Method for determining crustal stress direction

Abstract

The invention provides a method for determining a crustal stress direction, and belongs to the field of geomechanics. The method comprises the following steps: collecting core data, logging data and geochemical data, identifying deposition characteristics, a sequence interface and single well lithology of a to-be-analyzed area, carrying out rock mechanical parameter logging interpretation, establishing a rock dynamic-static mechanical parameter conversion model, and determining single well rock mechanical parameter distribution of a target area; rock core observation and imaging logging interpretation are carried out through rock core data and logging data, the trend distribution rule of cracks in the vertical direction is determined, and the fast transverse wave orientation is further determined; and establishing a corresponding relation model between the fast transverse wave orientation and the trend distribution rule of the vertical crack, and establishing a ground stress direction discrimination standard to realize the determination of the ground stress direction. Compared with the prior art, the method for judging the direction of the maximum principal stress suitable for a complex structural area and a complex lithologic section is provided.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of geomechanics, and particularly relates to a method for determining the direction of in-situ stress. BACKGROUND

[0002] The field of oil and gas development gradually shifts to deep, complex and unconventional formations, increasing the difficulty of oil and gas development. In the exploration and development of oil and gas, the boundaries between geology and engineering are gradually blurred, and an integrated evaluation theory and method of geological and engineering sweet spots has gradually formed. Reservoir geomechanics modeling, as a key bridge and tool for converting from geological sweet spots to engineering sweet spots, also forces it to further improve technical methods and expand research fields.

[0003] In-situ stress research runs through the entire oil and gas exploration and development: (1) In the early stage of oil and gas exploration, the main applications include prediction of formation pressure, evaluation of fault sealing, and prediction of oil and gas column height; (2) In the drilling stage, the main applications include wellbore stability optimization, horizontal well drilling trajectory design, and fracture permeability tensor prediction; (3) In the early development stage, the applications include optimization of completion methods, development well pattern design, hydraulic fracturing simulation and prediction, and simulation of reservoir dynamic parameters during formation energy attenuation; (4) In the secondary and tertiary development stages, the main applications include developing a reasonable water injection scheme and optimizing a steam injection scheme.

[0004] The complexity of rock makes it impossible to accurately determine the magnitude and direction of in-situ stress; therefore, it is necessary to address the variations and uncertainties in stress measurement results and conduct detailed screening and diagnosis in the study of in-situ stress direction.

[0005] Various integrated methods can be used in the prior art to determine the stress state of a reservoir.

[0006] For example, the invention patent CN113868976B discloses a method for determining the magnitude of in-situ stress in a well, which calculates the magnitude of in-situ three-dimensional stress of each single well by using the water pressure fracturing method. By plotting the relationship between arrival time and ringing count, cumulative energy, and load, it can be seen that there are multiple obvious mutation points on the arrival time and cumulative energy curve, each mutation point represents a rock fracture, and each Kaiser point corresponds to a rock acoustic emission Kaiser point. The three-dimensional stress values calculated at each Kaiser point are compared with the in-situ stress magnitude values determined by the water pressure fracturing method, and the most similar group is selected as the in-situ stress magnitude. The invention overcomes the shortcomings of the traditional regional stress evolution method and acoustic emission waveform analysis method in reflecting the Kaiser effect point of in-situ stress magnitude, which is complicated and difficult to quantitatively identify, improves the acoustic emission in-situ stress magnitude calibration precision, has good application effect and strong application value, and provides a basis for later exploration and well drilling.

[0007] Cross-dipole logging is a potential logging method in anisotropy and in-situ stress detection. The existing technology has been applied, such as the invention patent CN113504569B provides a method, system, equipment and medium for identifying and evaluating rock mass weak surface by array acoustic logging. The method comprises: using an automatic gain recovery coefficient to recover the gain of the collected array acoustic logging waveform data; using a variation function to statistically process the array acoustic logging waveform data after gain recovery; the waveform data after statistical variation processing is gray-mapped in a variable density manner to draw a first waveform variable density graph after statistical variation processing, and the position and size of the rock mass weak surface are displayed on the first waveform variable density graph; and calculating a rock mass weak surface representation index, and evaluating the rock mass weak surface based on the rock mass weak surface representation index.

