Method for multi-dimensionally analyzing layering state of ancient lake water body based on lamina features

Abstract

The invention belongs to the technical field of petroleum and natural gas exploration and development, and particularly relates to a method for multi-dimensionally analyzing a layering state of a water body of an ancient lake based on lamina features. The method comprises the steps of sample treatment, biological disturbance level grading, lamina thickness statistics, PCAS-based analysis test, lamina feature FIB-SEM three-dimensional reconstruction, lamina formation cause identification of lamina microcell elements and isotope verification, and fully combines the current advanced characterization and test technology. Qualitative and quantitative analysis evaluation is carried out on the layering state of the ancient lake water body from multiple dimensions of lamina layering performance, lamina thickness, lamina characteristics and lamina formation causes, the defect that the layering state of the water body is not accurately judged in a single dimension is overcome, and the characteristics of the internal microlayers and the spatial distribution condition of the internal microlayers are more visually displayed.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil and gas exploration and development, and particularly relates to a method for multi-dimensional analysis of the stratification state of ancient lake water bodies based on lamination characteristics. Background Art

[0002] Stratification is an important feature of lake hydro-ecology, which is mainly controlled by temperature, density, salinity, and oxygen content. Identifying the stratification state of lake water bodies is of great significance for studying the development of lake biological communities, biogeochemical processes, sediment deposition, and organic matter enrichment.

[0003] Currently, the research on the stratification state of lake water bodies mainly focuses on single-dimensional research. For example, the gammacerane index (GI) is used to reveal salinity stratification, phytane (Ph), Pr / nC 18 values, and the particle size of strawberry pyrite are used to reflect the redox environment under stratification conditions, and trace element indicators are used to reconstruct the sediment water environment. The main existing problems are as follows: (1) The gammacerane index (GI) only targets the water body stratification caused by salinity for identifying the stratification state of lake water bodies. Phytane (Ph), Pr / nC 18 values, and strawberry pyrite are applicable to the water body stratification caused by oxygen content, while the controlling factors of the stratification state of lake water bodies are diverse; (2) Trace element indicators can only reflect the redox conditions of sediment water bodies, and are too single and not fine enough for analyzing the stratification state of lake water bodies. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for multi-dimensional analysis of the stratification state of ancient lake water bodies based on lamination characteristics, and to conduct qualitative and quantitative analysis and evaluation from multiple dimensions such as lamination bedding, lamination thickness, lamination characteristics, and lamination origin, so as to solve the technical problem that the existing technology cannot accurately evaluate due to limitations such as single analysis index and single analysis dimension.

