A method for comprehensive evaluation of ground stress anisotropy

Abstract

The present application relates to the field of oil and gas field exploration and development, especially to a method for comprehensive evaluation of geostress anisotropy of multiple factors. Through rock mechanics parameters and geostress logging calculation, combined with rock triaxial mechanics experiment, the mechanical properties of super deep reservoir, the size and direction of present geostress are determined. The finite element method is used to establish a full-layer series geomechanical model of the study area, and the three-dimensional distribution of present geostress is accurately predicted. The geostress anisotropy index is used to reveal the mechanism of present geostress anisotropy from the aspects of structural position, burial depth, fracture, stress and fracture angle, and rock heterogeneity. The present application proposes a method for comprehensive evaluation of geostress anisotropy of multiple factors, which has high practical value, and the prediction results have reference value for guiding the exploration and development of super deep reservoirs and the construction of gas storage.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of oil and gas field exploration and development, and particularly relates to a method for comprehensively evaluating anisotropy of in-situ stress. BACKGROUND

[0002] Exploration practice shows that the present in-situ stress and the permeability of fractures controlled thereby are important factors for determining the productivity of super-deep layers. Under the background of overall low-permeability and tightness of super-deep reservoirs, the high-quality reservoirs with small difference in horizontal stress and developed fractures are the key targets for exploration and development. The present in-situ stress, especially the anisotropy of in-situ stress, is a key factor for formulating an oil and gas development plan, evaluating the "engineering dessert" of super-deep reservoirs, designing a drilling trajectory, and practicing geological engineering integration, and is also an important reason for problems such as water flooding and water channeling of gas wells, rapid rise of water injection pressure, and rapid decrease of productivity. At present, the key to effective implementation of two key core technologies for super-deep gas development, i.e., deviated well technology and fracturing technology, lies in clarifying the present in-situ stress state of the gas reservoir. Deep rock is in a stress state of three-way extrusion, and the principal stresses are generally not the same. At present, the previous studies are mostly on the anisotropic acoustic behavior in isotropic sandstone caused by anisotropic stress field, and attention is paid to the influence of the anisotropy of in-situ stress on the reservoir physical property and rock mechanical property, while the influence of the anisotropy of rock itself, fracture, tectonic position, and reservoir heterogeneity on the anisotropy of in-situ stress has not been studied in detail, which affects the exploration of super-deep gas reservoirs, drilling design, construction safety, and efficient development of gas reservoirs. SUMMARY

[0003] The present application aims at solving the above problems, and provides a method for comprehensively evaluating anisotropy of in-situ stress, which can determine the position of a paleo-stress conversion zone.

[0004] The technical scheme of the present application is as follows: a method for comprehensively evaluating anisotropy of in-situ stress, characterized in that it comprises: first in-situ stress and rock mechanical parameter logging interpretation.

[0005] The rock mechanical parameters are interpreted by using logging data, and the relevant calculation formulae are as follows:

[0006]

[0007]

[0008] S c =E d [0.008V sh +0.0045(1-V sh )] (3)

[0009] In formulae (1)-(3), E d is a dynamic Young's modulus of rock, MPa; μ dS is Poisson's ratio, dimensionless; c The uniaxial compressive strength is expressed in MPa; V sh ρ represents the percentage of clay content, dimensionless; b Density of rock, kg / m³ 3 ;Δt p and Δt s These are the P-wave time difference and the S-wave time difference, respectively, in μs / ft;

[0010] Calculation of horizontal principal stress using well logging data:

[0011]

[0012]

[0013] In formulas (4)-(5), S hmin S Hmax These represent the minimum and maximum horizontal principal stresses, respectively, in MPa; ν is the static Poisson's ratio, σ v P is the pressure of the overlying strata, MPa; α is the Biot elastic coefficient, dimensionless; P p ε is the pore pressure, MPa; E is the static Young's modulus, MPa; ε x and ε y ε represents the strain along the directions of the minimum and maximum horizontal principal stresses, respectively, and is dimensionless; x and ε y It is mainly used to characterize the additional horizontal ground stress generated by tectonic stress, and is dimensionless;

[0014] Second fracture discrete network modeling;

[0015] Large-scale fault distribution is determined through seismic interpretation, and the location of medium-scale faults is determined based on the repetition of strata during drilling. The development location of small faults is determined by the faulting of laminae and the changes in stratum dip angles in imaging logging.

