A method for determining whether a siliceous shale is a fossilized product of a deep-water microbial mat

Abstract

This invention provides a method for determining whether siliceous shale is a petrification product of deep-sea microbial mats. The method includes: determining whether the target siliceous shale possesses at least one of characteristics 1-3; if so, it is a petrification product of deep-sea microbial mats. Characteristic 1: A dominant rock microdomain of Class I, with Class II and III rock microdomains scattered within Class I; Characteristic 2: A rock skeleton composed of aggregates of porous micro- to nano-quartz particles, with organic matter rich in honeycomb nanopores distributed within the rock skeleton; Characteristic 3: A rock skeleton dominated by aggregates of porous micro- to nano-quartz particles, containing non-porous micron-sized quartz particles and a composite of porous nano-quartz particles and clay on its surface, exhibiting Class II rock microdomains. If the siliceous shale is a petrification product of deep-sea microbial mats, it indicates that the area where the siliceous shale is located is a shale gas sweet spot with high exploration and development potential.

Description

Technical Field

[0001] This invention relates to a method for determining whether siliceous shale is a petrification product of deep-sea microbial mats. Background Technology

[0002] Shale gas reservoirs exhibit diverse lithofacies types, including siliceous shale, carbonate shale, clayey shale, and mixed shale. Among these, siliceous shale is the dominant lithofacies type in the sweet spot region of shale gas. Exploration and development have confirmed that shale gas production from horizontal wells in siliceous shale varies significantly. This is manifested in the lack of a correlation between siliceous shale thickness and gas production, substantial differences in gas production among adjacent wells with similar siliceous shale thickness, and inconsistent production characteristics across large-scale gas fields. These phenomena indicate substantial differences in the petrological characteristics of siliceous shale, which is considered a high-quality reservoir. Current research on shale gas reservoirs primarily focuses on shale lithofacies classification and the description of petrological characteristics and sedimentary environment analysis of different lithofacies, lacking research on the petrological characterization and sedimentary environment analysis of siliceous shale with different petrological characteristics. Currently, there is an urgent need to conduct petrological characterization studies on siliceous shale with different petrological characteristics, clarify the distribution patterns and ranges of siliceous shale with different petrological characteristics, identify the petrological characteristics of siliceous shale as high-quality reservoirs, and select sweet spots for shale gas, thereby achieving efficient exploration and development of shale gas.

[0003] Currently, the lithofacies classification and petrological characterization of shale generally rely on whole-rock analysis data and total organic carbon (TOC) test data, while the analysis of sedimentary environments depends on inorganic geochemical test data. Research results using these analytical data as evidence indicate that organic-rich shale, including siliceous shale, is a product of still water, stratified, deep-water, anoxic environments. Regarding siliceous shale, current research suggests that the silica and organic matter mainly originate from silica-rich and carbohydrate-rich microorganisms in the sea surface. After the silica-rich microorganisms die, they settle to the anoxic deep-water seabed, forming biomass silica detritus in the sediments. After the carbohydrate-rich microorganisms die, they settle to the anoxic deep-water seabed, forming the organic matter portion of the sediments. Biomass silica and organic matter together constitute the main body of deep-water sediments—siliceous mud. Through burial and diagenesis, the siliceous mud solidifies into siliceous shale. However, whole-rock analysis methods cannot capture the occurrence state information of minerals such as quartz, calcite, dolomite, and clay, and total organic carbon testing methods cannot observe the occurrence state information of organic matter. Their analytical test results only obtain the mineral types and contents that make up the shale and the organic matter content, resulting in a flattened understanding of shale lithofacies, including siliceous shale. It is difficult to obtain key information reflecting siliceous shale with different petrological characteristics, and it is even more impossible to achieve sedimentary environment analysis of siliceous shale with different petrological characteristics.

[0004] Petrological characterization is the primary data source for studying the characteristics of oil and gas reservoirs. The interpretation of other data, such as whole-rock analysis data, total organic carbon (TOC) test data, and inorganic geochemical test data, must conform to the results of petrological characterization. Combining macroscopic scales (outcrops, drill cores, hand specimens, etc.) with microscopic scales (optical microscopy, electron microscopy, etc.) is a commonly used and effective method for analyzing the petrological characteristics of coarse-grained clastic rocks. However, due to the fine grain size and high organic matter content of shale, these methods are difficult to apply to analyzing the petrological characteristics of shale. Based on this, argon ion polishing (argon ion polishing) and MAPS (Magnetic Parametric Analysis) techniques have been developed for the petrological characterization of shale. However, due to the diversity and complexity of the mineral and organic matter occurrence states in shale, current research using argon ion polishing and MAPS techniques mainly focuses on the description of organic pores and organic matter in shale, and has not yet systematically conducted petrological characterization of shale, let alone petrological characterization of siliceous shale with different petrological characteristics.

[0005] In summary, further research is needed on the petrological characteristics of siliceous shale that can serve as high-quality reservoirs to facilitate the identification of shale gas sweet spots and thus achieve efficient exploration and development of shale gas. Summary of the Invention

[0006] The purpose of this invention is to provide a technical solution that can determine whether siliceous shale can serve as a high-quality reservoir, thereby promoting the identification of sweet spots for shale gas and achieving efficient exploration and development of shale gas.

[0007] To achieve the above objectives, the present invention provides a method for determining whether siliceous shale is a petrification product of deep-water microbial mats. If the siliceous shale is a petrification product of deep-water microbial mats, it indicates that the area where the siliceous shale is located is a sweet spot for shale gas and has high exploration and development potential.

[0008] Specifically, this invention provides a method for determining whether siliceous shale is a petrification product of deep-sea microbial mats, comprising:

[0009] Obtain the target siliceous shale; wherein the target siliceous shale has a quartz content of more than 80% by mass, a clay content of not less than 1% by mass, and a total organic carbon content of more than 4% by mass;

[0010] Determine whether the target siliceous shale possesses at least one of the three characteristics: characteristic 1, characteristic 2, and characteristic 3.

[0011] Feature 1: Category I rock microdomains dominate (over 90% of the rock volume), while Category II and Category III rock microdomains are scattered within Category I. The petrological characteristics of Category I rock microdomains are that quartz accounts for over 70% of the microdomain volume, while calcite and dolomite account for no more than 20%. Quartz, calcite, and dolomite together form the rock framework, with honeycomb-like nanoporous organic matter occupying the space within the rock framework. The petrological characteristics of Category II rock microdomains are nearly horizontally distributed clay bands, where "nearly horizontal" refers to an inclination angle not exceeding 30°. These clay bands contain no organic matter and contain calcite particles, dolomite particles, and micron-sized non-porous quartz particles. Category III rock microdomains exhibit branched distribution of non-porous organic matter, which contains platy clay with flow characteristics (i.e., parallel to the branches).

[0012] Feature 2: The rock skeleton of siliceous shale is composed of aggregates of porous micro-nano quartz particles, with organic matter rich in honeycomb nanopores distributed between the rock skeletons.

[0013] Feature 3: The rock skeleton of siliceous shale is dominated by aggregates of porous micro-nano quartz particles. The volume ratio of the aggregates of porous micro-nano quartz particles in the rock skeleton is more than 75%. It also contains non-porous micron-sized quartz particles and composites of porous nano-sized quartz particles and clay located on the surface of non-porous micron-sized quartz particles. It belongs to the Class II rock micro-domain.

[0014] If the target siliceous shale exhibits at least one of the three characteristics (characteristic 1, characteristic 2, and characteristic 3), then the target siliceous shale is a petrified product of deep-sea microbial mats.

