Method for determining oil and gas accumulation period based on apatite in-situ U-Pb dating

Abstract

The invention provides a method for determining the oil and gas reservoir-forming period based on apatite in-situ U-Pb dating, which comprises the following steps: collecting a shale sample in a petroliferous basin, making the shale sample into a probe sheet, and selecting apatite particles from the probe sheet; carrying out in-situ U-Pb dating on the apatite particles to obtain the U-Pb age of the sample; establishing a mapping relation between the oil reservoir hydrothermal fluid and the oil and gas accumulation and reservoir formation period, determining the period of the hydrothermal fluid in the oil reservoir according to the sample U-Pb age, matching the period of the hydrothermal fluid in the oil reservoir with the mapping relation between the oil reservoir hydrothermal fluid and the oil and gas accumulation and reservoir formation period, and obtaining the period of the oil and gas accumulation event of the basin oil and gas reservoir; the basin oil and gas reservoir forming period is determined according to the period of the basin oil and gas accumulation event and transmission light and reflection light photographing, the problem that the oil and gas reservoir forming period cannot be accurately determined through oil exploration and development is solved, the oil and gas reservoir forming period is determined according to the apatite in-situ U-Pb dating result, and reference is provided for understanding the basin thermal evolution history.

Description

Technical Field

[0001] The present invention relates to the technical field of geology, and in particular, to a method for in-situ determination of the hydrocarbon accumulation stages based on apatite U-Pb dating. Background Art

[0002] The study of hydrocarbon accumulation stages is the key to the study of the distribution and formation law of hydrocarbon reservoirs in hydrocarbon-bearing basins. A correct understanding of hydrocarbon accumulation chronology is an important basis and prerequisite for the study of hydrocarbon accumulation models and hydrocarbon enrichment laws. The hydrocarbon accumulation stages of traditional hydrocarbon reservoirs are mainly determined by geochemical indicators of hydrocarbon components in hydrocarbon reservoirs and geological tectonic movements. There are some uncertain factors in these methods because the hydrocarbons generated by source rocks are generated through the evolution and exchange in a long geological history period. There are great differences in hydrocarbon composition, maturity and physical and chemical characteristics between the hydrocarbons in the current hydrocarbon reservoirs and the ancient hydrocarbons. Basin numerical simulation, forward and inverse modeling of hydrocarbon generation and expulsion of source rocks can only roughly and qualitatively infer the time of hydrocarbon reservoirs, which belongs to an indirect method for determining hydrocarbon accumulation age. In related technologies, the Re-Os isotope dating method is used to directly date source rocks, solid bitumen, oil sands, etc., but the accuracy of this method is poor. For the Tertiary basins with a relatively short hydrocarbon accumulation history, the accuracy of this method is far from being able to completely solve the problem of the formation time of hydrocarbon reservoirs. Summary of the Invention

[0003] The present invention provides a method for determining hydrocarbon accumulation stages based on in-situ U-Pb dating of apatite, so as to solve the defect that the traditional Re-Os isotope dating method has poor accuracy and cannot solve the formation time of hydrocarbon reservoirs in regions with a relatively short hydrocarbon accumulation history.

[0004] The present invention provides a method for determining hydrocarbon accumulation stages based on in-situ U-Pb dating of apatite, including: Collecting shale samples in a hydrocarbon-bearing basin, making the shale samples into probe slices, and selecting apatite grains from the probe slices; Carrying out in-situ U-Pb dating on the apatite grains to obtain the U-Pb age of the samples; Establishing a mapping relationship between hydrothermal fluids in the reservoir and hydrocarbon accumulation stages, determining the activity stages of hydrothermal fluids in the reservoir according to the U-Pb age of the samples, and matching the activity stages of hydrothermal fluids in the reservoir with the mapping relationship between hydrothermal fluids in the reservoir and hydrocarbon accumulation stages to obtain the periods of hydrocarbon accumulation events in the basin hydrocarbon reservoirs; Determining the hydrocarbon accumulation stages in the basin according to the periods of hydrocarbon accumulation events in the basin hydrocarbon reservoirs and the transmitted light and reflected light photography of the samples.

