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

Abstract

The present application belongs to the field of petroleum geology, and particularly relates to a method for theoretically calculating the upper limit of the temperature and pressure of inclusion preservation in a sedimentary basin. On the basis of analyzing and determining the weak direction of deformation of common minerals in a sedimentary basin, the tension or burst differential pressure analysis is performed on the common diagenetic minerals, the homogenization temperature, salinity, and CO2 and CH4 concentration settings of fluid inclusions under different systems, the isochore lines of fluid inclusions under different salinities under different systems are drafted, and the formation temperature and pressure gradient curve is drafted, and finally the theoretical temperature and pressure of the fluid inclusions occurring tension or burst with the formation uplifting / deep burying are obtained by the difference between the isochore lines of the fluid inclusions under different salinities under different systems and the formation temperature and pressure gradient line. The method is an important supplement to the basic theory and analysis method of fluid inclusions, is a deepened understanding of the re-equilibrium mechanism of fluid inclusions, and is helpful to promote the development of fluid inclusion geochemistry.

Description

Technical Field

[0001] This invention belongs to the field of petroleum geology, specifically relating to a method for theoretically calculating the upper limit of temperature and pressure for the preservation of inclusions in sedimentary basins. Background Technology

[0002] Fluid inclusions record information about paleofluid activity during geological processes and are important research objects in the physicochemical study of fluids in basin diagenesis, mineralization, and hydrocarbon accumulation. Ensuring that fluid inclusions remain in a closed system since capture is a fundamental prerequisite for ensuring that the obtained data accurately reflects the properties of paleofluids. When selecting inclusions for analysis, it is essential to rigorously screen experimental samples that have not undergone later reequilibrium to maintain their originality and representativeness. However, in sedimentary basins (especially for carbonate minerals), as burial depth increases, temperature and pressure rise, causing fluid inclusions captured in the early diagenetic stages to potentially reequilibrium, thus preventing them from recording information about early diagenesis or hydrocarbon accumulation. Although more and more scholars recognize that inclusions can reequilibrium after capture, current research on fluid inclusion reequilibrium mainly focuses on describing this phenomenon and the influencing factors of reequilibrium. The temperature and pressure limits at which fluid inclusions in different host minerals can maintain a closed system are still poorly understood and lack systematic research. Based on the above analysis, the study of the upper temperature and pressure limits for fluid inclusion preservation in sedimentary basin minerals is not only an important supplement to the basic theory and analytical methods of fluid inclusions, but also can further deepen the understanding of the rebalancing mechanism of fluid inclusions, which will help promote the development of fluid inclusion geochemistry. At the same time, its research results are of great significance for the study of deep stratigraphy diagenesis and hydrocarbon accumulation.

[0003] In general, it is reasonable to search for the lower limit temperature and pressure at which inclusions trapped within minerals undergo reequilibrium from the perspective of the deformation mechanics properties of diagenetic minerals. Based on fundamental knowledge of rock mechanics and the main deformation mechanisms of minerals, we know that minerals possess a yield strength limit for plastic deformation and a bursting strength limit. Corresponding to inclusion reequilibrium, if a mineral undergoes permanent plastic deformation, it will cause the inclusions within it to stretch, leading to reequilibrium. If external pressure causes the mineral to exceed its strength limit, the inclusions will burst.

[0004] Because inclusions are relatively microscopic within geological bodies, they can be treated as point masses within the strata. In this case, the static rock pressure they experience is consistent with the external pressure. However, an internal fluid pressure exists within the inclusion, creating a pressure difference with the static rock pressure at its tail. If this pressure difference causes plastic deformation of the main mineral within the inclusion, it will lead to stretching of the inclusion, distorting the homogenization temperature data obtained from its measurement.