[0015] The inventors of this invention, through analysis and characterization of the petrological characteristics of siliceous shale, discovered that siliceous shale, as a lithification product of deep-sea microbial mats, possesses high exploration and development potential. At least one of the three characteristics—characteristic 1, characteristic 2, and characteristic 3—can effectively characterize siliceous shale as a lithification product of deep-sea microbial mats. Specifically, regarding characteristics 1, 2, and 3:

[0016] Feature 1: The presence of Class I rock microdomains (accounting for more than 90% of the rock volume), Class II rock microdomains, and Class III rock microdomains scattered within Class I rock microdomains is a typical petrological feature of microbial mat lithification of siliceous shale formed by deep-water traction flow altering argillaceous sediments. This indicates that the siliceous shale is a lithification product of deep-water microbial mats.

[0017] Feature 2: The rock skeleton of the siliceous shale is composed of aggregates of porous micro-nano quartz particles, and organic matter with rich honeycomb nanopores is distributed between the rock skeleton, indicating that this siliceous shale is a petrified product of deep-sea microbial mats.

[0018] Feature 3: In siliceous shale where the rock skeleton is dominated by aggregates of porous micro-nano quartz particles (accounting for more than 75% by volume), non-porous micron-sized quartz particles and the composite of porous nano-sized quartz particles and clay on the surface of non-porous micron-sized quartz particles, as well as the Class II rock microdomains, are two basic petrological markers for identifying siliceous shale as a product of microbial mat lithification formed during the process of deep-water traction flow altering argillaceous sediments. This indicates that such siliceous shale is a product of deep-water microbial mat lithification.

[0019] According to a preferred embodiment of the method for determining whether siliceous shale is a petrification product of deep-sea microbial mats, obtaining the target siliceous shale includes:

[0020] Whole-rock analysis and total organic carbon testing were performed on the siliceous shale to be tested to determine the mass content of quartz, clay, and total organic carbon in the siliceous shale.

[0021] If the quartz content of the siliceous shale to be tested is higher than 80%, the clay content is not less than 1%, and the total organic carbon content is higher than 4%, then the siliceous shale to be tested will be used as the target siliceous shale.

[0022] According to a preferred embodiment of the method for determining whether siliceous shale is a petrification product of deep-sea microbial mats, determining whether the target siliceous shale possesses at least one of the three characteristics: characteristic 1, characteristic 2, and characteristic 3 includes:

[0023] Argon-ion polished discs of the target siliceous shale were prepared using the target siliceous shale core.

[0024] MAPS rock image data of argon-ion polished sections of the target siliceous shale were acquired;

[0025] Based on the MAPS rock image data of the argon-ion polished section of the target siliceous shale, observe whether the target siliceous shale has at least one of the three features: feature 1, feature 2, and feature 3.

[0026] More preferably, the resolution of the MAPS rock image data volume of the argon-ion polished slide of the target siliceous shale is 4-10 nm.

[0027] More preferably, the length of the argon-ion polishing disc for the target siliceous shale is 0.8-2 cm;

[0028] More preferably, the width of the argon-ion polishing sheet for the target siliceous shale is 0.8-2 cm;

[0029] More preferably, the thickness of the argon-ion polishing sheet for the target siliceous shale is 0.3-0.8 cm (e.g., 0.5 cm);

[0030] More preferably, the polished surface of the argon-ion polishing disc of the target siliceous shale is parallel to the cylindrical surface of the target siliceous shale core;

[0031] More preferably, the acquisition of MAPS rock image data volume of argon-ion polished sheet of target siliceous shale includes: selecting an area with a length and width not exceeding 400 μm on the polished surface of argon-ion polished sheet of target siliceous shale, and acquiring MAPS rock image data volume;

[0032] More preferably, during the acquisition of MAPS rock image data volumes from argon-ion polished discs of the target siliceous shale, the top surface of the argon-ion polished disc of the target siliceous shale is located above the field of view, and the bottom surface of the argon-ion polished disc of the target siliceous shale is located below the field of view, thereby ensuring that all phenomena observed in the acquired MAPS rock image data volumes are merely magnifications of natural phenomena.

[0033] More preferably, in the process of observing whether the target siliceous shale has at least one of the three features (feature 1, feature 2, and feature 3) based on the MAPS rock image data volume of the acquired argon-ion polished slide of the target siliceous shale, the MAPS rock image data volume is observed on a computer using an image editor (e.g., the offline image editor ATLASTM BROWSER-BASED VIEWER).

[0034] According to a preferred embodiment of the method for determining whether siliceous shale is a lithological product of deep-sea microbial mats, wherein, in feature 1, category I rock microdomains include 6 types of rock microdomains:

[0035] Type I1 rock microdomains are aggregates of porous nano-quartz particles;

[0036] Type I2 rock microdomains are aggregates of porous micron-sized quartz particles;

[0037] The rock microdomains of type I3 ​​consist of non-porous micron-sized quartz particles and a composite of porous nano-sized quartz particles and clay located on the surface of the non-porous micron-sized quartz particles.

[0038] Type I4 rock microdomains consist of irregular calcite particles and the filling material in their dissolution pores;

[0039] Category I5 rock microdomains consist of dolomite with a rhombic morphology and the filling material in its dissolution pores;

[0040] I6 type rock microdomains are organic matter with rich honeycomb nanopores;

[0041] More preferably, Class I4 rock microdomains include at least one of the following four subclasses of rock microdomains:

[0042] Ⅰ4 1The subclass of rock microdomains consists of aggregates of porous nano-quartz particles filling the calcite dissolution pores.

[0043] Ⅰ4 2 The subclass of rock microdomains consists of aggregates of porous micron-sized quartz particles that fill the calcite dissolution pores.

[0044] Ⅰ4 3 The subclass of rocks consists of organic matter with honeycomb-like nanopores filling the calcite dissolution pores.

[0045] Ⅰ4 4 The subclass of rocks consists of calcite-dissolved pores filled with non-porous organic matter.

[0046] More preferably, Class I5 rock microdomains include at least one of the following four subclasses of rock microdomains:

[0047] Ⅰ5 1 The subclass of rock microdomains consists of aggregates of porous nano-quartz particles filling the dissolution pores of dolomite.

[0048] Ⅰ5 2 The subclass of rock microdomains consists of aggregates of porous micron-sized quartz particles filling the dissolution pores of dolomite.

[0049] Ⅰ5 3 The subclass of rocks consists of organic matter with rich honeycomb-like nanopores filling the dissolution pores of dolomite;

[0050] Ⅰ5 4 The subclass of rocks consists of dolomite dissolution pores filled with non-porous organic matter.

[0051] The technical solution provided by this invention enables the determination of whether siliceous shale is a lithification product of deep-water microbial mats by characterizing its petrological features. If the siliceous shale is indeed a lithification product of deep-water microbial mats, it indicates that the area where the siliceous shale is located is a shale gas sweet spot with high exploration and development potential. The technical solution provided by this invention helps to optimize the distribution range of siliceous shale formed by the lithification of deep-water microbial mats, promotes the identification of shale gas sweet spots, and thus guides the efficient exploration and development of shale gas. The proposed technical solution of this invention breaks through the bottleneck in the study of deep-water shale sedimentary environments and contributes to the development of deep-water sedimentology. Attached Figure Description

[0052] Figure 1 This is an observation diagram of the MAPS rock image data volume in the image editor in Embodiment 1 of the present invention.

[0053] Figure 2 This is an observation diagram of the MAPS rock image data volume in the image editor in Embodiment 2 of the present invention.

[0054] Figure 3This is an observation diagram of the MAPS rock image data volume in the image editor in Embodiment 3 of the present invention. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. Here, the illustrative embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention.

