Dolomite protolith structure recovery analysis method and system

Abstract

The invention provides a dolomite protolith structure recovery analysis method and system, and relates to the technical field of geological exploration. The dolomite protolith structure recovery analysis method comprises the following steps: performing cause type division on dolomite according to dolomite crystal characteristics of to-be-analyzed dolomite, observing a dolomitization complete region or layer section of the to-be-analyzed dolomite, and analyzing a dolomite residual structure, carrying out residual limestone structure type identification on the dolomitization incomplete area or layer section of the same layer section of the dolomite to be analyzed, analyzing silicification nodules and stripes in the dolomite to be analyzed, and carrying out dolomite protolith structure recovery; according to the method, dolomite genetic type analysis is incorporated into dolomite protolith structure recovery, and the dolomite protolith structure recovery is obtained through matching analysis of siliceous nodule and stripe internal structures and dolomite structure genetic evolution, structural identification of silicified nodule and stripes in dolomite and matching analysis of silicified nodule and stripe reflection sedimentary structures and dolomite structures. And the dolomite protolith structure can be accurately recovered.

Description

Technical Field

[0001] The present invention relates to the technical field of geological exploration, and particularly to a method and system for restoring and analyzing the original rock structure of dolomite. Background Art

[0002] Dolomite is an important type of oil and gas reservoir. Restoring the original rock structure of dolomite is of great significance for analyzing the dolomite sedimentary environment, the development and distribution laws of dolomite, and predicting the development and distribution of dolomite reservoirs. Due to the easily variable characteristics of carbonate rocks, after the formation of dolomite, it is easily transformed by strong diagenetic processes, and the original sedimentary appearance can be completely changed, making it quite difficult to restore the original rock structure of dolomite.

[0003] Existing research has to some extent addressed the restoration of the original rock structure of dolomite. For example, Zhang Yinben elaborated in detail in 1985 on the observation methods, types and significance of residual structures of carbonate rocks; Bi Yiquan et al. discussed in 2001 that the micrite envelope and its fine identification are not only of important identification significance but also important research methods for restoring the original rock structure characteristics and sedimentary environment of secondary dolomite; Yang Bo et al. believed in 2010 that the evolution of dolomite structure is mainly affected by the original rock chemical composition, sedimentary structure and dolomitization fluid, and proposed the structure evolution of dolomite in marl, grain-bearing marl, packstone, etc.; Zhang Xuefeng et al. elaborated in 2017 on the identification of the residual structure of the Middle and Lower Ordovician dolomite in the Tazhong area and its important indicative significance for analyzing the origin and sedimentary environment of dolomite. Obviously, existing research focuses on restoring the original rock structure from the residual structures inside dolomite, but it is not systematic and comprehensive enough to meet the needs of the work of restoring the original rock structure of dolomite and predicting dolomite reservoirs.

[0004] In terms of technical process, Qiao Zhanfeng disclosed in his invention patent CN107728232B a method and system for petrological and geochemical identification of dolomite genetic types. This method uses data such as outcrops, cores and thin sections to identify typical petrological markers, including rock types, sedimentary structures, associated lithofacies and combinations, sedimentary environments and dolomite crystal characteristics, etc., to preliminarily identify the dolomitization mode of dolomite formation; on the basis of petrological identification, according to the exclusive geochemical indicators corresponding to the dolomitization mode, samples are selected to carry out corresponding geochemical analysis; the dolomite genetic type is comprehensively judged based on petrological and geochemical analysis.

[0005] Specifically, it is mentioned that a gasket (a 70g A4 paper) is placed under the microscope slide, and the original rock structure of dolomite can be better observed by adjusting the transmitted light intensity. The original rock structure analysis is carried out by using fluorescence thin sections and combining outcrop sedimentary structures to assist in the analysis of dolomite genesis. However, in terms of the method for restoring the original rock structure of dolomite, its technical solution is not comprehensive enough to complete the restoration of the original rock structure of dolomite. At present, there is no reliable and dedicated method process for restoring the original rock structure of dolomite.

[0006] It can be seen that how to provide a method for restoring the original rock structure of dolomite is one of the problems that need to be solved urgently by those skilled in the art. Summary of the Invention

[0007] In view of the lack of a reliable and dedicated method for restoring the original rock structure of dolomite in the prior art, the present invention provides an analysis method and system for restoring the original rock structure of dolomite, which can more comprehensively and accurately restore the original rock structure of dolomite and better serve the research on dolomite sedimentary facies and reservoirs.

[0008] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0009] On the one hand, the present invention provides an analysis method for restoring the original rock structure of dolomite, including the following steps:

[0010] S1. Classify the genesis type of dolomite according to the crystal characteristics of dolomite crystals in the dolomite to be analyzed;

[0011] S2. Observe the completely dolomitized area or section of the dolomite to be analyzed, and analyze the residual structure of the dolomite;

[0012] S3. Identify the structural types of the residual limestone in the incompletely dolomitized area or section of the same section of the dolomite to be analyzed;

[0013] S4. Analyze the silicified nodules and bands in the dolomite to be analyzed to restore the original rock structure of the dolomite;

[0014] When the dolomite to be analyzed has a crystalline texture and it is difficult to restore its original rock structure, the following steps are further included:

[0015] S5. Analyze the rock layer characteristics and the structure of the original sediment of the dolomite to be analyzed to assist in restoring the original rock structure of the dolomite.

