A method for fine division of deep shale gas geological development units

Abstract

The present application belongs to the field of geological development, and specifically relates to a method for fine division of deep shale gas geological development units. Sedimentary paleogeomorphology is restored by integrating multi-source data, and multi-level unit division is performed in combination with a variety of analysis methods. Based on the restoration of sedimentary paleogeomorphology, paleogeomorphic features are reconstructed through the imprint method to provide a basis for the division of the first-level geological development unit; on the basis of the first-level unit, the hierarchical analysis method is used to further refine the division, and cluster analysis and other methods are combined to more finely characterize the second-level geological development unit; compared with the existing technology, the present application can comprehensively characterize the internal heterogeneity of the reservoir of the target development unit, ensure that the nonlinear relationship between multiple parameters is reflected, and improve the scientific nature of the development unit division and reservoir evaluation.

Description

Technical Field

[0001] This application belongs to the field of geological development, and specifically relates to a method for fine division of deep shale gas geological development units. Background Art

[0002] China boasts abundant unconventional oil and gas reserves, and their exploration and development have become a crucial task in meeting the enormous energy demands of the future. In recent years, large-scale commercial development of shallow shale gas in the Sichuan Basin has been achieved in areas within 3,500 meters in depth, including Fuling, Changning, Weiyuan, and Zhaotong. However, to meet growing energy demands, deep shale gas formations at depths of 3,500 meters or more, with their enormous potential, are becoming a key area of natural gas exploration and development in China.

[0003] Deep shale formations are characterized by their ancient geological age, strong heterogeneity, deep burial depth, advanced thermal evolution, complex tectonic history, differential shale gas enrichment, and diverse preservation conditions. Most deep shale reservoirs have undergone multiple phases of tectonic transformation, exhibiting unique reservoir properties, complex occurrence mechanisms, and significant variations in gas content. Therefore, the precise delineation of geological development units is crucial for the efficient development of deep shale gas.

[0004] However, existing shale geological evaluation technologies mostly focus only on "geological sweet spot" parameters such as total organic carbon (TOC), gas content, porosity, shale thickness and brittleness index, while ignoring the control of sedimentary paleo-geomorphology on shale reservoirs. For example, the invention patent "A method for quantitative evaluation of geological sweet spots based on parameter optimization" (application number: 201710209547.6) proposes a method for quantitative evaluation of geological sweet spots based on parameter optimization. The method includes: determining the main geological sweet spot parameters by using the correlation between geological sweet spot parameters and gas production; determining the weight of each of the main geological sweet spot parameters; calculating the geological sweet spot coefficient of the shale formation represented by the weight based on the weight of the main geological sweet spot parameters; and quantitatively evaluating the geological sweet spot of the shale formation according to the geological sweet spot coefficient. However, this method does not take into account the impact of paleo-geomorphology on shale reservoirs, ignores the important role of paleo-geomorphology in geological formation and distribution, lacks a multi-level division process from macro to micro in the quantitative evaluation of geological sweet spot parameters, and is not in-depth enough in understanding the heterogeneity of the reservoir. At the same time, this technology mainly relies on the correlation between geological sweet spot parameters and gas production, ignoring the differences between reservoirs in different geological environments, and it is difficult to fully reflect the spatial heterogeneity of the reservoir. The sweet spot coefficient calculation of this technology is based on a simple linear combination, ignoring the nonlinear relationship and interaction between multiple parameters, and it is difficult to fully reflect the reservoir characteristics. In addition, in the process of selecting and weighting the main parameters, it relies on the experience and judgment of engineers and is subjective.

[0005] It can be seen that the existing technology fails to scientifically classify the importance of parameters such as TOC, gas content, and porosity, making it difficult to provide accurate guidance in the development of deep shale reservoirs. Summary of the Invention

[0006] This application aims to address the shortcomings of existing technologies by proposing a method for fine-grained delineation of deep shale gas geological development units. This method uses multi-source data to restore sedimentary paleo-geomorphology and combines multiple analytical methods to perform multi-level unit delineation. Based on the restoration of sedimentary paleo-geomorphology, paleo-geomorphological features are reconstructed using the imprint method to provide a basis for the delineation of primary geological development units. Based on this primary unit, the analytic hierarchy process (AHP) is used to further refine the delineation, and cluster analysis and other methods are combined to more precisely characterize secondary geological development units.

