CN115563822A - Multi-factor comprehensive evaluation method for geostress anisotropy - Google Patents
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Abstract
The invention relates to the field of oil and gas field exploration and development, in particular to a comprehensive evaluation method for multiple factors of ground stress anisotropy. And determining the mechanical property of the ultra-deep reservoir and the magnitude and direction of the current ground stress by rock mechanical parameters and ground stress logging calculation and combining a rock triaxial mechanical experiment. By adopting a finite element method, a full-layer system connected-slice geomechanical model of a research area is established, and the three-dimensional distribution of the ground stress at present is accurately predicted; the ground stress anisotropy index is adopted to disclose the current ground stress anisotropy mechanism from the aspects of construction position, burial depth, fracture, stress and crack included angle, rock heterogeneity and the like. The invention provides a comprehensive evaluation method for the anisotropy of the geostress based on multiple factors, which has high practical value, and the prediction result has reference value for guiding the exploration and development of oil and gas in an ultra-deep reservoir and the construction of a gas storage reservoir.
Description
Technical Field
The invention relates to the field of oil and gas field exploration and development, in particular to a comprehensive evaluation method for multiple factors of ground stress anisotropy.
Background
Exploration practice shows that the stress of the earth and the crack permeability under the control of the stress are important factors for determining the ultra-deep layer energy production nowadays. Under the overall low-permeability compact background of an ultra-deep reservoir, a high-quality reservoir with small horizontal stress difference and crack development is a key target of exploration and development; the existing geostress, especially the geostress anisotropy, is a key factor for formulating an oil and gas development scheme, evaluating an engineering dessert in an ultra-deep reservoir, designing a drilling track and carrying out geological engineering integrated practice, and is also an important reason for causing the problems of gas well flooding water channeling, rapid rise of water injection pressure, rapid decline of productivity and the like. At present, the key to effective implementation of the deviated well technology and the fracturing technology, which are two key core technologies for ultra-deep natural gas development, lies in clearing the current geostress state of a gas reservoir. Deep rock is in the stress state of three-dimensional extrusion, and the main stress is generally different. At present, many people study the anisotropic acoustic behavior in the isotropic sandstone caused by the anisotropic stress field, and pay attention to the influence of the ground stress anisotropy on the physical properties and the mechanical properties of the reservoir, but the influence of the anisotropy, fracture and structural positions of the rock and the reservoir anisotropy on the ground stress anisotropy is not studied in detail, so that the ultra-deep gas reservoir exploration, drilling design, construction safety and high-efficiency gas reservoir development are influenced.
Disclosure of Invention
The invention aims to solve the problems and provides a comprehensive multi-factor evaluation method for the ground stress anisotropy, which can determine the position of a paleo-stress conversion zone.
The technical scheme of the invention is as follows: a multi-factor comprehensive evaluation method for geostress anisotropy is characterized by comprising the following steps: logging and interpreting a first geostress and rock mechanical parameter;
the logging information is used for explaining the rock mechanical parameters, and the related calculation formula is as follows:
S c ＝E d [0.008V sh +0.0045(1-V sh )] (3)
in formulas (1) to (3), E d The dynamic Young's modulus of elasticity of the rock is MPa; mu.s d Is Poisson's ratio and is dimensionless; s c Uniaxial compressive strength, MPa; v sh The mud content is percentage, and has no dimension; ρ is a unit of a gradient b Is rock density, kg/m 3 ；Δt p And Δ t s Respectively longitudinal wave time difference and transverse wave time difference, mu s/ft;
and (3) calculating the horizontal principal stress by using logging data:
in formulas (4) to (5), S hmin 、S Hmax Respectively horizontal minimum and maximum principal stress, MPa; v is the static Poisson's ratio, σ v Is overburden pressure, MPa; alpha is the Biao elastic coefficient and is dimensionless; p p Pore pressure, MPa; e is the static Young's modulus, MPa; epsilon x And epsilon y The strain in the direction of the minimum horizontal main stress and the strain in the direction of the maximum horizontal main stress are respectively and dimensionless; epsilon x And epsilon y Mainly used for characterizing the extra horizontal ground stress generated by the construction stress, and is dimensionless;
