Method for evaluating complex fine-grained sedimentary reservoirs

Abstract

The application discloses a kind of complex fine-grained sedimentary rock reservoir evaluation method, which comprises the following steps: step 1: the reservoir to be studied as target reservoir;Step 2: target reservoir is stratified according to lithology category and thickness;Step 3: gas-bearing property in target reservoir is analyzed, and favorable stratigraphic system is preliminarily selected according to gas-bearing property characteristics;Step 4: favorable stratigraphic system, carry out stratigraphic system development scale characterization, stratigraphic system reservoir property characterization, organic matter abundance characterization and gas-bearing property characterization analysis, according to reservoir evaluation parameter and the weight corresponding to each parameter and determine the gas-bearing property evaluation index REI value of the stratigraphic system type;Step 5: according to the type of target reservoir, establish the evaluation system of complex fine-grained sedimentary rock reservoir.The application considers the heterogeneity of fine-grained sedimentary rock reservoir internal structure, and proposes a reasonable reservoir property evaluation parameter calculation method.

Description

Technical Field

[0001] This invention belongs to the field of geological technology, specifically relating to an evaluation method for complex fine-grained sedimentary rock reservoirs. Background Technology

[0002] Complex fine-grained sedimentary reservoirs are formed by the vertical stacking of various rock types, including mudstone, shale, siltstone, limestone, and dolomite, under the influence of sedimentary environments. Due to their complex lithology and strong heterogeneity, a mature reservoir evaluation method and technology have not yet been established for the evaluation of complex fine-grained sedimentary reservoirs.

[0003] Currently, the evaluation of complex fine-grained sedimentary reservoirs often employs methods used for tight sandstone or shale gas reservoirs. For example, this involves characterizing pore-throat structure to identify reservoir "sweet spots" and evaluating reservoirs based on parameters such as TOC, porosity, gas content, and brittle mineral content. However, when characterizing reservoir parameters, complex fine-grained sedimentary reservoirs are often treated as homogeneous lithological groups, neglecting their heterogeneous nature due to their diverse lithological composition. This can easily lead to significant deviations between parameter values ​​and actual conditions when the lithological composition is complex. Furthermore, characterizing pore-throat structure presents the problem of unquantifiable reservoir evaluation results; and the weighting of evaluation parameters is often arbitrary, raising concerns about the accuracy and reliability of the evaluation results. Summary of the Invention

[0004] The purpose of this invention is to provide an evaluation method for complex fine-grained sedimentary rock reservoirs. This invention solves the problems of existing technologies, which easily lead to large deviations between parameter values ​​and actual conditions when the lithological composition is complex, and the inability to quantify existing reservoir evaluation results.

[0005] To achieve the above objectives, this invention provides a method for evaluating complex fine-grained sedimentary rock reservoirs. The invention employs the following technical solution: A method for evaluating complex fine-grained sedimentary rock reservoirs, comprising the following steps:

[0006] Step 1: Select the reservoir to be studied as the target reservoir.

[0007] Step 2: The target reservoir is divided into seven categories based on lithology and thickness: mudstone and shale, siltstone, carbonate, mud-sand interbedded, mud-carbon interbedded, sand-carbon interbedded, and mixed strata. Five categories of mudstone and shale, siltstone, carbonate, mud-sand interbedded, and mixed strata are identified in the target reservoir.

[0008] Step 3: Analyze the gas-bearing properties of the mudstone and shale formations, siltstone formations, carbonate formations, mudstone-sand interbedded formations, and mixed formations identified in the target reservoir, and preliminarily select favorable formations based on their gas-bearing characteristics.

[0009] Among them, the gas content of the strata is calculated using a thickness-weighted method, and the calculation formula is as follows:

[0010]

[0011] In the formula V la —Total gas content of the strata;

[0012] V i —Total gas content of mudstone and shale;

[0013] V j —Total gas content of siltstone;

[0014] V k —Total gas content of carbonate rocks;

[0015] H i —Thickness of mudstone and shale;

[0016] H j —Thickness of siltstone;

[0017] H k —Carbonate rock thickness;

[0018] m—number of mudstone and shale layers;

[0019] n—Number of siltstone layers;

[0020] p—Number of carbonate rock layers;

[0021] The average gas content of the mudstone and shale formations, siltstone formations, and interbedded mudstone and sandstone formations is greater than 1 m³. 3 / t, which is a favorable stratum, with gas content less than 1m³ in carbonate rock strata and mixed strata. 3 / t represents an unfavorable stratum.