[0016] The development characteristics of natural fractures were determined through thin section and core observations and imaging logging. Using core data and grinding corresponding thin sections, the fracture development characteristics at different scales in the core were determined, including fracture orientation, mechanical properties, sequence, and infilling properties. Next-generation oil-based mud imaging logging data underwent capacitance and dielectric correction, followed by multi-frequency inversion processing to generate clear static and dynamic resistivity images, as well as images of the imaginary portion of the gap between the button electrode and the formation. These inverted images were combined and comprehensively interpreted to identify open and closed fractures. For open fractures, due to oil-based mud filling, the resistivity image shows a bright color along the fracture surface, indicating high resistivity; the image of the gap between the electrode and the formation shows a dark color, indicating a large gap distance. For closed fractures, the resistivity image shows a dark or bright color along the fracture surface, while the image of the gap between the electrode and the formation shows a bright color or the same color as the surrounding rock, indicating a near-zero gap. Through these methods, the fracture development characteristics of the imaging logging in the study area were determined.

[0017] The distribution of natural fractures was determined by thin section and core observation and imaging logging, and a discrete fracture network model was established by combining the distribution of faults.

[0018] Third, establish parameters to characterize geostress anisotropy;

[0019] Establish the geostress anisotropy index K h The formula for characterizing the anisotropy of geostress is as follows:

[0020]

[0021] In formula (6), S hmin S Hmax These are the minimum and maximum principal stresses at horizontal levels, in MPa.

[0022] Fourth reservoir geomechanical multi-scale modeling;

[0023] Using structural maps and combining rock mechanics parameters, geomechanical models at the zone, block, and single-well scales were established. The zone-scale geomechanical model refers to a geomechanical model of multiple contiguous imbricate structures, used to analyze the influence of burial depth and faults on stress anisotropy. The block-scale geomechanical model refers to a geomechanical model of a single imbricate structure, used to analyze the influence of stress-fracture angle, fracture, and reservoir mechanics heterogeneity on stress anisotropy. The single-well-scale geomechanical model refers to a one-dimensional geomechanical model based on single-well mechanical parameters, used to analyze the influence of principal stress and stress difference on stress anisotropy.

[0024] Fifth, establish geomechanical models for different fracture densities;

[0025] Combined with the fracture discrete network model, a geomechanical model of fractured rock mass is established, different mechanical parameters are given to different directions of the unit, and the stress size and the anisotropy of in-situ stress caused by the fracture density are analyzed; by adjusting the boundary conditions of the model, the influence of the angle between the fracture and stress on the anisotropy of in-situ stress is analyzed;

[0026] Sixth, the geomechanical model of different mechanical heterogeneity is established;

[0027] By using the established block-scale geomechanical model, combined with the change of sedimentary facies, the mechanical parameter decreasing rule is set to simulate the influence of the change of rock mechanical parameters on the anisotropy of in-situ stress; in the simulation, the homogeneous model and the heterogeneous model are established respectively to analyze the influence of the change of rock mechanical parameters on stress; by using the established single-well-scale geomechanical model, the influence of the principal stress and stress difference on the anisotropy of in-situ stress is analyzed;

[0028] Seventh, the anisotropy of in-situ stress is comprehensively evaluated by multiple factors;

[0029] Combined with numerical simulation and geophysical data, the anisotropy of in-situ stress is systematically evaluated from the aspects of tectonic position, burial depth, fracture, angle between stress and fracture, principal stress, stress difference and reservoir mechanical heterogeneity, and the anisotropy of in-situ stress is comprehensively evaluated from the aspects of plane, vertical, zone, block and single well.

