Exploration method for restricted tidal flat facies carbonate gas reservoir

Abstract

The present application belongs to the technical field of oil and gas exploration, and particularly relates to a kind of exploration method of restricted tidal flat facies carbonate rock gas reservoir. Based on rock, logging data, seismic data, experimental test analysis data, through microfabric analysis, macro and micro combination approach, through rock fabric and mineral identification, restricted tidal flat facies rock development characteristics and regional scope are identified and defined; wherein the rock samples include pore development samples and samples with lithology of dark mudstone and argillaceous carbonate rock; frequency spectrum analysis method, weighted average method, organic matter mass balance method and coherent technology method are used to construct high-frequency sequence lithology-electricity interpretation model and multi-scale through-source fault transport pattern; thus, restricted tidal flat facies carbonate rock gas reservoir accumulation mode is obtained to explore restricted tidal flat facies carbonate rock gas reservoir. The present application innovatively explores restricted tidal flat facies carbonate rock gas reservoir, and solves the technical problems of identification and fine description of this type of gas reservoir.

Description

Technical Field

[0001] This invention relates to the field of oil and gas exploration technology, and in particular to an exploration method for confined tidal flat facies carbonate gas reservoirs. Background Technology

[0002] Carbonate reservoirs play a vital role in global oil and gas production. Statistics show that 60% of global oil and gas production comes from carbonate reservoirs. my country's marine carbonate strata cover an area of ​​300 × 10⁻⁶. 4 km 2 These reservoirs are mainly distributed within the three major craton basins of Sichuan Basin, Tarim Basin, and Ordos Basin in my country. Through continuous research and exploration, new large-scale oil and gas reservoirs have been discovered in the marine carbonate rock strata of these three basins, yielding fruitful oil and gas exploration results. Studies show that these reservoirs are mainly "reef-shoal type" reservoirs formed under high-energy sedimentary backgrounds and "karst type" reservoirs associated with weathering crusts, with numerous related research findings. However, there are fewer exploration results for "restricted tidal flat facies dolomite" oil and gas reservoirs formed under relatively low-energy sedimentary backgrounds, and no large-scale oil and gas fields have been discovered. The research level is also relatively low, resulting in a lack of research on identification techniques for this type of reservoir. As exploration continues to deepen, the effective identification and detailed characterization of restricted tidal flat facies carbonate rock gas reservoirs are crucial to the direction of oil and gas exploration and development. Therefore, it is urgent to solve the technical methods for identifying and detailed characterizing this type of reservoir to provide theoretical guidance and technical support for the next stage of exploration and development. Summary of the Invention

[0003] The purpose of this invention is to provide an exploration method for confined tidal flat facies carbonate gas reservoirs, addressing the technical problem of difficulty in identifying and finely characterizing such reservoirs in existing technologies.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] An exploration method for confined tidal flat facies carbonate gas reservoirs includes the following steps:

[0006] Step 1: Based on geological data, drilling data, logging data, and seismic data, the rock texture and minerals in the target study area are identified through microstructural analysis, using a combination of macroscopic and microscopic approaches. The development characteristics and regional range of the restricted tidal flat facies rocks are determined. The rock data includes samples with well-developed pores and samples with lithology of dark mudstone and argillaceous carbonate rocks. Among them, argillaceous carbonate rocks are mostly formed in restricted lacustrine facies, have an associated relationship with restricted tidal flat facies, have high organic matter abundance, constitute their own dominant source rocks, and are an important gas source for restricted tidal flat facies gas reservoirs.

[0007] Step 2: Using spectral analysis, weighted average method, organic matter mass balance method, and coherence technique, a high-frequency sequence lithology-electrical property interpretation model and a multi-scale source fault transport pattern are constructed.

[0008] Step 3: Based on the restricted tidal flat facies carbonate gas reservoir formation model obtained in Step 2, conduct restricted tidal flat facies carbonate gas reservoir exploration.

