Method and system for inverting tectonic stress in strike-slip fracture formation period

Abstract

The invention discloses a method and system for inverting the tectonic stress in the strike-slip fracture formation period, and the method comprises the steps: determining the strike-slip fracture formation period of a current work area according to the data of a to-be-researched work area, and constructing a three-dimensional geologic model; according to the current work area data, rock mechanical parameter assignment is carried out on each unit in the three-dimensional geologic model, and gridding processing is carried out on the three-dimensional rock mechanical model; according to the relationship between the fractures with different mechanical properties and the tectonic stress, determining constraint conditions for inversion of the paleotectonic stress, and based on the constraint conditions, performing paleotectonic stress inversion on the three-dimensional rock mechanics grid model; and obtaining the tectonic stress state in the strike-slip fracture formation period according to the stress relative parameters and direction obtained by inversion. According to the method, the triaxial paleotectonic stress state in the strike-slip fracture formation period can be quantitatively inverted.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas field exploration and development, and in particular to a method and system for inverting tectonic stress during the formation period of a strike-slip fault. Background Art

[0002] In the process of oil and gas field exploration and development, the relative magnitude and direction of paleo-tectonic stress are crucial for paleo-tectonic evolution analysis and structural fracture prediction.

[0003] There are two main methods for determining the size and direction of paleo-tectonic stress fields: observation, measurement and statistics based on field outcrops; and determination of paleo-tectonic stress states based on indoor experiments. In the field, paleo-stress states are mainly inverted by observing and measuring scratch lineations, tension joints, shear joints and the occurrence of folds on fault sections. Indoor experiments mainly invert paleo-stress states by statistical analysis of microscopic deformation structures under the microscope or by acoustic emission experiments on core samples. However, inverting paleo-stress from field outcrops requires a large amount of field measurement data, and indoor experiments require a certain amount of core samples. Moreover, these two methods can only obtain the relative size and direction of one or two components of paleo-stress, which are limited in accuracy and high in cost during actual application.

[0004] Therefore, the prior art needs to provide a solution for accurately and inexpensively measuring the three-dimensional paleo-tectonic stress during the formation period of strike-slip faults using a small amount of field test data. Summary of the invention

[0005] The purpose of the present invention is to provide a tectonic stress inversion method for the formation period of a strike-slip fault, in order to address the problems of limited accuracy and high cost of the current tectonic stress inversion method for the formation period of a strike-slip fault, so as to quantitatively invert the triaxial stress state of the strike-slip fault.

[0006] In order to solve the above technical problems, an embodiment of the present invention provides a method for inverting tectonic stress during the formation period of a strike-slip fault, comprising: determining the formation period of a strike-slip fault in a current work area and constructing a three-dimensional geological model based on data from a work area to be studied; assigning rock mechanics parameters to each unit in the three-dimensional geological model based on data from the current work area, and gridding the three-dimensional rock mechanics model; determining constraint conditions for inverting paleo-tectonic stress based on the relationship between cracks with different mechanical properties and tectonic stress, and performing paleo-tectonic stress inversion on the three-dimensional rock mechanics grid model based on the constraint conditions; and obtaining the tectonic stress state during the formation period of the strike-slip fault based on the relative parameters and directions of the stress obtained by inversion.

[0007] Preferably, in the step of determining the constraint conditions for inverting paleo-tectonic stress according to the relationship between cracks of different mechanical properties and tectonic stress, and performing paleo-tectonic stress inversion on the three-dimensional rock mechanics grid model based on the constraint conditions, the steps include: establishing tectonic stress index expressions for shear cracks, tension cracks and compression cracks respectively, thereby establishing a comprehensive fracture constraint index expression according to the mean of the tectonic stress index of cracks of different mechanical properties; using the Monte Carlo random simulation method to give the boundary stress state during the formation period of the strike-slip fault, based on which, using the comprehensive fracture constraint index expression as the objective function, and using the three-dimensional iterative boundary element method to simulate the global stress distribution; comparing the comprehensive fracture constraint index of each simulation, and when the value of the comprehensive fracture constraint index is the smallest, taking the relative parameters and directions of the stress currently applied to the model as the inversion result consistent with the stress state during the formation period of the strike-slip fault.

[0008] Preferably, the tectonic stress index expression of the shear fracture, the tectonic stress index expression of the tension fracture, the tectonic stress index expression of the compression fracture, and the comprehensive constraint index expression of the fracture are respectively:

[0009]

[0010]

[0011]

[0012] C=(C s +C e +C p ) / 3

[0013] Among them, C s , C e and C p They represent the structural stress indexes of shear cracks, tension cracks and compression cracks respectively, C represents the comprehensive constraint index of cracks, represent the maximum principal stress and the minimum principal stress respectively, Represents the normal vector of the crack surface with different mechanical properties, Represents the internal friction angle of rock.

[0014] Preferably, the step of obtaining the tectonic stress state during the strike-slip fault formation period according to the stress relative parameters and directions obtained by inversion includes: determining the stress mode of the current work area according to the stress relative parameters obtained by inversion; determining the stress generated by the gravity of the overlying strata as the vertical principal stress during the strike-slip fault formation period according to the drilling data and paleontological fossil data of the rock samples in the study area; and determining the maximum principal stress and the minimum principal stress in the horizontal direction according to the relationship between the stress relative parameters corresponding to different stress modes and the tectonic stress, combined with the acoustic emission experiment of the rock samples in the study area and the vertical principal stress.