[0056] Shale is primarily composed of quartz, feldspar, calcite, dolomite, pyrite, clay, and organic matter. Rigid particles such as quartz, feldspar, calcite, dolomite, and pyrite form the rock framework, while plastic components, clay minerals and organic matter, are distributed among these framework minerals. The clay mineral content varies greatly, ranging from a few percent to over 50%, resulting in significant variations in shale's resistance to compaction. The organic matter is bitumen, a product of the thermal evolution of sedimentary organic matter through stages such as kerogen, pre-oil bitumen, solid bitumen, and petroleum. Both solid bitumen and petroleum are completely converted into bitumen. Bitumen-modified solid bitumen exhibits honeycomb-like nanopores, while bitumen-modified petroleum lacks porosity. Shale framework particles with low clay mineral content have strong resistance to compaction, while the organic matter bears limited pressure from the overlying strata. The honeycomb-rich bitumen-modified solid bitumen and the non-porous bitumen-modified petroleum each retain their original state. Shales with high clay mineral content have weak resistance to compaction. Organic matter and clay minerals bear the pressure from the overlying strata, causing the nanopores in the asphalt to collapse and disappear, resulting in asphalt and petroleum having similar morphological characteristics and being difficult to distinguish. It is precisely because of the influence of compaction that the occurrence state of asphalt is diverse and complex, leading to a lack of systematic characterization of shale petrology at present.

[0057] To minimize the interference of compaction, the systematic characterization of shale petrology needs to be implemented in at least three stages. The first stage involves characterizing shale with low clay mineral content, low compaction intensity, and high organic matter content, analyzing its petrological characteristics, and identifying the depositional environment. Once the first stage is completed, the second stage begins. The second stage involves characterizing shale with moderate clay mineral content and moderate compaction, analyzing its petrological characteristics, and identifying the depositional environment. Once the second stage is completed, the third stage begins. The third stage involves characterizing shale with high clay mineral content and strong compaction, analyzing its petrological characteristics, and identifying the depositional environment. Only by completing these three stages—where the results of the first stage constrain the results of the second stage, and vice versa—can the interference of compaction be truly eliminated, enabling a systematic characterization of shale petrological characteristics and analysis of the depositional environment.

[0058] Deep-water sedimentary environments mainly include still-water physicochemical sedimentary environments, deep-water gravity flow sedimentary environments, and deep-water traction flow sedimentary environments, corresponding to still-water physicochemical sedimentation, deep-water gravity flow sedimentation, and deep-water traction flow sedimentation, respectively. Currently, it is generally believed that coarse-grained clastic rocks formed in deep-water environments are deep-water gravity flow and deep-water traction flow sedimentations, while fine-grained clastic rocks rich in organic matter (shale) are formed by still-water physicochemical sedimentation. The main basis for the assertion that deep-water shale forms in still-water physicochemical sedimentary environments is inorganic geochemical testing data, but this data is highly ambiguous.

[0059] The inventors of this invention have pioneered the characterization and analysis of shale petrological features. By completing only the first stage of systematic characterization and analysis of shale petrological features, they have been able to characterize the petrological features of a siliceous shale suitable for high-quality reservoirs. Furthermore, by analyzing the petrological features of this siliceous shale, they have determined that it is a petrified product of deep-water microbial mats, and that the formation of these mats is closely related to deep-water traction flow deposition. Based on this, this invention provides a method for determining whether siliceous shale is a petrified product of deep-water microbial mats. If the siliceous shale is indeed a petrified product of deep-water microbial mats, it indicates that the area where the siliceous shale is located is a shale gas sweet spot with high exploration and development potential. The proposed technical solution of this invention will help promote the identification of shale gas sweet spots, thereby achieving efficient exploration and development of shale gas.

[0060] In one specific embodiment, the method for determining whether siliceous shale is a petrification product of deep-sea microbial mats provided by the present invention includes:

[0061] Obtain the target siliceous shale; wherein the target siliceous shale has a quartz content of more than 80% by mass, a clay content of not less than 1% by mass, and a total organic carbon content of more than 4% by mass;

[0062] Determine whether the target siliceous shale possesses at least one of the three characteristics: characteristic 1, characteristic 2, and characteristic 3.

[0063] Feature 1: Category I rock microdomains account for more than 90% of the rock volume, while Category II and Category III rock microdomains are scattered within Category I rock microdomains;

[0064] The petrological characteristics of the rock microdomains of Class I are that quartz accounts for more than 70% of the volume of the microdomain, while calcite and dolomite do not exceed 20% of the volume of the microdomain. Quartz, calcite and dolomite together constitute the rock skeleton, and organic matter rich in honeycomb nanopores occupies the space of the rock skeleton.

[0065] The petrological characteristics of the rock microdomains of Class II are nearly horizontally distributed clay bands, where nearly horizontal means the dip angle does not exceed 30°. There is no organic matter in the clay bands, but calcite grains, dolomite grains and micron-sized non-porous quartz grains are developed.

[0066] The Class III rock microdomains are characterized by a branched distribution of non-porous organic matter, which contains flaky clay with flow characteristics (i.e. parallel to the branches).

[0067] Feature 2: The rock skeleton of siliceous shale is composed of aggregates of porous micro-nano quartz particles, with organic matter rich in honeycomb nanopores distributed between the rock skeletons.

[0068] Feature 3: The rock skeleton of siliceous shale is dominated by aggregates of porous micro-nano quartz particles. The volume ratio of the aggregates of porous micro-nano quartz particles in the rock skeleton is more than 75%. It also contains non-porous micron-sized quartz particles and composites of porous nano-sized quartz particles and clay located on the surface of non-porous micron-sized quartz particles. It belongs to the Class II rock micro-domain.

[0069] If the target siliceous shale exhibits at least one of the three characteristics (characteristic 1, characteristic 2, and characteristic 3), then the target siliceous shale is a petrified product of deep-sea microbial mats.

[0070] The inventors of this invention, through analysis and characterization of the petrological characteristics of siliceous shale, discovered that siliceous shale, as a lithification product of deep-sea microbial mats, possesses high exploration and development potential. At least one of the three characteristics—characteristic 1, characteristic 2, and characteristic 3—can effectively characterize siliceous shale as a lithification product of deep-sea microbial mats. Specifically, regarding characteristics 1, 2, and 3:

[0071] Feature 1: The dominant rock microdomains of Class I (more than 90% of the rock volume), with Class II and Class III rock microdomains scattered within Class I rock microdomains, are typical petrological features of microbial mat lithification of siliceous shale formed by deep-water traction flow altering argillaceous sediments. This indicates that the siliceous shale is a lithification product of deep-water microbial mats.

[0072] Feature 2: The rock skeleton of the siliceous shale is composed of aggregates of porous micro-nano quartz particles, and organic matter with rich honeycomb nanopores is distributed between the rock skeleton, indicating that this siliceous shale is a petrified product of deep-sea microbial mats.

[0073] Feature 3: In siliceous shale where the rock skeleton is dominated by aggregates of porous micro-nano quartz particles (accounting for more than 75% by volume), non-porous micron-sized quartz particles and the composite of porous nano-sized quartz particles and clay on the surface of non-porous micron-sized quartz particles, as well as the Class II rock microdomains, are two basic petrological markers for identifying siliceous shale as a product of microbial mat lithification formed during the process of deep-water traction flow altering argillaceous sediments. This indicates that such siliceous shale is a product of deep-water microbial mat lithification.

[0074] Further, the target siliceous shale was obtained, including:

[0075] Whole-rock analysis and total organic carbon testing were performed on the siliceous shale to be tested to determine the mass content of quartz, clay, and total organic carbon in the siliceous shale.

[0076] If the quartz content of the siliceous shale to be tested is higher than 80%, the clay content is not less than 1%, and the total organic carbon content is higher than 4%, then the siliceous shale to be tested will be used as the target siliceous shale.

[0077] Furthermore, determining whether the target siliceous shale possesses at least one of the three characteristics: characteristic 1, characteristic 2, and characteristic 3 includes:

[0078] Argon-ion polished discs of the target siliceous shale were prepared using the target siliceous shale core.

