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

Abstract

The invention provides a method for determining an oil and gas reservoir forming period based on xenotime in-situ U-Pb dating, which comprises the following steps: collecting a sedimentary rock sample of a petroliferous basin, selecting xenotime particles from the sedimentary rock sample, and carrying out in-situ U-Pb dating to obtain U-Pb age data of the sample; determining the rock thermal evolution history according to the U-Pb age; the method comprises the following steps: establishing a mapping model of a basin thermal evolution history and an oil and gas accumulation and accumulation period, matching a thermal evolution history after rock autodeposition and diagenesis with the mapping model of the basin thermal evolution history and the oil and gas accumulation and accumulation period, obtaining a period of an oil and gas accumulation event of a basin oil and gas reservoir, and determining the basin oil and gas accumulation period according to the period of the oil and gas accumulation event. According to the method, the early diagenesis is determined by using the xenotime, and the period of each main fluid and thermal event influencing the sedimentary basin can be determined, so that a breakthrough from'indirect inference 'to'direct dating' is realized, the dating precision of oil and gas reservoirs is improved, and the quantitative development of fluid activity research of the sedimentary basin is promoted.

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 U-Pb dating of xenotime. 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 means of geochemical indexes 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 illite K-Ar method and the homogenization temperature method of fluid inclusions are used for dating, but these methods rely on indirect correlations, such as the coupling of mineral formation temperature and hydrocarbon migration time, and are easily interfered by late thermal events, resulting in multiple solutions for age interpretation, and 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 xenotime, so as to solve the defects that the traditional dating method relies on indirect correlation, is easily interfered by late thermal events, 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 xenotime, including: Collecting sedimentary rock samples from a hydrocarbon-bearing basin, selecting xenotime particles from the sedimentary rock samples of the hydrocarbon-bearing basin, and performing in-situ U-Pb dating on the xenotime particles to obtain U-Pb age data of the samples; Determining the thermal evolution history of the rock since sedimentation and diagenesis according to the U-Pb age of the samples; Establishing a mapping model between the basin thermal evolution history and the hydrocarbon accumulation stages, matching the thermal evolution history of the rock since sedimentation and diagenesis with the mapping model between the basin thermal evolution history and the hydrocarbon accumulation stages, obtaining the period of hydrocarbon accumulation events in the basin hydrocarbon reservoirs, and determining the hydrocarbon accumulation stages of the basin hydrocarbon reservoirs according to the period of hydrocarbon accumulation events in the basin hydrocarbon reservoirs.

[0005] The method for determining the hydrocarbon accumulation stages based on in-situ U-Pb dating of xenotime provided by the present invention, the establishment of the mapping model of the basin thermal evolution history and the hydrocarbon accumulation stages includes: Dividing the sedimentation age of sedimentary rocks according to the U-Pb age data of xenotime; Analyzing the zoning structure of xenotime and identifying multi-stage fluid flow events through the zoning structure of xenotime; Correlating the sedimentation age with the multi-stage fluid flow events, establishing a mapping model of the basin thermal evolution history and the hydrocarbon accumulation stages, and the mapping model of the basin thermal evolution history and the hydrocarbon accumulation stages includes the corresponding relationship of time, temperature and fluid activity.

[0006] The method for determining the hydrocarbon accumulation stages based on in-situ U-Pb dating of xenotime provided by the present invention, the sedimentation age of the sedimentary rocks includes the diagenetic stage, the main hydrocarbon accumulation stage and the adjustment stage, and the correlation of the sedimentation age with the multi-stage fluid flow events includes: Associating sedimentation diagenesis or hydrocarbon generation from source rocks with the diagenetic stage; associating large-scale hydrocarbon filling with the main hydrocarbon accumulation stage; associating hydrocarbon adjustment or destruction with the adjustment stage.

[0007] The method for determining the hydrocarbon accumulation stages based on in-situ U-Pb dating of xenotime provided by the present invention, the obtaining of the period of hydrocarbon accumulation events in the basin oil and gas reservoirs includes: Matching the U-Pb age data of the sample with geological time segments, and determining fluid flow events according to the matching results of the geological time segments; Obtaining the period of hydrocarbon accumulation events in the basin oil and gas reservoirs according to the determined fluid flow events and the corresponding relationship of time, temperature and fluid activity.