[0005] According to the method for determining the hydrocarbon accumulation stages based on in-situ U-Pb dating of apatite provided by the present invention, establishing the mapping relationship between the hydrothermal fluids in the reservoir and the hydrocarbon accumulation stages, and determining the stages of the hydrothermal fluids in the reservoir according to the U-Pb ages of the samples, including: Simultaneously detecting isotopes through a double collector system 204 Pb + 、 206 Pb + 、 238 U 16 O + 、 238 U 16 O2 + ; Based on the isotopes 204 Pb + 、 206 Pb + 、 238 U 16 O + 、 238 U 16 O2 + Fitting the U-Pb isochron; Calculating the U-Pb age of apatite according to the U-Pb isochron; Matching the activity stages of the hydrothermal fluids in the reservoir according to the U-Pb age of apatite.

[0006] According to the method for determining the hydrocarbon accumulation stages based on in-situ U-Pb dating of apatite provided by the present invention, determining the hydrocarbon accumulation stages in the basin according to the periods of hydrocarbon accumulation events in the basin's hydrocarbon reservoirs and the transmitted light and reflected light photography of the samples, including: Determining the hydrocarbon charging time according to the activity stages of the hydrothermal fluids in the reservoir; Determining the periods of hydrocarbon accumulation events in the basin's hydrocarbon reservoirs according to the hydrocarbon charging time; Determining whether apatite is an authigenic mineral or a paragenetic mineral according to the transmitted light and reflected light photography of the samples; If apatite is an authigenic mineral, the age of the apatite directly represents the hydrocarbon accumulation stage; if apatite is detrital apatite, the hydrocarbon accumulation constraint time is obtained by combining the ages of the paragenetic minerals of the apatite.

[0007] According to the method for determining the hydrocarbon accumulation stages based on in-situ U-Pb dating of apatite provided by the present invention, determining whether apatite is an authigenic mineral or a paragenetic mineral according to the transmitted light and reflected light photography of the samples, including: Preliminarily distinguishing apatite from other transparent minerals by observing the optical properties of the minerals through transmitted light, and judging whether apatite is an authigenic mineral; Observing opaque or translucent minerals by reflected light to assist in judging whether apatite is a symbiotic mineral related to hydrocarbon accumulation.

[0008] According to the method for determining the hydrocarbon accumulation period based on in-situ U-Pb dating of apatite provided by the present invention, the specification of the shale sample in the hydrocarbon-bearing basin is not less than 6×12×18 cm 3 .

[0009] According to the method for determining the hydrocarbon accumulation period based on in-situ U-Pb dating of apatite provided by the present invention, the preparation of the shale sample into a probe slice includes: Performing sample cutting - rough grinding - fine grinding - rough polishing - sticking - slicing - grinding - rough polishing - fine polishing on the shale sample in sequence, wherein, 0.3μm alumina or silica suspension is used for rough polishing treatment, and 0.05μm alumina or silica suspension is used for fine polishing treatment.

[0010] According to the method for determining the hydrocarbon accumulation period based on in-situ U-Pb dating of apatite provided by the present invention, the thickness of the probe slice is about 50 - 80μm, and the size of its carrier glass is 2.5×5 cm 2 ; the number of the probe slices is determined according to the amount of minerals for dating, specifically: For rocks containing more minerals for dating, grind 5 or 6 probe slices; For rocks containing fewer minerals for dating or having special requirements, grind 10 - 15 probe slices.

[0011] According to the method for determining the hydrocarbon accumulation period based on in-situ U-Pb dating of apatite provided by the present invention, the selection of apatite grains from the probe slices includes: Selecting apatite grains with a particle size greater than a preset value in the probe slices; Placing the selected apatite grains at the center of the microscope crosshair, marking and numbering them with a marker pen; When multiple apatite grains are selected in one probe slice, connecting the multiple apatite grains with a straight line and taking a micrograph.

