阅读说明：本技术 一种深层古岩溶流体的综合判识方法 (Comprehensive identification method for deep paleo-karst fluid ) 是由 刘嘉庆 李忠 杨柳 于 2020-12-14 设计创作，主要内容包括：本发明提供一种深层古岩溶流体的综合判识方法,该方法包括：样品准备,在阴极发光仪下进行矿物学成岩序列观测,基于二次离子探针(SIMS)、激光剥蚀-等离子体质谱仪(LA-ICP-MS)和电子探针三种原位微区技术的配套分析,获取每期流体的碳氧同位素、微量稀土元素和元素信息,流体包裹体获得古流体的温度和盐度值分布,锶同位素判断流体来自于陆源还是幔源,综合上述地化指标,厘定不同期次古岩溶流体性质,结合区域埋藏史曲线恢复其演化历史。本方法可以准确厘定流体性质、来源及演化过程,大大提高了对深层构造-流体-岩石作用效应的认识,对深部规模岩溶储集层的改造和保存机制的研究将成为指导深层油气勘探的重要依据,为叠合盆地深层勘探工作提供重要的理论指导。(The invention provides a comprehensive identification method of deep paleo-karst fluid, which comprises the following steps: preparing a sample, observing a mineralogy diagenetic sequence under a cathode luminoscope, acquiring carbon-oxygen isotope, trace rare earth element and element information of fluid at each stage based on the matching analysis of three in-situ micro-area technologies of a secondary ion probe (SIMS), a laser ablation-plasma mass spectrometer (LA-ICP-MS) and an electronic probe, acquiring the temperature and salinity value distribution of paleo-fluid by a fluid inclusion, judging whether the fluid is from a land source or a mantle source by a strontium isotope, integrating the geochemical indexes, determining the properties of paleo-karst fluid at different stages, and recovering the evolution history by combining a regional burial history curve. The method can accurately determine the property, source and evolution process of the fluid, greatly improves the understanding of the effect of deep structure-fluid-rock, and the research on the transformation and preservation mechanism of deep karst reservoirs becomes an important basis for guiding deep oil and gas exploration, thereby providing important theoretical guidance for the deep exploration work of the superimposed basin.)

1. A comprehensive identification method for deep paleo-karst fluid comprises the following steps:

step (1): sample preparation, the rock sample is prepared and ground into two types of slices, which are respectively: 1) a double-side polished probe sheet, 2) a double-side polished wrapper sheet or thickened sheet;

step (2): cathodoluminescence observation is carried out to establish a diagenetic sequence, and the sample prepared in the step (1) is observed through cathodoluminescence test to establish the diagenetic sequence, wherein the diagenetic sequence comprises samples of different diagenetic stages;

and (3): in-situ micro-area ion probe (SIMS) carbon-oxygen isotope analysis, drilling a diagenetic sequence on a probe sheet by using a micro-drill sampling instrument for sampling and targeting, then plating gold on the ion probe, and testing and analyzing the carbon-oxygen isotope characteristics of each stage of cementing material on a machine according to the composition (delta) of a mineral oxygen isotope¹⁸O) analysis of salinity and temperature changes, delta, of a body of water¹³C value distribution indicates carbon source, and delta is judged¹³Whether C is a local source or is affected by organic carbon;

and (4): performing electronic probe element analysis, namely plating carbon on an electronic probe, analyzing the contents of elements such as Na, Si, Mn, Ca, Mg, Sr, Fe, Ba, Al and the like of subcarbonate in different diagenesis periods, presuming the redox state of the subcarbonate according to the contents of the elements Fe and Mn, reflecting the salinity of a water body by a Na index, indicating whether the influence of terrestrial clastic is caused or not by Si, reflecting the diagenesis action degree by Sr content, and judging the closure of a diagenesis system by 1000Sr/Ca and Mn;

and (5): LA-ICP-MS trace rare earth element analysis, wherein when LA-ICP-MS analysis is performed on a carbonate rock sample, a thickening sheet is used, through LA-ICP-MS in-situ micro-area rare earth trace element analysis, whether a fluid is seawater, atmospheric water or a high-temperature hot fluid is judged according to a rare earth distribution mode, and U, Th and other content changes also have an indication effect on an oxidation-reduction state;

and (6): analyzing the temperature and salinity of the fluid inclusion, analyzing the type and characteristics of the fluid inclusion in detail under a transmission light and fluorescence microscope, acquiring the temperature and salinity information of the diagenetic fluid at each stage on a geological cold and hot platform, wherein the atmospheric water has the characteristics of low temperature and low salt, the buried brine has medium-high temperature and medium-high salinity, and the abnormal high temperature is hot fluid;

and (7): strontium isotope analysis, sampling the cementing material in the crack by a micro-drill sampling instrument, and drilling 50mg of powder according to⁸⁷Sr/⁸⁶The Sr value distribution judges whether the fluid is a shell source or a valance source;

and (8): comprehensive analysis of properties of the paleo-karst fluid can obtain the geological information of the formation of the secondary diagenetic cement in different phases on the basis of the analysis of the three matched micro-area in-situ carbon-oxygen isotopes, the primary trace elements and the rare earth trace elements in the steps (3) to (5), then combines the fluid inclusion in the step (6) and the temperature, salinity and other information of the formation of the strontium isotope of the secondary diagenetic cement in different phases in the step (7), integrates all index information, further accurately analyzes the properties of the diagenetic fluid in each phase, and determines the fluid source and the time of diagenetic transformation events by combining a regional buried history curve, thereby remolding the fluid evolution process and the influence of the fluid evolution process on the reservoir development.