[0005] To solve the above technical problems, on the basis of fully considering the importance of lamination for identifying water body stratification, the present invention proposes a method for multi-dimensional analysis of the stratification state of ancient lake water bodies based on lamination characteristics under actual geological conditions. This method comprehensively determines the stratification state of ancient lake water bodies by combining the bioturbation index, lamination thickness statistics, three-dimensional reconstruction of lamination characteristics, and micro-area element and isotope verification of lamination. The specific method is as follows: Step S1: Sample Processing Prepare the sample into a thin slice sample with a thickness greater than 100 μm, the longest direction of the thin slice does not exceed 5 cm, and it is prohibited to apply glue, paste gummed labels, and place cover glasses on the surface. The sample meets the requirements of microscope, field emission scanning electron microscope, and in-situ laser ablation test experiments; Step S2: Classification of bioturbation levels Observe the sample under a microscope and record the clarity of trace fossils, the distribution and overlapping of burrows, and the degree of damage to the original bedding; Step S3: Laminar thickness statistics - based on PCAS analysis and testing Use a particle (pore) and crack image recognition system (PCAS) to quantitatively identify and structurally analyze mineral particles, fissures, pores, etc. in the micrographs of microscope slides taken under a polarized light microscope. Binarize the images, remove noise points, automatically segment and identify particles, pores, and cracks, and output their geometric parameters, including the number, length, width, etc., to achieve the statistics of laminar types and thicknesses at the ten-micron scale; Step S4: 3D reconstruction of laminar characteristics by FIB-SEM Determine the target area by observing with a focused ion beam scanning electron microscope. The size of the target area is generally selected to be about 10μm×10μm. Rotate the sample stage by 52 ° to ensure that the ion beam is perpendicular to the sample surface. Spray platinum on the surface of the target area to reduce the damage of the ion beam to it. Use a 30kV gallium ion beam to pre-cut the sample, and then use the Slice&View software to control the FIB and SEM to continuously cut and image the shale cross-section more than 500 times to obtain a series of SEM images. During the continuous cutting process, the acceleration voltage of the electron beam is generally selected to be 2kV, the current is 0.2nA, and the backscattered mode is used for imaging; Step S5: Identification of laminar genesis Seasonal laminae can be used to identify suspension sedimentation; flocculent ripple marks can be used to identify flocculent sedimentation; massive siltstone can be used to identify debris flow deposition; lenticular laminae can be used to identify the erosion and transportation of cement-bearing shale; turbidite mudstone can be used to identify low-density turbidity current deposition; wave-enhanced sediment gravity flow genesis lamina sets can be used to identify wave-enhanced sediment gravity flow deposition; Step S6: Verification of micro-area elements and isotopes of laminae - based on in-situ laser ablation and in-situ carbon and oxygen isotope analysis and testing S61 In-situ laser ablation analysis and testing of micro-areas Use a GeoLasPro 193nm ArF excimer laser and an Agilent 7900 inductively coupled plasma mass spectrometer to determine the major elements. Before testing, optimize the performance of the ICP-MS using SRM610, calculate its content using the multi-external standard and total normalization method, and analyze and process the data using ICPMS Data Cal to obtain the major element content (Na2O, Al2O3, SiO2, K2O) of the sample; S62 In-situ carbon and oxygen isotope analysis and testing of micro-areas Use a dental drill of a micro-area sampler to drill at a low speed at the sampling site to obtain a powder sample. The sample amount is 10-50 μg, and 1-2 drill holes are made. Use a micropipette to collect the powder and transfer it into a 12 mL borosilicate bottle. After purging with helium, add about 50 μL of 99.9% orthophosphoric acid and react at 72 °C for 10 minutes to produce CO2 gas, which enters a MAT-253 mass spectrometer for analysis with He as the carrier gas. The analysis results are given in the VPDB standard (‰). All δ 13 C and δ 18 O values are standardized by NBS19. The precision of carbon isotope analysis is better than 0.1‰, and the precision of oxygen isotope analysis is better than 0.15‰; Step S7: Discrimination of the stratification state of the ancient lake water body Based on the experimental results of steps S3 and S61 and the bioturbation classification in step S2 and the origin identification of laminations in step S5, the stratification state of the ancient lake water body is discriminated. MCAL + OL + CL indicates a deep lake water body with high paleo-salinity, low terrigenous material supply, and strong reducibility; SCAL + OCL indicates a deep lake water body; QFCL + OCL indicates a semi-deep lake water body with low paleo-salinity and stable terrigenous clastic supply under dry and cold climatic conditions. Based on the FIB-SEM three-dimensional reconstruction results in step S4, analyze the indication effect of the structure and texture of the lens bodies inside the three different types of lenticular laminations on the stratification state of the ancient lake water body. Type I lenticular lamination is characterized by a micrite calcite lens body with a central bulge and tapering ends at both ends, indicating a relatively turbulent water body; Type II lenticular lamination is characterized by a flat and narrow intermittent lens body, indicating a semi-deep lake water body with sufficient terrigenous supply; Type III lenticular lamination is characterized by an irregular micrite calcite lens body, indicating a deep lake water body with strong bioturbation.

[0006] The present invention has the following beneficial effects: Before this invention, the analysis of the stratification state of the ancient lake water body mainly focused on single-dimensional analysis, and only quantitative analysis was carried out using proxy indicators. For example, the gammacerane index (GI) was used to reveal salinity stratification, and phytane (Ph), Pr / nC 18 values and the particle size of strawberry pyrite were used to reflect the redox environment under stratification conditions, and trace element indicators were used to reconstruct the sedimentary water environment. The main problems of these methods are as follows: The gammacerane index (GI) only targets the water body stratification caused by salinity for the identification of the stratification state of the lake water body, and phytane (Ph), Pr / nC 18Values and framboidal pyrite are applicable to the water stratification caused by oxygen content, while the control factors of lake water stratification are diverse; the trace element index can only reflect the redox conditions of sedimentary water bodies, and it is too single and not fine enough to be used to analyze the lake water stratification state. The present invention fully combines the current advanced characterization and testing technologies, and proposes a method for multi-dimensional analysis of the paleo-lake water stratification state based on lamination characteristics, solving the drawback of inaccurate judgment of the water stratification state in a single dimension. The main improvements of the present invention compared with the traditional method are as follows: Statistically analyze the lamination thickness based on PCAS analysis and testing, and improve the traditional analysis scale from the mm-cm level to the μm level scale.

