CN111521692A - Method for judging type of dolomite petrochemical fluid - Google Patents
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- 229910000514 dolomite Inorganic materials 0.000 title claims abstract description 106
- 239000012530 fluid Substances 0.000 title claims abstract description 94
- 238000000034 method Methods 0.000 title claims abstract description 42
- 239000011777 magnesium Substances 0.000 claims abstract description 154
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 claims abstract description 110
- 229910052749 magnesium Inorganic materials 0.000 claims abstract description 110
- 239000011435 rock Substances 0.000 claims description 29
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 21
- 239000013535 sea water Substances 0.000 claims description 18
- 239000007787 solid Substances 0.000 claims description 15
- 230000015572 biosynthetic process Effects 0.000 claims description 12
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- HPALAKNZSZLMCH-UHFFFAOYSA-M sodium;chloride;hydrate Chemical compound O.[Na+].[Cl-] HPALAKNZSZLMCH-UHFFFAOYSA-M 0.000 claims description 10
- 239000007790 solid phase Substances 0.000 claims description 10
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- 239000011148 porous material Substances 0.000 claims description 9
- 238000010813 internal standard method Methods 0.000 claims description 8
- JLVVSXFLKOJNIY-UHFFFAOYSA-N Magnesium ion Chemical compound [Mg+2] JLVVSXFLKOJNIY-UHFFFAOYSA-N 0.000 claims description 7
- 229910001425 magnesium ion Inorganic materials 0.000 claims description 7
- 235000019738 Limestone Nutrition 0.000 claims description 5
- 239000006028 limestone Substances 0.000 claims description 5
- 239000003673 groundwater Substances 0.000 claims description 4
- 238000005341 cation exchange Methods 0.000 claims description 2
- 150000001768 cations Chemical class 0.000 claims description 2
- 150000002500 ions Chemical class 0.000 claims description 2
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- 239000000126 substance Substances 0.000 description 5
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- 239000007789 gas Substances 0.000 description 4
- 229910052761 rare earth metal Inorganic materials 0.000 description 4
- VTYYLEPIZMXCLO-UHFFFAOYSA-L Calcium carbonate Chemical compound [Ca+2].[O-]C([O-])=O VTYYLEPIZMXCLO-UHFFFAOYSA-L 0.000 description 3
- 238000004458 analytical method Methods 0.000 description 3
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 2
- 241000195493 Cryptophyta Species 0.000 description 2
- 229910052782 aluminium Inorganic materials 0.000 description 2
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 2
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- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 229910052612 amphibole Inorganic materials 0.000 description 1
- QZPSXPBJTPJTSZ-UHFFFAOYSA-N aqua regia Chemical compound Cl.O[N+]([O-])=O QZPSXPBJTPJTSZ-UHFFFAOYSA-N 0.000 description 1
- 229910000019 calcium carbonate Inorganic materials 0.000 description 1
- 239000002734 clay mineral Substances 0.000 description 1
- 238000009833 condensation Methods 0.000 description 1
- 230000005494 condensation Effects 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
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- 230000002906 microbiologic effect Effects 0.000 description 1
- 244000005700 microbiome Species 0.000 description 1
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- 238000013508 migration Methods 0.000 description 1
- 230000002285 radioactive effect Effects 0.000 description 1
- 238000010992 reflux Methods 0.000 description 1
- 230000000717 retained effect Effects 0.000 description 1
- 238000005070 sampling Methods 0.000 description 1
- 239000004576 sand Substances 0.000 description 1
- CIOAGBVUUVVLOB-UHFFFAOYSA-N strontium atom Chemical compound [Sr] CIOAGBVUUVVLOB-UHFFFAOYSA-N 0.000 description 1
- 230000001360 synchronised effect Effects 0.000 description 1
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- 239000011573 trace mineral Substances 0.000 description 1
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
- G01N30/02—Column chromatography
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- G—PHYSICS
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
- G01N30/02—Column chromatography
- G01N30/62—Detectors specially adapted therefor
- G01N30/72—Mass spectrometers
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
- G01N30/02—Column chromatography
- G01N30/86—Signal analysis
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Abstract
The application discloses a method for judging the type of a dolomitic fluid, which comprises the following steps: determining the fluid magnesium isotope ratio of the dolomite sample; and matching the fluid magnesium isotope ratio with a preset magnesium isotope comparison library to determine the dolomite fluid type of the dolomite sample, wherein the magnesium isotope comparison library stores the corresponding relation between different dolomite fluid types and the fluid magnesium isotope ratio. The method and the device can improve the accuracy of the conjecture of the type of the dolomitic fluid.