[0008] Currently, the cross-dipole logging method is to combine the cross-dipole instrument with the monopole acoustic wave, which includes the function of the traditional array acoustic logging.

[0009] And array acoustic logging is an effective and practical method for determining stress tensor. Because the tectonic stress causes the difference of the horizontal principal stress in the crust, the drilling changes the natural balance of the stress in the well wall and causes the tangential stress to concentrate on the well wall perpendicular to the maximum horizontal principal stress. When the tangential stress reaches or exceeds the rock strength limit, the rock will produce micro-cracks. The shear wave mainly propagates in two directions; the fast shear wave propagates along the crack direction and propagates faster, while the slow shear wave propagates perpendicular to the crack direction and propagates slower. The existence of shear wave splitting in the local layer indicates that the shear wave anisotropy is related to the change of the fast shear wave speed and the slow shear wave speed; therefore, the shear wave splitting can be represented by the shear wave anisotropy.

[0010] But if the shear wave anisotropy is caused only by the in-situ stress, and the fast shear wave direction is consistent with the direction of the horizontal maximum principal stress, the value of the horizontal principal stress can also be determined by the stress-velocity equation.

[0011] It can be seen that it is difficult to determine the direction of the present-day stress in many cases by directly using array acoustic logging.

[0012] With the application of array acoustic logging in the field, how to fully utilize the obtained array acoustic logging data and fully play the role of array acoustic logging in determining the stress tensor, an improved method for determining the stress direction is expected. SUMMARY

[0013] The present application provides a method for determining the stress direction, which can be used to identify the present-day horizontal maximum principal stress direction in complex tectonic areas and complex lithology sections, to solve the problem of lacking a means for determining the stress direction by array acoustic logging in the prior art.

[0014] To achieve the above object, the technical scheme adopted by the present application is as follows:

[0015] A method for determining the direction of ground stress, comprising the following steps:

[0016] S1. Collecting core data, logging data and geochemical data of the area to be analyzed;

[0017] S2. Identifying the sedimentary characteristics, sequence interface and single-well lithology of the area to be analyzed based on the core data, logging data and geochemical data collected in step S1;

[0018] S3. Carrying out rock mechanics parameter logging interpretation based on the logging data collected in step S1, establishing a rock dynamic-static mechanics parameter conversion model, and determining the single-well rock mechanics parameter distribution of the target area;

[0019] S4. Determining the strike distribution of vertical fractures by core observation and imaging logging interpretation on the core data and logging data collected in step S1;

[0020] S5. Determining the fast shear wave orientation based on the logging data collected in step S1;

[0021] S6. Establishing a corresponding relationship model between the fast shear wave orientation and the strike distribution of vertical fractures according to the single-well lithology identified in step S2, the single-well rock mechanics parameter distribution determined in step S3, the strike distribution of vertical fractures determined in step S4, and the fast shear wave orientation determined in step S5;

[0022] S7. Identifying the natural fracture strike and the fast shear wave orientation based on the corresponding relationship model between the fast shear wave orientation and the strike distribution of vertical fractures established in step S6, determining the thickness and rock mechanics properties of the rock layer section where the natural fracture strike and the fast shear wave orientation are inconsistent, establishing a ground stress direction discrimination standard, and realizing the determination of the ground stress direction.

[0023] Preferably, the logging data in step S1 includes logging curves, energy spectrum curves and imaging logging data.

[0024] Preferably, the means for obtaining the logging data in step S1 is array acoustic logging.

[0025] Preferably, the method for identifying the sedimentary characteristics, sequence interface and single-well lithology of the area to be analyzed in step S2 comprises the following steps:

[0026] ① Identifying the sedimentary characteristics of the area to be analyzed according to the logging curves, imaging logging data and core data;

[0027] ② According to the logging curve, imaging logging data, core data, energy spectrum curve and geochemical data, the sequence interface of the region to be analyzed is determined;

[0028] ③ According to the sedimentary characteristics and sequence interface obtained in steps ① and ②, further combined with the imaging logging data and core data, the single-well lithology is identified and interpreted.