[0030] The beneficial effects of the present application are: through the calculation of rock mechanical parameters and in-situ stress logging, combined with rock triaxial mechanical experiment, the mechanical properties of ultra-deep reservoir, the size and direction of present in-situ stress are determined. By using the fault of ultra-deep reservoir, a full-layer series geomechanical model of Bozi-Dabei area is established by using finite element method, and the three-dimensional distribution of present in-situ stress is accurately predicted; by using the anisotropy index of in-situ stress, the mechanism of present in-situ stress anisotropy is revealed from the aspects of tectonic position, burial depth, fracture, angle between stress and fracture and rock heterogeneity. It is found that the burial depth controls the macroscopic distribution rule of in-situ stress anisotropy of ultra-deep layer, and the in-situ stress anisotropy of the research area gradually decreases from north to south; the strike of fault is nearly perpendicular to the direction of present horizontal maximum principal stress, which leads to the low value of stress difference coefficient near the fault; in addition, the angle between fracture and stress can significantly control the distribution rule of in-situ stress anisotropy, and the heterogeneity of reservoir mechanical properties has less influence on the in-situ stress anisotropy. The research results have reference value for guiding the sweet spot optimization of ultra-deep reservoir engineering, well trajectory design and fracturing reconstruction. The present application proposes a multi-factor comprehensive evaluation method for in-situ stress anisotropy, which has high practical value, low prediction cost and strong operability, can greatly reduce the expenditure of manpower and financial resources, and the prediction results have reference value for guiding the exploration and development of ultra-deep reservoir and the construction of gas storage. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 The flow chart of a geostress anisotropy multi-factor comprehensive evaluation method in an embodiment of the present application.

[0032] Figure 2 The structural features and the formation structure map of the target layer in the research area in an embodiment of the present application: (a) the structural position of the Kelasu structural belt; (b) the nearly south-north geological profile of the Kuqa Depression; (c) the formation structure of the Bashijiqike Formation.

[0033] Figure 3 The geomechanical parameter logging interpretation of Bozi 1203 well in an embodiment of the present application.

[0034] Figure 4 The fracture development characteristics of different filling degrees in the Bozi-Dabeit area in an embodiment of the present application.

[0035] Figure 5 The fracture discrete network model of the research area in an embodiment of the present application.

[0036] Figure 6 The geomechanical modeling process of the Bozi-Dabeit area in an embodiment of the present application.

[0037] Figure 7 The numerical simulation results of the present stress field of the Bozi 12 block in an embodiment of the present application: (A) the minimum principal stress; (B) the intermediate principal stress; (C) the maximum principal stress.

[0038] Figure 8 The geostress anisotropy distribution when the fracture orientation is parallel to the horizontal maximum principal stress in an embodiment of the present application: (A) no fracture development; (B) fracture density 0.067 m-1; (C) fracture density 0.013 m-1.

[0039] Figure 9 The geostress anisotropy distribution when the fracture orientation is perpendicular to the horizontal maximum principal stress in an embodiment of the present application: (A) no fracture development; (B) fracture density 0.067 m-1; (B) fracture density 0.013 m-1.

[0040] Figure 10 The relationship between the angle β between the horizontal principal stress direction and the fracture orientation and the stress difference coefficient in an embodiment of the present application.

[0041] Figure 11 The influence of the reservoir heterogeneity degree on the geostress anisotropy in an embodiment of the present application: (A) model A, Young's modulus 27 GPa; (B) Young's modulus distribution range 24-30 GPa; (C) Young's modulus distribution range 21-33 GPa.

[0042] Figure 12 The geostress and the geostress anisotropy index K hRelationship between the horizontal minimum principal stress S hmin and K h ; (B) Relationship between the vertical principal stress S v and K h ; (C) Relationship between the horizontal maximum principal stress S Hmax and K h ; (D) Relationship between the horizontal stress difference and K h .

[0043] Figure 13 is the horizontal stress difference coefficient distribution law of Bozi-Beibu area in the embodiment of the present application.