[0005] Current understanding suggests that fluid inclusion rebalancing is prevalent in deep carbonate reservoirs of sedimentary basins. Whether fluid inclusions from the early diagenetic stage record the physicochemical characteristics of early diagenetic fluids is a question worth considering. Furthermore, due to the widespread presence of natural gas derived from crude oil cracking, such as in the Sichuan and Tarim Basins of my country, crude oil inclusions captured during early crude oil charging undergo cracking as strata depth or geothermal temperatures increase. This leads to changes in the composition of the inclusions, and even rupture and leakage due to excessive internal pressure. These phenomena further complicate the petrographic and analytical interpretation of fluid inclusions in ancient deep carbonate reservoirs. Therefore, it is necessary to conduct in-depth and quantitative research on the upper limits of preservation temperature and pressure of fluid inclusions in basin diagenetic minerals, providing effective methods and theoretical support for the analysis and interpretation of fluid inclusions in different diagenetic minerals. Summary of the Invention

[0006] To achieve the above objectives, this invention provides a method for theoretically calculating the upper limit of temperature and pressure for the preservation of inclusions in sedimentary basins. This method can effectively and simply determine the upper limit of temperature and pressure that inclusions in sedimentary basin strata can preserve. The specific technical solution is as follows:

[0007] S1. Analysis of Mechanical Properties of Common Minerals in Sedimentary Basins

[0008] The crystal structure and optical characteristics of common diagenetic minerals (quartz, fluorite, potassium feldspar, sodium feldspar, and calcite) in sedimentary basins were analyzed. Based on this, the mechanical characteristics and deformation mechanisms of common diagenetic minerals were analyzed. The direction of deformation weakness of diagenetic minerals was analyzed by combining crystal structure, optical characteristics, mineral mechanical characteristics, and mineral deformation mechanism characteristics.

[0009] S2. Tensile and burst pressure differential analysis of common diagenetic minerals in sedimentary basins

[0010] Based on identifying the weak direction of deformation in diagenetic minerals, uniaxial compression and tensile tests were conducted on the weak direction. The yield strength and ultimate tensile strength of common diagenetic minerals (quartz, fluorite, potassium feldspar, sodium feldspar, and calcite) in sedimentary basins at different temperatures were determined. The pressure difference required for different diagenetic minerals to most easily undergo tensile or bursting at different temperatures was analyzed.

[0011] S3. Setting the homogenization temperature, salinity, and CO2 and CH4 concentrations of fluid inclusions in different systems.

[0012] Identify the main and characteristic components of diagenetic fluids in sedimentary basins, such as CO2 and CH4; analyze the fluid systems in actual strata; and use theoretical experience to set the homogenization temperature, salinity, and CO2 and CH4 concentrations of fluid inclusions in diagenetic minerals under different systems.

[0013] S4. Determination of isochoric curves for fluid inclusions with different salinities in different systems

[0014] Based on theoretical experience, homogenization temperature, salinity, and CO2 and CH4 concentration parameters were set to perform PVT simulations on fluid inclusions in different systems to obtain different pressures of the inclusions at different set temperatures; the isochoric curves of fluid inclusions in different systems used for theoretical calculations were determined by the functional relationship between homogenization temperature, homogenization pressure, capture temperature, and capture pressure.

[0015] S5. Formation temperature and pressure gradient curve formulation

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

[0017] S6. Calculation of theoretical tensile and burst temperature and pressure

[0018] Establish isochoric function relationships for fluid inclusions with different salinities under different systems; establish function relationships for temperature and pressure gradient lines in different formations; obtain the theoretical temperature and pressure of fluid inclusions stretching as the formation is uplifted, and the theoretical temperature and pressure of fluid inclusions bursting as the formation is buried deeper, by subtracting the isochoric lines of fluid inclusions with different salinities and the temperature and pressure gradient lines in different formations at the same temperature.

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

[0020] This invention provides a theoretical basis for calculating the upper temperature and pressure limits of fluid inclusion preservation in sedimentary basins, offering a valuable foundation for studying these limits in different minerals within sedimentary basins. It avoids the complex experimental requirements of testing actual samples, providing effective verification of previous studies on actual samples from a theoretical perspective. This method not only significantly supplements the fundamental theory and analytical methods of fluid inclusions but also deepens our understanding of the rebalancing mechanism of fluid inclusions, contributing to the advancement of fluid inclusion geochemistry. Furthermore, its research findings are of great significance for the study of deep stratigraphic diagenesis and hydrocarbon accumulation. Attached Figure Description

[0021] Figure 1 A schematic flowchart illustrating a method for theoretically calculating the upper limit of temperature and pressure for the preservation of inclusions in sedimentary basins, provided by the present invention.

[0022] Figure 2 Figure 1 shows the anisotropy characteristics of common diagenetic mineral crystals in sedimentary basins as analyzed in this invention.

