Method for quantitatively evaluating paleo-productivity of hydrocarbon source rock in sedimentary period

Abstract

The invention provides a method for quantitatively evaluating the paleo-productivity of hydrocarbon source rock in a sedimentary period. The method comprises the following steps: acquiring a representative rock sample in a target hydrocarbon source rock stratum; carrying out total organic carbon content test, total rock mineral composition analysis and organic petrology analysis on the selected rock sample; determining the deposition rate of the rock sample in the deposition period; and establishing a quantitative evaluation model for the ancient productivity in the deposition period based on a carbon element substance conservation principle. The method for evaluating the ancient productivity is based on the principle of conservation of carbon elements, and the ancient productivity of hydrocarbon source rocks is quantitatively evaluated through the steps of organic matter thermal evolution hydrocarbon generation recovery, organic matter anaerobic oxidation consumption recovery, terrestrial source organic matter input and removal and the like. The method is widely applied to ancient productivity evaluation of hydrocarbon source rocks in marine facies and continental sedimentary environments in different regions, and provides technical support for formation mechanism research and distribution prediction of continental facies high-quality hydrocarbon source rocks in China.

Description

Technical Field

[0001] The invention relates to the technical field of geological exploration and resource evaluation of oil and gas resources, and in particular to a method for quantitatively evaluating the paleoproductivity of source rocks during the sedimentation period. Background Art

[0002] Organic matter in source rocks is the source of oil and gas generation, and its relative content and chemical structure composition control the rate and production capacity of organic matter in source rocks to be converted into oil and gas. As the main source of sedimentary organic matter in source rocks, the paleoproductivity of sedimentary water bodies plays a vital role in exploring the formation of high organic matter-abundant source rocks.

[0003] Previous studies have mainly evaluated the paleoproductivity of source rocks in a qualitative way, that is, the paleoproductivity of sedimentary water bodies is reflected by the relative changes in the species and combination of microfossils, trace elements (copper, zinc, barium, etc.) and biomarkers (enones, sterols, etc.) in rocks, and the content of stable isotopes (δ13C and δ18O, etc.). In addition, a variety of restoration models have been established for the quantitative evaluation of the paleoproductivity of source rocks, including the organic carbon content restoration method, the organic carbon accumulation rate method, and the trace element accumulation rate method. However, the current mainstream paleoproductivity quantitative evaluation methods are mainly based on the empirical formula method of modern ocean / lake measured productivity, such as the paleoproductivity quantitative evaluation methods proposed by Müller and Suess (1979) and Schoepfer et al. (2015). However, the above analysis methods lack quantitative analysis based on the transformation process of sedimentary organic matter; and the current paleoproductivity quantitative evaluation models are mostly based on marine sediments, lacking paleoproductivity quantitative evaluation models for lake sedimentary water bodies. The main source rocks in my country's oil and gas basins since the Triassic are mostly terrestrial lake sedimentary strata.

[0004] In summary, previous quantitative evaluation methods mainly relied on empirical formulas and had limitations in terms of universality and accuracy for different rock types. Therefore, a more objective and effective quantitative evaluation method for paleoproductivity during the source rock deposition period is needed. Summary of the invention

[0005] In view of the shortcomings of the prior art, the main purpose of the present invention is to propose a method for quantitatively evaluating the paleoproductivity of source rocks during the sedimentary period. The method is based on the principle of carbon conservation, and through the steps of organic matter thermal evolution hydrocarbon generation recovery, organic matter anaerobic oxidation consumption recovery and terrestrial organic matter input elimination, etc., based on the total organic carbon content test of rock samples, whole rock mineral composition analysis, organic petrology analysis and sedimentation rate analysis, a quantitative evaluation model of source rock paleoproductivity is established. The paleoproductivity evaluation method established by the present invention can be widely used in the paleoproductivity evaluation of source rocks in marine and terrestrial sedimentary environments, and provides technical support for the formation mechanism research and distribution prediction of high-quality terrestrial source rocks in my country.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is: A method for quantitatively evaluating the paleoproductivity of source rocks during their sedimentary period comprises the following steps: S1. Obtain representative rock samples from the target source rock formation; S2. Conduct total organic carbon content test, whole rock mineral composition analysis and organic petrology analysis on selected rock samples; S3. Analyze the sedimentation rate of the selected rock samples during the sedimentation period; S4. Based on the principle of conservation of carbon, a quantitative evaluation model of paleoproductivity during the sedimentary period is established.