[0015] Preferably, the relationship between the stress relative parameters corresponding to the different stress modes and the tectonic stress is expressed by the following expression:

[0016]

[0017]

[0018]

[0019] Among them, σ1, σ2 and σ3 are the maximum principal stress, intermediate principal stress and minimum principal stress respectively, and R represents the relative stress parameter of different stress modes, among which R1 represents the relative stress parameter of normal fault, R2 represents the relative stress parameter of strike-slip fault, and R3 represents the relative stress parameter of reverse fault.

[0020] Preferably, the stress generated by the gravity of the overlying strata is obtained by one of the following methods: determining the amount of stratum erosion based on the current structural characteristics of the work area to be studied, restoring the paleo-structural characteristics of the overlying strata during the formation period of the strike-slip fault, thereby obtaining the stress generated by the gravity of the overlying strata during the formation period of the strike-slip fault; or using the paleontological data of the work area to be studied to determine whether the overlying strata were eroded during the formation period of the strike-slip fault. If standard paleontological fossils develop continuously, it indicates that the strata are continuously deposited, thereby determining the stress generated by the gravity of the overlying strata under the current continuous deposition state.

[0021] Preferably, in the process of determining the strike-slip fault formation period of the current work area, one of the following methods is adopted to obtain it: according to the tectonic background of the work area to be studied, the slip distance of the fault is analyzed to evaluate the activation intensity of different tectonic evolution periods, and then the strike-slip fault formation period is determined; the strike-slip fault formation period is determined by the geochemical characteristics of the fault fillings in the work area to be studied; the strike-slip fault formation period is assisted by the characteristics of the en-echelon faults and strike-slip faults cutting the structure-sedimentary geological body in the overlying strata of the strike-slip main displacement zone of the work area to be studied.

[0022] Preferably, in the step of assigning rock mechanical parameters to each unit in the three-dimensional geological model based on the current work area data, the step includes: using the dipole acoustic logging data of the work area to be studied to obtain the dynamic rock mechanical parameters of the work area to be studied; obtaining the static rock mechanical parameters of the work area to be studied through triaxial rock mechanical experiments on rock samples in the work area to be studied; establishing a conversion relationship between the dynamic rock mechanical parameters and the static rock mechanical parameters, based on which, determining the rock mechanical parameters of the geological model, thereby completing the assignment of the rock mechanical parameters of each unit of the model.

[0023] Preferably, the work area data include but are not limited to: seismic data, core observation data, imaging logging data, mechanical experimental data, drilling data and geological recognition data.

[0024] On the other hand, an embodiment of the present invention provides a system for inverting tectonic stress during the formation period of a strike-slip fault, comprising: a geological model construction module, which is configured to determine the strike-slip fault formation period of a current work area and construct a three-dimensional geological model based on data from the work area to be studied; a rock mechanics model construction module, which is configured to assign rock mechanics parameters to each unit in the three-dimensional geological model based on data from the current work area, and to grid the three-dimensional rock mechanics model; a stress characteristic inversion module, which is configured to determine constraints for inverting paleo-tectonic stress based on the relationship between cracks with different mechanical properties and tectonic stress, and based on the constraints, perform paleo-tectonic stress inversion on the three-dimensional rock mechanics grid model; a tectonic stress generation module, which is configured to obtain the tectonic stress state during the formation period of the strike-slip fault based on the relative parameters and directions of the stress obtained by inversion.

[0025] Compared with the prior art, one or more embodiments of the above scheme may have the following advantages or beneficial effects:

[0026] The present invention proposes a method and system for inverting tectonic stress during the formation of a strike-slip fault. The method and system provide a scheme for inverting and predicting tectonic stress during the formation of a strike-slip fault, which has the advantages of low cost and strong practicality. The magnitude and direction of the stress during the formation of a strike-slip fault can be used to predict the distribution of associated structural fractures during the formation of a strike-slip fault, providing a basis for subsequent exploration and development of fault-controlled fracture-type oil reservoirs. In this way, the present invention can quantitatively invert the triaxial paleo-tectonic stress state during the formation of a strike-slip fault.

[0027] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0029] Figure 1 Schematic diagram of the steps of a method for inverting tectonic stress during the formation period of a strike-slip fault according to an embodiment of the present application.

[0030] Figure 2 This is a schematic diagram of a specific process of a method for inverting tectonic stress during the formation period of a strike-slip fault according to an embodiment of the present application.

[0031] Figure 3 This is a schematic diagram of the structural position of the northern section of a certain fault zone in the method for inverting tectonic stress during the formation period of a strike-slip fault according to an embodiment of the present application.

[0032] Figure 4 This is a schematic diagram of a three-dimensional geological model of the northern section of a certain fault zone in the method for inverting tectonic stress during the formation period of a strike-slip fault according to an embodiment of the present application.

[0033] Figure 5 This is a schematic diagram of a three-dimensional grid model of the northern section of a fault zone in the method for inverting tectonic stress during the formation period of a strike-slip fault according to an embodiment of the present application.

[0034] Figure 6 This is a schematic diagram of the inversion results of an inversion well in the northern section of a fault zone in the method for inverting tectonic stress during the formation period of a strike-slip fault according to an embodiment of the present application.