[0022] Step 4: Conduct analysis on the favorable strata development scale, reservoir capacity, organic matter abundance, and gas content of the favorable strata in Step 3 to determine reservoir evaluation parameters; and determine the REI value of the gas content evaluation index for the favorable strata type based on the reservoir evaluation parameters and the weight of each parameter.

[0023] Characterization of favorable gas content in strata: calculated using the above formula (1);

[0024] The scale of favorable stratigraphic development was characterized by statistical analysis of stratigraphic thickness.

[0025] Characterizing the reservoir properties of favorable strata: The porosity of the strata is calculated using a thickness-weighted method, as shown in the following formula.

[0026]

[0027] In the formula:

[0028] φ la —Layer porosity;

[0029] φ i —Porosity of mudstone and shale;

[0030] φ j —Porosity of siltstone;

[0031] φ k —Porosity of carbonate rocks;

[0032] H i —Thickness of mudstone and shale;

[0033] H j —Thickness of siltstone;

[0034] H k —Carbonate rock thickness;

[0035] m—number of mudstone and shale layers;

[0036] n—Number of siltstone layers;

[0037] p—Number of carbonate rock layers;

[0038] The abundance of organic matter in favorable strata was characterized by taking the percentage of lithological thickness with TOC greater than 1% as H. TOC>1％ / H 层系 .

[0039] Step 5: Based on the type of the target reservoir in Step 4, obtain the Reservoir Evaluation Index (REI) values ​​corresponding to each layer of the target reservoir, determine the type of the target reservoir, and establish a comprehensive evaluation system for complex fine-grained sedimentary rock reservoirs.

[0040] The target reservoirs are classified into Class I, Class II, and Class III reservoirs with REI values ​​of 0.6 and 0.2 as the boundaries. The REI value of Class I reservoirs is ≥0.6 to 1, the REI value of Class II reservoirs is ≥0.2 to 0.6, and the REI value of Class III reservoirs is <0.2.

[0041] Further, in step 1, a comprehensive lithological columnar section is established based on the data of the target study area. Based on the comprehensive lithological columnar section and combined with well logging data, lithological correction is performed to classify the rock types of the target reservoir into three major categories: mudstone, shale, siltstone, and carbonate rocks.

[0042] Furthermore, the comprehensive evaluation system standard for complex fine-grained sedimentary rock reservoirs in step 5 is as follows:

[0043] Class I reservoirs have a thickness ≥75–150 m and a porosity ≥2%, H TOC>1％ / H层系 ≥0.5~1, gas content ≥2m 3 / t.

[0044] Class II reservoirs have a thickness ≥50–75 m and a porosity ≥1%–2%, H TOC>1％ / H 层系 <0.5, gas content ≥1~2m 3 / t.

[0045] Class III reservoirs have a layer thickness of <50m or ≥150m, porosity <1%, and H TOC>1％ / H 层系 <0.5, gas content <1m 3 / t.

[0046] Furthermore, the REI value can be obtained using the following method:

[0047]

[0048] Where REI is the gas-bearing index for a certain stratum, and E i a is a parameter for evaluating gas content. i This is the weight corresponding to this parameter.

[0049] The beneficial effects of this invention are:

[0050] 1. This invention proposes a geological evaluation method for complex fine-grained sedimentary reservoirs. Based on the stratigraphic division of complex fine-grained sedimentary rock reservoirs according to lithology, the method evaluates the complex fine-grained sedimentary rock reservoirs in two steps. First, favorable stratigraphic types are preliminarily selected based on the gas content evaluation results. Then, the reservoirs of favorable stratigraphic types are evaluated by considering the scale, reservoir properties, and organic matter abundance.