[0016] Preferably, the crystal characteristics in step S1 include: crystal size, crystal morphology, and crystal surface characteristics.

[0017] Preferably, the genesis types in step S1 include syngenetic high-salinity genesis dolomite, early-middle diagenetic buried genesis dolomite, and hydrothermal genesis dolomite.

[0018] Further preferably, the syndepositional high-salinity origin dolomite includes two types:

[0019] The identification marks of one type include: the dolomite crystals are of powder-microcrystalline structure, and gypsum crystals or gypsum mold pores can develop;

[0020] The identification marks of the other type include: the dolomite crystals are of powder-fine-grained anhedral structure.

[0021] Further preferably, the identification marks of the early-middle diagenetic buried origin dolomite include that the dolomite crystals are of powder-fine-medium crystalline structure, the dolomite has a high degree of automorphism, and zonation structures can develop.

[0022] Further preferably, the identification marks of the hydrothermal origin dolomite include that the dolomite is mainly saddle dolomite, the crystals have undulatory extinction characteristics, and the crystal faces are not straight.

[0023] Preferably, the tools used for the observation in step S2 include a microscope.

[0024] Further preferably, the observation methods include direct observation, observation with a gasket placed, and fluorescence thin section observation to analyze the residual structure of dolomite.

[0025] Preferably, the method for analyzing the residual structure of dolomite in step S2 is as follows:

[0026] For the syndepositional high-salinity origin dolomite, its protolith structure can be preserved, showing a dolomite with a granular structure, algal binding structure or bioherm structure composed of powder-microcrystalline structure dolomite or the arrangement of powder-microcrystalline dolomite; or a dolomite with a crystalline grain structure composed of powder-fine-grained dolomite; or the phantom of a granular structure, algal binding structure or bioherm structure is restored by the gasket method;

[0027] For the early-middle diagenetic buried origin dolomite and hydrothermal origin dolomite, dolomitization causes the destruction of the protolith structure; it is necessary to observe whether there is a shadow of the protolith structure in the rock, or restore the protolith structure through the intentional combination of heterogeneous crystalline grain structures under thin sections.

[0028] Most preferably, for the case of superimposed burial dolomitization of syndepositional high-salinity origin dolomite, it can be discriminated by the distribution characteristics of dolomite crystals restricted by bioclasts; during the syndepositional dolomitization process, due to the development of matrix micropores, the fluid seepage conditions are not restricted, and the microcrystalline calcite matrix particles, gravel sand debris, ooids and other microcrystalline calcite particles are more likely to be dolomitized into powder-microcrystalline dolomite. As a whole, the fluid is not easily infiltrated into the bioclasts, so it is not easily dolomitized and is preserved in the form of calcite composition and bioclast morphology; however, during the subsequent burial dolomitization process, this part of bioclastic calcite can be dolomitized. Thus, through the different crystal structure characteristics of the two-stage dolomitization before and after, the original rock structure characteristics of dolomite are shown.

[0029] Preferably, the structural types of the residual limestone described in step S3 include: grain structure, algal bound structure, bioherm structure and microcrystalline structure.

[0030] Preferably, the analysis described in step S4 includes the following steps:

[0031] Identify the internal structure of the silicified nodules and bands in the dolomite, and analyze the matching between the internal structure reflected by the silicified nodules and bands and the dolomite structure;

[0032] Silicified nodules and bands widely exist in limestone and dolomite. The silicified nodules and bands are the products of the differentiation and aggregation silicification of SiO2 particles in the early diagenetic stage. The silicification follows the principle of mimetic replacement and can better retain the original rock structure characteristics; observations on the limestone strata show that the internal structure of the siliceous nodules and bands is consistent with the limestone structure; in the coexistence of dolomite and residual limestone patches, siliceous nodules and bands, the internal structure of the siliceous nodules and bands is consistent with the internal structure of the residual limestone patches and has a genetic evolution matching with the dolomite structure.

[0033] Further preferably, the structures involved in the internal structure identification include: grain structure, algal bound structure, bioherm structure and microcrystalline structure.

[0034] Most preferably, the matching analysis is to restore the original rock structure of dolomite through the genetic evolution matching between the internal structure of the siliceous nodules and bands and the dolomite structure;

[0035] The part of the silicified nodules and bands that is microcrystalline quartz under the microscope is the product of the early silicification of limestone, and the original rock is microcrystalline calcite;

[0036] The part of the silicified nodules and bands that is chalcedony under the microscope indicates the granular calcite cement in the intergranular pores, window-shaped pores or pores between biological skeletons.

[0037] Preferably, the formation characteristics described in step S5 include rock color, rock layer thickness, and sedimentary structures.

[0038] More preferably, the rock color includes light color and dark color;

[0039] The rock layer thickness includes thin layer, medium bedding, thick bedding, and massive;

[0040] The sedimentary structures include cross-bedding, grading bedding, bird's eye structure, and mud crack structure.