[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 2As shown in Figure b, these silicon-oxygen tetrahedra are connected by shared vertices and arranged spirally along the c-axis (optical axis) in three-dimensional space. This highly symmetrical structure is the physical basis of all the unique properties of quartz, therefore the anisotropy of quartz's mechanical properties is extremely weak. Quartz has a very high Mohs hardness (HM=7). This is attributed to the three-dimensional network structure formed by strong covalent silicon-oxygen (Si-O) bonds in the crystal. A large amount of energy is required to break this structure. Therefore, quartz has almost no plastic deformation ability at room temperature. When subjected to stress, it directly reaches its fracture strength. Quartz does not develop cleavage; its elastic modulus differs mainly in the direction parallel to and perpendicular to the c-axis, exhibiting a certain direction dependence. Therefore, it is necessary to conduct experimental comparisons of these two directions to find the most easily deformable direction, such as... Figure 3 As shown in b in the figure.

[0033] Fluorite belongs to the isometric crystal system and has a cubic structure, such as... Figure 2 As shown in Figure a, this structure exhibits extremely high symmetry, which is the physical root of isotropy. Fluorite has a Mohs hardness of only 4, meaning it is more prone to deformation. Fluorite possesses perfect cleavage, meaning it easily fractures along specific crystallographic planes ({111} planes). In its crystal structure, the {111} planes are the stacking planes of fluorine ions, where atomic bonds are relatively weak. When subjected to stress, the crystal preferentially fractures along the intersection lines of these cleavage planes, such as... Figure 3 As shown in Figure a.

[0034] Potassium feldspar belongs to the triclinic crystal system and has a complex structure. It consists of silicon-oxygen tetrahedra (SiO4) and aluminum-oxygen tetrahedra (AlO4) connected by shared vertices to form a three-dimensional framework structure, such as... Figure 2 As shown in c. The triclinic crystal system has the lowest symmetry among the seven crystal systems, meaning its physical properties vary significantly in different directions (significant anisotropy). Potassium feldspar has two sets of perfect cleavage, with cleavage planes parallel to the {001} and {010} crystal planes, and the cleavage angle is approximately 90°. When subjected to external force, the crystal preferentially fractures along the direction of these weakest bonding planes, thus forming smooth cleavage planes. Potassium feldspar has a Mohs hardness of 6. Although the silicon-oxygen framework is strong, the structure contains large channels and weak KO bonds, resulting in generally average overall compressive and tensile strength. As a common rock-forming mineral, potassium feldspar is a typical brittle material, fracturing directly under impact rather than undergoing plastic deformation. When subjected to stress, the crystal preferentially fractures along the intersection of these cleavage planes, such as... Figure 3 As shown in d.

[0035] As a sodium-rich end-member of the plagioclase series, the optical and mechanical properties of albite are controlled by its triclinic framework structure, such as... 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 strength and ultimate tensile strength of minerals obtained from uniaxial compression tests correspond to the pressure difference required for inward stretching and bursting of fluid inclusions developed in the host mineral; the yield strength and ultimate tensile strength of minerals obtained from uniaxial tensile tests correspond to the pressure difference required for outward stretching and bursting of fluid inclusions developed in the host mineral. To ensure the accuracy of the ultimate tensile data obtained from uniaxial compression and tensile tests, the mineral samples used should be pure minerals, not rocks (i.e., mineral mixtures). Furthermore, the direction of the weakest point of the mineral must be clearly identified, preferably the intersection of cleavage planes, as this direction is usually where the mineral is most likely to fracture, helping to minimize the risk of rebalancing at the depth of inclusions. However, minerals in nature often develop multiple sets of cleavage, and the mechanical properties of different cleavage planes of the same mineral may differ. Therefore, uniaxial compression and tensile tests should be performed separately on the intersections of different cleavage planes of the same mineral to further determine its mechanical behavior. If there is a significant difference in compressive and tensile strength between the intersections of different cleavage planes at room temperature, the direction of the intersection of the weakest cleavage plane should be recorded, and the test should be conducted along this direction in subsequent heating tests. Only the weakest direction can represent the critical mechanical conditions for the reequilibrium of inclusions. The reequilibrium temperature and pressure parameters obtained based on this direction can provide a basis for subsequent researchers to select the stratigraphic depth least likely to reequilibrium in inclusion testing in sedimentary basins, thereby minimizing the possibility of significant errors in the test data.