[0079] MAPS rock image data of argon-ion polished sections of the target siliceous shale were acquired;

[0080] Based on the MAPS rock image data of the argon-ion polished section of the target siliceous shale, observe whether the target siliceous shale has at least one of the three features: feature 1, feature 2, and feature 3.

[0081] Furthermore, the resolution of the MAPS rock image data volume of the argon-ion polished slides of the target siliceous shale is 4nm-10nm.

[0082] Furthermore, the length of the argon-ion polished sheet for the target siliceous shale is 0.8cm-2cm;

[0083] Furthermore, the width of the argon-ion polished sheet for the target siliceous shale is 0.8cm-2cm;

[0084] Furthermore, the thickness of the argon-ion polished sheet for the target siliceous shale is 0.3cm-0.8cm;

[0085] Furthermore, the polished surface of the argon-ion polishing disc of the target siliceous shale is parallel to the cylindrical surface of the target siliceous shale core;

[0086] Furthermore, the acquisition of MAPS rock image data from the argon-ion polished sheet of the target siliceous shale includes: selecting an area with a length and width not exceeding 400 μm on the polished surface of the argon-ion polished sheet of the target siliceous shale, and acquiring the MAPS rock image data.

[0087] Furthermore, during the acquisition of MAPS rock image data volumes from argon-ion polished discs of the target siliceous shale, the top surface of the argon-ion polished discs of the target siliceous shale is positioned above the field of view, and the bottom surface of the argon-ion polished discs of the target siliceous shale is positioned below the field of view, thereby ensuring that all phenomena observed in the acquired MAPS rock image data volumes are merely magnifications of natural phenomena.

[0088] Furthermore, based on the MAPS rock image data of the acquired argon-ion polished sections of the target siliceous shale, in the process of observing whether the target siliceous shale possesses at least one of the three features (feature 1, feature 2, and feature 3), an image editor (e.g., the offline image editor ATLAS) is used. TM The BROWSER-BASED VIEWER allows users to view MAPS rock image data volumes on a computer.

[0089] Furthermore, in Feature 1, Category I rock microdomains include six types of rock microdomains:

[0090] Type I1 rock microdomains are aggregates of porous nano-quartz particles;

[0091] Type I2 rock microdomains are aggregates of porous micron-sized quartz particles;

[0092] The rock microdomains of type I3 ​​consist of non-porous micron-sized quartz particles and a composite of porous nano-sized quartz particles and clay located on the surface of the non-porous micron-sized quartz particles.

[0093] Type I4 rock microdomains consist of irregular calcite particles and the filling material in their dissolution pores;

[0094] Category I5 rock microdomains consist of dolomite with a rhombic morphology and the filling material in its dissolution pores;

[0095] I6 type rock microdomains are organic matter with rich honeycomb nanopores;

[0096] Furthermore, Class I4 rock microdomains include at least one of the following four subclasses of rock microdomains:

[0097] Ⅰ4 1 The subclass of rock microdomains consists of aggregates of porous nano-quartz particles filling the calcite dissolution pores.

[0098] Ⅰ4 2 The subclass of rock microdomains consists of aggregates of porous micron-sized quartz particles that fill the calcite dissolution pores.

[0099] Ⅰ4 3 The subclass of rocks consists of organic matter with honeycomb-like nanopores filling the calcite dissolution pores.

[0100] Ⅰ44 The subclass of rocks consists of calcite-dissolved pores filled with non-porous organic matter.

[0101] Furthermore, Class I5 rock microdomains include at least one of the following four subclasses of rock microdomains:

[0102] Ⅰ5 1 The subclass of rock microdomains consists of aggregates of porous nano-quartz particles filling the dissolution pores of dolomite.

[0103] Ⅰ5 2 The subclass of rock microdomains consists of aggregates of porous micron-sized quartz particles filling the dissolution pores of dolomite.

[0104] Ⅰ5 3 The subclass of rocks consists of organic matter with rich honeycomb-like nanopores filling the dissolution pores of dolomite;

[0105] Ⅰ5 4 The subclass of rocks consists of dolomite dissolution pores filled with non-porous organic matter.

[0106] The rock framework of siliceous shale is composed of quartz grains, exhibiting strong resistance to compaction. The overlying strata have limited compaction effect on organic matter. The organic matter, rich in honeycomb-like nanopores, is asphalt-refined solid bitumen, while the non-porous organic matter is asphalt-refined petroleum. Specifically: rock microdomains of type I6 are asphalt-refined solid bitumen, and type I4... 3 Subclass rock microdomains and I5 3 The organic matter in the subclass rock microdomains is asphalt-refined solid bitumen, and the microdomains of Class III rocks are dendritic asphalt-refined petroleum. 4 Subclass rock microdomains and I5 4 The organic matter in the subclass rock microdomains is asphalt-refined petroleum.

[0107] Combining the thermal evolution of sedimentary organic matter into hydrocarbon generation and pore formation processes, the asphalt-based solid bitumen in the microdomains of rock type I6 occupies the positions of sedimentary organic matter and pre-oil bitumen filling the primary pores, while type I4 3 Subclass rock microdomains and I5 3 In subclass rock microdomains, the asphalt-based solid bitumen occupies the positions of sedimentary organic matter or pre-oil bitumen. In Class III rock microdomains, the branched asphalt is formed by petrothermal evolution filling hydrocarbon-generating pressure fractures. (I4) 4 Subclass rock microdomains and I5 4 In the subclass rock microdomains, the petroleum-filled dissolution pores are formed by the dissolution of carbonates by organic acids.

[0108] The skeletons of siliceous organisms, through dissolution and precipitation reactions, eventually transform into porous quartz with enlarged secondary quartz margins. Specifically: Type I1 rock microdomains contain porous nano-quartz particle aggregates, which are fossils of nano-siliceous microbial mats; Type I2 rock microdomains contain porous micron-sized quartz particle aggregates, which are fossils of micron-sized siliceous microbial mats; Type I3 ​​rock microdomains contain non-porous micron-sized quartz particles, which are terrigenous clastic materials; Type I4… 1 Subclass rock microdomains and I5 1 The aggregates of porous nano-quartz particles in the subclass rock microdomains are fossils of nano-siliceous microbial mats, I4 2 Subclass rock microdomains and I5 2 The aggregates of porous micron-sized quartz particles in the subclass rock microdomains are fossils of micron-sized siliceous microbial mats.

[0109] In the Class I3 rock microdomains, the clay on the surface of the non-porous micron-sized terrigenous quartz clasts was analyzed to be residual clay resulting from re-modification after terrigenous quartz deposition; the modified sediments were clayey sediments containing terrigenous quartz. The aggregates of porous nano-quartz particles on the surface of the terrigenous clasts were fossils of nano-siliceous microbial mats. In contrast to the Class I4 and I5 rock microdomains, which remained in a relatively open environment undergoing intense dissolution and filling of dissolution pores with different materials, the carbonate mineral particles in the Class II rock microdomains lacked dissolution pores, and the dolomite maintained a complete rhomboid morphology, indicating that the clayey bands remained in a closed state. Integrating the analytical results of each rock microdomain, it is believed that the siliceous shale exhibiting these petrological characteristics is a petrified product of microbial mats formed during the modification of argillaceous sediments by deep-water traction currents.

[0110] The deposition process of deep-sea microbial mats can be divided into three stages: the first deposition stage is the formation stage of nano-silica microbial mats, the second deposition stage is the formation stage of micron-silica microbial mats, and the third deposition stage is the formation stage of carbohydrate-rich microbial mats.