[0041] Preferably, in the analysis described in step S5, the matching criterion between the formation characteristics and the original sediment structure is:

[0042] The original rock structure of dolomite with light color, thick bedding, and well-developed cross-bedding is granular structure;

[0043] The original rock structure of dark-colored, thin-layered dolomite is microcrystalline structure;

[0044] The original rock structure of light-colored, thin-layered dolomite with well-developed mud crack structure is microcrystalline structure.

[0045] Preferably, the basis for determining the structure of the original sediment in step S5 includes the sedimentary water depth, water extraction energy, and redox state results determined based on the formation characteristics described in step S5.

[0046] Preferably, the analysis in step S5 also includes analyzing the matching between the sedimentary structure reflected by silicified nodules and bands and the dolomite structure.

[0047] On the other hand, the present invention provides a system for analyzing and restoring the original rock structure of dolomite, which includes:

[0048] The first unit is used to identify the dolomite crystal characteristics of the dolomite to be analyzed and classify the genetic types of dolomite;

[0049] The second unit is used to identify the characteristics of the completely dolomitized area or layer section, and analyze the residual structure of dolomite;

[0050] The third unit is used to identify the residual limestone structure types in the incompletely dolomitized area or layer section, and restore the original rock structure of dolomite;

[0051] The fourth unit is used to analyze the silicified nodules and band structures and restore the original rock structure of dolomite;

[0052] The fifth unit is used to analyze the formation characteristics to assist in restoring the original rock structure of dolomite.

[0053] Preferably, the first unit specifically includes the following steps:

[0054] Observe the crystal size, crystal morphology and crystal surface characteristics of dolomite under a microscope to classify the genetic types of dolomite;

[0055] The genetic types of the dolomite include synsedimentary hypersaline genetic dolomite, early-middle diagenetic buried genetic dolomite and hydrothermal genetic dolomite;

[0056] The synsedimentary hypersaline genetic dolomite includes two types. The identification marks of one type include that the dolomite crystals are powder-microcrystalline structures and can develop gypsum crystals or gypsum mold pores; the identification marks of the other type include that the dolomite crystals are powder-fine-grained anhedral structures and the dolomite surface is relatively dirty. The synsedimentary hypersaline genetic dolomite is prone to develop in microcrystalline mud, algal boundstone, biogenic reef rock and grainstone at the top of reef flat in the high and low parts of the sedimentary environment;

[0057] The identification marks of the early-middle diagenetic buried genetic dolomite include that the dolomite crystals are powder-fine-medium crystalline structures, the dolomite has a high degree of automorphism and can develop a zonal structure; it is prone to select microcrystalline mud that has not undergone diagenetic transformation in the early stage;

[0058] The identification marks of the hydrothermal genetic dolomite include that the dolomite is mainly saddle dolomite, the crystals have undulatory extinction characteristics and the crystal faces are not straight.

[0059] The synsedimentary hypersaline genetic powder-microcrystalline structure dolomite and the synsedimentary hypersaline genetic powder-fine-grained anhedral structure dolomite can retain remnants of the original rock structure to a certain extent. The method described by Qiao Zhanfeng et al. in the patent (A Petrological and Geochemical Identification Method and System for the Genetic Types of Dolomite, Patent No. ZL201711075901.7) can be used to restore the original rock structure of dolomite by placing gaskets under microscope slides;

[0060] The early-middle diagenetic buried dolomite and hydrothermal dolomite are composed of granular powder-fine-medium crystalline automorphic dolomite and saddle dolomite crystals, and it is difficult to restore the original rock structure by conventional means.

[0061] Preferably, the second unit specifically includes the following steps:

[0062] For the areas or intervals with complete and thorough dolomitization, analyze the residual structure of dolomite through direct observation under a microscope, observation with gaskets placed under a microscope and observation of fluorescence thin sections;

[0063] For syngenetic high-salinity dolomite, its original rock structure can be preserved, showing as dolomite with a powder-microcrystalline structure, or a granular structure, algal bonded structure, or bioherm structure composed of arranged powder-microcrystalline dolomite; it can also be a dolomite with a crystalline structure composed of powder-fine crystalline dolomite, or the phantom of a granular structure, algal bonded structure, or bioherm structure can be restored by adding a spacer.

[0064] For burial dolomite and hydrothermal dolomite of early to middle diagenetic period, dolomitization usually destroys the sedimentary structure of the original rock. It is necessary to observe whether there is a shadow of the original rock structure in the rock, or to restore the original rock structure through the intentional combination of heterogeneous grain structure under thin section.

[0065] The presence of syngenetic high-salinity dolomite superimposed on burial dolomitization can be identified by the presence of dolomite crystal distribution characteristics constrained by bioclastics. During the syngenetic dolomitization process, due to the development of matrix micropores, fluid seepage conditions were unrestricted, and microcrystalline calcite matrix particles, gravel sand fragments, and oolitic particles were more likely to undergo dolomitization and become powder-microcrystalline dolomite. The bioclastics as a whole were not easily penetrated by fluids and were therefore not easily dolomitized, but were preserved as calcite components and bioclastic forms. However, during the subsequent burial dolomitization process, this part of the bioclastic calcite could undergo dolomitization, thereby revealing the structural characteristics of the dolomite protolith through the different crystal structure characteristics of the two stages of dolomitization.

