Method for theoretically calculating preservation temperature and pressure upper limit of sedimentary basin inclusion

Abstract

The invention belongs to the field of petroleum geology, and particularly relates to a method for theoretically calculating the preservation temperature and pressure upper limit of a sedimentary basin inclusion. On the basis of analyzing and determining the deformation weakness direction of common minerals in the sedimentary basin, the common diagenetic minerals are subjected to stretching or burst pressure difference analysis, and the deformation weakness direction of the common minerals in the sedimentary basin is determined by setting the uniform temperature, salinity and CO2 and CH4 concentrations of fluid inclusions under different systems, drawing up isovolumetric lines of the fluid inclusions with different salinity under different systems and drawing up a formation temperature and pressure gradient curve. And finally, obtaining the theoretical temperature and pressure of stretching or bursting of the fluid inclusion along with formation lifting / deep burying through the difference between the isovolumetric line of the fluid inclusion with different salinity and the formation temperature and pressure gradient line under different systems. The method is an important supplement to the basic theory and the analysis method of the fluid inclusion, is a deepened understanding of the rebalance mechanism of the fluid inclusion, and is helpful for promoting the development of geochemistry of the fluid inclusion.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of petroleum geology, and particularly relates to a method for theoretically calculating the upper limit of temperature and pressure of inclusion preservation in a sedimentary basin. BACKGROUND

[0002] Fluid inclusions record the information of ancient fluid activities in geological processes, and are important research objects of fluid physical chemistry in geological processes such as basin diagenesis, mineralization and reservoir formation. Ensuring that the fluid inclusions are in a closed system since being captured is a basic prerequisite for ensuring that the obtained data can truly reflect the properties of ancient fluids. When selecting inclusions for analysis, it is necessary to strictly screen experimental samples that have not undergone post-capture re-equilibration to maintain their originality and representativeness. However, as the stratum burial depth increases in a sedimentary basin (especially for carbonate minerals), the temperature and pressure increase, which may cause the re-equilibration of fluid inclusions captured in the early diagenetic stage, thereby causing the fluid inclusions to fail to record the information of the early diagenetic or reservoir formation. Although more and more scholars have realized that the fluid inclusions can be re-equilibrated after being captured, the current research on the re-equilibration of fluid inclusions mainly stays in the description of this phenomenon and the influencing factors of the re-equilibration of fluid inclusions. The temperature and pressure limits at which the fluid inclusions in different host minerals can maintain a closed system are not well understood, and there is a lack of systematic research work. Based on the above analysis, the research on the temperature and pressure limits at which the fluid inclusions in the minerals in a sedimentary basin can be preserved is not only an important supplement to the basic theory and analysis method of fluid inclusions, but also helps to further understand the re-equilibration mechanism of fluid inclusions, promotes the development of fluid inclusion geochemistry, and has important significance for the research on deep stratum diagenesis and oil and gas reservoir formation.

[0003] In general, it is reasonable to find the lower limit temperature and pressure at which the captured inclusions in minerals are re-equilibrated from the perspective of the deformation mechanics properties of diagenetic minerals. According to the basic knowledge of rock mechanics and the main deformation mechanism of minerals, we know that there are yield limits and strength limits at which plastic deformation and burst occur in minerals. Corresponding to the re-equilibration of inclusions, if the mineral undergoes permanent plastic deformation, it will cause the inclusions in the mineral to be stretched, resulting in the re-equilibration of the inclusions. If the external pressure causes the mineral to exceed its strength limit, the inclusions will burst.

[0004] Because the inclusions are relatively microscopic in a geological body, we can regard them as a particle in the stratum, so that the external static lithostatic pressure acting on them is uniform. There is a fluid pressure in the inclusions, and the fluid pressure and the tail static lithostatic pressure produce a certain degree of pressure difference. If the pressure difference causes the host mineral of the inclusions to undergo plastic deformation, the inclusions will be stretched, and the homogeneous temperature data obtained by testing will be distorted.