[0029] Further preferably, the energy spectrum curve is selected from thorium (TH), potassium (K) and uranium-free gamma (KTH).

[0030] In some embodiments, the method for determining the single-well rock mechanics parameter distribution of the target area in step S3 can be realized by the following process:

[0031] Representative cores are selected, and the cores are processed into rock samples with flat end faces, a diameter of 2.5 cm and a length of 5.0 cm using a drilling machine or a slicing machine device; according to the “Standard for Engineering Rock Mass Test Methods (GB / T 50266-99)”, the rock samples are placed in a high-pressure chamber during the triaxial compression test, different confining pressures are applied around the rock samples, the vertical stress of the rock samples is gradually increased, and the axial and radial strain values of the rock samples are recorded respectively to obtain the corresponding rock stress-strain curve, and the static mechanical parameters of the rock are calculated;

[0032] It should be noted that the rock triaxial mechanics experiment directly simulates the real three-dimensional stress environment underground, and has high measurement accuracy, but is affected by the number of sampling points and the size, and it is difficult to reflect the change range of the reservoir mechanical parameters; the dynamic mechanical parameters of the rock calculated using the logging data can fully consider the continuity of the rock mechanical parameters in the vertical direction, and the related formulas are as follows:

[0033]

[0034] In formulas (1)-(3), E d is the dynamic Young's modulus of the rock, MPa; μ d is the dynamic Poisson's ratio of the rock, dimensionless; ρ b is the rock density interpreted from the logging, kg / m 3 ; Δt p is the longitudinal wave time difference of the rock, μs / ft; Δt s is the transverse wave time difference of the rock, μ s / ft; is the internal friction angle of the rock, which is determined by the rock triaxial mechanics experiment; Φ is the porosity interpreted from the logging, %;

[0035] By calibrating the results of the rock mechanics experiment and the dynamic mechanical parameters interpreted from the logging, a rock dynamic-static mechanical parameter conversion model is established, and the single-well rock mechanics parameter distribution in the study area is determined.

[0036] Preferably, the method for determining the strike distribution of the vertical fractures in step S4 comprises the following steps.

[0037] The core is returned to the original position by using the paleomagnetic method or the rock occurrence method.

[0038] It should be noted that in the present application, the paleomagnetic method is a method for returning the core to the original position by measuring the natural residual magnetism of rocks and some ancient objects, analyzing their magnetization history, studying the characteristics of the geomagnetic field that causes their magnetization, and then returning the core to the original position.

[0039] The spatial orientation of the rock in the earth's crust is called the occurrence of the rock. Due to different sedimentary environments and tectonic movements, the occurrence of the rock can be different. The rock occurrence method is a method for analyzing the characteristics of the rock in which the core is located by analyzing the different occurrences, and then returning the core to the original position.

[0040] It should be noted that the determination of the fast shear wave direction in step S5 comprises the following:

[0041] Shear waves mainly propagate in two directions; fast shear waves propagate along the fracture direction and propagate faster, while slow shear waves propagate perpendicular to the fracture direction and propagate slower. The existence of shear wave splitting in the local layer indicates that shear wave anisotropy is related to the changes in fast shear wave speed and slow shear wave speed; therefore, shear wave splitting can be represented by shear wave anisotropy.

[0042] If the shear wave anisotropy is caused only by the in-situ stress, and the fast shear wave direction is consistent with the direction of the horizontal maximum principal stress, then the value of the horizontal principal stress can also be determined by the stress-velocity equation, and then the fast shear wave direction is determined.

[0043] Preferably, the method for establishing the stress direction discrimination standard in step S7 comprises the following:

[0044] The local stress direction obtained by array acoustic logging is compared with the stress direction obtained from borehole breakouts, well deviation, drilling-induced fractures, hydraulic fractures, and GPS data, as well as the direction of natural fractures.