[0044] Figure 14 is the simulation result comparison and analysis of the anisotropy coefficient of geostress in Bozi 12 block in the embodiment of the present application. DETAILED DESCRIPTION

[0045] The specific implementation of the present application will be described below in conjunction with the accompanying drawings:

[0046] Figure 1 is a specific implementation process of a geostress anisotropy multi-factor comprehensive evaluation method. The Kelasu structural belt in the study area is located in the north of Kuqa depression in Tarim basin, is a thrust fold belt extending in the northeast-east-west direction, has the characteristics of east-west segmentation and north-south zonation, is famous for strong extrusion and large deformation, and has an exploration area of about 4800km 2 . The Kelasu structural belt can be divided into Keshen, Beibu, Bozi and Awate zones from east to west. The Kelasu structural belt has a complete oil and gas system, and has huge potential of deep-ultra deep oil and gas, and the Paleogene is a regional sealing gypsosalt rock layer; the south of the Kelasu structural belt is adjacent to a hydrocarbon generation sag, the lower Cretaceous Bashijicike group develops a thrust nappe structural trap, and the reservoir-cap assemblage develops well, so it has good geological conditions for hydrocarbon accumulation. A series of long strip imbricate anticlines develop in the north-south direction in the Bozi-Beibu area of the study area, and the extrusion intensity gradually weakens from north to south; the salt layer is used as the boundary to divide the structure into three structural layers in the vertical direction: the salt overlying structural layer (E2s-Q), the salt structural layer (E 1-2 km), and the salt underlying structural layer (T-K). Under the regulation of the gypsosalt rock layer, the deformation of the salt overlying layer is mainly in the form of faults and related folds, the salt underlying layer forms a series of common mountain front structural styles such as anticlines, faulted anticlines and pop-up structures, and common structural combinations such as double structures, stacked structures and wedge-shaped structures, and the salt layer forms salt-related structures such as salt pillows and salt domes Figure 2 .

[0047] First geostress and rock mechanics parameter logging interpretation;

[0048] The rock mechanics parameters are interpreted by using logging data, and the related calculation formula is as follows:

[0049]

[0050]

[0051] S c =E d [0.008V sh +0.0045(1-V sh (3)

[0052] In formulas (1)-(3), E d The dynamic Young's modulus of rock is expressed in MPa and μ. d S is Poisson's ratio, dimensionless; c The uniaxial compressive strength is expressed in MPa; V sh ρ represents the percentage of clay content, dimensionless; b Density of rock, kg / m³ 3 ;Δt p and Δt s These are the P-wave time difference and the S-wave time difference, respectively, in μs / ft;

[0053] Calculation of horizontal principal stress using well logging data:

[0054]

[0055]

[0056] In formulas (4)-(5), S hmin S Hmax These represent the minimum and maximum horizontal principal stresses, respectively, in MPa; ν is the static Poisson's ratio, σ v P is the pressure of the overlying strata, MPa; α is the Biot elastic coefficient, dimensionless; P p ε is the pore pressure, MPa; E is the static Young's modulus, MPa; ε x and ε y ε represents the strain along the directions of the minimum and maximum horizontal principal stresses, respectively, and is dimensionless; x and ε y It is mainly used to characterize the additional horizontal ground stress generated by tectonic stress, and is dimensionless;

[0057] Using the above formula, such as Figure 3 As shown, the dynamic mechanical parameters of the rock were obtained through calculation. The rock mechanical parameters of the target layer, gypsum-salt layer and above-salt strata in the study area were determined by comprehensively utilizing uniaxial compression test, triaxial compression test and well logging data, and through uniaxial-triaxial correction and dynamic-static correction. Based on this, a mechanical model of the Bozi-Dabei area was established.

[0058] like Figure 3The horizontal principal stress is calculated by using the stress calculation formula. The average of the minimum horizontal principal stress is 140 MPa. There is a clear stress layering phenomenon in the vertical direction. The lower part of the second member of the Bashijicike Formation and the second member of the Baxiqimiao Formation is a low stress section. The gradient of the minimum horizontal principal stress is 2.15SG, and the gradient of the maximum horizontal principal stress is 2.5-2.7SG. From north to south, the burial depth gradually increases, and the absolute value of the stress of the gas reservoir increases, but the stress gradient gradually decreases. The difference in depth increases the difference in stress value, and the stress gradient in the gas reservoir is relatively similar.