[0012] According to the method for determining the hydrocarbon accumulation period based on in-situ U-Pb dating of apatite provided by the present invention, it further includes: Performing a 5-minute raster scan of 15μm×15μm on the surface of the apatite grains.

[0013] According to the method for determining the hydrocarbon accumulation period based on in-situ U-Pb dating of apatite provided by the present invention, after selecting apatite grains from the probe slices, it further includes: Placing the apatite grains in a vacuum chamber, heating them with a lamp for a preset duration, and then introducing them into a NanoSIMS50 ion probe for analysis and testing.

[0014] The method for determining the hydrocarbon accumulation stages based on in-situ U-Pb dating of apatite provided by the present invention involves collecting shale samples from an oil and gas-bearing basin, making the shale samples into probe slices, and selecting apatite grains from the probe slices; conducting in-situ U-Pb dating on the apatite grains to obtain the U-Pb age of the samples; establishing the mapping relationship between the hydrothermal fluids in the reservoir and the hydrocarbon accumulation stages, determining the stages of the hydrothermal fluids in the reservoir based on the U-Pb age of the samples, matching the stages of the hydrothermal fluids in the reservoir with the mapping relationship between the hydrothermal fluids in the reservoir and the hydrocarbon accumulation stages to obtain the periods of hydrocarbon accumulation events in the basin's oil and gas reservoirs; and determining the hydrocarbon accumulation stages in the basin based on the periods of hydrocarbon accumulation events in the basin's oil and gas reservoirs and transmitted light and reflected light photography. This solves the problem that the current oil exploration and development industry cannot accurately determine the hydrocarbon accumulation stages. By combining the in-situ U-Pb dating results of apatite with corresponding geological data, the hydrocarbon accumulation stages are determined, providing an important reference for understanding the thermal evolution history of the basin. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0016] Figure 1 It is a schematic flow chart of the method for determining the hydrocarbon accumulation stages based on in-situ U-Pb dating of apatite provided by the embodiments of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0017] To make the objectives, technical solutions, and advantages of the present invention clearer, the following will clearly and completely describe the technical solutions in the present invention with reference to the drawings in the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0018] Figure 1 It is a flow chart of the method for determining the hydrocarbon accumulation stages based on in-situ U-Pb dating of apatite provided by the embodiments of the present invention. As Figure 1 shown, the method for determining the hydrocarbon accumulation stages based on in-situ U-Pb dating of apatite provided by the embodiments of the present invention includes: Step 101: Collect shale samples from an oil and gas-bearing basin, make the shale samples into probe slices, and select apatite grains from the probe slices; Step 102: Conduct in-situ U-Pb dating on the apatite particles to obtain the U-Pb age of the sample. Uranium ([[$ 238 U and [[$ 235 U) in common uranium-bearing minerals undergoes radioactive decay to form stable isotopes [[$ 206 Pb and [[$ 207 Pb. Based on the determination of the contents and isotope ratios of the parent isotopes ([[$ 238 U and [[$ 235 U) and daughter isotopes ([[$ 206 Pb and [[$ 207 Pb) in the uranium-bearing minerals, the time since the sample formed a closed system can be calculated according to the radioactive decay law, that is, the age since the uranium-bearing minerals formed. Apatite, as a common uranium-bearing accessory mineral in sedimentary rocks, is widely used in thermochronology research. Compared with zircon, the U-Th-Pb isotope closure temperature of apatite is relatively low, usually 325 - 550 °C. For terranes with a complex evolutionary history, apatite dating can provide age information for the relatively low-temperature stage in PTt path research. Therefore, in-situ U-Pb dating of authigenic apatite has great potential in determining the stages of hydrocarbon accumulation.

[0019] The embodiment of the present invention uses a new method of determining the stages of hydrocarbon accumulation by in-situ U-Pb dating of authigenic apatite, which solves many drawbacks of the existing methods and provides a good method for determining the stages of hydrocarbon accumulation.