2. The method of claim 1, wherein in step (1): 1) the thickness of the probe sheet is 0.03mm, and the probe sheet is used for analyzing an ion probe and an electronic probe without being covered with a glass slide; 2) and the thickness of the sheet of the inclusion sheet or the thickened sheet is more than or equal to 0.1mm, and the sheet is used for LA-ICP-MS trace rare earth element and fluid inclusion analysis without a cover glass.

3. The method as claimed in claim 1, wherein the apparatus used in the cathodoluminescence test in step (2) is RELIOTRON, model RELION III, the working voltage is between 5-8kV, the current is between 300-400 μ A, and the diagenesis sequence of carbonate rocks including cementation, erosion and the like is established by observation under thin cathode luminescence.

4. The method of claim 1, wherein the in-situ micro-area ion probe (SIMS) carbon-oxygen isotope test analysis in step (3) is performed on a Cameca IMS-1280 type dual ion source multi-receiver Secondary Ion Mass Spectrometer (SIMS) instrument using a dual ion source¹³³Cs⁺Making a primary ion beam bombardment sample, wherein the acceleration voltage is 10kV, the beam intensity is 2nA, a Gaussian illumination mode is adopted, the beam spot diameter is about 10 mu m, the analysis adopts UWC-3 calcite of a American Wisconsin university standard sample as an internal standard and Oka calcite of a national first-class standard sample (GBW04481) as an external standard, the carbon isotope precision is 0.6 per mill, and the oxygen isotope precision is 0.6 per millThe element precision is 0.4 per mill.

5. The method according to claim 1, wherein the electron probe elemental analysis in step (4) is performed on a CAMECA SXFiveFE high resolution field emission electron probe, France, with an instrument acceleration voltage range of 5-30 kV and a spatial resolution of 6 nm.

6. The method of claim 1, wherein the LA-ICP-MS analyzer in step (5) is a HR-ICP-MS high resolution magnetic mass spectrometer model Element XR, manufactured by Thermo Fisher, USA, the laser spot size is 35 μm, the ablation frequency is 8Hz, and the laser flow rate is 4.0J/cm 2. the test is that the sample is placed in an ablation system, the laser is emitted to ablate the sample at the corresponding position, the laser forms an aerosol after the sample is broken, the aerosol is transported to a mass spectrometer system through a carrier gas, the aerosol is plasmatized in the mass spectrometer system to analyze the component of the Element, NIST SRM 610 is an external standard, and ARM-1, BIR and BCR standards control quality monitoring.

7. The method of claim 6, wherein the sample normalization in step (5) is performed using the late ancient Australian shale (PAAS) and the outlier calculation is formulated as: Ce/Ce^*＝2Ce_n/(La_n+Pr_n)；Pr/Pr^*＝2Pr_n/(Ce_n+Nd_n)；Eu/Eu^*＝Eu_n/((Sm_n ²*Tb_n)^1/3) The subscript n refers to the value of the average shale in australia, ancient later; the Th/U ratio can not only represent whether the forming environment is oxidation or reduction, but also can judge the fluid source, and the lower the Th/U ratio is, the closer the fluid source is to the mantle.

8. The method according to claim 1, wherein the homogeneous temperature (Th) and salinity test analysis of the fluid inclusions in step (6) is performed using Linkam Coo1ing Systems hot and cold stage model THMS600, the calibration standards are pure water and CO2 inclusions, the temperature rise rate is 2 ℃/min, the accuracy is + -0.1 ℃, and the salinity is determined by the formula: salinity of 0.00+1.78T_m-0.0442T_m ²+0.000557T_m ³Calculating and obtaining; identifying primary, secondary and pseudo secondary inclusion on the basis of lithofacies observation of the fluid inclusion, and distinguishing a saline inclusion from a hydrocarbon inclusion by using a fluorescence phenomenon observed under a fluorescence microscope; wherein, T_mIs the freezing temperature.

9. The method of claim 1, wherein the strontium isotope test of step (7) is performed on a VG354 solid isotope mass spectrometer, pre-treated with ultra-pure acetic acid, measured⁸⁷Sr/⁸⁶Sr value according to⁸⁷Sr/⁸⁶The strontium isotope of the NBS987 standard sample is measured as the average (0.710272 + -0.000012) by correcting for the mass fraction standard of Sr 0.1194.

10. The method according to any of claims 1-9, wherein in step (6) representative fluid inclusions are selected, the rationality of thermometry is verified by the FIA (fluid classification assemblies) method, i.e. uniform temperatures of inclusions of different size and shape within one FIA (difference < 15%) indicate no secondary neckline or non-uniform trapping; large and elongated fluid inclusions may have developed deformation leaks and the measured temperature does not represent the lowest temperature at formation and is therefore rejected at the time of analysis.

Technical Field

The invention relates to the technical field of petroleum geological exploration and development, in particular to a method for comprehensively identifying an ancient karst fluid by utilizing petrology and geochemistry.