[0035] Figure 7 This is a schematic diagram of the tectonic stress state during the formation period of a northern section of a fault zone in the method for inverting the tectonic stress during the formation period of a strike-slip fault in an embodiment of the present application.

[0036] Figure 8 This is a module block diagram of a system for inverting tectonic stress during the formation period of a strike-slip fault according to an embodiment of the present application. DETAILED DESCRIPTION

[0037] The following will describe the implementation methods of the present invention in detail with reference to the accompanying drawings and embodiments, so that the implementation process of how the present invention applies technical means to solve technical problems and achieve technical effects can be fully understood and implemented accordingly. It should be noted that as long as there is no conflict, the various embodiments of the present invention and the various features in the embodiments can be combined with each other, and the technical solutions formed are all within the protection scope of the present invention.

[0038] In addition, the steps shown in the flowchart of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions. Also, although a logical sequence is shown in the flowchart, in some cases, the steps shown or described can be performed in a sequence different from that here.

[0039] The terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments. Unless the context clearly indicates otherwise, the singular forms "one", "one" and "item" used herein are also intended to include plural numbers. It should also be understood that the terms "include" and / or "comprise" used herein specify the existence of stated features, integers, steps, operations, units and / or components, without excluding the existence or addition of one or more other features, integers, steps, operations, units, components and / or combinations thereof.

[0040] In the process of oil and gas field exploration and development, the relative magnitude and direction of paleo-tectonic stress are crucial for paleo-tectonic evolution analysis and structural fracture prediction.

[0041] There are two main methods for determining the size and direction of paleo-tectonic stress fields: observation, measurement and statistics based on field outcrops; and determination of paleo-tectonic stress states based on indoor experiments. In the field, paleo-stress states are mainly inverted by observing and measuring scratch lineations, tension joints, shear joints and the occurrence of folds on fault sections. Indoor experiments mainly invert paleo-stress states by statistical analysis of microscopic deformation structures under the microscope or by acoustic emission experiments on core samples. However, inverting paleo-stress from field outcrops requires a large amount of field measurement data, and indoor experiments require a certain amount of core samples. Moreover, these two methods can only obtain the relative size and direction of one or two components of paleo-stress, which are limited in accuracy and high in cost during actual application.

[0042] Therefore, the prior art needs to provide a solution for accurately and inexpensively measuring the three-dimensional paleo-tectonic stress during the formation period of strike-slip faults using a small amount of field test data.

[0043] In order to solve the technical problems in the above-mentioned background technology, the embodiment of the present application proposes a method and system for inverting tectonic stress during the formation period of strike-slip faults. The method and system establish a three-dimensional geological model based on the results of three-dimensional seismic interpretation; determine the rock mechanics parameters based on the results of dipole acoustic logging interpretation and rock mechanics experiments, and grid the model; determine the different mechanical properties of the constrained inversion based on core and resistivity imaging logging, and use the three-dimensional iterative boundary element method to invert the triaxial stress state during the formation period of strike-slip faults; and determine the specific size and direction of the triaxial stress during the formation period of strike-slip faults through comprehensive analysis of acoustic emission experiments and paleo-tectonic characteristics. The present invention solves the problem of quantitative inversion of the tectonic stress state during the formation period of strike-slip faults.

[0044] Embodiment 1

[0045] Figure 1 Schematic diagram of the steps of a method for inverting tectonic stress during the formation period of a strike-slip fault according to an embodiment of the present application. Figure 2 This is a schematic diagram of a specific process of the method for inverting tectonic stress during the formation period of a strike-slip fault according to an embodiment of the present application. Figure 1 and Figure 2 , the specific steps of the method for inverting tectonic stress during the formation period of strike-slip faults (also called "tectonic stress inversion method") described in an embodiment of the present invention are described.

[0046] Step S110 determines the strike-slip fault formation period of the current work area and constructs a three-dimensional geological model based on the data of the work area to be studied.

[0047] In the embodiment of the present invention, the work area data include but are not limited to: seismic data, core observation data, imaging logging data, mechanical experimental data, drilling data and geological recognition data.

[0048] In step S110, the strike-slip fault formation period of the current work area is determined according to the work area data of the work area to be studied.

[0049] In the process of determining the formation period of the strike-slip fault in the current work area, one of the following methods is used to obtain it:

[0050] In one embodiment, according to the structural background of the work area to be studied (see Figure 3 ), analyzing the slip distance of the fault, thereby evaluating the activation intensity at different stages of tectonic evolution and then determining the formation period of the strike-slip fault; or

[0051] In one embodiment, the formation period of the strike-slip fault is determined by the geochemical characteristics of the fault filling in the work area to be studied; or

[0052] In one embodiment, the formation period of the strike-slip faults is determined by using the characteristics of the en echelon faults and strike-slip faults cutting the structural-sedimentary geological bodies in the overlying strata of the strike-slip main displacement zone in the work area to be studied.

[0053] Then, step S110 will also build a 3D geological model based on the 3D seismic interpretation results of the work area to be studied. In one embodiment, the 3D geological model is constructed using the faults and layers of the high-precision 3D seismic data interpretation results (see Figure 4 ).

[0054] Step S120 assigns rock mechanics parameters to each unit in the three-dimensional geological model constructed in step S110 according to the current work area data, and grids the three-dimensional rock mechanics model.