Description
Technical Field
The application relates to the technical field of oil exploration, in particular to a method for judging the type of a dolomitic petrochemical fluid.
Background
Dolostone is an important oil and gas reservoir, and the dolostone type oil and gas reservoir accounts for more than 80 percent of the domestic carbonate oil and gas reservoirs. But the formation of dolomite, the rock of which mainly consists of dolomites, is still a century mystery at present. Although there are many causes explanations such as sabkhah, infiltration-reflux, burial, tectonic-hydrothermal, microbiological, etc., none of the above causes can properly explain the cause of dolomite. The geological knowledge and oil and gas exploration of the dolomite reservoir are always restricted by the knowledge limitations and the multiple solution of the origin of dolomite.
At present, in the process of explaining the origin of dolomite, the nature of each type of origin explanation is to explain the nature and source of the magnesium-rich fluid that plays a major role in dolomite. As recognized by sabkha origin, the formation of dolomite is a "saltwater dolomite" which is formed by the addition of high magnesium (Mg) or high calcium (Ca) brines under dry, hot climatic conditions, as a result of calcite or aragonite deposits carried by lagoons, tidal flats, and the like; the cause of burial is believed that dolomite is "calcite formed early", and "buried or hydrothermal dolomite" is formed under burial conditions due to the addition of magnesium-rich fluids such as high salinity formation water, hot brine, etc. It can be seen that the cause problem of dolomite is attributed to the type discrimination and source tracking problem of the dolomitic magnesium-rich fluid.
In the traditional technical means, the deposition and diagenetic environment of dolomite is inferred indirectly mainly through isotopes of carbon (C), oxygen (O), strontium (Sr) and other elements, or main trace elements, rare earth elements and the like, and the possible fluid type of dolomitic chemistry is further inferred. However, the mode has multiple resolvability and uncertainty, such as Sr element, which is mainly present in the dolomite crystal mineral in a similar mode, the content and87Sr/86the Sr isotope ratio is influenced by various factors such as rock fragments and the like, so that the presumed accuracy of the possible fluid type of the dolomitic chemistry is low.
Disclosure of Invention
The embodiment of the application provides a method for judging a type of a dolomite petrochemical fluid, which is used for improving the accuracy of conjecture of the type of the dolomite petrochemical fluid, and comprises the following steps:
determining the fluid magnesium isotope ratio of the dolomite sample; and matching the fluid magnesium isotope ratio with a preset magnesium isotope comparison library to determine the dolomite fluid type of the dolomite sample, wherein the magnesium isotope comparison library stores the corresponding relation between different dolomite fluid types and the fluid magnesium isotope ratio.
In the examples of the present application, the dolomitic fluid type of a dolomite sample of the dolomite sample was determined by measuring the fluid magnesium isotope ratio in the dolomite sample. In the dolomite formation process, the magnesium isotope is transferred from liquid to solid, the property and the composition of the magnesium isotope are kept unchanged, the magnesium isotope is not easily influenced by later-stage modification, and more fluid characteristics of the formed dolomite are stored, so that the accuracy of judging the type of the dolomite petrochemical fluid through the magnesium isotope ratio is higher.
Drawings
In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts. In the drawings:
FIG. 1 is a flowchart illustrating a method for determining a type of a dolomitic fluid according to an embodiment of the present disclosure;
FIG. 2 is a schematic illustration of magnesium isotope ratios for different geological reservoirs provided by an embodiment of the present application;
FIG. 3 is a schematic illustration of magnesium isotope ratios for various fluid media provided in accordance with an embodiment of the present disclosure;
fig. 4 is a schematic diagram of a change of a magnesium isotope ratio of modern-new generation seawater provided by an embodiment of the present application.
Detailed Description
To make the objects, technical solutions and advantages of the embodiments of the present application more apparent, the embodiments of the present application are further described in detail below with reference to the accompanying drawings. The exemplary embodiments and descriptions of the present application are provided herein to explain the present application and not to limit the present application.