modeling a second fractured discrete network;
determining large-scale fault distribution through seismic interpretation, and determining the position of a medium-scale fault based on the repetition of strata in the drilling process; determining the development position of the small fault through the dislocation of the streak layer and the change of the stratum inclination angle in the imaging logging;
determining natural fracture development characteristics through slice and core observation and imaging logging; determining the fracture development characteristics of different sizes of the rock core, including fracture appearance, mechanical properties, set system and filling property, by utilizing coring data and grinding corresponding slices; carrying out capacitance correction and dielectric correction on the new generation of oil-based mud imaging logging data, then carrying out multi-frequency inversion processing to generate clear resistivity static images and dynamic images and imaginary part images of the interval between the button electrode and the borehole wall stratum, combining the inversion images, carrying out comprehensive interpretation, and identifying Zhang Kaifeng and a closed seam; for Zhang Kaifeng, due to oil based mud filling, the resistivity image shows a bright color along the fracture face, representing a high resistance feature; the image of the gap between the electrode and the well wall stratum displays dark color and is characterized by larger gap distance; for a closed seam, a dark color or a bright color is displayed on the resistivity image along the surface of the seam, and meanwhile, the electrode and the borehole wall stratum gap image displays a bright color or the same color as that of the surrounding rock and shows a characteristic of no gap basically; determining the development characteristics of the imaging logging fracture in the research area by the method;
determining natural fracture spread by utilizing slice and core observation and imaging logging, and establishing a fracture discrete network model by combining fault distribution;
thirdly, establishing a ground stress anisotropy characterization parameter;
establishing the ground stress anisotropy index K h Characterizing the stress anisotropy of the earth, the calculation formula is as follows:
in the formula (6), S hmin 、S Hmax Respectively horizontal minimum and maximum principal stress, MPa;
performing geomechanical multi-scale modeling on a fourth reservoir;
respectively establishing a zone, a block and a single-well-scale geomechanical model by using a constructional diagram and combining the rock mechanical parameter university; the zone scale geomechanical model is a geomechanical model of a plurality of shingled structure connected pieces and is used for analyzing the influence of the buried depth and the fault on the ground stress anisotropy; the block scale geomechanical model is a single shingled structure geomechanical model and is used for analyzing the influence of stress and crack included angles, cracks and reservoir mechanics heterogeneity on the ground stress anisotropy; the single-well-scale geomechanical model is a one-dimensional geomechanical model established based on single-well mechanical parameters and used for analyzing the influence of main stress and stress difference on the anisotropy of the ground stress.
Fifthly, establishing geomechanical models with different fracture densities;
combining with a fracture discrete network model, establishing a geomechanical model of a fractured rock mass, endowing different mechanical parameters to different directions of the unit body, and analyzing the change of the rock mass stress size and the crustal stress anisotropy caused by fracture density; analyzing the influence of the included angle between the crack and the stress on the anisotropy of the ground stress by adjusting the boundary condition of the model;
sixthly, establishing geomechanical models with different mechanical heterogeneous degrees;
setting a mechanical parameter decreasing rule by using the established block scale geomechanical model and combining with deposition phase change, and simulating the influence of the change of rock mechanical parameters on the ground stress anisotropy; respectively establishing a homogeneous model and a heterogeneous model in the simulation, and analyzing the influence of the change of the rock mechanical parameters on the stress; analyzing the influence of the main stress and the stress difference on the anisotropy of the ground stress by using the established single-well scale geomechanical model;
seventhly, comprehensively evaluating the multiple factors of the anisotropy of the crustal stress;
the method is characterized in that numerical simulation and geophysical data are combined, the existing geostress anisotropy is evaluated systematically from the angles of structure positions, burial depths, fractures, stress-fracture included angles, main stress, stress differences and reservoir mechanics heterogeneity, and the geostress anisotropy is comprehensively evaluated from three dimensions of zones, blocks and single wells in a plane and a vertical direction.