[0007] To this end, the technical solution of this application discloses a method for fine division of deep shale gas geological development units, including two-level geological development unit division, specifically:

[0008] Division of first-level geological development units:

[0009] Carry out paleo-geomorphological restoration on the target development unit and divide it into different geomorphological units. Compare the reservoir quality of different geomorphological units through reservoir parameter characteristics to achieve the first-level division of geomorphological units.

[0010] Secondary geological development unit division:

[0011] The correlation analysis between reservoir parameters and gas content was conducted on each geomorphological unit after the first level division to obtain the importance ranking of reservoir parameters. The weight of each reservoir parameter was determined by analytic hierarchy process, and the reservoir quality evaluation equation was obtained by fitting. The reservoir quality of each unit was calculated.

[0012] Based on K-Means cluster analysis and linear fitting equations, the reservoir quality division standards within each morphological unit are obtained, and the secondary division within the primary geomorphological development unit is achieved.

[0013] Furthermore, the different landform units include underwater uplifts, underwater slopes, and underwater depressions.

[0014] Furthermore, the reservoir parameters include TOC, gas content, porosity, and clay mineral content.

[0015] Furthermore, after the secondary division, it also includes drawing the reservoir quality contour map of each morphological unit, and superimposing it with the primary development unit division map to achieve the secondary refined division under the primary geomorphological unit division.

[0016] Furthermore, the hierarchical analysis method includes six steps: constructing a hierarchical structure model, assigning weights according to importance ranking, constructing a judgment matrix, normalizing and calculating eigenvectors, matrix one-time test, calculating comprehensive weights, and ranking comprehensive weights.

[0017] The beneficial effects of the present invention are as follows: This application restores sedimentary paleo-geomorphology by integrating multi-source data and combines multiple analytical methods to perform multi-level unit division. Based on the restoration of sedimentary paleo-geomorphology, paleo-geomorphological features are reconstructed through the imprint method to provide a basis for the division of primary geological development units. Based on the primary units, the hierarchical analysis method is used to further refine the division, and cluster analysis and other methods are combined to more accurately characterize the secondary geological development units. Compared with existing technologies, this application can comprehensively characterize the internal heterogeneity of the target development unit reservoir, ensuring that the nonlinear relationship between multiple parameters is reflected, and improving the scientific nature of development unit division and reservoir evaluation.

[0018] The method uses the impression method to restore sedimentary paleo-geomorphology and the principle of compensatory sedimentation to accurately calculate sediment thickness. This method also removes the interference of faults and folds on the landform, laying a scientific foundation for the division of primary geological development units. Effect: This method considers the control of sedimentary paleo-geomorphology on reservoirs, thereby improving the scientific nature of development unit division.

[0019] Through the division of primary and secondary geological development units, a refined delineation is performed based on sedimentary paleo-geomorphological characteristics and incorporating multiple parameters such as TOC, gas content, porosity, and clay mineral content. The primary unit division takes into account the differences between different geomorphological units, while the secondary unit division further refines the description of internal reservoir heterogeneity through cluster analysis and parameter weight classification. The result: The multi-level unit division method improves the accuracy of the primary and secondary development unit divisions, more comprehensively reflects the internal differences of deep shale reservoirs, and optimizes subsequent well location design and mining plans. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of seismic horizon interpretation for deep marine shale;

[0021] Figure 2 This is a schematic diagram of the sedimentary paleo-geomorphology restoration process;

[0022] Figure 3 It is the distribution characteristics of underwater sedimentary paleo-geomorphology;

[0023] Figure 4 It is a division map of the first-level geological development unit;

[0024] Figure 5 is the reservoir parameter correlation diagram;

[0025] Figure 6 is the correlation diagram between reservoir quality (RQ) and test production;

[0026] Figure 7 is the reservoir quality (RQ) contour map;

[0027] Figure 8 This is a secondary geological development unit map. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0029] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0030] The term "reservoir parameters" in this application is used to describe various physical and chemical indicators of rock characteristics and fluid behavior, such as porosity, permeability, water saturation, and mineral composition. These parameters are used to assess the storage capacity, fluid mobility, and potential production of a reservoir.

