A method for reconstructing paleo-tectonic stress field based on vertical displacement amount of vertical faulting

Abstract

The application discloses a method for reconstructing a paleo-tectonic stress field based on vertical displacement of vertical fractures, and aims at solving the problem of low accuracy of the prior art in establishing a paleo-tectonic stress field. V V‑MAX V‑MIN V V V‑MAX V‑MIN V V‑MAX V‑MIN H V h H The method avoids the possible large human errors in the identification of typical structures and the matching with the theoretical model, and significantly improves the accuracy.​​​​​​​​​​​​​

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of reservoir geomechanics in geology. BACKGROUND

[0002] The study of the along-strike slip of pre-existing near-vertical faults and their associated structural fracture zones has very important oil and gas geological and carbon storage significance (Bergmo, P. E. S., Grimstad, A.-A. & Lindeberg, E. G. B., 2011. Simultaneous CO2 injection and water production to optimise aquifer storage capacity, International Journal of Greenhouse Gas Control, 5, 555-564), and the structural fractures caused by paleo-tectonic stress are an important factor controlling the development of faults and structural fractures (Ding, W. L., Fan, T. L., Yu, B. S., Huang, X. B. & Liu, C., 2012. Ordovician carbonate reservoir fracture characteristics and fracture distribution forecasting in the Tazhong area of Tarim Basin, Northwest China, Journal of Petroleum Science and Engineering, 86-87, 62-70; Huang, L., Liu, C., He, F., Jia, H., Zhou, Y., Wang, Z., Wang, J., Liu, Y. & Li, X., 2022. Strike-slip deformation characteristics of fault in craton Basin, Journal of Northwest University. Natural Science Edition, 52(6), 930-942), so the study of the along-strike slip of pre-existing near-vertical faults and their associated structural fracture zones is actually the study of the coupling relationship of faults-paleo-tectonic stress field-structural fractures, and an important part of this is the reconstruction (determination) of the regional paleo-tectonic stress field. At present, the methods for reconstructing the regional paleo-tectonic stress field based on the along-strike slip characteristics of pre-existing near-vertical fault zones mainly include:

[0003] Method one: use the azimuthal constraint of the principal displacement zone in the positive relief and negative relief segments of the vertical fault and the corresponding regional horizontal maximum principal stress (σH) direction (Li, Y.T., Ding, W.L., Zeng, T., Xia, W.Q., Cheng, X.Y., Shi, S.Y. & Ding, S.H., 2023. Structural geometry and kinematics of a strike-slip fault zone in an intracontinental thrust system: A case study of the No. 15 fault zone in the Fuling area, eastern Sichuan Basin, southwest China. Journal of Asian Earth Sciences, 242, 1-29; Sun, Q.Q., Fan, T.L., Holdsworth, R.E., Gao, Z.Q., Wu, J., Gao, S.C., Wang, M. & Yuan, Y.X., 2023. The spatial characterization of stepovers along deeply-buried strike-slip faults and their influence on reservoir distribution in the central Tarim Basin, NW China. Journal of Structural Geology, 170, 1-22);

[0004] Method two: use the typical associated structure of the vertical fault along its strike, such as the horse-tail structure, to indicate the kinematic characteristics of the vertical fault and the regional horizontal stress direction (Deng, S., Li, H.L., Zhang, Z.P., Zhang, J.B. & Yang, X., 2019. Structural characterization of intracratonic strike-slip faults in the central Tarim Basin. AAPG Bulletin, 103(1), 109-137);

[0005] Method three: the correspondence between the geometric and kinematic differences of each sub-fault in the vertical fault zone and the synthetic shear, reverse shear, P-shear, Y-shear, T-rupture and fold in the Riedel shear model, as well as the corresponding strike-slip rupture mode (including simple shear, conversion extension and conversion compression) constraints on the type and direction of regional tectonic stress (Deng, S., Zhao, R., Kong, Q. F., Li, Y. T. & Li, B., 2022. Two distinct strike-slip fault networks in the Shunbei area and its surroundings, Tarim Basin: Hydrocarbon accumulation, distribution, and controlling factors, Aapg Bulletin, 106(1), 77-102; Yao, Y. T., Zeng, L. B., Mao, Z., Han, J., Cao, D. S. & Lin, B., 2023. Differential deformation of a strike-slip fault in the Paleozoic carbonate reservoirs of the Tarim Basin, China, Journal of Structural Geology, 173, 1-12);

[0006] Method four: Based on the fault slip data collected in the field outcrop, the regional paleo-tectonic stress field is reconstructed by using computer software (such as Win_Tensor, T-Tecto and FaultKin, etc.) and fault slip inversion method (Nkodia, H. M. D., Boudzoumou, F., Miyouma, T., Kongota, E., Ganza, G. B., Lahogue, P. & Delvaux, D., 2024. Brittle faulting and tectonic stress history on the western margin of the Congo Basin between Kinshasa and Brazzaville: Implications for the evolution of the Malebo Pool and the Congo River, Tectonophysics, 877, 1-27; Dasgupta, S., Mukherjee, S., Vanik, N., Chatterjee, R. & Pal, S. K., 2023. Paleostress analysis and rift kinematics of the petroliferous Barmer rift basin, western Rajasthan, India, Marine and Petroleum Geology, 156, 1-29). SUMMARY

[0007] The present application provides a method for reconstructing a paleo-tectonic stress field based on the vertical displacement amount of vertical fractures, aiming to solve the problem of low precision in establishing a paleo-tectonic stress field in the prior art.

[0008] In a first aspect, a method for reconstructing a paleo-tectonic stress field based on the vertical displacement amount of vertical fractures is provided, comprising:

[0009] Step S1: determining the study area, target layer system and vertical fractures as the research object, and obtaining the data of core, conventional logging and array sonic logging of the target layer system, and solving the static rock mechanics parameters of the target layer system;

[0010] Step S2: constructing a geomechanical model and a mathematical model related to the strike-slip of the vertical fractures, and carrying out a tectonic stress field numerical simulation test, obtaining the vertical deformation characteristics of the strata on both sides of the vertical fractures from the test results, and drawing the vertical displacement amount D of the vertical fractures corresponding to different models, and counting the D of each model V curve, and counting the D of each model VMaximum value D V-MAX and minimum value D V-MIN ratio D V-MAX / D V-MIN , and zero position L(D V =0) of D V ;

[0011] Step S3, constructing a conversion model between L(D V =0) and D V-MAX / D V-MIN ;

[0012] Step S4, calculating L(D V =0) and D V / D V-MAX according to the D V-MIN curve;

[0013] Step S5, obtaining corresponding σ V / σ V-MAX , σ V-MIN / σ H and θ according to the vertical fracture L(D V =0) and D h / D H obtained from Step S4 and the conversion model proposed in Step S3, and reconstructing the regional paleo-tectonic stress field related to the along-strike activity of the vertical fracture.