[0007] Establish a three-dimensional reconstructed image of the lamination based on the FIB-SEM three-dimensional reconstruction technology. Compared with the traditional analysis method, it more intuitively shows the characteristics of the internal micro-layers and their spatial distribution.

[0008] Compared with the traditional method that only considers the paleo-lake water stratification state from a single dimension and only uses proxy indicators for discrimination, the present invention analyzes more finely and accurately from multiple dimensions such as lamination bedding, lamination thickness, lamination characteristics, and lamination genesis. Brief Description of the Drawings

[0009] Figure 1 The figure is a processed sample diagram of the shale core of Well Guan XX provided by the example of the present invention; Figure 2 The figure is a bioturbation discrimination diagram of the sample of Well Guan XX provided by the example of the present invention; Figure 3 The figure is a FIB-SEM three-dimensional reconstruction selected area diagram of the sample of Well Guan XX provided by the example of the present invention; Figure 4 The figure is a FIB-SEM three-dimensional reconstructed diagram inside the lens body of the sample of Well Guan XX provided by the example of the present invention; Figure 5 The figure is a lamination genesis discrimination diagram of the sample of Well Guan XX provided by the example of the present invention Figure 6 The figure is a paleo-lake water stratification state discrimination diagram provided by the example of the present invention. Detailed Description of the Invention

[0010] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the 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 of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0011] In this embodiment, for a certain shale formation in the Paleogene of the Bohai Bay Basin, Well Guan XX with complete data is selected as the research object for detailed description. A large number of laminations formed by different sedimentation processes are developed in this set of shale, providing a good basis for the verification of the invention.

[0012] The specific implementation steps of the invention are as follows: Step S1: Sample processing As Figure 1 shown, in this study, the core of the Paleogene shale in Well Guan XX is first prepared into thin-section samples. The preparation process undergoes five steps: "drilling - cutting - oil washing - grinding - polishing". The length of the finished glass slide is 5 cm, without a cover glass, and the thickness of the sample part is 100 μm. Step S2: Classification of bioturbation levels Observe the sample under a microscope, record the clarity of trace fossils, the distribution and overlapping situation of burrows, and the degree of damage to the original bedding. Use the bioturbation index (BI) to evaluate the bioturbation level. As Figure 2 shown, it can be divided into a total of 5 levels: BI1, the disturbance proportion is 1% - 5%, very little disturbance, clear bedding, and sporadic trace fossils can be seen; BI2, the disturbance proportion is 6% - 30%, low disturbance degree, and low density of trace fossils; BI3, the disturbance proportion is 31% - 60%, medium disturbance degree, the continuity of bedding becomes worse but the interface is relatively clear; BI4, the disturbance proportion is 61% - 90%, high disturbance degree, the bedding interface is blurred, the density of trace fossils is high, and the phenomenon of layer overlapping and crossing can be seen; BI5: the disturbance proportion is 91% - 99%, strong disturbance degree, the bedding is completely damaged, and the degree of sedimentary reworking is incomplete. Step S3: Lamination thickness statistics - based on PCAS analysis and testing In the depth range of 3440 - 3500 m, four thin sections are collected per meter. On average, 20 - 30 microscopic photos are taken for each thin section. Use the Particle (Pore) and Crack Image Recognition System (PCAS) to quantitatively identify and structurally analyze mineral particles, fissures, pores, etc. in the microscopic thin-section photos taken under a polarized light microscope. Binarize the images, remove noise points, automatically segment and identify particles, pores, and cracks, and output their geometric parameters, including the number, length, width, etc., so as to realize the statistics of lamination types and thickness at the scale of ten micrometers, and obtain the lamination thickness statistical table (Table 1);