[0005] At present, the fluid inclusion re-equilibrium phenomenon in the deep carbonate reservoir of the sedimentary basin is universal, and whether the fluid inclusion in the early diagenetic stage records the physicochemical characteristics of the early diagenetic fluid is a problem worth considering. In addition, due to the wide existence of natural gas caused by oil cracking, such as Sichuan Basin and Tarim Basin in China, the oil in the early oil charging trapped in the fluid inclusion will crack as the formation depth increases or the ground temperature rises, resulting in the change of the composition in the fluid inclusion, and even the leakage caused by the rupture of the fluid inclusion due to the over-high pressure in the fluid inclusion, which makes the petrographic and analytical data interpretation of the fluid inclusion in the ancient deep carbonate reservoir more complex. Therefore, it is necessary to further explore and quantitatively study the upper limit of the preservation temperature and pressure of the diagenetic mineral fluid inclusion in the basin, and provide effective methods and theoretical support for the analysis and data interpretation of the fluid inclusion in different diagenetic minerals. SUMMARY

[0006] To achieve the above object, the present application provides a method for theoretically calculating the upper limit of the preservation temperature and pressure of the fluid inclusion in the sedimentary basin, which can effectively determine the upper limit of the preservation temperature and pressure of the fluid inclusion in the sedimentary basin formation, and the specific technical scheme is as follows:

[0007] S1, analysis of mechanical properties of common minerals in sedimentary basins

[0008] The crystal structure, crystal optical characteristics of common diagenetic minerals (quartz, fluorite, potassium feldspar, sodium feldspar and calcite) in the sedimentary basin are analyzed; on this basis, the mechanical characteristics and deformation mechanism characteristics of the common diagenetic minerals are analyzed; the weak deformation direction of the diagenetic minerals is analyzed in combination with the crystal structure, crystal optical characteristics, mineral mechanical characteristics and mineral deformation mechanism characteristics.

[0009] S2, analysis of tensile and burst pressure difference of common diagenetic minerals in sedimentary basins

[0010] On the basis of determining the weak deformation direction of the diagenetic minerals, uniaxial compression and tensile test are carried out on the weak direction; the yield limit and strength limit of the common diagenetic minerals (quartz, fluorite, potassium feldspar, sodium feldspar and calcite) in the sedimentary basin at different temperatures are determined; the pressure difference required for the most likely tensile or burst of different diagenetic minerals at different temperatures is analyzed.

[0011] S3, setting of homogenization temperature, salinity and CO2 and CH4 concentration of fluid inclusion under different systems

[0012] The main components and characteristic components such as CO2 and CH4 in the diagenetic fluid in the sedimentary basin are determined; the fluid system in the actual formation is analyzed; the homogenization temperature, salinity and CO2 and CH4 concentration of the fluid inclusion in the diagenetic minerals under different systems are set by using theoretical experience.

[0013] S4, isochores of fluid inclusions of different salinity under different systems are drawn

[0014] PVT simulation is carried out on fluid inclusions of different systems based on theoretically and empirically set homogenization temperature, salinity and CO2 and CH4 concentration parameters to obtain different pressures of the inclusions under different set temperatures; the isochores of the fluid inclusions of different systems for theoretical calculation are determined through the functional relationship between the homogenization temperature, the homogenization pressure, the trapping temperature and the trapping pressure.

[0015] S5, formation temperature and pressure gradient curve is drawn

[0016] The distribution range of the geothermal gradient in the actual sedimentary basin is determined; the actual geothermal gradient fluctuation range is selected as a reasonable variation interval for the theoretical calculation of the geothermal gradient; and the formation temperature and pressure gradient curve is obtained through the functional relationship between the formation burial depth, the formation temperature and the formation pressure.

[0017] S6, theoretical stretching and bursting temperature and pressure calculation

[0018] The functional relationship of the isochores of fluid inclusions of different salinity under different systems is established; the functional relationship of the different formation temperature and pressure gradient lines is established; the theoretical temperature and pressure of the fluid inclusions when stretching occurs with the formation uplift and the theoretical temperature and pressure of the fluid inclusions when bursting occurs with the deep burial of the formation are obtained by subtracting the isochores of the fluid inclusions of different salinity under different systems from the different formation temperature and pressure gradient lines at the same temperature.