[0014] In the above scheme, optionally, the step S1 comprises:

[0015] For a research area with core data and without array sonic logging data, rock mechanics tests are carried out on core samples to obtain static rock mechanics parameters; wherein each static rock mechanics parameter is the average value of the corresponding parameters of all samples; the static rock mechanics parameters include static Young's modulus, static Poisson's ratio and density;

[0016] For a research area without core data, on the basis of identifying the main lithology of the target layer, static rock mechanics parameters of the corresponding lithology in the nearby area are obtained by consulting literature;

[0017] For a research area with core data, conventional logging and array sonic logging data, dynamic rock mechanics parameters are calculated according to the conventional logging and array sonic logging, and the formula is:

[0018]

[0019] wherein E d represents dynamic Young's modulus, unit: GPa; μ d represents dynamic Poisson's ratio; Δt pThe longitudinal wave time difference (DTC) is expressed in μs / ft; Δt s The transverse wave time difference (DTS) is expressed in μs / ft; ρ represents density, expressed in g / cm³. 3 The dynamic rock mechanics parameters include dynamic Young's modulus and dynamic Poisson's ratio.

[0020] Based on the static rock mechanics parameters obtained from the rock mechanics tests of the core samples, a fitting process is performed on the dynamic and static rock mechanics parameters to obtain a conversion model for the dynamic and static rock mechanics parameters of the target strata. The dynamic rock mechanics parameters are then converted to static rock mechanics parameters using the conversion model. The conversion formula is as follows:

[0021]

[0022]

[0023] In the formula, E d Represents the dynamic Young's modulus, with units of GPa; μ d denoted by ; E represents the static Young's modulus, in GPa; μ represents the static Poisson's ratio.

[0024] Optionally, in the above scheme, step S2 includes:

[0025] Based on the geological characteristics of the study area, a three-dimensional geomechanical model was constructed, which includes the location, strike, and extension length of the vertical fracture, as well as the geometric characteristics of the target strata. The vertical fracture was set as a discontinuity with a certain friction coefficient to simulate the relative sliding of the strata on both sides of the fracture.

[0026] The geomechanical model is transformed into a mathematical model, and the model is divided into several elements and nodes by meshing using finite element analysis software.

[0027] The static rock mechanics parameters obtained from step S1 are assigned to each element in the mathematical model; the boundary conditions and constraints of the mathematical model are set according to the requirements of research accuracy; numerical simulation experiments of tectonic stress field are carried out to obtain the simulation results corresponding to each experiment;

[0028] The vertical displacement D of the vertical fracture corresponding to each set of numerical simulation experiments of tectonic stress field is obtained based on the vertical displacement of the top interface of the model. V Curve D, establishing the boundary conditions and vertical displacement curves for numerical simulation of the structural stress field. V One-to-one correspondence;

[0029] Based on the vertical displacement D V The curve was used to calculate the vertical displacement D of each model. V The maximum value D V-MAX and minimum value DV-MIN the ratio D V-MAX / D V-MIN , and the vertical displacement amount D V of the zero value position L(D V = 0).

[0030] Optionally in the above solution, the step S3 comprises:

[0031] When the ratio σ H / σ V takes different values, the effective data of the zero value position L(D V = 0) and the ratio D V-MAX / D V-MIN of the maximum value and the minimum value of the vertical displacement amount obtained from all the models in step S2 are fitted to obtain a first conversion model of L(D V = 0) and D V-MAX / D V-MIN .

[0032] When the angle θ between the vertical fault and the direction of the regional horizontal maximum principal stress σ H takes different values, the effective data of L(D V = 0) and D V-MAX / D V-MIN obtained from all the models in step S2 are fitted to obtain a second conversion model of L(D V = 0) and D V-MAX / D V-MIN .

[0033] When the ratio σ h / σ H of the regional horizontal minimum principal stress and the regional horizontal maximum principal stress takes different values, the effective data of L(D V = 0) and D V-MAX / D V-MIN obtained from all the models in step S2 are fitted to obtain a third conversion model of L(D V = 0) and D V-MAX / D V-MIN .

[0034] Optionally in the above solution, the constructing the first, second and third conversion models further comprises:

[0035] When the ratio σ H / σ V takes different values, the effective data of L(D V = 0) and D V-MAX / D V-MIN are fitted, and if multiple different σ H / σV The numerical values are fitted to obtain a plurality of fitting functions, and are denoted as a first conversion model.

[0036] In the first conversion model, all the fitting functions belong to the same type, but the constant coefficients are different. The function relationship between the constant coefficient in each fitting function and σ H / σ V is fitted. If the fitting function is not clear, a first correlation curve graph is drawn as a discrimination chart according to the one-to-one correspondence between the constant coefficient and σ H / σ V , wherein the horizontal axis of the first correlation curve graph is σ H / σ V , and the vertical axis is each constant coefficient. A curve is drawn for each constant coefficient to be determined.

[0037] When θ takes different numerical values, L(D V = 0) and D V-MAX / D V-MIN effective data are fitted. If a plurality of different θ numerical values are set, a plurality of fitting functions corresponding to the fitting are obtained, and are denoted as a second conversion model.

[0038] In the second conversion model, all the fitting functions belong to the same type, but the constant coefficients are different. The function relationship between the constant coefficient in each fitting function and θ is fitted. If the fitting function is not clear, a second correlation curve graph is drawn as a discrimination chart according to the one-to-one correspondence between the constant coefficient and σ H / σ V , wherein the horizontal axis of the second correlation curve graph is σ H / σ V , and the vertical axis is each constant coefficient. A curve is drawn for each constant coefficient to be determined.

[0039] When σ h / σ H takes different numerical values, L(D V = 0) and D V-MAX / D V-MIN effective data are fitted. If a plurality of different σ h / σ H numerical values are set, a plurality of fitting functions corresponding to the fitting are obtained, and are denoted as a third conversion model.

[0040] In the third conversion model, all the fitting functions belong to the same type, but the constant coefficients are different. The function relationship between the constant coefficient in each fitting function and σ h / σ H is fitted. If the fitting function is not clear, a third correlation curve graph is drawn as a discrimination chart according to the one-to-one correspondence between the constant coefficient and σ h / σH a one-to-one correspondence relationship, and draw a third correlation curve as a discrimination chart, wherein an abscissa of the third correlation curve is σ h / σ H , and an ordinate is each constant coefficient, and one curve is drawn for each constant coefficient to be determined.

[0041] In the above scheme, further alternatively, constructing the first, second and third conversion models further comprises:

[0042] When σ H / σ V takes different values, fitting L(D V =0) and D V-MAX / D V-MIN effective data, and the fitting formula is:

[0043] Y=a-b·c X

[0044] wherein X represents D V-MAX / D V-MIN , Y represents L(D V =0), and a, b and c all represent constant coefficients; and an exponential function model between parameters X and Y is specified as the first conversion model by using the parameter σ H / σ V

[0045]

[0046] In the formula, X represents D V-MAX / D V-MIN , and Y represents (D V =0); a1, b1 and c1 represent constant coefficients of the first conversion model;

[0047] When θ takes different values, fitting L(D V =0) and D V-MAX / D V-MIN effective data by using the fitting formula;

[0048] The fitting formula is specified as the second conversion model by using the parameter θ:

[0049]

[0050] wherein X represents D V-MAX / D V-MIN , and Y represents L(D V =0); a2, b2 and c2 represent constant coefficients of the second conversion model;

[0051] When σ h / σ H ​When taking different values, the fitting formula is used to apply L(D) to the desired values. V =0) and D V-MAX / D V-MIN Fit the valid data;

[0052] Using parameter σ h / σ H The fitting formula is then concretized into a third transformation model:

[0053]

[0054] Where X represents D V-MAX / D V-MIN Y represents L(D) V =0); a3, b3 and c3 represent the constant coefficients of the third transformation model.