[0040] Quartz, potassium feldspar, plagioclase, and calcite are typical brittle materials that fracture directly upon impact without undergoing plastic deformation. The deformation limits of quartz, fluorite, potassium feldspar, sodium feldspar, and calcite can be obtained using stress-pressure conversion formulas.

[0041] ①

[0042] Among them, P d The pressure difference required for the stretching or fracturing of diagenetic minerals is expressed in MPa; F is the limit of the uniaxial compression / tension test, expressed in kN; π is pi.

[0043] The calculated deformation limits for quartz, potassium feldspar, sodium feldspar, and calcite are 401.87 MPa, 97.07 MPa, 70.19 MPa, and 27.56 MPa, respectively. Fluorite exhibits plastic deformation behavior, with a pressure difference of 23.06 MPa required for plastic deformation and a pressure difference of 46.94 MPa required for fracture.

[0044] S3. Setting the homogenization temperature, salinity, and CO2 and CH4 concentrations of fluid inclusions in different systems.

[0045] The fluids inside the inclusions include common systems such as: H2O-NaCl, H2O-KCl, H2O-CaCl2, H2O-NaCl-KCl, H2O-NaCl-CaCl2, H2O-KCl-CaCl2, H2O-NaCl-KCl-CaCl2, H2O-NaCl-CO2, H2O-KCl-CO2, H2O-CaCl2-CO2, H2O-NaCl-KCl-CO2, and H2O-NaCl-NaCl-CO2 systems. The system includes l-CaCl2-CO2, H2O-KCl-CaCl2-CO2, H2O-NaCl-KCl-CaCl2-CO2, H2O-NaCl-CH4, H2O-KCl-CH4, H2O-CaCl2-CH4, H2O-NaCl-KCl-CH4, H2O-NaCl-CaCl2-CH4, H2O-KCl-CaCl2-CH4, and H2O-NaCl-KCl-CaCl2-CH4 systems.

[0046] After determining the system, the weight percentages of the material components within it need to be set. Different proportions of material components have different effects on the changes in temperature and pressure of the inclusions, thus leading to different calculated reequilibrium temperature and pressure results. Ideally, the theoretical calculations should study all commonly occurring systems in sedimentary strata to ensure the reliability of the final reequilibrium temperature and pressure data.

[0047] Homogenization temperature, salinity, and CO2 and CH4 concentrations for different systems were determined using theoretical experience. Homogenization temperature was set from 0 to 400℃, with a new homogenization temperature value set at 5℃ intervals; salinity was set from 0 to 20 wt.%, with a new salinity value set at 5 wt.% intervals; CO2 concentration was set from 0 to 100 mol%, with a new homogenization temperature value set at 5 mol% intervals; CH4 concentration was set from 0 to 100 mol%, with a new homogenization temperature value set at 5 mol% intervals.

[0048] S4. Determination of isochoric curves for fluid inclusions with different salinities in different systems

[0049] Based on the S3 analysis, the capture temperature of the fluid inclusions was set to 600℃. Then, PVT simulations were performed on fluid inclusions of different systems and salinities to obtain the pressure of the inclusions at the set capture temperature. The isochoric curves of the fluid inclusions in different systems used for theoretical calculations were determined by the functional relationship between homogenization temperature, homogenization pressure, capture temperature and capture pressure.

[0050] The specific functional relationships are as follows:

[0051] ②

[0052] Where T h P is the homogenization temperature of the fluid inclusions. h T represents the uniform pressure of the fluid inclusion; t P is the capture temperature of the fluid inclusion; t The capture pressure of the fluid inclusion.

[0053] The determined isochoric line is, for example Figure 5 As shown.

[0054] S5. Formation temperature and pressure gradient curve formulation

[0055] The geothermal gradient in sedimentary basins is generally between 1-4℃ / 100m. Therefore, in order to make the theoretical calculations more consistent with geological reality, we selected a geothermal gradient of 1-4℃ / 100m as a reasonable range for the variation of the geothermal gradient, with a 0.5℃ / 100m interval between geothermal gradients. Based on this, we obtained the geothermal-pressure gradient curve by using the functional relationship between stratum depth, stratum temperature and stratum pressure.

[0056] The specific functional relationships are as follows:

[0057] ③

[0058] Where P1 is the pressure corresponding to the current burial depth; P2 is the pressure corresponding to the ancient burial depth; T1 is the temperature corresponding to the current burial depth; and T2 is the temperature corresponding to the ancient burial depth.

