A method for identifying the formation process of microbial dolomite

Abstract

The present invention discloses a method for identifying the formation process of microbial dolomite. The present invention comprehensively applies multiple technical means to select samples, uses high-resolution scanning electron microscope, atomic force microscope-laser Raman, etc., and integrates the results of microbial culture experiments to establish indicative markers of the biogenesis of microbial dolomite. Boron isotopes are used to estimate the ancient pH value of seawater in the early Paleozoic era, and conventional carbon oxygen and strontium isotopes are used to restore ancient temperature and ancient alkalinity, and then simulate (such as: PHREEQC software) the influence and restriction of changes in seawater properties (including differences in physical and chemical conditions and different components) on dolomite precipitation, providing new ideas for solving the ancient "dolomite problem" and having exploratory theoretical significance; clarifying the characteristics of microbial dolomite, the formation environment and other properties, and also has a guiding role in the prediction of dolomite reservoirs.

Description

Technical Field

[0001] The invention relates to the technical field of geological survey, and in particular to a method for identifying the formation process of microbial dolomite. Background Art

[0002] Dolomite is an important reservoir rock for oil and gas resources, and the amount of oil and gas resources discovered has reached more than 50%, but the "Dolomite Genesis Problem" is a century-old mystery that has not been solved by the sedimentology community. Under the temperature and pressure on the earth's surface, inorganic experiments cannot precipitate primary dolomite. Currently, only microbial intervention has been proven to be a mechanism that can directly precipitate primary dolomite from a solution.

[0003] The first mechanism of microbial intervention in the formation of dolomite recognized by the academic community was the experiment reported by Vásconcelos and McKenzie et al. (1995). Under a constant temperature of 4°C, sulfate-reducing bacteria isolated from salt lakes directly precipitated orderly dolomite from the solution on the surface of quartz (Vásconcelos et al., 1995). Vásconcelos and McKenzie studied dolomite in black organic-rich sediments in Lagoa Vermelha, a high-salinity lagoon near Rio de Janeiro, Brazil, and believed that sulfate-reducing bacteria would release excessive magnesium ions during metabolism, thereby saturating the microenvironment (around the cell body) with magnesium ions, leading to the precipitation of dolomite. They called this special mechanism of dolomite formation at normal surface temperature the microbial dolomite (rock) model. According to current research, in anaerobic environments, not only sulfate-reducing bacteria (SRB) can promote the precipitation of primary dolomite; methane anaerobic bacteria also play an important role in promoting the precipitation of dolomite (Pierre and Rouchy, 2004; Rodriguez et al., 2000; Sassen et al., 2004; Roberts et al., 2004; Kenward et al., 2009). Even high salinity is no longer required. Under the salinity conditions of seawater alone, marine sulfate-reducing bacteria D. mediterraneus can precipitate primary dolomite at low temperatures of 21°C (Krause et al., 2012). At the same time, not only anaerobic conditions are not limited to, some halophilic aerobic bacteria can also precipitate ordered dolomite crystals in an oxygen-rich environment (Sánchez-Román et al., 2008, 2009a, 2009b).

[0004] Although only a few microorganisms have been proven to promote (mediate) the precipitation of primary dolomite, the addition of microbial factors has undoubtedly had a revolutionary impact on the study of dolomite genesis and has become a new research hotspot in the field of sedimentology. However, the application of microbial dolomite theory and models to study dolomite genesis lacks detailed work and similar research comparable to that abroad, which is even related to the prediction of dolomite oil and gas reservoir distribution.

[0005] However, there is no systematic and reliable method to determine the genetic type and process of microbial dolomite. Most of the predecessors conducted core observations and took samples for typical phenomena; conducted a variety of geochemical tests and analyses; and determined the genesis type of dolomite reservoirs based on petrological characteristics, combined with sedimentation, diagenesis, and paleoclimate evolution. This research method can be used to identify the genesis of dolomite to a certain extent, but there are still limitations in the study of the genesis of microbial dolomite. For example, first, a variety of geochemical methods were used to analyze the genesis of dolomite replacement, but the specificity of the genesis of a certain special dolomite was not strong. After a lot of manpower and material resources were spent on testing, analysis, and artificial interpretation, it was found that it might not be applicable to special dolomite genesis phenomena, such as microbial dolomite. Second, there is a lack of petrological identification and calibration for microbial dolomite, so there are large differences in the test and analysis results of microbial dolomite. Third, microbial dolomite can roughly restore the environmental conditions of the sedimentary period, but whether the results of various geochemical tests and analyses are affected by various diagenesis during the burial period will lead to large errors in the analysis of the genesis of microbial dolomite. Therefore, it is necessary to exclude the influence of diagenesis on geochemical indicators, and this problem has not yet been solved. Summary of the invention

[0006] The purpose of the present invention is to provide a method for identifying the formation process of microbial dolomite.