[0055] Optionally, in the above scheme, step S5 includes:

[0056] respectively with σ H / σ V , θ and σ h / σ H Using L(D) as the horizontal axis, V Plot the corresponding discriminant curve with 0 as the vertical axis;

[0057] According to L(D) obtained from step S4 V =0), and plot the ordinate on the corresponding discrimination curve, which is always equal to L(D). V =0) horizontal line, and based on the intersection of the horizontal line and the discrimination curve, reconstruct the regional paleotectonic stress field related to the strike-direction activity of the vertical fault.

[0058] Optionally, in the above scheme, step S5 further includes:

[0059] With σ H / σ V Using L(D) as the horizontal axis, V Plot the first discriminant curve with L(D = 0) as the vertical axis; if the horizontal line L(D) = 0, then... V =0) intersects with the first discrimination curve, then the intersection point is recorded as the first intersection point; if the horizontal line L(D) intersects with the first discrimination curve, then the intersection point is recorded as the first intersection point; V =0) has no intersection with the first discrimination curve, then in L(D V =0) Regarding σ H / σ V Find the horizontal line L(D) on the function curve graph. V =0) The point closest to the first intersection point is then recorded as the first intersection point;

[0060] With θ as the horizontal axis and L(D) as the vertical axis, VPlot the second discriminant curve with L(D = 0) as the vertical axis; if the horizontal line L(D) = 0, then... V =0) intersects with the second discrimination curve, then it is recorded as the second intersection point; if the horizontal line L(D) intersects with the second discrimination curve, then it is recorded as the second intersection point; V =0) and the second discrimination curve have no intersection, then in L(D V Find the curve of the function with respect to θ (=0) and the horizontal line L(D) on the graph. V The point closest to (=0) is denoted as the second intersection point;

[0061] With σ h / σ H Using L(D) as the horizontal axis, V Plot the third discriminant curve with L(D = 0) as the vertical axis; if the horizontal line L(D) = 0, then... V =0) intersects with the third discrimination curve, then it is recorded as the third intersection point; if the horizontal line L(D) intersects with the third discrimination curve, then it is recorded as the third intersection point; V =0) has no intersection with the third discriminant curve, then in L(D V =0) Regarding σ h / σ H Find the point on the function curve that is closest to the horizontal line L, and mark it as the third intersection point;

[0062] The abscissas of the first, second, and third intersection points represent the σ values ​​of the corresponding regional tectonic stress fields when the vertical fracture under study undergoes sliding along its strike. H / σ V , θ and σ h / σ H , where σ H / σ V and σ h / σ H It reflects the relative magnitudes of the regional horizontal maximum principal stress, regional horizontal minimum principal stress, and vertical stress, reflecting the type of tectonic stress; θ reflects the angle between the regional horizontal maximum principal stress and the vertical fracture. Combined with the direction of the vertical fracture's strike-slip, the precise azimuth of the regional horizontal maximum principal stress can be quantitatively determined, thus completing the reconstruction of the paleotectonic stress field.

[0063] Compared with the prior art, this application has at least the following beneficial effects:

[0064] Based on further analysis and research on the problems in the prior art, it is realized that, compared with the prior art which generally uses the azimuthal angle constraint area of the main displacement zone in the upstanding faulted relief to constrain the direction of the maximum horizontal principal stress of the area, uses typical structures such as horse-tail structures to indicate the direction of the regional horizontal stress, and uses the correspondence between each secondary fault in the upstanding faulted relief and each element in the Riedel shear model and the strike-slip rupture mode to constrain the type and direction of the regional tectonic stress, the method proposed in the present application does not rely on all the above typical structures, but only uses the vertical displacement of the upstanding fault, which is very high in quantitative degree and has very low human decision factors, thus avoiding the relatively large human errors that may exist in the identification of the typical structures and the matching with the theoretical mode, and significantly improving the accuracy.

[0065] Compared with the prior art which can only limit the range of the direction of the maximum horizontal principal stress of the area and the relative strength of the regional stress, the method proposed in the present application can accurately determine the azimuthal angle of the maximum horizontal principal stress of the area and the ratio of the maximum horizontal principal stress, the minimum horizontal principal stress and the vertical stress of the area, and realizes complete quantification.

[0066] Compared with the prior art which can only be applied to the case where the tectonic activity is weak after the deformation along the strike of the upstanding fault, and in this case some typical structures can be well preserved, but when the regional strong compressive stress causes the destruction of the typical structures related to strike-slip rupture, the applicability of the prior art is greatly reduced, while the method proposed in the present application is more adaptable in this case, because the deformation degree of the strata on both sides of the upstanding fault is improved, and the vertical deformation amplitude and the vertical displacement of the upstanding fault are more significant. BRIEF DESCRIPTION OF DRAWINGS

[0067] Figure 1 A flowchart of a method for reconstructing a paleo-tectonic stress field based on the vertical displacement of an upstanding fault provided for an embodiment of the present application.

[0068] Figure 2 A linear conversion mathematical model of AC and DTC obtained from the AC and DTC data of the target layer system of the study area provided for an embodiment of the present application.

[0069] Figure 3 A linear conversion mathematical model of DTC and DTS obtained from the DTC and DTS data of the target layer system of the study area provided for an embodiment of the present application.

[0070] Figure 4This application provides a geomechanical model size setting, vertical fracture setting, boundary condition setting, and nine different geomechanical models corresponding to nine different values ​​of the angle θ between the vertical fracture and one side of the geomechanical model, as well as the corresponding mathematical models (the number of elements and nodes of the mathematical model are also marked below each model).

[0071] Figure 5 This embodiment of the application provides the vertical deformation amplitude of the top interface node of the model obtained from the numerical simulation results of the tectonic stress field. `fault` refers to the projection of the vertical fracture onto the top interface of the model, and the angle between `fault` and true north is set to 45°. The boundary conditions of the tectonic stress field simulation associated with each figure are labeled below each figure, where the maximum horizontal principal stress in the region is set to 100 MPa.

[0072] Figure 6 This embodiment of the application provides the vertical deformation amplitude of the top interface node of the model obtained from the numerical simulation results of the tectonic stress field. `fault` refers to the projection of the vertical fracture onto the top interface of the model, and the angle between `fault` and the due north direction is set to 45°. The boundary conditions of the tectonic stress field simulation associated with each figure are marked below each figure, wherein the ratio of the minimum horizontal principal stress to the maximum horizontal principal stress in the region is 0.3.

[0073] Figure 7 The vertical displacement (D) at the top of the upright fracture F1 obtained from numerical simulation results of tectonic stress field provided in one embodiment of this application. V The boundary conditions for the numerical simulation of the tectonic stress field corresponding to each curve are marked on the figure. The horizontal axis of all curves represents the distance along the fracture strike. When the data point is located at the southernmost side of the fracture, the distance is -2500m; when the data point is located at the center of the fracture, the distance is 0m; and when the data point is located at the northernmost side of the fracture, the distance is 2500m.

[0074] Figure 8 For one embodiment of this application, when σ H / σ V When D equals 1, 2 and 3 respectively, V-MAX / D V-MIN and L(D) V =0), and all fitting functions are fitted by equation (5), where X represents D. V-MAX / D V-MIN Y refers to L(D) V =0).