The invention has the beneficial effects that: and determining the mechanical property of the ultra-deep reservoir and the magnitude and direction of the current ground stress by rock mechanical parameters and ground stress logging calculation and combining a rock triaxial mechanical experiment. By utilizing an ultra-deep reservoir fault and adopting a finite element method, a full-system continuous geomechanical model of the Bozimin-big north region is established, and the three-dimensional distribution of the existing ground stress is accurately predicted; the ground stress anisotropy index is adopted to disclose the current ground stress anisotropy mechanism from the aspects of construction position, burial depth, fracture, stress and crack included angle, rock heterogeneity and the like. Research finds that the buried depth controls the macroscopic distribution rule of the anisotropy of the ultra-deep crustal stress, so that the anisotropy of the crustal stress in a research area is gradually reduced from north to south; the fault trend is nearly vertical to the current horizontal maximum principal stress direction, so that the stress difference coefficient near the fault is a low value; in addition, the included angle between the crack and the stress can obviously control the distribution rule of the ground stress anisotropy, and the heterogeneity of the mechanical properties of the reservoir has small influence on the ground stress anisotropy. The research result has reference value for guiding the optimization of the engineering dessert of the ultra-deep reservoir, the design of the well track of the well and the fracturing modification. The invention provides a comprehensive multi-factor evaluation method for the anisotropy of the ground stress, which has higher practical value, low prediction cost and strong operability, can greatly reduce the expenditure of manpower and financial resources, and has reference value for guiding the exploration and development of oil and gas in an ultra-deep reservoir and the construction of a gas storage reservoir according to the prediction result.
Drawings
Fig. 1 is a flowchart of a method for comprehensively evaluating multiple factors of geostress anisotropy in an embodiment of the invention.
FIG. 2 is a diagram of the stratigraphic structure of the structural features and the target layer of the research area in the embodiment of the invention: (a) carat Su Gouzao tape build position; (b) a basement south-north geological profile; (c) baschikungular group stratigraphic structures.
Fig. 3 is a geomechanical parameter logging explanation of a bosun 1203 well in the embodiment of the invention.
FIG. 4 shows crack growth characteristics of different filling degrees in Bozi-Dabei region in the embodiment of the present invention.
FIG. 5 is a discrete network model of region of interest fragmentation in an embodiment of the present invention.
Fig. 6 is a geomechanical modeling process of bocui-northland area in an embodiment of the present invention.
Fig. 7 shows the present stress field numerical simulation result of the bocui 12 block in the embodiment of the present invention: (a) minimum principal stress; (B) intermediate principal stresses; (C) maximum principal stress.
FIG. 8 is the distribution of the anisotropy of the geostress when the fracture strike is parallel to the horizontal maximum principal stress in an embodiment of the invention: (A) no crack development; (B) the crack density is 0.067 strips/m; (C) crack density 0.013 stripes/m.
FIG. 9 shows the distribution of the anisotropy of the crustal stress when the fracture strike is perpendicular to the horizontal maximum principal stress in an embodiment of the present invention: (A) no crack development; (B) crack density 0.067 stripes/m; (B) the crack density was 0.013 stripes/m.
FIG. 10 is a graph showing the relationship between the stress difference coefficient and the angle β between the horizontal principal stress direction and the crack orientation in the embodiment of the present invention.
FIG. 11 is a graph showing the effect of reservoir heterogeneity on the anisotropy of geostress in an embodiment of the present invention: (A) model A, young's modulus 27GPa; (B) Young's modulus distribution range 24-30GPa; (C) the Young's modulus distribution range is 21-33GPa.
FIG. 12 shows the anisotropy index K of the ground stress and the ground stress in the embodiment of the present invention h The relationship between: (A) Horizontal minimum principal stress S hmin And K h The relationship of (1); (B) Vertical principal stress S v And K h Relation (C) horizontal maximum principal stress S Hmax And K h Relationship (D) horizontal stress difference and K h The relationship (2) of (c).
Fig. 13 is a distribution rule of the horizontal stress difference coefficient in the borzim-northeast region in the embodiment of the present invention.
Fig. 14 is a comparative analysis of the simulation results of the stress anisotropy coefficient of the bocui 12 block in the embodiment of the present invention.