[0019] The present application has the following beneficial effects:

[0020] The method for calculating the upper limit of the preservation temperature and pressure of the inclusions in the sedimentary basin of the present application provides a good basis for the research on the upper limit of the preservation temperature and pressure of the fluid inclusions in different minerals in the sedimentary basin from the theoretical point of view, avoids various complex experimental requirements for the actual sample testing, and provides effective verification for the actual sample testing of the predecessors from the theoretical point of view. The method is not only an important supplement to the basic theory and analysis method of the fluid inclusions, but also a deepening understanding of the re-equilibrium mechanism of the fluid inclusions, which is helpful to promote the development of fluid inclusion geochemistry, and the research results have important significance for the deep formation diagenesis and oil and gas accumulation research. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 Fig. 1 is a flowchart of the method for theoretically calculating the upper limit of the preservation temperature and pressure of the inclusions in the sedimentary basin provided by the present application;

[0022] Figure 2 Fig. 2 is an anisotropy characteristic analysis diagram of the crystal of the common diagenetic mineral in the sedimentary basin of the present application;

[0023] Figure 3 This is an analysis diagram of the cleavage intersection directions of common diagenetic minerals in sedimentary basins, as presented in this invention.

[0024] Figure 4 The results are from uniaxial compression / tension tests on common diagenetic minerals in sedimentary basins.

[0025] Figure 5 The diagram shows the isochoric curves of fluid inclusions in the H2O-NaCl-KCl-CaCl2 system of this invention.

[0026] Figure 6 The diagram shows the intersection of homogenization temperature and critical temperature when brine inclusions in fluorite with different homogenization temperatures and salinity in the H2O-NaCl-KCl-CaCl2 system burst at different geothermal gradients of 2.5℃ / 100m.

[0027] Figure 7 The diagram shows the intersection of homogenization temperature and critical temperature of brine inclusions in fluorite with different homogenization temperatures and salinity under stretching conditions when the geothermal gradient is 2.5℃ / 100m. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments in this specification without creative effort are within the scope of protection of this application.

[0029] The Gaoshiti-Moxi area is located in the central part of the Sichuan Basin, China. This area possesses unique and complex geological structures within the basin, making it an important region for deep oil and gas resource exploration. Situated in the central uplift zone of the Sichuan Basin, the Gaoshiti-Moxi area exhibits complex and diverse geological structures, a large span of stratigraphic uplift, and well-developed diagenetic minerals. The proposed scheme in this application is illustrated with the attached figures:

[0030] S1. Analysis of Mechanical Properties of Common Minerals in Sedimentary Basins

[0031] The study of the crystal structure and mechanical properties of common rock-forming minerals reveals that mineral deformation mechanisms are mainly divided into brittle fracture and crystalline plastic deformation. First, the mechanical properties of common mineral crystals in sedimentary basins are clarified based on their optical properties, such as… Figure 2 As shown.

[0032] Quartz belongs to the trigonal crystal system, and its basic structural unit is the silicon-oxygen tetrahedron (SiO4), such as... Figure 2The Si-O bonds form a three-dimensional network structure. It requires a lot of energy to break this structure. Therefore, quartz has almost no plastic deformation ability at room temperature. When stressed, it directly reaches the breaking strength. Quartz does not develop cleavage, and the elastic modulus in the direction parallel and perpendicular to the c-axis is different, showing a certain direction dependence, so experiments need to be compared in these two directions to find the most easily deformed direction, such as Figure 3 b in FIG. 1.

[0033] Fluorite belongs to the isometric crystal system and has a cubic structure, as shown in Figure 2 a in FIG. 2. This structure has very high symmetry, which is the physical root of isotropy. The Mohs hardness of fluorite is only 4, which means it is easier to deform. Fluorite has very complete cleavage, that is, it is very easy to crack along a specific crystallographic plane ({111} plane). In its crystal structure, the {111} plane is the stacking plane of fluorine ion layers, and the atomic bonding force on this plane is weak. When stressed, the crystal preferentially breaks along the intersection direction of these cleavage planes, as shown in Figure 3 a in FIG. 3.