[0008] The method for determining the hydrocarbon accumulation stages based on in-situ U-Pb dating of xenotime provided by the present invention, the collection of sedimentary rock samples from an oil and gas basin includes: The sedimentary rock samples include metamorphic argillaceous rocks and clastic sedimentary rocks, and xenotime of diagenesis mainly exists in different types of clastic sedimentary rocks from shale to conglomerate from river to ocean.

[0009] The method for determining the hydrocarbon accumulation stages based on in-situ U-Pb dating of xenotime provided by the present invention, the selection of xenotime particles from the sedimentary rock samples of the oil and gas basin includes: Making the sedimentary rock sample into a probe slice; Observing the composition and microstructure of the probe slice using an optical microscope and a scanning electron microscope; Analyzing the micro-area mineral composition using backscattering and an energy spectrometer; Screening out authigenic xenotime particles with a zoning structure according to the composition and microstructure of the probe slice and the micro-area mineral composition.

[0010] According to the method for determining the hydrocarbon accumulation stages based on in-situ U-Pb dating of xenotime provided by the present invention, the in-situ U-Pb dating of the xenotime particles to obtain the U-Pb age data of the sample includes: Fix the xenotime particles and a standard zircon reference sample on the surface of an epoxy resin disc and polish them; Perform in-situ micro-area U-Pb geochronological analysis using an ion probe with a beam spot smaller than a preset threshold; Calibrate the analysis results of the U-Pb geochronology using the reference sample to obtain the U-Pb age data of the sample; Among them, the reference sample is a group of xenotime reference samples with different ages and chemical compositions, which are placed separately in a base.

[0011] According to the method for determining the hydrocarbon accumulation stages based on in-situ U-Pb dating of xenotime provided by the present invention, the calibration of the analysis results of the U-Pb geochronology using the reference sample includes: Select a group of xenotime reference samples with different ages and chemical compositions to cover the possible age range and chemical composition of the sample; Perform cyclic interpolation analysis on the reference sample and the zircon containing xenotime particles, so that the reference sample and the zircon containing xenotime particles are alternately tested, and calibrate the analysis results of the U-Pb geochronology according to the test results.

[0012] According to the method for determining the hydrocarbon accumulation stages based on in-situ U-Pb dating of xenotime provided by the present invention, the calibration of the analysis results of the U-Pb geochronology using the reference sample includes: Collect data on multiple rare earth elements, which are used to calibrate the U-Pb isotope ratio, correct the matrix effect, and correct the instrumental mass fractionation.

[0013] According to the method for determining the hydrocarbon accumulation stages based on in-situ U-Pb dating of xenotime provided by the present invention, after calibrating the U / Pb and Th / Pb ratios, monitoring the matrix effect, and monitoring the instrumental mass fractionation effect, it further includes: Input the calibrated U-Pb isotope ratio and error data into the Isoplot-3 software to generate a concordia diagram to display the in-situ U-Pb dating results.

[0014] The method for determining the hydrocarbon accumulation period based on in-situ U-Pb dating of xenotime provided by the present invention collects sedimentary rock samples from an oil and gas-bearing basin, selects xenotime particles from the sedimentary rock samples of the oil and gas-bearing basin, and performs in-situ U-Pb dating on the xenotime particles to obtain the U-Pb age data of the samples; determines the thermal evolution history of the rock since sedimentation and diagenesis according to the U-Pb age of the samples; establishes a mapping model between the basin thermal evolution history and the hydrocarbon accumulation period, matches the thermal evolution history of the rock since sedimentation and diagenesis with the mapping model between the basin thermal evolution history and the hydrocarbon accumulation period to obtain the period of hydrocarbon accumulation events in the basin oil and gas reservoir, determines the hydrocarbon accumulation period of the basin according to the period of hydrocarbon accumulation events in the basin oil and gas reservoir, uses xenotime to determine early diagenesis, and can determine the periods of each major fluid and thermal event affecting the sedimentary basin, achieving a breakthrough in the hydrocarbon accumulation period from "indirect inference" to "direct dating", improving the dating accuracy of oil and gas reservoirs, and promoting the quantitative development of the study of fluid activities in sedimentary basins. 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, other drawings can be obtained based on these drawings without creative efforts.