[0055] In step S120, it is necessary to first assign rock mechanical parameters to each unit in the three-dimensional geological model constructed in step S110 according to the current work area data. Specifically, first, the dynamic rock mechanical parameters of the work area to be studied are obtained by using the dipole acoustic logging data of the work area to be studied, and then the static rock mechanical parameters of the work area to be studied are obtained through triaxial rock mechanical experiments on rock samples in the work area to be studied. Finally, a conversion relationship between dynamic rock mechanical parameters and static rock mechanical parameters is established, based on which the rock mechanical parameters of the geological model are determined, thereby completing the assignment of rock mechanical parameters to each unit of the model.

[0056] Dynamic rock mechanics parameters are obtained using dipole acoustic logging data, static rock mechanics parameters are obtained through triaxial rock mechanics experiments, the conversion relationship between dynamic rock mechanics parameters and static rock mechanics parameters is established, and the rock mechanics parameters of the three-dimensional geological model are determined.

[0057] After the three-dimensional geological model is completed, it is necessary to assign rock mechanical parameters to the model, so as to convert the three-dimensional geological model into a rock mechanical model. In the process of assigning values, the rock mechanical parameters of the formation include but are not limited to: Poisson's ratio and Young's modulus, both of which can be obtained through rock mechanical experiments. When assigning values, the rock mechanical experimental results of this area and neighboring areas are also referred to, so as to complete the assignment of rock mechanical parameters for each unit in the three-dimensional geological model.

[0058] Then, the assigned three-dimensional rock mechanics model is meshed. In one embodiment, the three-dimensional geological model of the study area is meshed into triangular units, and the strata and faults in the study area are subdivided into a series of triangular units, and finally the following is obtained: Figure 5 The three-dimensional grid model shown is a three-dimensional rock mechanics grid model, thereby entering step S130.

[0059] Step S130 determines the constraint conditions for inverting paleo-tectonic stress according to the relationship between cracks with different mechanical properties and tectonic stress, and performs paleo-tectonic stress inversion on the three-dimensional rock mechanics grid model obtained in step S120 based on the established constraint conditions.

[0060] In step S130, as a first step, tectonic stress index expressions for shear cracks, tension cracks and compression cracks are respectively established, so as to establish a comprehensive constraint index expression for cracks according to the average values ​​of tectonic stress indexes of cracks with different mechanical properties.

[0061] Specifically, the mechanical properties of fractures are mainly determined based on core, thin section and resistivity imaging logging. According to the relationship between fractures with different mechanical properties and tectonic stress, the constraint function in the paleostress inversion model can be determined. First, the normal vector of the fracture surface of fractures with different mechanical properties is set as For shear fractures, the inverted minimum principal stress direction should be consistent with the normal vector of the shear fracture surface interpreted on the well. The angle between them can be calculated using the Coulomb criterion; for tension fractures, the inverted minimum principal stress direction and the normal vector of the tension fracture surface interpreted by the wellbore are In carbonate rocks, stylolites are the most typical compression fractures. The compression fracture plane is usually perpendicular to the maximum principal stress direction. The inverted maximum principal stress direction is consistent with the normal vector of the stylolite. Based on this, the constraint functions of cracks with different mechanical properties in the stress inversion model are defined, where the shear crack is C s , the tension crack is C e , compression seam is C p And the comprehensive constraint function is C.

[0062] In one embodiment, the tectonic stress index expression of shear cracks, the tectonic stress index expression of tension cracks, the tectonic stress index expression of compression cracks, and the comprehensive constraint index expression of cracks are respectively:

[0063]

[0064]

[0065]

[0066] C=(C s +C e +C p ) / 3 (4)

[0067] Among them, C s , C e and C p They represent the structural stress indexes of shear cracks, tension cracks and compression cracks respectively, C represents the comprehensive constraint index of cracks, represent the maximum principal stress and the minimum principal stress respectively, Represents the normal vector of the crack surface with different mechanical properties, Represents the internal friction angle of rock (in degrees).

[0068] In the second step, the boundary stress state of the strike-slip fault formation period is given by the Monte Carlo random simulation method. Based on this, the expression of the comprehensive constraint index of the crack is used as the objective function, and the global stress distribution is simulated by the three-dimensional iterative boundary element method. In the third step, the comprehensive constraint index of the cracks simulated each time is compared. When the value of the comprehensive constraint index of the cracks is the minimum, the relative parameters and directions of the stress currently applied to the model are taken as the inversion results consistent with the stress state of the strike-slip fault formation period.

[0069] In the actual strike-slip fault formation period stress inversion process, the boundary stress state of the given strike-slip fault formation period is simulated by Monte Carlo random simulation; then, the fracture comprehensive constraint index expression is used as the objective function, and the fault of the well to be inverted in the three-dimensional rock mechanics grid model is inverted by the three-dimensional iterative boundary element method (see Figure 6 ) to perform multiple global stress distribution simulations, and compare the local stress state obtained in each simulation with the input (given) cracks of various mechanical properties. When the value C of all the fracture constraint functions involved in the stress inversion is the smallest, that is, when the value of the comprehensive function formula (4) is the smallest, the relative magnitude (relative stress parameter) and direction of the stress applied to the model are most consistent with the stress state during the formation period of the strike-slip fault in this geological model.