Dolomite CaMg (CO)3)2Is Mg in the magnesium-rich fluid2+Ca in alternate calcium carbonate mineral2+Formed by the following steps:
2CaCO3(solid) + Mg2+(liquid) ═ 2CaMg (CO)3)2(solid) + Ca2+(liquid)
During the cross-substitution, the nature and composition of the magnesium isotope remains unchanged, except that a liquid to solid migration occurs. Even though the earlier formed dolomite is subjected to various geological action transformations such as tectonic action, erosion action and the like in the later evolution process, the existing research shows that the magnesium isotope of the dolomite crystal is not easily affected by the later transformation, and the magnesium isotope information in the dolomite crystal more preserves the fluid characteristics of the formed dolomite.
Magnesium (Mg) as the basic constituent element of dolomite has three stable isotopes, respectively24Mg、25Mg、26Mg with corresponding relative abundances of 78.99%, 10.00%, 11.01%, wherein26Mg may consist of short-lived radionuclides26Al decays to26Mg is called a radioactive cause26And Mg. Therefore, the type of the dolomite petrochemical fluid can be judged directly through the research on Mg in the dolomite component elements, particularly by utilizing the tracing and comparison of Mg isotopes.
At present, mature instruments and devices and methods can test the magnesium isotope ratio of dolomite, but the core problem to be solved is how to deduce the type of dolomite fluid in the dolomite diagenetic process in the geological history period according to the measured magnesium isotope ratio.
In order to solve the above problem, an embodiment of the present application provides a method for determining a type of a dolomite petrochemical fluid. As shown in fig. 1, the method includes steps 101 and 102:
When the dolomite sample is selected, the lithology and micro-texture characteristics of the sample can be determined according to the characteristics of a hand specimen and a microscope, and the dolomite sample to be selected is determined according to the lithology and micro-texture characteristics. Specifically, a whole rock sample with uniform lithology is taken, and the sample is crushed into 200-mesh powder; the micro-texture is complex, and different micro-components are drilled by a micro drill aiming at different micro-textures. Meanwhile, in order to conveniently test the diagenesis temperature of the dolomite sample subsequently, the fluid inclusion sheet can be prepared for standby by correspondingly cutting rock slices at the same position.
Optionally, the step 101 of determining the fluid magnesium isotope ratio of the dolomite sample may include the following steps 1011 to 1013:
step 1011, determining the solid magnesium isotope ratio of the dolomite sample by using an internal standard method.
Optionally, before the solid magnesium isotope ratio of the dolomite sample is determined by using the internal standard method, the dolomite sample needs to be treated to a certain extent so as to ensure that the solid magnesium isotope ratio in the dolomite sample is measured more accurately. Specifically, a dolomite powder sample with a certain mass is weighed and placed in a beaker heated at a high temperature of 160 ℃ for 24 hours, and then aqua regia (HF: HNO) is added into the beaker33: 1) the sample was dissolved at 130 ℃ for about 12 hours. After dissolving the sample for about 12 hours, ultrapure HNO was used3And repeatedly dissolving the early-stage erosion matters until the dolomite powder sample is completely dissolved in the solution. Then, the solution dissolved with the dolomite powder sample is moved to a cation exchange chromatographic column for treatment until the solution reaches the following conditions:
① removal of magnesium ions (Mg)2+) Moles of other cations than Mg2+The ratio of the mole number of (a) is less than 0.02;
② removing Mg2+In addition, the mass of the remaining ions in the solution is less than 10 nanograms per kilogram (ng/kg).
The mass of the weighed dolomite powder sample can be determined by the user, and the specific mass is not limited herein.
The internal standard method is a method for measuring the percentage of a component to be measured in a sample. Since the internal standard method is a mature measurement method, the specific process for determining the solid magnesium isotope ratio of the dolomite sample by using the internal standard method is not described herein again.
In determining the solid magnesium isotope ratio of a dolomite sample using the internal standard method, a multi-receiver plasma mass spectrometer was used. And testing the Mg isotope value in a multi-receiving plasma mass spectrometer, and ensuring that the 2-time mean square deviation of the tested value is less than 0.05 per thousand.
