Deep shale gas geological development unit fine division method

Abstract

The invention belongs to the field of geological development, and particularly relates to a deep shale gas geological development unit fine division method. The sedimentary ancient landform is recovered by integrating multi-source data, and multi-level unit division is performed in combination with multiple analysis methods. On the basis of restoration of sedimentary ancient landforms, ancient landform features are reconstructed through an impression method, and a basis is provided for division of first-level geological development units; on the basis of the first-level unit, the analytic hierarchy process is used for further detailed division, and a second-level geological development unit is depicted more finely in combination with methods such as clustering analysis; compared with the prior art, the method has the advantages that the heterogeneity in the reservoir of the target development unit can be comprehensively described, the non-linear relationship among multiple parameters is ensured to be embodied, and the scientificity of development unit division and reservoir evaluation is improved.

Description

Technical Field

[0001] 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. Background Art

[0002] China has rich reserves of unconventional oil and gas resources, and the exploration and development of unconventional oil and gas resources has become an important task to cope with the huge energy demand in the future. In recent years, the shallow shale gas in the Sichuan Basin has achieved large-scale commercial development in the depth blocks within 3,500 meters in Fuling, Changning, Weiyuan and Zhaotong. However, in order to meet the growing energy demand, deep shale gas with a depth of more than 3,500 meters with huge potential is gradually becoming a key area for China's natural gas exploration and development.

[0003] Deep shale formations are characterized by long geological age, strong heterogeneity, great burial depth, high degree of thermal evolution, complex tectonic history, differential enrichment of shale gas, and diverse preservation conditions. Most deep shale reservoirs have undergone multiple stages of tectonic transformation, showing special reservoir properties, complex occurrence mechanisms, and significant differences in gas content. Therefore, fine division of geological development units is the key to achieving efficient development of deep shale gas.

[0004] However, most existing shale geological evaluation technologies only focus on "geological sweet spots" 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 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 represented by the weight of the shale formation 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 the heterogeneity of the reservoir; at the same time, this technology mainly relies on the correlation between geological sweet spot parameters and gas production, ignores the differences in reservoirs in different geological environments, and is difficult to fully reflect the spatial heterogeneity of reservoirs; and the sweet spot coefficient calculation of this technology is based on a simple linear combination, ignoring the nonlinear relationship and interaction between multiple parameters, making it difficult to fully reflect the reservoir characteristics; and in the process of selecting and determining the weights of 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 solve the shortcomings of the existing technology and proposes a method for fine division of deep shale gas geological development units. It restores sedimentary paleo-geomorphology by integrating multi-source data and combines multiple analysis methods to perform multi-level unit division. Based on the restoration of sedimentary paleo-geomorphology, the paleo-geomorphological characteristics are reconstructed through the impression 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 the second-level geological development unit is more finely characterized by combining methods such as cluster analysis.

[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 geomorphic unit after the first-level division, and the importance ranking of reservoir parameters was obtained. Then, the weight of each reservoir parameter was determined by analytic hierarchy process to obtain the reservoir quality evaluation equation, and 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 to achieve secondary division within the primary geomorphological development unit.

[0013] Furthermore, the different geomorphic 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 analytic hierarchy process includes six steps: constructing a hierarchical model, assigning weights according to importance ranking, constructing a judgment matrix, normalizing and calculating eigenvectors, one-time matrix testing, calculating comprehensive weights, and ranking comprehensive weights.

[0017] The beneficial effects of the present invention are as follows: the present application restores sedimentary paleo-geomorphology by integrating multi-source data, and performs multi-level unit division in combination with a variety of analysis methods. Based on the restoration of sedimentary paleo-geomorphology, the paleo-geomorphological features are reconstructed by the impression method to provide a basis for the division of primary geological development units; on the basis of the primary units, the hierarchical analysis method is used to further refine the division, and the secondary geological development units are more finely characterized by combining methods such as cluster analysis; compared with the prior art, 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.

[0018] The impression method is used to restore the sedimentary paleo-geomorphology, the compensation sedimentation principle is used to accurately calculate the sedimentary thickness, and the interference of faults and folds on the landform is removed, laying a scientific foundation for the division of the first-level geological development unit. Effect: The present invention takes into account the control of sedimentary paleo-geomorphology on the reservoir, thereby improving the scientific nature of the division of development units.

[0019] Through the division of primary and secondary geological development units, based on the characteristics of sedimentary paleo-geomorphology, combined with multiple parameters such as TOC, gas content, porosity, and clay mineral content, a refined division is carried out. The primary unit division takes into account the differences between different geomorphological units, and the secondary unit further refines the description of the internal heterogeneity of the reservoir through cluster analysis and parameter weight classification. Effect: The multi-level unit division method improves the accuracy of the primary and secondary development unit division, more comprehensively reflects the internal differences of deep shale reservoirs, and optimizes the subsequent well location design and mining plan. 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 map of the division of the first-level geological development units;

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

[0025] Figure 6 It 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 the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0029] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below in conjunction with 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 evaluate the storage capacity, fluid mobility, and potential production of the 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 geomorphic unit after the first-level division, and the importance ranking of reservoir parameters was obtained. Then, the weight of each reservoir parameter was determined by analytic hierarchy process to obtain the reservoir quality evaluation equation, and 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 to achieve secondary division within the primary geomorphological development unit.