Detailed Description
The following description of the embodiments of the present invention refers to the accompanying drawings:
FIG. 1 is a specific implementation flow of a comprehensive multi-factor evaluation method for the anisotropy of the ground stress. The Kela Su Gouzao belt in the research area is located in the north of the depression of the Tarim basin garage, is a broken wrinkle belt spreading in the east-west directions, has the characteristics of east-west segmentation and south-north splitting, is known as strong extrusion and large deformation, and has an exploration area of about 4800km 2 . The Clara Su Gouzao band is divided into Kyor, dabei, bocumin and Arwatt zones from east to west. The Clar Su Gouzao zone has a complete oil-gas-containing system, has great deep-layer-ultra-deep-layer oil-gas potential and is a region-closed mucartate layer in the ancient system; the south part of the Clara Su Gouzao is adjacent to the hydrocarbon-producing recess, the development of the Chalk system Bashiki-Kjeldahl group is reversed to push the structure to be enclosed, the storage cover combination develops well, and the geological condition of the reservoir is good. A series of long shingles develop in the north and south directions of Bozi in the research area, and the extrusion strength gradually weakens from the north to the south; the salt layer is taken as a boundary and divided into 3 structural layers in the longitudinal direction: structural layer on salt (E) 2 s-Q), salt structural layer (E) 1-2 km), sub-salt structural layer (T-K). Under the conditioning action of the cream-salt rock stratum, the deformation of the salt-upper stratum is mainly caused by faults and related folds thereof, and the salt-lower stratum formsCommon mountain front structure patterns such as a series of anticlines, broken anticlines and burst structures, and common structure combinations such as a double structure, a stacking structure and a wedge-shaped structure, wherein salt layers form salt-related structures such as salt pillows and salt dunes (figure 2).
Logging and explaining the first ground stress and rock mechanical parameters;
the logging information is used for explaining the rock mechanical parameters, and the related calculation formula is as follows:
S c ＝E d [0.008V sh +0.0045(1-V sh )] (3)
in formulas (1) to (3), E d The dynamic Young's modulus of elasticity of rock is MPa; mu.s d Is Poisson's ratio and is dimensionless; s c Uniaxial compressive strength, MPa; v sh The mud content is percentage, and has no dimension; rho b Is rock density, kg/m 3 ；Δt p And Δ t s Respectively longitudinal wave time difference and transverse wave time difference, mu s/ft;
and (3) calculating the horizontal principal stress by using logging data:
in formulas (4) to (5), S hmin 、S Hmax Respectively horizontal minimum and maximum principal stress, MPa; v is the static Poisson's ratio, σ v Is overburden pressure, MPa; alpha is the Biao elastic coefficient and is dimensionless; p p Pore pressure, MPa; e is the static Young's modulus, MPa; epsilon x And epsilon y The strain in the direction of the minimum horizontal main stress and the strain in the direction of the maximum horizontal main stress are respectively and dimensionless; epsilon x And epsilon y Mainly used for characterizing the extra horizontal ground stress generated by the construction stress, and is dimensionless;
by utilizing the formula, as shown in fig. 3, dynamic mechanical parameters of the rock are obtained through calculation, rock uniaxial compression test, triaxial compression test and logging data calculation are comprehensively utilized, rock mechanical parameters of a target layer, a cream salt layer and a stratum on salt in a research area are determined through uniaxial-triaxial correction and dynamic-static correction, and a mechanical model of the Bozi-Dabei area is established on the basis of the rock mechanical parameters.
As shown in fig. 3, the magnitude of the horizontal principal stress is calculated by using a stress calculation formula, and the current minimum horizontal principal stress has an average value of 140MPa, and a stress delamination phenomenon is obvious in the longitudinal direction. The lower part of the two sections of the baschique group and the Brazil reorganization is a low stress section. The gradient of the horizontal minimum principal stress is 2.15SG, and the gradient of the horizontal maximum principal stress is 2.5-2.7SG; from north to south, the burial depth gradually increases, the absolute value of the gas reservoir stress increases, but the stress gradient gradually decreases, the difference of the stress values is increased by the depth difference, and the gradient of the gas reservoir internal stress is approximate.