Step 1012, determining the diagenesis temperature of the dolomite sample.
Optionally, determining the diagenesis temperature of the dolomite sample comprises: determining the diagenesis temperature of the dolomite sample by using a fluid inclusion method to obtain a first diagenesis temperature; if the first rock formation temperature is more than or equal to 100 ℃, determining the first rock formation temperature as the rock formation temperature of the dolomite sample; and if the first diagenesis temperature is less than 100 ℃, determining the diagenesis temperature of the dolomite sample by using a binary isotope method.
The fluid inclusion is a medium which causes various crystal lattice defects to be generated on the mineral being formed (or formed) due to various factors in the mineral forming process, is retained and preserved by the mineral enclosed in the defects, and the diagenetic temperature T of the mineral can be estimated by testing the uniform temperature of the fluid inclusion in the mineral crystal. The binary isotope mainly utilizes the 'heavy isotope enrichment' effect in the formation process of carbonate rock and mineral crystals13C～18And solving the diagenetic temperature T of the minerals by the principle that the distribution of the O chemical bonds is balanced under the control of the temperature.
Similarly, since the fluid inclusion method and the binary isotope method are relatively mature measuring methods, the detailed description of how to measure the diagenetic temperature by using the methods is omitted.
And 1013, determining the difference value of the magnesium isotopes of the solid phase and the liquid phase of the dolomite sample according to the diagenetic temperature.
Optionally, determining the difference between the magnesium isotopes of the solid phase and the liquid phase of the dolomite sample according to the diagenetic temperature comprises: if the diagenetic temperature T is more than or equal to 100 ℃, utilizing a formula
Calculating the difference delta between the magnesium isotopes in the solid and liquid phases26Mg; if the diagenetic temperature T is less than 100 ℃, utilizing a formula
Calculating the difference delta between the magnesium isotopes in the solid and liquid phases26Mg。
And 1014, determining the fluid magnesium isotope ratio of the dolomite sample according to the solid magnesium isotope ratio and the magnesium isotope difference between the solid phase and the liquid phase.
Alternatively, if at Δ26MgSample (I)The solid magnesium isotope ratio of the dolomite sample is expressed, and the fluid magnesium isotope ratio of the dolomite sample26MgFluid, especially for a motor vehicleCan be expressed as:
26Mgfluid, especially for a motor vehicle＝Δ26MgSample (I)-Δ26Mg
And 102, matching the fluid magnesium isotope ratio with a preset magnesium isotope comparison library to determine the dolomite fluid type of the dolomite sample.
Wherein, the magnesium isotope comparison library stores the corresponding relation between different types of the dolomite fluid and the ratio of the fluid magnesium isotope.
Optionally, the dolomitic fluid types include seawater, fresh water, brine, wherein the brine includes pore water, limestone area ground water and karst cave water, and hydrothermal fluids associated with magma action. The ratio of the magnesium isotopes of the fluids in seawater, fresh water and brine can be measured to obtain the approximate range of the ratio, the ratio of the magnesium isotopes of the fluids in hydrothermal fluid related to magma action is difficult to directly measure, and the data of the magnesium isotopes of the fluids in crusta, mantle and spherulite related to the ratio are analyzed for reference in the embodiment of the application. The following is a brief analysis of the fluid magnesium isotope ratios for the four dolomitic fluid types described above:
(1) seawater, its production and use
The water in the earth, which accounts for three-quarters of the earth's surface area, determines the formation and evolution of sedimentary rocks. The research on seawater samples in different regions of the world shows that the seawater at present has a very uniform magnesium isotope composition of-0.87 to-0.75 per thousand with an average value of-0.83 per thousand, wherein the value of the magnesium isotope composition is obtained by analyzing 25 samples (namely n is 25), and the error is within a two-fold standard deviation range (namely 2 SD). This homogeneity is consistent with the longer residence time of magnesium in seawater, indicating that magnesium has been well mixed in seawater and isotopic homogeneity has been achieved.
(2) Fresh water
The fresh water is mainly river water, rainwater, pore water and the like of the continental facies, and the magnesium isotope composition of the fresh water is extremely non-uniform and the fresh water is not uniform26The variation range of Mg value is more than 4 per thousand, the range is-2.93 per thousand to +1.14 per thousand, and n is 217. Generally, fresh water is widely distributed and has large difference, and the difference is related to the geological condition of water flowing through, particularly rock properties, such as the flowing water of a siliceous rock area and a carbonate rock area has different magnesium isotope characteristics.