[0070] Thus, the stress relative parameters and the maximum principal stress orientation applied to the model can be obtained, and the stress relative parameters and the maximum principal stress orientation corresponding to the minimum value of the current crack constraint function are taken as the current inversion result, and then the process proceeds to step S140.

[0071] Step S140 obtains the three-dimensional tectonic stress state of the work area to be studied during the strike-slip fault formation period according to the relative stress parameters and directions (horizontal maximum principal stress orientation) obtained by the inversion in step S130. The tectonic stress state during the strike-slip fault formation period includes: the magnitude of the triaxial principal stress and the direction of the maximum principal stress. Among them, the triaxial principal stress includes the horizontal maximum principal stress, the intermediate principal stress and the horizontal minimum principal stress.

[0072] In one embodiment, the stress mode of the current work area is determined according to the relative stress parameters obtained by inversion. The stress mode includes but is not limited to: normal fault, strike-slip fault and reverse fault.

[0073] In one embodiment, based on the drilling data and paleontological fossil data of rock samples in the research area, the stress generated by the gravity of the overlying strata is determined as the vertical principal stress during the strike-slip fault formation period, and the vertical principal stress is used as the intermediate principal stress.

[0074] In one embodiment, the maximum principal stress and the minimum principal stress in the horizontal direction are determined based on the relationship between the relative stress parameters corresponding to different stress modes and the tectonic stress, combined with the acoustic emission experiment of the rock samples in the study area and the obtained vertical principal stress.

[0075] Specifically, according to the Anderson fault theory, one of the three principal stresses is in the vertical direction, and the other two are the maximum and minimum principal stresses in the horizontal direction. R It can be expressed by the two parameters of the maximum horizontal principal stress direction θ and the stress relative parameter R, where R is the relative magnitude of stress when the comprehensive constraint function value is the smallest. On this basis, the vertical principal stress during the formation period of the strike-slip fault is the stress generated by the gravity of the overlying strata, and the vertical principal stress is determined.

[0076] In one embodiment, the stress tension σ R It can be expressed as follows:

[0077] σ R =σ(θ, R) (5)

[0078] Among them, σ R represents the stress tensor, σ represents the stress function, θ represents the horizontal maximum principal stress direction, and R represents the stress relative parameter corresponding to the minimum value of the comprehensive constraint index of the crack during the inversion process.

[0079] In addition, the magnitude of the horizontal principal stress needs to be determined in combination with the results of rock acoustic emission experiments, the vertical principal stress, and the relationship between the relative stress parameters corresponding to different stress modes and the tectonic stress.

[0080] In one embodiment, the relationship between the stress relative parameters corresponding to different stress modes and the structural stress is expressed by the following expression:

[0081]

[0082]

[0083]

[0084] Among them, σ1, σ2 and σ3 are the maximum principal stress, intermediate principal stress and minimum principal stress respectively, and R represents the relative stress parameter of different stress modes. Among them, R1 represents the relative stress parameter of normal fault, R2 represents the relative stress parameter of strike-slip fault, and R3 represents the relative stress parameter of reverse fault.

[0085] In the embodiment of the present invention, the stress generated by the gravity of the overlying strata is obtained by one of the following methods:

[0086] According to the present structural characteristics of the research area, the amount of stratum denudation is determined, and the paleo-structural characteristics of the overlying strata during the formation of the strike-slip fault are restored, so as to obtain the stress generated by the gravity of the overlying strata during the formation of the strike-slip fault; or

[0087] Using the paleontological data of the work area to be studied, it is determined whether the overlying strata were eroded during the formation period of the strike-slip fault. If standard paleontological fossils develop continuously, it indicates that the strata are continuously deposited, thus determining the stress generated by the gravity of the overlying strata under the current continuous deposition state.

[0088] In this way, the present invention provides a solution that can quantitatively invert the triaxial paleo-tectonic stress state during the formation period of the strike-slip fault by using the above steps S110 to S140.

[0089] Embodiment 2

[0090] Based on the above-mentioned first embodiment, the Shunbei 5 fault zone is taken as an example to illustrate the steps of the tectonic stress inversion method described in the embodiment of the present invention.

[0091] The Shunbei 5 fault zone is a large intracratonic strike-slip fault with a total length of 308 km, which runs from south to north through the Tazhong uplift, the Shuntuoguole low uplift, and the Tabei uplift. In plane, the Shunbei 5 fault shows obvious segmentation. According to the plane strike characteristics, it can be divided into three sections, namely, the northern section with a strike of NW20°, a right-lateral left-step strike-slip fault dominated by the pressure uplift section and the translation section; the middle section with a strike of north-south, except for the difference in strike from the northern section, is also a right-lateral left-step strike-slip fault dominated by the pressure uplift section and the translation section; and the southern section is a left-lateral composite strike-slip fault with a strike of NE20° (such as Figure 3 The oil and gas in this area are mainly distributed in fault-controlled fractured carbonate reservoirs. The stress state when the strike-slip fault is formed plays a vital role in the exploration and development of oil and gas reservoirs.

[0092] Step 1: Determine the formation period of the fault and establish a three-dimensional geological model of the work area.