Modeling a second fractured discrete network;
the crack development types of different sections have obvious difference, and the Bozi section mainly takes development shear cracks as the main part, the inclination angle mainly takes high-angle cracks and then takes vertical cracks as the secondary part. As shown in fig. 4, filling gaps are few in the research area, and core observation of layer position cracks including open gaps, closed gaps, half-open gaps and the like in the research area indicates that the kela Su Gouzao zone develops shear cracks with different filling degrees and different scales. In the aspect of crack filling degree, the structural crack filling degree of the big north area is integrally higher, and three types of cracks, namely full filling, half (local) filling and unfilled, can be seen; the full filling degree of the botminum area is low, and the crack effectiveness is high. The research area is strongly extruded, so that the target layer cracks develop, and the method has the characteristics of high angle, opening and multi-stage cutting; fracture development is the key to the stimulation of deep-ultra deep reservoirs, and leads to anisotropy of the mechanical properties of the reservoirs.
And (3) determining the natural fracture distribution by using the thin slice and core observation and imaging logging, and establishing a fracture discrete network model (figure 5) by combining the distribution of the fault.
Thirdly, establishing a ground stress anisotropy characterization parameter;
establishing the ground stress anisotropy index K h Characterizing the stress anisotropy of the earth, the calculation formula is as follows:
in the formula (6), S hmin 、S Hmax The horizontal minimum and maximum principal stress, MPa, respectively.
Performing geomechanical multi-scale modeling on a fourth reservoir;
and (3) calculating dynamic mechanical parameters of the rock by using array acoustic logging, and obtaining vertical distribution of the static mechanical parameters of the single-well rock by combining rock triaxial mechanical experiment results and through rock dynamic and static mechanical parameter conversion. And establishing a surface model (figure 6B) by combining the point cloud distribution (figure 6A) of the target horizon in the research region, determining the cutting relation between the bedding surface and the fault (figure 6C), and establishing a finite element model (figure 6D). And dividing a ground stress grid by combining rock mechanical parameters of different layers, and establishing a full-layer geomechanical model of the research area (shown in figures 6E-F). The existing ground stress value obtained by utilizing the well logging information interpretation is a numerical value of a single well point and is influenced by factors such as structural fluctuation, and the single well ground stress value cannot be directly applied to a mechanical model as a regional stress load, but needs to be fitted through numerical simulation so as to obtain a proper regional ground stress value. The regional ground stress value is finally determined by mainly depending on the determined key well ground stress, combining the actual geological condition of a research area and utilizing a linear superposition principle through repeated inversion fitting. Because of the complexity of stress distribution, the boundary conditions during numerical simulation are difficult to accurately set at one time, so that the numerical simulation of the ground stress field is actually a process of repeatedly calculating and correcting for multiple times in forward modeling and inversion. The inversion standard is that the error between the numerical simulation result of the key well ground stress and the actual measurement result is minimum, and two aspects of stress azimuth and stress magnitude are considered. Finally, a horizontal minimum principal stress of 145MPa is applied to the north east-south west boundary of the model, a horizontal maximum principal stress of 168MPa is applied to the north east-south east boundary, and a vertical stress is applied to the top of the model (fig. 6G); and finally obtaining the three-dimensional distribution of the stress field of the connecting piece in the complex structure area. Respectively establishing a geomechanical model (figure 7) with a zone, a block and a single well scale by utilizing a constructional diagram and combining with the university of rock mechanical parameters; in order to systematically reveal the mechanism of influence of the earth stress anisotropy, the earth stress anisotropy mechanism is mainly analyzed through numerical simulation and geophysical data. According to a target horizon Bashki-Chick group structural diagram of a research area, a zone scale geomechanical model is established, and the influence of different factors on the ground stress anisotropy is comprehensively analyzed. The influence of the buried depth and the large fault on the anisotropy of the ground stress is analyzed by establishing a big connected piece model of Bozi Dabei. The bocui 12 block is a double-anticline structure, and the structural form is very complex, so the influence of the structural position and form on the anisotropy of the ground stress is analyzed by utilizing the block scale geomechanical model.
And fifthly, establishing geomechanical models with different fracture densities.
Establishing a geomechanical model of a fractured rock mass by combining a fracture discrete network model, endowing different mechanical parameters to the unit body in different directions, and analyzing the changes of the rock mass stress magnitude and the ground stress anisotropy caused by fracture density; and analyzing the influence of the included angle between the crack and the stress on the anisotropy of the ground stress by adjusting the boundary condition of the model.
