Method for judging whether siliceous shale is subjected to still water physical and chemical deposition or not

Abstract

The invention provides a method for judging whether siliceous shale is subjected to still water physical and chemical deposition or not. The method comprises the following steps: determining whether target siliceous shale has a feature 1, a feature 2, a feature 3 and a feature 4 or not, and if so, determining that the target siliceous shale is still water physical and chemical deposition; the method is characterized in that 1, biological siliceous accounts for 70-95% of the total volume of quartz and terrestrial feldspar in the rock, and the total volume of terrestrial quartz and terrestrial feldspar accounts for 5-30% of the total volume of quartz and terrestrial feldspar in the rock; 2, calcite and dolomite are contained; 3, common berry-shaped pyrite is contained, and the common berry-shaped pyrite is berry-shaped pyrite with intergranular pores filled with organic matters; and 4, an organic clay particle complex with honeycomb-shaped nano pores is contained. Whether the siliceous shale is subjected to still water physical and chemical deposition or not is judged, determination of the shale gas dessert area of the siliceous shale is promoted, and therefore efficient exploration and development of the shale gas of the siliceous shale are achieved.

Description

Technical Field

[0001] The invention relates to a method for judging whether siliceous shale is hydrostatic physical and chemical deposit. Background Art

[0002] As the primary lithofacies in shale oil and gas sweet spots and the target for horizontal shale oil and gas wells, the sedimentation type of siliceous shale has always been a hot topic in the industry. A review of existing research results reveals that the main methods for studying the sedimentation type of deepwater organic-rich shales, including siliceous shales, are geochemical methods and petrological characterization methods. Geochemical research results indicate that all siliceous shales are deposited offshore or in relatively closed bays, collectively referred to as hydrostatic physical and chemical deposition. Based on the bedding characteristics of shales observed in rock thin sections, the sedimentation types of deepwater black shales, including siliceous shales, are divided into hydrostatic physical and chemical deposition, deepwater gravity flow deposition, and deepwater traction flow deposition.

[0003] Based on geochemical test data, the redox properties of deepwater bodies are judged to be entirely hydrostatic physical and chemical deposits, including siliceous shales. The siliceous shales, targets for horizontal shale oil and gas wells, are believed to be the lithification of siliceous mud formed by the sedimentation of surface marine organisms to the deepwater seafloor. Geochemical methods cannot provide information on the distribution of minerals and organic matter, making it impossible to characterize and interpret the petrological characteristics of siliceous shales, leading to a narrow understanding of sedimentary processes. The assumption that all deepwater black shales, including siliceous shales, are hydrostatic physical and chemical deposits also contradicts marine sedimentology theory: deepwater environments not only develop hydrostatic physical and chemical sedimentation, but also deepwater traction current and gravity flow deposits.

[0004] Thin section observation revealed that the shale developed four types of horizontal bedding: transitional type, sand-mud transitional type, sand-mud interbedded type, and book-page type. It is believed that the transitional type and sand-mud transitional type horizontal bedding are both caused by deep-water turbidity currents, the sand-mud interbedded type horizontal bedding is caused by deep-water contour currents, and the book-page type horizontal bedding is caused by hydrostatic physical and chemical deposition. The interpretation of shale sedimentation type based on bedding phenomena observed through thin section only considers the changes in mineral grain size but not the origin of the minerals, resulting in the following defects: the main minerals of deep-water shales, such as quartz and calcite, mainly come from the surface water of the ocean. Quartz is the dissolution and precipitation product of siliceous biological skeletons, and calcite is the metabolic product of microorganisms that secrete calcium carbonate in the surface water of the ocean. They are suspended and settled to the seabed to form hydrostatic physical and chemical deposits; when the primary productivity of marine surface water organisms changes with the seasons, the content of quartz and calcite also changes accordingly, forming hydrostatic physical and chemical deposits with transitional and sand-mud transitional horizontal bedding, which are mistakenly interpreted as deep-water gravity flow deposits based on thin section observations; when siliceous shale mainly formed by sand-grade siliceous biological skeletons and siliceous shale mainly formed by mud-grade siliceous biological skeletons form sand-mud interbedded horizontal bedding, this hydrostatic physical and chemical sedimentary combination may be interpreted as deep-water traction flow deposits based on the phenomena observed in thin section. Therefore, the horizontal bedding observed in thin sections cannot clarify the depositional type of deep-water black shales, including siliceous shales.

[0005] Due to the small size of shale mineral particles and the high organic matter content, it is difficult to effectively observe the occurrence of minerals and organic matter in shale at multiple macro and microscales. This is one of the main reasons for the long-standing weakness in shale sedimentation research. The North American shale revolution at the beginning of this century made shale reservoir research a hot topic in the petroleum geology community. The introduction of MAPS technology has made it possible to obtain high-resolution, large-field shale petrographic images, providing primary data for the study of shale sedimentation. MAPS technology divides argon ion polished samples into a series of regular grids, scans and images each grid, obtains a secondary electron scanning image, and then stitches all the grid images together to produce a two-dimensional, large-field scanning image data volume. Currently, research results on MAPS rock image data volumes mainly focus on the description of organic pores. A small number of studies have achieved petrological characterization and interpretation of organic matter and organic pores. However, systematic petrological characterization and interpretation of deepwater black shales, including siliceous shales, have not yet been achieved.

[0006] Although the introduction of MAPS technology has provided technical possibilities for shale petrological characterization and analysis, the complexity of the occurrence state of shale minerals and organic matter caused by large differences in compaction intensity has resulted in no systematic research results on shale petrological characterization.

[0007] In summary, there is still a need to study the petrological characteristics of hydrostatic physical and chemical sedimentary siliceous shales to promote the identification of shale gas sweet spots where siliceous shales are high-quality reservoirs, thereby realizing the efficient exploration and development of shale gas where siliceous shales are high-quality reservoirs. Summary of the Invention

[0008] The purpose of the present invention is to provide a technical solution that can determine whether siliceous shale is a hydrostatic physical and chemical deposit, thereby promoting the determination of shale gas sweet spots where siliceous shale is a high-quality reservoir, and thus realizing the efficient exploration and development of shale gas where siliceous shale is a high-quality reservoir.

[0009] To achieve the above object, the present invention provides a method for determining whether siliceous shale is a hydrostatic physical and chemical deposit, comprising:

[0010] Obtaining target siliceous shale; wherein the target siliceous shale has a quartz mass content greater than 50%, a clay mass content not less than 5%, and a total organic carbon mass content greater than 2%;

[0011] Determine whether the target siliceous shale has the following characteristics 1, 2, 3, and 4:

[0012] Feature 1: Biogenic silica accounts for 70-95% of the total volume of quartz and terrigenous feldspar in the rock, and terrigenous quartz and terrigenous feldspar together account for 5-30% of the total volume of quartz and terrigenous feldspar in the rock;

[0013] Feature 2: Contains calcite and dolomite;

[0014] Feature 3: Contains raspberry pyrite; raspberry pyrite includes common raspberry pyrite, which refers to raspberry pyrite with organic matter filling the intercrystalline pores;

[0015] Feature 4: Contains organic matter, wherein the organic matter comprises an organic clay complex with honeycomb-like nanopores;

[0016] If the target siliceous shale has characteristics 1, 2, 3, and 4, the target siliceous shale is a hydrostatic physical and chemical deposit.

[0017] The inventors of the present invention analyzed and characterized the petrological characteristics of siliceous shales, clarifying the distribution range of hydrostatic physical and chemically deposited siliceous shales, which helps guide the efficient exploration and development of shale gas. If a siliceous shale possesses characteristic 1 (biogenic silica accounts for 70-95% of the total volume of quartz and terrigenous feldspar in the rock, and terrigenous quartz and terrigenous feldspar together account for 5-30% of the total volume of quartz and terrigenous feldspar in the rock), characteristic 2 (the presence of calcite and dolomite), characteristic 3 (the presence of common raspberry pyrite), and characteristic 4 (the presence of organic clay complexes with honeycomb nanopores), then the siliceous shale is the lithification product of siliceous mud formed by hydrostatic physical and chemical deposition. Therefore, characteristics 1, 2, 3, and 4 can effectively characterize it as a hydrostatic physical and chemical deposition.