[0075] Figure 9The fitting functions of D V-MAX / D V-MIN and L(D V = 0) when θ is equal to 10°, 20°, 30°, 40°, 45°, 50°, 60°, 70° and 80° respectively are provided for an embodiment of the present application, all of which are fitted by equation (5), wherein X represents D V-MAX / D V-MIN , and Y represents L(D V = 0).

[0076] Figure 10 The curves of constants a, b and c in equation (7) with respect to θ are provided for an embodiment of the present application.

[0077] Figure 11 The fitting functions of D h / σ H when σ V-MAX / σ V-MIN is equal to 0.1-0.9 at intervals of 0.1 are provided for an embodiment of the present application, all of which are fitted by equation (5), wherein X represents D V-MAX / D V-MIN , and Y represents L(D V = 0).

[0078] Figure 12 The curves of constants a, b and c in equation (8) with respect to σ h / σ H are provided for an embodiment of the present application.

[0079] Figure 13 The vertical displacement curve (A) of the vertical fault F1 as a research object, the function curves (B) of σ V-MAX / σ V-MIN , σ H / σ V , σ h / σ H and θ with respect to L(D V = 0) when D d / D d is equal to 0.308, and the reconstruction result (C) of the regional paleo-tectonic stress field related to the strike-slip of the vertical fault F1 are provided for an embodiment of the present application. DETAILED DESCRIPTION

[0080] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, and are not used to limit the present application.

[0081] In the description of the present application: unless otherwise specified, the meaning of "multiple" is two or more than two. The terms "first", "second", "third" and the like in the present application are intended to distinguish the objects referred to, and do not have a special meaning in the technical connotation aspect (for example, it should not be understood as emphasizing importance or order, etc.). The expressions "include", "contain", "have" and the like also mean "not limited to" (certain units, components, materials, steps, etc.).

[0082] The methods mentioned in the background art still have some problems at present:

[0083] Problem one: methods one and two can usually only be used to limit the range of the horizontal stress direction (azimuth) of the region and cannot obtain more accurate values;

[0084] Problem two: in method three, the correspondence between each fracture and the typical structure in the Riedel shear model is affected by the subjective judgment of the researchers, and has strong multiple solutions;

[0085] Problem three: in methods three and four, when the typical structure related to strike-slip rupture is destroyed by regional strong tectonic movement occurring after the strike-slip rupture, it is difficult to reconstruct the regional paleo-tectonic stress field through the Riedel shear model or rich fault slip data.

[0086] The regional strong compressive stress causes the typical structure related to strike-slip rupture to be destroyed, which is an unfavorable factor, but it causes the strata on both sides of the vertical fracture to be strongly deformed, and this strong deformation is reflected in the very obvious vertical deformation amplitude and vertical displacement amount of the strata on both sides of the vertical fracture. The quantitative study of this strong deformation can have very important significance for reconstructing the regional paleo-tectonic stress field.

[0087] The purpose of the present application is to provide a method for reconstructing a paleo-tectonic stress field based on the vertical displacement amount of a vertical fracture, in order to solve the problem in the prior art that when the typical structure related to the along-strike sliding of the vertical fracture has a high degree of destruction, it is difficult to quantitatively predict the regional paleo-tectonic stress field related to the along-strike sliding of the vertical fracture through structural analysis, and to promote the process of oil and gas field exploration and development and the study of reservoir geomechanics.

[0088] Therefore, in one embodiment of the present application, a method for reconstructing a paleo-tectonic stress field based on the vertical displacement amount of a vertical fracture is provided, which comprises the following steps S1-S5.

[0089] Step S1, determine the research area, target layer system and vertical fracture as the research object, and understand the core, conventional logging and array sonic logging data of the target layer system, and solve the static rock mechanics parameters of the target layer system in the research area.

[0090] Step S11, according to the actual research needs of oil and gas exploration and development, determining the research area, target layer series and the vertical fault as the research object.

[0091] According to the actual research needs of oil and gas exploration and development, selecting the research area and target layer series, and determining the lithology of the target layer series and the depth distribution characteristics of the top and bottom boundaries in the research area. The vertical fault to be carried out for paleo-tectonic stress field reconstruction is determined, which requires complete faulting through the target layer series, and the intersection line of the top and bottom boundaries of the target layer series should have continuity on the plane and be clearly visible.

[0092] In an embodiment of the present application, a vertical fault F1 with a left-lateral slip occurring along its strike in China A Basin with a plane extension length of about 6.834 km and a plane trace almost as a straight line is selected as the research object, which faults through an important oil and gas production layer B (as the target layer series in an embodiment of the present application). When carrying out strata-structure comprehensive interpretation based on three-dimensional seismic data in this area, the conversion of two-way travel time and actual depth is not carried out, so the depth with time as the scale is used. The top boundary depth of the oil and gas production layer is about 2400 ms, the bottom boundary depth is about 2600 ms, and the total thickness is about 200 ms. The vertical fault F1 faults through the oil and gas production layer.

[0093] Step S12, understanding the core, conventional logging and array acoustic logging data of the target layer series in the research area.

[0094] The core, conventional logging and array acoustic logging data of each well drilled through the target layer series in the research area are statistically analyzed in detail. If the target layer series in the research area does not have any well data and core data, or only has conventional logging data, it is determined as a type I research area; if the target layer series in the research area has core data but does not have array acoustic logging data, it is determined as a type II research area; if the target layer series in the research area has core, conventional logging and array acoustic logging data, it is determined as a type III research area; if the target layer series in the research area has conventional logging and array acoustic logging data but does not have core data, it is determined as a type IV research area.

[0095] In an embodiment of the present application, the layer series B in A Basin has core data, conventional logging data and array acoustic logging data, so it belongs to a type III research area.

[0096] Step S13, solving the static rock mechanics parameters of the target layer series in the research area.

[0097] For the Type II study area mentioned in step S12, rock mechanics tests were conducted on the core samples to obtain parameters such as the static Young's modulus, static Poisson's ratio, and density of the rock. Each parameter was taken as the average value of the corresponding static parameters of all samples. For the Type III study area mentioned in step S12, the dynamic rock mechanics parameters are first calculated based on conventional logging and array sonic logging. Then, based on the static Young's modulus and static Poisson's ratio obtained from the rock mechanics test of the core sample, the dynamic rock mechanics parameters are converted into static rock mechanics parameters, as follows: In conventional logging data, sonic transit time (AC) logging data, longitudinal transit time (DTC) logging data, and transverse transit time (DTS) logging data are time-difference data and are considered to have good correlation. Therefore, the conversion model of AC and DTC is first constructed, and the conversion model of DTC and DTS is constructed based on the array sonic logging data. Based on these two conversion models, DTC and DTS can be calculated, and the dynamic Young's modulus and dynamic Poisson's ratio of all wells in the target stratum can be calculated according to the following formulas (1) and (2):

[0098]

[0099] Where E d For dynamic Young's modulus, GPa; μ d The dynamic Poisson's ratio; Δt p The longitudinal wave time difference (DTC) is in μs / ft; Δt s The transverse wave time difference (DTS) is in μs / ft; ρ is the density in g / cm³. 3 .