[0009] Muddy carbonate source rocks form in restricted lagoonal facies adjacent to restricted tidal flats. The relatively calm sedimentary waters of lagoons are conducive to the enrichment and preservation of organic matter, resulting in high organic matter abundance and making them important source rocks for gas reservoirs. Identifying restricted tidal flat carbonate gas reservoirs requires accurate identification of the lithofacies assemblages using sedimentary characteristics to overcome discrepancies in facies sequence identification and sedimentary facies classification. Based on accurate identification of the lithofacies assemblages, the use of spectral analysis, weighted average methods, organic matter mass balance methods, and coherence techniques not only ensures the reliability of the data results but also allows for the acquisition of multiple attribute data, enabling cross-validation and data verification of the conclusions.

[0010] Accurate identification is based on a comprehensive assessment of lithofacies. For tidal flat facies, the prominent sedimentary characteristics can be summarized as follows:

[0011] (1) It has a herringbone cross-bedding and a re-acting surface that are completely opposite to the direction of water flow.

[0012] (2) Flattened bedding, wavy bedding and lenticular bedding are well developed, reflecting the alternation of strong and weak water flow.

[0013] (3) It has signs of intermittent terrestrial exposure such as dry cracks, rain marks, plant root traces, animal footprints, evaporites, peat and thin coal seams.

[0014] (4) The alternating exposure and deposition of waterway scouring, muddy fragments and winnowed sandy lenses are signs of this.

[0015] If a sedimentary profile contains all of the aforementioned structural combinations or the first three characteristics, then it can be interpreted as a tidal flat.

[0016] As a preferred embodiment of the present invention, step 1, identifying and defining the development characteristics and regional extent of the confined tidal flat facies rocks, includes the following steps:

[0017] Step 101: Select wells with high core integrity from the target study area, conduct core observation and detailed recording, and take samples according to the designed test items of rock mineral identification, rock property analysis and source rock analysis, and sampling requirements of exploration well geological test analysis items. For key rock types and oil and gas-bearing layers, increase the sampling density and prioritize the preparation of thin sections. The sampling density shall not be less than 3 samples / m.

[0018] Step 102: Based on the rock thin sections in Step 101, combined with the macroscopic characteristics of the core, and in accordance with the classification and naming principles of carbonate rocks, the rock texture and minerals are identified and named, special sedimentary structures are described, and the rock physical properties, total organic carbon content, and vitrinite reflectance of the selected rock samples are analyzed.

[0019] Step 103: Based on rock type and special sedimentary structures, and combined with the criteria for sedimentary facies classification, the sedimentary facies of the study area are classified, the sedimentary environment is analyzed, the restricted tidal flat facies of the target study area are identified, the development characteristics and regional range of the restricted tidal flat facies rocks are determined, and their identification marks are summarized.

[0020] Physical property analysis yields rock porosity and permeability. Porosity, the ratio of pore volume to surface volume, is a crucial indicator for calculating reserves and evaluating reservoir characteristics. Rock permeability, the ability of a rock to allow fluids to pass through under pressure differential, is a parameter characterizing the rock's liquid conductivity and representing its permeability. Total organic carbon (TOC) content refers to the mass of organic carbon per unit mass of rock, usually expressed as a mass fraction (%). It is the most important indicator for evaluating the abundance of organic matter in source rocks, indicating the richness of organic matter in the source rocks and determining oil and gas generation efficiency to calculate oil and gas production. Vitrin reflectance analysis is the most important indicator of organic matter maturity and is used to calibrate the thermal evolution of organic matter from early diagenesis to deep metamorphic stages, determining the maturity of kerogen.

[0021] As a preferred embodiment of the present invention, in step 2, a high-frequency sequence identification model is constructed using spectral analysis; the specific steps are as follows:

[0022] Step 201: Based on the vertical development characteristics of the single-well core obtained in Step 1, analyze the development characteristics of the single-well sequence interface and lithological combination, summarize the high-frequency sequence structure type, combine the relationship between rock-electrical curves, select gamma and sonic logging electrical curves, and then use the spectrum analysis method to construct a high-frequency sequence identification model.

[0023] Preferably, the thickness of the high-frequency sequence is typically less than 4m.