[0034] Potassium feldspar belongs to the triclinic crystal system and has a complex structure, with silicon-oxygen tetrahedrons (SiO4) and aluminum-oxygen tetrahedrons (AlO4) connected by sharing vertices to form a three-dimensional framework structure, as shown in Figure 2 c in FIG. 4. The triclinic crystal system is the lowest in symmetry among the seven crystal systems, which means that its physical properties differ significantly in different directions (obvious anisotropy). Potassium feldspar has two complete cleavages, with cleavage planes parallel to the {001} and {010} crystal planes, and the cleavage angle is about 90°. When stressed, the crystal preferentially breaks along the face net direction where the bonding force is weakest, thereby forming a smooth cleavage plane. The Mohs hardness of potassium feldspar is 6. Although the silicon-oxygen framework is strong, there are large channels and weak K-O bonds in the structure, and the overall compressive and tensile strength is general. As a common rock-forming mineral, potassium feldspar is a typical brittle material that directly breaks when impacted by external forces, and generally does not undergo plastic deformation. When stressed, the crystal preferentially breaks along the intersection direction of these cleavage planes, as shown in Figure 3 d in FIG. 5.

[0035] Sodium feldspar, as the sodium-rich end member of the plagioclase series, has its optical and mechanical properties controlled by its triclinic crystal system framework structure, as shown in Figure 2As shown in Figure c, the crystal exhibits two sets of perfect cleavage with an included angle of approximately 86°. It has a Mohs hardness of 6, is brittle, and readily fractures along the weaker bond direction. These characteristics are directly related to the strength of the silicon (aluminum) oxygen framework and the weakness of the sodium ion bonds in its structure. When subjected to stress, the crystal preferentially fractures along the intersection of these cleavage planes, as shown in Figure c. Figure 3 As shown in e.

[0036] Calcite belongs to the trigonal crystal system, such as Figure 2 As shown in Figure d, the crystal structure contains a network of weak bonding planes parallel to the rhombohedral faces, which directly determines the development of its perfect cleavage. Calcite has a Mohs hardness of 3, mainly exhibiting perfect cleavage and low hardness. This is the core mechanical property of calcite. It develops three sets of perfect cleavage, with cleavage planes parallel to the rhombohedral faces. Under external force, calcite crystals almost always fracture along these three sets of cleavage planes, forming perfect rhombohedral fragments (rhombohedrons). Calcite is a typical brittle material and generally does not undergo plastic deformation. When subjected to stress, the crystal preferentially fractures along the intersection lines of these cleavage planes, such as... Figure 3 As shown in c.

[0037] S2. Tensile and burst pressure differential analysis of common diagenetic minerals in sedimentary basins

[0038] The yield strength F1 and ultimate tensile strength F2 of common diagenetic minerals (quartz, fluorite, potassium feldspar, sodium feldspar, and calcite) in sedimentary basins at different temperatures were determined through uniaxial compression and tensile tests. Figure 4 As shown.

[0039] The yield limit and strength limit of the minerals obtained by uniaxial compression test correspond to the required pressure difference for the inward stretching and bursting of the fluid inclusions developed in the host minerals; the yield limit and strength limit of the minerals obtained by uniaxial tension test correspond to the required pressure difference for the outward stretching and bursting of the fluid inclusions developed in the host minerals. In order to ensure the accuracy of the limit data obtained by uniaxial compression and tension test, the mineral samples used should be pure minerals, not rocks (i.e. mixtures of minerals). In addition, the direction of the weakest mineral needs to be determined, and the intersection of the cleavage planes is preferably selected as the test direction, because this direction is usually the position where the mineral is most likely to break, which helps to avoid the depth of the inclusion that may be rebalanced to the greatest extent in the subsequent test. However, minerals in nature usually develop multiple cleavages, and the mechanical properties of different cleavage planes of the same mineral may differ. Therefore, uniaxial compression and tension tests need to be conducted on the intersections of different cleavage planes of the same mineral to further determine their mechanical behavior. If there is a significant difference in the compression and tension strength of the intersections of different cleavage planes at room temperature, the direction of the weakest cleavage plane intersection should be recorded, and the test should be conducted along this direction in the subsequent temperature test. Only the weakest direction can represent the critical mechanical conditions for the rebalancing of inclusions. The rebalancing temperature and pressure parameters of inclusions obtained based on this direction can provide a basis for subsequent scholars to select the stratum depth that is least likely to rebalance in the test of inclusions in sedimentary basins, so as to maximize the avoidance of major errors in the test data.

[0040] Among them, quartz, potassium feldspar, plagioclase and calcite are typical brittle materials, which directly break under external force impact, and generally do not undergo plastic deformation. According to the stress pressure conversion formula, the deformation limit of quartz, fluorite, potassium feldspar, sodium feldspar and calcite can be obtained.