[0031] The first embodiment of the present application discloses a method for fine division of deep shale gas geological development units, including two-level geological development unit division, specifically:

[0032] Division of first-level geological development units:

[0033] Carry out paleo-geomorphological restoration on the target development unit and divide it into different geomorphological units. Compare the reservoir quality of different geomorphological units through reservoir parameter characteristics to achieve the first-level division of geomorphological units.

[0034] Secondary geological development unit division:

[0035] The correlation analysis between reservoir parameters and gas content was conducted on each geomorphological unit after the first level division to obtain the importance ranking of reservoir parameters. The weight of each reservoir parameter was determined by analytic hierarchy process, and the reservoir quality evaluation equation was obtained by fitting. The reservoir quality of each unit was calculated.

[0036] Based on K-Means cluster analysis and linear fitting equations, the reservoir quality division standards within each morphological unit are obtained, and the secondary division within the primary geomorphological development unit is achieved.

[0037] In this embodiment, the paleo-geomorphology restoration is completed by the impression method. This method is based on the principle of compensatory sedimentation. On the basis of determining the overlying marker layer, the thickness of the stratum between the marker layer and the reference surface is calculated to reflect the underwater paleo-geomorphology. The specific steps are as follows:

[0038] 1. First, based on the well-seismic calibration of the target development unit, a detailed interpretation of the horizons in the study area is conducted and a three-dimensional structural model of the study area is established.

[0039] 2. Comprehensively analyze the tectonic and sedimentary evolution history and select an isochronous interface across the entire area as a marker layer. The selection of a marker layer must adhere to three key principles: a stable isochronous interface across the entire area, a close proximity to the weathering crust, and an easily identifiable lithologic interface.

[0040] 3. Compaction correction is performed based on the lithology of different strata to restore the true thickness of the sediment at that time.

[0041] 4. Remove the impact of faults and folds on landform restoration by removing faults and folds.

[0042] 5. Finally, the final sedimentary paleo-geomorphological characteristics of the study area are obtained by integrating the regional sedimentary characteristics and combining them with the paleo-tectonic development characteristics.

[0043] In this embodiment, after paleo-geomorphological restoration, the morphology of the underwater paleo-geomorphology can be used to determine the source, transportation path, and sedimentation filling process of the sediments. Therefore, different underwater paleo-geomorphological units will lead to strong heterogeneity in the shale reservoir of the target development unit. Therefore, the underwater paleo-geomorphological unit can first be divided into different geomorphological units, including underwater uplifts, underwater slopes, and underwater depressions. Then, various reservoir parameters of each well in different geomorphological units are statistically analyzed, such as TOC, gas content, porosity, silica mineral content, clay mineral content, etc. By comparing the reservoir parameter data, the priority ranking of the three geomorphological units is derived based on the comparison results, which is the first-level geological development unit division. After the division is completed, a first-level development unit division map should be drawn.

[0044] It should be noted that after the first-level development unit division, due to the existence of reservoir heterogeneity within the same geomorphic unit, a more refined geological development unit division is required to achieve priority sorting within the same geomorphic unit. This is the second-level geological development unit division, specifically:

[0045] The correlation analysis between reservoir parameters and gas content was conducted on each first-level geomorphic unit to obtain the importance ranking of reservoir parameters.

