower 5 high resistance peaks, the resistivity range of Ⅳ sub-section is 1.2-13Ω, the curve has 4 sets of high resistance peaks, the resistivity range of Ⅲ sub-section is 0.5-3Ω, the curve is jagged, 7-8 sawtooth cycles, the resistivity range of Ⅱ sub-section is 1.8-4.3Ω, the curve is low amplitude arc, the resistivity range of Ⅰ sub-section is 0.6-1.5Ω; The division plane of sub-section can be compared with 2 or more wells.

4. The method of claim 3, wherein the favorable lithofacies assemblage of continental mixed-shale is characterized by, According to the characteristics of resistivity RT and gamma GR curve, Ⅳ and Ⅴ sub-sections are divided into Ⅳ-8 to Ⅳ-1 and V-10 to V-1 respectively from bottom to top, a total of 18 small layers.

5. The method of claim 4, wherein the favorable lithofacies assemblage of continental mixed-shale is characterized by, According to the characteristics of resistivity RT and gamma GR curve, V-4 to V-8 and Ⅳ-2 to Ⅳ-7 are divided into 15 subdivided small layers from bottom to top; V-4 to V-8 has 4 sets of GR, RT layers, the electrical characteristics of which are GR: 81-92 API, RT: 27-92Ω, thickness 2.5-5m, 2 sets of GR, RT layers, the electrical characteristics of which are GR: 107-115 API, RT: 6-7Ω, thickness 1.3-1.9m; Ⅳ-2 to Ⅳ-7 has 5 sets of GR, RT layers, the electrical characteristics of which are GR: 77-93 API, RT: 8-99Ω, thickness 1.5-6m, GR, RT layers, the electrical characteristics of which are GR: 95-105 API, RT: 5-8Ω, thickness 3.5m.

6. The method of claim 1-5, wherein the method further comprises: In step S2, using the difference of feldspar quartz mineral, carbonate mineral and clay mineral content, according to mineral component triangular chart, lithology type is divided; Lithology type includes: gray shale, clay-containing felsic gray shale, felsic gray mixed shale, felsic clay mixed shale, clay-containing felsic gray longeng shale, gray clay-containing felsic longeng shale, felsic longeng shale.

7. The method of claim 1-5, wherein the method further comprises: In step S3, the special sedimentary structures developed in the mixed shale are described by core observation and thin section identification, including sandy laminae or bands, dolomitic laminae, calcite veins, and dolomite bands. The dolomitic laminae, calcite veins, and dolomite bands are collectively referred to as carbonate laminae or bands. Three lithofacies assemblages are classified, including mixed shale, mixed shale with carbonate laminae or bands, and mixed shale with sandy laminae or bands. The top and bottom depths of different lithofacies assemblages are constrained by the thickness and top and bottom depths of the small layers in step S2.

8. The method of claim 1-5, wherein the favorable lithofacies assemblage of continental mixed depositional shale is characterized by, In step S4, the three-dimensional reservoir characteristics analysis includes: testing the dual-energy CT of the 10 cm diameter core sample to analyze the number and thickness of different attribute laminae, bands, and fractures; testing the μm CT of the 3 mm diameter plunger sample to analyze the micron-level pore radius, throat radius, pore throat coordination number, and shape factor; and testing the FIB-SEM of the less than 25 mm diameter sheet sample to analyze the nanometer-level pore radius, throat radius, pore throat coordination number, and shape factor.

9. The method of claim 1-5, wherein the favorable lithofacies assemblage of continental mixed depositional shale is characterized by, In step S4, the two-dimensional reservoir characteristics analysis includes: In step S4, the two-dimensional reservoir characteristics analysis includes:

10. The method of claim 1-5, wherein the favorable lithofacies assemblage of continental mixed depositional shale is characterized by, In step S5, the static geological parameters of different lithofacies assemblages, including total organic carbon (TOC) content, S1 content of liquid nitrogen freezing pyrolysis, oil saturation index (OSI), porosity (φ) four-property parameters, and reservoir characteristics, are compared. The dynamic parameters of different lithofacies assemblages, including water content and oil production contribution rate, are developed. The favorable lithofacies assemblages are determined in both directions.

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