Background art:

in marine carbonate oil and gas reservoirs in ancient China, reservoir types mainly comprise reef reservoirs, karst reservoirs, dolomite reservoirs and the like. The karst reservoir is one of the important reservoir types at present, and the reservoir space is characterized by solution pores, solution caves and solution seams. The narrow definition of "karst" is "karst", which is a general term for the comprehensive geological actions of chemical erosion, mechanical erosion, material migration and re-deposition of water on soluble rocks such as carbonate and sulfate rocks, and the phenomena caused thereby. The non-structural selection holes and caves formed in the surface karst action process form the most main reservoir space of a karst reservoir, and in the deep burying process, the deep burying, stacking and reforming enable the reservoir to be complex in development and extremely strong in heterogeneity.

In recent years, a plurality of sets of effective reservoirs are found in the arctic region of the Tarim basin in the western China and the Hanwu-Ordovician strata in the Tower, and the stratum burial depth of the reservoirs exceeds a deep layer (the burial depth is more than 4500m), and a plurality of reservoirs even is an ultra-deep layer (the burial depth is more than 6000 m). The formation and development of the marine carbonate reservoir are mainly controlled by the original deposition environment and the later diagenetic fluid modification factors. The later stage fluid corrosion modification effect mainly comprises the influence of surface atmospheric precipitation and organic acid and CO generated by the mature hydrocarbon generation of organic matters in the burying stage₂、H₂S and other acidic fluids, deep hydrothermal solution corrosion modification and the like. For a typical complex superposed basin of a Tarim basin in the west of China, the complicated superposed basin is influenced by the superposition of multi-phase structure movement, the change of multi-phase structure-fluid activity is experienced, the reservoir is further reformed by the interaction of fluid and rocks after the hydrocarbon is filled, and a multi-phase complex fluid field with different diagenesis environments and properties is formed. For a deep oil and gas reservoir, due to the fact that the fluid activities of the deep oil and gas reservoir are complicated and changeable after the deep oil and gas reservoir undergoes multiple stages of superposition transformation of burial-tectonic effects, the remodeling and prediction of basin fluid activities have great challenges, and a comprehensive judgment method for deep ancient karst fluids of a system is not established.

With the cross fusion of new technology application and disciplines, the development of micro-area in-situ observation technologies such as secondary ion probes (SIMS) and laser ablation-plasma mass spectrometers (LA-ICP-MS) provides powerful technical support for the study of basin fluid activities.

The traditional technical method for acquiring the paleo-karst fluid information is based on the whole-rock analysis on the basis of inaccurate structural type division of rock causes, and the obtained result is often the result of average multi-stage fluid mixing, so that the fine lithogenesis and basin fluid property stage and evolution thereof cannot be revealed. And the conventional single technical means has multiple solutions and uncertainties in identifying the fluid type, so that the interpretation reliability of the fluid property is low.

The invention content is as follows:

the invention aims to provide a method for obtaining deep paleo-karst fluid comprehensive judgment based on an in-situ micro-area matching test technology, which improves the effectiveness of the diagenesis mechanism of a karst reservoir and the prediction of reservoir distribution rule, and simultaneously solves the problems that in the traditional test in the past, the test analysis cannot be performed due to small sample amount, or the analyzed result is often an average multi-stage fluid mixing result.

The technical scheme adopted by the invention is that on the basis of detailed rock and mineral analysis, the properties of the diagenetic fluid at each stage and the modification of the diagenetic fluid to a reservoir are revealed based on the matching analysis of three micro-area methods of an in-situ micro-area ion probe (SIMS), a laser ablation-plasma mass spectrometer (LA-ICP-MS) and an electronic probe and the comprehensive analysis of a fluid inclusion and a strontium isotope.

In order to achieve the above object, the present invention provides a method for comprehensively identifying deep paleo-karst fluid, the method comprising:

step (1): sample preparation, the rock sample is prepared and ground into two types of slices, which are respectively: 1) a double-side polished probe sheet, 2) a double-side polished wrapper sheet or thickened sheet;

step (2): cathodoluminescence observation is carried out to establish a diagenetic sequence, and the sample prepared in the step (1) is observed through cathodoluminescence test to establish the diagenetic sequence, wherein the diagenetic sequence comprises samples of different diagenetic stages;

and (3): in-situ micro-area ion probe (SIMS) carbon-oxygen isotope analysis, drilling a diagenetic sequence on a probe sheet by using a micro-drill sampling instrument to carry out sampling and target making, then plating gold on the ion probe, carrying out on-machine test and analysis on the carbon-oxygen isotope characteristics of the cemented object at each stage, analyzing the salinity and temperature change of a water body according to the mineral oxygen isotope composition (delta 18O), indicating a carbon source by delta 13C value distribution, and judging whether delta 13C is a local source or is influenced by organic carbon;

and (4): performing electronic probe element analysis, namely plating carbon on an electronic probe, analyzing the contents of elements such as Na, Si, Mn, Ca, Mg, Sr, Fe, Ba, Al and the like of subcarbonate in different diagenesis periods, presuming the redox state of the subcarbonate according to the contents of the elements Fe and Mn, reflecting the salinity of a water body by a Na index, indicating whether the influence of terrestrial clastic is caused or not by Si, reflecting the diagenesis action degree by Sr content, and judging the closure of a diagenesis system by 1000Sr/Ca and Mn;

and (5): LA-ICP-MS trace rare earth element analysis, wherein when LA-ICP-MS analysis is performed on a carbonate rock sample, a thickening sheet is used, through LA-ICP-MS in-situ micro-area rare earth trace element analysis, whether a fluid is seawater, atmospheric water or a high-temperature hot fluid is judged according to a rare earth distribution mode, and U, Th and other content changes also have an indication effect on an oxidation-reduction state;