[0007] To achieve the above object, the present invention is implemented according to the following technical solutions:

[0008] (1) Combining macroscopic core and field profile observations with microscopic thin section analysis, the sedimentary microfacies of the microbial dolomite development layer were divided in detail to clarify the characteristics of the coexisting rock combination and microscopic sedimentary environment;

[0009] (2) Analyze the petrological characteristics, organic matter characteristics, geochemical indicators indicating diagenetic changes, nanoscale characteristic structures and in-situ micro-regional mineral composition of microbial dolomite. Select samples, identify indicative signs of microbial genesis, and analyze the formation mechanism of microbial dolomite.

[0010] Most dolomites undergo strong recrystallization and strong transformation of later diagenesis, so it is necessary to study the petrological characteristics of dolomites, the preservation of organic matter, and the characteristics of trace and rare earth elements that can indicate the strength of diagenetic changes, so as to screen out dolomites that have not undergone recrystallization or have little influence of recrystallization and diagenesis, observe the microstructure and characteristics, and analyze the mineral composition of the in-situ micro-region. From the aspects of morphological characteristics, mineral composition, particle size distribution law and nano-level structure, the difference between metasomatic dolomite and primary dolomite precipitated in modern microbial culture experiments is compared to identify the indicative signs of microbial origin. Based on the remaining bacterial fossils, the positional relationship between dolomite and remaining organic matter, the process of microbial mediation of dolomite in geological history is analyzed, and the process of microbial participation in the morphological evolution of dolomite from nucleation to the formation of complete euhedral crystals is verified, so as to verify the formation mechanism of microbial dolomite in the Lower Paleozoic.

[0011] (3) By using the conventional carbon, oxygen and strontium isotopes and the unconventional boron isotopes, we can reasonably estimate the properties of the ancient seawater during the same period of microbial dolomite precipitation and various physical and chemical conditions. We can also use software (e.g. PHREEQC) to calculate the changes in dolomite saturation, the concentrations of various weak acids, weak bases and hydrated ions in seawater, etc., so as to analyze the influence of early Paleozoic seawater on dolomite precipitation and the main controlling factors.

[0012] (4) Since microbial dolomite has good preservation of the original sedimentary signal, the characteristics of its isotopic geochemical data can be more accurately indicated by careful screening of samples and analysis of its characteristics. The dolomite saturation index and the concentration of various ions in the solution under low temperature conditions are calculated using software simulation (e.g. PHREEQC), and the main controlling factors of how different physical and chemical conditions and components affect dolomite precipitation and ion concentration changes are clarified, so as to analyze the influence and constraints of different seawater properties on dolomite precipitation.

[0013] The present invention comprises the following steps:

[0014] S1: Detailed classification of sedimentary microfacies based on rock associations, sedimentary structural associations, and relationships with other adjacent rock formations;

[0015] S2: Select samples with original signals from the early stage of microbial dolomite crystal formation;

[0016] S3: Observe the nanoscale morphological features of the selected samples, conduct in-situ composition analysis of micro-areas, and combine the results of microbial-mediated primary dolomite in the laboratory to comprehensively establish indicative markers representing microbial origin in rocks;

[0017] S4: Estimate the properties of seawater during sedimentation using conventional carbon, oxygen, strontium isotopes and unconventional boron isotopes;

[0018] S5: Study the effects of different seawater properties on dolomite precipitation and identify the main controlling factors.