[0051] 2. Compared with traditional methods that treat complex fine-grained sedimentary rock reservoirs as homogeneous tight sandstone or shale gas reservoirs, the method for evaluating complex fine-grained sedimentary rock reservoirs in this invention fully considers the heterogeneity of complex fine-grained sedimentary rocks. The selection and calculation methods for reservoir evaluation parameters are more accurate. At the same time, a scientific method is used to assign weights to the reservoir evaluation parameters and quantify the reservoir evaluation results. Using this method, sweet spots can be reliably identified, laying the foundation for oilfield geological development evaluation. Attached Figure Description

[0052] Figure 1 This is a schematic flowchart of the method for evaluating complex fine-grained sedimentary rock reservoirs according to the present invention;

[0053] Figure 2 This is a bar chart showing the stratigraphic type classification results of Well X in this embodiment of the invention;

[0054] Figure 3This is a schematic diagram illustrating the relationship between the thickness of siltstone and carbonate rock and total hydrocarbons in an embodiment of the present invention;

[0055] Figure 4 This is a schematic diagram illustrating the relationship between the mud-to-soil ratio and total hydrocarbons in the study area of ​​this invention embodiment;

[0056] Figure 5 This is a statistical chart of gas content in various strata according to embodiments of the present invention;

[0057] Figure 6 This is a diagram showing the relationship between layer thickness and gas content in an embodiment of the present invention;

[0058] Figure 7 This is a diagram showing the relationship between porosity and gas content in the layered system according to an embodiment of the present invention.

[0059] Figure 8 H is an embodiment of the present invention. TOC>1％ / H 层系 Relationship with gas content;

[0060] Figure 9 This is a statistical chart of the REI values ​​of the layer system according to an embodiment of the present invention;

[0061] Figure 10 This is a schematic diagram illustrating the relationship between the interlayer / interlayer density and total hydrocarbon display of complex fine-grained sedimentary reservoir structural parameters according to an embodiment of the present invention. Detailed Implementation

[0062] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0063] like Figure 1 As shown, an evaluation method for complex fine-grained sedimentary rock reservoirs specifically includes the following steps:

[0064] Step 1: First, determine the target area to be studied, and obtain geological data of the target study area through surveys. This geological data includes outcrop and core data, drilling data, well logging data, well logging data, and analytical testing data of the target study area. Obtain data of the study area and determine the target reservoir.

[0065] In practical research, the reservoir corresponding to the formation depth is determined according to the actual needs of oil and gas exploration and development. Based on the data of the study area, a comprehensive lithological columnar section is established. Based on the comprehensive lithological columnar section, XDR whole-rock analysis is performed on the collected samples. At the same time, lithological correction is performed in combination with well logging data to identify the rock types of the target reservoir, which are divided into three major categories: mudstone, shale, and carbonate rocks.

[0066] Step 2: The target reservoir is divided into seven categories based on lithology and thickness: mudstone and shale, siltstone, carbonate, mud-sand interbedded, mud-carbon interbedded, sand-carbon interbedded, and mixed strata.

[0067] In actual research, the target reservoir may have incompletely developed strata. Based on the actual research situation, this invention classifies the target reservoir in the target research area into five categories: shale strata, siltstone strata, carbonate rock strata, interbedded shale and mudstone strata, and mixed strata. The strata classification is illustrated using Well X as an example. Figure 2 .