[0007] The method of the present invention systematically obtains and analyzes rock samples, combines the basic principles of organic geochemistry and sedimentology, and establishes a reliable quantitative evaluation model for paleoproductivity during the sedimentary period. This method not only improves the accuracy and scientificity of source rock evaluation, but also provides an important geological basis for oil and gas exploration.

[0008] According to some embodiments of the present invention, in step S1, the method for obtaining a representative rock sample in a target source rock formation comprises the following steps: S101. Analyze the stratigraphic characteristics and sedimentary phase characteristics of the target layer, determine typical drilling of the target layer, and obtain core or cuttings samples; S102. After pre-processing the obtained rock samples, the density and porosity of the rock samples are measured.

[0009] According to some embodiments of the present invention, in step S102, the pretreatment is to first remove weathering products on the surface of the sample, thereby retaining the original geochemical characteristics of the rock sample to facilitate subsequent analysis and testing.

[0010] According to some embodiments of the present invention, in step S102, after the sample is pre-processed, the density (ρ) and porosity (φ) of the rock sample are measured according to the national standard "GB / T 23561.3-2009 Method for Determination of Physical and Mechanical Properties of Coal and Rock" Part 3 Coal and Rock Block Density Determination Method and the industry standard "SY / T 6385-2016 Method for Determination of Porosity and Permeability of Rocks under Overburden Pressure"; and the paleoproductivity of the source rock during the deposition period is calculated according to the following formula:

[0011] Where m1 is the rock mass per unit area (g); ρ is the rock density (g / cm 3 ); φ is rock porosity (%); m2 is the mass of organic matter per unit area of ​​rock (g); PP is the paleoproductivity of source rock during sedimentation (g C / (m 2 a) ); t is the deposition time (kyr).

[0012] According to some embodiments of the present invention, in step S2, the rock sample is first crushed into small particles, and then the crushed rock sample is subjected to a total organic carbon content test, a whole-rock mineral composition analysis, and an organic petrology analysis, including the following steps: S201. crushing the above small particle samples again, and conducting rock total organic carbon content test and whole rock mineral composition analysis on the crushed samples; S202. Determine the organic microscopic components and vitrinite reflectance (Ro) of the above-mentioned small particle samples to determine the degree of thermal evolution of the organic matter in the sedimentary rock samples.

[0013] According to some embodiments of the present invention, in step S201, a rock powder sample is taken from the crushed sample to carry out a measured TOC value (TOC C ) determination and whole-rock mineral composition analysis, and organize the analytical data of rock mineral composition determination to quantitatively calculate the relative content of sulfide minerals (C SM ).

[0014] According to some embodiments of the present invention, in step S202, the method for measuring the organic microscopic components and the vitrinite reflectance of the small-grained rock sample includes the following steps: (1) Take small-grain rock samples and mix them evenly, then cast them with epoxy resin, cut them to expose the rock particles, and then use water sandpaper grinders and aluminum oxide polishing liquid of different mesh sizes to grind and polish them, and then dry them to obtain rock slices; (2) Observe the morphology and optical properties of the organic microscopic components of the rock sections under an optical microscope, identify and count the organic microscopic components in the rocks, and determine the relative proportion of the organic microscopic components formed by the paleoproductivity of the sedimentary water body (CS ); at the same time, the vitrinite reflectance (Ro) in the rock microscopic components is measured to determine the degree of thermal evolution of organic matter in sedimentary rocks.

[0015] According to some embodiments of the present invention, in step S202, the mesh sizes of the water sandpaper grinding and polishing machine are 100 mesh, 600 mesh, 1500 mesh and 2500 mesh respectively.

[0016] According to some embodiments of the present invention, in step S3, the geological characteristics of the target source rock area are analyzed to obtain the paleoclimate parameters of the rock strata, and the sedimentation rate of the selected rock sample during the sedimentation period is analyzed using the principle of cyclostratigraphy to obtain the sedimentation rate SAR of the rock sample; the expression is: ; Where t is the deposition time (kyr); SAR is the rock deposition rate (cm / kyr).