[0019] The beneficial effects of the present invention are:

[0020] The present invention is a method for identifying the formation process of microbial dolomite. Compared with the prior art, the present invention uses a variety of technical means to select samples, uses high-resolution scanning electron microscopy, atomic force microscopy-laser Raman, etc., and integrates the results of microbial culture experiments to establish indicative markers of the biogenesis of microbial dolomite. Boron isotopes are used to estimate the ancient pH value of seawater in the early Paleozoic era, and conventional carbon oxygen and strontium isotopes are used to restore ancient temperature and ancient alkalinity, and then simulate (such as: PHREEQC software) the influence and restriction of changes in seawater properties (including differences in physical and chemical conditions and different components) on dolomite precipitation, providing new ideas for solving the ancient "dolomite problem" and having exploratory theoretical significance; clarifying the characteristics of microbial dolomite, the formation environment and other properties, and also has a guiding role in the prediction of dolomite reservoirs. DETAILED DESCRIPTION

[0021] The present invention is further described below with specific examples. The illustrative examples and descriptions of the present invention are used to explain the present invention but are not intended to limit the present invention.

[0022] The ocean is the reservoir of carbonate elements and the place of large-scale precipitation. Changes in calcium and magnesium concentrations, pH (little research), etc. will have an important impact on the formation of carbonate minerals. However, the composition of seawater in the geological history is constantly changing. Therefore, the geochemical characteristics of microbial dolomite, which can better preserve the original seawater information during deposition (such as unconventional boron isotopes can calculate the ancient pH value), are used to reasonably reconstruct the physical and chemical conditions and composition of seawater in the early Paleozoic era, and then quantitatively simulate the constraints and influences of seawater on dolomite precipitation in the ancient geological history. This is the basis for establishing a model of the formation process of microbial dolomite, and it is also another important way and method to explore and solve the "dolomite problem".

[0023] An important factor closely related to the formation of carbonate rocks is the pH value in seawater. To restore the ancient pH value of seawater in the geological history, we can only use the unconventional isotopes of marine carbonate rocks - boron isotopes. Boron isotopes can be used to calculate pH values ​​because dissolved boron mainly exists in two forms: B(OH)3 (boric acid; planar triangular structure) and B(OH)-4 (borate; three-dimensional tetrahedral structure). The relative content of the two is controlled by the pH value of seawater due to the ionization equilibrium of weak acids, namely:

[0024] pH=pK B -lg(B(OH)3 / B(OH) -4)

[0025] where pK B is the apparent ionization constant of boric acid.

[0026] In B(OH)3 and B(OH) - The difference in isotope distribution function will produce isotope fractionation. However, boron is only or mainly in the form of B(OH) - 4 forms participate in the crystal lattice of biological carbonate minerals, at which time boron isotope fractionation can be ignored, so biological carbonate rock samples are good materials for studying boron isotopes.

[0027] If dolomite is precipitated directly from seawater, the following chemical equation must be satisfied:

[0028] Ca 2+ +Mg 2+ +2(CO3 2- )→CaMg(CO3)2

[0029] According to the formula, the chemical equilibrium constant K = ([Ca 2+ ][Mg 2+ ][CO3 2- ] 2 ) / [CaMg(CO3)2], [x] in brackets represents dissolved phase and solid phase components. Hsu (1967) and Hardie (1987) both gave estimated values ​​of K. Although modern seawater cannot precipitate dolomite, it is one to two orders of magnitude supersaturated for dolomite formation. The seawater in the early Paleozoic is different from modern seawater. Therefore, exploring the different physical and chemical conditions of seawater at that time, and the influence and constraints of different composition on dolomite precipitation, may become another important way and method to solve the "dolomite problem".

[0030] Therefore, the research basis of this patent is to conduct in-depth research on samples of microbial dolomite deposited during this period, and use the good preservation of early Paleozoic seawater information in these samples to further reconstruct the unique properties of early Paleozoic ancient seawater (such as reconstructing the ancient pH value at this time), and study its influence and constraints on dolomite precipitation, restore the sedimentary environment of microorganisms during the sedimentary period, and restore the formation process of microbial dolomite, so as to provide new ideas and approaches for the genesis of dolomite and the comprehensive solution of the "dolomite problem", and ultimately guide the prediction of the distribution of dolomite oil and gas reservoirs.

[0031] The present invention comprises the following steps:

[0032] S1: The sedimentary microfacies are divided in detail through rock combinations, sedimentary structural combinations, and the relationship with other adjacent rock layers. The hydrodynamic conditions and ancient water depth at the time of formation are inferred based on the microscopic sedimentary structure and structural characteristics and particle characteristics under the microscope, combined with the characteristics of adjacent rock layers, to determine the sedimentary environment of microbial dolomite.