[0024] Step 202: Based on the high-frequency sequence structure type, combined with the microscopic characteristics of the rock under a microscope and the rock physical property analysis data, clarify the pore type and vertical distribution characteristics of the reservoir, and conduct a detailed quantitative evaluation of the reservoir according to the relationship between the porosity and permeability of the reservoir and with reference to the oil and gas reservoir evaluation method (SY / T 6285-2011).

[0025] Step 203: Based on the total organic carbon content (TOC, %) and maturity (R) of the regional potential source rock in Step 102. O Based on the analysis of data (%), and referring to the geochemical evaluation method for source rocks (SY / T 5735-2019), the lower limit of total organic carbon content (TOC,%) for different types of effective source rocks was determined, and the grade of different types of source rocks was quantitatively evaluated.

[0026] Step 204: Analyze the rock type of the source rock, combine the relationship between the rock and electrical properties curves, clarify the corresponding relationship between the source rock lithology and well logging data, construct a lithology-electrical property interpretation model for the source rock, and correct it using known well source rock data to ensure the feasibility and accuracy of the lithology-electrical property interpretation model.

[0027] As a preferred technical solution of the present invention

[0028] The process also includes step 205, which involves identifying source rocks in the study area based on a lithological-electrical interpretation model of the source rocks, calculating the cumulative thickness of source rocks in individual wells, and determining the TOC using a weighted average method. 平均 ;

[0029] Step 206: Based on the organic matter mass balance method, the hydrocarbon generation intensity calculation formula in the source rock geochemical evaluation method (SY / T 5735-2019) is used to determine the parameters involved in the formula in combination with basic data and existing research results. The hydrocarbon generation intensity of the source rock is calculated, and then a planar distribution map of the hydrocarbon generation intensity of the source rock is drawn. The planar distribution characteristics of the source rock are analyzed to clarify the hydrocarbon supply conditions of the confined tidal flat carbonate reservoir.

[0030] As a preferred technical solution of the present invention:

[0031]

[0032] Among them, TOC n Indicates the total organic matter content of a single well section;

[0033] H n Indicates the thickness of the source rock in a single well section;

[0034] D g =H×ρ×TOC×P gmax ×T rg ×10-6 Equation 2

[0035] Among them, D g Indicates the intensity of anger.

[0036] H represents the thickness of the source rock.

[0037] ρ represents the density of the source rock.

[0038] TOC indicates the abundance of organic matter in source rocks.

[0039] P gmax Indicates the maximum potential for life.

[0040] T rg This indicates the gas conversion rate.

[0041] As a preferred embodiment of the present invention, in step 207...

[0042] Based on the 3D seismic data in step 1, the regional structures are interpreted to clarify the major structural combinations and relationships. Coherence techniques are used to finely characterize small faults and fractures in the study area using the maximum positive curvature attribute, and their combination relationship with regional structures is analyzed. Based on the distribution characteristics of source rocks, a multi-scale source-fault transport pattern is established.

[0043] As a preferred technical solution of the present invention, in step 3, the rock type, high-frequency sequence structure type, hydrocarbon generation intensity of source rocks, and source-transmission fault pattern of steps 1-2 are comprehensively analyzed to determine the reservoir formation characteristics of confined tidal flat facies carbonate gas reservoirs, clarify the geological conditions for natural gas reservoir formation, establish identification criteria for the formation of confined tidal flat facies carbonate gas reservoirs, and thus achieve accurate identification and detailed characterization of this type of gas reservoir, providing data support for the prediction of favorable oil and gas areas in confined tidal flat facies carbonate rocks. The above-mentioned reservoir formation characteristics, reservoir formation geological conditions, and identification criteria are used as exploration basis for the exploration of confined tidal flat facies carbonate gas reservoirs.