[0016] Figure 1 It is a schematic flow chart of the method for determining the hydrocarbon accumulation period based on in-situ U-Pb dating of xenotime provided by the embodiment 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 accompanying drawings in the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0018] Figure 1 As shown in Figure 1 the flow chart of the method for determining the hydrocarbon accumulation period based on in-situ U-Pb dating of xenotime provided by the embodiment of the present invention includes: Step 101: Collect sedimentary rock samples from an oil and gas-bearing basin, select xenotime particles from the sedimentary rock samples of the oil and gas-bearing basin, and perform in-situ U-Pb dating on the xenotime particles to obtain the U-Pb age data of the samples; Step 102: Determine the thermal evolution history of the rock since sedimentation and diagenesis according to the U-Pb age of the sample. Step 103: Establish a mapping model between the basin thermal evolution history and the hydrocarbon accumulation and reservoir formation stages. Match the thermal evolution history of the rock since sedimentation and diagenesis with the mapping model between the basin thermal evolution history and the hydrocarbon accumulation and reservoir formation stages to obtain the period of hydrocarbon accumulation events in the basin hydrocarbon reservoir. Determine the hydrocarbon reservoir formation stages in the basin according to the period of hydrocarbon accumulation events in the basin hydrocarbon reservoir.

[0019] Since the accurate dating of the sedimentation age of sedimentary rocks is based on the fact that sedimentary rock samples (shales) contain abundant bedding-parallel veins, indicating significant fluid overpressure and post-depositional vertical extension. The vertical extension causes the pores, voids or fractures parallel to the bedding to open and be filled with low-temperature fluids, which carry a series of hydrothermal minerals including xenotime. The dating data of these minerals directly record the time of fluid flow events. In hydrocarbon-bearing basins, fluid flow events can promote the generation and accumulation of hydrocarbons. Xenotime is susceptible to alteration and metamorphism by fluid action, and is easily dissolved and reprecipitated to form composite grains, which can preserve the ages of multiple geological events. During diagenesis, due to the change in the concentrations of U and heavy rare earth elements (HREE) in the sediment pore water, xenotime crystals usually have compositional zoning. On the other hand, petrographic structures show that xenotime is wrapped by other diagenetic minerals, indicating that it is an earlier diagenetic mineral. Since xenotime is formed in the diagenetic stage shortly after sedimentation, the measured U-Pb age can be regarded as the approximate age of sediment deposition.

[0020] Traditional methods for determining hydrocarbon reservoir formation stages, such as the illite K-Ar method and the homogenization temperature method of fluid inclusions, rely on indirect correlations, such as the coupling of mineral formation temperature and hydrocarbon migration time, and are susceptible to interference from late thermal events, resulting in multiple interpretations of ages.

[0021] In the embodiments of the present invention, based on the fact that authigenic xenotime crystallizes directly from hydrothermal fluids during hydrocarbon reservoir formation, its U-Pb age directly corresponds to the fluid activity time, eliminating the error of indirect calculation and providing an absolute reservoir formation age.

[0022] Moreover, in-situ micro-area U-Pb dating (such as LA-ICP-MS, SIMS) can achieve micron-scale analysis of single-grain xenotime, with an accuracy of ±1-2 Ma, which is significantly better than the error range of traditional methods (such as the K-Ar method often has an error of more than ±10 Ma). Xenotime is sensitive to short-term thermal events and can solve the problem of dating hydrocarbon reservoirs in regions with a relatively short reservoir formation history.