(3) Brine
The brine has complex components, is influenced by the action of microorganisms, the lithology of bedrock (surrounding rock) and material components in a water body, has large difference and wide distribution range of magnesium isotopes, and the magnesium isotopes are often more positive than seawater values if the magnesium isotopes have more clay mineral components in the water body and are influenced by substances such as continental clashes, igneous rocks and the like.
Firstly, pore water: the fluid magnesium isotope ratio is: -2.56 ‰ - +1.13 ‰. Influenced by rock types and pore water components, wherein the range of magnesium isotopes in the pore water in the Sabraha area is as follows: -0.59 to-0.40%, and most of pore water in modern marine sediments is: -0.91 to-0.15 per mill; the pore water in the biological cavity is: -0.6 to-0.8 per mill, which is similar to the seawater value.
Secondly, underground water and karst cave water in the limestone area: -1.97 to-1.06 permillage.
(4) Hydrothermal fluid associated with magma action
Earth crust
The magnesium isotope in the crust is influenced by the magma differentiation process, the surface weathering and the sedimentary diagenesis relative to the mantleRemarkably, the isotope ratios vary greatly. Biotite as in southern California type I granite of the United states26Mg is-0.4 ‰ - +0.44 ‰; big bieshan I type granite and granite spangle rock whole rock26Mg ═ 0.26 ‰ -0.14 ‰, wherein the amphibole is present26Mg ═ 0.31 ‰ -0.14 ‰, biotite26Mg is-0.23 to-0.12 per mill; whole rock of Australian type I and S granite26Mg is-0.25 to-0.14 per mill; new Zealand and southwest loess of America26Mg is-0.32 ‰ - +0.05 ‰; australian shale26Mg is-0.27 ‰ - +0.49 ‰; combined sample of granite of crust of east China26Mg＝-0.35‰～-0.16‰；
Of carbonate rocks, as opposed to igneous and clastic rock combinations26Mg has a large negative value, and different types of organisms are combined, and the difference of the deposition and evolution processes is large. Referring to FIG. 2, FIG. 2 shows the ratio of magnesium isotopes in different geological reservoirs, from which it can be seen that dolomite, limestone, and shells of stalactite, coral, and porous worms are formed26The Mg values are all greatly negative.
Mantle
The mantle is the largest chemical reservoir in the earth, where more than 90% of the magnesium is present. Thus, the average magnesium isotopic composition of the mantle essentially represents the magnesium isotopic composition of the earth.
After a great deal of scholars' efforts, the composition characteristics of Mg isotopes in the mantle are recognized as follows:
the mantle has a homogeneous composition of magnesium isotopes; the average composition value of the magnesium isotope of the mantle is the same as that of the meteorite of the spherulite, and is-0.23 per mill +/-0.19 per mill, 2 SD; the mantle may have homology with the spherulite merle.
(iii) spherulites
Meteorites represent the origin and the primary reference point of elements, minerals, rocks, and the spherulites and calcium-rich aluminum refractory inclusions (Ca, Al-rich Inclusion, CAI) in spherulite meteorites vary greatly, indicating that the magnesium isotope produces a very large fraction during condensation and evaporation of the solar astrology. The relative content of magnesium isotopes in spherulites and CAIs among the different types of spherulite merles also vary greatly, and thus, theoretically, different types of spherulite merles may have significantly different magnesium isotope compositions.
Currently, data has been obtained for the magnesium isotope of spherulite merle showing that the magnesium isotope composition of the spherulite merle varies over a range of: -0.49 ‰ 0.06 ‰, and there is a certain difference between the above ranges. However, in order to accurately characterize the composition of the magnesium isotope in the meteorite, analysis of the various types of spherulite magnesium isotopes revealed that the ratio of magnesium isotopes for spherulite magnesium isotopes is not uniform on the mineral scale, but is indeed very uniform on the whole rock scale, where it is26The range of Mg values is: -0.35 to-0.2%, with an average value of-0.28 ± 0.06% (2SD, n-38).