[0044] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0045] 1. In the technical solution of this invention, based on multi-type data such as rock, well logging data, seismic data, and experimental test analysis results, the rock texture and minerals are identified using microstructural analysis and macro-micro combined techniques. The development characteristics and regional range of restricted tidal flat facies rocks are determined and defined. The high-frequency sequence lithology-electrical interpretation model and multi-scale source fault transport patterns are constructed by successively employing spectral analysis, weighted average method, organic matter mass balance method, and coherence technology. This enables accurate identification and detailed characterization of restricted tidal flat facies carbonate gas reservoirs and provides support for predicting favorable oil and gas areas in restricted tidal flat facies carbonate rocks.

[0046] 2. Based on the full utilization of basic data, the technical solution of this invention employs a variety of technical means to clarify the sedimentary-tectonic development characteristics of confined tidal flat facies carbonate gas reservoirs, enabling accurate identification and detailed characterization of this type of gas reservoir. This not only deepens the understanding of the source-reservoir configuration relationship of confined tidal flat facies carbonate gas reservoirs, but also provides a reference for the exploration, development, and production enhancement of gas reservoirs under similar geological backgrounds, thereby reducing the overall exploration risk of gas reservoirs and improving the economic benefits of development. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of the steps of the present invention;

[0048] Figure 2 A high-frequency hierarchical sequence identification marker model;

[0049] Figure 3 A lithological-electrical interpretation model for the reservoir;

[0050] Figure 4 A planar distribution map of the hydrocarbon generation intensity of its own carbonate source rocks;

[0051] Figure 5 This is a planar distribution map of the hydrocarbon generation intensity of the underlying mudstone source rock;

[0052] Figure 6 For analyzing the distribution of fracture development zones using the seismic curvature method;

[0053] Figure 7 This represents a multi-scale channel-source fracture transport pattern. Detailed Implementation

[0054] The present invention will now be described in detail with reference to the accompanying drawings.

[0055] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0056] Example 1

[0057] This embodiment takes the Leikoupo Formation of the Middle Triassic in the western depression of the Sichuan Basin as the research object and summarizes the characteristic accumulation features of confined tidal flat carbonate gas reservoirs. The research results show that confined tidal flat carbonate gas reservoirs have the following characteristic accumulation features: (1) In terms of reservoirs, in addition to conventional crystalline dolomite, confined tidal flat carbonate reservoirs also develop large-scale microbial dolomite, and the microbial rocks contribute greatly to the reservoirs; the reservoirs are characterized by thin thickness, multiple superpositions, and stable lateral distribution. (2) In terms of hydrocarbon sources, the Leikoupo Formation can form effective source rocks of carbonate rocks with good organic matter type and high hydrocarbon generation potential under confined evaporation environment, and supply hydrocarbons to the Leikoupo Formation reservoir itself, while regional accumulation of hydrocarbons from multiple sources is still the basis. (3) In terms of oil and gas migration and accumulation, the Leikoupo Formation reservoir is closely associated with tight gypsum rocks, and the micro-fractures within the formation can serve as an effective hydrocarbon source transport system, but regional accumulation of hydrocarbons from connecting fractures is the key.

[0058] The technical solution of the present invention is combined with Figure 1-7 Step 1: Based on geological data, drilling data, logging data and seismic data, through microstructure analysis, combining macro and micro approaches, the rock structure and minerals in the target study area are identified, and the development characteristics and regional range of the limited tidal flat facies rocks are determined.

[0059] In this study area, regarding reservoir rock types, confined tidal flat facies carbonate reservoirs, in addition to conventional crystalline dolomite, also exhibit large-scale microbial dolomite. Therefore, microbial rocks contribute significantly to the reservoir composition. This is a typical difference between relatively low-energy confined tidal flat facies reservoirs and "reef-shoal" and weathering crust-related "karst" reservoirs formed under high-energy sedimentary backgrounds. Details are shown in Table 1 below.

[0060] Table 1: Statistical Table of Different Lithological Properties in the Upper Subsection of Lei 4 in the Western Sichuan Gas Field

[0061]

[0062] Specifically, step 1, identifying and defining the development characteristics and regional extent of the limited tidal flat facies rocks, includes the following steps:

[0063] Step 101: Select wells with high core integrity from the target study area, conduct core observation and detailed recording, and take samples according to the designed test items of rock mineral identification, rock property analysis and source rock analysis, and sampling requirements of exploration well geological test analysis items. For key rock types and oil and gas-bearing layers, increase the sampling density and prioritize the preparation of thin sections. The sampling density shall not be less than 3 samples / m.