[0066] Preferably, the third unit specifically includes the following steps:

[0067] For areas or intervals in the same layer as the target dolomite but with incomplete dolomitization, the original rock structure of the dolomite is restored by identifying the structural type of the residual limestone.

[0068] The structural types of the residual limestone include: granular structure, algae-bonded structure, bioherm structure and microcrystalline structure;

[0069] A genetic evolution matching analysis is carried out between the limestone structure and the related dolomite structure to identify the original rock structure type of the dolomite, thereby determining whether the original rock of the dolomite is a granular structure, algal bond structure, bioherm structure or microcrystalline structure.

[0070] Preferably, the fourth unit specifically includes the following steps:

[0071] First, the internal structure of the siliceous nodules and strips is determined under a microscope, wherein the internal structure is selected from a granular structure, an algae-bonded structure, a bioherm structure, or a microcrystalline structure;

[0072] The siliceous nodules and bands that appear as microcrystalline quartz under the microscope are the products of early silicification of the limestone, and the original rock is microcrystalline calcite;

[0073] Under the microscope, the siliceous nodules and bands of chert indicate intergranular pores, fenestral pores or pores between biogenic frameworks, and granular calcite cement;

[0074] Furthermore, through the matching analysis of the genetic evolution of the internal structure of siliceous nodules and bands and the dolomite structure, the original structure of dolomite is restored. The original structure is selected from grain structure, algal boundstone structure, bioherm structure, micritic structure or other structures that may exist in the original dolomite rock.

[0075] Through the structural identification of silicified nodules and bands in dolomite and the matching analysis of the sedimentary structure reflected by silicified nodules and bands and the dolomite structure, the relevant original structure of dolomite is restored; silicified nodules and bands are widely present in limestone and dolomite. Silicified nodules and bands are the products of the differentiation and aggregation of SiO2 particles during the early diagenetic stage. The silicification process follows the principle of mimetic replacement and can better retain the characteristics of the original rock structure; the internal structure of siliceous nodules and bands is consistent with the limestone structure; in the coexistence body of dolomite, residual limestone patches, siliceous nodules and bands, the internal structure of siliceous nodules and bands is consistent with the internal structure of residual limestone patches and has a genetic evolution matching relationship with the dolomite structure.

[0076] Preferably, the fifth unit specifically includes the following steps:

[0077] For dolomite with a grain structure under the microscope and difficult to restore the original rock structure, the sedimentary water depth, water energy, redox state are judged through the rock color, layer thickness and sedimentary structure, and then the structure of the original sediment is judged;

[0078] Through the combined judgment of color, layer thickness and sedimentary structure by naked-eye observation, the possibility analysis of the original sediment structure is carried out; then the matching analysis of the sedimentary structure reflected by siliceous nodules and bands and the dolomite structure is carried out;

[0079] The color of the rock includes light color and dark color;

[0080] The layer thickness of the rock includes thin layer, medium bedded, thick bedded and massive;

[0081] The sedimentary structure includes cross-bedding, grading bedding, bird's-eye structure and mud crack structure;

[0082] The matching criteria of the color, layer thickness and sedimentary structure with the original sediment structure are as follows:

[0083] The original rock of dolomite with light color, thick bedded and well-developed cross-bedding should be grain structure;

[0084] The original rock structure of dark-colored, thin-layered dolomite is micritic structure;

[0085] The protolith structure of the light-colored, thin-bedded dolomite with well-developed mud cracks is microcrystalline structure;

[0086] Furthermore, through the matching analysis of the genetic evolution of the internal structure of siliceous nodules and bands and the dolomite structure, the protolith structure of dolomite is restored. The protolith structure is selected from grain structure, algal binding structure, bioherm structure, microcrystalline structure or other structures that can exist in the protolith of dolomite.

[0087] Through the structure identification of silicified nodules and bands in dolomite and the matching analysis of the sedimentary structure reflected by silicified nodules and bands and the dolomite structure, the restoration of the relevant protolith structure of dolomite is carried out; silicified nodules and bands widely exist in limestone and dolomite. Silicified nodules and bands are the products of the differentiation and aggregation silicification of SiO2 particles in the early diagenetic stage. The silicification follows the principle of mimetic replacement and can better retain the characteristics of the protolith structure; the internal structure of siliceous nodules and bands is consistent with the limestone structure; in the coexistence body of dolomite, residual limestone patches, siliceous nodules and bands, the internal structure of siliceous nodules and bands is consistent with the internal structure of residual limestone patches and has a genetic evolution matching with the dolomite structure.