and (6): analyzing the temperature and salinity of the fluid inclusion, analyzing the type and characteristics of the fluid inclusion in detail under a transmission light and fluorescence microscope, acquiring the temperature and salinity information of the diagenetic fluid at each stage on a geological cold and hot platform, wherein the atmospheric water has the characteristics of low temperature and low salt, the buried brine has medium-high temperature and medium-high salinity, and the abnormal high temperature is hot fluid;

and (7): strontium isotope analysis, sampling the cementing material in the crack by a micro-drill sampling instrument, and drilling 50mg of powder according to⁸⁷Sr/⁸⁶The Sr value distribution judges whether the fluid is a shell source or a valance source;

and (8): comprehensive analysis of properties of the paleo-karst fluid can obtain the geological information of the formation of the secondary diagenetic cement in different phases on the basis of the analysis of the three matched micro-area in-situ carbon-oxygen isotopes, the primary trace elements and the rare earth trace elements in the steps (3) to (5), then combines the fluid inclusion in the step (6) and the temperature, salinity and other information of the formation of the strontium isotope of the secondary diagenetic cement in different phases in the step (7), integrates all index information, further accurately analyzes the properties of the diagenetic fluid in each phase, and determines the fluid source and the time of diagenetic transformation events by combining a regional buried history curve, thereby remolding the fluid evolution process and the influence of the fluid evolution process on the reservoir development.

Wherein, in the step (1): 1) the thickness of the probe sheet is 0.03mm, and the probe sheet is used for analyzing an ion probe and an electronic probe without being covered with a glass slide; 2) and the thickness of the sheet of the inclusion sheet or the thickened sheet is more than or equal to 0.1mm, and the sheet is used for LA-ICP-MS trace rare earth element and fluid inclusion analysis without a cover glass.

Wherein, the instrument used in the cathodoluminescence test in the step (2) is RELIOTRON with the model of RELION III, the working voltage is between 5 and 8kV, the current is between 300 and 400 mu A, and the diagenesis sequence of the carbonate rock including cementation, corrosion and other effects is established through observation under the sheet cathodoluminescence.

Wherein, the carbon-oxygen isotope test analysis of the in-situ micro-area ion probe (SIMS) in the step (3) is carried out on a Cameca IMS-1280 type double ion source multi-receiver Secondary Ion Mass Spectrometer (SIMS) instrument by using¹³³Cs⁺The sample is bombarded by primary ion beams, the accelerating voltage is 10kV, the beam intensity is 2nA, a Gaussian illumination mode is adopted, the beam spot diameter is about 10 mu m, the American Wisconsin university standard sample UWC-3 calcite is used as an internal standard and the national first-class standard sample (GBW04481) Oka calcite is used as an external standard in analysis, the carbon isotope precision is 0.6 per mill, and the oxygen isotope precision is 0.4 per mill.

And (3) performing element analysis on the electron probe in the step (4) on a French CAMECA SXFiveFE high-resolution field emission electron probe, wherein the acceleration voltage range of the instrument is 5-30 kV, and the spatial resolution is 6 nm.

Wherein the LA-ICP-MS analyzer in the step (5) is an HR-ICP-MS high-resolution magnetic mass spectrometer with the model of Element XR, the company of Thermo Fisher, USA, the laser spot size is 35 mu m, the ablation frequency is 8Hz, and the laser flow is 4.0J/cm²The test is that a sample is placed in an ablation system, laser is emitted to remove the sample at a corresponding position for ablation, the laser forms aerosol after the sample is broken, the aerosol is conveyed to a mass spectrometer system through carrier gas, plasmatization is carried out in the mass spectrometer system, the components of elements are analyzed, NIST SRM 610 is an external standard, and ARM-1, BIR and BCR standard samples control quality monitoring.

Wherein, the sample standardization in the step (5) adopts the ancient Australian shale (PAAS), and the abnormal value calculation formula is as follows: Ce/Ce^*＝2Ce_n/(La_n+Pr_n)；Pr/Pr^*＝2Pr_n/(Ce_n+Nd_n)；Eu/Eu^*＝Eu_n/((Sm_n ²*Tb_n)^1/3) The subscript n refers to the value of the average shale in australia, ancient later; the Th/U ratio can not only represent whether the forming environment is oxidation or reduction, but also can judge the fluid source, and the lower the Th/U ratio is, the closer the fluid source is to the mantle.

Wherein, the apparatus adopted for testing and analyzing the uniform temperature (Th) and salinity of the fluid inclusion in the step (6) is Linkam Coo1ing Systems cold and hot table, the model is THMS600, and the calibration standard sample of the apparatus is pure water and CO₂The temperature rise rate of the inclusion is 2 ℃/min, the precision is +/-0.1 ℃, and the salinity is represented by the formula: salinity of 0.00+1.78T_m-0.0442T_m ²+0.000557T_m ³Calculating and obtaining, wherein Tm is the freezing point temperature; primary, secondary and pseudo-secondary inclusion are identified on the basis of lithofacies observation of the fluid inclusion, and the saline inclusion or the hydrocarbon inclusion is distinguished by the fluorescence phenomenon observed under a fluorescence microscope. When selecting representative fluid inclusions, an FIA (fluid inclusion assemblies) method is adopted to verify the rationality of temperature measurement, namely if the uniform temperatures of inclusions with different sizes and shapes in one FIA are consistent (the difference is less than 15%), the secondary neckerchief or non-uniform capture does not occur; large and elongated fluid inclusions may have developed deformation leaks and the measured temperature does not represent the lowest temperature at formation and is therefore rejected at the time of analysis.