[0059] Second, the discrete fracture network modeling is established.

[0060] The development types of structural fractures in different sections are significantly different. In the Bozi section, shear fractures are mainly developed, and the dip angles are mainly high-angle fractures, followed by vertical fractures. Figure 4 As shown, filling fractures are rare in the study area. The fractures in the target zone of the study area include open fractures, closed fractures, and half-open fractures. Core observation shows that the Kelasu structural belt develops shear fractures with different filling degrees and different scales. In the Dabei area, the filling degree of structural fractures is generally high, and three types of fractures, i.e., full filling, half (local) filling, and unfilled, can be seen. In the Bozi area, the filling degree is generally low, and the fractures are highly effective. Due to strong compression in the study area, fractures are developed in the target zone, and have the characteristics of high angle, opening, and multiple cutting. Fracture development is the key to increasing production in deep-ultra-deep reservoirs, and also leads to the anisotropy of the mechanical properties of the reservoir.

[0061] The distribution of natural fractures is determined by using thin sections, core observation, and imaging logging, and a discrete fracture network model is established in combination with the distribution of faults. Figure 5 ).

[0062] Third, the anisotropy characterization parameters of in-situ stress are established.

[0063] The anisotropy index K h is established to characterize the anisotropy of in-situ stress, and the calculation formula is as follows:

[0064]

[0065] In formula (6), S hmin and S Hmax are the minimum and maximum horizontal principal stresses, respectively, in MPa.

[0066] Fourth, the multi-scale modeling of reservoir geomechanics is established.

[0067] The dynamic mechanical parameters of rock are calculated by using array sonic logging, and the vertical distribution of static mechanical parameters of rock in a single well is obtained by converting the dynamic and static mechanical parameters of rock in combination with the results of rock triaxial mechanical experiments. In combination with the point cloud distribution of the target zone in the study area (Fig. 6A), a surface model is established. Figure 6B), determine the cutting relationship between the layer and the fault Figure 6 C), build finite element model Figure 6 D) combined with the rock mechanics parameters of different layers, divide the stress grid, and build the full-layer geomechanical model of the study area Figure 6 E-F) The present-day stress values obtained from well logging data interpretation are single well point values, which are affected by factors such as structural relief. Single well stress values cannot be directly applied as regional stress load on the mechanical model, but need to be fitted through numerical simulation to obtain appropriate regional stress values. Regional stress values mainly rely on the stress of key wells that have been determined, combined with the actual geological conditions of the study area, using the linear superposition principle, and finally determined after multiple inversion fitting. Due to the complexity of stress distribution, the boundary conditions during numerical simulation are difficult to accurately set at one time, so the numerical simulation of the stress field is actually a process of multiple iterations of forward and inverse calculations and corrections. The standard for inversion is that the numerical simulation results of key well stress are closest to the actual measured results, and both stress orientation and stress size are considered. Finally, a horizontal minimum principal stress of 145 MPa is applied to the northeast-southwest boundary of the model, a horizontal maximum principal stress of 168 MPa is applied to the north-northwest-south-southeast boundary, and a vertical stress is applied to the top of the model Figure 6 G); Finally, the three-dimensional distribution of the continuous stress field in the complex structure area is obtained. Using the structure map, combined with rock mechanics parameters, the geomechanical model of different scales is established Figure 7 ); In order to systematically reveal the influencing mechanism of stress anisotropy, numerical simulation and geophysical data analysis are mainly used to analyze the stress anisotropy mechanism. According to the structure map of the target Bashijiqike Formation in the study area, the zonal scale geomechanical model is established, and the influence of different factors on stress anisotropy is comprehensively analyzed. By establishing the continuous large model of Bozi Dabei, the influence of burial depth and large faults on stress anisotropy is analyzed. Bozi 12 block is a double anticline structure, with very complex structure. Therefore, by using the block scale geomechanical model, the influence of structure position and shape on stress anisotropy is analyzed.