[0068] The relationship between the thickness and gas content of siltstone and carbonate rocks in the study area was statistically analyzed to define the upper limit of the thickness of siltstone and carbonate rocks as interlayers or the lower limit of the thickness of the main lithology of the strata. Figure 3 The relationship between siltstone and carbonate rocks and gas content in the target study area is shown. A clear inflection point appears in the curve when the thickness exceeds 5m. Therefore, the upper limit for siltstone and carbonate rocks to be considered interlayers or the lower limit for the main lithology of a stratum is defined as 5m. That is, when the thickness is less than 5m, siltstone or carbonate rocks can be considered interlayers within mudstone and shale strata; when the thickness is greater than 5m, siltstone or carbonate rocks can be classified as the main lithology within siltstone or carbonate strata. The ratio of the cumulative thickness of mudstone and shale to the total thickness of the strata in the target study area, i.e., the mudstone-soil ratio, is statistically analyzed. The relationship between the mudstone-soil ratio and total hydrocarbon content is shown below. Figure 4 As shown, the curve shows a clear inflection point when the mud-to-soil ratio is equal to 0.6. Therefore, the lower limit of the mud-to-soil ratio for mudstone and shale strata is defined as 0.6. Based on the lower limit of the mud-to-soil ratio, the lower limit of the sand-to-soil ratio for siltstone strata is defined as 0.6, and the lower limit of the carbon-to-soil ratio for carbonate strata is defined as 0.6. Specifically, when the mud-to-soil ratio of a stratum is greater than or equal to 0.6, it is defined as a mudstone-shale stratum; when the sand-to-soil ratio is greater than or equal to 0.6, it is defined as a siltstone stratum; when the carbon-to-soil ratio is greater than or equal to 0.6, it is defined as a carbonate stratum; when the carbon-to-soil ratio is 0 and the mud-to-soil ratio and sand-to-soil ratio are both less than 0.6, it is defined as an interbedded mudstone-sand stratum; when the sand-to-soil ratio is 0 and the mud-to-soil ratio and carbon-to-soil ratio are both less than 0.6, it is defined as an interbedded mudstone-carbonaceous stratum; when the mud-to-soil ratio is 0 and the sand-to-soil ratio and carbon-to-soil ratio are both less than 0.6, it is defined as an interbedded sandstone-carbonaceous stratum; and when the mud-to-soil ratio, sand-to-soil ratio, and carbon-to-soil ratio are all less than 0.6, it is defined as a mixed stratum.

[0069] Step 3: Step 2 analyzes the gas-bearing properties of five major types of formations identified in the target reservoir: mudstone and shale formations, siltstone formations, carbonate formations, mudstone and sandstone interbedded formations, and mixed formations. Based on the gas-bearing properties, favorable formations are initially selected.

[0070] The specific method used to initially select favorable strata based on gas-bearing characteristics is as follows:

[0071] The gas content of the strata is calculated using a thickness-weighted method to characterize the gas content of the strata. The calculation formula is as follows:

[0072]

[0073] In the formula:

[0074] V la —Total gas content of the system, m 3 / t;

[0075] V i —Total gas content of mudstone and shale, m 3 / t;

[0076] V j —Total gas content of siltstone, m 3 / t;

[0077] V k —Total gas content of carbonate rocks, m 3 / t;

[0078] H i —Thickness of mudstone and shale, in meters;

[0079] H j —Thickness of siltstone, in meters;

[0080] H k — Carbonate rock thickness, m;

[0081] m—Number of mudstone and shale layers;

[0082] n—Number of siltstone layers;

[0083] p—Number of carbonate rock layers, in terms of layers.

[0084] Based on data from the target study area, five major categories of strata were identified in the target study reservoir: mudstone and shale strata, siltstone strata, carbonate rock strata, mudstone and sandstone interbedded strata, and mixed strata.

[0085] Statistical analysis of the gas content of the strata, such as... Figure 5 As shown, the gas-bearing properties of the above five types of strata exhibit a distinct two-stage characteristic, divided into favorable and unfavorable strata. Among them, the average gas content of the mudstone and shale strata, siltstone strata, and interbedded mudstone and sandstone strata is greater than 1 m³. 3 / t represents a favorable stratum, while the gas content of carbonate rock strata and mixed strata is less than 1m³. 3 / t represents an unfavorable stratum.

[0086] Since the gas content of the non-favorable strata is below the industrial lower limit, they are classified as non-reservoirs and will not be further evaluated. Instead, the mudstone and shale strata, siltstone strata, and mud-sand interbedded strata are selected as favorable strata for the next stage of reservoir evaluation.

[0087] Step 4: For the favorable strata initially selected in Step 3 based on gas-bearing characteristics, conduct analysis on the development scale, reservoir capacity, organic matter abundance, and gas-bearing characteristics of the strata to determine the reservoir evaluation parameters; based on the reservoir evaluation parameters, with the gas-bearing index as the main sequence, determine the weight of each parameter and determine the REI value of the reservoir evaluation index for the strata type.