[0045] Further preferably, the method for comparison is:

[0046] Excluding unreliable stress directions, the exclusion cases are selected from one of the following:

[0047] ① The local stress direction obtained by array acoustic logging is consistent with the direction of natural fractures;

[0048] ② The local stress direction obtained by array acoustic logging is inconsistent with the direction of natural fractures, and is also different from the stress direction obtained from borehole breakouts, well deviation, drilling-induced fractures, hydraulic fractures, and GPS data.

[0049] Most preferably, the establishing method of the geostress direction discrimination criterion further comprises: determining a rock stratum section corresponding to the array sonic logging of the reliable geostress direction, and determining the thickness and rock mechanics properties of the rock stratum section.

[0050] Compared with the prior art, the present application has the following beneficial effects:

[0051] The present application provides a method for discriminating the maximum principal stress direction suitable for complex structure areas and complex lithology sections, 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 significance for reservoir geomechanical modeling, stress field numerical modeling, reservoir fracture prediction and engineering evaluation, etc. BRIEF DESCRIPTION OF DRAWINGS

[0052] Figure 1 It is a lithology interpretation map based on core and logging of the embodiment of the present application;

[0053] Figure 2 It is a rock triaxial mechanics experiment result graph of the embodiment of the present application, wherein the black curve represents a fitting curve segment, and the equation in the graph is obtained by fitting the black segment;

[0054] Figure 3 It is a single well rock mechanics parameter experiment result graph of the embodiment of the present application;

[0055] Figure 4 It is a core fracture observation photo of the embodiment of the present application;

[0056] Figure 5 It is a fast shear wave azimuth and structure fracture interpretation chart of the embodiment of the present application;

[0057] Figure 6 It is a present geostress direction discrimination criterion graph based on lithology, rock mechanics parameters and layer thickness of the embodiment of the present application. DETAILED DESCRIPTION

[0058] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The following definitions are applied to the descriptions and claims herein unless otherwise explicitly provided.

[0059] As used herein, the recitation of one or more items shall not be construed as excluding the presence of others.

[0060] As used herein, the term "about" means a range of ±20% of the value that follows. In some embodiments, the term "about" means a range of ±10% of the value that follows. In some embodiments, the term "about" means a range of ±5% of the value that follows.

[0061] As used herein, numerical ranges are understood to be shorthand for describing each and every value that falls within the range. For example, a range of 1 to 20 is understood to include any number, combination, or sub-range from the group consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20.

[0062] The terms "comprises" or "comprising" as used herein are meant to be interpreted in an open-ended manner, i.e., to include any and all features, elements, integers, steps, or components that are described in the specification, but not limited to those features, elements, integers, steps, or components that are recited in the claims. Thus, the terms "comprises" or "comprising" are not meant to be construed as limiting the term "consisting of. In one embodiment, the term "comprising" as used in the specification and in the claims can be replaced with the term "consisting of.

[0063] The terms "optional", "any", "any of", or "any one of" as used herein means that the subsequently described event or circumstance can or can not occur, and the description includes instances where the event or circumstance occurs and instances where it does not. As used in the present application, "a" and "an" are used in the singular sense to mean one or more than one of the grammatical object of the article.

[0064] The term "and / or", as used herein, is to be taken as a specific interpretation of either one of the items that the term connects or a combination of any two or more of the items that the term connects.

[0065] In order to make the objects, technical solutions and advantages of the present application clearer, the following further describes the present application in conjunction with embodiments. If specific conditions are not indicated in the embodiments, the conditions are implemented according to conventional conditions or conditions suggested by manufacturers. If manufacturers of all reagents or instruments are not indicated, the reagents or instruments are conventional products that can be purchased in the market. In order to better illustrate the present application, numerous specific details are given in the following specific embodiments. The specific embodiments described herein are only used to explain the present application and do not constitute any limitation on the present application. In addition, in the following description, the description of well-known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present application. Such structures and technologies are also described in many publications.

[0066] Embodiment A method for determining the direction of tectonic stress

[0067] At step S1, core data, logging data, and geochemical data of a target area are acquired, the logging data including conventional logging curves, spectral curves, and imaging logging data.