[0041] ①

[0042] Among them, P d is the pressure difference required for the stretching or breaking of diagenetic minerals, with the unit of MPa; F is the limit of uniaxial compression / tension test, with the unit of kN; π is the circular constant.

[0043] The deformation limits of quartz, potassium feldspar, sodium feldspar and calcite are calculated to be 401.87 MPa, 97.07 MPa, 70.19 MPa and 27.56 MPa, respectively, and fluorite has a plastic deformation behavior, and the pressure difference required for its plastic deformation is 23.06 MPa, and the pressure difference required for its breaking is 46.94 MPa.

[0044] S3, setting of fluid inclusion homogenization temperature, salinity and CO2 and CH4 concentration under different systems

[0045] The internal fluid of the inclusion includes common systems, such as: H2O-NaCl system, H2O-KCl system, H2O-CaCl2 system, H2O-NaCl-KCl system, H2O-NaCl-CaCl2 system, H2O-KCl-CaCl2 system, H2O-NaCl-KCl-CaCl2 system, H2O-NaCl-CO2 system, H2O-KCl-CO2 system, H2O-CaCl2-CO2 system, H2O-NaCl-KCl-CO2 system, H2O-NaCl-CaCl2-CO2 system, H2O-KCl-CaCl2-CO2 system, H2O-NaCl-KCl-CaCl2-CO2 system, H2O-NaCl-CH4 system, H2O-KCl-CH4 system, H2O-CaCl2-CH4 system, H2O-NaCl-KCl-CH4 system, H2O-NaCl-CaCl2-CH4 system, H2O-KCl-CaCl2-CH4 system, H2O-NaCl-KCl-CaCl2-CH4 system, etc.

[0046] After determining the system, the weight percentage of the material composition in the system needs to be set. Different proportions of material composition have different effects on the change of the temperature and pressure of the inclusion, thereby resulting in different final calculation rebalancing temperature and pressure performances. The theoretical calculation is preferably to study the systems commonly occurring in the sedimentary strata to ensure the reliability of the final rebalancing temperature and pressure data.

[0047] The homogenization temperature, salinity, CO2 concentration and CH4 concentration of the fluid inclusion under different systems are set by theoretical experience. The homogenization temperature is set to 0-400℃, and a homogenization temperature value is set every 5℃ interval; the salinity is set to 0-20wt.%, and a salinity value is set every 5wt.% interval; the CO2 concentration is set to 0-100mol%, and a homogenization temperature value is set every 5mol% interval; the CH4 concentration is set to 0-100mol%, and a homogenization temperature value is set every 5mol% interval.

[0048] S4, isochoric line setting of fluid inclusion under different systems and different salinities

[0049] On the basis of S3 analysis, the capture temperature of the fluid inclusion is set to 600℃, and then the pressure of the inclusion at the set capture temperature is obtained through PVT simulation of the fluid inclusion under different systems and different salinities. The isochoric line of the fluid inclusion under different systems for theoretical calculation is determined through the functional relationship between the homogenization temperature, the homogenization pressure, the capture temperature and the capture pressure.

[0050] The specific functional relationship is as follows:

[0051] ②

[0052] where T h is the homogenization temperature of the fluid inclusion; P h is the homogenization pressure of the fluid inclusion; T t is the trapping temperature of the fluid inclusion; P t is the trapping pressure of the fluid inclusion.

[0053] An example of the determined isochore is shown in FIG. 1. Figure 5

[0054] S5, stratigraphic temperature-pressure gradient curve fitting

[0055] The geothermal gradient in a sedimentary basin is generally 1-4℃ / 100m, and therefore in order to make the theoretical calculation more in line with geological reality, we selected 1-4℃ / 100m geothermal gradient as a reasonable variation interval of the geothermal gradient, with an interval of 0.5℃ / 100m between the geothermal gradients, and on this basis, the stratigraphic temperature-pressure gradient curve was obtained through the functional relationship between the stratigraphic burial depth, the stratigraphic temperature and the stratigraphic pressure.

[0056] The specific functional relationship is as follows:

[0057] ③

[0058] where P1 is the present-day burial depth corresponding pressure; P2 is the paleo-burial depth corresponding pressure; T1 is the present-day burial depth corresponding temperature; and T2 is the paleo-burial depth corresponding temperature.