[0018] According to a preferred embodiment of the method for determining whether siliceous shale is a hydrostatic physical and chemical deposit, obtaining target siliceous shale includes:

[0019] Conduct whole-rock analysis and total organic carbon testing on the siliceous shale to be tested to determine the mass content of quartz, clay, and total organic carbon in the siliceous shale to be tested;

[0020] If the quartz mass content of the siliceous shale to be tested is higher than 50%, the clay mass content is not less than 5%, and the total organic carbon mass content is higher than 2%, the siliceous shale to be tested is taken as the target siliceous shale.

[0021] According to a preferred embodiment of the method for determining whether siliceous shale is hydrostatic physical and chemical deposited, determining whether the target siliceous shale has the following characteristics 1, 2, 3, and 4 includes:

[0022] using a target siliceous shale core to produce an argon ion polished sheet of the target siliceous shale;

[0023] Collect MAPS rock image data of argon ion polished slices of target siliceous shale;

[0024] Based on the MAPS rock image data volume of the argon ion polished slice of the target siliceous shale, observe whether the target siliceous shale has features 1, 2, 3, and 4;

[0025] More preferably, the resolution of the MAPS rock image data volume of the argon ion polished slice of the target siliceous shale collected is 4-10 nm;

[0026] More preferably, the length of the argon ion polished sheet of the target siliceous shale is 0.8-2 cm;

[0027] More preferably, the width of the argon ion polished sheet of the target siliceous shale is 0.8-2 cm;

[0028] More preferably, the thickness of the argon ion polished sheet of the target siliceous shale is 0.3-0.8 cm;

[0029] More preferably, the polishing surface of the argon ion polishing sheet of the target siliceous shale is parallel to the cylindrical surface of the target siliceous shale core;

[0030] More preferably, collecting the MAPS rock image data volume of the argon ion polished wafer of the target siliceous shale comprises: selecting an area with a length and a width not exceeding 400 μm on the polished surface of the argon ion polished wafer of the target siliceous shale, and collecting the MAPS rock image data volume;

[0031] More preferably, during the process of acquiring the MAPS rock image data volume of the argon ion polished sheet of the target siliceous shale, the top surface of the argon ion polished sheet of the target siliceous shale is located above the field of view, and the bottom surface of the argon ion polished sheet 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;

[0032] More preferably, based on the MAPS rock image data volume of the argon ion polished slice of the target siliceous shale, in the process of observing whether the target siliceous shale has at least one of the four features 1, 2, 3 and 4, an image editor (such as an offline image editor ATLAS TM BROWSER-BASEDVIEWER) is used to observe the MAPS rock image data on a computer.

[0033] According to a preferred embodiment of the method for determining whether siliceous shale is a hydrostatic physical and chemical deposit, in feature 2, the calcite is irregular particles.

[0034] According to a preferred embodiment of the method for determining whether siliceous shale is a hydrostatic physical and chemical deposit, in feature 2, the dolomite is rhombic iron-containing dolomite encapsulating dolomite particles.

[0035] According to a preferred embodiment of the method for determining whether siliceous shale is a hydrostatic physical and chemical deposit, in feature 3, the berry-shaped pyrite also includes overgrown berry-shaped pyrite, and the overgrown berry-shaped pyrite is berry-shaped pyrite with residual intercrystalline pores that are not filled with organic matter.

[0036] According to a preferred embodiment of the method for determining whether siliceous shale is a hydrostatic physical and chemical deposit, in feature 3, ordinary berry-shaped pyrite includes at least one of berry-shaped pyrite with linear contact of grains, berry-shaped pyrite with point contact of grains, and berry-shaped pyrite with grains floating in organic matter.

[0037] According to a preferred embodiment of the method for determining whether siliceous shale is a hydrostatic physical and chemical deposit, in feature 4, the organic matter also includes pure organic matter (pure organic matter, as the opposite of a complex of organic matter with other substances, refers to organic matter that exists alone rather than in the form of a complex with other substances), and the pure organic matter includes at least one of pure organic matter with honeycomb nanopores and pure organic matter without pores.

[0038] According to a preferred embodiment of the method for determining whether siliceous shale is a hydrostatic physical and chemical deposit, the method for determining whether siliceous shale is a hydrostatic physical and chemical deposit further comprises:

[0039] When the target siliceous shale is a hydrostatic physical and chemical deposit, determining whether the target siliceous shale is a multi-cavity biogenic siliceous shale, a single-cavity biogenic siliceous shale, or a cavity-free biogenic siliceous shale;

[0040] Among hydrostatically deposited siliceous shales, horizontal shale gas wells with multi-cavity biogenic siliceous shales as targets have high yields, those with single-cavity biogenic siliceous shales as targets have medium yields, and those with no-cavity biogenic siliceous shales as targets have low yields. Distinguishing hydrostatically deposited siliceous shales as multi-cavity biogenic siliceous shales, single-cavity biogenic siliceous shales, or no-cavity biogenic siliceous shales is more helpful in determining the development potential of hydrostatically deposited siliceous shales and guiding efficient shale gas exploration and development.

[0041] More preferably, in the target siliceous shale, if biogenic silica accounts for more than 90% of the total volume of quartz and terrigenous feldspar in the rock, and the total of terrigenous quartz and terrigenous feldspar accounts for less than 10% of the total volume of quartz and terrigenous feldspar in the rock, and the cavities of the biogenic silica are filled with pure organic matter with honeycomb-like nanopores, then the target siliceous shale is multi-cavity biogenic siliceous shale;

[0042] More preferably, in the target siliceous shale, if the biogenic silica accounts for more than 90% of the total volume of quartz and terrigenous feldspar in the rock, and the total of terrigenous quartz and terrigenous feldspar accounts for less than 10% of the total volume of quartz and terrigenous feldspar in the rock, and the cavity of the biogenic silica is filled with organic silica particle complexes and / or calcite, then the target siliceous shale is a single-cavity biogenic siliceous shale;

[0043] More preferably, in the target siliceous shale, if the biogenic silica accounts for less than 90% and greater than or equal to 70% of the total volume of quartz and terrigenous feldspar in the rock, and the total of terrigenous quartz and terrigenous feldspar accounts for greater than 10% and less than or equal to 30% of the total volume of quartz and terrigenous feldspar in the rock, then the target siliceous shale is cavity-free biogenic siliceous shale.

[0044] The technical solution provided by this invention enables characterization of the petrological characteristics of siliceous shales to determine whether they are lithified products of hydrostatic physical and chemical deposition. This technical solution helps to optimize the distribution range of siliceous shales formed by hydrostatic physical and chemical deposition, facilitates the identification of shale gas sweet spots, and guides efficient shale gas exploration and development. This technical solution breaks the bottleneck in the study of deepwater shale depositional environments and contributes to the development of deepwater sedimentology. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is an observation diagram of the MAPS rock image data volume in the image editor in Example 1 of the present invention.

[0046] Figure 2 This is an observation diagram of the MAPS rock image data volume in the image editor in Example 2 of the present invention.

[0047] Figure 3 This is an observation diagram of the MAPS rock image data volume in the image editor in Example 3 of the present invention. DETAILED DESCRIPTION

[0048] To make the purpose, technical solutions and advantages of the embodiments of the present invention more clear, the embodiments of the present invention are further described in detail below with reference to the accompanying drawings. Here, the exemplary embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention.

[0049] To eliminate the interference of compaction, systematic shale petrology characterization needs to be implemented in at least three stages. The first stage involves petrological characterization of shales with low clay mineral content, low compaction intensity, and high organic matter content, analyzing their petrological characteristics and identifying the sedimentary environment and sedimentary type. The second stage involves petrological characterization of shales with moderate clay mineral content and moderate compaction, analyzing their petrological characteristics and identifying the sedimentary environment and sedimentary type. The third stage involves petrological characterization of shales with high clay mineral content and strong compaction, analyzing their petrological characteristics and identifying the sedimentary environment and sedimentary type. The results of the first stage must constrain those of the second stage, and vice versa, in order to truly eliminate the interference of compaction and achieve systematic characterization of shale petrology and analysis of sedimentary environment.

[0050] The inventors of this invention have pioneered a method for characterizing and analyzing the petrological characteristics of shale. By characterizing and analyzing the petrological characteristics of siliceous shales, they can determine whether the siliceous shales are hydrostatic physical and chemical deposits. This method provides an effective reference for systematic characterization and analysis of shale petrology. Compared to current research methods that require different approaches for shale petrological characterization and sedimentary environment analysis, the method provided by this invention addresses shale petrological characterization and sedimentation analysis, achieving twice the result with half the effort.