[0017] According to some embodiments of the present invention, in step S3, the paleoclimate parameters include natural gamma, magnetic susceptibility, rock color scale and other data.

[0018] According to some embodiments of the present invention, based on the principle of conservation of carbon, a quantitative evaluation model of paleoproductivity during the sedimentary period is established as follows: ; Among them, TOC C is the current measured TOC value of the rock sample; K is the organic matter hydrocarbon recovery coefficient, dimensionless; C S is the relative proportion of the maceral components of the paleoproductivity of the sedimentary water body (%); C SM is the relative content of sulfide minerals in the rock (%); SAR is the rock deposition rate (cm / kyr); ρ is the rock density (g / cm 3 ), φ is the rock porosity (%).

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention analyzes the biogeochemical effects of organic carbon in the process of biological-organic matter-oil and gas conversion, reconstructs the changes of organic carbon elements in the process of primary productivity conversion into sedimentary organic matter, organic matter thermal evolution hydrocarbon generation, etc., and then quantitatively evaluates the paleoproductivity of source rock during sedimentation. By comparing and verifying with the existing paleoproductivity quantitative evaluation, it is shown that this method can more objectively quantitatively evaluate the paleoproductivity of source rock during sedimentation.

[0020] 2. The present invention is based on the principle of conservation of carbon element matter. From the perspective of the organic carbon transformation process, the paleoproductivity is quantitatively evaluated by obtaining the basic parameters in the organic carbon transformation process, thereby solving the problem of the limited applicability of traditional paleoproductivity quantitative evaluation methods. The paleoproductivity evaluation method established by the present invention can be widely used in the paleoproductivity evaluation of source rocks in marine / continental sedimentary environments, providing technical support for the research on the formation mechanism and distribution prediction of high-quality terrestrial source rocks in my country. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention will be further described below in conjunction with the accompanying drawings: Figure 1 It is a flow chart of the method for quantitatively evaluating the paleoproductivity of source rocks during the sedimentary period of the present invention; Figure 2 It is a cross-sectional diagram of the quantitative evaluation of paleoproductivity of the present invention; In the figure, PP1 represents the quantitative evaluation model results of the present invention; PP2 represents the evaluation model results of Müller and Suess (1979); PP3 represents the evaluation model results of Schoepfer et al. (2015). DETAILED DESCRIPTION

[0022] The present invention is described in detail through the following examples so that those skilled in the art can more fully understand the present invention, but these examples do not constitute any limitation to the scope of the present invention.

[0023] The method for quantitatively evaluating the paleoproductivity of source rocks during the sedimentation period proposed by the present invention specifically comprises the following steps: S1. Obtain representative rock samples from the target source rock formation; S101. Analyze the stratigraphic characteristics and sedimentary phase characteristics of the target layer, determine typical drilling of the target layer, and obtain a certain number of core or cuttings samples; S102. After removing the surface weathering products of the obtained samples, the density (ρ) and porosity (φ) of the rock samples were determined according to the national standard "GB / T 23561.3-2009 Methods for determination of physical and mechanical properties of coal and rock" Part 3 Methods for determination of density of coal and rock blocks and the industry standard "SY / T 6385-2016 Methods for determination of porosity and permeability of rocks under overburden pressure"; the expression is:

[0024] Where m1 is the rock mass per unit area (g); ρ is the rock density (g / cm 3 ); φ is rock porosity (%); m2 is the mass of organic matter per unit area of ​​rock (g); PP is the paleoproductivity of source rock during sedimentation (mg C / (m 2a)); t is the deposition time (kyr).

[0025] S2. Firstly, the rock samples are crushed into small particles, and then the crushed samples are subjected to total organic carbon content test, whole rock mineral composition analysis and organic petrology analysis; S201. Total organic carbon content determination and whole rock mineral composition analysis: After the above-mentioned small particle samples were crushed again, the total organic carbon content (TOC) of the rock powder samples and the whole rock mineral composition analysis were carried out according to the national standard "GB / T 19145-2003 Determination of total organic carbon in sedimentary rocks" and the industry standard "SY / T 5163-2018 X-ray diffraction analysis method of clay minerals and common non-clay minerals in sedimentary rocks". The analytical data of the rock mineral composition determination were sorted out, and the relative content (C SM ).