[0023] The method for determining the hydrocarbon accumulation stages based on in-situ U-Pb dating of xenotime provided by the embodiments of the present invention includes collecting sedimentary rock samples from an oil and gas-bearing basin, selecting xenotime grains from the sedimentary rock samples of the oil and gas-bearing basin, performing in-situ U-Pb dating on the xenotime grains to obtain U-Pb age data of the samples; determining the thermal evolution history of the rock since sedimentation and diagenesis according to the U-Pb age of the samples; establishing a mapping model of the basin thermal evolution history and the hydrocarbon accumulation stages, matching the thermal evolution history of the rock since sedimentation and diagenesis with the mapping model of the basin thermal evolution history and the hydrocarbon accumulation stages to obtain the periods of hydrocarbon accumulation events in the basin oil and gas reservoirs, determining the hydrocarbon accumulation stages in the basin according to the periods of hydrocarbon accumulation events in the basin oil and gas reservoirs, using xenotime to determine early diagenesis, and being able to determine the stages of each major fluid and thermal event affecting the sedimentary basin, achieving a breakthrough in hydrocarbon accumulation stages from "indirect inference" to "direct dating", improving the dating accuracy of oil and gas reservoirs, and at the same time promoting the quantitative development of the research on fluid activities in sedimentary basins. Moreover, xenotime can record multiple hydrothermal events, and the complex hydrocarbon accumulation history can be analyzed through age spectrum analysis.

[0024] Based on any of the above embodiments, according to the method for determining the hydrocarbon accumulation stages based on in-situ U-Pb dating of xenotime provided by the present invention, the establishment of the mapping model of the basin thermal evolution history and the hydrocarbon accumulation stages includes: Step 201: Divide the sedimentation age of the sedimentary rock according to the U-Pb age data of xenotime; Step 202: Analyze the zonation structure of xenotime and identify multiple fluid flow events through the zonation structure of xenotime; Step 203: Correlate the sedimentation age with the multiple fluid flow events to establish a mapping model of the basin thermal evolution history and the hydrocarbon accumulation stages, and the mapping model of the basin thermal evolution history and the hydrocarbon accumulation stages includes the corresponding relationship of time, temperature and fluid activity.

[0025] Since the growth of different zones of xenotime is related to burial diagenesis, contact metamorphism, hydrothermal alteration or regional metamorphism. With the help of petrology, geochemical microanalysis and isotope techniques with fine spatial resolution, xenotime can be used to determine early diagenesis, and the stages of each major fluid and thermal event affecting the sedimentary basin can be determined. Therefore, the U-Pb age of metamorphic hydrothermal xenotime can represent the evolution stage of oil cracking into gas in an oil and gas-bearing basin.

[0026] In the embodiments of the present invention, the sedimentation age of the sedimentary rock includes the diagenetic stage, the main hydrocarbon accumulation stage and the adjustment stage, and the correlation of the sedimentation age with the multiple fluid flow events includes: The diagenesis period is associated with sedimentary diagenesis or hydrocarbon generation in source rocks; the main accumulation period is associated with large-scale injection of oil and gas; and the adjustment period is associated with oil and gas adjustment or destruction.

[0027] In the embodiment of the present invention, the formation temperature of xenotime is usually 120-200°C, which overlaps with the oil and gas window, and its age can be used to calibrate the key thermal evolution node.

[0028] Based on any of the above embodiments, the step of obtaining the period of oil and gas accumulation events in the oil and gas reservoir of the basin includes: matching the U-Pb age data of the sample with the geological age segment, and determining the fluid flow event according to the geological age segment matching result; The period of the oil and gas accumulation event in the oil and gas reservoir of the oil and gas accumulation event basin is obtained according to the correspondence between the determined fluid flow event and the time, temperature and fluid activity.

[0029] According to the method for determining the oil and gas accumulation period based on in-situ U-Pb dating of xenotime provided by the present invention, the sedimentary rock samples of the oil and gas-bearing basin are collected, comprising: The sedimentary rock samples include meta-pelite and clastic sedimentary rocks, and the diagenetic xenotime mainly exists in different types of clastic sedimentary rocks from rivers to shales and conglomerates in the ocean.

[0030] In the embodiment of the present invention, the number of samples must meet the production requirements of the probe sheet. For rocks containing more dating minerals, grinding 5 to 6 probe sheets can meet the dating requirements; for rocks containing fewer dating minerals or with special requirements, generally one dating sample needs to be ground into 10 to 15 probe sheets to obtain the number of minerals required for dating. The specific number of grinding depends on the specific situation.