[0020] Step 103: Establish the mapping relationship between the hydrothermal fluids in the reservoir and the stages of hydrocarbon accumulation. Determine the active stages of the hydrothermal fluids in the reservoir according to the U-Pb age of the sample, and match the active stages of the hydrothermal fluids in the reservoir with the mapping relationship between the hydrothermal fluids in the reservoir and the stages of hydrocarbon accumulation to obtain the periods of hydrocarbon accumulation events in the basin's hydrocarbon reservoirs. In the embodiment of the present invention, for rocks that have experienced multiple stages of metamorphism and deformation and have a complex metamorphic history, determining the combination of dating minerals is the key to this dating method. Mainly use a polarized light microscope to study the symbiotic combinations of different-stage rock-forming minerals in the probe slices, analyze the spatio-temporal relationship between the dating minerals and the main mineral combinations in the rock, and then identify uranium-bearing minerals such as apatite in different generations, different stages, and different genetic domains, and then conduct targeted chronology research.

[0021] Step 104: Determine the stages of hydrocarbon accumulation in the basin according to the periods of hydrocarbon accumulation events in the basin's hydrocarbon reservoirs and the transmitted light and reflected light photography of the sample.

[0022] The traditional method for determining the formation time of oil and gas reservoirs is to directly date source rocks, solid bitumen, oil sands, etc. using the Re-Os isotope dating method. However, the accuracy of this method is poor. For the Tertiary basins with relatively short hydrocarbon accumulation histories, the accuracy of this method is far from being able to fully solve the problem of the formation time of oil and gas reservoirs.

[0023] The method for determining the hydrocarbon accumulation stages based on in-situ U-Pb dating of apatite provided by the embodiments of the present invention includes collecting shale samples in an oil and gas basin, making the shale samples into probe slices, and selecting apatite grains from the probe slices; conducting in-situ U-Pb dating on the apatite grains to obtain the U-Pb age of the samples; establishing a mapping relationship between hydrothermal fluids in the reservoir and hydrocarbon accumulation stages, determining the stages of hydrothermal fluids in the reservoir according to the U-Pb age of the samples, matching the stages of hydrothermal fluids in the reservoir with the mapping relationship between hydrothermal fluids in the reservoir and hydrocarbon accumulation stages to obtain the time of hydrocarbon accumulation events in the basin oil and gas reservoir; and determining the hydrocarbon accumulation stages in the basin according to the time of hydrocarbon accumulation events in the basin oil and gas reservoir and transmitted light and reflected light photography, which solves the problem that the current oil exploration and development industry cannot accurately determine the hydrocarbon accumulation stages. By combining the in-situ U-Pb dating results of apatite with corresponding geological data, the hydrocarbon accumulation stages are determined, providing an important reference for understanding the thermal evolution history of the basin.

[0024] Based on any of the above embodiments, the establishment of the mapping relationship between hydrothermal fluids in the reservoir and hydrocarbon accumulation stages, and the determination of the active stages of hydrothermal fluids in the reservoir according to the U-Pb age of the samples includes: Synchronously detecting isotopes through a double collector system 204 Pb + 、 206 Pb + 、 238 U 16 O + 、 238 U 16 O2 + ; Based on 204 Pb + 、 206 Pb + 、 238 U 16 O + 、 238 U 16 O2 + Fitting the U-Pb isochron; Calculating the U-Pb age of apatite according to the U-Pb isochron; Matching the active stages of hydrothermal fluids in the reservoir according to the U-Pb age of apatite.