[0111] Deep-water traction currents possess the ability to erode and modify sediments, washing away muddy sediments and transporting clay, but they cannot transport calcite, dolomite, or micron-sized terrigenous quartz particles, leaving these large particles in situ. As a result, the muddy sediments transform into flocculated material with labyrinthine water flow channels. Deep-water traction currents bring oxygen and nutrients, leading to the flourishing of siliceous microorganisms. To resist water erosion and adapt to the environment, these microorganisms are small, live in colonies, and mostly attach to the surfaces of mineral particles or in carbonate dissolution pores. With the continued activity of the deep-water traction current, most clay minerals are carried away, leaving only large particles such as calcite, dolomite, and terrigenous quartz, and a small amount of unmodified or weakly modified banded muddy sediments. During this stage, the water is clean, oxygen and nutrients are abundant, and the water flow speed slows down. Siliceous microorganisms increase in size, live in colonies, and attach to nano-siliceous microbial mats. Next, the overgrowth of micron-sized silica-forming microorganisms led to obstructed water flow channels and insufficient oxygen and nutrients. This environment was no longer suitable for the growth of silica-forming microorganisms, and they were replaced by carbohydrate-rich microorganisms that occupied the space left by the silica-forming microorganisms. During the deposition process, it was not uncommon for clay to adhere to the surface of terrigenous quartz particles and fail to be removed. The environment was under CCD conditions, resulting in intense dissolution of carbonate minerals. In the first deposition stage, the carbonate dissolution pores were filled with nano-sized silica-forming microorganisms; in the second deposition stage, the dissolution pores were filled with micron-sized silica-forming microorganisms; and in the third deposition stage, the dissolution pores were filled with carbohydrate-rich microorganisms.

[0112] The diagenetic process of microbial mats is divided into four stages: shallow burial diagenesis stage, early diagenesis stage of medium burial, late diagenesis stage of medium burial, and deep burial diagenesis stage.

[0113] During the shallow burial diagenesis stage, sedimentary organic matter composed of carbohydrate-rich microbial remains is transformed into kerogen through condensation reactions.

[0114] In the early diagenetic stage of intermediate burial, kerogen is completely transformed into pre-oil bitumen. The volume of kerogen expanding during the pre-oil bitumen formation fills the space of all biomass silica skeletons and fills the carbonate dissolution pores.

[0115] During the late diagenetic stage of intermediate burial, pre-oil bitumen is transformed into solid bitumen and petroleum, expanding in volume. The petroleum fills the carbonate dissolution pores and generates hydrocarbon-generating pressure fractures, which serve as channels for the initial migration of petroleum.

[0116] During the deep-buried diagenesis stage, solid bitumen and petroleum are transformed into tar pitch and generate natural gas. Among them, tar pitch solid bitumen develops honeycomb-like nanopores, while tar pitch petroleum lacks pores. The honeycomb-like organic pores of tar pitch solid bitumen store natural gas and become an effective part of shale gas reservoirs, while the non-porous tar pitch petroleum is an ineffective reservoir part.

[0117] During burial and diagenesis, biomass silica transforms into porous quartz, nano-silica microorganisms transform into porous nano-quartz particles, and nano-silica microbial mats transform into porous nano-quartz particle aggregates; micron-silica microorganisms transform into porous micron-quartz particles, and micron-silica microbial mats transform into porous micron-quartz particle aggregates. These quartz states fuse together to form the rock skeleton of siliceous shale, effectively protecting organic matter from compaction. Residual mudstone sediments, under the pressure of the overlying strata, become dense Class II rock microdomains; petroleum filling hydrocarbon-generating pressure fractures transforms into non-porous pyrophosphate, i.e., Class III rock microdomains; overall, Class II and Class III rock microdomains are distributed within Class I rock microdomains.

[0118] Example 1:

[0119] This embodiment provides a method for determining whether the siliceous shale in target siliceous shale area A is a petrification product of deep-water microbial mats, including:

[0120] 1. Perform whole-rock analysis and total organic carbon testing on the core samples taken from the target siliceous shale area A to determine the mass content of quartz, clay, and total organic carbon in the siliceous shale to be tested. If the mass content of quartz in the siliceous shale to be tested is higher than 80%, the mass content of clay is not less than 1%, and the mass content of total organic carbon is higher than 4%, then the siliceous shale to be tested will be regarded as the target siliceous shale.

[0121] In this embodiment, the quartz content of the siliceous shale to be tested is higher than 80%, the clay content is not less than 1%, and the total organic carbon content is higher than 4%. Therefore, the siliceous shale to be tested is used as the target siliceous shale, and the core of the siliceous shale to be tested can be directly used as the core of the siliceous shale to be tested.

[0122] 2. Prepare argon-ion polished discs of the target siliceous shale using the core of the target siliceous shale; wherein the argon-ion polished disc of the target siliceous shale is 2cm long, 2cm wide, and 0.5cm thick; the polished surface of the argon-ion polished disc of the target siliceous shale is parallel to the cylindrical surface of the target siliceous shale core, and the top and bottom surfaces of the argon-ion polished disc are marked.

[0123] 3. Select an area with a length and width not exceeding 400 μm on the polished surface of the argon-ion polished disc of the target siliceous shale, and acquire MAPS rock image data volume with a resolution of 4 nm. During the acquisition of MAPS rock image data volume, the top surface of the argon-ion polished disc of the target siliceous shale is located above the field of view, and the bottom surface of the argon-ion polished disc of the target siliceous shale is located below the field of view, thereby ensuring that all phenomena observed in the acquired MAPS rock image data volume are merely magnified natural phenomena.

[0124] 4. Use an image editor (the offline version of the image editor ATLAS). TM The BROWSER-BASEDVIEWER is used to observe the acquired MAPS rock image data on a computer; to observe whether the target siliceous shale has at least one of the three features: feature 1, feature 2, and feature 3.

[0125] A. Feature 1 indicates that rock microdomains of Class I are dominant, while rock microdomains of Class II and Class III are scattered within rock microdomains of Class I.

[0126] Among them, the petrological characteristics of the rock microdomains of Class I are that quartz is absolutely dominant, with small amounts of calcite and dolomite. Quartz, calcite and dolomite together form the rock skeleton, and organic matter rich in honeycomb nanopores occupies the space of the rock skeleton. The petrological characteristics of the rock microdomains of Class II are that of nearly horizontally distributed clay bands, which lack organic matter and have abundant calcite particles, dolomite particles and micron-sized non-porous quartz particles. The rock microdomains of Class III are characterized by branched distribution of non-porous organic matter, which contains flaky clay with flow characteristics.

[0127] In Feature 1, Category I rock microdomains include six types of rock microdomains: Category I1 rock microdomains are aggregates of porous nano-quartz particles; Category I2 rock microdomains are aggregates of porous micron-quartz particles; Category I3 rock microdomains are non-porous micron-quartz particles and composites of porous nano-quartz particles and clay located on the surface of non-porous micron-quartz particles; Category I4 rock microdomains are irregular calcite particles and the filling material in their dissolved pores; Category I5 rock microdomains are dolomite with a rhombic morphology and the filling material in its dissolved pores; and Category I6 rock microdomains are organic matter with rich honeycomb nanopores.

[0128] Category I4 rock microdomains include at least one of the following four subcategories of rock microdomains: Category I4 1 Subclass rock microdomains are aggregates of porous nano-quartz particles filling the calcite dissolution pores; I4 2 Subclass rock microdomains are aggregates of porous micron-sized quartz particles filling calcite dissolution pores; I4 3 The subclass of rocks consists of calcite dissolution pores filled with organic matter rich in honeycomb-like nanopores; I4 4 The subclass of rocks consists of calcite-dissolved pores filled with non-porous organic matter.

[0129] Class I5 rock microdomains include at least one of the following four subclasses of rock microdomains: I5 1 Subclass rock microdomains are aggregates of porous nano-quartz particles filling the dissolution pores of dolomite; I5 2Subclass rock microdomains are aggregates of porous micron-sized quartz particles filling the dissolution pores of dolomite; I5 3 The subclass of rocks consists of microdomains filled with organic matter rich in honeycomb-like nanopores, which fills the dissolution pores of dolomite; I5 4 The subclass of rocks consists of dolomite dissolution pores filled with non-porous organic matter.