As shown in fig. 8, stress field simulation in borzi-northeast region indicates that the stress difference coefficient near the fault is a low value, which is less than 0.03, i.e. the stress difference near the fault is a low value, which approaches to 0; the stress coefficient near the fault in the study area is low, which may be a nearly vertical correlation between the fault orientation in the study area and the present earth stress, and the earth stress anisotropy coefficient is high when the fault orientation is nearly parallel to the horizontal minimum principal stress orientation. As shown in fig. 8, when the crack trend is nearly parallel to the horizontal maximum principal stress direction, the crack changes the distribution rule of the ground stress anisotropy of the bocui 12 block; when the crack does not develop, the ground stress anisotropy is mainly controlled by the structural form, the core part has a high value, and the wing part has a low value; when the crack develops, the high value zone of the ground stress anisotropy is mainly distributed along the axis.
As shown in fig. 9, the crack density and the force slit angle are important factors for strong anisotropy in the study region, and when the force slit angle is large, the ground stress anisotropy is weakened along with the development of cracks, and the value is low along the anticline. When the crack develops, the low value zone of the ground stress anisotropy is mainly distributed along the axis. When the horizontal maximum main stress and the back slope are intersected at a large angle, the horizontal stress difference coefficient of the connected back slope axis is large in change, the crack growth rule is more complex, and the stress difference coefficient of the south wing and the north wing is small. When the horizontal maximum main stress and the back slope are intersected at a large angle, the peak of the connected back slope is a high value, and the valley is a low value.
And simulating the influence of the included angle between the horizontal main stress direction and the crack direction on the anisotropy coefficient of the ground stress by changing the direction of the boundary stress of the model. As shown in fig. 10, the stress difference coefficient is the largest when the horizontal maximum principal stress is parallel to the axis; the stress difference coefficient is the smallest when the horizontal maximum principal stress is perpendicular to the axis. It is found that the fracture development and the force seam angle are important reasons for strong anisotropy in a research area, when the force seam angle is small, the ground stress anisotropy is enhanced along with the further development of cracks, and the value of the wing part is high and the value of the wing part is low on the anticline.
Sixthly, establishing geomechanical models with different mechanical heterogeneous degrees;
by establishing a big north 14 block model and combining deposition phase change, mechanical parameters are set to decrease from west to east, and the influence of the change of the mechanical parameters of the rock on the anisotropy of the ground stress is simulated. And respectively establishing a homogeneous model and a heterogeneous model in the simulation, and analyzing the influence of the change of the rock mechanical parameters on the stress. And simulating the influence of a reservoir with rock mechanics heterogeneous degree on the ground stress anisotropy by utilizing the established geomechanical model of the big north 14 block and writing a computer program. Embedding different normally distributed models into a geomechanical model through computer programming; and (3) setting mechanical parameters to be decreased from west to east in combination with deposition phase change, and simulating the influence of the change of the mechanical parameters of the rock on the anisotropy of the ground stress. As shown in fig. 11, in homogeneous reservoirs, the geostress anisotropy is primarily dominated by the formation morphology. In heterogeneous reservoirs, the geostress anisotropy is primarily controlled by the heterogeneity of the reservoir; from the frequency distribution of the ground stress anisotropy, the degree of anisotropy does not greatly affect the ground stress anisotropy (fig. 11A-C).
As shown in fig. 12, the relationship between the geostress and the geostress anisotropy index is analyzed using single well scale geomechanical modeling results; the statistical result shows that the horizontal main stress and the vertical main stress are in a negative correlation relationship with the ground stress anisotropy index, wherein the correlation between the horizontal minimum main stress and the ground stress anisotropy index is the largest, and the correlation between the horizontal maximum main stress and the ground stress anisotropy index is the weakest. It was found that the horizontal stress difference has little relation to the ground stress anisotropy index, which is substantially consistent with the results of Liu et al (2017) [ Liu, J., ding, W., yang, H., wang, R., yin, S., li, A., & Fu, (2017). 3D geometrical modeling and numerical association of in-situ stress fields in short stresses: a case study of the lower Cambrian Nitutiand formation in the Cen' g block, south China. The reason why the horizontal stress difference has little relation with the ground stress anisotropy index may be that the buried depth span of the tight sandstone in the research area is large, the buried depth of the target layer in the research area is 4500-8100m, and the depth span range of the research area is about 3600m.