[0051] The inventors of the present invention have analyzed and characterized the petrological characteristics of siliceous shales and found that the siliceous shales formed by hydrostatic physical and chemical deposition include multi-cavity biogenic siliceous shales, single-cavity biogenic siliceous shales and non-cavity biogenic siliceous shales. The rock skeletons of these siliceous shales are composed of biogenic silica (usually quartz with a ring structure), terrigenous quartz (usually quartz without a ring structure), carbonates, and raspberry pyrites, while clay and organic matter are distributed between the skeletons. The common characteristics of hydrostatic physical and chemical deposition of siliceous shales are as follows: ① Biogenic silica accounts for 70-95% of the total volume of quartz and terrigenous feldspar in the rock, and terrigenous quartz and terrigenous feldspar together account for 5-30% of the total volume of quartz and terrigenous feldspar in the rock; ② Contains calcite and dolomite, of which calcite is mostly irregular particles and dolomite is mostly rhombic iron-bearing dolomite wrapped in dolomite particles; ③ Contains raspberry pyrite, which includes overgrown raspberry pyrite and ordinary raspberry pyrite. ④ The overgrown berry-shaped pyrite has intercrystalline pores that are not filled with organic matter. Ordinary berry-shaped pyrite includes berry-shaped pyrite with linear contact of grains, berry-shaped pyrite with point contact of grains and berry-shaped pyrite with grains floating in organic matter. The intercrystalline pores of ordinary berry-shaped pyrite are filled with organic matter; ④ Contains organic matter, which includes organic clay complexes with honeycomb nanopores, pure organic matter with honeycomb nanopores and pure organic matter without pores. The differences among these siliceous shales are as follows: ① The types of biosiliceous fossils are different, including siliceous shales formed by biosiliceous fossils with no less than two cavities, siliceous shales formed by biosiliceous fossils with only one cavity, and siliceous shales formed by biosiliceous fossils without cavities; ② Multi-cavity biosiliceous and single-cavity biosiliceous have a three-layer structure consisting of inner and outer secondary quartz enlargements and porous quartz transformed from biosiliceous skeletons in the middle, while non-cavity biosiliceous has a double-layer structure consisting of porous quartz transformed from biosiliceous skeletons as the inner core and secondary quartz enlargements as the outer shell; ③ The cavity filling of multi-cavity biosiliceous Honeycomb nanopores are filled with pure organic matter; the cavities of single-cavity biosilica are filled with organic silicon particle complexes and / or calcite; these phenomena are absent in non-cavity biosilica. ④ In multi-cavity biosilica shale and single-cavity biosilica shale, the volume of biosilica is more than 90% of the total volume of quartz and terrigenous feldspar in the rock, while the volume of terrigenous quartz and feldspar is less than 10% of the total volume of quartz and terrigenous feldspar in the rock. In non-cavity biosilica shale, the volume of biosilica is 70-90% of the volume of the rock, while the volume of terrigenous quartz and feldspar is 10-30% of the total volume of quartz and terrigenous feldspar in the rock. Based on this, the inventors of the present invention have identified petrological characteristics that can be used to identify whether siliceous shale is a hydrostatic physical and chemical deposit, and further proposed the present invention's method for determining whether siliceous shale is a hydrostatic physical and chemical deposit.

[0052] In one embodiment, the present invention provides a method for determining whether siliceous shale is a hydrostatic physical and chemical deposit, comprising:

[0053] Obtaining target siliceous shale; wherein the target siliceous shale has a quartz mass content greater than 50%, a clay mass content not less than 5%, and a total organic carbon mass content greater than 2%;

[0054] Determine whether the target siliceous shale has the following characteristics 1, 2, 3, and 4:

[0055] Feature 1: Biogenic silica accounts for 70-95% of the total volume of quartz and terrigenous feldspar in the rock, and terrigenous quartz and terrigenous feldspar together account for 5-30% of the total volume of quartz and terrigenous feldspar in the rock;

[0056] Feature 2: Contains calcite and dolomite;

[0057] Feature 3: Contains raspberry pyrite; raspberry pyrite includes common raspberry pyrite, which refers to raspberry pyrite with organic matter filling the intercrystalline pores;

[0058] Feature 4: Contains organic matter, wherein the organic matter comprises an organic clay complex with honeycomb-like nanopores;

[0059] If the target siliceous shale has characteristics 1, 2, 3, and 4, the target siliceous shale is a hydrostatic physical and chemical deposit.

[0060] Furthermore, obtaining the target siliceous shale includes:

[0061] Conduct whole-rock analysis and total organic carbon testing on the siliceous shale to be tested to determine the mass content of quartz, clay, and total organic carbon in the siliceous shale to be tested;

[0062] If the quartz mass content of the siliceous shale to be tested is higher than 50%, the clay mass content is not less than 5%, and the total organic carbon mass content is higher than 2%, the siliceous shale to be tested is taken as the target siliceous shale.

[0063] Furthermore, determining whether the target siliceous shale has the following characteristics 1, 2, 3, and 4 includes:

[0064] using a target siliceous shale core to produce an argon ion polished sheet of the target siliceous shale;

[0065] Collect MAPS rock image data of argon ion polished slices of target siliceous shale;

[0066] Based on the MAPS rock image data volume of the argon ion polished slice of the target siliceous shale, observe whether the target siliceous shale has features 1, 2, 3, and 4;

[0067] Furthermore, the resolution of the MAPS rock image data volume of the argon ion polished slice of the target siliceous shale is 4-10nm;

[0068] Furthermore, the length of the argon ion polished slice of the target siliceous shale is 0.8-2 cm;

[0069] Furthermore, the width of the argon ion polished slice of the target siliceous shale is 0.8-2 cm;

[0070] Furthermore, the thickness of the argon ion polished slice of the target siliceous shale is 0.3-0.8 cm;

[0071] Furthermore, the polishing surface of the argon ion polishing sheet of the target siliceous shale is parallel to the cylindrical surface of the target siliceous shale core;

[0072] Furthermore, collecting a MAPS rock image data volume of an argon ion polished wafer of a target siliceous shale includes: selecting an area with a length and a width not exceeding 400 μm on a polished surface of the argon ion polished wafer of the target siliceous shale, and collecting the MAPS rock image data volume;

[0073] Furthermore, during the acquisition of the MAPS rock image data volume of the argon ion polished slice of the target siliceous shale, the top surface of the argon ion polished slice of the target siliceous shale is located above the field of view, and the bottom surface of the argon ion polished slice 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;

[0074] Furthermore, based on the MAPS rock image data volume of the argon ion polished slice of the target siliceous shale, in the process of observing whether the target siliceous shale has the four features of feature 1, feature 2, feature 3, and feature 4, an image editor (such as the offline image editor ATLAS TM BROWSER-BASED VIEWER) is used to observe the MAPS rock image data on a computer.

[0075] Furthermore, in feature 2, the calcite is in the form of irregular particles.

[0076] Furthermore, in feature 2, the dolomite is rhombic iron-containing dolomite wrapped in dolomite particles.

[0077] Furthermore, in feature 3, the berry-like pyrite also includes overgrown berry-like pyrite, and the overgrown berry-like pyrite is berry-like pyrite with residual intercrystalline pores that are not filled with organic matter.

[0078] Furthermore, in Feature 3, the ordinary berry-shaped pyrite includes at least one of berry-shaped pyrite with linear contact of grains, berry-shaped pyrite with point contact of grains, and berry-shaped pyrite with grains floating in organic matter.

[0079] Furthermore, in feature 4, the organic matter also includes pure organic matter (pure organic matter, as the opposite of a complex of organic matter and other substances, refers to organic matter that exists independently rather than in the form of a complex with other substances), and the pure organic matter includes at least one of pure organic matter with honeycomb nanopores and pure organic matter without pores.

[0080] Furthermore, the method for determining whether the siliceous shale is a hydrostatic physical and chemical deposit also includes:

[0081] When the target siliceous shale is a hydrostatic physical and chemical deposit, determining whether the target siliceous shale is a multi-cavity biogenic siliceous shale, a single-cavity biogenic siliceous shale, or a cavity-free biogenic siliceous shale;

[0082] Among hydrostatically deposited siliceous shales, horizontal shale gas wells with multi-cavity biogenic siliceous shales as targets have high yields, those with single-cavity biogenic siliceous shales as targets have medium yields, and those with no-cavity biogenic siliceous shales as targets have low yields. Distinguishing hydrostatically deposited siliceous shales as cavity biogenic siliceous shales, single-cavity biogenic siliceous shales, or no-cavity biogenic siliceous shales is more helpful in determining the development potential of hydrostatically deposited siliceous shales and guiding efficient shale gas exploration and development.