[0068] Next, go to step S2.

[0069] At step S2, the sedimentary characteristics, sequence interface and single-well lithology of the target area are identified, including:

[0070] S201: Identify the sedimentary characteristics of the target area based on imaging logging, conventional logging curves and core data;

[0071] S202: The sequence interface can be determined by imaging logging, conventional logging curves, energy spectrum curves (TH, K, KTH), core data, and geochemical index characteristics;

[0072] S203: Based on the identified sedimentary characteristics and sequence interface, combined with core data and imaging logging data, the sedimentary characteristics are divided and the single-well lithology is identified and interpreted.

[0073] Next, go to step S3.

[0074] At step S3: Based on the logging data of array sonic logging, rock mechanics parameter logging interpretation is carried out, rock dynamic-static mechanics parameter conversion model is established, and single-well rock mechanics parameter distribution of the target area is determined;

[0075] Specifically, representative cores are selected, and the cores are processed into rock samples with flat end faces, a diameter of 2.5 cm and a length of 5.0 cm by using drilling machines, slicing machines and other equipment; and the test is completed according to the “Standard for Engineering Rock Mass Test (GB / T 50266-99)”.

[0076] During the triaxial compression test, the rock sample is placed in a high-pressure chamber, different confining pressures are applied around it, the vertical stress of the rock is gradually increased, and the axial and radial strain values of the rock sample are recorded respectively to obtain the corresponding rock stress-strain curve and calculate the static mechanics parameters of the rock.

[0077] Rock triaxial mechanics experiment directly simulates the real three-dimensional stress environment underground, and has high measurement accuracy, but is affected by the number of sampling points and scale, and it is difficult to reflect the change range of reservoir mechanics parameters; calculating the dynamic mechanics parameters of the rock using logging data can fully consider the vertical continuity of rock mechanics parameters, and the related formulas are as follows:

[0078]

[0079] In formulas (1)-(3), E d is the dynamic Young's modulus of the rock, MPa; μ d is the dynamic Poisson's ratio of the rock, dimensionless; ρ b is the rock density calculated by logging interpretation, kg / m 3 ; Δt p is the longitudinal wave time difference of the rock, μ s / ft; Δts is the shear wave time difference of the rock, μ s / ft; is the internal friction angle of the rock, determined by rock triaxial mechanics experiment; Φ is the porosity interpreted from well logging, %;

[0080] By calibrating the results of rock mechanics experiment and dynamic mechanical parameters interpreted from well logging, a rock dynamic-static mechanical parameter conversion model is established to determine the rock mechanics parameter distribution of single well in the study area.

[0081] Next, go to step S4.

[0082] At step S4: the fracture strike distribution in the vertical direction is determined by core observation and imaging logging interpretation; wherein the core orientation is achieved by paleomagnetic method or rock occurrence method to determine the fracture strike.

[0083] Next, go to step S5.

[0084] At step S5: the fast shear wave direction is determined based on the logging data obtained by array sonic logging.

[0085] Shear waves mainly propagate in two directions; fast shear waves propagate along the fracture direction and propagate faster, while slow shear waves propagate perpendicular to the fracture direction and propagate slower, the existence of shear wave splitting in local layers indicates that shear wave anisotropy is related to the changes of fast shear wave speed and slow shear wave speed; therefore, shear wave splitting can be represented by shear wave anisotropy.

[0086] If shear wave anisotropy is only caused by in-situ stress, and the fast shear wave direction is consistent with the direction of the horizontal maximum principal stress, the value of the horizontal principal stress can also be determined by the stress-velocity equation, and then the fast shear wave direction is determined.

[0087] Next, go to step S6.

[0088] At step S6: the correspondence model between the fast shear wave direction and the fracture strike distribution in the vertical direction is established by using the single well lithology obtained in step S2, the single well rock mechanics parameters obtained in step S3, the fracture strike distribution in the vertical direction obtained in step S4, and the fast shear wave direction obtained in step S110.

[0089] Next, go to step S7.