[0100] Based on the drilling locations and depths of core samples used in rock mechanics tests, dynamic rock mechanics parameters are obtained at the corresponding locations. These parameters are then combined with static rock mechanics parameters obtained from the tests to construct a conversion model between dynamic and static rock mechanics parameters. Using this model, the calculated dynamic rock mechanics parameters of all wells within the study area in the target strata can be converted into static rock mechanics parameters. The average static rock mechanics parameters of all wells within the study area in the target strata are then calculated.

[0101] For the Class I or Class IV study areas mentioned in step S12, the static rock mechanics parameters of the corresponding lithologies in the nearby areas are obtained by consulting the literature after identifying the main lithologies of the target stratigraphy in the study area.

[0102] In one embodiment of this application, Basin A belongs to a Type III study area. Therefore, a conversion model for AC and DTC is constructed based on AC and DTC data from all wells within the study area, as shown in the attached figure. Figure 2 As shown, using linear fitting, the goodness of fit R0 is... 2DTC = 0.66DTS. Then, the conversion model between DTC and DTS is built according to the DTC and DTS data of all the wells in the study area, as shown in Figs. 1 and 2, and the linear fitting is adopted, and the goodness of fit R Figure 3 2 = 0.86. According to the conversion model shown in Figs. 1 and 2, all the AC data in the study area can be converted into DTC and DTS data, and then the dynamic Young's modulus and dynamic Poisson's ratio can be calculated according to the formulas (1) and (2). The static rock mechanics parameters can be obtained from the rock mechanics experiments of the rock samples of the target layer system in the study area, and the corresponding relationship between the static rock mechanics parameters and the dynamic rock mechanics parameters calculated at the corresponding well and the corresponding depth is shown in Table 1. Figure 2 Figure 3 The conversion model between the dynamic and static rock mechanics parameters in Table 1 is obtained by performing fitting work, and the formulas (3) and (4) are respectively obtained:

[0103] Table 1

[0104]

[0105] The conversion model between the dynamic and static rock mechanics parameters in Table 1 is obtained by performing fitting work, and the formulas (3) and (4) are respectively obtained:

[0106]

[0107] The goodness of fit of the formulas (3) and (4) is 0.62 and 0.63, respectively. According to the formulas (3) and (4) and the dynamic rock mechanics parameters calculated for the target layer system in the study area, the static rock mechanics parameters of the target layer system in the study area can be calculated. The calculation results show that the average value of the static Young's modulus is 39.15 GPa, the average value of the static Poisson's ratio is 0.232, and the average value of the rock density is 2.683 g / cm 3 .

[0108] In step S2, the geological mechanics model and the mathematical model related to the along-strike slip of the vertical fault are built, and the numerical simulation test of the tectonic stress field is performed, the vertical deformation characteristics of the strata on both sides of the vertical fault are obtained from the test results, and the vertical displacement (D V ) curve of the vertical fault corresponding to different models is drawn, and the ratio of the maximum value (D V ) and the minimum value (D V-MAX ) of D V-MIN and the zero value position (L(D V = 0)) of D V are counted for each model.

[0109] In step S21, the size of the right rectangular prism geological mechanics model is set, the vertical fault is set as the contact pair in the finite element analysis, and a plurality of different right rectangular prism geological mechanics models are set according to the planar extension direction of the vertical fault. ​​

[0110] The geomechanical model is set as a right quadrangular prism, and the top and bottom interfaces of the right quadrangular prism are congruent squares. In order to facilitate subsequent mathematical model construction and result analysis, the side length of the top and bottom interfaces of the right quadrangular prism is set as 6000 m, and the height H of the right quadrangular prism is set as 5000 m. The vertical fault is set as a cavity surrounded by four vertical planes with a height of H. The four planes can be divided into two groups, and the planes belonging to different groups are perpendicular to each other. Each group is composed of two planes. The interval of the planes in the first group is set as 5 m, and the plane extension length is 5000 m. The interval of the planes in the second group is 5000 m, and the plane extension length is 5 m. The top and bottom surfaces of the pre-existing fault region are both rectangles with a length of 5000 m and a width of 5 m. The height of the region is H, and the volume is 1.25*10 8 m 3 The pre-existing fault region penetrates the geomechanical model from top to bottom. The center of the intersection line of the region and the top surface of the geomechanical model is consistent with the center of the top surface of the geomechanical model. The center of the intersection line of the fault and the bottom surface of the geomechanical model is consistent with the center of the bottom surface of the geomechanical model.

[0111] The concept of contact pair used in the contact analysis of the statics module in the finite element analysis is introduced and used in the setting of the pre-existing fault in the three-dimensional geomechanical model. The contact pair is composed of a contact surface and a target surface, which are two planes (or curved surfaces). The contact surface is the side of the fault plane that undergoes passive deformation, and is defined as the side of the fault plane that undergoes passive deformation in the regional tectonic stress field. The target surface is the side of the fault plane that undergoes active deformation, and is defined as the side of the fault plane that undergoes active deformation in the regional tectonic stress field. According to the regional stress direction related to the activity of the fault F1 and the target layer system in the study area, the side of the fault plane close to the regional stress direction is set as the target surface, and the side of the fault plane far from the regional stress direction is set as the contact surface. The plane extension length of both is 5000 m, the height is 5000 m, and the interval is 5 m. According to the friction coefficient of the vertical fault in the stratum close to the lithology of the target layer system, the friction coefficient between the contact surface and the target surface is set. Under the action of the regional tectonic stress, when the stress intensity at the fault plane exceeds the stress intensity threshold value at which the contact surface and the target surface slide relative to each other, the contact surface and the target surface can slide relative to each other, thereby realizing the relative displacement of the strata on both sides of the pre-existing fault. After completing the size setting of the geomechanical model and the contact pair setting of the vertical fault, the angle between the vertical fault and any side surface Surface of the geomechanical model is set as θ. According to the research accuracy requirement, n values θ i (1≤i≤n) are selected within 0-90°. Each θ i corresponds to a different geomechanical model, thereby the deformation characteristics difference of the strata on both sides of the fault F1 when the angle between the vertical fault and the regional horizontal stress is different can be studied.

[0112] In one embodiment of the present application, the three-dimensional geomechanical model is set as a regular quadrangular prism, the length and width of the top surface are both 6000 m, and the height H of the geomechanical model is equal to 5000 m. The vertical fracture is set as a cavity enclosed by four vertical planes with a height of 5000 m. The four planes can be divided into two groups, the planes belonging to different groups are perpendicular to each other, and each group is composed of two planes: the interval of the planes in the first group is 5 m, and the length of the plane extension is 5000 m; the interval of the planes in the second group is 5000 m, and the length of the plane extension is 5 m. The top surface and the bottom surface of the pre-existing basement fracture region are both rectangular with a length of 5000 m and a width of 5 m, and the height of the region is 5000 m, and the volume of the region is 1.25 x 10 8 m 3 The pre-existing basement fracture region penetrates the geomechanical model from top to bottom, the center of the intersection line of the region and the top surface of the geomechanical model is consistent with the center of the top surface of the geomechanical model, and the center of the intersection line of the fracture and the bottom surface of the geomechanical model is consistent with the center of the bottom surface of the geomechanical model.