[0130] B. Feature 2 refers to the fact that Class I1 and / or Class I2 rock microdomains serve as the rock framework of siliceous shale, while Class I6 rock microdomains are distributed between the rock frameworks.

[0131] C. Feature 3 refers to the development of terrigenous quartz clasts and argillaceous bands with clay on the surface of siliceous shale in which the rock skeleton is the main body of the rock microdomain of Class I1 and / or Class I2 rock microdomain (accounting for more than 75% of the rock volume).

[0132] If the target siliceous shale exhibits at least one of the three characteristics (characteristic 1, characteristic 2, and characteristic 3), then the target siliceous shale is a petrified product of deep-sea microbial mats.

[0133] In this embodiment, as Figure 1 As shown, the target siliceous shale consists of 3 major types of lithospheres, 6 types of lithospheres, and 8 subtypes of lithospheres, with complete lithosphere development. Type I1 lithospheres (such as...) Figure 1 (as shown in a) is a lithological product of the nano-siliceous microbial mat formed in the first depositional stage; I4 1 Subclass rock microdomains (e.g.) Figure 1 f and i) are lithological products of nano-siliceous microorganisms that occupied the dissolution pores of calcite during the first depositional stage; I5 1 Subclass rock microdomains (e.g.) Figure 1 The "k" in the text refers to the lithification products of nano-siliceous microorganisms that occupied the dissolution pores of dolomite during the first depositional stage. Class I2 rock microdomains (such as...) Figure 1 a) in the text refers to the lithification product of the micron-sized siliceous microbial mat formed during the second sedimentary stage; I4 2 Subclass rock microdomains (e.g.) Figure 1 f and i) are lithological products of micron-sized siliceous microorganisms occupying the dissolution pores of calcite during the second depositional stage; I5 2 Subclass rock microdomains (e.g.) Figure 1 The "k" in the text refers to the lithification products of micron-sized siliceous microorganisms that occupied the dissolution pores of dolomite during the second depositional stage. Type I3 ​​rock microdomains (such as...) Figure 1 In the example d), the clay on the surface of the terrigenous quartz fragments is a product of the remodeling by deep-water traction currents, and the clay is a residue of argillaceous sediments (such as...). Figure 1 (The arrow in 'e'). Class I6 rock microdomains (such as...) Figure 1a) and c) in the text refer to the lithification products of carbohydrate-rich microbial mats formed during the third sedimentary stage: in the shallow burial diagenesis stage, the carbohydrate-rich microbial mats transform into kerogen; in the early diagenesis stage of intermediate burial, kerogen transforms into pre-oil bitumen; in the late diagenesis stage of intermediate burial, pre-oil bitumen transforms into solid bitumen and petroleum; in the deep burial diagenesis stage, solid bitumen transforms into pyroasphalt and generates natural gas, and the pyroasphalted solid bitumen develops rich honeycomb nanopores. Ⅰ4 3 Subclass rock microdomains (e.g.) Figure 1 f, g, h) and I5 3 Subclass rock microdomains (e.g.) Figure 1 The k and l in the figure may be lithological products of carbohydrate-rich microorganisms occupying carbonate dissolution pores during the third sedimentary stage: in the shallow burial diagenetic stage, carbohydrate-rich microorganisms transform into kerogen; in the early diagenetic stage of intermediate burial, kerogen transforms into pre-oil bitumen; in the late diagenetic stage of intermediate burial, pre-oil bitumen transforms into solid bitumen and petroleum; in the deep burial diagenetic stage, solid bitumen transforms into pyroasphalt and generates natural gas, and the pyroasphalted solid bitumen develops honeycomb-like nanopores. Ⅰ4 3 Subclass rock microdomains (e.g.) Figure 1 f, g, h) and I5 3 Subclass rock microdomains (e.g.) Figure 1 The k and l in the text may also be lithological products of pre-oil bitumen occupying carbonate dissolution pores during the early diagenetic stage of intermediate burial: kerogen transforms into pre-oil bitumen while simultaneously producing organic acids, which react with carbonates to form carbonate dissolution pores, which are then quickly filled by pre-oil bitumen; in the late diagenetic stage of intermediate burial, pre-oil bitumen transforms into solid bitumen and petroleum, with the petroleum being carried away through hydrocarbon-generating pressure fractures; in the deep diagenetic stage, solid bitumen transforms into coking bitumen rich in honeycomb nanopores. Ⅰ4 4 Subclass rock microdomains (e.g.) Figure 1 (i and j) and I5 4 Subclass rock microdomains (e.g.) Figure 1 In the latter case (m and n), the petroleum coking asphalt products occupying carbonate dissolution pores during the late diagenetic stage of intermediate burial are: pre-oil asphalt transforms into solid asphalt and petroleum, simultaneously producing organic acids. These organic acids react with carbonates, forming carbonate dissolution pores, which are then quickly filled by petroleum. In the deep burial diagenetic stage, petroleum transforms into non-porous coking asphalt. Class II rock microdomains (such as...) Figure 1 The o in the text refers to residual muddy sediments that, under the pressure of the overlying strata, transformed into dense clayey bands, with the dolomite within maintaining a rhomboid morphology (e.g., Figure 1 p), distributed in the microdomains of rock class I. Microdomains of rock class III (such as...) Figure 1The q, r, s, and t in the text refer to the products of asphaltification of petroleum that filled hydrocarbon-generating pressure fractures during the late diagenetic stage of medium burial, and the sporadically distributed flaky clay parallel to the hydrocarbon-generating pressure fractures, exhibiting flow characteristics (e.g., ...). Figure 1 The 's' in the text indicates that clay minerals migrated with petroleum. Overall, rock microdomains of Group II and Group III were scattered within rock microdomains of Group I. When an argon-ion polished sheet was used to cross-cut the hydrocarbon-generating pressure fracture, the branched, non-porous organic matter appeared as a pseudomorph of "agglomerated organic matter filling intergranular pores" (e.g., Figure 1 (t in the text)

[0134] In summary, in this embodiment, the target siliceous shale satisfies the condition of having at least one of the three characteristics 1, 2, and 3, and is a petrification product of deep-water microbial mats. The area where the target siliceous shale is located (i.e., the A target siliceous shale area) is a sweet spot for shale gas and has high exploration and development potential.

[0135] Example 2

[0136] This embodiment provides a method for determining whether the siliceous shale in the target siliceous shale area is a petrification product of deep-water microbial mats.

[0137] The method used in this embodiment is the same as that used in Embodiment 1.