[0088] (i) Characterize the scale of favorable strata development and statistically analyze the thickness of favorable strata.

[0089] (ii) The reservoir properties of favorable strata are characterized, and the porosity of favorable strata is calculated using a thickness-weighted method.

[0090] The porosity of favorable strata is calculated using a thickness-weighted method, which considers the contribution of lithology at different thicknesses to porosity. This avoids the problem of results being too high or too low due to uneven sample size caused by the direct averaging method. The specific calculation formula is as follows:

[0091]

[0092] In the formula:

[0093] φ la —Layer porosity, %;

[0094] φ i —Porosity of mudstone and shale, %;

[0095] φ j —Silty sandstone porosity, %;

[0096] φ k —Porosity of carbonate rocks, %;

[0097] H i —Thickness of mudstone and shale, in meters;

[0098] H j —Thickness of siltstone, m;

[0099] H k — Carbonate rock thickness, m;

[0100] m—Number of mudstone and shale layers;

[0101] n—Number of siltstone layers;

[0102] p—Number of carbonate rock layers, in terms of layers.

[0103] (III) The abundance of organic matter in favorable strata is characterized by the percentage of lithological thickness with TOC greater than 1% to the total thickness of the strata, i.e., H. TOC>1％ / H 层系 Characterize the abundance of organic matter in favorable strata.

[0104] (iv) Characterize the gas content of favorable strata: use formula (1) for calculation.

[0105] Based on the reservoir evaluation parameters and the weights corresponding to each parameter, the gas-bearing evaluation index REI value for favorable formation types is determined.

[0106] Among them, the evaluation parameters for favorable reservoir formations include: formation thickness, formation porosity, and H. TOC>1％ / H 层系 .

[0107] The complex fine-grained sedimentary rock evaluation system constructed in this invention is based on the gas-bearing evaluation of favorable strata. Therefore, it is necessary to obtain the gas-bearing evaluation index REI value corresponding to each favorable strata type. The magnitude of the REI value indicates the gas-bearing level of the strata. The better the gas-bearing level, the higher the evaluation of the strata, and vice versa.

[0108] The REI value can be obtained using the following method:

[0109]

[0110] Where REI is the gas-bearing index for a certain stratum, and E i a is a parameter for evaluating gas content. i The weights corresponding to this parameter are: layer thickness, layer porosity, and H. The gas-bearing evaluation parameters include: layer thickness, layer porosity, and H. TOC>1％ / H 层系 Table 1 is a statistical table of the original data of reservoir evaluation parameters corresponding to some favorable strata.

[0111] Table 1

[0112] Layer type <![CDATA[Gas content of formation series (m 3 / t)]]> Layer thickness (m) Layer porosity (%) <![CDATA[H TOC>1％ / H 层系 ]]> Shale 1.62 42.9 1.50 0.11 Shale 1.07 45.0 0.80 0.69 Shale 2.25 136.3 2.20 0.95 siltstone strata 0.90 180.0 0.55 0.00 siltstone strata 0.80 28.0 0.90 0.05 siltstone strata 1.35 50.0 1.33 0.00 interbedded mud and sand 0.74 21.0 0.72 0.00 interbedded mud and sand 1.46 50.2 1.36 0.19 interbedded mud and sand 1.20 173.1 0.59 0.17

[0113]

[0114] Among them, E i Let X be the standardized value of the i-th reservoir evaluation parameter. i X represents the original value of the evaluation parameter for the i-th reservoir in each lithological combination. max and X min These are the maximum and minimum values ​​of the evaluation parameters for the i-th reservoir in each lithological combination.

[0115] To obtain E iIt is necessary to normalize the original data of gas content evaluation parameters corresponding to each type of stratum. In this invention, (Formula 4) is used to normalize the original data of gas content evaluation parameters to obtain the standardized value of each parameter. Table 2 shows the statistical results of the standardized values ​​of reservoir evaluation parameters corresponding to some favorable strata.