[0013] Step S4: 3D reconstruction of lamination characteristics by FIB-SEM Determine the target area through observation with a focused ion beam scanning electron microscope. The size of the target area is generally selected to be about 10 μm × 10 μm. Rotate the sample stage by 52 °To ensure that the ion beam is perpendicular to the sample surface, platinum is sprayed on the surface of the target area to reduce the damage of the ion beam to it. The sample is pre-cut with a 30 kV gallium ion beam, and then the Slice&View software is used to control the FIB and SEM to continuously cut and image the shale cross-section more than 500 times to obtain a series of SEM images. During the continuous cutting process, the acceleration voltage of the electron beam is generally selected as 2 kV, the current is 0.2 nA, and the backscattering mode is used for imaging. As Figure 3 shown, taking a long and narrow lens with fine bedding inside as an example, a region with a size of 35.02 µm × 47.95 µm × 50 µm is selected to be sliced using the FIB-SEM three-dimensional reconstruction technology. The slicing resolution is 30 nm, and a total of 1598 slices are made. All the slices are synthesized to obtain a three-dimensional data volume, and each bedding is peeled off and superimposed in sequence to image its spatial distribution, as Figure 4 ; Step S5; Identification of bedding origin As Figure 5 shown, seasonal bedding can be used to identify suspension sedimentation. The characteristics of suspension sedimentation are slow sedimentation rate, small particle size of planktonic organic matter and graptolites, orderly arrangement of large particles, and development of seasonal bedding; flocculation ripples can be used to identify flocculation sedimentation, and its characteristics are slightly inclined bedding, bottom set, and bottom erosion; massive siltstone can be used to identify debris flow sedimentation, and its characteristics are a thickness of 5-15 cm and small development scale; sand balls and mudstone tear clasts are developed; the top, bottom, and adjacent rock layers are all in abrupt contact, with a scoured surface at the bottom and gradually transitioning to turbidity current sedimentation at the top; lenticular bedding can be used to identify the erosion and transportation of water-bearing mudstone; turbidite mudstone can be used to identify low-density turbidity current sedimentation, and its characteristics are that it is located between turbidite sand and laminated mud in the facies sequence; the contact surface between massive mud and laminated mud often shows an abrupt change; the particles inside the massive mudstone are arranged disorderly, silt bands and bioturbation traces are developed; the wave-enhanced sediment gravity flow origin bedding group can be used to identify wave-enhanced sediment gravity flow sedimentation, and its characteristics are that the bottom is a positive graded bedding composed of silt-sized particles or intraclasts; alternately occurring wavy or straight silt or mud laminations, and bioturbation can be seen in the mud laminations; Step S6: Verification of micro-area elements and isotopes of bedding - Based on in-situ laser ablation and in-situ carbon and oxygen isotope analysis and testing S61 In-situ laser ablation analysis and testing of micro-areas The major element determination was carried out using a GeoLasPro 193nm ArF excimer laser and an Agilent 7900 inductively coupled plasma mass spectrometer. During the analysis process, the working frequency of the laser was 5Hz, the energy density was 4 - 5J / cm, and the beam spot was selected as 32μm and 44μm according to different samples. Before the test, the performance of ICP-MS was optimized using SRM610, and its content was calculated using a multi-external standard and total normalization method. The external standards used were USGS glasses (NIST610, NIST612, BCR-2G, BIR-1G, and BHVO-2G). CGSG-1 and CGSG-2 were used as quality control samples. The ICPMS Data Cal was used to analyze and process the data to obtain the major element content (Na2O, Al2O3, SiO2, K2O) of the samples (Table 2).