In summary, the magnesium isotope ratio of spherulite meteorite: (26Mg) is greater than the isotope ratio of magnesium in seawater, fresh water and other fluids26Mg) are as follows: -0.49 ‰ - +0.44 ‰.
Illustratively, referring to FIG. 3, FIG. 3 provides fluid magnesium isotope values for various fluid media.
13C、18C、87Sr/86Sr, Fe, Mn, Sr and rare earth elements are effective geochemical indexes for judging the environment and the later diagenesis type of the dolomite diagenesis. In order to further improve the accuracy of the determined type of the dolomitic fluid, in the embodiment of the present application, an isotope ratio and a trace and rare earth element ratio of C, O, Sr may also be tested to assist in determining the type of the dolomitic diagenetic fluid. Specifically, the same sample corresponding to the Mg isotope test may be sent to different analyzers, such as an isotope ratio mass spectrometer, a thermal ionization isotope ratio mass spectrometer, an Inductively coupled plasma mass spectrometry (ICP-MS), and the like, to test geochemical index values of the above elements, to assist in determining the type of the dolomitic/petrosynthetic fluid, and to determine the cause of the dolomite. Since the method of determining the type of dolomitic fluid by the element C, O, etc. already exists in the prior art, it will not be described herein.
In the examples of the present application, the dolomitic fluid type of a dolomite sample of the dolomite sample was determined by measuring the fluid magnesium isotope ratio in the dolomite sample. In the dolomite formation process, the magnesium isotope is transferred from liquid to solid, the property and the composition of the magnesium isotope are kept unchanged, the magnesium isotope is not easily influenced by later-stage modification, and more fluid characteristics of the formed dolomite are stored, so that the accuracy of judging the type of the dolomite petrochemical fluid through the magnesium isotope ratio is higher.
According to the determination method of the types of the dolomitic fluids, 3 typical dolomitic rock samples such as a 1-well of western science of the west sand archipelagic, a 10-1-well of the kachthy basin, a pioneer profile and the like are respectively selected in the embodiment of the application, and the basic element information of the samples is shown in the following table one:
Wherein DSM3 is a standard substance for magnesium isotope test, PDB is a standard substance for carbon (C), oxygen (O) isotope test;13c is used to indicate in the sample13The per-mille ratio of the C isotope to the standard,18o is used to indicate in the sample18The ratio of the O isotope to the standard in parts per thousand.
From the hand specimen and microscopic observation, the lithology, texture characteristics, heterogeneity, etc. of the sample can be determined. Through observation of a hand specimen and a microscope, samples with uniform lithology are subjected to whole rock sampling by XK1-4 and XK1-7, and the selected samples are crushed into 200-mesh powder. The GS10-1 sample mainly comprises dark mud powder crystal dolomite and light saddle-shaped dolomite, the light saddle-shaped dolomite is selected as an analysis sample in an experiment and is crushed to 200 meshes; meanwhile, the saddle-shaped dolomite is cut into millimeter-sized rock slices by a slicer, and the millimeter-sized rock slices are sent to a laboratory to be made into a fluid inclusion body so as to test the uniform temperature of the saddle-shaped dolomite, and the result is shown in the first table and is 140 ℃.
According to the method flow, the obtained 200-mesh powder samples are respectively inspected to test the magnesium isotope ratio, the binary isotope value (delta 47),13C、18C、87Sr/86Sr, Fe, Mn, Sr, rare earth elements and the like, and the test results are shown in the table I. And areCalculating the fluid magnesium isotope ratio of different samples according to the formula steps 1011 to 1014.
Two algae cuttings of nephrite XK1-4 and XK1-7 of Xinyuan in Xisha Yongxing island26Mg is-0.367 and-0.379 respectively, and the contents of the Mg in the modern to new generation seawater recorded by the foramen26Mg is substantially the same, see the area within the box in fig. 4, where fig. 4 is a schematic diagram of the change of the Mg isotope ratio in modern-new generation seawater. Lower than it87Sr/86Sr, Fe, Mn and Sr values and lower diagenesis temperature (27.2 ℃), and proves that the dolomite petrochemical fluid of XK1-4 and XK1-7 algae debris dolomite is synchronous seawater. Sample (I)13C、18O is 2-3 per mill, slightly higher than the isotope value of C, O in the same period of seawater, and has certain salinity, which indicates that the seawater may be concentrated to some extent.