Wherein the strontium isotope test in the step (7) is carried out on a VG354 solid isotope mass spectrometer, ultrapure acetic acid is used for pretreatment, and the measured result is⁸⁷Sr/⁸⁶Sr value according to⁸⁷Sr/⁸⁶The strontium isotope of the NBS987 standard sample is measured as the average (0.710272 + -0.000012) by correcting for the mass fraction standard of Sr 0.1194.

Because the superposed hydrocarbon-containing basin which develops in multiple stages in China is greatly different from a single-cycle one-stage basin or a multi-cycle continuous inheritance basin in China, the superposed hydrocarbon-containing basin mainly shows that the superposed hydrocarbon-containing basin undergoes multi-stage structural evolution, the types of reservoirs are various and diagenetic fluid is complex, and particularly deep-layer and ultra-deep-layer reservoirs are obtained. The method provided by the invention can accurately determine the property, source and evolution process of the fluid, and greatly improves the understanding of the effect of the deep structure-fluid-rock. The research on the transformation and preservation mechanism of the deep karst reservoir layer becomes an important basis for guiding deep oil and gas exploration, and provides important theoretical guidance for the deep exploration work of the superimposed basin.

Compared with the traditional method for judging the properties of the fluid, the method has two remarkable characteristics: 1) the high-precision in-situ micro-area analysis can reach the micron level, and can finely analyze the fluid activity in each period; 2) and multiple localization means are matched and combined for analysis, so that the accuracy of analyzing the fluid property is greatly improved. The comprehensive identification method provides reliable technical support for research on the cause mechanism of the deep paleo-karst reservoir stratum, and can be widely popularized and applied to exploration and research of other types of carbonate reservoir stratum.

Drawings

FIG. 1 is an analysis flow chart of deep paleo-karst fluid identification performed in the present invention.

FIG. 2 is a graph of the oxidation-reduction state change and diagenesis stage division of cathodoluminescence based on the change of Fe and Mn content.

Fig. 3 shows the source of the carbon-oxygen isotope fluid for secondary ion probe (SIMS) detection.

FIG. 4 shows the Mn and 1000Sr/Ca obtained by implementing the electron probe to analyze the sealing property of the diagenetic system.

Fig. 5 is a trace rare earth element partitioning pattern for different fluid properties based on laser ablation-plasma mass spectrometer (LA-ICP-MS) analysis.

Detailed Description

The concrete implementation method of the present invention will be further described in detail below with reference to the drawings, taking the ancient karst reservoir of late aotao mazengshan group in oil field in a Tarim basin tower as an example.

Referring to fig. 1, fig. 1 is a flowchart of a comprehensive identification method for deep paleo-karst fluid according to the present invention, as shown in fig. 1, the method includes:

the first step is as follows: sample preparation

Rock samples were prepared by flaking, milling two types of flakes: 1) the probe sheet with two polished surfaces is 0.03mm thick, is not covered with a glass slide and is used for the analysis of an ion probe and an electronic probe; 2) the two-side polished inclusion sheet or thickened sheet has the thickness of more than or equal to 0.1mm, is not added with a cover glass, and is used for LA-ICP-MS trace rare earth element and fluid inclusion analysis. Wherein the rock sample is a fracture carbonate cement.

The second step is that: cathodoluminescence observation to establish diagenesis sequence

The cathodoluminescence test instrument is RELIOTRON, model number is RELION III, working voltage is between 5-8kV, and current is between 300-400 muA. The diagenetic sequence of carbonate rocks including cementation, erosion and the like is established through observation under the cathode luminescence of the thin sheet.

Cathodoluminescence enables a more rapid and successful identification of sequences of diagenetic mineralisation events than other techniques, and calcite/dolomite cements with different cathodoluminescence colour zones can be used to indicate changes in the physicochemical conditions of diagenetic pore water over time, enabling us to infer mineral substitution during diagenesis. Furthermore, cathodoluminescence enables "see through" the structure of the original rock prior to recrystallization, which is the only feasible way to determine the alteration history and mineralisation sequence of carbonates. The cathodoluminescence of carbonate rock is caused by the presence of trace elements and is generally expressed in yellow, orange, red. Fe is a luminescent agent and Mn is a quencher. Typically, cements formed during the seawater phase do not glow, while cements undergoing diagenetic transformation exhibit different non-optical characteristics.

Cathodoluminescence is based on the oxidation-reduction state change reflected by the content change of Fe and Mn and diagenesis stage division (see figure 2), early diagenesis is an oxidation condition, and cathodoluminescence does not emit light; along with the buried depth of the stratum into the buried diagenesis, the early oxidation condition is changed into the reduction condition, and the cathodoluminescence is in a ring-shaped luminescence to be in multiple luminescence characteristics of yellow, orange, red and the like; and lifting the later structure to enable the stratum to enter a surface formation rock environment, wherein cathode luminescence can be from annular band luminescence to non-luminescence, and the fluid environment is indicated to be converted from a reduction condition to an oxidation environment. The fine diagenetic sequences were identified by the different luminescence characteristics of the cathodoluminescence, and the following geological fluid analysis work was performed on different stages of the cement identified at this step.