[0014]

[0015] S62 In-situ micro-area carbon and oxygen isotope analysis and testing Observe and search for the position to be sampled under the microscope. Use absorbent cotton dipped in absolute ethanol to wipe the surface of the thin section and the drill bit of the micro-area sampler, and wait for 1 - 2 minutes for the absolute ethanol to volatilize. Use the dental drill of the micro-area sampler to slowly drill the sampling location to obtain a powder sample, with a sample amount of 10 - 50μg and 1 - 2 drill holes. After obtaining a single micro-area sample, use absorbent cotton dipped in absolute ethanol to wipe the surface of the thickened thin section and the micro-drill bit, and then drill the micro-area sample at the next location. Use a micropipette to collect the powder and transfer it into a 12mL borosilicate bottle. After purging with helium, add about 50μL of 99.9% orthophosphoric acid and react at 72°C for 10 minutes to produce CO2 gas, which enters a MAT-253 mass spectrometer for analysis, and the analysis results are given in the VPDB standard (‰). All δ 13 C and δ 18 O values are standardized by NBS19. The precision of carbon isotope analysis is better than 0.1‰, and the precision of oxygen isotope analysis is better than 0.15‰. Taking the samples of Well Guan XX as an example, the in-situ micro-area carbon and oxygen isotope analysis and testing results are shown in Table 3.

[0016]

[0017] S7 Discrimination of the stratification state of ancient lake water Based on the experimental results of steps S3 and S61 and the bioturbation classification in step S2 and the origin identification of laminations in step S5, the stratification state of ancient lake water is discriminated. Taking Figure 6For example, the thickness of the micrite calcite laminae (MCAL) is 20–120 μm, containing a large amount of quartz and albite; the thickness of the organic-rich clay laminae (OCL) is 10-35 μm, with good mineral sorting, flaky distribution, weak orientation, containing a small amount of quartz and feldspar particles, and organic matter is evenly distributed in the clay minerals. Through FE-SEM observation, electron probe micro-area line scanning shows that light-colored laminae and dark-colored laminae often have abrupt contact, clear laminae boundaries, individual points have high Si, Al and K contents, and Sr and B contents are slightly higher overall. Therefore, MCAL+OL+CL indicates deep lake water bodies with high paleo-salinity, low terrigenous material supply, and strong reduction. A small amount of albite or quartz is sandwiched between the spar calcite particles inside the spar calcite laminae (SCAL), and the laminae boundaries are continuous and clear; the thickness of the organic-rich clay laminae (OCL) is 20~50 μm, containing a small amount of quartz and feldspar. Electron probe micro-area line scanning shows that there is a sudden contact between the laminae, the Ca content of SCAL is about 75%, and the Si, Al, and K contents of OCL are relatively high. Therefore, SCAL+OCL indicates deep lake water. The quartz-feldspar-clay mixed laminae (QFCL) is 30-50μm thick, with complex mineral composition, including quartz, feldspar, clay minerals and biological shells, disordered particles, poor sorting, and high content of terrigenous debris. The organic-rich clay laminae (OCL) has good lateral continuity, with a layer thickness of 10μm, and spar calcite and quartz particles are distributed along the laminae boundary. Electron probe micro-area line scanning shows that OCL and QFCL are in gradual contact, and the laminae boundary is not clear. The Si, Al, and K contents do not change much in different laminae, and the Sr and B contents are generally low. Therefore, QFCL+OCL indicates a semi-deep lake water body with low paleo-salinity and stable supply of terrigenous debris under dry and cold climate conditions. Based on the FIB-SEM 3D reconstruction results of step S4, the structure and texture of the lenses inside the three different types of lenticular laminae are analyzed to indicate the stratification state of the ancient lake water body. Type I lenticular laminae, characterized by a micrite calcite lens with a central bulge and two ends that tapers off, indicate relatively turbulent semi-deep lake water bodies, where the micrite calcite laminae (MCAL) decompose and resuspend to produce lenticular features; Type II lenticular laminae, characterized by a flat, narrow, discontinuous lens, are formed by the erosion and transportation of mud-bearing rocks, indicating sufficient terrestrial supply; Type III lenticular laminae, characterized by an irregular micrite calcite lens, indicate deep lake water bodies with strong bioturbation.