[0088] Compared with the prior art, the present invention has the following beneficial effects:

[0089] The present invention incorporates the analysis of dolomite genetic types into the restoration of the protolith structure of dolomite. Through the dolomite genetic types, the preservation and destruction status of the protolith structure can be analyzed. Through this technical means, the subsequent protolith structure analysis method can be effectively matched and the accuracy of the protolith structure analysis can be improved;

[0090] The present invention also provides a method for the genetic evolution matching analysis of the residual limestone patch structure and the dolomite structure. Through the genetic evolution matching analysis of the residual limestone structure in dolomite and the relevant dolomite structure, the accuracy of the protolith structure analysis of dolomite can be further improved;

[0091] The understanding of the internal structure of siliceous nodules and bands and the matching analysis of their genetic evolution with the dolomite structure in the present invention are also the innovation points of the present invention. The present invention proposes another way and technology for the restoration of the protolith structure of dolomite in combination with the foregoing content. Through the matching analysis of the internal structure of siliceous nodules and bands and the genetic evolution of the relevant dolomite structure, the accuracy of the restoration of the protolith structure of dolomite is ensured;

[0092] The present invention also proposes to adopt the rock color and structure analysis method. Through the matching analysis of the relevant sedimentary environment information reflected by color, layer thickness and sedimentary structure with the protolith structure of dolomite restored previously, it is used as an effective means to assist in the restoration of the protolith structure of dolomite. Brief Description of the Drawings

[0093] Figure 1This is a flow chart of a method for restoring and analyzing the original rock structure of dolomite according to an embodiment of the present invention;

[0094] Figure 2 、 Figure 3 and Figure 4 It is powder-microcrystalline dolomite of evaporation pump origin under contemporaneous high salinity conditions;

[0095] Figure 5 、 Figure 6 and Figure 7 It is powdery-fine crystalline heteromorphic dirty dolomite formed by seepage backflow under contemporaneous high salinity conditions. Figure 8 、 Figure 9 and Figure 10 It is a diagenetic buried medium-powder crystal euhedral dolomite;

[0096] Figure 11 、 Figure 12 and Figure 13 It is a coarse-megacrystal saddle-shaped dolomite of hydrothermal origin during the diagenetic period;

[0097] Figure 14 The original rock is microcrystalline limestone, with fine-grained euhedral dolomite of burial origin;

[0098] Figure 15 The original rock is micro-spar crystalline psammitic limestone, with fine-grained euhedral dolomite of burial origin.

[0099] Figure 16 and Figure 17 It is the residual structural change of dolomite whose original rock is granular structure;

[0100] Figure 18 and Figure 19 It is the residual structural change of dolomite whose original rock is bioherm limestone;

[0101] Figure 20 and Figure 21 It is the residual structural change of dolomite whose original rock is algae-bonded structure;

[0102] Figure 22 and Figure 23 The original rock has a crystalline or microcrystalline structure;

[0103] Figure 24 It is a residual limestone patch in the dolomite;

[0104] Figure 25 It is a patch of silicified nodules in microcrystalline limestone;

[0105] Figure 26 It is a patch of silicified nodules in granular limestone;

[0106] Figure 27 It is a patch of silicified nodules in algae-bound limestone;

[0107] Figure 28 It is a silicified nodule patch in dolomite;

[0108] Figure 29 It is a silicified nodule patch in dolomite;

[0109] Figure 30 It is a silicified nodule patch in dolomite;

[0110] Figure 31 It is an example for analyzing the original rock structure of dolomite microscopically;

[0111] Figure 32 It is an example for analyzing the original rock structure of dolomite macroscopically. Specific implementation manners

[0112] In order to make the present invention clearer and more understandable, the present invention will be described in more detail below through specific embodiments, but it should not be construed as a limitation on the implementable scope of the present invention.

[0113] An embodiment of the present invention provides a system for restoring and analyzing the original rock structure of dolomite, which determines the genetic type of dolomite according to the characteristics of dolomite crystals; for different types of dolomite, through the analysis of the residual structure of the dolomite part, the rock structure analysis of the residual limestone patches, the internal structure analysis of the silicified nodules and bands, and the analysis of the rock color, layer thickness and sedimentary structure characteristics, the restoration of the original rock structure of dolomite is realized.

[0114] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0115] Embodiment A method for restoring and analyzing the original rock structure of dolomite

[0116] Figure 1 It is a flow chart of the system for restoring and analyzing the original rock structure of dolomite in this embodiment. As Figure 1 shown, the system for restoring and analyzing the original rock structure of dolomite shown includes the following steps:

[0117] Step S1: Classify the genetic type of dolomite according to the characteristics of dolomite crystals of the dolomite to be analyzed;

[0118] First, judge the genetic type of dolomite according to the degree of retention of the original rock structure;

[0119] Specifically, dolomite that clearly preserves and shows the protolith structure is formed by syndiagenetic dolomitization. For example, Figure 2 , Figure 3 and Figure 4 represent powdery - microcrystalline dolomite formed by the evaporation pump under syndiagenetic high - salinity conditions. The protolith has a microcrystalline structure, sparitic sand structure, and algal boundstone structure, indicating deposition in the supratidal zone, algal mat in the intertidal zone, and sand shoal;

[0120] Specifically, Figure 5 , Figure 6 and Figure 7 represent powdery - fine - grained anhedral dirty dolomite formed by permeation reflux under syndiagenetic high - salinity conditions. They better retain the protolith structure. For example, Figure 6 has a sparitic oolitic structure, indicating oolitic shoal deposition, Figure 7 has an algal boundstone structure, indicating tidal flat deposition;

[0121] Specifically, Figure 8 , Figure 9 and Figure 10 represent medium - powdery euhedral dolomite formed by burial diagenesis, which has the characteristic of obviously destroying the sedimentary structure. The dolomite rock composed of this type of dolomite shows no protolith structure characteristics under plane - polarized light microscopy;

[0122] Specifically, Figure 11 , Figure 12 and Figure 13 represent coarse - giant - crystal saddle - shaped dolomite formed by hydrothermal diagenesis, which also has the characteristic of destroying the sedimentary structure. The dolomite rock composed of this type of dolomite shows no protolith structure characteristics.