[0090] At step S7: based on the established correspondence model between the fast shear wave direction and the fracture strike distribution in the vertical direction, the natural fracture strike and the fast shear wave direction are identified, the thickness and rock mechanics properties of the rock layer where the two are inconsistent are determined, the present-day stress direction discrimination standard is established, and the present-day stress direction in the complex structure area is determined based on array sonic logging.

[0091] Next, the method for determining the direction of in-situ stress according to the embodiment of the present application will be described with the southwest region of the Tarim Basin as an example. Figures 1 to 2

[0092] As shown in the figure, the lithology is identified and interpreted based on the imaging logging, conventional logging and core, division and sedimentary characteristics; the sequence interface is determined through the imaging logging data, conventional logging curve and TH, K, KTH energy spectrum curve, lithology characteristics and geochemical index characteristics, and the single-well lithology is identified and interpreted in combination with the core, imaging logging, division and sedimentary characteristics. Figure 1

[0093] As shown in the figure, representative cores are selected, and the cores are processed into rock samples with flat end faces, a diameter of 2.5 cm and a length of 5.0 cm by using a drilling machine, a slicing machine and other equipment; and the test is completed according to the Standard for Engineering Rock Mass Test Methods (GB / T 50266-99). In the triaxial compression test process, the rock sample is placed in a high-pressure chamber, different confining pressures are applied around the rock sample, the vertical stress of the rock sample is gradually increased, and the strain values of the rock sample in the axial direction and the radial direction are recorded respectively to obtain the corresponding rock stress-strain curve and calculate the static mechanical parameters of the rock. The rock triaxial mechanical test directly simulates the real three-dimensional stress environment underground, and has high measurement accuracy, but is difficult to reflect the change range of the mechanical parameters of the reservoir due to the influence of the number and scale of the sampling points; the dynamic mechanical parameters of the rock calculated by using the logging data can fully consider the continuity of the mechanical parameters of the rock in the vertical direction, and the related formulas are as follows: Figure 2

[0094]

[0095] In formulas (1)-(3), E d is the dynamic Young's modulus of the rock, MPa; μ d is the dynamic Poisson's ratio of the rock, dimensionless; ρ b is the rock density interpreted from the logging, kg / m 3 ; Δt p is the longitudinal wave time difference of the rock, μs / ft; Δt s is the transverse wave time difference of the rock, μs / ft; is the internal friction angle of the rock, which is determined by the rock triaxial mechanical test, °; and Φ is the porosity interpreted from the logging, %.

[0096] As shown in the figure, the rock dynamic-static mechanical parameter conversion model is established through the calibration of the dynamic mechanical parameter results of the rock mechanical test and the logging interpretation, and the distribution of the rock mechanical parameters of the single well in the study area is determined. Figure 3

[0097] As shown in the figure, the representative cores are selected, and the cores are processed into rock samples with flat end faces, a diameter of 2.5 cm and a length of 5.0 cm by using a drilling machine, a slicing machine and other equipment; and the test is completed according to the Standard for Engineering Rock Mass Test Methods (GB / T 50266-99). In the triaxial compression test process, the rock sample is placed in a high-pressure chamber, different confining pressures are applied around the rock sample, the vertical stress of the rock sample is gradually increased, and the strain values of the rock sample in the axial direction and the radial direction are recorded respectively to obtain the corresponding rock stress-strain curve and calculate the static mechanical parameters of the rock. The rock triaxial mechanical test directly simulates the real three-dimensional stress environment underground, and has high measurement accuracy, but is difficult to reflect the change range of the mechanical parameters of the reservoir due to the influence of the number and scale of the sampling points; the dynamic mechanical parameters of the rock calculated by using the logging data can fully consider the continuity of the mechanical parameters of the rock in the vertical direction, and the related formulas are as follows: Figure 4 ​​​​The fracture azimuth distribution in the vertical direction is determined by core observation and imaging logging interpretation. The core orientation is achieved by paleomagnetic method or stratum occurrence method, and then the fracture azimuth is determined.