[0059] An example of the determined stratigraphic temperature-pressure gradient curve is shown in FIG. 2. Figure 5

[0060] S6, theoretical stretching and burst temperature-pressure calculation

[0061] The theoretical stretching and burst temperature and pressure of the fluid inclusion were obtained by subtracting the isochore of the fluid inclusion of different systems and different salinity from the stratigraphic temperature-pressure gradient curve at the same temperature.

[0062] According to the theoretical calculation of the isochore of the fluid inclusion of different systems and the stratigraphic temperature-pressure gradient used for the theoretical calculation, a reasonable calculation formula of the theoretical stretching or burst temperature and pressure of the fluid inclusion can be established.

[0063] The calculation formula is as follows:

[0064] ④

[0065] ⑤

[0066] ⑥

[0067] ​​Wherein formula (IV) is the curve function of the isochore line of the fluid inclusion of different systems and different salinity; formula (V) is the curve function of the temperature and pressure gradient of the formation; formula (VI) is the function of the pressure difference inside and outside the fluid inclusion; Y1 is the set system pressure inside the fluid inclusion, and the unit is MPa; X1 is the critical temperature when the fluid inclusion is rebalanced; a1 is the slope of the isochore line; b1 is the intercept of the isochore line; Y2 is the static rock pressure of the formation, and the unit is MPa; X2 is the temperature of the depth of the fluid inclusion; a2 is the slope of the temperature and pressure gradient line of the formation; b2 is the intercept of the temperature and pressure gradient line of the formation; z is the yield limit or strength limit obtained by the compression or stretching test of the host mineral, and the unit is MPa.

[0068] The finally calculated X1 and Y1 are the theoretical temperature and pressure of the stretching or bursting of the fluid inclusion under different systems, as shown in the examples. Figure 6 、 Figure 7

[0069] Through the scheme provided by the embodiment of the application, first, the yield limit and strength limit of different minerals at different temperatures are determined through the uniaxial compression / stretching test, and the pressure difference required for the stretching or bursting of different minerals at different temperatures is determined; the homogenization temperature, salinity and CO2 and CH4 concentration of the fluid inclusion under different systems are artificially set, and the above set values are important parameters for determining the isochore line of the fluid inclusion; the different pressures of the fluid inclusion under different set temperatures are obtained through the PVT simulation of the fluid inclusion under different systems, so that the isochore line of the fluid inclusion under different salinity under different systems for theoretical calculation is determined; the temperature and pressure gradient of the formation for theoretical calculation is determined; the theoretical temperature and pressure of the stretching of the fluid inclusion with the uplift of the formation, and the theoretical temperature and pressure of the bursting of the fluid inclusion with the deep burial of the formation are obtained by the difference between the isochore line of the fluid inclusion under different salinity under different systems and the temperature and pressure gradient line of the formation. The method provides a scientific basis for the upper limit of the temperature and pressure preservation of the fluid inclusion in different minerals in the sedimentary basin from the theoretical level, effectively avoids the cumbersome experimental technical requirements and uncertainty in the actual sample test, and significantly improves the operability and universality of the research. From the theoretical point of view, the method not only can cross-verify and reasonably evaluate the test results obtained by the predecessors based on the actual samples, further consolidate the reliability of the existing understanding, but also expand the research scope of the behavior of the fluid inclusion under extreme conditions.

[0070] ​In summary, by stretching or bursting the inclusions with different homogenization temperature and salinity in different systems, the temperature and pressure conditions of the inclusions in the sedimentary basin can be effectively determined from the theoretical point of view. Combined with the upper limit of the re-equilibrium temperature and pressure calculated by us, the depth zone where the inclusions in different basins are likely to re-equilibrate can be divided, and suitable test samples of fluid inclusions can be found by avoiding these depth zones. The most core breakthrough of the establishment of this method is to provide a theoretical and data-based clear guidance for the selection of inclusions that can effectively preserve the original fluid information in the follow-up.