Seventhly, comprehensively evaluating the multiple factors of the anisotropy of the crustal stress;
the method is characterized in that numerical simulation and geophysical data are combined, the existing geostress anisotropy is evaluated systematically from the angles of structure positions, burial depths, fractures, stress-fracture included angles, main stress, stress differences and reservoir mechanics heterogeneity, and the geostress anisotropy is comprehensively evaluated from three dimensions of zones, blocks and single wells in a plane and a vertical direction.
As shown in fig. 13, the ground stress anisotropy is a key factor for controlling the efficient drilling and development of the ultra-deep reservoir; the extrusion direction and the paste-salt layer distribution jointly control the ground stress anisotropy of different structural positions, so that the stress difference coefficient of a anticline core part is large, and the stress difference coefficient of a wing part is low; the buried depth controls the macroscopic distribution rule of the anisotropy of the ultra-deep layer ground stress, and the two are in a linear negative correlation relationship. The fault of the research area is nearly vertical to the horizontal maximum main stress direction, so that the stress anisotropy index near the fault approaches 0. The horizontal main stress, the vertical main stress and the ground stress anisotropy index are in a negative correlation relationship, wherein the correlation between the horizontal minimum main stress and the ground stress anisotropy index is the largest, the correlation between the horizontal maximum main stress and the ground stress anisotropy index is the weakest; the horizontal stress difference has little relation with the ground stress anisotropy index, and the heterogeneity of the reservoir mechanical properties has little influence on the ground stress anisotropy.
Calculating the anisotropy of the stress field of the Bozi 12 blocks by utilizing the established Bozi 12 block fine geomechanical model; as shown in fig. 14, for comparison of the simulation results and the actual results of different wells, the earth stress anisotropy is substantially consistent between different wells, wherein the error of the Bz1201 well is the largest and is about 0.025, and the errors of the other three wells are smaller and are less than 0.01. Therefore, the simulation result is accurate and reliable, and the analysis result of the ground stress anisotropy is reliable.
The present invention has been described above by way of example, but the present invention is not limited to the above-described specific embodiments, and any modification or variation made based on the present invention is within the scope of the present invention as claimed.
Claims (2)
1. A multi-factor comprehensive evaluation method for geostress anisotropy is characterized by comprising the following steps:
logging and explaining the first ground stress and rock mechanical parameters;
the logging information is used for explaining the rock mechanical parameters, and the related calculation formula is as follows:
S c ＝E d [0.008V sh +0.0045(1-V sh )] (3)
in formulas (1) to (3), E d The dynamic Young's modulus of elasticity of rock is MPa; mu.s d Is Poisson's ratio and is dimensionless; s c Uniaxial compressive strength, MPa; v sh The mud content is percentage, and has no dimension; rho b Is rock density, kg/m 3 ；Δt p And Δ t s Respectively longitudinal wave time difference and transverse wave time difference, mu s/ft;
and (3) calculating the horizontal principal stress by using logging data:
in formulas (4) to (5), S hmin 、S Hmax Respectively horizontal minimum and maximum principal stress, MPa; v is the static Poisson's ratio, σ v Is overburden pressure, MPa; alpha is the Biao elastic coefficient and is dimensionless; p p Pore pressure, MPa; e is the static Young's modulus, MPa; epsilon x And epsilon y The strain in the direction of the minimum horizontal main stress and the strain in the direction of the maximum horizontal main stress are respectively and dimensionless; epsilon x And epsilon y Mainly used for characterizing the extra horizontal ground stress generated by the construction stress, and is dimensionless;
modeling a second fractured discrete network;
determining large-scale fault distribution through seismic interpretation, and determining the position of a medium-scale fault based on the repetition of the stratum in the drilling process; determining the development position of the small fault through the dislocation of the streak layer and the change of the stratum inclination angle in the imaging logging;