[0031] Based on any of the above embodiments, the step of selecting xenotime particles from the sedimentary rock sample of the oil and gas-bearing basin comprises: Step 301, making a sedimentary rock sample into a probe sheet; Step 302: using an optical microscope and a scanning electron microscope to observe the composition and microstructure of the probe sheet; Step 303, analyzing the mineral composition of the micro-area using backscattering and energy spectrometer; Step 304: Screen out authigenic xenotime particles having a ring-shaped structure according to the composition and microstructure of the probe sheet and the mineral composition of the micro-region.

[0032] In the embodiment of the present invention, the preparation of the probe sheet follows the following steps: cutting - rough grinding - fine grinding - rough polishing - sticking - slicing - grinding - rough polishing - fine polishing. The thickness of the prepared probe sheet is about 50-80 μm, and the size of the carrier glass is 2.5×5 cm 2 .

[0033] After the preparation of the probe slice, an optical microscope and a scanning electron microscope are used to observe the rock composition and the characteristics of the microscopic structure. The backscattered electron (BSE) of the scanning electron microscope and the energy spectrometer are used to analyze the mineral composition and structure of the micro-region and image. According to the image, xenotime forms a secondary growth rim on the surface of detrital zircon grains. Most of these secondary growth rims range from irregular to conical, from small (<0.5μm) fine serrations to large (200μm) conical prisms, and are attached to the surface of detrital zircon grains. At the same time, xenotime crystals usually have a zoned structure. Select autogenous xenotime grains with a zoned structure, and then perform in-situ U-Pb dating on the selected xenotime grains.

[0034] Based on any of the above embodiments, the in-situ U-Pb dating of the xenotime grains to obtain the U-Pb age data of the sample includes: Step 401: Fix the xenotime grains and the standard zircon standard on the surface of an epoxy resin disc and polish them; Step 402: Perform in-situ micro-region U-Pb geochronological analysis using an ion probe with a beam spot smaller than a preset threshold; Step 403: Calibrate the analysis results of the U-Pb geochronological analysis using the standard to obtain the U-Pb age data of the sample; Among them, the standard is a set of xenotime standards with different ages and chemical compositions, which are placed separately in the base.

[0035] In the embodiment of the present invention, the zircon rich in the secondary growth rim of xenotime separated (or the wedge cut from the polished thin section) and the standard zircon are mounted on the surface of an epoxy resin disc, and then polished. An in-situ micro-region U-Pb geochronological analysis of xenotime at the thin section scale is carried out using a small beam spot (generally ≤10μm, erosion depth <1μm) ion probe (SHRIMP).

[0036] The dating process of the embodiment of the present invention is completed on a SHRIMP II (Sensitive High-Resolution Ion MicroProbe II). The SHRIMP II can exclude the interference of common lead and improve the reliability of the age data. Xenotime highlights the importance of the microbeam in-situ analysis technique. Adjust the Kohler aperture of the SHRIMP II instrument to achieve a small beam spot (≤10μm, erosion depth <1μm). At the same time, to compensate for the weakening of the primary and secondary flow signals caused by the small beam spot, the number of data acquisition groups also needs to be increased accordingly, for example, increased to 8 groups.

[0037] In the test, a set of reference samples with differences in age and chemical composition, i.e., monazite reference samples (MG1, Xeno1, Xeno2), need to be selected and placed in separate bases. Before each SHRIMP analysis, the bases are cleaned and gold-plated (purity 99.99%, thickness 40 nm).

[0038] Based on any of the above embodiments, using the reference samples to verify the U-Pb geochronology analysis results includes: Step 501: Select a set of monazite reference samples with different ages and chemical compositions to cover the possible age range and chemical composition of the samples; Step 502: Perform cyclic interpolation analysis on the reference samples and zircon containing monazite grains, so that the reference samples and zircon containing monazite grains are alternately tested, and verify the U-Pb geochronology analysis results according to the test results.

[0039] In the embodiments of the present invention, secondary ion mass spectrometry (SIMS) analysis data is affected by the sample matrix effect. In the test, a set of reference samples with differences in age and chemical composition need to be selected. In the embodiments of the present invention, monazite MG1, Xeno1, and Xeno2 will be selected to perform cyclic interpolation analysis together with the samples. By alternately inserting reference samples (such as MG1, Xeno1, and Xeno2) between sample analyses, the instrument response changes are dynamically tracked and the data is corrected in real time.