[0093] Based on the study of the evolution history of the Shunbei 5 strike-slip fault and the analysis of the tectonic evolution characteristics of the study area, the Ordovician in the Shunbei area has mainly experienced multi-stage and multi-episode tectonic movements. On the seismic profile, the northern section of the Shunbei 5 strike-slip fault is a nearly vertical strike-slip fault that breaks upward to the top of the Ordovician System. At the same time, a series of nearly northeast-trending en echelon normal faults formed on the top of the Ordovician System have an angle of less than 45° with the underlying strike-slip main displacement zone. These together indicate that the northern section of the Shunbei 5 strike-slip fault was formed in the Caledonian Middle Episode III tectonic movement. The tectonic stress field during the fault formation period mentioned below refers to the tectonic stress field of the Caledonian Middle Episode III. Then, a three-dimensional geological model is constructed based on the faults and stratigraphic interpretations of high-precision three-dimensional seismic data, such as Figure 4 shown.

[0094] Step 2: Determine rock mechanical parameters and establish a three-dimensional grid model.

[0095] After the three-dimensional geological model is completed, it is necessary to assign mechanical parameters to the model and convert the three-dimensional geological model into a mechanical model. Since the study area is a typical marine open platform facies, the lithology is relatively simple, mainly mudstone limestone. In order to quickly converge the simulation results, the research object is treated as a uniform linear elastic medium. In the assignment process, the rock force parameters of the strata mainly refer to Poisson's ratio and Young's modulus. These two parameters can be obtained through rock mechanics experiments. The rock mechanics experimental results of this area and neighboring areas were referred to during the simulation. The specific rock mechanics parameters are shown in Table 1. The geological model of the study area is meshed with triangular units, and the strata and faults are subdivided into a series of triangular units. Finally, the following is obtained. Figure 5 The three-dimensional mesh model shown in the figure contains a total of 374,894 computing nodes and 734,930 triangular units.

[0096] Table 1 Mechanical parameters of the Lower Ordovician in the Shunbei 5 strike-slip fault zone

[0097]

[0098] Step 3: Iterative boundary element inversion of crack constraints with different mechanical properties.

[0099] The determination of the mechanical properties of fractures mainly relies on core and resistivity imaging logging. Shear fractures on the core are characterized by small fracture width, relatively flat fracture surface, visible scratches and steps, and mainly medium to high dip angles; tension fractures are usually wide, irregular fracture surface, and high dip angles; compression fracture dip angles are multi-dimensional medium to low angles. Under the calibration of core identification results, the mechanical properties of imaging logging fractures are defined. According to the relationship between fractures with different mechanical properties and tectonic stress, the constraint function in the paleostress inversion model is constructed, such as expressions (1) to (3). The actual fault model is as follows Figure 6 As shown, the wells involved in stress inversion are SHB5-3 and SHB5-12H.

[0100] In the actual stress inversion process of the strike-slip fault formation period, the Monte Carlo random simulation method is used to give the boundary stress state of the strike-slip fault formation period. The three-dimensional iterative boundary element method is used to simulate the stress distribution of the entire area each time. The local stress state obtained in each simulation is compared with the input cracks of various mechanical properties. When the value of all the fracture constraint functions involved in the stress inversion is the smallest, that is, when the value of the comprehensive function formula (4) is the smallest, the relative size and direction of the stress applied to the model are most consistent with the stress state of the strike-slip fault formation period in this geological model.

[0101] Step 4: Determine the tectonic stress state during the strike-slip fault formation period.

[0102] The tectonic stress state during the formation of the strike-slip fault includes the magnitude of the triaxial principal stress and the direction of the maximum principal stress. According to the Anderson fault theory, one of the triaxial principal stress directions is the vertical direction. The stress tensor σ can be expressed by two parameters, θ and R, as shown in expression (5). R is the relative magnitude of the stress when the value of the comprehensive constraint function is the smallest in the previous step. Through a large number of iterative boundary element random inversions in the previous step, it is finally determined that Figure 7 The stress state (relative stress parameters) under different stress modes is shown, among which, Figure 7The minimum value of the medium constraint function is 0.259. At this time, the stress state is a strike-slip stress state. The maximum horizontal principal stress orientation is 17° northeast, and the stress ratio R is 1.76. On this basis, it can be determined that the vertical principal stress during the formation of the strike-slip fault is the stress generated by the gravity of the overlying strata, and the vertical principal stress is the intermediate principal stress. Nine wells in the study area revealed that the Upper Ordovician is mainly composed of dark gray mudstone and marl, indicating that the Upper Ordovician strata in the study area have always been in an underwater reducing sedimentary environment. In addition, the standard conodont fossil zones found in the upper part of the Middle Ordovician and the bottom of the Upper Ordovician indicate that there is uninterrupted continuous deposition between the Middle-Lower Ordovician and the Upper Ordovician. Therefore, the thickness of the Upper Ordovician strata in the study area today can be approximated as the thickness of the strata when the fractures of the third curtain of the middle Caledonian were formed. The thickness of the Upper Ordovician strata revealed by the nine wells in the study area was statistically analyzed, with an average thickness of 685m, and the intermediate principal stress was calculated to be 17.5MPa. The results of acoustic emission experiments on rocks in the study area and adjacent areas show that the maximum horizontal principal stress range during the fault formation period is between 51.8 and 62.4 MPa. Based on the stress ratio and intermediate principal stress value obtained from the inversion results, the maximum horizontal principal stress and the minimum horizontal principal stress when the northern section of the Shunbei 5 strike-slip fault was formed were obtained through planning solution to be 62.4 MPa and 3.3 MPa, respectively.