[0064] Step 102: Based on the rock thin sections in Step 101, combined with the macroscopic characteristics of the core, and in accordance with the classification and naming principles of carbonate rocks, the rock texture and minerals are identified and named, special sedimentary structures are described, and the rock physical properties, total organic carbon content, and vitrinite reflectance of the selected rock samples are analyzed.

[0065] Step 103: Based on rock type and special sedimentary structures, and combined with the criteria for sedimentary facies classification, the sedimentary facies of the study area are classified, the sedimentary environment is analyzed, the restricted tidal flat facies of the target study area are identified, the development characteristics and regional range of the restricted tidal flat facies rocks are determined, and their identification marks are summarized.

[0066] In step 2, a high-frequency sequence identification model is constructed using spectral analysis (e.g., Figure 2 (As shown); the specific steps are as follows:

[0067] Step 201: Based on the vertical development characteristics of the single-well core obtained in Step 1, analyze the development characteristics of the single-well sequence interface and lithological assemblage, summarize the high-frequency sequence structure types, and combine the relationship between rock-electrical logging curves to select gamma and sonic logging electrical logging curves. Then, use spectral analysis to construct a high-frequency sequence identification model. Preferably, in the high-frequency sequence, the fifth-order sequence range is 3-4m.

[0068] Through field outcrops, well cores, and thin section analysis, it was found that various rock types developed in the upper sub-member of Lei 4 in western Sichuan. Multiple high-frequency cyclic lithological transformation surfaces could be identified. Based on the analysis and research of single-well sequence interfaces and lithological combinations, a total of 12 types of high-frequency sequence structures with upward shallowing were summarized in the upper sub-member of Lei 4: (1) microcrystalline dolomite-argillaceous dolomite, (2) dissolution-porous algal dolomite-argillaceous dissolution-porous dolomite, (3) algal limestone-algal sandstone-argillaceous algal sandstone, (4) microcrystalline dolomite-microcrystalline dolomite-algal-veined algal dolomite, (5) argillaceous microcrystalline dolomite-dissolution-porous algal dolomite-algal-veined dolomite, (6) (7) Dolomitic limestone-porosity algae-muddy algae-porosity microcrystalline dolomite, (8) Dolomitic limestone-lime dolomite-algae-veined dolomite, (9) Microcrystalline dolomite-dolomite-algae sandstone dolomite, (10) Microcrystalline dolomite-porosity algae-muddy ...

[0069] Step 202: Based on the high-frequency sequence stratigraphy type, combined with microscopic features of the rock and rock physical property analysis data, clarify the pore type and vertical distribution characteristics of the reservoir. Based on the porosity-permeability relationship of the reservoir, and referring to the oil and gas reservoir evaluation method (SY / T 6285-2011), conduct a refined quantitative evaluation of the reservoir and construct a lithological-electrical property interpretation model for the reservoir, such as... Figure 3 As shown.

[0070] Step 203: Based on the total organic carbon content (TOC, %) and maturity (R) of the regional potential source rock in Step 102 O Based on the analysis of data (%), and referring to the geochemical evaluation method for source rocks (SY / T 5735-2019), the lower limit of total organic carbon content (TOC,%) of different types of effective source rocks was determined, and the grade of different types of source rocks was quantitatively evaluated and subdivided into four categories: non-source rocks, general source rocks, good source rocks, and high-quality source rocks.

[0071] Step 204: Analyze the rock type of the source rock, combine the relationship between the rock and electrical properties curves to clarify the correspondence between the source rock lithology and well logging data, construct a lithology-electrical property interpretation model for the source rock, and correct it using known well source rock data to ensure the feasibility and accuracy of the lithology-electrical property interpretation model.