[0033] S2: Select samples with original signals from the early stage of microbial dolomite crystal formation; observe the structure, texture and grain size of the microbial dolomite in detail through thin sections, and select mud crystal-microcrystal samples with little later fluid transformation and unobvious recrystallization phenomenon; use cathode luminescence to further observe the uniformity of the crystal luminescence of mud crystal-microcrystals, and select dolomite samples that were formed in a single stage and have no obvious multi-stage transformation; use a fluorescence microscope to observe the color and distribution characteristics of the residual biofilm, bacterial remains and luminescent groups of organic matter, and study the preservation, distribution and type of organic matter.

[0034] S3: Observe the nano-scale morphological characteristics of the selected samples, conduct in-situ component analysis of the micro-area, and combine the results of microbial-mediated primary dolomite in the laboratory to comprehensively establish indicative signs of microbial origin in the rock; study the formation mechanism of microbial dolomite, prepare the selected samples into small flakes less than 0.5cm×0.5cm, clean them with alcohol ultrasonic, divide the samples into two parts, one is etched with dilute hydrochloric acid, and the other is not etched with acid, and nano-gold (Au) is sprayed using a precision etching coating instrument, and the total thickness of the spraying is strictly controlled to be less than 15nm to prevent the partially aggregated coating from being mistaken for the original microstructure of the sample under a high-resolution scanning electron microscope. Through control experiments, the most suitable chemical treatment method for observing the surface structure of microbial rocks is determined to use dilute hydrochloric acid to treat the sample surface.

[0035] In the process of microbial-mediated primary dolomite, microorganisms will produce a large number of nano-scale spherulite dolomite particles, but due to the self-protection mechanism of microorganisms, the microorganisms themselves will not be buried in the mineralized minerals (Bontognalie et al., 2008). These particles are distributed in extracellular polymers and some cell membranes. They will further aggregate to form aggregates with a diameter range of 50 to 100 nm, and only a small number of them are in the range of 100 to 200 nm. This is the nano-spherulite structure (Sánchez-Román et al. 2008), which may represent the initial nucleation stage of microbial-mediated dolomite. In addition, establishing the mineral morphology evolution sequence of dolomite from the nucleation stage to the final growth into complete eumorphic crystals will be able to reconstruct the specific process of microbial-mediated dolomite and the different stages of microbial participation. Therefore, by using high-resolution scanning electron microscopy, atomic force microscopy-laser Raman and other techniques to observe nano-spherical structures, mineral morphological sequences and mineral components in in-situ micro-regions, we can comprehensively establish biomineral morphological characteristics and compositional characteristics that represent indicative signs of microbial origin, and study the genesis process and mechanism of microbial dolomite.

[0036] S4: Use conventional carbon, oxygen, strontium isotopes and unconventional boron isotopes to estimate the properties of seawater during the sedimentary period; microbial dolomite without recrystallization and diagenesis preserves the geochemical signals of the original sedimentary environment, and uses the oxygen isotope geothermometer of primary dolomite mediated by microorganisms (Vasconcelos et al., 2005):

[0037] 1000lnα 白云石-方解石 =0.5×10 6 ×T -2 (300~210℃)

[0038] 1000lnα 白云石-方解石 =0.45×10 6 ×T -2 -0.4(100~650℃)

[0039] 1000lnα 白云石-方解石 =0.52×10 6 ×T -2 -0.5(0~100℃)

[0040] 1000lnα 白云石-方解石 =0.42×10 6 ×T -2 -0.41(100~500℃)

[0041] Where: α 白云石-方解石 is the oxygen isotope fractionation coefficient between dolomite and calcite; T is the thermodynamic temperature;

[0042] 1000lnα dolomite-water

[0043] =1000×ln(1000+δ 18 O dolomite ) / (1000+δ 18 Owater)

[0044] =2.73×10 6 T -2 +0.26

[0045] dolomite refers to dolomite, water refers to the seawater at the time of precipitation, α dolomite-water is the oxygen isotope fractionation coefficient between dolomite and seawater; δ value represents the thousandth difference, which is the thousandth deviation of the isotope ratio of an element in the sample (Rm) relative to the isotope ratio of the standard sample (Rs), δ = (Rm-Rs) / Rs*1000; dolomite represents the oxygen isotope value of dolomite; Owater represents the oxygen isotope value of seawater;

[0046] Boron isotopes have a special indicative significance for changes in the marine environment. The pH value of seawater and the boron isotopes of carbonate deposits in the ocean have the following theoretical calculation relationship:

[0047] pH=pK B -lg{(δ 11 B 海水 -δ 11 B 碳酸盐 ) / [α -1 δ 11 B 碳酸盐 -δ 11 B 海水 +10 3 (α -1 -1)]}

[0048] Where: 11 B 碳酸盐 Indicates the boron (B) isotope value of carbonate; δ 11 B 海水 Indicates the boron (B) isotope value of seawater; δ 11 B 碳酸盐 Given by the measured data of the sample;

[0049] The ancient pH value of seawater in the early ancient times can be estimated by calculating the above formula.