[0113] In one embodiment of the present application, the direction of the horizontal maximum principal stress is fixed as from south to north, therefore the south side section of the vertical fracture is set as the target surface, and the north side section is set as the contact surface, the plane extension length of both is 5000 m, the height of both is 5000 m, and the interval is 5 m. The friction coefficient of the pre-existing fracture is considered to be 0.15, therefore the friction coefficient between the contact surface and the target surface is set to 0.15. Under the action of the regional tectonic stress, when the stress intensity at the section exceeds the stress intensity threshold value at which the relative sliding between the contact surface and the target surface occurs, the relative sliding between the contact surface and the target surface can occur, and the relative displacement of the strata on both sides of the pre-existing fracture is realized. θ is set to 10°, 20°, 30°, 40°, 45°, 50°, 60°, 70° and 80°, corresponding to 9 different three-dimensional geomechanical models.

[0114] Step S22, the geomechanical model constructed in step S21 is meshed with tetrahedral elements in the finite element analysis software, to obtain the corresponding mathematical model, wherein the grid division density of the top surface of the model is higher than that of other positions of the model. After the mathematical model is constructed, the coordinates of all elements and nodes of the geomechanical model are exported from the finite element analysis software.

[0115] The geomechanical model is meshed with triangular (two-dimensional) or tetrahedral (three-dimensional) elements, and the geomechanical model is divided into a series of elements and nodes. The grid division accuracy of the top surface of the geomechanical model is higher than that of the bottom surface and the four side surfaces, because in the present application, the vertical deformation amplitude (vertical displacement amount) of the nodes of the top surface of the model is analyzed. After the mathematical model is constructed, the spatial coordinates (E_X, E_Y, E_Z) of all elements and the spatial coordinates (N_X, N_Y, N_Z) of the nodes of the geomechanical model are exported from the finite element analysis software.

[0116] In one embodiment of the present application, tetrahedral units are used to divide the three-dimensional geomechanical model into a series of units and nodes. The ANSYS computer software is used to divide the geomechanical model into a grid, and SOLID 45 units are selected based on the characteristics of the units to divide the three-dimensional geomechanical model in one embodiment of the present application into a grid. The improvement in the accuracy of the grid division is achieved by using a free grid division method, and the accuracy of the grid division on the top surface of the geomechanical model is higher than that on the bottom surface and the four side surfaces. After the mathematical model is constructed, the spatial coordinates (E_X, E_Y, E_Z) of all units and the spatial coordinates (N_X, N_Y, N_Z) of nodes of the geomechanical model are exported from the finite element analysis software. The total number of units and the total number of nodes of each three-dimensional geomechanical model after being gridded in step S21 are shown in Table 1. Figure 4 .

[0117] In step S23, the static rock mechanics parameters (Young's modulus, Poisson's ratio and density) of the target layer system of the study area obtained by solving in step S13 are assigned to each unit in the mathematical model, and different boundary conditions and constraint conditions are set for the mathematical model to carry out tectonic stress field numerical simulation, and the simulation results corresponding to each test are obtained.

[0118] According to the calculation results of the static rock mechanics parameters in step S13, the static rock mechanics parameters (Young's modulus, Poisson's ratio and density) are assigned to all units of all geomechanical models. The three parameters of θ, the ratio of the regional horizontal maximum principal stress to the vertical stress (σ H / σ V ), and the ratio of the regional horizontal minimum principal stress to the regional horizontal maximum principal stress (σ h / σ H ) are defined as key parameters affecting the numerical simulation results of the tectonic stress field, wherein the influence of θ has been embodied in step S21, and the influences of σ H / σ V and σ h / σ H need to be realized by changing the boundary conditions of the mathematical model. According to the need for research accuracy, the test data sets of σ H / σ V and σ h / σ H are set, wherein σ h / σ HLess than 1. The boundary conditions and constraints of the mathematical model mainly include the stress application mode, application strength and displacement constraint mode of the area stress of the side and top surface of the mathematical model. After setting reasonable boundary conditions and constraints for each mathematical model, the tectonic stress field numerical simulation is carried out, and the simulation results corresponding to each test are obtained, wherein the focus is to statistically analyze the vertical displacement of the nodes on the top surface of the model in each tectonic stress field numerical simulation.

[0119] In an embodiment of the present application, according to the calculation results of the static rock mechanics parameters in step S13, the same static rock elastic parameters are assigned to all elements of all mathematical models, specifically the static Young's modulus (39.15 GPa), the static Poisson's ratio (0.232) and the rock density (2.683 g / cm 3 ). When the tectonic stress field numerical simulation is carried out for each mathematical model, σ V is set to 100 MPa to study the deformation characteristics of the model under the action of the same overburden gravity. σ H / σ V is set to 1, 2 and 3, i.e. 100, 200 and 300 MPa, to study the deformation characteristics of the model under different σ H / σ V . σ h / σ H is set to 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 and 0.9 to study the deformation characteristics of the model under different σ h / σ H . Considering the comprehensiveness of the present study and the efficiency of the FEM-based numerical simulation operation, when σ h / σ H is equal to 0.3, three-dimensional tectonic stress field numerical simulations are additionally carried out when σ H / σ V is equal to 1.25, 1.50, 1.75, 2.25, 2.50 and 2.75 to more clearly show the influence of σ H / σ V on the deformation of the model. Therefore, in an embodiment of the present application, a total of 297 three-dimensional tectonic stress field numerical simulation experiments are involved.

[0120] As shown in the attached Figure 4 , the displacement of the nodes on the XZ surface on the south side of the three-dimensional geomechanical model is not constrained, and is applied with σ H , the displacement of the nodes on the YZ surface on the east side is not constrained, and is applied with the horizontal minimum principal stress (σ h). The X and Y direction displacements of the nodes on the XZ plane of the north side and the YZ plane of the west side of the geomechanical model are set as constant value 0, and the Z direction displacement is not constrained. The displacements of the nodes on the XY plane of the top side of the geomechanical model are not constrained, and a vertical stress (σ V ) is applied vertically downward. The Z direction displacement of the nodes on the XY plane of the bottom side of the model is set as constant value 0, and the X and Y direction displacements are not constrained. The entire three-dimensional geomechanical model is given a vertical downward gravity acceleration, so that the simulation result is closer to the feature that the vertical stress increases with the increase of depth in the actual geological condition. Under the above boundary conditions and constraint conditions, the tectonic stress field numerical simulation is carried out for each mathematical model, and the simulation result corresponding to each model is obtained, wherein the vertical displacement amount of the model top surface node in each tectonic stress field numerical simulation is focused on, and the boundary conditions of several mathematical models of one embodiment of the present application and the vertical displacement amount of the model top surface node are partially shown in Figs. 1-3. Figure 5 and Figure 6 .

[0121] Step S24, according to the vertical displacement amount of the model top interface in step S23, the vertical displacement amount (D V ) curve of the vertical fracture corresponding to each group of tectonic stress field numerical simulation experiments is obtained, and a one-to-one correspondence relationship between the boundary conditions {θ,σ H / σ V ,σ h / σ H} of the tectonic stress field numerical simulation and the D V curve is established.