[0018] Those of ordinary skill in the art should understand that the discussions of the above embodiments are only exemplary and are not intended to imply that the scope of the present invention is limited to these examples; under the concept of the present invention, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations in different aspects of the present invention as described above, which are not provided in detail for the sake of brevity. Any omission, modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for multi-dimensional analysis of the stratification state of ancient lake water bodies based on lamination features, characterized in that, It includes the following steps: Step S1: Sample treatment Prepare the sample into a thin slice, and the sample meets the experimental requirements of microscopy, field emission scanning electron microscopy, and in-situ laser ablation testing; Step S2: Classification of bioturbation levels Observe the sample under a microscope, and record the clarity of trace fossils, the distribution and overlapping of burrows, and the degree of damage to the original bedding; Step S3: Laminar thickness statistics - based on PCAS analysis and testing Use the particle and crack image recognition system PCAS to quantitatively identify and structurally analyze mineral particles, fissures, and pores in the microscope thin section photos taken under a polarized light microscope, binarize the images, remove noise points, automatically segment and identify particles, pores, and cracks, and output their geometric parameters, including the number, length, and width, to achieve the statistics of laminar types and thicknesses at the ten-micron scale; Step S4: 3D reconstruction of laminar features by FIB-SEM Determine the target area through observation with a focused ion beam scanning electron microscope, use the FIB-SEM 3D reconstruction technology to slice the target area, synthesize all the slices to obtain a 3D data volume, and stack and image each peeled laminar in sequence to obtain its spatial distribution; Step S5: Identification of laminar genesis Analyze the 3D reconstruction results of Step S4, identify different genesis laminars, and restore the sedimentation process at that time; Step S6: Verification of micro-area elements and isotopes of laminars Verify the micro-area elements and isotopes of laminars based on in-situ laser ablation and in-situ carbon and oxygen isotope analysis and testing; Step S7: Discrimination of the stratification state of the ancient lake water body Based on the test results of Steps S3 and S6, the bioturbation classification in Step S2, and the identification of laminar genesis in Step S5, discriminate the stratification state of the ancient lake water body; based on the FIB-SEM 3D reconstruction results in Step S4, analyze the indication of the structure and texture of the lens bodies inside different types of lenticular laminars on the stratification state of the ancient lake water body.

2. The method for multi-dimensional analysis of the stratification state of ancient lake water bodies based on lamination characteristics according to claim 1, wherein In Step S1, the thickness of the prepared thin slice is greater than 100μm, the longest direction of the thin slice does not exceed 5cm, and it is prohibited to apply glue, paste gummed labels, and place cover glasses on the surface.

3. A method for multi-dimensional analysis of the stratification state of ancient lake water bodies based on lamination features according to claim 1, characterized in that, The specific method of Step S4 is as follows: Determine the target area through observation with a focused ion beam scanning electron microscope, the size of the target area is 10μm×10μm, rotate the sample stage by 52° to ensure that the ion beam is perpendicular to the sample surface, spray platinum on the surface of the target area to reduce the damage of the ion beam to it, use a 30kV gallium ion beam to perform cutting pretreatment on the sample, and then use the Slice&View software to control the FIB and SEM to continuously cut and image the shale cross-section more than 500 times to obtain a series of SEM images. During the continuous cutting process, the acceleration voltage of the electron beam is generally selected as 2kV, the current is 0.2nA, and the backscattered mode is used for imaging.

4. A method for multi-dimensional analysis of the stratification state of ancient lake water bodies based on lamination features according to claim 1, characterized in that The specific method of Step S6 is as follows: S61. Micro-area in-situ laser ablation analysis and testing The major element determination was carried out using a GeoLasPro 193nm ArF excimer laser and an Agilent 7900 inductively coupled plasma mass spectrometer. Before the test, the performance of the ICP-MS was optimized using SRM610, and its content was calculated using the multi-external standard and total normalization method. The ICPMS Data Cal was used to analyze and process the data to obtain the contents of the major elements Na2O, Al2O3, SiO2, and K2O in the sample; S62. In-situ micro-area carbon and oxygen isotope analysis and testing Use a dental drill of a microarea sampler to drill at a low speed at the sampling site to obtain a powder sample. The sample amount is 10 - 50 μg, with 1 - 2 drill holes. Use a micropipette to collect the powder and transfer it into a 12 mL borosilicate bottle. After purging with helium, add about 50 μL of 99.9% orthophosphoric acid and react at 72 °C for 10 minutes to produce CO2 gas. Enter the MAT-253 mass spectrometer with He as the carrier gas for analysis. The analysis results are given in the VPDB standard. All δ 13 C, δ 18 O values are standardized by NBS19. The precision of carbon isotope analysis is better than 0.1‰, and the precision of oxygen isotope analysis is better than 0.15‰.

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