[0025] Based on any of the above embodiments, determining the hydrocarbon accumulation stages of the basin hydrocarbon reservoir according to the period of the hydrocarbon accumulation event in the basin and the transmitted light and reflected light photography of the sample includes: Determining the hydrocarbon charging time according to the active stages of the hydrothermal fluid in the reservoir; Determining the period of the hydrocarbon accumulation event in the basin hydrocarbon reservoir according to the hydrocarbon charging time; Determining whether apatite is an authigenic mineral or a symbiotic mineral according to the transmitted light and reflected light photography; If apatite is an authigenic mineral, the age of the apatite directly represents the hydrocarbon accumulation stage; if apatite is detrital apatite, the hydrocarbon accumulation constraint time is obtained by combining the ages of the symbiotic minerals of the apatite.

[0026] In the embodiment of the present invention, determining whether apatite is an authigenic mineral or a symbiotic mineral according to the transmitted light and reflected light photography of the sample includes: Preliminarily distinguishing apatite from other transparent minerals by observing the optical properties of the minerals through transmitted light to judge whether apatite is an authigenic mineral; Observing opaque or semi-transparent minerals through reflected light to assist in judging whether apatite is a symbiotic mineral related to hydrocarbon accumulation.

[0027] According to the method for determining hydrocarbon accumulation stages based on in-situ U-Pb dating of apatite provided by the present invention, the specification of the shale sample in the oil and gas bearing basin is not less than 6×12×18 cm 3 .

[0028] In the embodiment of the present invention, the collection requirements for marine sedimentary rock samples in the oil and gas bearing basin include: conducting field investigations on the geological bodies to be studied, and the collected samples are required to be fresh and representative. The sample specification is generally not less than 6×12×18 cm 3 , and for lithologies with less dating mineral content, the sample collection amount should be appropriately increased. Record the position, rock characteristics, occurrence of the sampling point, and sketch or take pictures, and number the samples.

[0029] Based on any of the above embodiments, fabricating the shale sample into a probe slice includes: Performing cutting - rough grinding - fine grinding - rough polishing - sticking - slicing - grinding - rough polishing - fine polishing on the shale sample in sequence, where 0.3μm alumina or silica suspension is used for rough polishing, and 0.05μm alumina or silica suspension is used for fine polishing.

[0030] In the embodiment of the present invention, the thickness of the probe slice is about 50 - 80μm, and the size of its carrier glass is 2.5×5 cm 2 ; the number of the probe slices is determined according to the amount of dating minerals, specifically: For rocks containing more dating minerals, grind 5 or 6 probe slices; For rocks containing fewer dating minerals or with special requirements, grind 10 - 15 probe slices.

[0031] Based on any of the above embodiments, the selection of apatite grains from the probe slices according to the transmitted light and reflected light photography includes: Select apatite grains with a grain size larger than a preset value in the probe slices; Place the selected apatite grains at the center of the microscope crosshairs, mark and number them with a marker pen; When multiple apatite grains are selected in one probe slice, connect the multiple apatite grains with a straight line and take a micrograph.

[0032] In the embodiments of the present invention, micrographs are taken to search for dating minerals for cathodoluminescence image analysis and U - Pb isotope determination.

[0033] Based on any of the above embodiments, the method for determining the hydrocarbon accumulation period based on in - situ U - Pb dating of apatite further includes: Perform a 15μm×15μm raster scan on the surface of the apatite grains for 5 minutes.

[0034] In the embodiments of the present invention, to solve the problem of samples with high common lead content and low U content. To obtain statistically sufficient counts, focus a high - order primary o - beam current of about 10 nA on a sample with a diameter of about 15μm. Before actual analysis, perform a 15μm square raster on the sample surface for 5 min to reduce the contribution of surface contaminant Pb to the analysis. Extract sputtered secondary positive ions at an acceleration voltage of 8 kV. The generated secondary ions are focused and transferred for mass analysis and detection. Under the condition of 1% peak height, the mass spectrometry resolution of the mass spectrometer is 4100, which can separate 206 Pb and 143 Nd 31 P 16 O2, and there are sufficient flat top peaks.

[0035] Based on any of the above embodiments, after selecting the apatite grains from the probe slices, it further includes: Place the apatite grains in a vacuum chamber, heat them with a lamp for a preset duration, and then introduce them into a NanoSIMS50 ion probe for analysis and testing.