[0122] The vertical displacement amount (D V ) of a certain position of the vertical fracture is defined as the difference between the displacement amount of the node on the contact surface along the Z axis and the displacement amount of the node on the target surface along the Z axis, and thus the vertical displacement amount (D V ) curve of the vertical fracture corresponding to each mathematical model is calculated, and the abscissa of the curve is the distance of the displacement amount data point from the south end of the fracture. In order to enhance the particularity of the central position of the vertical fracture, the distance of the displacement amount data point located at the central position of the vertical fracture from the south end of the fracture is set as 0 m, and the distance of the displacement amount data point of the southmost end of the fracture from the south end of the fracture is set as -2500 m, and the distance of the displacement amount data point of the northmost end of the fracture from the south end of the fracture is set as 2500 m, so that the abscissa range of each D V curve is -2500-2500 m. When the abscissa of any point on the D V curve is less than 0, the point is located on the south side of the central part of the vertical fracture, and vice versa. Each mathematical model and the corresponding tectonic stress field numerical simulation result correspond to a D Vcurve, and the boundary condition {θ, σ H / σ V ,σ h / σ H} of the numerical simulation of the tectonic stress field can be constructed.

[0123] In an embodiment of the present application, the D V curve corresponding to each mathematical model is shown in the attached figure, the horizontal axis of each curve is the distance of the displacement data point from the southern end of the vertical fault, the numerical range is -2500-2500m, the horizontal coordinate of the displacement data point in the central position of the vertical fault is 0m, the horizontal coordinate of the displacement data point in the southern end of the vertical fault is -2500m, and the horizontal coordinate of the displacement data point in the northern end of the vertical fault is 2500m. Each mathematical model and the corresponding numerical simulation result of the tectonic stress field correspond to a D V curve, and the boundary condition {θ, σ H / σ V ,σ h / σ H} of the numerical simulation of the tectonic stress field can be constructed. In an embodiment of the present application, there are 297 models, and thus there are 297 D V curves.

[0124] In step S25, according to the D V curve obtained in step S24, the ratio (D V / D V-MAX ) of the maximum value (D V-MIN ) and the minimum value (D V-MAX ) of D V-MIN for each model, and the zero position (L(D V =0)) of D V are calculated.

[0125] According to the D V curve obtained in step S24, the ratio (D V-MAX / D V-MIN ) of the maximum value (D V-MAX ) and the minimum value (D V-MIN ) of D V for each curve is calculated first. D V of the vertical fault usually has positive and negative values, and the positive or negative of D V represents the relative rise and fall of the strata on both sides of the vertical fault, but the absolute value thereof represents the deformation intensity of the strata, and thus the ratio (D V / D V-MAX ) of the maximum value (D V-MIN ) and the minimum value (D V-MAX ) of D V-MIN for each curve is calculated.The absolute value of the ratio of the maximum and minimum values ​​obtained from the calculation results will be used as D in this application. V Maximum value (D) V-MAX ) and minimum value (D V-MIN The ratio of (D) V-MAX / D V-MIN ).

[0126] Then obtain each D V curve D V The zero position (L(D)) V =0), it is important to note that each D V The curve has three zero points in most cases, two of which are located at the southernmost and northernmost ends of the vertical fracture, respectively, that is, when the x-coordinate of the displacement data point takes the minimum value of -2500m and the maximum value of 2500m. However, in this application, L(D V =0) is not one of the two zeros mentioned above, that is, L(D) V =0) is not equal to -2500m and 2500m, but rather to some value between -2500 and 2500. Use L(D) V =0) divided by 2500m and then L(D V =0) is standardized to a decimal between -1 and 1, when L(D V When D approaches -1 (=0), V The zero point of the curve is infinitely close to the southernmost side of the vertical fracture, when L(D) V When D approaches 1 (=0), V The zero point of the curve is infinitely close to the northernmost side of the vertical fracture, when L(D) V When D approaches 0 (=0), V The zero point of the curve is infinitely close to the center of the vertical fracture. When the D of a certain model... V If a curve has only two zeros, it is not included in the analysis of subsequent steps because in this case D V The curve does not have a third zero, L(D) V =0) is meaningless. It's important to note that in D... V When the curve has only two zeros, the parameter D V-MAX / D V-MIN It also has no meaning, because D, as the denominator... V-MIN It approaches 0 infinitely, therefore the parameter D at this point... V-MAX / D V-MIN They will not be included in subsequent analyses.

[0127] In one embodiment of this application, based on the 297 D obtained in step S24 V The curve is first calculated by counting each D line. V curve DV Maximum value (D) V-MAX ) and minimum value (D V-MIN The ratio of (D) V-MAX / D V-MIN ). Vertical fracture of D V It usually has both positive and negative values ​​(as shown in the appendix). Figure 7 As shown), D V The positive or negative value represents the relative uplift or subsidence of the strata on both sides of a vertical fault, but only its absolute value can represent the strength of strata deformation. Therefore, according to the D of each curve... V The absolute value of the ratio of the maximum and minimum values ​​obtained from the calculation results will be used as D in this application. V Maximum value (D) V-MAX ) and minimum value (D V-MIN The ratio of (D) V-MAX / D V-MIN ).

[0128] In one embodiment of this application, each D V The curve has three zeros in most cases (as shown in the attached figure). Figure 7 As shown), L(D) V =0) are not the two zero points located at the vertical fracture end, i.e., L(D) V =0) is not equal to -2500m and 2500m. Use L(D V =0) divided by 2500m and then L(D V =0) is standardized to a decimal between -1 and 1, when L(D V When D approaches -1 (=0), V The zero point of the curve is infinitely close to the southernmost side of the vertical fracture, when L(D) V When D approaches 1 (=0), V The zero point of the curve is infinitely close to the northernmost side of the vertical fracture, when L(D) V When D approaches 0 (=0), V The zero point of the curve is infinitely close to the center of the vertical fracture. When the D of a certain model... V If a curve has only two zeros, it is not included in the analysis of subsequent steps. D used in embodiments of this application V-MAX / D V-MIN and L(D) V =0) and the boundary conditions {θ,σ} for numerical simulation of the structural stress field H / σ V ,σ h / σ H The one-to-one correspondence between data columns is shown in Table 2, where data column D... V-MAX / D V-MIN and L(D) VThe model and its construction marked with " / " in L(D V The curve has only two zeros.

[0129] Table 2

[0130]

[0131]

[0132]

[0133]

[0134]

[0135]

[0136]

[0137]

[0138] Step S3, constructing the conversion model between L(D V =0) and D V-MAX / D V-MIN .

[0139] Step S31, when σ H / σ V takes different values, fitting the L(D V =0) and D V-MAX / D V-MIN effective data obtained from all models to obtain the conversion model 1 of L(D V =0) and D V-MAX / D V-MIN .

[0140] According to the σ H / σ V interval and value set in step S23, when σ H / σ V takes different values, fitting the L(D V =0) and D V-MAX / D V-MIN effective data obtained from step S25, if n different σ H / σ VThe numerical values are obtained by fitting n fitting functions corresponding to the n different numerical values. The combination of these function equations is referred to as conversion model 1. In conversion model 1, all the fitting functions should belong to the same type, only the constant coefficients are different, so after constructing conversion model 1, the function relationship between the constant coefficients in each fitting function and σ H / σ V needs to be fitted. If the fitting function is not clear, a related curve graph is drawn as a discrimination chart according to the one-to-one correspondence between the constant coefficient and σ H / σ V . The value of σ H / σ V is taken as the horizontal axis of the curve graph, and the constant coefficient is taken as the vertical axis. Each undetermined constant coefficient needs to draw a curve.