[0026] S202. A method for determining an organic microscopic component and its vitrinite reflectance (Ro), comprising: (1) The above-mentioned small-grain rock samples are uniformly mixed and cast with epoxy resin, cut to expose the rock particles, and then polished with water sandpaper grinders and aluminum oxide polishing liquid of different mesh sizes, and then dried to obtain rock slices; (2) The prepared rock sections were placed under an optical microscope, and the morphology and optical properties of the organic microscopic components were observed using reflected light and fluorescence. The organic microscopic components in the rock were identified and counted according to the industry standard "SY / T 6414-2014 Identification and Statistical Analysis of Whole Rock Microscopic Components" to clarify the relative proportion of organic microscopic components (mainly algae and amorphous sapropelic bodies) formed by the paleoproductivity of sedimentary water bodies (C S ); According to the industry standard "SY / T 5124-2012 Method for Determination of Vitrinite Reflectance in Sedimentary Rocks", the vitrinite reflectance (Ro) in the rock microscopic components is measured to clarify the degree of thermal evolution of organic matter in sedimentary rocks; the relevant formula is:

[0027] Among them, TOC0 is the organic carbon content contributed by primary productivity in rocks (%); TOC1 is the total organic carbon content in rocks (%); C S is the relative proportion of the microscopic components of the ancient productivity of the sedimentary water body (%); TOC2 is the organic carbon content in the rock after anaerobic oxidation and consumption of organic matter (%); C SM is the relative content of sulfide minerals in rocks (%); TOC Cis the currently measured TOC value of the rock sample; K is the organic matter hydrocarbon recovery coefficient, dimensionless.

[0028] S3. Analyze the sedimentation rate of the above rock samples during the sedimentation period; Analyze the geological characteristics of the target source rock area, obtain the paleoclimate parameters of the rock strata (such as natural gamma, magnetic susceptibility, rock color, etc.), use the principle of cyclostratigraphy to analyze the sedimentation rate of the pre-treated rock samples during the sedimentation period, and obtain the sedimentation rate SAR (cm / kyr) of the rock samples. The relevant formula is: ; Where t is the deposition time (kyr); SAR is the rock deposition rate (cm / kyr).

[0029] S4. Based on the principle of carbon conservation, a quantitative evaluation model of paleoproductivity during the sedimentation period of source rocks is established; Based on the principle of conservation of carbon, the transformation of primary productivity into sedimentary organic matter and the post-depositional effects of organic matter were analyzed, and a quantitative evaluation model for paleoproductivity during the sedimentary period was established according to the above formula: .

[0030] Specifically, the present invention is described in detail through the following specific practical applications.

[0031] The study area of ​​this example is the Upper Triassic Yanchang Formation in Well Y56 in the Yanchi-Dingbian area of ​​the Ordos Basin.

[0032] A method for quantitatively evaluating the paleoproductivity of source rocks during their sedimentary period, comprising the following steps: 1. The source rock of the 7th section of the Y56 well was selected for sample collection, and a total of 39 typical lacustrine source rock samples including shale, mudstone and argillaceous siltstone were collected; 2. The surface weathering layer of the collected rock samples is stripped off to retain the original geochemical characteristics of the rock, and the density (ρ) and porosity (φ) of the rock samples are measured; then the rock samples with the weathered surface removed are crushed into small particles of 20 mesh, and then evenly divided into two parts, A and B; 3. Part A was further crushed to 200 mesh, and 100 mg of rock powder was taken to determine the organic carbon content (TOC C ); Take another rock powder sample to analyze the whole rock mineral composition and quantitatively calculate the relative content of sulfide minerals (such as pyrite, galena, sphalerite, etc.) (C SM ); 4. Mix the rock samples of part B evenly and cast them with epoxy resin. Cut them to expose the rock particles, and then grind and polish them with 100 mesh, 600 mesh, 1500 mesh and 2500 mesh water sandpaper and aluminum oxide polishing liquid. After drying the samples for 12 hours, rock slices are formed for organic petrology analysis. 5. Place the prepared rock slides under an optical microscope, use reflected light and fluorescence to observe the morphology and optical characteristics of the organic microscopic components, identify and count the organic microscopic components in the rock, and clarify the relative proportion of organic microscopic components (mainly algae and amorphous sapropelite) formed by the paleoproductivity of the sedimentary water body (C S ); In addition, the vitrinite reflectance (Ro) in the rock microscopic components is measured to clarify the thermal evolution degree of organic matter in sedimentary rocks; 6. Analyze the sedimentation rate of the rock sample during its sedimentation period using the cyclostratigraphic method to obtain the sedimentation rate SAR of the rock sample; 7. Quantitative evaluation model of lake paleoproductivity established based on carbon conservation law: The paleoproductivity of the source rocks of the Chang 7th Member in the Yanchi-Dingbian area of ​​the Ordos Basin during the sedimentary period was quantitatively evaluated. The results showed that the paleoproductivity (PP1) of the source rocks of the Chang 7th Member in the area during the sedimentary period was mainly distributed in the range of 7688.7-133330.5 mg C / cm 2 / kyr, with an average value of 49636.2 mg C / cm 2 / kyr, indicating a meso-eutrophic level.