[0116] Table 2

[0117] Layer type <![CDATA[Gas content of formation series (m 3 / t)]]> Layer thickness (m) Layer porosity (%) <![CDATA[H TOC>1％ / H 层系 ]]> Shale 0.29 0.14 0.52 0.11 Shale 0.12 0.15 0.19 0.69 Shale 0.49 0.72 0.86 0.97 siltstone strata 0.06 0.99 0.07 0.00 siltstone strata 0.03 0.04 0.24 0.05 siltstone strata 0.21 0.18 0.44 0.00 interbedded mud and sand 0.01 0.00 0.15 0.00 interbedded mud and sand 0.24 0.18 0.46 0.19 interbedded mud and sand 0.16 0.94 0.09 0.17

[0118] like Figures 6-8 As shown, this invention includes reservoir evaluation parameters such as layer thickness, layer porosity, and H0. TOC>1％ / H 层系 A cross-plot was created showing the relationship between gas content and hydrocarbon content. By comparing the slope and goodness of fit of each plot, the sensitivity of gas content to each parameter can be determined. The larger the slope, the greater the change in total hydrocarbon content caused by the change in this parameter. Table 3 shows the weight values ​​of the reservoir evaluation parameters calculated using the grey relational analysis method, based on the sensitivity analysis results.

[0119] Table 3

[0120] parameter Layer thickness (m) Layer porosity (%) <![CDATA[H TOC>1％ / H 层系 ]]> Weighting coefficient 0.32 0.32 0.36

[0121] Step 5: Based on the type of the target complex fine-grained sedimentary rock reservoir in Step 4, and based on the REI values ​​of the reservoir evaluation index corresponding to each layer of the target complex fine-grained sedimentary rock reservoir, determine the type of the target complex fine-grained sedimentary rock reservoir and establish a comprehensive evaluation system for complex fine-grained sedimentary rock reservoirs.

[0122] The type of the target complex fine-grained sedimentary reservoir is determined based on the Reservoir Evaluation Index (REI) values ​​corresponding to the favorable strata within the reservoir. The statistical results of the REI values ​​for the favorable strata are as follows: Figure 9 As shown, the formations are distributed in a stepped pattern. This classifies favorable reservoirs into three categories. The present invention uses REI values ​​of 0.6 and 0.2 as boundaries to classify favorable layers in the target reservoir into Class I, Class II, and Class III reservoirs.

[0123] Specifically, the relationship between the reservoir comprehensive evaluation index and gas content is as follows: Figure 10 When the comprehensive evaluation index is 0.6, the corresponding gas content is approximately 2m³. 3 / t, with a comprehensive evaluation index of 0.2, corresponds to a gas content of approximately 1m³. 3 / t, and then based on the gas content and layer thickness, layer porosity and H TOC>1％ / H 层系 The relationship determines the boundaries of the above parameters.

[0124] Table 4

[0125]

[0126]

[0127] Table 4 shows the reservoir evaluation system for the target study. Class I reservoirs have a thickness ≥75–150 m and a porosity ≥2%. TOC>1％ / H 层系 ≥0.5~1, gas content ≥2m 3 / t, reservoir comprehensive evaluation index (REI) value ≥0.6~1.

[0128] Class II reservoirs have a thickness ≥50–75 m and a porosity ≥1%–2%, H TOC>1％ / H 层系 <0.5, gas content ≥1~2m 3 / t, reservoir comprehensive evaluation index (REI) value ≥0.2~0.6.

[0129] Class III reservoirs have a layer thickness of <50m or ≥150m, porosity <1%, and H TOC>1％ / H 层系 <0.5, gas content <1m 3 / t, Reservoir Comprehensive Evaluation Index (REI) value <0.2.