[0037] In this embodiment, the ancient landform 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 ancient landform morphology. The specific steps are:

[0038] 1. First, based on the well-seismic calibration of the target development unit, the strata in the study area are finely interpreted and a three-dimensional structural model of the study area is established.

[0039] 2. Comprehensively analyze the structural and sedimentary evolution history, select the isochronous interface of the whole area, and use this interface as the marker layer. The selection of the marker layer must have three principles: isochronous surfaces that are stably distributed throughout the whole area, close to the weathering crust, and easy to identify the lithological interface.

[0040] 3. Compaction correction is carried out through the lithology of different strata to restore the actual thickness of the sediments 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 characteristics of the sedimentary paleo-geomorphology of the study area are obtained by integrating the regional sedimentary characteristics and combining them with the characteristics of paleo-tectonic development.

[0043] In this embodiment, after paleo-geomorphology restoration, the source, transportation path and sedimentation filling process of the sediments can be judged by the morphology of underwater paleo-geomorphology. Therefore, different underwater paleo-geomorphological units will lead to strong heterogeneity of the shale reservoir of the target development unit. Therefore, the underwater paleo-geomorphological unit can 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 counted, such as TOC, gas content, porosity, siliceous mineral content, clay mineral content, etc. By comparing the reservoir parameter data, the priority ranking of the three geomorphological units is obtained according to 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 primary development unit division, due to the reservoir heterogeneity within the same geomorphic unit, a more refined geological development unit division is needed to achieve the priority sorting within the same geomorphic unit. This is the secondary geological development unit division, specifically:

[0045] The correlation analysis between reservoir parameters and gas content was conducted on each geomorphic unit after the first-level division, and the importance ranking of reservoir parameters was obtained;

[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 to achieve secondary division within the primary geomorphological development unit.

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

[0049] In a further implementation, the steps of the hierarchical analysis method are: 1. clarify the problem and construct a hierarchical model (target layer, criterion layer, solution layer); 2. assign a weight to each pair of elements according to importance, and construct a judgment matrix according to the results of pairwise comparison; 3. obtain the eigenvector and eigenvalue of the judgment evidence through normalization and calculation of eigenvectors; 4. complete the matrix consistency test. 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. sort the comprehensive weight of each solution to obtain the optimal decision solution.

[0050] The present application is described in more detail below in conjunction with specific embodiments.

[0051] Example 1 A detailed division is made for a deep geological shale gas development unit in the Sichuan Basin, as follows:

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

[0053] like Figure 1 As shown in (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-12 submember and the top of the Long-1 submember are the sequence interface 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 sedimentation, that is, there is an uneven underwater uplift pattern during the sedimentation process, and the sediments in the low parts of the underwater landform are filled up towards the ancient uplift due to the effect of filling and leveling.

[0055] Therefore, the impression method is used to complete the ancient landform restoration ( Figure 2 : Schematic diagram of the process of sedimentary paleogeomorphology restoration). The basis for selecting the isochronous datum is as follows: 1) Within the paleogeomorphology restoration area, the late stage of the Long-1 sub-member has basically completed the filling and filling process; 2) This layer has the characteristics of relative isochrony. In the work area, the Long-1-2 sub-member and the Long-1 sub-member are deposited continuously and are stably distributed in the area.

[0056] 2. Division of primary 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 paleo-geomorphology, 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 underwater uplifts and underwater depressions. Therefore, it can be concluded that the reservoir quality is: underwater slopes> underwater uplifts> underwater depressions. Therefore, the first-level geological development unit division can be divided into categories I, II, and III according to underwater slopes, underwater uplifts, and underwater depressions, completing the first-level division of geomorphological units, and then the paleo-geomorphological 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 is highly positively correlated with gas content, TOC is weakly positively correlated with gas content, siliceous minerals are uncorrelated with gas content, and clay minerals are negatively correlated with gas content. Therefore, gas content, porosity, TOC, and clay minerals are preferred as reservoir parameters for the division of 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; 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 means 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). Through K-Means cluster analysis, the cluster mean of test production greater than 300,000 cubic meters is 5.3, and the linear fitting intersection is (4.71, 30); the cluster mean of test production greater than 200,000 cubic meters and less than 300,000 cubic meters is 3.51, and the linear fitting equation is (3.57, 20); the mean of test production less than 200,000 cubic meters is 2.71, and the linear fitting intersection is (3.57, 20). Based on this, a classification standard can be obtained, RQ values ​​greater than 5 are classified as Class 1, RQ values ​​less than 5 and 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 aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not make the essence of the corresponding technical solutions 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 geomorphic unit after the first-level division, and the importance ranking of reservoir parameters was obtained. Then, the weight of each reservoir parameter was determined by analytic hierarchy process to obtain the reservoir quality evaluation equation, and the reservoir quality of each unit was calculated. Based on K-Means cluster analysis and linear fitting equations, the reservoir quality division standards within each morphological unit are obtained to achieve secondary division within the primary geomorphological development unit.

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

3. The division method according to claim 1, characterized in that: The reservoir parameters include TOC, gas content, porosity, and clay mineral content.

4. 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 geomorphological unit division.

5. The division method according to claim 1, characterized in that: The analytic hierarchy process includes six steps: constructing a hierarchical model, assigning weights according to importance ranking, constructing a judgment matrix, normalizing and calculating eigenvectors, one-time matrix inspection, calculating comprehensive weights, and ranking comprehensive weights.

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