[0033] In addition, this study used the widely used paleoproductivity quantitative evaluation model proposed by Müller and Suess (1979) and Schoepfer et al. (2015) to evaluate the paleoproductivity of the source rock in the Chang 7 section of Well Y56. The results showed that the paleoproductivity evaluated by the organic carbon method of Müller and Suess (1979) and the model of Schoepfer et al. (2015) were distributed in the range of 42793.1-515092.8 mg C / cm 2 / kyr(PP2: mean value is 309751.2mg C / cm 2 / kyr) and 39228.5-544193.0mg C / cm 2 / kyr(PP3: mean value is 288002.4mg C / cm 2 / kyr), indicating that the paleoproductivity level of the source rocks in the Chang 7 member of the study area is eutrophic to hypereutrophic.

[0034] Figure 2This is a profile diagram of paleoproductivity evaluation calculated by the quantitative evaluation method of the present invention, the organic carbon method of Müller and Suess (1979), and the model of Schoepfer et al. (2015). By comparing the paleoproductivity calculated by different models (PP1, PP2, and PP3), and combining the range of paleoproductivity changes in modern lake sediments, it is found that the paleoproductivity calculated by the method of the present invention is more in line with reality.

[0035] By comparing the paleoproductivity evaluation model established by the present invention with the previous achievements, it is found that the lake paleoproductivity quantitative evaluation model established by the present invention can more objectively evaluate the proportion of endogenous organic matter input into the lake by restoring the thermal evolution consumption of organic matter, anaerobic oxidation consumption of organic matter and the elimination steps of terrigenous organic matter, thereby improving the objectivity of the evaluation of hydrocarbon generation potential of source rocks.

[0036] The above embodiments are only preferred technical solutions of the present invention and should not be regarded as limiting the present invention. The protection scope of the present invention shall be the technical solutions recorded in the claims, including equivalent replacement solutions of the technical features in the technical solutions recorded in the claims. That is, equivalent replacement improvements within this scope are also within the protection scope of the present invention.

Claims

1. A method for quantitatively evaluating the paleoproductivity of source rocks during their depositional period, characterized in that: The following steps are involved: S1. Obtain representative rock samples from the target source rock formation; S2. Conduct total organic carbon content test, whole rock mineral composition analysis and organic petrology analysis on selected rock samples; S3. Analyze the sedimentation rate of the selected rock samples during the sedimentation period; S4. Based on the principle of conservation of carbon, a quantitative evaluation model of paleoproductivity during the sedimentary period is established.

2. The method for quantitatively evaluating the paleoproductivity of source rocks during the sedimentary period according to claim 1, characterized in that: In step S1, the method for obtaining a representative rock sample in a target source rock formation comprises the following steps: S101. Analyze the stratigraphic characteristics and sedimentary phase characteristics of the target layer, determine typical drilling of the target layer, and obtain core or cuttings samples; S102. After pre-processing the obtained rock samples, the density and porosity of the rock samples are measured.