[0123] In view of the fact that some scholars believe that the fog - core part of the medium - powdery euhedral dolomite formed by burial diagenesis is the indication of particle residue, and the protolith of the dolomite rock composed of this type of dolomite is a particle structure. In this embodiment, Figure 14 and Figure 15 are used to prove that the fog - core of the medium - powdery euhedral dolomite is not necessarily an indication of particle residue; Figure 14 The protolith is micritic limestone, and fine - grained euhedral dolomite formed by burial diagenesis develops. A fog - core bright - edge can be seen, and some fog - cores also show a rhombic shape; Figure 15 The protolith is micro - sparitic sandstone limestone, and fine - grained euhedral dolomite formed by burial diagenesis is seen, and no fog - core related to sand grains exists. Therefore, the fog - core of the medium - powdery euhedral dolomite is not necessarily an indication of sand - grain residue.

[0124] Step S2: Observe the completely dolomitized area or section of the dolomite to be analyzed, and analyze the residual structure of the dolomite;

[0125] For the dolomite section, determine the type of the residual structure of the dolomite according to the crystal characteristics and crystal arrangement characteristics of the dolomite;

[0126] Specifically, Figure 16 and Figure 17 show the residual structural changes of dolomite with the protolith being granular structure dolomite;

[0127] Specifically, Figure 18 and Figure 19 show the residual structural changes of dolomite with the protolith being bioclastic limestone dolomite;

[0128] Specifically, Figure 20 and Figure 21 show the residual structural changes of dolomite with the protolith being algal boundstone dolomite;

[0129] Specifically, Figure 22 and Figure 23 show the characteristics of the protolith being crystalline grain structure or microcrystalline structure.

[0130] Step S3: Identify the structural types of residual limestone in the incomplete dolomitization area or layer of the dolomite to be analyzed in the same layer;

[0131] Through the structural analysis of the residual limestone patches associated with the dolomite, determine the protolith structure of the dolomite;

[0132] Specifically, Figure 24 reveal the residual limestone patches in the dolomite. The residual limestone patches can be microcrystalline structure, granular structure, or granular microcrystalline structure, showing that the protolith of the dolomite is microcrystalline structure, granular structure, granular microcrystalline structure, or granular microcrystalline structure containing particles.

[0133] Step S4: Analyze the silicified nodules and bands in the dolomite to be analyzed, and restore the protolith structure of the dolomite.

[0134] Through the internal structure analysis of the silicified nodules and bands associated with the dolomite, determine the protolith structure of the dolomite;

[0135] Specifically, Figure 25 is the silicified nodule patch in micrite limestone. It can be seen that it also has a microcrystalline structure and has the characteristics of mimicking replacement and inheriting the protolith structure of the limestone.

[0136] Specifically, Figure 26 is the silicified nodule patch in grain limestone. It can be seen that the internal structure of these silicified nodule patches clearly shows a granular structure and has the characteristics of mimicking replacement and inheriting the protolith structure of the limestone.

[0137] Specifically, Figure 27 is the silicified nodule patch in algal boundstone limestone. It can be seen that the internal structure of these silicified nodule patches clearly shows an algal boundstone structure and has the characteristics of mimicking replacement and inheriting the protolith structure of the limestone.

[0138] Specifically, Figure 28They are silicified concretion patches in dolomite. It can be seen that the internal part of these silicified concretion patches clearly shows a microcrystalline structure, indicating that the original rock of the dolomite is microcrystalline limestone with a microcrystalline structure.

[0139] Specifically, Figure 29 They are silicified concretion patches in dolomite. It can be seen that the internal part of these silicified concretion patches clearly shows a granular structure, indicating that the original rock of the dolomite is granular limestone with a granular structure.

[0140] Specifically, Figure 30 They are silicified concretion patches in dolomite. It can be seen that the internal part of these silicified concretion patches clearly shows an algal bound structure, and window-like pores are developed, indicating that the original rock of the dolomite is algal bound limestone with an algal bound structure.

[0141] Step S5: Analyze the rock layer characteristics and original sediment structure of the dolomite to be analyzed, and assist in restoring the original rock structure of the dolomite;

[0142] Specifically, Figure 31 and Figure 32 They are respectively examples of analyzing the original rock structure of dolomite by combining microcosmic and macroscopic methods. Under the microscope, the dolomite shows a crystalline grain structure, and the original rock structure is difficult to distinguish. However, combined with the fact that the compound coral structure on the macroscopic core remains intact, it can be inferred that the original rock of this dolomite is coral bioherm limestone.