[0083] Furthermore, in the target siliceous shale, if biogenic silica accounts for more than 90% of the total volume of quartz and terrigenous feldspar in the rock, and the total of terrigenous quartz and terrigenous feldspar accounts for less than 10% of the total volume of quartz and terrigenous feldspar in the rock, and the cavities of the biogenic silica are filled with pure organic matter with honeycomb-like nanopores, then the target siliceous shale is multi-cavity biogenic siliceous shale;

[0084] Furthermore, in the target siliceous shale, if the biogenic silica accounts for more than 90% of the total volume of quartz and terrigenous feldspar in the rock, and the total of terrigenous quartz and terrigenous feldspar accounts for less than 10% of the total volume of quartz and terrigenous feldspar in the rock, and the cavity of the biogenic silica is filled with organic silica grain complexes and / or calcite, then the target siliceous shale is a single-cavity biogenic siliceous shale;

[0085] Furthermore, in the target siliceous shale, if the biogenic silica accounts for less than 90% and greater than or equal to 70% of the total volume of quartz and terrigenous feldspar in the rock, and the total volume of terrigenous quartz and terrigenous feldspar in the rock is greater than 10% and less than or equal to 30%, then the target siliceous shale is cavity-free biogenic siliceous shale.

[0086] The rock skeleton of siliceous shale is composed of rigid particles such as biogenic silica, terrigenous quartz, calcite, dolomite, and pyrite, demonstrating strong resistance to compaction. The overlying strata exert limited compaction on the organic matter. Therefore, the organic matter with honeycomb nanopores is interpreted as a pyroasphalt clay complex derived from sedimentary organic clay complexes, the pure organic matter with honeycomb nanopores is pyroasphalted solid asphalt, and the pure organic matter without pores is pyroasphalted petroleum. The skeleton of siliceous organisms is ultimately transformed into porous quartz with a layered structure through dissolution and precipitation reactions. Therefore, the quartz with a layered structure is interpreted as biogenic silica, while the quartz without a layered structure is interpreted as terrigenous quartz. The irregular calcite with obvious dissolution is the remnant of calcite formed in surface waters, some of which fill the cavities of the single-cavity biogenic silica. The rhombic dolomite formed near the water-sediment interface and during shallow burial diagenesis. Raspberry pyrite formed in the BSR near the sulfidic water and water-sediment interface, as well as in the AOM-SR during shallow burial diagenesis. Analysis of minerals, organic matter, and organic clay and silica complexes suggests that the siliceous shales with these characteristics represent the lithification of siliceous mud formed by hydrostatic physical and chemical sedimentation.

[0087] Clarifying the sedimentary diagenesis of these siliceous shales strengthens the plausibility and reliability of the siliceous pelitic formation of these siliceous shales through hydrostatic physical and chemical sedimentation. The sedimentary diagenesis of these siliceous shales can be divided into three (sub)processes and six stages: sedimentation, water-sediment interface diagenesis, and burial diagenesis. The sedimentation process is further subdivided into upper water column sedimentation and lower water column sedimentation, while the burial diagenesis is further subdivided into shallow burial diagenesis, early intermediate burial diagenesis, late intermediate burial diagenesis, and deep burial diagenesis. During the upper water column sedimentation stage, above the CSD, siliceous organism skeletons, terrigenous quartz, calcite, clay, and other debris were suspended and settled. The cavities of radiolarian siliceous skeletons were filled with calcite. Following the death of the siliceous organisms, the siliceous skeletons began to dissolve and precipitate. During the lower water sedimentation phase, calcite dissolved beneath the CSD, particularly intensely below the CLD and CCD. Organic silicate complexes occupied the calcite dissolution pores within the cavities of radiolarian shells. Water sulfidation led to the precipitation of pyrite berries. Clays absorbed dissolved organic matter to form organic clay complexes. At the deep seafloor, siliceous bioskeletons (multi-cavity, monocavity, and acavity-free bioskeletons), calcite (including radiolarian shell cavity calcite), organic clay complexes, organic silicate complexes within radiolarian shell cavities, pyrite berries, and terrigenous debris (such as quartz and clay) formed siliceous mud. During diagenesis at the water-sediment interface, pyrite berries continued to precipitate and proliferate under the influence of the BSR, and dolomite precipitated. During the shallow burial diagenetic stage, AOM-SR induced the precipitation and growth of rhombic pyrite, while ferruginous dolomite precipitated and formed rhombic ferruginous dolomite encasing dolomite. Sedimentary organic matter transformed into kerogen, and organic clay complexes transformed into kerogen clay complexes, and organic silica complexes into kerogen silica complexes. During the early diagenetic stage of intermediate burial, kerogen transformed into pre-oil asphalt, kerogen clay complexes into pre-oil asphalt clay complexes, and kerogen silica complexes into pre-oil asphalt silica complexes. During the formation of pre-oil asphalt, kerogen volume expansion generated abnormally high pressure, driving the pre-oil asphalt into pores. When the abnormally high pressure was sufficiently high, hydrocarbon-generating pressurized fractures formed, serving as the primary migration pathways for the pre-oil asphalt. During the late diagenetic stage of intermediate burial, pre-oil asphalt is converted into solid asphalt and oil, pre-oil asphalt clay complex is converted into solid asphalt clay complex, and pre-oil asphalt silica complex is converted into solid asphalt silica complex. During the process of oil generation, the volume of organic matter expands to produce abnormally high pressure, driving the oil to migrate into the pores; when the abnormally high pressure is large enough, hydrocarbon-generating pressurized fractures are generated, which serve as the primary migration channel of oil; the siliceous biological skeleton is converted into porous quartz with enlarged secondary quartz (biogenic silica with a ring structure) under the action of dissolution and precipitation.During the deep burial diagenesis stage, solid asphalt is converted into pyroasphalt with honeycomb pores, petroleum is converted into pyroasphalt without pores, solid asphalt clay complex is converted into pyroasphalt (organic) clay complex with honeycomb pores, and solid asphalt silica complex is converted into pyroasphalt (organic) silica complex with honeycomb pores.

[0088] Example 1:

[0089] This embodiment provides a method for determining whether the siliceous shale in target siliceous shale area A is a hydrostatic physical and chemical deposit, including:

[0090] 1. Perform whole rock analysis and total organic carbon test on the core of the siliceous shale to be tested taken from 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 quartz mass content of the siliceous shale to be tested is higher than 50%, the clay mass content is not less than 5%, and the total organic carbon mass content is higher than 2%, the siliceous shale to be tested will be regarded as the target siliceous shale.

[0091] In this example, whole-rock testing data for the siliceous shale to be tested showed that quartz, feldspar, calcite, dolomite, ferruginous dolomite, clay, and pyrite accounted for 75.3%, 1.1%, 4.5%, 7.9%, 1.6%, 8.2%, and 1.4% of the rock volume, respectively. Total organic carbon testing data showed that total organic carbon accounted for 4.2% of the rock mass fraction. Therefore, the quartz mass content of the siliceous shale to be tested was greater than 50%, the clay mass content was not less than 5%, and the total organic carbon mass content was greater than 2%. Therefore, the siliceous shale to be tested was selected as the target siliceous shale, and the core of the siliceous shale to be tested was directly used as the core of the siliceous shale to be tested.

[0092] 2. Use the core of the target siliceous shale to make an argon ion polishing sheet of the target siliceous shale; wherein, the argon ion polishing sheet of the target siliceous shale is 2 cm long, 2 cm wide, and 0.5 cm thick; the polishing surface of the argon ion polishing sheet 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 polishing sheet are marked.

[0093] 3. Select an area with a length and width not exceeding 400 μm on the polished surface of the argon ion polished wafer of the target siliceous shale, and collect a MAPS rock image data volume with a resolution of 4 nm; wherein, during the process of collecting the MAPS rock image data volume, the top surface of the argon ion polished wafer of the target siliceous shale is located above the field of view, and the bottom surface of the argon ion polished wafer of the target siliceous shale is located below the field of view, thereby ensuring that all phenomena observed in the collected MAPS rock image data volume are merely magnifications of natural phenomena.