The third step: in situ micro-zone ion probe (SIMS) carbon-oxygen isotope analysis

Drilling a typical area with relatively complete diagenetic sequence on a probe sheet by using a micro-drill sampling instrument to perform sampling and target making, then plating gold on an ion probe, and performing on-machine test and analysis on the carbon-oxygen isotope characteristics of the cement at each stage according to the mineral oxygen isotope composition (delta)¹⁸O) analysis of salinity and temperature changes, delta, of a body of water¹³C value distribution indicates carbon source, and delta is judged¹³Whether C is a local source or is affected by organic carbon. The test analysis is carried out on a Cameca IMS-1280 type double ion source multi-receiver Secondary Ion Mass Spectrometer (SIMS). Use of¹³³Cs⁺And (3) bombarding the sample by a primary ion beam, wherein the accelerating voltage is 10kV, the beam intensity is 2nA, and a Gaussian illumination mode is adopted, and the beam spot diameter is about 10 mu m. The analysis uses UWC-3 calcite, a standard sample of the university of Wisconsin USA, as an internal standard and Oka calcite, a national first-class standard (GBW04481) as an external standard. The carbon isotope precision is 0.6 per mill, and the oxygen isotope precision is 0.4 per mill.

Mineral oxygen isotope composition (delta)¹⁸O) is controlled primarily by the salinity and temperature of its body of water (see fig. 3): generally, carbonate minerals are low delta¹⁸The O value may be derived from atmospheric precipitation or as a result of mineral precipitation at relatively high temperatures, the temperature increase being such that delta is¹⁸O is biased negative. And delta¹⁸The O value appears to be positively biased, possibly due to the influence of evaporation. Different from delta¹⁸O，δ¹³C is mainly controlled by the carbon source. Delta of cement¹³The C value distribution range is more concentrated, and is close to the current sea water range, which shows delta¹³C is mainly a local source. Delta¹³The high value of C may be influenced by the biological fermentation, and the cement related to the biological fermentation may have a high delta¹³And C value. Delta¹³C is low reflecting the presence of sources of organic oxidation¹³The influence of C. From the fine analysis of the carbon-oxygen isotope change characteristics, if the atmospheric water shows the change trend of a J line (figure 3), the method provides identification for deep ancient karst atmospheric fresh waterAnd new evidence support is provided, so that clues are provided for further deep research.

The fourth step: electron probe elemental analysis

Firstly, plating carbon on an electronic probe, completing analysis of the electronic probe on a French CAMECA SXFiveFE high-resolution field emission electronic probe, wherein the acceleration voltage range of an instrument is 5-30 kV, the spatial resolution can reach 6nm, then analyzing the contents of elements such as Na, Si, Mn, Ca, Mg, Sr, Fe, Ba, Al and the like of the subcarbonates in different diagenesis periods, presuming the redox states of the subcarbonates according to the contents of the elements such as Fe and Mn, wherein the Na index reflects the salinity of a water body, Si indicates whether the subcarbonates are influenced by land-source debris or not, the Sr content reflects the diagenesis degree, and 1000Sr/Ca and Mn determine the closure of the diagenesis system.

Fe. Mn reflects continental source material input, and good Fe/Al correlation indicates high Fe continental source debris effect. The Sr/Ba ratio can reflect the salinity of the diagenetic fluid, Ba is easy to form barite to precipitate when seawater is evaporated, and the larger the Sr/Ba ratio is, the higher the salinity of the seawater is. The sealing property of the diagenetic system can be judged by 1000Sr/Ca and Mn (see figure 4), wherein the Sr/Ca value of the closed diagenetic system is high, and the Mn value is low ((C))<200ppm) and open systems with high Mn and low Sr/Ca, the seal of diagenetic systems has a significant impact on reservoir erosion/precipitation and preservation. Generally, atmospheric water is a relatively open diagenetic system, while a buried is a closed system. Na influences salinity, water depth, biological fractionation, hydrodynamic forces and minerals, and Na is lost due to recrystallization in the buried marine environment. In addition, diagenetic transformation leads Sr and delta in the step (3)¹⁸Because of the loss of O and the increase of Mn, Mn/Sr can be used as a criterion for judging whether the diagenetic transformation is carried out.

For an ancient karst reservoir, a specific karst structure is presented on a vertical phase and can be divided into a surface karst zone, a vertical seepage zone and a horizontal subsurface flow zone. Cavities near the horizontal subsurface flow zone develop in large quantities to form the main storage space of the karst reservoir. Fe obtained by the electronic probe can be used for dividing a karst zone, a fresh water seepage zone belongs to an oxidation environment, and ferric iron cannot enter carbonate mineral lattices, so that granular brilliant crystal calcite cement formed by the fresh water seepage zone is called iron-free calcite; the fresh water undercurrent zone is often a reducing environment and contains iron granular brilliant calcite.