[0068] Fifth, establish geomechanical models with different fracture densities.

[0069] Combined with the fracture discrete network model, the geomechanical model of fractured rock mass is established, different mechanical parameters are assigned to different directions of the unit, and the change of stress size and stress anisotropy caused by fracture density is analyzed; by adjusting the boundary conditions of the model, the influence of the angle between fracture and stress on stress anisotropy is analyzed.

[0070] As Figure 8As shown, stress field simulation in the Bozi-Dabei area indicates that the stress difference coefficient near the fault is low, less than 0.03, meaning the current stress difference near the fault is low, approaching 0. The stress coefficient near the fault in the study area is also low, which may be due to a near-vertical correlation between the fault orientation and the current geostress. When the fault orientation is nearly parallel to the orientation of the horizontal minimum principal stress, the geostress anisotropy coefficient is high. Figure 8 As shown, when the direction of the crack is nearly parallel to the direction of the maximum horizontal principal stress, the crack will change the distribution pattern of geostress anisotropy in the Bozi 12 block; when the crack is not developed, the geostress anisotropy is mainly controlled by the tectonic morphology, with high values ​​in the core and low values ​​in the limbs; when the crack is developed, the high geostress anisotropy area is mainly distributed along the axis.

[0071] like Figure 9 As shown, crack density and the angle between the cracks are important reasons for the strong anisotropy in the study area. When the angle between the cracks is large, the anisotropy of geostress weakens with crack development, and the value is low along the anticline axis. When cracks develop, the low-value area of ​​geostress anisotropy is mainly distributed along the axis. When the maximum horizontal principal stress intersects the anticline at a large angle, the difference coefficient of horizontal stress along the axis of the connected anticline changes greatly, and the development law of pressure cracks is more complex, with small difference coefficients of stress on the south and north wings. When the maximum horizontal principal stress intersects the anticline at a large angle, the peaks of the connected anticline have high values, while the valleys have low values.

[0072] By changing the direction of the boundary stress in the model, the influence of the angle between the horizontal principal stress direction and the crack orientation on the geostress anisotropy coefficient is simulated. For example... Figure 10 As shown, the stress difference coefficient is largest when the maximum horizontal principal stress is parallel to the axis; and smallest when the maximum horizontal principal stress is perpendicular to the axis. It was found that fracture development and the force-fracture angle are important reasons for the strong anisotropy in the study area. When the force-fracture angle is small, with further fracture development, the anisotropy of geostress increases, and the values ​​are high along the anticline axis and low in the flanks.

[0073] Sixth, establish geomechanical models with different degrees of mechanical heterogeneity;

[0074] By establishing a model of the Dabei 14 block and incorporating sedimentary facies variations, the mechanical parameters were set to decrease from west to east to simulate the impact of changes in rock mechanical parameters on stress anisotropy. Homogeneous and heterogeneous models were established in the simulation to analyze the influence of changes in rock mechanical parameters on stress. Using the established geomechanical model of the Dabei 14 block, a computer program was written to simulate the influence of reservoirs with varying degrees of rock mechanical heterogeneity on stress anisotropy. Through computer programming, models with different normal distributions were embedded into the geomechanical model; by incorporating sedimentary facies variations and setting the mechanical parameters to decrease from west to east, the impact of changes in rock mechanical parameters on stress anisotropy was simulated. Figure 11As shown, in homogeneous reservoirs, stress anisotropy is mainly controlled by structural morphology. In heterogeneous reservoirs, stress anisotropy is mainly controlled by the reservoir's heterogeneity; however, based on the frequency distribution of stress anisotropy, the degree of heterogeneity has little impact on stress anisotropy. Figure 11 AC).