[0036] In the embodiments of the present invention, the sample is evacuated overnight in the air - rock system of NanoSIMS to reduce the hydride interference that may be caused by water absorbed on the surface of the sample holder. In addition, before dating, the surface of the sample target is cleaned and gold - plated.

[0037] The Matattach-Herzog geometry mass analyzer used in NanoSIMS enables simultaneous acquisition of 31 P + 、 43 Ca + 、 204 Pb + 、 206 Pb + 、 238 U 16 O + 、 238 U 16 O2 + while significantly shortening the cycle time. All ions are detected using a low-noise ion counter. All ions are detected using a low-noise ion counter. In NanoSIMS, since 204 Pb and 206 Pb are only 2 mm apart on the focal plane, the ion dispersion at high mass numbers will become very short after the magnet, making it impossible for NanoSIMS to simultaneously detect 204 Pb and 206 Pb. To improve the analysis efficiency and accuracy, a dual collector system has been installed on the NanoSIMS at the University of Tokyo, which can simultaneously detect 204 Pb and 206 Pb. The integration time for each analysis is set to 10 minutes to obtain statistically sufficient counts. In this setting, the total time required for each analysis is 15 minutes, including rastering.

[0038] The method for determining the hydrocarbon accumulation period based on in-situ U-Pb dating of apatite provided by the embodiments of the present invention makes thin sections of marine sedimentary rock samples collected from oil and gas bearing basins, and uses an optical microscope and a Raman spectrometer to identify apatite grains therein. The selected apatite specimens are polished until the middle section of the grains is exposed. After the samples are heated with a lamp in a vacuum chamber for about 12 h, they are introduced into a NanoSIMS50 ion probe for analysis and testing. This method effectively avoids the errors of traditional isotope dating methods, accurately determines the U-Pb age of apatite grains, and thus achieves the purpose of determining the hydrocarbon accumulation period. By utilizing the relatively high closure temperature of apatite, approximately 325 - 550 °C, the apatite U-Pb isotope system becomes a useful tool for accurately determining the hydrocarbon accumulation period, solving the problem that the current oil exploration and development industry cannot accurately determine the hydrocarbon accumulation period. Based on the in-situ U-Pb dating results of authigenic apatite and combined with corresponding geological data, it also has important reference significance for understanding the basin thermal evolution history on the basis of determining the hydrocarbon accumulation period.

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for determining the hydrocarbon accumulation stages based on in-situ U-Pb dating of apatite, characterized in that, Comprising: Collecting shale samples in an oil and gas-bearing basin, making the shale samples into probe slices, and selecting apatite grains from the probe slices; Carrying out in-situ U-Pb dating on the apatite grains to obtain the U-Pb age of the samples; Establishing the mapping relationship between the hydrothermal fluid in the reservoir and the stages of oil and gas accumulation and entrapment, determining the active stages of the hydrothermal fluid in the reservoir according to the U-Pb age of the samples, and matching the active stages of the hydrothermal fluid in the reservoir with the mapping relationship between the hydrothermal fluid in the reservoir and the stages of oil and gas accumulation and entrapment to obtain the periods of oil and gas accumulation events in the basin oil and gas reservoirs; Determining the stages of oil and gas accumulation in the basin according to the periods of oil and gas accumulation events in the basin oil and gas reservoirs and the transmitted light and reflected light photography of the samples.

2. The method for determining the hydrocarbon accumulation stages based on in-situ U-Pb dating of apatite according to claim 1, characterized in that The establishing of the mapping relationship between the hydrothermal fluid in the reservoir and the stages of oil and gas accumulation and entrapment, and determining the active stages of the hydrothermal fluid in the reservoir according to the U-Pb age of the samples, includes: Synchronous detection of isotopes through a dual collector system 204 Pb + 、 206 Pb + 、 238 U 16 O + 、 238 U 16 O2 + ; Based on isotopes 204 Pb + 、 206 Pb + 、 238 U 16 O + 、 238 U 16 O2 + Fitting the U-Pb isochron Calculating the U-Pb age of apatite according to the U-Pb isochron; Matching the active stages of the hydrothermal fluid in the reservoir according to the U-Pb age of the apatite.