[0094] 4. Use image editor (offline image editor ATLASTM Observe the collected MAPS rock image data volume on a computer using a BROWSER-BASEDVIEWER to observe whether the target siliceous shale has the four features of Feature 1, Feature 2, Feature 3, and Feature 4;

[0095] Feature 1: Biogenic silica accounts for 70-95% of the total volume of quartz and terrigenous feldspar in the rock, and terrigenous quartz and terrigenous feldspar together account for 5-30% of the total volume of quartz and terrigenous feldspar in the rock;

[0096] Feature 2: Contains calcite and dolomite; calcite is irregular particles, and dolomite is rhombic iron-containing dolomite wrapped in dolomite particles;

[0097] Characteristic 3: Contains common berry pyrite and overgrown berry pyrite. Common berry pyrite refers to berry pyrite with intercrystalline pores filled with organic matter, while overgrown berry pyrite refers to berry pyrite with intercrystalline pores remaining inside that are not filled with organic matter. Common berry pyrite includes at least one of berry pyrite with linear contact of grains, berry pyrite with point contact of grains, and berry pyrite with grains floating in organic matter.

[0098] Feature 4: Contains organic clay complexes with honeycomb nanopores and pure organic matter (pure organic matter, as opposed to organic matter complexed with other substances, refers to organic matter that exists independently rather than in the form of a complex with other substances); pure organic matter includes at least one of pure organic matter with honeycomb nanopores and pure organic matter without pores;

[0099] If the target siliceous shale has characteristics 1, 2, 3, and 4, the target siliceous shale is a hydrostatic physical and chemical deposit.

[0100] In this embodiment, quartz, calcite, iron-containing dolomite encapsulated dolomite, and raspberry pyrite constitute the rock skeleton, and clay, organic matter, and organic clay complexes are distributed between the skeletons (e.g. Figure 1 Quartz consists of biogenic silica (showing a layered structure, see Figure 1 a and red arrows in ef) and terrigenous quartz (showing a non-layered structure, see Figure 1 The rock is composed of 64.6% of the rock volume, and terrigenous quartz and feldspar account for 3.3% of the rock volume. Figure 1 The blue arrow in e) accounts for 4.6% of the rock volume, and the rhombic ferruginous dolomite encloses the dolomite (see Figure 1 Green arrows in e) account for 12.5% ​​of the rock volume. Raspberry pyrite includes overgrown raspberry pyrite (see Figure 1l) and common raspberry pyrite, which includes raspberry pyrite with linear contact of grains (see Figure 1 m in), berry-shaped pyrite with point-like contact of grains (see Figure 1 n) and berry-shaped pyrites with grains floating in organic matter (see Figure 1 o in the rock), raspberry pyrite accounts for 0.6% of the rock volume. Clay is banded (see Figure 1 Arrows in h) and clumps (see Figure 1 i) in the above, accounting for 5.9% of the rock volume. Pure organic matter with honeycomb nanopores and organic clay complex with honeycomb nanopores (see Figure 1 The cd in the rock is distributed in the rock skeleton composed of quartz, carbonate and pyrite and is difficult to distinguish, accounting for 6.9% of the rock volume; pure organic matter with honeycomb nanopores occupies the cavity of biogenic silica, accounting for 1.2% of the rock volume; pure organic matter without pores fills the cracks in the form of strips (see Figure 1 jk), accounting for 0.4% of the rock volume.

[0101] In summary, in this embodiment, the target siliceous shale meets the four characteristics of characteristics 1, 2, 3, and 4, and is a hydrostatic physical and chemical deposit.

[0102] 5. Determine whether the target siliceous shale is multi-cavity biogenic siliceous shale, single-cavity biogenic siliceous shale, or cavity-free biogenic siliceous shale;

[0103] Among them, in the target siliceous shale, if biogenic silica accounts for more than 90% of the volume of quartz in the rock, and terrigenous quartz and terrigenous feldspar account for less than 10% of the volume of quartz in the rock, and the cavity of the biogenic silica is filled with pure organic matter with honeycomb-like nanopores, then the target siliceous shale is multi-cavity biogenic siliceous shale;

[0104] Among them, in the target siliceous shale, if the biogenic silica accounts for more than 90% of the volume of quartz in the rock, and the total of terrigenous quartz and terrigenous feldspar accounts for less than 10% of the volume of quartz in the rock, and the cavity of the biogenic silica is filled with organic silica particle complexes and / or calcite, then the target siliceous shale is a single-cavity biogenic siliceous shale;

[0105] Among them, in the target siliceous shale, if the biogenic silica accounts for less than 90% and greater than or equal to 70% of the volume of quartz in the rock, and the total volume of terrigenous quartz and terrigenous feldspar accounts for greater than 10% and less than or equal to 30% of the volume of quartz in the rock, then the target siliceous shale is cavity-free biogenic siliceous shale.

[0106] In this embodiment, in the target siliceous shale, biogenic silica accounts for more than 90% of the volume of quartz in the rock, and terrigenous quartz and terrigenous feldspar together account for less than 10% of the volume of quartz in the rock, and the cavities of the biogenic silica are filled with pure organic matter in honeycomb-shaped nanopores. Therefore, the target siliceous shale is multi-cavity biogenic siliceous shale.

[0107] Multi-cavity biogenic silica formed during surface water sedimentation and transformed into quartz with a lamellar structure during the late diagenetic stage of intermediate burial. Calcite formed in the upper water column and descended to the lower water column along with terrigenous quartz, feldspar, and clay. Calcite dissolved, and the dissolved organic matter combined with clay to form an organic clay complex. Sulfidic waters favored the precipitation of rhombic pyrite. At the deep seafloor, a complex of multi-cavity biogenic silica, calcite, terrigenous quartz, feldspar, rhombic pyrite, clay, and organic clay formed siliceous mud. During diagenesis at the water-sediment interface, dolomite and rhombic pyrite precipitated. During shallow burial diagenesis, the environment for rhombic pyrite precipitation evolved from sulfidic waters through BSR to AOM-SR. Rhombic ferruginous dolomite encased dolomite in the sediment, and the sedimentary organic clay complex transformed into a kerogen clay complex. During the early diagenetic stage of intermediate burial, kerogen clay complexes transform into pre-oil asphalt clay complexes. As kerogen converts to pre-oil asphalt, it expands, and the expanded portion migrates and occupies pores. During the late diagenetic stage of intermediate burial, pre-oil asphalt clay complexes transform into solid asphalt clay complexes. As pre-oil asphalt converts to solid asphalt and oil, it expands, leading to abnormally high pressures and cracks, forming pathways for the initial migration of oil. During the deep diagenetic stage, the solid asphalt clay complexes transform into pyroasphalt clay complexes with honeycomb nanopores, solid asphalt transforms into pyroasphalt with honeycomb nanopores, and oil transforms into non-porous pyroasphalt. The oil filling hydrocarbon-generated pressurized fractures transforms into long, non-porous strips of pyroasphalt.

[0108] The area where the target siliceous shale is located (i.e., target siliceous shale area A) is a shale gas sweet spot. The shale gas horizontal wells targeting the area where the target siliceous shale is located (i.e., target siliceous shale area A) are highly productive and have high exploration and development potential.

[0109] Example 2

[0110] This embodiment provides a method for determining whether the siliceous shale in target siliceous shale area B is a hydrostatic physical and chemical deposit, including:

[0111] 1. Perform whole rock analysis and total organic carbon test on the core of the siliceous shale to be tested taken from the target siliceous shale area B to determine the mass content of quartz, clay, and total organic carbon in the siliceous shale to be tested; if the quartz mass content of the siliceous shale to be tested is higher than 50%, the clay mass content is not less than 5%, and the total organic carbon mass content is higher than 2%, the siliceous shale to be tested will be regarded as the target siliceous shale.

[0112] In this example, whole-rock testing data for the siliceous shale to be tested showed that quartz, feldspar, calcite, dolomite, ferruginous dolomite, clay, and pyrite accounted for 69.8%, 2.8%, 13.1%, 3.2%, 3.8%, 5.4%, and 1.9% of the rock volume, respectively. Total organic carbon testing data showed that total organic carbon accounted for 5.3% of the rock mass fraction. Therefore, the quartz mass content of the siliceous shale to be tested was greater than 50%, the clay mass content was not less than 5%, and the total organic carbon mass content was greater than 2%. Therefore, the siliceous shale to be tested was selected as the target siliceous shale, and the core of the siliceous shale to be tested was directly used as the core of the siliceous shale to be tested.