The fifth step: analysis of trace rare earth elements by LA-ICP-MS

When the LA-ICP-MS analysis of the carbonate rock sample is carried out, a thickening sheet is needed to be used for preventing signals from penetrating the sample to obtain unreal data, through LA-ICP-MS in-situ micro-area rare earth trace element analysis, whether the fluid is seawater, atmospheric water or high-temperature hot fluid is judged according to a rare earth distribution mode, and U, Th and other content changes also have an indication effect on the redox state. The analytical instrument was a HR-ICP-MS high resolution magnetic mass spectrometer model Element XR, produced by Thermo Fisher, USA. The laser spot size is 35 μm, the ablation frequency is 8Hz, and the laser flow is 4.0J/cm². The test is that the sample is put in an ablation system, and laser is emitted to ablate the sample at the corresponding position. The laser forms an aerosol after the sample is broken up, and the aerosol is transported to a mass spectrometer system through a carrier gas. Plasmatizing in a mass spectrometer system, and analyzing the components of the elements. NIST SRM 610 is an external standard, and ARM-1, BIR and BCR standard samples control quality monitoring.

Sample standardization was followed with the ancient Australian shale (PAAS). The outlier calculation is: Ce/Ce^*＝2Ce_n/(La_n+Pr_n)；Pr/Pr^*＝2Pr_n/(Ce_n+Nd_n)；Eu/Eu^*＝Eu_n/((Sm_n ²*Tb_n)^1/3). The subscript n refers to the value after the calibration of the average Australian shale from the late ancient time.

The samples to be analyzed are interpreted as contaminants. Common contaminants include: 1) contamination with debris; 2) phosphate contamination; 3) iron, manganese oxide contamination, and the like. Al <900ppm and Th <0.3ppm should be selected, above these values to reject. The lack of correlation between Al and the total amount of rare earth elements may preclude the effects of land-based detritus.

Different fluids have different rare earth partitioning patterns (see fig. 5): 1) the seawater rare earth element is characterized by loss of light rare earth (LREE) and a distribution mode of enrichment of heavy rare earth (HREE), wherein Ce is negative abnormity, La is positive abnormity, Gd is positive abnormity, Y is positive abnormity, and Y/Ho is more than 35-40; 2) the rare earth element of the hot fluid is characterized by being enriched in light rare earth, and the Eu is positive abnormal in a distribution mode of heavy rare earth loss; 3) the rare earth element of the atmospheric water is characterized by light rare earth enrichment, and Y/Ho is less than 35-40; 4) the recipe of the buried fluid REY is characterized in that medium rare earth (MREE) is enriched, and Ce negative anomaly is not obvious.

The delta Eu values for the source of the lower crust or mantle are generally greater than 1, and the appearance of a positive Eu anomaly represents hydrothermal heterocrystallization of the magma. Ce is commonly used to indicate the oxidizing environment of seawater. Ce has Ce³⁺And Ce⁴⁺Two valence states, oxidized to Ce in an oxidizing environment⁴⁺Therefore, the marine carbonate rock has the characteristic of negative Ce anomaly, but has no negative Ce anomaly under the reducing condition.

V, U, Co, Ni, Zn, Cd, V, Cr and the like are redox sensitive elements, and the content of the elements can obviously change along the sequence of layers. For example, the average contents of Mo, Ni and V under the oxidation condition are 2, 10 and 28ppm, while the average contents of Mo, Ni and V under the reduction condition are increased to 139, 107 and 253 ppm. U is usually more abundant in the mantle, and the Th/U ratio can not only represent whether the formation environment is oxidation or reduction, but also can judge the fluid source. The lower the Th/U ratio, the closer the fluid source is to the mantle.

And a sixth step: fluid inclusion temperature and salinity analysis

The method comprises the steps of firstly analyzing the type and the characteristics of a fluid inclusion in detail under a transmission light and fluorescence microscope, obtaining the temperature and salinity information of diagenetic fluid at each stage on a geological cold and hot platform, wherein atmospheric water has the characteristics of low temperature and low salt, the buried brine has medium-high temperature and medium-high salinity, and the abnormal high temperature is hot fluid.

Fluid enclosure uniform temperature (T)_h) And the salinity test and analysis adopts an instrument of Linkam Coo1ing Systems cold and hot tables, and the model is THMS 600. The instrument calibration standard sample is pure water and CO₂The temperature rise rate of the inclusion is 2 ℃/min, and the precision is +/-0.1 ℃. The salinity is calculated and obtained by a formula, and is 0.00+1.78T_m-0.0442T_m ²+0.000557T_m ³(ii) a Wherein Tm is the freezing temperature.

The selection of fluid inclusions should be closely focused on 3 preconditions for inclusion: homogeneous systems, closed systems and isochoric systems. Non-uniform trapping, the phenomenon of a neck, and thermal equilibrium can all cause uniform temperatures to deviate from the actual trapping temperature. Therefore, in selecting representative fluid inclusions, the FIA (fluid inclusion assemblies) method should be used to verify the rationality of thermometry, i.e., if the uniform temperatures of inclusions of different sizes and shapes are consistent within a FIA (difference < 15%), then no secondary entrapment or non-uniform trapping occurs. Large and elongated fluid inclusions may have developed deformation leaks and the measured temperature does not represent the lowest temperature at formation and is therefore rejected at the time of analysis.