3. The method for determining the hydrocarbon accumulation stages based on in-situ U-Pb dating of apatite according to claim 2, wherein The determining of the stages of oil and gas accumulation in the basin according to the periods of oil and gas accumulation events in the basin oil and gas reservoirs and the transmitted light and reflected light photography of the samples includes: Judging the oil and gas injection time according to the active stages of the hydrothermal fluid in the reservoir; Determining the periods of oil and gas accumulation events in the basin oil and gas reservoirs according to the oil and gas injection time; Determining whether the apatite is an authigenic mineral or a symbiotic mineral according to the transmitted light and reflected light photography; If the apatite is an authigenic mineral, the age of the apatite directly represents the stages of oil and gas accumulation; if the apatite is detrital apatite, the constraint time of oil and gas accumulation is obtained by combining the age of the symbiotic minerals of the apatite.

4. The method for determining the hydrocarbon accumulation stage based on in-situ U-Pb dating of apatite according to claim 3, wherein The determining of whether the apatite is an authigenic mineral or a symbiotic mineral according to the transmitted light and reflected light photography of the samples includes: Preliminarily distinguishing apatite from other transparent minerals by observing the optical properties of the minerals through transmitted light, and judging whether the apatite is an authigenic mineral; Observing opaque or semi-transparent minerals through reflected light to assist in judging whether the apatite is a symbiotic mineral related to oil and gas accumulation.

5. The method for determining the hydrocarbon accumulation stage based on in-situ U-Pb dating of apatite according to claim 1, wherein The specifications of the shale samples in the oil and gas bearing basin are not less than 6×12×18 cm 3 .

6. The method for determining the hydrocarbon accumulation stages based on in-situ U-Pb dating of apatite according to claim 1, wherein The making of the shale samples into probe slices includes: Successively carrying out sample cutting - rough grinding - fine grinding - rough polishing - sticking - slicing - grinding - rough polishing - fine polishing on the shale samples, wherein, 0.3μm alumina or silica suspension is used for rough polishing, and 0.05μm alumina or silica suspension is used for fine polishing.

7. The method for determining the hydrocarbon accumulation stages based on in-situ U-Pb dating of apatite according to claim 1 or 5, characterized in that, The thickness of the probe slice is about 50 - 80 μm, and the size of its carrier glass is 2.5×5 cm 2 ; The number of the probe slices is determined according to the amount of the dating mineral contained. Specifically: For rocks containing more dating minerals, grinding 5 or 6 probe slices; For rocks containing fewer dating minerals or having special requirements, grinding 10 - 15 probe slices.

8. The method for determining the hydrocarbon accumulation stages based on in-situ U-Pb dating of apatite according to claim 1, wherein The selecting of apatite grains from the probe slices according to the transmitted light and reflected light photography includes: Selecting apatite grains with a particle size greater than a preset value in the probe slices; Placing the selected apatite grains at the center of the microscope crosshair, marking and numbering them with a marker pen; When multiple apatite grains are selected in one probe slice, connecting the multiple apatite grains with a straight line and taking a micrograph.

9. The method for determining the hydrocarbon accumulation stages based on in-situ U-Pb dating of apatite according to claim 1 or 5, characterized in that, Also including: Performing a 5-minute raster scan of 15μm × 15μm on the surface of the apatite grains.

10. The method for determining the hydrocarbon accumulation stages based on in-situ U-Pb dating of apatite according to claim 1, wherein After the selecting of apatite grains from the probe slices, it also includes: After heating the apatite particles in a vacuum chamber with a lamp for a preset duration, they are introduced into a NanoSIMS50 ion probe for analysis and testing.

Images