3. The method for quantitatively evaluating the paleoproductivity of source rocks during the sedimentary period according to claim 2, characterized in that: In step S102, the pretreatment is to first remove the weathering products on the sample surface, retain the original geochemical characteristics of the rock sample, and then measure the density and porosity of the rock sample; and calculate the paleoproductivity of the source rock during the deposition period according to the following formula: Where m1 is the rock mass per unit area (g); ρ is the rock density (g / cm 3 ); φ is rock porosity (%); m2 is the mass of organic matter per unit area of ​​rock (g); PP is the paleoproductivity of source rock during sedimentation (g C / (m 2 a) ); t is the deposition time (kyr).

4. The method for quantitatively evaluating the paleoproductivity of source rocks during the sedimentary period according to claim 1, characterized in that: In step S2, the pretreated rock sample is first crushed into small particles, and then the crushed rock sample is subjected to a total organic carbon content test, a whole-rock mineral composition analysis, and an organic petrology analysis, including the following steps: S201. crushing the above small particle samples again, and conducting rock total organic carbon content test and whole rock mineral composition analysis on the crushed samples; S202. Determine the organic microscopic components and vitrinite reflectance of the above-mentioned small particle samples to determine the degree of thermal evolution of the organic matter in the sedimentary rock samples.

5. The method for quantitatively evaluating the paleoproductivity of source rocks during the sedimentary period according to claim 4, characterized in that: In step S201, the whole-rock mineral composition analysis is carried out on the sample after re-crushing, and the relative content of sulfide minerals is quantitatively calculated.

6. The method for quantitatively evaluating the paleoproductivity of source rocks during their sedimentation period according to claim 4, characterized in that: In step S202, the method for measuring the organic microscopic components and the vitrinite reflectance of the small-grain rock sample comprises the following steps: (1) Take small-grain rock samples and mix them evenly, then cast them with epoxy resin, cut them to expose the rock particles, and then use water sandpaper grinders and aluminum oxide polishing liquid of different mesh sizes to grind and polish them, and then dry them to obtain rock slices; (2) Under an optical microscope, observe the morphology and optical characteristics of the organic microscopic components of the rock slices, identify and count them, and determine the relative proportion of the organic microscopic components formed by the paleoproductivity of the sedimentary water body; at the same time, measure the vitrinite reflectance in the sample microscopic components to determine the thermal evolution degree of organic matter in the sedimentary rock; the relevant expressions are: Among them, TOC0 is the organic carbon content contributed by primary productivity in rocks (%); TOC1 is the total organic carbon content in rocks (%); C S is the relative proportion of the microscopic components of the ancient productivity of the sedimentary water body (%); TOC2 is the organic carbon content in the rock after anaerobic oxidation and consumption of organic matter (%); C SM is the relative content of sulfide minerals in rocks (%); TOC C is the currently measured TOC value of the rock sample; K is the organic matter hydrocarbon recovery coefficient, dimensionless.

7. The method for quantitatively evaluating the paleoproductivity of source rocks during the sedimentary period according to claim 1, characterized in that: In step S3, the geological characteristics of the target source rock area are analyzed to obtain the paleoclimate parameters of the rock strata, and the deposition rate of the pre-treated rock sample during the deposition period is analyzed using the principle of cyclostratigraphy to obtain the deposition rate of the rock sample; the expression is: ； Where t is the deposition time (kyr); SAR is the rock deposition rate (cm / kyr).

8. A method for quantitatively evaluating the paleoproductivity of source rocks during the sedimentary period according to claim 7, characterized in that: In step S3, the paleoclimate parameters include natural gamma, magnetic susceptibility, and rock color scale.

9. The method for quantitatively evaluating the paleoproductivity of source rocks during the sedimentary period according to claim 1, characterized in that: Based on the principle of carbon conservation, a quantitative evaluation model for paleoproductivity during the sedimentary period is established: ； Among them, TOC C is the current measured TOC value of the rock sample; K is the organic matter hydrocarbon recovery coefficient, dimensionless; C S is the relative proportion of the maceral components of the paleoproductivity of the sedimentary water body (%); C SM is the relative content of sulfide minerals in the rock (%); SAR is the rock deposition rate (cm / kyr); ρ is the rock density (g / cm 3 ), φ is the rock porosity (%).

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