Since the fluid inclusion nucleation temperature limit is typically between 40-60 ℃, the presence of a pure liquid phase brine enclosure indicates that the capture temperature does not exceed 50 ℃, typically the atmospheric water formation cause on exposure. The temperature of the inclusion formed in the embedding stage is generally higher, and the temperature range of the fluid inclusion from shallow embedding to medium-deep embedding is 60-160 ℃ taking a Tarim basin Ordovician carbonate rock sea phase reservoir in the western China as an example. When the uniform temperature of the bag body is abnormally higher than the formation temperature by 5 ℃, indicating the activity of the hot fluid from the outside. Salinity indicators can also be effective in revealing fluid information, such as seawater salinity of 3.5 wt% NaCl; the salinity of the atmospheric fresh water is very low and is 0 wt% of NaCl; the salinity of the buried brine is higher and is more than 3.5 wt% of NaCl. Some fluid inclusions present high temperature and low salinity, the cause of which may be that surface atmospheric fresh water seeps down into the carbonate rock and mixes with the high temperature fluid from the deep part in a high proportion, thus inheriting the low salinity of the fresh water, but still keeping the higher temperature; it is also possible that atmospheric fresh water seeps down the fractures into the deep formations and then migrates up the dredging layer to become a low salinity high temperature fluid.

The seventh step: isotope analysis of strontium

Sampling the cement in the crack by using a micro-drill sampling instrument, and drilling 50mg of powder according to the method⁸⁷Sr/⁸⁶The Sr value distribution judges whether the fluid is a shell source or a valance source. Strontium isotope samples were completed in Rb-Sr isotope ultra-clean laboratory of institute of geology and geophysical of Chinese academy of sciences, and the tests were performed on VG354 solid isotope mass spectrometer, with ultra-pure acetic acid instead of hydrochloric acid being used for pretreatment. Measured⁸⁷Sr/⁸⁶Sr value according to⁸⁷Sr/⁸⁶Sr is 0.1194 mass fractionThe distillation standard was corrected, and the average value of the strontium isotope of NBS987 standard sample was determined to be (0.710272. + -. 0.000012).

The strontium isotope composition of the seawater is mainly controlled by strontium from a shell source and a mantle source, and the shell source and the mantle source can be well indicated. Generally, shell source materials provide high⁸⁷Sr/⁸⁶Sr ratio (0.7119), while volcanic hot liquid can provide low heat⁸⁷Sr/⁸⁶Sr (0.7040). Of carbonates⁸⁷Sr/⁸⁶The Sr ratio is close to that of the seawater at that time, which shows that the influence of the properties of the seawater source fluid is mainly. For the diagenetic process of the eagle mountain carbonate in the tower, the cementite in the crack is obviously higher than that of the seawater in the same period⁸⁷Sr/⁸⁶The Sr ratio, which reflects its influence by shell source debris.

Eighth step: comprehensive analysis of properties of paleo-karst fluids

On the basis of determining a diagenesis sequence by cathodoluminescence analysis, geological information of carbon-oxygen isotopes, major trace elements and rare earth trace elements during formation of different-phase secondary diagenesis cement can be obtained on the basis of three matched micro-area in-situ technologies of an ion probe (SIMS), an electronic probe and a laser ablation-plasma mass spectrometer (LA-ICP-MS), then information such as temperature, salinity and the like during formation of different-phase secondary diagenesis cement is obtained by combining a fluid inclusion test and a strontium isotope test, all indexes are integrated, the properties of diagenesis fluid in each phase are accurately analyzed, the fluid source and the time of diagenesis modification events are determined by combining a regional buried history curve, the evolution process of the fluid and the influence of the fluid evolution process on reservoir development are further remolded, and a diagenesis-reservoir evolution mode is established.

Taking the deep carbonate rock reservoir of the eagle mountain group of the Ordovician in the oil field in the Tarim basin tower as an example, the cathode luminescence reveals the existence of six-stage cementation (C1-C6) of matrix pores, and the comprehensive judgment method reveals that the six-stage diagenetic fluids are respectively early seawater C1, early atmospheric water/mixed water C2, shallow-medium buried C3, medium-deep buried C4, late atmospheric water C5 and hot fluid C6. Of these, the last two phases C5 and C6 develop mainly along fractures, the second phase C2 being the fluid activity that plays the most important constructive role for the reservoir. Diagenetic evolution can be divided into several successive stages of intergrowth, epigenesis, early shallow burial, shallow-medium burial, tectonic thermal fluids and medium-deep burial. The comparative research of oil and gas wells and non-oil and gas wells shows that the difference between the two wells is mainly that the lithofacies basis is different, the karst is more developed in the intrabay beach/algae limestone, and the reservoir in the low-energy intrabay is not developed. The lithofacies in the early stage has an important control function on the development of karst, and thermal fluid activities occur in oil and gas wells and non-oil and gas wells, so that the lithofacies and the unconformity are determined to be main control factors of reservoir development, and an important guiding function is provided for the next deep oil and gas exploration. The method provides useful insight for the activity evolution of diagenetic fluid of a deep-buried carbonate reservoir, and effectively guides the next oil and gas exploration and distribution prediction.

Through the comprehensive implementation of the analysis method, the invention can accurately obtain the properties and the sources of fluids in different phases under the background of complex multi-phase structures, can be widely applied to the research of fluid-rock interaction, reservoir mechanism, reservoir cause models and the like, and has important application prospect. The invention provides an effective technical means for the identification of deep ancient karst fluid, in particular to the matching and combination analysis of three micro-area in-situ technologies, realizes the high-precision extraction of diagenetic fluid information from rock and ore records, can recover the fine evolution process of deep fluid, and establishes a diagenetic-diagenetic geological model of a deep carbonate rock reservoir.

The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.