[0138] like Figure 2 As shown, the target siliceous shale region within Target B consists of three major rock microdomains: I, II, and III. All six rock microdomains within Major Rock Domain I are fully developed. Within Rock Microdomain I4, I4... 1 Subclass rock microdomains and I4 4 Subclass rock microdomains, missing I4 2 Subclass rock microdomains and I4 3 Subclass rock microdomains; within class I5 rock microdomains, class I5 is developed. 3 Subclass rock microdomain, missing I5 1 Subclass rock microdomains, I5 2 Subclass rock microdomains and I5 4 Subclass rock microdomains. Class I1 rock microdomains (e.g. Figure 2 a) in the text refers to the lithification product of the nano-siliceous microbial mat formed during the first sedimentary stage, I4. 1 Subclass rock microdomains (e.g.) Figure 2 e) in the text refers to the lithification products of nano-siliceous microorganisms that occupied the dissolution pores of calcite during the first sedimentary stage. Type I3 ​​rock microdomains (such as...) Figure 2 c) in the text refers to the remodeling of terrigenous quartz fragments by deep-water traction currents. The clay on the surface of the terrigenous quartz fragment particles is a residue of argillaceous sediments (such as...). Figure 2 (The arrow in d in the text). Class I6 rock microdomains (such as...) Figure 2a) and b) in the text are lithological products of carbohydrate-rich microbial mats formed during the third sedimentary stage: In the shallow burial diagenetic stage, the carbohydrate-rich microbial mats transform into kerogen; in the early diagenetic stage of intermediate burial, kerogen transforms into pre-oil bitumen, expanding in volume and completely occupying the original pores; in the late diagenetic stage of intermediate burial, pre-oil bitumen transforms into solid bitumen and petroleum, continuing to expand in volume, generating hydrocarbons and pressure to create fractures, and petroleum undergoes its first migration through these hydrocarbon-generating and pressure-increasing fractures; in the deep burial diagenetic stage, solid bitumen transforms into pitch and generates natural gas, and pitched solid bitumen develops honeycomb-like nanopores. Ⅰ5 3 Subclass rock microdomains (e.g.) Figure 2 h and i) in the text may be lithological products of carbohydrate-rich microorganisms occupying carbonate dissolution pores during the third sedimentary stage: in the shallow burial diagenetic stage, carbohydrate-rich microorganisms transform into kerogen; in the early diagenetic stage of intermediate burial, kerogen transforms into pre-oil bitumen; in the late diagenetic stage of intermediate burial, pre-oil bitumen transforms into solid bitumen and petroleum; in the deep burial diagenetic stage, solid bitumen transforms into pyroasphalt and generates natural gas, and the pyroasphalted solid bitumen develops honeycomb-like nanopores. Ⅰ5 3 Subclass rock microdomains (e.g.) Figure 2 h and i) in the text may also be lithological products of pre-oil bitumen occupying carbonate dissolution pores during the early diagenetic stage of intermediate burial: organic acids are produced during the transformation of kerogen into pre-oil bitumen, and these organic acids react with carbonates to form carbonate dissolution pores, which are then filled by pre-oil bitumen; in the late diagenetic stage of intermediate burial, pre-oil bitumen is transformed into solid bitumen and petroleum, with the petroleum being carried away through hydrocarbon-generating pressure fractures; in the diagenetic stage of deep burial, solid bitumen is transformed into coking bitumen rich in honeycomb nanopores. Ⅰ4 4 Subclass rock microdomains (e.g.) Figure 2 In the latter (f and g), the petroleum coking asphalt products occupying calcite dissolution pores during the late diagenetic stage of intermediate burial are: pre-oil bitumen transforms into solid bitumen and petroleum, simultaneously producing organic acids. These organic acids react with calcite, forming calcite dissolution pores, which are then quickly filled by petroleum. In the deep burial diagenetic stage, petroleum transforms into non-porous coking asphalt. Class II rock microdomains (such as...) Figure 2 In section j), residual muddy sediments, under the pressure of the overlying strata, transformed into dense clayey bands containing dolomite that retained a rhomboid morphology, are distributed within microdomains of Group I rocks. Microdomains of Group III rocks (such as...) Figure 2 The "k" and "l" in the text refer to the asphaltification products of petroleum that filled hydrocarbon-generating and pressurizing fractures during the late diagenetic stage of medium burial. When an argon-ion polishing disc cross-cuts the hydrocarbon-generating and pressurizing fractures, the branched, non-porous organic matter appears as a pseudomorph of "agglomerated organic matter filling the intergranular pores" (e.g., ...). Figure 2 (m in the text). Overall, rock microdomains of category II and category III are scattered within rock microdomains of category I.

[0139] In summary, in this embodiment, the target siliceous shale satisfies the condition of having at least one of the three characteristics 1, 2, and 3, and is a petrification product of deep-water microbial mats. The area where the target siliceous shale is located (i.e., the B target siliceous shale area) is a sweet spot for shale gas and has high exploration and development potential.

[0140] Example 3

[0141] This embodiment provides a method for determining whether the siliceous shale in the target C siliceous shale area is a petrification product of deep-water microbial mats.

[0142] The method used in this embodiment is the same as that used in Embodiment 1.

[0143] like Figure 3 As shown, siliceous shale consists of 3 major types of lithospheres, 6 types of lithospheres, and 8 subtypes of lithospheres, with all types of lithospheres fully developed. Type I1 lithospheres (such as...) Figure 3 a) in the text refers to the lithification product of the nano-siliceous microbial mat formed during the first sedimentary stage, I4. 1 Subclass rock microdomains (e.g.) Figure 3 g) is a petrification product of nano-siliceous microorganisms that occupied the dissolution pores of calcite during the first depositional stage, I5 1 Subclass rock microdomains (e.g.) Figure 3 j) represents the lithification product of nano-siliceous microorganisms that occupied the dissolution pores of dolomite during the first depositional stage. Class I2 rock microdomains (such as...) Figure 3 c) in the text refers to the lithification product of the micron-sized siliceous microbial mat formed during the second sedimentary stage, I4. 2 Subclass rock microdomains (e.g.) Figure 3 g) is a petrification product of micron-sized siliceous microorganisms that occupied the dissolution pores of calcite during the second depositional stage, I5 2 Subclass rock microdomains (e.g.) Figure 3 (j) in the text refers to the lithification products of micron-sized siliceous microorganisms that occupied the dissolution pores of dolomite during the second depositional stage. Class I3 rock microdomains (such as...) Figure 3 In this context, e) represents the product of terrigenous quartz fragments being remodeled by deep-water traction currents. The clay on the surface of the terrigenous quartz fragment particles is a residue of argillaceous sediments (such as...). Figure 3 (The arrow of f in the text). Class I6 rock microdomains (such as...) Figure 3a), b), c), and d) in the text refer to the lithological products of carbohydrate-rich microbial mats formed during the third sedimentary stage: In the shallow burial diagenetic stage, the carbohydrate-rich microbial mats transform into kerogen; in the early diagenetic stage of intermediate burial, kerogen transforms into pre-oil bitumen, expanding in volume and completely occupying the original pores; in the late diagenetic stage of intermediate burial, pre-oil bitumen transforms into solid bitumen and petroleum, continuing to expand in volume, generating hydrocarbons and pressure to create fractures, and petroleum undergoes its first migration through these hydrocarbon-generating and pressure-increasing fractures; in the deep burial diagenetic stage, solid bitumen transforms into pitch and generates natural gas, and the pitched solid bitumen develops honeycomb-like nanopores. Ⅰ4 3 Subclass rock microdomains (e.g.) Figure 3 g) and I5 3 Subclass rock microdomains (e.g.) Figure 3 j) in the text may be the lithological product of carbohydrate-rich microorganisms occupying carbonate dissolution pores during the third sedimentary stage: in the shallow burial diagenetic stage, carbohydrate-rich microorganisms transform into kerogen; in the early diagenetic stage of intermediate burial, kerogen transforms into pre-oil bitumen; in the late diagenetic stage of intermediate burial, pre-oil bitumen transforms into solid bitumen and petroleum, with petroleum undergoing its first migration through hydrocarbon-generating pressure fractures; in the deep burial diagenetic stage, solid bitumen transforms into pyroasphalt and generates natural gas, with the pyroasphalted solid bitumen developing rich honeycomb nanopores. Ⅰ4 3 Subclass rock microdomains (e.g.) Figure 3 g and h) and I5 3 Subclass rock microdomains (e.g.) Figure 3 J and K in the text may also be lithological products of pre-oil bitumen occupying carbonate dissolution pores during the early diagenetic stage of intermediate burial: organic acids are produced during the transformation of kerogen into pre-oil bitumen, and these organic acids react with carbonates to form carbonate dissolution pores, which are then filled by pre-oil bitumen; in the late diagenetic stage of intermediate burial, pre-oil bitumen is transformed into solid bitumen and petroleum, with the petroleum being carried away through hydrocarbon-generating pressure fractures; in the diagenetic stage of deep burial, solid bitumen is transformed into coking bitumen rich in honeycomb nanopores. Ⅰ4 4 Subclass rock microdomains (e.g.) Figure 3 g and i) and I5 4 Subclass rock microdomains (as shown in the figure) Figure 3 In the middle-period diagenetic stage (j and l), the petroleum coking asphalt products occupying carbonate dissolution pores are formed: Before oil production, asphalt transforms into solid asphalt and petroleum, organic acids are produced. These organic acids react with carbonates, forming carbonate dissolution pores, which are then quickly filled by petroleum. In the deep-period diagenetic stage, petroleum transforms into non-porous coking asphalt. Class II rock microdomains (such as...) Figure 3 In the m) section, residual muddy sediments, under the pressure of the overlying strata, transform into dense clayey bands, with porous nano-quartz particles "floating" within the clay (e.g., Figure 3The surface of the n) and terrigenous quartz particles is encapsulated by clay and porous nano-quartz (e.g. Figure 3 The presence of "o" indicates that it has been eroded by nano-silica microorganisms, but the erosion is relatively weak. Class III rock microdomains (such as...) Figure 3 The p, q, and r values ​​in the text refer to the asphaltification of petroleum that filled hydrocarbon-generating and pressurizing fractures during the late diagenetic stage of intermediate burial. This process, which appears as filling "intergranular pores," is primarily caused by the transverse cutting of hydrocarbon-generating and pressurizing fractures by argon-ion polishing discs. Overall, rock microdomains of Group II and Group III are distributed within rock microdomains of Group I.