[0103] Therefore, the present invention has carried out actual data application in the northern section of Shunbei No. 5 fault zone, established a geological model based on the faults and stratigraphic positions interpreted from the seismic data, and under the constraints of cracks with different mechanical properties in the two wells, obtained the inversion result that the stress state of the northern section of Shunbei No. 5 fault zone in the formation period is a strike-slip stress mode, the stress ratio R is 1.76, and the direction of the maximum horizontal principal stress is 17° northeast. Combining the acoustic emission experiment and the standard paleontological fossil data, it is finally determined that the maximum horizontal principal stress is 62.4 MPa, the vertical principal stress is 17.5 MPa, and the minimum horizontal principal stress is 3.3 MPa. The magnitude and direction of the triaxial stress in the formation period of the strike-slip fault can be used to predict the strike-slip fault-derived cracks, which has a high application value for the development of fault-controlled fracture-type reservoirs.

[0104] Embodiment 3

[0105] Based on the above-mentioned embodiment 1 and embodiment 2, the embodiment of the present invention further provides a system for inverting tectonic stress during the formation period of strike-slip faults (also called "tectonic stress inversion system").

[0106] Figure 8 Module block diagram of a system for inverting tectonic stress during the formation period of a strike-slip fault according to an embodiment of the present application. Figure 8 As shown, the tectonic stress inversion system described in the embodiment of the present invention includes: a geological model construction module 810, a rock mechanics model construction module 820, a stress characteristic inversion module 830 and a tectonic stress generation module 840.

[0107] Specifically, the geological model construction module 810 is implemented according to the method described in step S110 above, and is configured to determine the strike-slip fault formation period of the current work area and construct a three-dimensional geological model based on the data of the work area to be studied; the rock mechanics model construction module 820 is implemented according to the method described in step S120 above, and is configured to assign rock mechanics parameters to each unit in the three-dimensional geological model based on the data of the current work area, and grid the three-dimensional rock mechanics model; the stress characteristic inversion module 830 is implemented according to the method described in step S130 above, and is configured to determine the constraint conditions for inverting the ancient tectonic stress based on the relationship between cracks with different mechanical properties and tectonic stress, and based on the constraint conditions, perform ancient tectonic stress inversion on the three-dimensional rock mechanics grid model; the tectonic stress generation module 840 is implemented according to the method described in step S140 above, and is configured to obtain the tectonic stress state under the strike-slip fault formation period based on the relative stress parameters and directions obtained by inversion.

[0108] The present invention discloses a method and system for inverting tectonic stress during the formation of a strike-slip fault. The method and system provide a scheme for inverting and predicting tectonic stress during the formation of a strike-slip fault, which has the advantages of low cost and strong practicality. The magnitude and direction of the stress during the formation of a strike-slip fault can be used to predict the distribution of associated structural fractures during the formation of a strike-slip fault, providing a basis for subsequent exploration and development of fault-controlled fracture-type oil reservoirs. In this way, the present invention can quantitatively invert the triaxial paleo-tectonic stress state during the formation of a strike-slip fault.

[0109] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any person familiar with the technology within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

[0110] In the description of the present invention, unless otherwise specified, "plurality" means two or more than two; the orientations or positional relationships indicated by the terms "upper", "lower", "left", "right", "inner", "outer", "front end", "rear end", "head", "tail", etc. are based on the orientations or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", "third", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0111] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0112] It should be understood that the embodiments disclosed in the present invention are not limited to the specific structures, processing steps or materials disclosed herein, but should be extended to equivalent substitutions of these features understood by ordinary technicians in the relevant field. It should also be understood that the terms used herein are only used for the purpose of describing specific embodiments and are not meant to be limiting.

[0113] The "one embodiment" or "embodiment" mentioned in the specification means that the specific features, structures or characteristics described in conjunction with the embodiment are included in at least one embodiment of the present invention. Therefore, the phrases "one embodiment" or "embodiment" appearing in various places throughout the specification do not necessarily refer to the same embodiment.

[0114] Although the embodiments disclosed in the present invention are as above, the contents described are only embodiments adopted for facilitating the understanding of the present invention and are not intended to limit the present invention. Any technician in the technical field to which the present invention belongs can make any modifications and changes in the form and details of the implementation without departing from the spirit and scope disclosed in the present invention, but the patent protection scope of the present invention shall still be subject to the scope defined in the attached claims.

Claims

1. A method for inverting tectonic stress during the formation period of strike-slip faults, characterized in that: include: Based on the data of the work area to be studied, determine the formation period of the strike-slip fault in the current work area and construct a three-dimensional geological model; According to the current work area data, assign rock mechanics parameters to each unit in the three-dimensional geological model, and grid the three-dimensional rock mechanics model; According to the relationship between cracks with different mechanical properties and tectonic stress, the constraint conditions for inverting paleo-tectonic stress are determined, and paleo-tectonic stress inversion is performed on the three-dimensional rock mechanics grid model based on the constraint conditions; According to the relative parameters and directions of stress obtained by inversion, the tectonic stress state during the formation period of the strike-slip fault is obtained.