[0072] In step 205, based on the lithological-electrical interpretation model of source rocks, source rocks in the study area are identified, the cumulative thickness of source rocks in single wells is calculated, and the weighted average method is used to determine the TOC (Total Organic Carbon). 平均 ;

[0073] Step 206: Based on the organic matter mass balance method, using the hydrocarbon generation intensity calculation formula in the source rock geochemical evaluation method (SY / T 5735-2019), combined with basic data and existing research results, determine the parameters involved in the formula, calculate the hydrocarbon generation intensity of the source rock, and then draw a planar distribution map of the hydrocarbon generation intensity of the source rock, analyze the planar distribution characteristics of the source rock, and clarify the hydrocarbon supply conditions of the confined tidal flat carbonate reservoir; such as Figure 4-5 As shown.

[0074] Specifically,

[0075] Among them, TOC n Indicates the total organic matter content of a single well section;

[0076] H n Indicates the thickness of the source rock in a single well section, in meters (m).

[0077] D g =H×ρ×TOC×P gmax ×T rg ×10-6 Equation 2

[0078] Among them, D g Indicates the intensity of anger, 10 8 m 3 / km 2 ;

[0079] H represents the thickness of the source rock, in meters;

[0080] ρ represents the density of the source rock, t / m³ 3 ;

[0081] TOC indicates the abundance of organic matter in source rocks, in %;

[0082] P gmax The maximum potential for life is represented by m. 3 / t;

[0083] T rg This indicates the gas conversion rate.

[0084] In step 207, based on the 3D seismic data from step 1, the regional structures are interpreted to clarify the major structural combinations and relationships; coherence techniques are used, and the maximum positive curvature attribute is employed to finely characterize small faults and fractures within the study area, analyzing their combination relationships with the regional structures; such as Figure 6 The image shows the distribution of fracture zones in the Leikoupo Formation of the Western Sichuan Depression (analyzed by seismic curvature method). Due to the confined tidal flat facies carbonate gas reservoirs' limited evaporation depositional environment, reservoir development is typically associated with thick, dense gypsum rocks. For the source rocks of the Leikoupo Formation to successfully break through the multiple gypsum rock layers and form reservoirs, the development of micro-fractures within the formation is crucial. Predicting the distribution of network fractures within the Leikoupo Formation using the maximum positive curvature attribute at the top of the formation reveals highly developed network fractures, consistent with the fractured core and fractured characteristics of the Leikoupo Formation. Furthermore, the frequent occurrence of pump stalling and stuck drill pipe due to wellbore instability during drilling further supports the evidence of highly developed small faults and fractures within the Leikoupo Formation.

[0085] Based on the distribution characteristics of source rocks, a multi-scale source-fault transport model is established. For example... Figure 7As shown, regional hydrocarbon accumulation is based on multiple sources of hydrocarbon supply. Therefore, besides the microfractures within the formation serving as an effective hydrocarbon transport system, the efficient transport system of the Permian source rocks will be crucial for regional hydrocarbon accumulation. Thick strata such as the Feixianguan Formation and Jialingjiang Formation develop above the Permian, containing numerous tight mudstone and gypsum strata. Therefore, the main vertical migration channel for natural gas is the fault structures that deeply incise into the Permian. Currently discovered gas reservoirs in the Sichuan West Gas Field, the Majing Structure, and the Xinchang Leikoupo Formation all have fault structures deeply incising into the Permian around their traps, thus providing natural gas migration channels for these reservoirs. For migration channels composed of faults, there are two types: one is a direct source fault formed by the fault cutting through the Leikoupo Formation and the Permian; the other is a "relay" fault migration system composed of faults that cut through the Permian but do not extend to the Leikoupo Formation and internal faults within the Leikoupo Formation.

[0086] In step 3, by integrating the rock types, high-frequency sequence structure types, hydrocarbon generation intensity of source rocks, and source-transmission fault patterns from steps 1 and 2, the reservoir formation characteristics of confined tidal flat facies carbonate gas reservoirs are analyzed, the geological conditions for natural gas accumulation are clarified, and identification criteria for the formation of confined tidal flat facies carbonate gas reservoirs are established. This enables accurate identification and detailed characterization of this type of gas reservoir, providing data support for predicting favorable oil and gas areas in confined tidal flat facies carbonate rocks. The above-mentioned reservoir formation characteristics, geological conditions, and identification criteria are used as the basis for exploration work on confined tidal flat facies carbonate gas reservoirs.