[0050] Since organic matter plays an important role in the formation of microbial dolomite, the carbon and oxygen isotopes of microbial dolomite are unique, and microbial dolomites of different origins have significant differences in carbon and oxygen isotopes, which can be used to identify microbial dolomite and distinguish microbial dolomites of different origins. An important factor closely related to the formation of carbonate rocks is the pH value in seawater. To restore the ancient pH value of seawater in the geological history, only the unconventional isotopes of marine carbonate rocks, boron isotopes, can be used. Boron isotopes can be used to calculate pH values ​​because dissolved boron mainly exists in two forms: B(OH)3 (boric acid; planar triangular structure) and B(OH)-4 (borate; three-dimensional tetrahedral structure). The relative content of the two is controlled by the pH value of seawater due to the ionization equilibrium of weak acids. High pH values ​​promote the formation of dolomite.

[0051] S5: Study the effects of different seawater properties on dolomite precipitation and identify the main controlling factors. Use the obtained parameters to estimate the concentration ratio of magnesium and calcium ions in seawater during the microbial dolomite deposition period, set different restrictions and parameters, quantitatively calculate the dolomite saturation index and the changes in the concentrations of various ions in the solution, and study the effects and controlling factors of different physical and chemical conditions and seawater with different compositions on dolomite precipitation.

[0052] Step S5 is to finely characterize the characteristics of the seawater at that time based on step S4, and to study the influence and control factors of different physical and chemical conditions and seawater with different components on dolomite precipitation.

[0053] The quantitative calculation of the dolomite saturation index and the changes in the concentrations of various ions in the solution is as follows:

[0054]

[0055] Where: K d is the dolomite equilibrium constant, [Ca 2+ ]、[Mg 2+ ]、[CO3 2- ] is the molar activity of calcium, magnesium and carbonate ions. d = 0, indicating that the dolomite in the solution is in equilibrium; when SI d >0, indicating that the dolomite concentration in the solution exceeds saturation and dolomite precipitation may occur; when SI d When <0, it means that the dolomite in the solution is not yet saturated and more dolomite can be dissolved.

[0056] Both step S4 and step S5 determine the formation mechanism of microbial dolomite by studying the constraints and influencing conditions of the dolomite.

[0057] The present invention uses sedimentology, petrology, geochemistry and other methods and means to select suitable samples, and on the basis of the theory of geological microbiology, the results of microbial-mediated primary dolomite in the laboratory are linked to the microbial-induced dolomite in the ancient strata, and the indicative signs representing the microbial genesis in the rock are comprehensively established, so as to study the formation process and mechanism of microbial dolomite. At the same time, the properties of early Paleozoic seawater are estimated by isotope geochemistry, and the dolomite saturation index and the changes of various ion concentrations in the solution are quantitatively calculated by PHREEQC, so as to study the influence and control factors of different physical and chemical conditions and different components of ancient seawater on dolomite precipitation.

[0058] The technical solution of the present invention is not limited to the above-mentioned specific embodiments. All technical variations made according to the technical solution of the present invention fall within the protection scope of the present invention.