[0098] Based on the fast shear wave azimuth determined by array sonic logging, the shear wave mainly propagates in two directions. The fast shear wave propagates along the fracture direction and propagates faster, while the slow shear wave propagates perpendicular to the fracture direction and propagates slower. The existence of shear wave splitting in the local layer indicates that the shear wave anisotropy is related to the change of fast shear wave velocity and slow shear wave velocity. Therefore, the shear wave splitting can be represented by shear wave anisotropy. If the shear wave anisotropy is caused only by in-situ stress, and the fast shear wave azimuth is consistent with the direction of the horizontal maximum principal stress, the value of the horizontal principal stress can also be determined by the stress-velocity equation.

[0099] As shown in Figure 5 , the fast shear wave azimuth and tectonic fracture interpretation chart are established by using the interpreted lithology, rock mechanics parameters, tectonic fracture azimuth and fast shear wave azimuth. The azimuth of natural fractures and in-situ stress in different sections can be accurately determined in the tectonic fracture interpretation chart. Figure 5 The comparison of the natural fracture azimuth angle obtained by different depth imaging logging and the fast shear wave azimuth angle obtained by array sonic logging shows that the direction of natural fractures in sections A, B and C (thick mudstone, >8.0m) is not consistent with the azimuth angle of fast wave, which is in the NW-SE (140°-150°) direction, and the direction of fast wave is suspected to be the direction of the maximum principal stress. The fast wave azimuth angle of sections D and E (thinner mudstone, <8.0m), F (thick shale, >10.0m) and G (thick limestone, >10.0m) is in the NW-SE (30°-50°) direction, and the determined in-situ stress direction is unreliable, and the present stress direction cannot be determined.

[0100] Based on the established fast shear wave azimuth and tectonic fracture interpretation chart, the natural fracture azimuth and fast shear wave azimuth are identified, the thickness and rock mechanics properties of the rock layer where the two are inconsistent are determined, the present in-situ stress direction discrimination standard is established, and the in-situ stress direction in complex tectonic area is determined based on array sonic logging.

[0101] As shown in Table 1, according to array sonic logging, the direction of the fast shear wave is NE-SW (30°-40°). However, the local stress direction obtained from this fracture sonic logging is inconsistent with the stress direction obtained from borehole fracture, well deviation, drill-induced fracture, hydraulic fracture, and GPS data, but consistent with the direction of natural fractures (Table 1). The horizontal maximum principal stress azimuth angle measured in a single well using the differential strain method shows good consistency, indicating that the principal azimuth angle of the horizontal maximum principal stress is NW to NWW, with NWW being the principal direction. A caliper analysis was performed to determine the spatial pattern of the average SHmax azimuth around the borehole; the results based on the six-arm caliper logging data indicate that the main borehole breakthrough direction is NNE-SSW (10°-20°). Therefore, according to the in-situ stress principle determined by borehole fracture, the direction of the horizontal maximum principal stress is NWW-SEE (100°-110°). For vertical well drilling, the ideal trajectory is perfectly vertical, but under the influence of in-situ stress, the drill bit often deviates from the vertical direction, and the direction of deviation is usually parallel to the direction of the horizontal maximum principal stress. The results based on drilling data indicate that the well azimuth and average dip angle in the study area are NW-SE (120°-150°) and 0.75°, respectively. Therefore, based on the principle of determining the field stress according to the well azimuth information, the azimuth of the maximum horizontal principal stress is NW-SE (120°-150°).

[0102] Table 1 Comparison of maximum horizontal principal stresses determined by different measurement methods in the study area.

[0103]

[0104] like Figure 5 As shown, in the middle of thick mudstone, the direction of natural fractures is inconsistent with the direction of fast shear waves, while the direction of fast shear waves is consistent with the direction of the horizontal principal stress. Fast shear waves in the middle of thick mudstone (>8.0m) likely record accurate information about the current geostress direction. When the mudstone thickness is less than 8m or when there are reservoirs and limestone within the thick mudstone, using fast shear waves to determine the direction of in-situ stress is unreliable. Furthermore, the direction of fast shear waves cannot be used to determine the stress direction in thick sandstone (6.36m), fine sandstone (16.25m), silty mudstone (11.09m), and limestone (14.31m). Finally, based on the above criteria, the direction of the current maximum horizontal principal stress in the study area was determined. Figure 6 ).