[0113] 2. Use the core of the target siliceous shale to make an argon ion polishing sheet of the target siliceous shale; wherein, the argon ion polishing sheet of the target siliceous shale is 2 cm long, 2 cm wide, and 0.5 cm thick; the polishing surface of the argon ion polishing sheet 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 polishing sheet are marked.

[0114] 3. Select an area with a length and width not exceeding 400 μm on the polished surface of the argon ion polished wafer of the target siliceous shale, and collect a MAPS rock image data volume with a resolution of 4 nm; wherein, during the process of collecting the MAPS rock image data volume, the top surface of the argon ion polished wafer of the target siliceous shale is located above the field of view, and the bottom surface of the argon ion polished wafer of the target siliceous shale is located below the field of view, thereby ensuring that all phenomena observed in the collected MAPS rock image data volume are merely magnifications of natural phenomena.

[0115] 4. Use image editor (offline image editor ATLAS TM Observe the collected MAPS rock image data volume on a computer using a BROWSER-BASEDVIEWER to observe whether the target siliceous shale has the four features of Feature 1, Feature 2, Feature 3, and Feature 4;

[0116] Feature 1: Biogenic silica accounts for 70-95% of the total volume of quartz and terrigenous feldspar in the rock, and terrigenous quartz and terrigenous feldspar together account for 5-30% of the total volume of quartz and terrigenous feldspar in the rock;

[0117] Feature 2: Contains calcite and dolomite; calcite is irregular particles, and dolomite is rhombic iron-containing dolomite wrapped in dolomite particles;

[0118] Characteristic 3: Contains common berry pyrite and overgrown berry pyrite. Common berry pyrite refers to berry pyrite with intercrystalline pores filled with organic matter, while overgrown berry pyrite refers to berry pyrite with intercrystalline pores remaining inside that are not filled with organic matter. Common berry pyrite includes at least one of berry pyrite with linear contact of grains, berry pyrite with point contact of grains, and berry pyrite with grains floating in organic matter.

[0119] Feature 4: Contains organic clay complexes with honeycomb nanopores and pure organic matter (pure organic matter, as opposed to organic matter complexed with other substances, refers to organic matter that exists independently rather than in the form of a complex with other substances); pure organic matter includes at least one of pure organic matter with honeycomb nanopores and pure organic matter without pores;

[0120] If the target siliceous shale has characteristics 1, 2, 3, and 4, the target siliceous shale is a hydrostatic physical and chemical deposit.

[0121] In this embodiment, quartz, calcite, iron-containing dolomite encapsulated dolomite, and raspberry pyrite constitute the rock skeleton, and clay, organic matter, organic clay complexes, and organic silicon complexes are distributed between the skeletons (e.g., Figure 2 Quartz is composed of biogenic silica (shown as a ring-layer structure, see Figure 2 a and i in Figure 2 The blue solid circle in the middle d is defined as the inner layer of biosilica, and the areas outside the blue solid circle are the inner and outer layers of biosilica), biosilica debris (shown as a layered structure, see Figure 2 The blue solid circle in the e in the figure is the core of the biogenic silica, and the part between the blue solid circle and the yellow solid circle is the shell of the biogenic silica) and terrigenous quartz and terrigenous feldspar (shown as a layerless structure, see Figure 2 b) in the composition. Biogenic silica and biogenic silicate account for 57.9% of the rock volume (the content of biogenic silicate is very low), and the total volume of terrigenous quartz and terrigenous feldspar accounts for 2.6% of the rock volume. Irregular calcite (see Figure 2 a, m) account for 4.6% of the rock volume, and rhombic iron-bearing dolomite encloses dolomite (see Figure 1 n in) accounts for 12.6% of the rock volume. Raspberry pyrite includes overgrown raspberry pyrite (see Figure 2 o) and common raspberry pyrite, which includes raspberry pyrite with linear contact of grains (see Figure 2 p in), berry-shaped pyrite with point-like contact of grains (see Figure 2q) and berry-shaped pyrite with grains floating in organic matter (see Figure 2 r in the rock), raspberry pyrite accounts for 0.8% of the rock volume. Clay is banded (see Figure 2 The yellow strip in h in the figure is the main component, accounting for 4.6% of the rock volume. The organic clay complex with honeycomb nanopores and the pure organic matter with honeycomb nanopores ( Figure 2 The green solid circle in j is defined as an organic clay complex with honeycomb nanopores, and the areas outside the green solid circle are pure organic matter with honeycomb nanopores) or pure organic matter with honeycomb nanopores and pure organic matter without pores ( Figure 2 The green solid line in f delineates the organic clay complex with honeycomb nanopores, the white solid line delineates the pure organic matter without pores, and the areas outside the green solid line and the white solid line are pure organic matter with honeycomb nanopores) coexist in one pore. The pure organic matter with honeycomb nanopores ( Figure 2 s) and pure organic matter without pores ( Figure 2 The t) can fill a pore alone or together ( Figure 2 The white solid circle in the u in the figure delimits pure organic matter without pores, and the area outside the white solid circle is pure organic matter with honeycomb-shaped nanopores). The cracks filled with pure organic matter without pores are strip-shaped (see Figure 2 v), where the organic clay complex with honeycomb nanopores accounts for 5.3% of the rock volume, the pure organic matter with honeycomb nanopores accounts for 3.9% of the rock volume, and the pure organic matter without pores accounts for 1.7% of the rock volume. The calcite pores in the biosiliceous cavity are filled with organic silica complexes with honeycomb nanopores (see Figure 2 a and c) and the biosilica cavity is fully filled with organic silicon particle composites with honeycomb nanopores (see Figure 2 In (i, k), the organic silicon particle complex with honeycomb nanopores accounts for 4.5% of the rock volume fraction.

[0122] In summary, in this embodiment, the target siliceous shale meets the four characteristics of characteristics 1, 2, 3, and 4, and is a hydrostatic physical and chemical deposit.

[0123] 5. Determine whether the target siliceous shale is multi-cavity biogenic siliceous shale, single-cavity biogenic siliceous shale, or cavity-free biogenic siliceous shale;

[0124] Among them, in the target siliceous shale, if biogenic silica accounts for more than 90% of the volume of quartz in the rock, and terrigenous quartz and terrigenous feldspar account for less than 10% of the volume of quartz in the rock, and the cavity of the biogenic silica is filled with pure organic matter with honeycomb-like nanopores, then the target siliceous shale is multi-cavity biogenic siliceous shale;

[0125] Among them, in the target siliceous shale, if the biogenic silica accounts for more than 90% of the volume of quartz in the rock, and the total of terrigenous quartz and terrigenous feldspar accounts for less than 10% of the volume of quartz in the rock, and the cavity of the biogenic silica is filled with organic silica particle complexes and / or calcite, then the target siliceous shale is a single-cavity biogenic siliceous shale;

[0126] Among them, in the target siliceous shale, if the biogenic silica accounts for less than 90% and greater than or equal to 70% of the volume of quartz in the rock, and the total volume of terrigenous quartz and terrigenous feldspar accounts for greater than 10% and less than or equal to 30% of the volume of quartz in the rock, then the target siliceous shale is cavity-free biogenic siliceous shale.

[0127] In this embodiment, in the target siliceous shale, biogenic silica accounts for more than 90% of the volume of quartz in the rock, and terrigenous quartz and terrigenous feldspar together account for less than 10% of the volume of quartz in the rock, and the cavities of the biogenic silica are filled with organic silicon particle complexes. Therefore, the target siliceous shale is a single-cavity biogenic siliceous shale.