Claims

1. A method for identifying the formation process of microbial dolomite, characterized in that: The following steps are involved: S1: Detailed classification of sedimentary microfacies based on rock associations, sedimentary structural associations, and relationships with other adjacent rock formations; S2: Select samples with original signals from the early stage of microbial dolomite crystal formation; specifically, observe the structure, texture and grain size of microbial dolomite in detail through thin sections, select mud crystal-microcrystal samples with little transformation and recrystallization by late fluids; use cathode luminescence to further observe the uniformity of crystal luminescence of mud crystal-microcrystals, and select dolomite samples that were formed in a single stage and have no obvious multi-stage transformation; use fluorescence microscopy to observe the color and distribution characteristics of the luminescent groups of residual biofilms, bacterial remains and organic matter, and study the preservation, distribution and type of organic matter; S3: Observe the nano-scale morphological features of the selected samples, conduct in-situ component analysis of the micro-area, and combine the results of microbial-mediated primary dolomite in the laboratory to comprehensively establish indicative signs of microbial origin in the rock; specifically: prepare the selected samples into small flake samples less than 0.5cm×0.5cm, clean them with alcohol ultrasonic, divide the samples into two parts, one is etched with dilute hydrochloric acid, and the other is not etched with acid, and use a precision etching coating instrument to spray nano-gold (Au), strictly controlling the total thickness of the spraying to be less than 15nm, and through control experiments, determine the most suitable chemical treatment method for the observation of the surface structure of microbial rock, and use dilute hydrochloric acid to treat the sample surface; S4: Use conventional carbon, oxygen, strontium isotopes and unconventional boron isotopes to estimate the properties of seawater during the sedimentary period; specifically: Microbial dolomite without recrystallization and diagenesis preserves the geochemical signals of the original sedimentary environment, and uses the oxygen isotope geothermometer of primary dolomite mediated by microorganisms: 1000lnα 白云石-方解石 =0.5×10 6 ×T -2 ,300~210℃; 1000lnα 白云石-方解石 =0.45×10 6 ×T -2 -0.4, 100~650℃; 1000lnα 白云石-方解石 =0.52×10 6 ×T -2 -0.5, 0~100℃; 1000lnα 白云石-方解石 =0.42×10 6 ×T -2 -0.41, 100~500℃; Where: α 白云石-方解石 is the oxygen isotope fractionation coefficient between dolomite and calcite; T is the thermodynamic temperature; 1000lnα dolomite-water =1000×ln(1000+δ 18 The dolomite ) / (1000+d 18 (The water) ＝2.73×10 6 T -2 +0.26 dolomite refers to dolomite, water refers to the seawater at the time of precipitation, α dolomite-water is the oxygen isotope fractionation coefficient between dolomite and seawater; δ value represents the thousandth difference, which is the thousandth deviation of the isotope ratio Rm of an element in the sample relative to the isotope ratio Rs of the standard sample, δ = (Rm-Rs) / Rs*1000; dolomite represents the oxygen isotope value of dolomite; Owater represents the oxygen isotope value of seawater; The pH value of seawater and the boron isotope of carbonate deposits in the ocean have the following theoretical relationship: pH=pK B -lg{(δ 11 B 海水 -d 11 B 碳酸盐 ) / [a -1 d 11 B 碳酸盐 -d 11 B 海水 +10 3 (a -1 -1)]} Where: 11 B 碳酸盐 Indicates the boron (B) isotope value of carbonate; δ 11 B 海水 Indicates the boron (B) isotope value of seawater; δ 11 B 碳酸盐 Given by the measured data of the sample; The ancient pH value of seawater in the early ancient times can be estimated by the above formula; S5: Study the effects of different seawater properties on dolomite precipitation and identify the main controlling factors. Specifically, use the obtained parameters to estimate the concentration ratio of magnesium and calcium ions in seawater during the microbial dolomite deposition period, set different restrictions and parameters, quantitatively calculate the dolomite saturation index and the changes in the concentrations of various ions in the solution, and study the effects and controlling factors of different physical and chemical conditions and seawater with different compositions on dolomite precipitation. The quantitative calculation of the dolomite saturation index and the changes in the concentrations of various ions in the solution is as follows: Where: K d is the dolomite equilibrium constant, [Ca 2+ ]、[Mg 2+ ]、 is the molar activity of calcium, magnesium and carbonate ions; when SI d = 0, indicating that the dolomite in the solution is in equilibrium; when SI d >0, indicating that the dolomite concentration in the solution exceeds saturation and dolomite precipitation may occur; when SI d When <0, it means that the dolomite in the solution is not yet saturated and more dolomite can be dissolved.

2. The method for identifying the formation process of microbial dolomite according to claim 1, characterized in that: The step S1 specifically includes: determining the depositional environment of the microbial dolomite by inferring the hydrodynamic conditions and ancient water depth at the time of formation based on the microscopic sedimentary structure and structural characteristics and particle characteristics under the microscope and combining the characteristics of adjacent rock layers.

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