[0105] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A method for determining the direction of tectonic stress, characterized in that, The method comprises the following steps: S1. collecting core data, logging data and geochemical data of a region to be analyzed; S2. identifying the sedimentary characteristics, sequence boundaries and single-well lithology of the region to be analyzed based on the core data, logging data and geochemical data collected in step S1; S3. performing rock mechanics parameter logging interpretation based on the logging data collected in step S1, establishing a rock dynamic-static mechanics parameter conversion model, and determining the single-well rock mechanics parameter distribution of the target region; S4. determining the strike distribution of vertical fractures by core observation and imaging logging interpretation on the core data and logging data collected in step S1; S5. determining the fast shear wave azimuth based on the logging data collected in step S1; S6. establishing a corresponding relationship model between the fast shear wave azimuth and the strike distribution of vertical fractures according to the single-well lithology identified in step S2, the single-well rock mechanics parameter distribution determined in step S3, the strike distribution of vertical fractures determined in step S4, and the fast shear wave azimuth determined in step S5; S7. identifying the natural fracture strike and the fast shear wave azimuth, determining the thickness and rock mechanics properties of the rock layer section where the natural fracture strike is inconsistent with the fast shear wave azimuth, establishing a geostress direction discrimination criterion, and determining the geostress direction based on the corresponding relationship model between the fast shear wave azimuth and the strike distribution of vertical fractures established in step S6.

2. The method of claim 1, wherein, The logging data in step S1 includes logging curves, energy spectrum curves and imaging logging data.

3. The method of claim 1, wherein, The logging data in step S1 is obtained by array acoustic logging.

4. The method of claim 1, wherein, The method for identifying the sedimentary characteristics, sequence boundaries and single-well lithology of the region to be analyzed in step S2 comprises the following steps: identifying the sedimentary characteristics of the region to be analyzed according to the logging curves, imaging logging data and core data.

5. The method of claim 4, wherein, The method for identifying the sedimentary characteristics, sequence boundaries and single-well lithology of the region to be analyzed in step S2 further comprises the following steps: determining the sequence boundaries of the region to be analyzed according to the logging curves, imaging logging data, core data, energy spectrum curves and geochemical data.

6. The method of claim 5, wherein, The method for identifying the sedimentary characteristics, sequence boundaries and single-well lithology of the region to be analyzed in step S2 further comprises the following steps: further identifying and interpreting the single-well lithology according to the sedimentary characteristics and the sequence boundaries, in combination with the imaging logging data and the core data.

7. The method of claim 5, wherein, The energy spectrum curves are selected from thorium, potassium and uranium-free gamma.

8. The method of claim 1, wherein, The method for determining the strike distribution of vertical fractures in step S4 comprises the following steps: implementing core homing by paleomagnetic method or rock occurrence method.

9. The method of claim 1, wherein, The establishment of the geostress direction discrimination criterion in step S7 comprises: comparing the local stress direction obtained by array acoustic logging with the stress direction obtained from drilling breakage, well deviation, drilling-induced fractures, hydraulic fractures and GPS data, and the direction of natural fractures.

10. The method of claim 9, wherein, The comparison method is: excluding unreliable geostress directions, and the exclusion condition is selected from one of the following: ① the local stress direction obtained by array acoustic logging is consistent with the direction of natural fractures; ②The local stress direction obtained by array sonic logging is inconsistent with the natural fracture direction, and is different from the stress direction obtained from drilling breakage, well deviation, drilling-induced fracture, hydraulic fracture and GPS data.

11. The method of claim 9, wherein, The establishment method of the in-situ stress direction discrimination criterion further includes: determining a rock stratum section corresponding to the array sonic logging of the reliable in-situ stress direction, and determining the thickness and rock mechanics properties of the rock stratum section.

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