[0040] Based on any of the above embodiments, using the reference samples to verify the U-Pb geochronology analysis results includes: Collect data on multiple rare earth elements, which are used to calibrate the U-Pb isotope ratio, correct the matrix effect, and instrument mass fractionation.

[0041] In the embodiments of the present invention, the rare earth element data is, for example, data such as La, Ce, Nd, and Y. These data are used not only to calibrate U / Pb and Th / Pb, but also to monitor the matrix effect and the instrument mass fractionation effect (IMF), and are corrected during data processing.

[0042] Based on any of the above embodiments, after calibrating the U / Pb and Th / Pb ratios, monitoring the matrix effect, and monitoring the instrument mass fractionation effect, it further includes: Input the calibrated U-Pb isotope ratio and error data into Isoplot-3 software to generate a concordia diagram to display the U / Pb in-situ dating results.

[0043] In the embodiments of the present invention, for complex data (such as multi-stage hydrothermal superimposition), Isoplot-3 can identify different age peaks through age spectrum decomposition algorithms (such as Unmix or TuffZirc), corresponding to multi-stage hydrocarbon charging events. If the age zoning between the rim and core of xenotime is obvious, the concordia diagram can visually display the two-stage ages and their confidence intervals.

[0044] The method for determining the hydrocarbon accumulation stages based on in-situ U-Pb dating of xenotime provided by the embodiments of the present invention is not easily affected by external factors and can effectively guide the generation and accumulation of hydrocarbons. Xenotime in clastic sedimentary rocks has significant characteristics: (1) The authigenic xenotime in sedimentary rocks has a relatively high U content (usually greater than 1000 ppm) and a low initial Pb content after formation. Therefore, it is a superior mineral for U-Pb dating; (2) Xenotime is often rich in Th and can usually provide ages of both the U-Pb and Th-Pb systems well, avoiding the phenomenon of 206Pb excess, so that a nearly concordant U-Pb age can be obtained. At the same time, the Pb closure temperature of apatite is relatively high and Pb loss is not likely to occur. (3) The formation of xenotime requires the presence of fluids rich in rare earth and yttrium and other elements, which determines that it is an important authigenic mineral during the diagenesis of sedimentary rocks. Therefore, in-situ U-Pb dating of authigenic xenotime has great potential in determining the hydrocarbon accumulation stages. Xenotime has strong resistance to later hydrothermal alteration and burial heating (even >300 °C), and the U-Pb system has good closure, making the age data more reliable. Compared with clay minerals (such as illite) that are easily affected by alteration, the xenotime age can better represent the original hydrocarbon accumulation event.

[0045] 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 recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for determining the hydrocarbon accumulation stages based on in-situ U-Pb dating of xenotime, characterized in that, Comprising: Collecting sedimentary rock samples from an oil and gas-bearing basin, selecting xenotime particles from the sedimentary rock samples of the oil and gas-bearing basin, and performing in-situ U-Pb dating on the xenotime particles to obtain U-Pb age data of the samples; Determining the thermal evolution history of the rock since sedimentation and diagenesis according to the U-Pb age of the samples; Establishing a mapping model of the basin thermal evolution history and the oil and gas accumulation and reservoir formation stages, matching the thermal evolution history of the rock since sedimentation and diagenesis with the mapping model of the basin thermal evolution history and the oil and gas accumulation and reservoir formation stages, obtaining the period of the oil and gas accumulation event in the basin oil and gas reservoir, and determining the oil and gas reservoir formation stages of the basin according to the period of the oil and gas accumulation event in the basin oil and gas reservoir.

2. The method for determining the hydrocarbon accumulation stages based on in-situ U-Pb dating of xenotime according to claim 1, wherein The establishing of the mapping model of the basin thermal evolution history and the oil and gas accumulation and reservoir formation stages includes: Dividing the sedimentation age of the sedimentary rock according to the U-Pb age data of xenotime; Analyzing the xenotime zoning structure and identifying multiple-stage fluid flow events through the xenotime zoning structure; Associating the sedimentation age with the multiple-stage fluid flow events to establish a mapping model of the basin thermal evolution history and the oil and gas accumulation and reservoir formation stages, and the mapping model of the basin thermal evolution history and the oil and gas accumulation and reservoir formation stages includes the corresponding relationship of time, temperature and fluid activity.