[0059] Example of the determined formation temperature and pressure gradient curve Figure 5 As shown.

[0060] S6. Calculation of theoretical tensile and burst temperature and pressure

[0061] By subtracting isochoric lines of fluid inclusions with different salinities and formation temperature and pressure gradients at the same temperature, the theoretical tensile and bursting temperatures and pressures of the inclusions can be obtained.

[0062] Based on the isochoric curves of fluid inclusions in different systems calculated theoretically, and the formation temperature and pressure gradient used for theoretical calculations, reasonable formulas for calculating the temperature and pressure of fluid inclusions during theoretical tensile or bursting can be established.

[0063] The calculation formula is as follows:

[0064] ④

[0065] ⑤

[0066] ⑥

[0067] Formula ④ represents the isochoric curve function of inclusions with different salinities in different systems; Formula ⑤ represents the temperature and pressure gradient curve function of different formations; Formula ⑥ represents the pressure difference function between the inside and outside of fluid inclusions; Y1 represents the internal pressure of inclusions in the set system, in MPa; X1 represents the critical temperature at which the inclusions reach reequilibrium; a1 represents the slope of the isochoric curve; b1 represents the intercept of the isochoric curve; Y2 represents the static rock pressure in the formation, in MPa; X2 represents the burial temperature experienced by the inclusions at the corresponding depth; a2 represents the slope of the formation temperature and pressure gradient line; b2 represents the intercept of the formation temperature and pressure gradient line; and z represents the yield strength or ultimate tensile strength obtained from the compression or tensile test of the host mineral, in MPa.

[0068] The final calculated X1 and Y1 represent the theoretical tensile or bursting temperature and pressure of the inclusions in different systems, as illustrated in the examples. Figure 6 , Figure 7 As shown.

[0069] The method provided by this invention first clarifies the yield strength and ultimate tensile strength of different minerals at different temperatures through uniaxial compression / tension tests, determining the pressure difference required for tensile or bursting events in different minerals at different temperatures. Homogenization temperature, salinity, and CO2 and CH4 concentrations of fluid inclusions in different systems are artificially set; these set values ​​are important parameters for determining the isochoric curves of fluid inclusions. PVT simulations of fluid inclusions in different systems are used to obtain different pressures of inclusions at different set temperatures, thereby determining the isochoric curves of fluid inclusions with different salinities in different systems for theoretical calculations. The formation temperature-pressure gradient is then determined for theoretical calculations. By subtracting the isochoric curves of fluid inclusions with different salinities in different systems from the formation temperature-pressure gradient curves, the theoretical temperature and pressure required for tensile events of fluid inclusions due to formation uplift, and the theoretical temperature and pressure required for bursting events of fluid inclusions due to deep burial, are obtained. This method systematically provides a scientific basis for studying the upper limits of temperature and pressure preservation of fluid inclusions in different minerals in sedimentary basins from a theoretical perspective, effectively avoiding the cumbersome experimental techniques and uncertainties in actual sample testing, and significantly improving the operability and universality of the research. From a theoretical perspective, this method can not only cross-validate and evaluate the rationality of previous test results based on actual samples, further consolidating the reliability of existing knowledge, but also expand the scope of research on the behavior of fluid inclusions under extreme conditions.

[0070] In summary, by conducting theoretical calculations on the stretching or bursting of fluid inclusions with different homogenization temperatures and salinities in various systems, we can effectively clarify the temperature and pressure conditions under which fluid inclusions in sedimentary basins undergo reequilibrium from a theoretical perspective. Combined with our calculated upper limits of reequilibrium temperature and pressure, we can delineate depth zones where fluid inclusions in different basins are likely to undergo reequilibrium. By avoiding these depth zones, suitable test sample fluid inclusions can be found. The most significant breakthrough of this method is that it provides clear theoretical and data-driven guidance for the selection of fluid inclusions that preserve effective original fluid information.