[0128] Single-cavity biogenic silica formed during surface water sedimentation and transformed into quartz with a lamellar structure during the late diagenetic stage of intermediate burial. Calcite formed in the upper water column and filled the biogenic silica cavity. It then descended to the lower water column along with terrigenous quartz, feldspar, and clay. The calcite dissolved, and the dissolved organic matter combined with the clay to form an organoclay complex. The calcite solution pores in the biogenic silica cavity were filled with organoclay complexes. Sulfidic waters favored the precipitation of pyrite fragility. At the deep seafloor, single-cavity biogenic silica, siliceous debris, cavity organoclay complexes, terrigenous quartz, feldspar, calcite, pyrite fragility, clay, and organoclay complexes formed siliceous mud. During diagenesis at the water-sediment interface, dolomite and pyrite fragility precipitated. During the shallow burial diagenesis stage, the environment for raspberry pyrite precipitation changed from sulfidic waters through BSR to AOM-SR. Rhombic ferruginous dolomite encased dolomite precipitation, and the sedimentary organic clay complex transformed into kerogen clay complex, and the sedimentary organic silica complex transformed into kerogen silica complex. During the early diagenesis stage of intermediate burial, the kerogen clay complex transformed into pre-oil asphalt clay complex, and the kerogen silica complex transformed into pre-oil asphalt silica complex. As the kerogen transformed into pre-oil asphalt, its volume expanded, and the expanded part migrated and occupied pores. During the late diagenesis stage of intermediate burial, the pre-oil asphalt clay complex transformed into solid asphalt clay complex, and the pre-oil asphalt silica complex transformed into solid asphalt silica complex. The volume expansion of the pre-oil asphalt as it transformed into solid asphalt and oil led to abnormally high pressures, generating fractures and forming pathways for the initial migration of oil. During the deep burial diagenesis stage, solid asphalt clay complexes are transformed into pyroasphalt clay complexes with honeycomb nanopores, solid asphalt silica complexes are transformed into pyroasphalt silica complexes with honeycomb nanopores, solid asphalt is transformed into pyroasphalt with honeycomb nanopores, petroleum is transformed into pore-free pyroasphalt, and petroleum filling hydrocarbon-generated pressurized fractures is transformed into long strips of pore-free pyroasphalt.

[0129] The shale gas horizontal wells targeting the area where the target siliceous shale is located (i.e., target siliceous shale area B) have moderate production and have medium exploration and development potential.

[0130] Example 3

[0131] This embodiment provides a method for determining whether the siliceous shale in the target siliceous shale area C is a hydrostatic physical and chemical deposit, including:

[0132] 1. Perform whole rock analysis and total organic carbon test on the core of the siliceous shale to be tested taken from the target siliceous shale area C to determine the mass content of quartz, clay, and total organic carbon in the siliceous shale to be tested; if the quartz mass content of the siliceous shale to be tested is higher than 50%, the clay mass content is not less than 5%, and the total organic carbon mass content is higher than 2%, then the siliceous shale to be tested will be regarded as the target siliceous shale.

[0133] In this example, whole-rock test data for the siliceous shale to be tested showed that quartz, feldspar, calcite, dolomite, ferruginous dolomite, clay, and pyrite accounted for 59.1%, 4.3%, 10.3%, 3.0%, 1.7%, 19.3%, and 2.3% of the rock volume, respectively. Total organic carbon test data showed that total organic carbon accounted for 3.7% of the rock mass fraction. Therefore, the quartz mass content of the siliceous shale to be tested was greater than 50%, the clay mass content was not less than 5%, and the total organic carbon mass content was greater than 2%. Therefore, the siliceous shale to be tested was selected as the target siliceous shale, and the core of the siliceous shale to be tested was directly used as the core of the siliceous shale to be tested.

[0134] 2. Use the core of the target siliceous shale to make an argon ion polishing sheet of the target siliceous shale; wherein, the argon ion polishing sheet of the target siliceous shale is 2 cm long, 2 cm wide, and 0.5 cm thick; the polishing surface of the argon ion polishing sheet 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 polishing sheet are marked.

[0135] 3. Select an area with a length and width not exceeding 400 μm on the polished surface of the argon ion polished wafer of the target siliceous shale, and collect a MAPS rock image data volume with a resolution of 4 nm; wherein, during the process of collecting the MAPS rock image data volume, the top surface of the argon ion polished wafer of the target siliceous shale is located above the field of view, and the bottom surface of the argon ion polished wafer of the target siliceous shale is located below the field of view, thereby ensuring that all phenomena observed in the collected MAPS rock image data volume are merely magnifications of natural phenomena.

[0136] 4. Use image editor (offline image editor ATLAS TM Observe the collected MAPS rock image data volume on a computer using a BROWSER-BASEDVIEWER to observe whether the target siliceous shale has the four features of Feature 1, Feature 2, Feature 3, and Feature 4;

[0137] Feature 1: Biogenic silica accounts for 70-95% of the total volume of quartz and terrigenous feldspar in the rock, and terrigenous quartz and terrigenous feldspar together account for 5-30% of the total volume of quartz and terrigenous feldspar in the rock;

[0138] Feature 2: Contains calcite and dolomite; calcite is irregular particles, and dolomite is rhombic iron-containing dolomite wrapped in dolomite particles;

[0139] Characteristic 3: Contains common berry pyrite and overgrown berry pyrite. Common berry pyrite refers to berry pyrite with intercrystalline pores filled with organic matter, while overgrown berry pyrite refers to berry pyrite with intercrystalline pores remaining inside that are not filled with organic matter. Common berry pyrite includes at least one of berry pyrite with linear contact of grains, berry pyrite with point contact of grains, and berry pyrite with grains floating in organic matter.

[0140] Feature 4: Contains organic clay complexes with honeycomb nanopores and pure organic matter (pure organic matter, as opposed to organic matter complexed with other substances, refers to organic matter that exists independently rather than in the form of a complex with other substances); pure organic matter includes at least one of pure organic matter with honeycomb nanopores and pure organic matter without pores;

[0141] If the target siliceous shale has characteristics 1, 2, 3, and 4, the target siliceous shale is a hydrostatic physical and chemical deposit.

[0142] In this embodiment, quartz, calcite, iron-containing dolomite encapsulated dolomite ( Figure 3 The arrow in a in the figure) and raspberry pyrite form the rock skeleton, and clay, organic matter and organic clay complex are distributed between the skeletons (such as Figure 3 Quartz is made of biogenic silica (shown as a layered structure, see Figure 3 a in Figure 3 The arrow in g in the figure points to the inner layer of the non-cavitary biogenic silica with pores, and the outer shell of the non-cavitary biogenic silica has no pores) and terrigenous quartz (showing a non-circular structure, see Figure 3 The rock volume is composed of biogenic silica (47.4%), terrigenous quartz and terrigenous feldspar (7.1%). Figure 3 a) accounts for 10.3% of the rock volume, and rhombic iron-bearing dolomite encloses dolomite (see Figure 3 The arrow in a in Figure 4) accounts for 4.2% of the rock volume. Raspberry pyrite includes overgrown raspberry pyrite (see Figure 3 o) and common raspberry pyrite, which includes raspberry pyrite with linear contact of grains (see Figure 3 p in), berry-shaped pyrite with point-like contact of grains (see Figure 3 q) and berry-shaped pyrite with grains floating in organic matter (see Figure 3 r in the rock), raspberry pyrite accounts for 1.5% of the rock volume. Clay is banded (see Figure 3 The main component is the ce) which accounts for 20.7% of the rock volume. The organic clay complex with honeycomb nanopores (see Figure 3b, g) are distributed in the rock skeleton composed of quartz, carbonate and pyrite, accounting for 4.7% of the rock volume; pure organic matter with honeycomb nanopores occupies secondary pores in the form of clusters (see Figure 3 f, h) or occupy the cracks in strips (see Figure 3 j, mn), accounting for 3.6% of the rock volume; the cracks filled with pure organic matter without pores are strip-shaped (see Figure 3 i, kl) in the rock, accounting for 0.5% of the rock volume.

[0143] In summary, in this embodiment, the target siliceous shale meets the four characteristics of characteristics 1, 2, 3, and 4, and is a hydrostatic physical and chemical deposit.

[0144] 5. Determine whether the target siliceous shale is multi-cavity biogenic siliceous shale, single-cavity biogenic siliceous shale, or cavity-free biogenic siliceous shale;

[0145] Among them, in the target siliceous shale, if biogenic silica accounts for more than 90% of the volume of quartz in the rock, and terrigenous quartz and terrigenous feldspar account for less than 10% of the volume of quartz in the rock, and the cavity of the biogenic silica is filled with pure organic matter with honeycomb-like nanopores, then the target siliceous shale is multi-cavity biogenic siliceous shale;

[0146] Among them, in the target siliceous shale, if the biogenic silica accounts for more than 90% of the volume of quartz in the rock, and the total of terrigenous quartz and terrigenous feldspar accounts for less than 10% of the volume of quartz in the rock, and the cavity of the biogenic silica is filled with organic silica particle complexes and / or calcite, then the target siliceous shale is a single-cavity biogenic siliceous shale;

[0147] Among them, in the target siliceous shale, if the biogenic silica accounts for less than 90% and greater than or equal to 70% of the volume of quartz in the rock, and the total volume of terrigenous quartz and terrigenous feldspar accounts for greater than 10% and less than or equal to 30% of the volume of quartz in the rock, then the target siliceous shale is cavity-free biogenic siliceous shale.