3. The method for determining the hydrocarbon accumulation stages based on in-situ U-Pb dating of xenotime according to claim 2, wherein The sedimentation age of the sedimentary rock includes the diagenesis stage, the main reservoir formation stage and the adjustment stage, and the associating the sedimentation age with the multiple-stage fluid flow events includes: Associating the diagenesis stage with sedimentation and diagenesis or hydrocarbon generation of the source rock; associating the main reservoir formation stage with large-scale hydrocarbon filling; associating the adjustment stage with hydrocarbon adjustment or destruction.

4. The method for determining the hydrocarbon accumulation stages based on in-situ U-Pb dating of xenotime according to claim 2, wherein The obtaining of the period of the oil and gas accumulation event in the basin oil and gas reservoir includes: Matching the U-Pb age data of the samples with geological time segments, and determining fluid flow events according to the matching results of the geological time segments; Obtaining the period of the oil and gas accumulation event in the basin oil and gas reservoir according to the determined fluid flow events and the corresponding relationship of time, temperature and fluid activity.

5. The method for determining the hydrocarbon accumulation stages based on in-situ U-Pb dating of xenotime according to claim 1, wherein The collecting of the sedimentary rock samples from the oil and gas-bearing basin includes: The sedimentary rock samples include metamorphic argillaceous rocks and clastic sedimentary rocks, and xenotime of diagenesis mainly exists in different types of clastic sedimentary rocks from shale to conglomerate from river to ocean.

6. The method for determining the hydrocarbon accumulation stages based on in-situ U-Pb dating of xenotime according to claim 1 or 5, characterized in that The selecting of the xenotime particles from the sedimentary rock samples of the oil and gas-bearing basin includes: Making the sedimentary rock samples into probe slices; Observing the composition and microstructure of the probe slices using an optical microscope and a scanning electron microscope; Analyzing the micro-area mineral composition using backscattering and an energy spectrometer; Screening out authigenic xenotime particles with a zoning structure according to the composition and microstructure of the probe slices and the micro-area mineral composition.

7. The method for determining the hydrocarbon accumulation stages based on in-situ U-Pb dating of xenotime according to claim 1, characterized in that The performing of in-situ U-Pb dating on the xenotime particles to obtain U-Pb age data of the samples includes: Fixing the xenotime particles and a standard zircon standard on the surface of an epoxy resin disc and polishing; Performing in-situ micro-area U-Pb geochronology analysis using an ion probe with a beam spot smaller than a preset threshold; Calibrating the analysis results of the U-Pb geochronology analysis using the standard to obtain U-Pb age data of the samples; Wherein the standard is a group of xenotime standards with different ages and chemical compositions, which are separately placed in a base.

8. The method for determining the hydrocarbon accumulation stages based on in-situ U-Pb dating of xenotime according to claim 7, wherein Using a reference sample to verify the analysis results of the U-Pb geochronology analysis includes: Selecting a set of xenotime reference samples with different ages and chemical compositions to cover the possible age range and chemical composition of the samples; Performing cyclic interpolation analysis on the reference samples and zircon containing xenotime grains, so that the reference samples and zircon containing xenotime grains are alternately tested, and verifying the analysis results of the U-Pb geochronology analysis according to the test results.

9. The method for determining the hydrocarbon accumulation stages based on in-situ U-Pb dating of xenotime according to claim 7, wherein Using a reference sample to verify the analysis results of the U-Pb geochronology analysis includes: Collecting a variety of rare earth element data, which is used to calibrate the U-Pb isotope ratio, correct the matrix effect and instrument mass fractionation.

10. The method for determining the hydrocarbon accumulation stages based on in-situ U-Pb dating of xenotime as claimed in claim 9, wherein After calibrating the U / Pb and Th / Pb ratios, monitoring the matrix effect and monitoring the instrument mass fractionation effect, it further includes: Inputting the calibrated U-Pb isotope ratio and error data into the Isoplot-3 software to generate a concordia diagram to display the in-situ U / Pb dating results.

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