[0130] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A method for evaluating complex fine-grained sedimentary rock reservoirs, characterized in that, Includes the following steps: Step 1: Select the reservoir to be studied as the target reservoir; Step 2: The target reservoir is divided into seven categories based on lithology and thickness: mudstone and shale, siltstone, carbonate, mud-sand interbedded, mud-carbonate interbedded, sand-carbonate interbedded, and mixed strata. Five categories of strata are identified within the target reservoir: mudstone and shale, siltstone, carbonate, mud-sand interbedded, and mixed strata. Step 3: Analyze the gas-bearing properties of the mudstone and shale formations, siltstone formations, carbonate formations, mudstone-sand interbedded formations, and mixed formations identified in the target reservoir, and preliminarily select favorable formations based on their gas-bearing characteristics; The gas content of the layer is calculated using a thickness-weighted method, and the calculation formula is as follows: (Equation 1) In the formula V la —Total gas content of the strata; V i —Total gas content of mudstone and shale; V j —Total gas content of siltstone; V k —Total gas content of carbonate rocks; H i —Thickness of mudstone and shale; H j —Thickness of siltstone; H k —Carbonate rock thickness; m—number of mudstone and shale layers; n—Number of siltstone layers; p—Number of carbonate rock layers; The average gas content of the mudstone, shale, siltstone, and interbedded mudstone-sandstone strata is greater than 1 m³. 3 / t, which is a favorable stratum, the gas content of the carbonate rock strata and mixed strata is less than 1m. 3 / t represents an unfavorable stratum; Step 4: Conduct analysis on the favorable strata in Step 3 to characterize the development scale, reservoir capacity, organic matter abundance, and gas content of the favorable strata, determine the reservoir evaluation parameters, and determine the REI value of the gas content evaluation index for the favorable strata type based on the reservoir evaluation parameters and the weight of each parameter. The gas-bearing properties of the favorable strata are characterized by calculation using the above formula (1); The scale of favorable strata development is characterized by statistical analysis of strata thickness. The reservoir properties of the favorable strata are characterized using a thickness-weighted method. The porosity of the strata is calculated using the following formula: (Equation 2) In the formula: φ la —Layer porosity; φ i —Porosity of mudstone and shale; φ j —Porosity of siltstone; φ k —Porosity of carbonate rocks; The organic matter abundance of the favorable strata was characterized by taking the percentage of lithological thickness with TOC greater than 1% as H. TOC>1% / H 层系 ; Step 5: Based on the type of the target reservoir in Step 4, obtain the Reservoir Evaluation Index (REI) value corresponding to each layer of the target reservoir, determine the type of the target reservoir, and establish a comprehensive evaluation system for complex fine-grained sedimentary rock reservoirs. The target reservoirs are divided into Class I, Class II, and Class III reservoirs with REI values ​​of 0.6 and 0.2 as the boundaries. The REI value of Class I reservoirs is ≥0.6~1, the REI value of Class II reservoirs is ≥0.2~0.6, and the REI value of Class III reservoirs is <0.

2.

2. The evaluation method for complex fine-grained sedimentary reservoirs as described in claim 1, characterized in that, Step 1 establishes a comprehensive lithological columnar section based on data from the target study area. Based on the comprehensive lithological columnar section and combined with well logging data, lithological correction is performed to classify the rock types of the target reservoir into three major categories: mudstone, shale, siltstone, and carbonate rocks.

3. The evaluation method for complex fine-grained sedimentary rock reservoirs as described in claim 1, characterized in that, The comprehensive evaluation system standard for complex fine-grained sedimentary rock reservoirs in step 5 is as follows: Class I reservoirs have a thickness ≥75~150m, porosity ≥2%, and H TOC>1% / H 层系 ≥0.5~1, gas content ≥2m 3 / t; Class II reservoirs have a thickness ≥50~75m, porosity ≥1%~2%, and H TOC>1% / H 层系 <0.5, gas content ≥1~2m 3 / t; Class III reservoirs have a layer thickness of <50m or ≥150m, porosity <1%, and H TOC>1% / H 层系 <0.5, gas content <1m 3 / t.

4. The evaluation method for complex fine-grained sedimentary rock reservoirs as described in claim 1, characterized in that, The REI value can be obtained using the following method: (Equation 3) Where REI is the gas-bearing index for a certain stratum, and E i a is a parameter for evaluating gas content. i This is the weight corresponding to this parameter.

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