[0075] like Figure 12 As shown, the relationship between geostress and geostress anisotropy index was analyzed using the results of single-well-scale geomechanical modeling. Statistical results show that the horizontal principal stress and vertical principal stress are negatively correlated with the geostress anisotropy index. Among them, the minimum horizontal principal stress has the strongest correlation with the geostress anisotropy index, followed by the vertical principal stress, while the maximum horizontal principal stress has the weakest correlation with the geostress anisotropy index. The study found that the horizontal stress difference was almost unrelated to the geostress anisotropy index, which is basically consistent with the results of Liu et al. (2017) [Liu, J., Ding, W., Yang, H., Wang, R., Yin, S., Li, A., & Fu, F. (2017). 3D geomechanical modeling and numerical simulation of in-situ stress fields in shale reservoirs: a case study of the lower Cambrian Niutitang formation in the Cen'gong block, South China. Tectonophysics, 712, 663-683.]. The reason why the horizontal stress difference was almost unrelated to the geostress anisotropy index may be that the dense sandstone in this study area has a large burial depth range. The burial depth of the target stratum in the study area is between 4500-8100m, and the depth range of the study area is about 3600m.

[0076] Seventh, a comprehensive evaluation of geostress anisotropy based on multiple factors;

[0077] Combining numerical simulations and geophysical data, the current geostress anisotropy is systematically evaluated from the perspectives of tectonic location, burial depth, fractures, stress and fracture angle, principal stress, stress difference, and reservoir mechanical heterogeneity. The geostress anisotropy is comprehensively evaluated at three scales: planar and vertical, zone, block, and single well.

[0078] like Figure 13As shown, the stress anisotropy is the key factor to control the efficient drilling and development of the ultra-deep reservoirs; the extrusion direction and the distribution of the gypsum salt layer jointly control the stress anisotropy in different structural positions, resulting in a large stress difference coefficient in the core of the anticline and a low stress difference coefficient in the wing; the burial depth controls the macroscopic distribution of the stress anisotropy in the ultra-deep layer, and the two are in a linear negative correlation. The fault in the study area is nearly vertical to the direction of the horizontal maximum principal stress, resulting in the stress anisotropy index near 0 near the fault. The horizontal principal stress, the vertical principal stress and the stress anisotropy index are in a negative correlation, among which, the correlation between the horizontal minimum principal stress and the stress anisotropy index is the largest, the correlation between the vertical principal stress and the stress anisotropy index is the second, and the correlation between the horizontal maximum principal stress and the stress anisotropy index is the weakest; the horizontal stress difference has little relationship with the stress anisotropy index, and the heterogeneity of the reservoir mechanical properties has little effect on the stress anisotropy.

[0079] The stress field anisotropy of the Bozi 12 block is calculated by using the established fine geomechanical model of the Bozi 12 block, as shown in Figure 14 The simulation results of different wells are compared with the actual results, and the stress anisotropy of different wells is basically consistent, among which, the error of the Bz1201 well is the largest, about 0.025, and the errors of the other three wells are smaller, less than 0.01. Therefore, it is considered that the simulation results are accurate and reliable, and the analysis results of the stress anisotropy are reliable.

[0080] The above describes the present application by way of example, but the present application is not limited to the above specific embodiments, and any modification or change made on the basis of the present application is within the scope of the present application.