[0087] The above research leads to the following conclusion: confined tidal flat carbonate rocks can form large-scale gas fields. Compared with "reef-shoal" oil and gas reservoirs formed in high-energy sedimentary backgrounds and "karst" oil and gas reservoirs associated with weathering crusts, confined tidal flat carbonate gas reservoirs have unique characteristics in terms of reservoir, hydrocarbon source, and oil and gas migration and accumulation.

[0088] In terms of reservoirs, in addition to conventional crystalline dolomite, large-scale microbial dolomite is also developed in confined tidal flat carbonate reservoirs, and microbial rocks contribute a great deal to the reservoirs; the reservoirs are characterized by thin thickness, multiple superpositions, and stable lateral distribution.

[0089] In terms of hydrocarbon sources, under limited evaporation conditions, the Leikoupo Formation can form effective source rocks of carbonate rocks with good organic matter type and high hydrocarbon generation potential, and supply hydrocarbons to the Leikoupo Formation's own reservoirs. However, regional hydrocarbon accumulation from multiple sources remains the foundation.

[0090] In terms of oil and gas migration and accumulation, the Leikoupo Formation reservoir is closely associated with tight gypsum rocks. Micro-fractures within the formation can serve as an effective transport system for its own hydrocarbon sources, but regional hydrocarbon accumulation and source-connecting faults are key.

[0091] In the technical solution of this invention, based on full utilization of basic data, various technical means are employed to clarify the sedimentary-tectonic development characteristics of confined tidal flat facies carbonate gas reservoirs, thereby achieving accurate identification and detailed characterization of the formation of this type of gas reservoir. This not only deepens the understanding of the source-reservoir configuration relationship of confined tidal flat facies carbonate gas reservoirs, but also provides a reference for the exploration, development, and production enhancement of gas reservoirs under similar geological backgrounds, thereby reducing the overall exploration risk of gas reservoirs and improving the economic benefits of development.