2. The method according to claim 1, characterized in that The steps of determining the constraint conditions for inverting the paleo-tectonic stress according to the relationship between the cracks with different mechanical properties and the tectonic stress, and performing paleo-tectonic stress inversion on the three-dimensional rock mechanics grid model based on the constraint conditions include: Establish tectonic stress index expressions for shear cracks, tension cracks and compression cracks respectively, so as to establish a comprehensive constraint index expression for cracks according to the mean value of tectonic stress index of cracks with different mechanical properties; The boundary stress state of the strike-slip fault formation period is given by Monte Carlo random simulation method. Based on this, the comprehensive constraint index expression of the crack is used as the objective function, and the global stress distribution is simulated by three-dimensional iterative boundary element method. The comprehensive fracture constraint index of each simulation is compared. When the value of the comprehensive fracture constraint index is the smallest, the relative parameters and directions of the stress currently applied to the model are taken as the inversion results consistent with the stress state during the formation period of the strike-slip fault.

3. The method according to claim 2, characterized in that The tectonic stress index expression of the shear crack, the tectonic stress index expression of the tension crack, the tectonic stress index expression of the compression crack, and the comprehensive constraint index expression of the crack are respectively: Among them, C s , C e and C p They represent the structural stress indexes of shear cracks, tension cracks and compression cracks respectively, C represents the comprehensive constraint index of cracks, denote the maximum principal stress and the minimum principal stress, respectively. Represents the normal vector of the crack surface with different mechanical properties, Represents the internal friction angle of rock.

4. The method according to any one of claims 1 to 3, characterized in that The step of obtaining the tectonic stress state during the formation period of the strike-slip fault according to the relative stress parameters and directions obtained by inversion includes: Determine the stress mode of the current work area based on the relative stress parameters obtained by inversion; Based on the drilling data and paleontological fossil data of rock samples in the research area, the stress generated by the gravity of the overlying strata was determined as the vertical principal stress during the formation period of the strike-slip fault; According to the relationship between the relative stress parameters corresponding to different stress modes and the tectonic stress, combined with the acoustic emission experiment of the rock samples in the work area to be studied and the vertical principal stress, the maximum principal stress and the minimum principal stress in the horizontal direction are determined.

5. The method according to claim 4, characterized in that The relationship between the stress relative parameters corresponding to the different stress modes and the tectonic stress is expressed by the following expression: Among them, σ1, σ2 and σ3 are the maximum principal stress, intermediate principal stress and minimum principal stress respectively, and R represents the relative stress parameter of different stress modes, among which R1 represents the relative stress parameter of normal fault, R2 represents the relative stress parameter of strike-slip fault, and R3 represents the relative stress parameter of reverse fault.

6. The method according to claim 4 or 5, characterized in that: The stress generated by the gravity of the overlying stratum is obtained by one of the following methods: According to the present structural characteristics of the research area, the amount of stratum denudation is determined, and the paleo-structural characteristics of the overlying strata during the formation of the strike-slip fault are restored, so as to obtain the stress generated by the gravity of the overlying strata during the formation of the strike-slip fault; or Using the paleontological data of the study area, it is determined whether the overlying strata were eroded during the formation period of the strike-slip fault. If standard paleontological fossils develop continuously, it indicates that the strata are continuously deposited, thus determining the stress generated by the gravity of the overlying strata under the current continuous deposition state.

7. The method according to any one of claims 1 to 6, characterized in that: In the process of determining the formation period of the strike-slip fault in the current work area, one of the following methods is used to obtain it: According to the tectonic background of the work area to be studied, the slip distance of the fault is analyzed to evaluate the activation intensity of different tectonic evolution periods, and then determine the formation period of the strike-slip fault; Determine the formation period of strike-slip faults through the geochemical characteristics of the fault fillings in the study area; The formation period of strike-slip faults is determined by the characteristics of en-echelon faults and strike-slip faults cutting the structural-sedimentary geological bodies in the overlying strata of the strike-slip main displacement zone in the study area.

8. The method according to any one of claims 1 to 7, characterized in that: The step of assigning rock mechanical parameters to each unit in the three-dimensional geological model according to the current work area data includes: Using the dipole acoustic logging data of the work area to be studied, the dynamic rock mechanical parameters of the work area to be studied are obtained; Through triaxial rock mechanics experiments on rock samples in the work area to be studied, the static rock mechanics parameters of the work area to be studied are obtained; A conversion relationship between the dynamic rock mechanics parameters and the static rock mechanics parameters is established, based on which the rock mechanics parameters of the geological model are determined, thereby completing the assignment of the rock mechanics parameters of each unit of the model.

9. The method according to any one of claims 1 to 8, characterized in that: The work area data include but are not limited to: seismic data, core observation data, imaging logging data, mechanical experimental data, drilling data and geological knowledge data.

10. A system for inverting tectonic stress during the formation period of strike-slip faults, characterized in that: include: A geological model building module, which is configured to determine the strike-slip fault formation period of the current work area and build a three-dimensional geological model based on the data of the work area to be studied; A rock mechanics model building module is configured to assign rock mechanics parameters to each unit in the three-dimensional geological model according to the current work area data, and to grid the three-dimensional rock mechanics model; A stress characteristic inversion module configured to determine the constraint conditions for inverting the paleo-tectonic stress according to the relationship between the fractures of different mechanical properties and the tectonic stress, and to perform paleo-tectonic stress inversion on the three-dimensional rock mechanics grid model based on the constraint conditions; The tectonic stress generation module is configured to obtain the tectonic stress state during the formation period of the strike-slip fault according to the relative stress parameters and directions obtained by inversion.

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