Claims

1. A method for comprehensive evaluation of ground stress anisotropy, characterized in that, The method comprises the following steps: First, the geostress and rock mechanics parameter logging interpretation; The rock mechanics parameters are interpreted by using the logging data, and the related calculation formula is as follows: S c = E d [0.008V sh + 0.0045(1-V sh )] (3) E d is the dynamic Young's modulus of the rock, MPa; μ d is the Poisson's ratio, dimensionless; S c is the uniaxial compressive strength, MPa; V sh is the shale content, dimensionless; p b is the rock density, kg / m 3 ; Δt p and Δt s are the P-wave and S-wave interval times, respectively, μs / ft; The horizontal principal stress is calculated by using the logging data: In the formulas (4)-(5), S hmin , S Hmax are the minimum and maximum principal stresses, respectively, MPa; v is the static Poisson's ratio; σ v is the overburden pressure, MPa; a is the Biot's modulus, dimensionless; P p is the pore pressure, MPa; E is the static Young's modulus, MPa; ε x and ε y are the strains in the directions of the minimum and maximum horizontal principal stresses, respectively, dimensionless. ε x and ε y Used primarily to characterize the additional horizontal stress due to tectonic stress, dimensionless; Second, the fracture discrete network modeling; The large-scale fault distribution is determined by seismic interpretation, the medium-scale fault position is determined based on the stratum repetition in the drilling process, and the small fault development position is determined by the fracture of the bedding in the imaging logging and the change of the stratum dip angle; The natural fracture development characteristics are determined by the slice observation, core observation and imaging logging; the core different scale fracture development characteristics are determined by using the coring data and grinding the corresponding slice, including the fracture occurrence, mechanical property, group system and filling property; the open fracture and closed fracture are identified by combining and comprehensively interpreting the inversion images of the resistivity static image and dynamic image and the electrode and well wall stratum gap imaginary image; for the open fracture, the resistivity image along the fracture surface shows bright color and has high resistance characteristics; The electrode and well wall stratum gap image shows dark color and has large gap distance characteristics; for the closed fracture, the resistivity image along the fracture surface shows dark color or bright color, and the electrode and well wall stratum gap image shows bright color or the same color as the surrounding rock, and has the basic no gap characteristics; the imaging logging fracture development characteristics of the research area are determined by the above method; The natural fracture distribution is determined by the slice observation, core observation and imaging logging, and the fracture discrete network model is established in combination with the fault distribution; Third, the geostress anisotropy representation parameter is established; Establishing the stress anisotropy index K h The stress anisotropy is characterized, and the calculation formula is as follows: In formula (6), S hmin , S Hmax are the minimum and maximum principal stresses, respectively, in MPa. Fourth, the reservoir geomechanics multi-scale modeling; The geomechanics model of the zone, block and single well scale is respectively established by using the structure map and combining the rock mechanics parameter university; Fifth, the geomechanics model of different fracture densities is established; The geomechanics model of the fractured rock mass is established in combination with the fracture discrete network model, different directions of the unit body are endowed with different mechanical parameters, the change of the rock mass stress size and the geostress anisotropy caused by the fracture density is analyzed, and the influence of the fracture and stress angle on the geostress anisotropy is analyzed by adjusting the boundary condition of the model; Sixth, the geomechanics model of different mechanical heterogeneity degrees is established; The influence of the change of the rock mechanics parameter on the geostress anisotropy is simulated by using the established block scale geomechanics model, combining the sedimentary facies change and setting the mechanical parameter decreasing rule; the influence of the rock mechanics parameter change on the stress is analyzed by respectively establishing the homogeneous model and the heterogeneous model in the simulation; the influence of the principal stress and stress difference on the geostress anisotropy is analyzed by using the established single well scale geomechanics model; Seventh, the geostress anisotropy multi-factor comprehensive evaluation; The present geostress anisotropy is systematically evaluated from the angles of the structure position, burial depth, fracture, stress and fracture angle, principal stress, stress difference and reservoir mechanical heterogeneity by combining the numerical simulation and geophysical data, and the geostress anisotropy is comprehensively evaluated from the zone, block and single well three scales in the plane and vertical direction.

2. The method of claim 1, wherein, The geomechanics model of the zone, block and single well scale is respectively established, and comprises the following steps: The zone-scale geomechanical model refers to a geomechanical model of multiple imbricate structures connected in pieces, and is used for analyzing the influence of burial depth and faults on the anisotropy of ground stress; the block-scale geomechanical model refers to a geomechanical model of a single imbricate structure, and is used for analyzing the influence of the angle between stress and cracks, cracks and reservoir mechanical heterogeneity on the anisotropy of ground stress; and the single-well-scale geomechanical model refers to a one-dimensional geomechanical model established based on single-well mechanical parameters, and is used for analyzing the influence of principal stress and stress difference on the anisotropy of ground stress.

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