[0092] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for exploring confined tidal flat facies carbonate gas reservoirs, characterized in that, Includes the following steps: Step 1: Based on geological data, drilling data, logging data, and seismic data, the rock texture and minerals in the target study area are identified through microstructural analysis, using a combination of macroscopic and microscopic approaches. The development characteristics and regional extent of the localized tidal flat facies rocks are determined. The rock data includes samples with well-developed pores and samples with lithology of dark mudstone and argillaceous carbonate rocks. Step 2: Using spectral analysis, weighted average method, organic matter mass balance method, and coherence technique, construct a lithological-electrical interpretation model of high-frequency sequence stratigraphy and a multi-scale source fault transport pattern; the specific steps are as follows: Step 201: Construct a high-frequency sequence identification model using spectral analysis; Based on the vertical development characteristics of single-well cores obtained in Step 1, analyze the development characteristics of single-well sequence interfaces and lithological combinations, summarize the high-frequency sequence structure types, combine the relationship between rock-electrical curves, select gamma and sonic logging electrical curves, and then use spectral analysis to construct a high-frequency sequence identification model, including a reservoir lithology-electrical interpretation model and a source rock lithology-electrical interpretation model; Step 202: Construct the lithology-electrical property identification model of the reservoir: Based on the high-frequency sequence structure type, combined with the microscopic characteristics of the rock under the microscope and the rock physical property analysis data, clarify the pore type and vertical distribution characteristics of the reservoir, and according to the relationship between the porosity and permeability of the reservoir, refer to the oil and gas reservoir evaluation method to conduct a fine quantitative evaluation of the reservoir; Step 203: Constructing a lithological-electrical interpretation model for source rocks: based on the total organic carbon (TOC) content and maturity (R) in regional potential source rocks. O By analyzing the data and referring to the geochemical evaluation method for source rocks, the lower limit of total organic carbon content for different types of effective source rocks was determined, and the grade of different types of source rocks was quantitatively evaluated. Step 204: Analyze the rock type of the source rock, combine the relationship between rock-electrical properties curves to clarify the correspondence between the source rock lithology and well logging data, construct a lithology-electrical properties interpretation model for the source rock, and correct it using known well source rock data; The establishment of the transmission pattern of a source fault includes the following steps: In step 205, based on the lithological-electrical interpretation model of source rocks, source rocks in the study area are identified, the cumulative thickness of source rocks in single wells is calculated, and the weighted average method is used to determine the TOC average. Step 206: Based on the organic matter mass balance method, the hydrocarbon generation intensity of the source rock is calculated using the hydrocarbon generation intensity calculation formula in the source rock geochemical evaluation method. Then, a planar distribution map of the hydrocarbon generation intensity of the source rock is drawn, the planar distribution characteristics of the source rock are analyzed, and the hydrocarbon supply conditions of the confined tidal flat carbonate reservoir are clarified. Step 207: Based on the 3D seismic data in Step 1, interpret the regional structures, clarify the major structural combinations and relationships; select coherence techniques and utilize the maximum positive curvature attribute to finely characterize the small faults and fractures in the study area, and analyze their combination relationship with the regional structures; establish multi-scale source fault transport patterns based on the distribution characteristics of source rocks. Step 3: Based on the reservoir formation model of confined tidal flat facies carbonate gas reservoir obtained in Step 2, subsequent exploration operations for confined tidal flat facies carbonate gas reservoirs will be carried out. In Step 3, the reservoir formation characteristics of confined tidal flat facies carbonate gas reservoirs will be analyzed by comprehensively considering the rock type, high-frequency sequence structure type, hydrocarbon generation intensity of source rocks, and source-transmission fault patterns obtained in Steps 1 and 2. The geological conditions for natural gas accumulation will be clarified, identification criteria for the formation of confined tidal flat facies carbonate gas reservoirs will be established, and the accurate identification and detailed characterization of the gas reservoir will be completed. Then, the above-mentioned reservoir formation characteristics, geological conditions, and identification criteria will be used as the basis for exploration to carry out exploration work for confined tidal flat facies carbonate gas reservoirs.

2. The exploration method for confined tidal flat facies carbonate gas reservoirs according to claim 1, characterized in that, Step 1, identifying and defining the development characteristics and regional extent of the restricted tidal flat facies rocks, includes the following steps: Step 101: Select wells with high core integrity from the target study area, conduct core observation and recording, and take samples. For key rock types and oil and gas-bearing layers, increase the sampling density and prioritize the preparation of thin sections. The sampling density shall not be less than 3 samples / m. Step 102: Based on the rock thin sections in Step 101, combined with the macroscopic characteristics of the core, the rock fabric and minerals are identified and named, special sedimentary structures are described, and the rock physical properties, total organic carbon content and vitrinite reflectance in the selected rock samples are analyzed. Step 103: Based on rock type and special sedimentary structures, and combined with the criteria for sedimentary facies classification, the sedimentary facies of the study area are classified, the sedimentary environment is analyzed, the restricted tidal flat facies of the target study area are identified, the development characteristics and regional range of the restricted tidal flat facies rocks are determined, and their identification marks are summarized.

3. The exploration method for confined tidal flat facies carbonate gas reservoirs according to claim 1, characterized in that, The weighted average method is calculated using the following formula: Formula 1; in, TOC i H represents the total organic matter content of the i-th well section; i This represents the thickness of the source rock in the i-th well section; i = 1 - n, where n is the total number of well sections; Hydrocarbon generation intensity is calculated using Equation 2: Formula 2; Among them, D g The expression represents hydrocarbon generation intensity, H represents source rock thickness, ρ represents source rock density, TOC represents source rock organic matter abundance, and P represents the hydrocarbon generation intensity. gmax T represents the maximum hydrocarbon generation potential. rg This indicates the gas conversion rate.

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