[0046] Then, the analytic hierarchy process is used to determine the weights of the parameters of each geological sweet spot, and the reservoir quality evaluation equation is obtained by fitting, and the respective reservoir quality (RQ value) is calculated;

[0047] Based on K-Means cluster analysis and linear fitting equations, the reservoir quality division standards within each morphological unit are obtained, and the secondary division within the primary geomorphological development unit is achieved.

[0048] It should be noted that after obtaining the reservoir quality evaluation equation, it is also necessary to use the correlation between reservoir quality and the test production of each well to judge the rationality of the equation.

[0049] In a further embodiment, the steps of the AHP are as follows: 1. Define the problem and construct a hierarchical model (goal layer, criterion layer, solution layer); 2. Assign a weight to each pair of elements based on importance, and construct a judgment matrix based on the pairwise comparison results; 3. Determine the eigenvectors and eigenvalues of the judgment evidence through normalization and eigenvector calculation; 4. Perform a matrix consistency check. Generally, when the consistency ratio (CR) is less than 0.1, the judgment matrix has satisfactory consistency; 5. Calculate the comprehensive weight of each solution; 6. Ranking the comprehensive weights of each solution to obtain the optimal decision solution.

[0050] The present application will be described in more detail below with reference to specific embodiments.

[0051] Example 1 makes a detailed division of a deep geological shale gas development unit in the Sichuan Basin, as follows:

[0052] 1. Restoration of sedimentary paleo-geomorphology in target development units

[0053] like Figure 1 As shown in the (Schematic diagram of seismic horizon interpretation of deep marine shale), there is a large change in lithology between the bottom shale of the Wufeng Formation and the underlying limestone, and a large difference in wave impedance, which forms a strong wave peak reflection; the bottom of the Long-1-2 sub-member and the top of the Long-1 sub-member are the sequence interfaces of a secondary cycle, and there are continuous medium-strong wave peak reflections on the seismic reflection interface.

[0054] In addition, the Longmaxi Formation shale in the Sichuan Basin has the nature of compensatory deposition, that is, there is an uneven underwater uplift pattern during the deposition process, and the sediments in the low parts of the underwater landform are filled in the direction of the ancient uplift under the effect of filling and leveling.

[0055] Therefore, the impression method was used to complete the ancient landform restoration ( Figure 2 (Figure 3: Schematic diagram of the sedimentary paleogeomorphology restoration process). The isochronous datum was selected based on the following: 1) Within the paleogeomorphology restoration area, the late filling and leveling process of the Long-1-1 submember has been essentially completed; 2) This layer exhibits relatively isochronous characteristics; within the work area, the Long-1-2 submember and the Long-1 submember were deposited continuously and are stably distributed within the region.

[0056] 2. Division of first-level geological development units

[0057] According to the paleo-geomorphological characteristics, three geomorphological units are divided: underwater depression, underwater slope and underwater uplift. Figure 3.Distribution characteristics of underwater sedimentary paleogeomorphology, and statistical characteristics of reservoir parameters of different geomorphological units (as shown in Table 1). The TOC, gas content, porosity and other reservoir parameters of the slope are better than those of the underwater uplift and underwater depression. Therefore, it can be concluded that the reservoir quality is: underwater slope > underwater uplift > underwater depression. Therefore, the first-level geological development unit can be divided into categories I, II and III according to the underwater slope, underwater uplift and underwater depression, completing the first-level division of the geomorphological unit. After that, the paleogeomorphological map is used to draw the first-level geological development unit division map ( Figure 4 .First-level geological development unit division map).

[0058] Table 1 Statistical results of reservoir parameters in different geomorphologies

[0059]

[0060] 3. Division of secondary geological development units

[0061] (1) Count the parameters of each reservoir and make the corresponding correlation diagram ( Figure 5 Reservoir parameter correlation diagram. Porosity and gas content are highly positively correlated, TOC and gas content are weakly positively correlated, siliceous minerals are uncorrelated, and clay minerals are negatively correlated. Therefore, gas content, porosity, TOC, and clay minerals are preferred reservoir parameters for delineating secondary geological development units.