[0071] Those skilled in the art should understand that the above embodiments are merely illustrative and are not intended to imply that the scope of the invention is limited to these examples. Within the framework of this invention, technical features of the above embodiments or different embodiments can be combined, steps can be implemented in any order, and many other variations of the different aspects of the invention as described above exist, which are not provided in detail for the sake of brevity. Any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for theoretically calculating the upper limit of temperature and pressure for the preservation of inclusions in sedimentary basins, characterized in that, Includes the following steps: S1. Analysis of the mechanical properties of common minerals in sedimentary basins: The crystal structure and optical characteristics of common diagenetic minerals in sedimentary basins are analyzed. Based on this, the mechanical characteristics and deformation mechanisms of diagenetic minerals are analyzed to identify the weak deformation directions of diagenetic minerals. S2. Tensile and burst pressure differential analysis of common diagenetic minerals in sedimentary basins: Based on identifying the weak deformation direction of diagenetic minerals, uniaxial compression and tensile tests were conducted on the weak direction to determine the yield limit and ultimate tensile strength of common diagenetic minerals in sedimentary basins at different temperatures. The pressure differential required for different diagenetic minerals to most easily undergo tensile and bursting at different temperatures was analyzed. S3. Set the homogenization temperature, salinity, and CO2 and CH4 concentrations of fluid inclusions under different systems, clarify the main and characteristic components of diagenetic fluids in sedimentary basins, analyze and determine the fluid system in actual strata, and use theoretical experience to set the homogenization temperature, salinity, and CO2 and CH4 concentrations of fluid inclusions in diagenetic minerals under different systems. S4. Isochoric curves for fluid inclusions with different salinities in different systems are determined by performing PVT simulations on fluid inclusions in different systems to obtain different pressures of the inclusions at different set temperatures; the isochoric curves for fluid inclusions in different systems used for theoretical calculations are determined by the functional relationship between homogenization temperature, homogenization pressure, capture temperature and capture pressure. S5. Formation of formation temperature and pressure gradient curve: Determine the distribution range of geothermal gradient in the actual sedimentary basin, select the actual geothermal gradient fluctuation range as the reasonable variation range for theoretical calculation of geothermal gradient, and on this basis, obtain the formation temperature and pressure gradient curve through the functional relationship between formation depth, formation temperature and formation pressure. S6. Theoretical stretching and bursting temperature and pressure calculations: Establish isochoric function relationships for fluid inclusions with different salinities under different systems, and establish temperature and pressure gradient function relationships for different formations. By subtracting the isochoric lines of fluid inclusions with different salinities under different systems and the temperature and pressure gradient lines of different formations at the same temperature, we can obtain the theoretical temperature and pressure of fluid inclusions stretching as the formation is uplifted, as well as the theoretical temperature and pressure of fluid inclusions bursting as the formation is buried deeper.

2. The method for theoretically calculating the upper limit of temperature and pressure for the preservation of inclusions in sedimentary basins as described in claim 1, characterized in that, 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 the preservation of inclusions in sedimentary basins as described in claim 1, characterized in that, In step S3, after analyzing and determining the fluid system in the actual formation, it is necessary to set the weight percentage of the material components in the system.

4. The method for theoretically calculating the upper limit of temperature and pressure for the preservation of inclusions in sedimentary basins as described in claim 1, characterized in that, In step S5, a geothermal gradient of 1-4℃ / 100m is selected as a reasonable range for the variation of the geothermal gradient.

5. The method for theoretically calculating the upper limit of temperature and pressure for the preservation of inclusions in sedimentary basins as described in claim 1, characterized in that, The specific steps of S6 are as follows: Based on the isochoric curves of fluid inclusions in different systems calculated theoretically and the formation temperature and pressure gradient used for theoretical calculations, establish reasonable temperature and pressure calculation formulas for the theoretical tensile and bursting of fluid inclusions: ④ ⑤ ⑥ Formula ④ represents the isochoric curve function of inclusions with different salinities in different systems; Formula ⑤ represents the temperature and pressure gradient curve function of different formations; Formula ⑥ represents the pressure difference function between the inside and outside of fluid inclusions; Y1 represents the internal pressure of inclusions in the set system, in MPa; X1 represents the critical temperature at which the inclusions reach reequilibrium; a1 represents the slope of the isochoric curve; b1 represents the intercept of the isochoric curve; Y2 represents the static rock pressure in the formation, in MPa; X2 represents the burial temperature experienced by the inclusions at the corresponding depth; a2 represents the slope of the formation temperature and pressure gradient line; b2 represents the intercept of the formation temperature and pressure gradient line; and z represents the yield strength or ultimate tensile strength obtained from the compression or tensile test of the host mineral, in MPa.

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