Calculated saddle dolomite dolomitic fluid26Mg is-1.862, and the negative bias is more. Comparing fig. 3, for different geological fluids26The distribution range of Mg corresponds to 5 fluids, which are respectively: river water, groundwater, karst cave drips, pore water in marine sediments, and magma. In combination with other analytical criteria, such as diagenesis temperature of 140 ℃;13C、18o is negatively biased, in particular18The negative bias of O is up to-10.5; and seawater beyond the same period87Sr/86Sr (0.7077-0.7090); in addition to the fact that saddle-shaped dolomite with curved crystal faces is generally a structural or hydrothermal cause, the dolomitic fluid type of saddle-shaped dolomite of GS10-1 can be found to be hydrothermal in connection with magma action.
The above-mentioned embodiments are further described in detail for the purpose of illustrating the invention, and it should be understood that the above-mentioned embodiments are only illustrative of the present invention and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (9)
1. A method for determining a type of a dolomitic fluid, the method comprising:
determining the fluid magnesium isotope ratio of the dolomite sample;
and matching the fluid magnesium isotope ratio with a preset magnesium isotope comparison library to determine the dolomite fluid type of the dolomite sample, wherein the magnesium isotope comparison library stores the corresponding relation between different dolomite fluid types and the fluid magnesium isotope ratio.
2. The method of claim 1, wherein determining the fluid magnesium isotope ratio for a dolomite sample comprises:
determining the solid magnesium isotope ratio of the dolomite sample by using an internal standard method;
determining the diagenesis temperature of the dolomite sample;
determining the difference value of the magnesium isotopes of the solid phase and the liquid phase of the dolomite sample according to the diagenesis temperature;
and determining the fluid magnesium isotope ratio of the dolomite sample according to the solid magnesium isotope ratio and the magnesium isotope difference between the solid phase and the liquid phase.
3. The method of claim 2, wherein prior to said determining the solid magnesium isotope ratio for the dolomite sample using the internal standard method, the method further comprises:
dissolving a dolomite sample to obtain a solution; and moving the solution to a cation exchange chromatographic column for treatment until the ratio of the mole number of other cations except magnesium ions in the solution to the mole number of the magnesium ions is less than 0.02, and the mass of the other ions except the magnesium ions in the solution is less than 10 nanograms per kilogram.
4. The method of claim 2, wherein determining the diagenesis temperature of the dolomite sample comprises:
determining the diagenesis temperature of the dolomite sample by using a fluid inclusion method to obtain a first diagenesis temperature;
if the first rock formation temperature is more than or equal to 100 ℃, determining the first rock formation temperature as the rock formation temperature of the dolomite sample;
and if the first diagenesis temperature is less than 100 ℃, determining the diagenesis temperature of the dolomite sample by using a binary isotope method.
5. The method of claim 2 or 4, wherein determining the difference in magnesium isotopes between the solid and liquid phases of a dolomite sample from the diagenetic temperature comprises:
if the diagenetic temperature T is more than or equal to 100 ℃, utilizing a formula
Calculating the difference delta between the magnesium isotopes in the solid and liquid phases26Mg；
If the diagenetic temperature T is less than 100 ℃, utilizing a formula
Calculating the difference delta between the magnesium isotopes in the solid and liquid phases26Mg。
6. The method of claim 1, wherein the dolomitic fluid type comprises seawater corresponding to a fluid magnesium isotope ratio in a range of-0.87% o to-0.75% o.
7. The method of claim 1, wherein the dolomitic fluid type comprises fresh water corresponding to a fluid magnesium isotope ratio in a range of-2.93% o to + 1.14% o.
8. The method of claim 1, wherein the dolomitic fluid type comprises brine, the brine comprising pore water corresponding to a fluid magnesium isotope ratio in a range of-2.56% o to + 1.13% o.
9. The method of claim 1, wherein the dolomitic fluid type comprises brine, the brine comprising limestone area groundwater and karst cave water, the limestone area groundwater and the karst cave water corresponding to a fluid magnesium isotope ratio in a range of-1.97% o to-1.06% o.
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