[0062] (2) Through the correlation diagram, the importance is obtained: A (gas content) > B (porosity) > C (TOC) > D (clay minerals), and the values 1, 3, 5, and 7 are assigned to them respectively, and the judgment matrix of the hierarchical analysis method is established (Table 2).

[0063] Table 2 Judgment Matrix

[0064]

[0065] After normalizing the matrix (Table 3).

[0066] Table 3 Normalized matrix

[0067]

[0068] After calculating the weights, the weight of A is (0.508+0.662+0.536+0.438) / 4=0.536; the weight of B is (0.169+0.221+0.321+0.313) / 4=0.256; the weight of C is (0.101+0.073+0.107+0.188) / 4=0.117; and the weight of D is (0.071+0.044+0.036+0.063) / 4=0.054.

[0069] Therefore, the equation is obtained: reservoir quality (RQ) = 0.536 × average gas content + 0.256 × average porosity + 0.117 × average TOC - 0.054 × clay minerals.

[0070] Finally, the matrix consistency judgment was completed, with the maximum eigenvalue λmax = 4.068, the consistency index CI = 0.0227, the random consistency index RI = 0.90, and the consistency ratio CR = 0.025. Since CR < 0.1, it shows that the matrix has satisfactory consistency.

[0071] 3. Calculate the RQ values of different wells and conduct correlation analysis between the RQ values and the test production of the corresponding wells ( Figure 6 Correlation diagram between reservoir quality (RQ) and test production. K-Means cluster analysis shows that the cluster mean for test production greater than 300,000 cubic meters is 5.3, with a linear fit intersection point at (4.71, 30); the cluster mean for test production greater than 200,000 cubic meters but less than 300,000 cubic meters is 3.51, with a linear fit equation of (3.57, 20); and the mean for test production less than 200,000 cubic meters is 2.71, with a linear fit intersection point at (3.57, 20). Based on this, a classification standard can be derived: RQ values greater than 5 are classified as Class 1, RQ values less than 5 but greater than 3.5 are classified as Class 2, and RQ values greater than 3.5 are classified as Class 3.

[0072] 4. Draw RQ contour map ( Figure 7 .Reservoir quality (RQ) contour map).

[0073] 5. Overlay the RQ contour map with the first-level geological development unit division map to divide the second-level geological development unit map ( Figure 8 . Secondary geological development unit map). Based on this, the study area is divided into 9 types of geological development units.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for fine division of deep shale gas geological development units, characterized in that: It includes two levels of geological development unit division, specifically: Division of first-level geological development units: Carry out paleo-geomorphological restoration on the target development unit and divide it into different geomorphological units. Compare the reservoir quality of different geomorphological units through reservoir parameter characteristics to achieve the first-level division of geomorphological units. Secondary geological development unit division: The correlation analysis between reservoir parameters and gas content was conducted on each geomorphological unit after the first level division to obtain the importance ranking of reservoir parameters. The weight of each reservoir parameter was determined by analytic hierarchy process, and the reservoir quality evaluation equation was obtained by fitting. The reservoir quality of each unit was calculated. Based on K-Means cluster analysis and linear fitting equations, the reservoir quality classification standards within each morphological unit are obtained to achieve secondary classification within the primary morphological development unit; The reservoir parameters include TOC, gas content, porosity, and clay mineral content.

2. The division method according to claim 1, characterized in that: The different landform units include underwater uplifts, underwater slopes, and underwater depressions.

3. The division method according to claim 1, characterized in that: After the secondary division, the process also includes drawing reservoir quality contour maps of each morphological unit and overlaying them with the primary development unit division map to achieve secondary refined division under the primary morphological unit division.

4. The division method according to claim 1, characterized in that: The hierarchical analysis method includes constructing a hierarchical structure model; assigning weights according to importance ranking and constructing a judgment matrix; normalizing and calculating characteristic vectors; and performing a one-time matrix test. Calculate the comprehensive weight; Six steps of comprehensive weight ranking.

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