[0143] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than a limitation on the protection scope of the present invention. Any simple modification or equivalent replacement of the technical solution of the present invention by those of ordinary skill in the art shall not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A method for restoring and analyzing the original structure of dolomite, characterized in that, It includes the following steps: S1. Classify the genetic types of dolomite according to the dolomite crystal characteristics of the dolomite to be analyzed; S2. Observe the completely dolomitized area or section of the dolomite to be analyzed, and analyze the residual structure of the dolomite; S3. Identify the structural types of residual limestone in the incompletely dolomitized area or section of the same layer of the dolomite to be analyzed; S4. Analyze the silicified nodules and bands in the dolomite to be analyzed, and restore the original rock structure of the dolomite; When the dolomite to be analyzed has a crystalline texture and it is difficult to restore its original rock structure, it also includes the following steps: S5. Analyze the rock layer characteristics and the original sediment structure of the dolomite to be analyzed to assist in restoring the original rock structure of the dolomite.

2. The dolomite protolith structure restoration analysis method according to claim 1, characterized in that The crystal characteristics described in step S1 include: crystal size, crystal morphology, and crystal surface characteristics.

3. The dolomite protolith structure restoration analysis method according to claim 1, wherein The genetic types described in step S1 include syndepositional high-salinity genetic dolomite, early-middle diagenetic burial genetic dolomite, and hydrothermal genetic dolomite.

4. The dolomite protolith structure restoration and analysis method according to claim 3, characterized in that, The syndepositional high-salinity genetic dolomite includes two types: One type of identification mark includes: the dolomite crystal is a powder-microcrystalline texture, and gypsum crystals or gypsum mold pores can be developed; Another type of identification mark includes: the dolomite crystal is a powder-fine-grained anhedral texture.

5. The dolomite protolith structure restoration analysis method according to claim 3, characterized in that The identification mark of the early-middle diagenetic burial genetic dolomite includes that the dolomite crystal is a powder-fine-medium crystalline texture, the dolomite has a high degree of autoform, and a zonal structure can be developed.

6. The method for analyzing the restoration of the original dolomite rock structure according to claim 3, characterized in that The identification mark of the hydrothermal genetic dolomite includes that the dolomite is mainly saddle dolomite, the crystal has a wavy extinction feature, and the crystal surface is not straight.

7. The dolomite protolith structure restoration analysis method according to claim 1, characterized in that The method for analyzing the residual structure of dolomite described in step S2 is: For syndepositional high-salinity genetic dolomite, it is dolomite showing a granular structure, algal binding structure, or bioherm structure composed of powder-microcrystalline dolomite or the arrangement of powder-microcrystalline dolomite, or dolomite showing a crystalline texture composed of powder-fine-grained dolomite; or the phantom of the granular structure, algal binding structure, or bioherm structure is restored by the gasket method; For early-middle diagenetic burial genetic dolomite and hydrothermal genetic dolomite, the dolomitization destroys the original rock structure; it is necessary to observe whether there is a shadow of the original rock structure in the rock, or restore the original rock structure through the intentional combination of heterogeneous crystalline textures under thin sections.

8. The dolomite protolith structure restoration analysis method according to claim 1, characterized in that The structural types of the residual limestone described in step S3 include: granular structure, algal binding structure, bioherm structure, and microcrystalline texture.

9. The dolomite protolith structure restoration analysis method according to claim 1, wherein The analysis described in step S4 includes the following steps: Identify the structure of the silicified nodules and bands in the dolomite, and analyze the matching of the sedimentary structure reflected by the silicified nodules and bands with the dolomite structure; the structures involved in the structure identification include: granular structure, algal binding structure, bioherm structure, and microcrystalline texture; the matching analysis is to restore the original rock structure of the dolomite through the matching of the internal structure of the siliceous nodules and bands with the genetic evolution of the dolomite structure; The part of the siliceous nodules and bands that is microcrystalline quartz under the microscope is the product of the early silicification of limestone, and the original rock is microcrystalline calcite; the part of the siliceous nodules and bands that is chalcedony under the microscope indicates granular calcite cements in intergranular pores, window-like pores, or pores between biological skeletons.

10. The dolomite protolith structure restoration analysis method according to claim 1, wherein The rock formation characteristics described in step S5 include rock color, rock layer thickness, and sedimentary structures: The rock color includes light color and dark color; The sedimentary structures include cross-bedding, graded bedding, bird's-eye structure, and mud crack structure; The rock layer thickness includes thin layer, medium bedding, thick bedding, and massive; In the analysis described in step S5, the matching criteria between the rock formation characteristics and the original sediment structure are: The original rock structure of dolomite with light color, thick bedding, and well-developed cross-bedding is granular structure; The original rock structure of dark-colored, thin-layered dolomite is microcrystalline structure; The original rock structure of dolomite with light color, thin layer, and well-developed mud crack structure is microcrystalline structure; The basis for determining the structure of the original sediment described in step S5 includes the results of sedimentary water depth, water extraction energy, and redox state judged according to the rock formation characteristics described in step S5; The analysis described in step S5 also includes an analysis of the matching between the sedimentary structures reflected by silicified nodules and bands and the dolomite structure.