determining natural fracture development characteristics through slice and core observation and imaging logging; determining the fracture development characteristics of different sizes of the rock core, including fracture appearance, mechanical properties, set system and filling property, by utilizing coring data and grinding corresponding slices; combining and comprehensively interpreting the inversion images by using resistivity static images and dynamic images and imaginary part images of the button electrodes and the borehole wall stratum gap, and identifying Zhang Kaifeng and a closed seam; for Zhang Kaifeng, due to oil based mud filling, the resistivity image shows a bright color along the fracture face, representing a high resistance feature; the image of the gap between the electrode and the well wall stratum displays dark color and is characterized by larger gap distance; for a closed seam, a dark color or a bright color is displayed on the resistivity image along the surface of the seam, and meanwhile, the electrode and the borehole wall stratum gap image displays a bright color or the same color as that of the surrounding rock and shows a characteristic of no gap basically; determining the development characteristics of the imaging logging fracture in the research area by the method;
determining natural fracture spread by utilizing slice and core observation and imaging logging, and establishing a fracture discrete network model by combining fault distribution;
thirdly, establishing a ground stress anisotropy characterization parameter;
establishing the ground stress anisotropy index K h Characterizing the stress anisotropy of the earth, the calculation formula is as follows:
in the formula (6), S hmin 、S Hmax Respectively horizontal minimum and maximum principal stress, MPa;
performing geomechanical multi-scale modeling on a fourth reservoir;
respectively establishing a zone, a block and a single-well-scale geomechanical model by using a constructional diagram and combining the rock mechanical parameter university;
fifthly, establishing geomechanical models with different fracture densities;
establishing a geomechanical model of a fractured rock mass by combining a fracture discrete network model, endowing different mechanical parameters to the unit body in different directions, and analyzing the changes of the rock mass stress magnitude and the ground stress anisotropy caused by fracture density; analyzing the influence of the included angle between the crack and the stress on the anisotropy of the ground stress by adjusting the boundary condition of the model;
sixthly, geomechanical models with different mechanical heterogeneous degrees are established;
setting a mechanical parameter decreasing rule by using the established block scale geomechanical model and combining with deposition phase change, and simulating the influence of the change of rock mechanical parameters on the ground stress anisotropy; respectively establishing a homogeneous model and a heterogeneous model in the simulation, and analyzing the influence of the change of the rock mechanical parameters on the stress; analyzing the influence of the main stress and the stress difference on the anisotropy of the ground stress by using the established single-well scale geomechanical model;
seventhly, comprehensively evaluating the multiple factors of the anisotropy of the crustal stress;
the method is characterized in that numerical simulation and geophysical data are combined, the existing geostress anisotropy is evaluated systematically from the angles of structure position, burial depth, fracture, included angle between stress and fracture, main stress, stress difference and mechanical heterogeneity of a reservoir, and the geostress anisotropy is comprehensively evaluated from three dimensions of zones, blocks and single wells in a plane and a vertical direction.
2. The method of claim 1, wherein the creating a zonal, and single-well-scale geomechanical model comprises:
the geomechanical model with the zone scale is a geomechanical model with a plurality of shingled structures connected in a sheet mode and is used for analyzing the influence of the buried depth and the fault on the anisotropy of the ground stress; the geomechanical model of the block scale is a geomechanical model of a single laminated structure and is used for analyzing the influence of stress and crack included angles, cracks and reservoir mechanics heterogeneity on the ground stress anisotropy; the single-well-scale geomechanical model is a one-dimensional geomechanical model established based on single-well mechanical parameters and used for analyzing the influence of main stress and stress difference on the anisotropy of the ground stress.
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| CN117074171A (en) * | 2023-07-21 | 2023-11-17 | 中国矿业大学(北京) | Deep coal rock stress field coupling induced coal rock instability early warning method |
| CN118134914A (en) * | 2024-05-06 | 2024-06-04 | 中国科学技术大学 | Ground stress intelligent interpretation processing method based on borehole wall geometry |
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| CN117074171A (en) * | 2023-07-21 | 2023-11-17 | 中国矿业大学(北京) | Deep coal rock stress field coupling induced coal rock instability early warning method |
| CN117074171B (en) * | 2023-07-21 | 2024-03-08 | 中国矿业大学(北京) | Deep coal rock stress field coupling induced coal rock instability early warning method |
| CN118134914A (en) * | 2024-05-06 | 2024-06-04 | 中国科学技术大学 | Ground stress intelligent interpretation processing method based on borehole wall geometry |
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