[0148] In this embodiment, in the target siliceous shale, biogenic silica accounts for less than 90% and greater than or equal to 70% of the volume of quartz in the rock, and the total volume of terrigenous quartz and terrigenous feldspar accounts for greater than 10% and less than or equal to 30% of the volume of quartz in the rock. Therefore, the target siliceous shale is cavity-free biogenic siliceous shale.

[0149] Non-cavitary biogenic silica formed during surface water sedimentation and transformed into quartz with a lamellar structure during the late diagenetic stage of intermediate burial. Calcite formed in the upper water column and descended to the lower water column along with terrigenous quartz, feldspar, and clay. Calcite dissolved, and the dissolved organic matter combined with clay to form an organic clay complex. Sulfidic waters favored the precipitation of rhombic pyrite. At the deep seafloor, a complex of non-cavitary biogenic silica, calcite, terrigenous quartz, feldspar, rhombic pyrite, clay, and organic clay formed siliceous mud. During diagenesis at the water-sediment interface, dolomite and rhombic pyrite precipitated. During shallow burial diagenesis, the environment for rhombic pyrite precipitation evolved from sulfidic waters through BSR to AOM-SR. Rhombic ferruginous dolomite encased dolomite in the sediment, and the sedimentary organic clay complex transformed into a kerogen clay complex. During the early diagenetic stage of intermediate burial, kerogen clay complexes transform into pre-oil asphalt clay complexes. As kerogen converts to pre-oil asphalt, its volume expands, creating hydrocarbon-generating pressurized pores (secondary pores) and fractures that serve as pathways for the initial migration of pre-oil asphalt. During the late diagenetic stage of intermediate burial, pre-oil asphalt clay complexes transform into solid asphalt clay complexes. As pre-oil asphalt converts to solid asphalt and oil, its volume expands, leading to abnormally high pressures and cracks, forming pathways for the initial migration of oil. During the deep diagenetic stage, solid asphalt clay complexes transform into pyroasphalt clay complexes with honeycomb nanopores, solid asphalt transforms into pyroasphalt with honeycomb nanopores, and oil transforms into pore-free pyroasphalt.

[0150] The shale gas horizontal wells targeting the target siliceous shale area (i.e., target siliceous shale area C) have low production and low exploration and development potential.

[0151] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is 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 in the scope of protection of the present invention.

Claims

1. A method for determining whether siliceous shale is a hydrostatic physical and chemical deposit, comprising: Obtaining target siliceous shale; wherein the target siliceous shale has a quartz mass content greater than 50%, a clay mass content not less than 5%, and a total organic carbon mass content greater than 2%; Determine whether the target siliceous shale has the following characteristics 1, 2, 3, and 4: Feature 1: Biogenic silica accounts for 70-95% of the total volume of quartz and terrigenous feldspar in the rock, and terrigenous quartz and terrigenous feldspar together account for 5-30% of the total volume of quartz and terrigenous feldspar in the rock; Feature 2: Contains calcite and dolomite; Feature 3: Contains raspberry pyrite; raspberry pyrite includes common raspberry pyrite, which refers to raspberry pyrite with organic matter filling the intercrystalline pores; Feature 4: Contains organic matter, wherein the organic matter comprises an organic clay complex with honeycomb-like nanopores; If the target siliceous shale has characteristics 1, 2, 3, and 4, the target siliceous shale is a hydrostatic physical and chemical deposit.

2. The method according to claim 1, wherein Obtaining target siliceous shale, including: Conduct whole-rock analysis and total organic carbon testing on the siliceous shale to be tested to determine the mass content of quartz, clay, and total organic carbon in the siliceous shale to be tested; If the quartz mass content of the siliceous shale to be tested is higher than 50%, the clay mass content is not less than 5%, and the total organic carbon mass content is higher than 2%, the siliceous shale to be tested is taken as the target siliceous shale.

3. The method according to claim 1, wherein Determining whether the target siliceous shale has the following characteristics 1, 2, 3, and 4 includes: using a target siliceous shale core to produce an argon ion polished sheet of the target siliceous shale; Collect MAPS rock image data of argon ion polished slices of target siliceous shale; Based on the MAPS rock image data volume of the argon ion polished slice of the target siliceous shale, observe whether the target siliceous shale has features 1, 2, 3, and 4; Preferably, the polishing surface of the argon ion polishing sheet of the target siliceous shale is parallel to the cylindrical surface of the target siliceous shale core; Preferably, the resolution of the MAPS rock image data volume of the argon ion polished slice of the target siliceous shale collected is 4-10 nm; Preferably, the length of the target siliceous shale argon ion polishing sheet is 0.8-2 cm, the width of the target siliceous shale argon ion polishing sheet is 0.8-2 cm, and the thickness of the target siliceous shale argon ion polishing sheet is 0.3-0.8 cm; Preferably, collecting the MAPS rock image data volume of the argon ion polished wafer of the target siliceous shale comprises: selecting an area with a length and a width not exceeding 400 μm on the polished surface of the argon ion polished wafer of the target siliceous shale, and collecting the MAPS rock image data volume; Preferably, during the process of collecting the MAPS rock image data volume of the argon ion polished sheet of the target siliceous shale, the top surface of the argon ion polished sheet of the target siliceous shale is located above the field of view, and the bottom surface of the argon ion polished sheet of the target siliceous shale is located below the field of view.

4. The method according to claim 1, wherein In feature 2, the calcite is irregular particles.

5. The method according to claim 1, wherein In feature 2, the dolomite is rhombic iron-bearing dolomite encapsulating dolomite particles.

6. The method according to claim 1, wherein In feature 3, berry-shaped pyrite also includes overgrown berry-shaped pyrite, and overgrown berry-shaped pyrite is berry-shaped pyrite with residual intercrystalline pores that are not filled with organic matter.

7. The method according to claim 1, wherein In feature 3, the ordinary berry pyrite includes at least one of berry pyrite with linear contact of grains, berry pyrite with point contact of grains, and berry pyrite with grains floating in organic matter.

8. The method according to claim 1, wherein In feature 4, the organic matter further includes pure organic matter, and the pure organic matter includes at least one of pure organic matter having honeycomb-shaped nanopores and pure organic matter without pores.

9. The method according to claim 1, wherein Methods for determining whether siliceous shale is hydrostatic physical and chemical deposition also include: When the target siliceous shale is a hydrostatic physical and chemical deposit, it is determined whether the target siliceous shale is a multi-cavity biogenic siliceous shale, a single-cavity biogenic siliceous shale, or a cavity-free biogenic siliceous shale.

10. The method according to claim 9, wherein: In the target siliceous shale, if biogenic silica accounts for more than 90% of the total volume of quartz and terrigenous feldspar in the rock, and the total of terrigenous quartz and terrigenous feldspar accounts for less than 10% of the total volume of quartz and terrigenous feldspar in the rock, and the cavities of the biogenic silica are filled with pure organic matter with honeycomb-like nanopores, then the target siliceous shale is multi-cavity biogenic siliceous shale; In the target siliceous shale, if the biogenic silica accounts for more than 90% of the total volume of quartz and terrigenous feldspar in the rock, and the total of terrigenous quartz and terrigenous feldspar accounts for less than 10% of the total volume of quartz and terrigenous feldspar in the rock, and the cavity of the biogenic silica is filled with organic silica grain complexes and / or calcite, then the target siliceous shale is a single-cavity biogenic siliceous shale; In the target siliceous shale, if the biogenic silica accounts for less than 90% and greater than or equal to 70% of the total volume of quartz and terrigenous feldspar in the rock, and the total volume of terrigenous quartz and terrigenous feldspar in the rock is greater than 10% and less than or equal to 30%, then the target siliceous shale is cavity-free biogenic siliceous shale.

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