[0144] In summary, in this embodiment, the target siliceous shale satisfies the condition of having at least one of the three characteristics 1, 2, and 3, and is a petrification product of deep-water microbial mats. The area where the target siliceous shale is located (i.e., the C target siliceous shale area) is a sweet spot for shale gas and has high exploration and development potential.

[0145] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for determining whether siliceous shale is a lithological product of deep-sea microbial mats, comprising: Obtain the target siliceous shale; wherein the target siliceous shale has a quartz content of more than 80% by mass, a clay content of not less than 1% by mass, and a total organic carbon content of more than 4% by mass; Determine whether the target siliceous shale possesses at least one of the three characteristics: characteristic 1, characteristic 2, and characteristic 3. Feature 1: Category I rock microdomains account for more than 90% of the rock volume, while Category II and Category III rock microdomains are scattered within Category I. The petrological characteristics of Category I rock microdomains are that quartz accounts for more than 70% of the volume, while calcite and dolomite do not exceed 20%. Quartz, calcite, and dolomite together form the rock skeleton, and organic matter rich in honeycomb-like nanopores occupies the space of the rock skeleton. The petrological characteristics of Category II rock microdomains are nearly horizontally distributed clay bands, where nearly horizontal means the dip angle does not exceed 30°. There is no organic matter in the clay bands, but calcite particles, dolomite particles, and micron-sized non-porous quartz particles are developed. Category III rock microdomains are characterized by branched distribution of non-porous organic matter, and the non-porous organic matter contains flaky clay with flow characteristics. Feature 2: The rock skeleton of siliceous shale is composed of aggregates of porous micro-nano quartz particles, namely, type I1 rock microdomains and / or type I2 rock microdomains, with organic matter rich in honeycomb nanopores distributed between the rock skeletons; wherein, type I1 rock microdomains are aggregates of porous nano quartz particles, and type I2 rock microdomains are aggregates of porous micron quartz particles. Feature 3: The rock skeleton of siliceous shale is dominated by aggregates of porous micro-nano quartz particles. The volume ratio of the aggregates of porous micro-nano quartz particles in the rock skeleton is more than 75%. It also contains non-porous micron-sized quartz particles and composites of porous nano-sized quartz particles and clay located on the surface of non-porous micron-sized quartz particles. It belongs to the Class II rock micro-domain. If the target siliceous shale has at least one of the three characteristics 1, 2, and 3, then the target siliceous shale is a petrified product of deep-sea microbial mats. Determining whether the target siliceous shale possesses at least one of the three characteristics: characteristic 1, characteristic 2, and characteristic 3 includes: Argon-ion polished discs of the target siliceous shale were prepared using the target siliceous shale core. MAPS rock image data volume of argon-ion polished slides of the target siliceous shale; Based on the MAPS rock image data of the argon-ion polished slides of the target siliceous shale, observe whether the target siliceous shale has at least one of the three features: feature 1, feature 2, and feature 3.

2. The method according to claim 1, wherein, Obtaining the target siliceous shale includes: Whole-rock analysis and total organic carbon testing were performed on the siliceous shale to be tested to determine the mass content of quartz, clay, and total organic carbon in the siliceous shale. If the quartz content of the siliceous shale to be tested is higher than 80%, the clay content is not less than 1%, and the total organic carbon content is higher than 4%, then the siliceous shale to be tested will be considered as the target siliceous shale.

3. The method according to claim 1, wherein, The polished surface of the argon-ion polishing disc of the target siliceous shale is parallel to the cylindrical surface of the target siliceous shale core.

4. The method according to claim 3, wherein, The resolution of the MAPS rock image data volume of the argon-ion polished slides of the target siliceous shale is 4-10 nm.

5. The method according to claim 3, wherein, The length, width, and thickness of the argon ion polishing sheet for the target siliceous shale are 0.8-2 cm.

6. The method according to claim 3, wherein, The acquisition of MAPS rock image data volume from argon-ion polished discs of the target siliceous shale includes: selecting an area with a length and width not exceeding 400 μm on the polished surface of the argon-ion polished disc of the target siliceous shale, and acquiring the MAPS rock image data volume.

7. The method according to claim 3, wherein, During the acquisition of MAPS rock image data from argon-ion polished sections of the target siliceous shale, the top surface of the argon-ion polished section of the target siliceous shale is located above the field of view, and the bottom surface of the argon-ion polished section of the target siliceous shale is located below the field of view.

8. The method according to claim 1, wherein, Feature 1, Category I rock microdomains include 6 types of rock microdomains: Type I1 rock microdomains are aggregates of porous nano-quartz particles; Type I2 rock microdomains are aggregates of porous micron-sized quartz particles; The rock microdomains of type I3 ​​consist of non-porous micron-sized quartz particles and a composite of porous nano-sized quartz particles and clay located on the surface of the non-porous micron-sized quartz particles. Type I4 rock microdomains consist of irregular calcite particles and the filling material in their dissolution pores; Category I5 rock microdomains consist of dolomite with a rhombic morphology and the filling material in its dissolution pores; Type I6 rock microdomains are organic matter with rich honeycomb nanopores.

9. The method according to claim 8, wherein, Category I4 rock microdomains include at least one of the following four subcategories of rock microdomains: Ⅰ4 1 The subclass of rock microdomains consists of aggregates of porous nano-quartz particles filling the calcite dissolution pores. Ⅰ4 2 The subclass of rock microdomains consists of aggregates of porous micron-sized quartz particles that fill the calcite dissolution pores. Ⅰ4 3 The subclass of rocks consists of organic matter with honeycomb-like nanopores filling the calcite dissolution pores. Ⅰ4 4 The subclass of rocks consists of calcite dissolution pores filled with non-porous organic matter.

10. The method according to claim 8, wherein, Category I5 rock microdomains include at least one of the following four subcategories of rock microdomains: Ⅰ5 1 The subclass of rock microdomains consists of aggregates of porous nano-quartz particles filling the dissolution pores of dolomite. Ⅰ5 2 The subclass of rock microdomains consists of aggregates of porous micron-sized quartz particles filling the dissolution pores of dolomite. Ⅰ5 3 The subclass of rocks consists of organic matter with rich honeycomb-like nanopores filling the dissolution pores of dolomite; Ⅰ5 4 The subclass of rocks consists of dolomite dissolution pores filled with non-porous organic matter.

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