[0071] Those skilled in the art should understand that the discussion of the above examples is only exemplary, and is not intended to suggest that the scope of the application is limited to these examples; under the idea of the present application, the technical features in the above examples or different examples can also be combined, the steps can be implemented in any order, and there are many other changes of different aspects of the present application as described above. In order to be brief, they are not provided in details. Any omission, modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method of theoretically calculating the upper limit of inclusion preservable temperature and pressure in a sedimentary basin, characterized by, The method comprises the following steps: S1, analysis of mechanical properties of common minerals in sedimentary basins, analysis of crystal structure and crystal optical characteristics of common diagenetic minerals in sedimentary basins, and analysis of mechanical characteristics and deformation mechanism characteristics of diagenetic minerals on the basis of the analysis, and determination of the weak deformation direction of diagenetic minerals; S2, analysis of tensile and burst pressure difference of common diagenetic minerals in sedimentary basins, on the basis of the determination of the weak deformation direction of diagenetic minerals, uniaxial compression and tensile test are carried out for the weak direction respectively, the yield limit and strength limit of common diagenetic minerals in sedimentary basins at different temperatures are determined, and the pressure difference required for the most likely tensile and burst of different diagenetic minerals at different temperatures is analyzed; S3, setting of homogenization temperature, salinity and CO2 and CH4 concentration of fluid inclusions in different systems, determining the main components and characteristic components in the diagenetic fluid in the sedimentary basin, and analyzing and determining the fluid system in the actual stratum, and setting the homogenization temperature, salinity and CO2 and CH4 concentration of fluid inclusions in diagenetic minerals in different systems by using theoretical experience; S4, isochoric line setting of fluid inclusions with different salinity in different systems, PVT simulation of fluid inclusions in different systems to obtain different pressures of inclusions at different set temperatures; the function relationship among homogenization temperature, homogenization pressure, trapping temperature and trapping pressure is used to determine the isochoric line of fluid inclusions in different systems for theoretical calculation; S5, determination of stratum temperature pressure gradient curve, determination of the distribution range of geothermal gradient in the actual sedimentary basin, selection of the actual geothermal gradient fluctuation range as the reasonable variation interval for theoretical calculation of geothermal gradient, and obtaining the stratum temperature pressure gradient curve through the function relationship among stratum burial depth, stratum temperature and stratum pressure; S6, theoretical tensile and burst temperature and pressure calculation, establishment of function relationship of isochoric line of fluid inclusions with different salinity in different systems, establishment of function relationship of different stratum temperature pressure gradient lines, and difference between the isochoric line of fluid inclusions with different salinity in different systems and the stratum temperature pressure gradient line at the same temperature to obtain the theoretical temperature and pressure of fluid inclusions tensile with the stratum uplift and the theoretical temperature and pressure of fluid inclusions burst with the stratum deep burial.

2. The method for theoretically calculating the upper limit of temperature and pressure for inclusion preservation in a sedimentary basin of claim 1, wherein, In step S1, the common diagenetic minerals in sedimentary basins mainly include quartz, fluorite, potassium feldspar, sodium feldspar and calcite.

3. The method for theoretically calculating the upper limit of temperature and pressure for inclusion preservation in a sedimentary basin of claim 1, wherein, In step S3, after analyzing and determining the fluid system in the actual stratum, the weight percentage of the material components in the system needs to be set.

4. The method for theoretically calculating the upper limit of temperature and pressure for inclusion preservation in a sedimentary basin of claim 1, wherein, In step S5, 1-4℃ / 100m geothermal gradient is selected as the reasonable variation interval of geothermal gradient.

5. A method of theoretically calculating the upper limit of temperature and pressure for inclusion preservation in a sedimentary basin according to claim 1, wherein, The specific steps of S6 are to establish reasonable temperature and pressure calculation formula of theoretical tensile and burst of inclusions according to the isochoric line of fluid inclusions in different systems calculated theoretically and the stratum temperature pressure gradient used for theoretical calculation: ④ ⑤ ⑥ Wherein formula (IV) is the curve function of the isochore line of different systems and different salinity inclusions; formula (V) is the curve function of the temperature and pressure gradient of different formations; formula (VI) is the function of the pressure difference inside and outside the fluid inclusion; Y1 is the set system inclusion pressure, unit: MPa; X1 is the critical temperature when the inclusion rebalances; a1 is the isochore line slope; b1 is the isochore line intercept; Y2 is the formation static rock pressure, unit: MPa; X2 is the depth temperature of the inclusion at the corresponding depth; a2 is the temperature and pressure gradient line slope; b2 is the temperature and pressure gradient line intercept; z is the yield limit or strength limit obtained by the compression or stretching test of the host mineral, unit: MPa.

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