11. A dolomite protolith structure restoration and analysis system, characterized in that, The system includes: The first unit, which is used to identify the dolomite crystal characteristics of the dolomite to be analyzed and classify the genetic types of dolomite; The second unit, which is used to identify the characteristics of completely dolomitized regions or intervals and analyze the residual structure of dolomite; The third unit, which is used to identify the residual limestone structure types in incompletely dolomitized regions or intervals and restore the original rock structure of dolomite; The fourth unit, which is used to analyze the silicified nodule and band structures and restore the original rock structure of dolomite; The fifth unit, which is used to analyze the rock color, layer thickness, and sedimentary structures to assist in restoring the original rock structure of dolomite.

12. The dolomite protolith structure restoration analysis system according to claim 11, characterized in that, The first unit specifically includes the following steps: Observe the crystal size, crystal morphology, and crystal surface characteristics of dolomite under a microscope to classify the genetic types of dolomite; the genetic types of dolomite include synsedimentary high-salinity genetic dolomite, early-middle diagenetic buried genetic dolomite, and hydrothermal genetic dolomite; The synsedimentary high-salinity genetic dolomite includes two types. One type is identified by dolomite crystals with a powder-microcrystalline structure that can develop gypsum crystals or gypsum mold pores; the other type is identified by dolomite crystals with a powder-fine-grained anhedral structure; the identification marks of the early-middle diagenetic buried genetic dolomite include dolomite crystals with a powder-fine-medium crystal structure, high dolomite idiomorphism, and the development of a zonal structure; The identification marks of the hydrothermal genetic dolomite include that the dolomite is mainly saddle dolomite, the crystals have undulatory extinction characteristics, and the crystal surfaces are not straight.

13. The dolomite protolith structure restoration analysis system according to claim 11, wherein The second unit specifically includes the following steps: For completely dolomitized regions or intervals, analyze the residual structure of dolomite through direct observation under a microscope, observation with a gasket under a microscope, and fluorescence thin section observation; For synsedimentary high-salinity genetic dolomite, it is manifested as dolomite with a granular structure, algal-bonded structure, or bioherm structure composed of powder-microcrystalline dolomite or the arrangement of powder-microcrystalline dolomite; or dolomite with a grain structure composed of powder-fine-grained dolomite; or the phantom of a granular structure, algal-bonded structure, or bioherm structure is restored by the gasket method; For burial dolomite and hydrothermal dolomite of early to middle diagenetic period, dolomitization usually destroys the sedimentary structure of the original rock. It is necessary to observe whether there is a shadow of the original rock structure in the rock, or to restore the original rock structure through the intentional combination of heterogeneous grain structure under thin section.

14. The dolomite protolith structure restoration analysis system according to claim 11, characterized in that The third unit specifically includes the following steps: For areas or intervals in the same layer as the target dolomite but with incomplete dolomitization, the original dolomite structure can be restored by identifying the structural type of the residual limestone; The structural types of the residual limestone include: granular structure, algae-bonded structure, bioherm structure and microcrystalline structure; A genetic evolution matching analysis is carried out between the limestone structure and the related dolomite structure to identify the original rock structure type of the dolomite, thereby determining whether the original rock of the dolomite is a granular structure, algal bond structure, bioherm structure or microcrystalline structure.

15. The dolomite protolith structure restoration analysis system according to claim 11, characterized in that, The fourth unit specifically includes the following steps: First, the internal structure of the siliceous nodules and strips is determined under a microscope, wherein the internal structure is selected from a granular structure, an algae-bonded structure, a bioherm structure, or a microcrystalline structure; Siliceous nodules and bands that appear as microcrystalline quartz under a microscope are the product of early silicification of limestone, and the original rock is microcrystalline calcite; Siliceous nodules and bands that appear as chalcedony under a microscope indicate intergranular pores, window-like holes, or granular calcite cements with holes between biological skeletons; Furthermore, by matching the internal structure of siliceous nodules and bands with the genetic evolution of dolomite structure, the original rock structure of dolomite is restored. The original rock structure is selected from granular structure, algae-bonded structure, bioherm structure, microcrystalline structure or other structures that may exist in the original rock of dolomite.

16. The dolomite protolith structure restoration analysis system according to claim 11, characterized in that, The fifth unit specifically includes the following steps: For dolomites that show a crystalline structure under a microscope and are difficult to restore to their original rock structure, we use visual observation to determine the combination of color, layer thickness, and sedimentary structure to analyze the possibility of the original sedimentary structure. We then analyze the matching between the sedimentary structure reflected by silicified nodules and bands and the dolomite structure. The color of the rock, including: light and dark; The thickness of the rock layer includes thin layer, medium layer, thick layer and massive; The sedimentary structures include cross-bedding, grain sequence bedding, bird's eye structure and mud crack structure; The matching criteria for the color, layer thickness and sedimentary structure with the original sediment structure are: The protolith of light-colored, thick-bedded, cross-bedding dolomite should be granular in texture; The original rock structure of the dark, thin-bedded dolostone is microcrystalline; The original rock structure of the light-colored, thin-layered dolomite with developed mud crack structure is microcrystalline structure.

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