[0141] In an embodiment of the present application, the value of σ H / σ V set in step S23 is 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75 and 3, but when the value of σ H / σ V is 1, 2 and 3, the data volume is larger, and the effective data is 62, 74 and 78 respectively, while when the value of σ H / σ V takes other values, the effective data is less than 10, so only the effective data when the value of σ H / σ V is 1, 2 and 3 is included in the analysis in this step. When the value of σ H / σ V is different, L(D V =0) and D V-MAX / D V-MIN effective data obtained from step S25 are fitted, and it is found that the function as shown in formula (5) has very high applicability at this time:

[0142] Y=a-b·c X (5)

[0143] where X represents D V-MAX / D V-MIN , Y represents L(D V =0), and a, b and c are constant coefficients. Three fitting function equations are obtained, and the fitting degrees are 0.96, 0.93 and 0.89 respectively, as shown in the attached Figure 8 . The combination of these function equations is referred to as conversion model 1. The constant coefficients a, b and c in formula (5) and σ H / σ V also need to be solved. When σ H / σ V When σ equals 1, 2 and 3, the constant coefficients a are 0.78, 0.75 and 0.72 respectively, the constant coefficients b are 1.14, 2.19 and 3.19 respectively, and the constant coefficients c are 0.57, 0.34 and 0.22 respectively, so the parameters σ H / σ V The exponential function model between the parameters X and Y is specified as the equation set (6) :

[0144]

[0145] Wherein, X refers to D V-MAX / D V-MIN , and Y refers to L(D V = 0). The equation set (6) is the final expression form of the conversion model 1, in which only the parameters σ H / σ V are needed to construct the conversion models of L(D V = 0) and D V-MAX / D V-MIN .

[0146] In step S32, the L(D V = 0) and D V-MAX / D V-MIN effective data obtained from all the models are fitted when the boundary condition θ takes different values, and the conversion model 2 of L(D V = 0) and D V-MAX / D V-MIN is obtained.

[0147] According to the θ interval and values set in step S21, the L(D V = 0) and D V-MAX / D V-MIN effective data obtained in step S25 are fitted when θ takes different values, if n different θ values are set, then n fitting functions corresponding to the n different values are obtained by fitting, and the combination of these function equations is called the conversion model 2. In the conversion model 2, all the fitting functions should belong to the same type, only the constant coefficients in them are different, so after the conversion model 2 is constructed, the function relationship between the constant coefficients in each fitting function and θ also needs to be fitted, if the fitting function is not clear, then according to the one-to-one correspondence between the constant coefficients and σ H / σ V , a related curve graph is drawn as a discrimination chart, the horizontal axis of the curve graph is the value of σ H / σ V , and the vertical axis is each constant coefficient, and a curve needs to be drawn for each constant coefficient to be determined.

[0148] In one embodiment of this application, the value of θ set in step S21 is 10°, 20°, 30°, 40°, 45°, 50°, 60°, 70°, and 80°. When θ takes different values, the L(D) obtained from step S25... V =0) and D V-MAX / D V-MIN Fitting the valid data, we found that equation (5) can still be used to construct the fitting function, and the results are shown in the appendix. Figure 9 As shown, the goodness of fit for all nine fitting functions is at least 0.88, indicating the applicability of equation (5) in this case. When fitting the relationship between the coefficients of each function and θ, it was found that... Figure 9 The relationship between the constant coefficients a, b, and c and θ cannot be well fitted by conventional functions. Therefore, the curves of the constant coefficients a, b, and c with respect to θ are shown in the attached figure. Figure 10 As shown, for θ between 10° and 80°, linear interpolation is used to obtain the corresponding constants a, b, and c. For θ less than 10° and greater than 80°, linear trend extrapolation is used to obtain the corresponding constants a, b, and c. The parameter θ is used to calculate L(D). V =0) and D V-MAX / D V-MIN The transformation model 2 is concretized into a system of equations (7):

[0149]

[0150] Where X refers to D V-MAX / D V-MIN Y refers to L(D) V =0). The graphs of the constant terms a, b, and c with respect to the parameter θ are attached. Figure 10 As shown.

[0151] Step S33, when the boundary condition σ h / σ H When taking different values, the L(D) obtained from all models V =0) and D V-MAX / D V-MIN The effective data is fitted to obtain L(D) V =0) and D V-MAX / D V-MIN Transformation Model 3.

[0152] According to the σ set in step S23 h / σ H Intervals and values, when σ h / σ H When taking different values, the L(D) obtained from step S25 is... V =0) and D V-MAX / D V-MINFitting the valid data, if a total of n different σ values ​​are set. h / σ H For the numerical values, n fitting functions are obtained by fitting these n different numerical values. The combination of these functional equations is called Transformation Model 3. In Transformation Model 3, all fitting functions should belong to the same type, only their constant coefficients differ. Therefore, after constructing Transformation Model 3, it is also necessary to fit the constant coefficients and σ of each fitting function. h / σ H The functional relationship, if the fitted function is unclear, is determined based on the constant coefficients and σ. h / σ H The one-to-one correspondence is plotted as a discriminant graph, with the horizontal axis of the graph representing σ. h / σ H The values ​​of are represented by the vertical axis, which represents the constant coefficients of each term. For each undetermined constant coefficient, a curve needs to be plotted.

[0153] In one embodiment of this application, the σ set in step S23 h / σ H The value ranges from 0.1 to 0.9, with intervals of 0.1. When σ h / σ H When taking different values, the L(D) obtained from step S25 is... V =0) and D V-MAX / D V-MIN The effective data is used for fitting, and equation (5) can still be used to construct the fitting function, but its applicability is reduced compared to steps S21 and S22. The results are shown in the appendix. Figure 11 As shown. When σ h / σ H A fitting function could not be constructed when the value was equal to 0.5, but this may be due to the higher value of the parameter L(D). V =0) corresponds to a small number of data points, and does not represent the exponential function in L(D V =0) The extension in the positive direction of the axis provides a better constraint effect. When σ h / σ H When the value is equal to 0.9, the data set (L(D)) V =0),D V-MAX / D V-MIN The distribution is irregular, so an exponential function could not be constructed, and when σ h / σ H When the value was increased from 0.7 to 0.8, the goodness of fit of the data set (L(D)) decreased rapidly from 0.93 to 0.67, indicating that the goodness of fit of the data set (L(D)) was significantly reduced. V =0),D V-MAX / D V-MIN One of the applicable conditions for fitting with equation (5) is σ.h / σ H Less than or equal to 0.7 (in the case of fitting equation (5), the goodness of fit is greater than or equal to 0.92). Therefore, in this step, 7 effective fitting functions are obtained, respectively, σ h / σ H Take 0.1, 0.2, 0.3, 0.4, 0.6, 0.7 and 0.8.

[0154] In the fitting of the coefficients of each function and σ h / σ H , it is found that the constant coefficients a, b and c in the appendix Figure 9 The relationship between σ h / σ H cannot be well fitted by a conventional function, so the curves of constant coefficients a, b and c about σ h / σ H are drawn as shown in the appendix Figure 12 , and for σ h / σ H between 0.1 and 0.9, the corresponding constant terms a, b and c are obtained by linear interpolation. For σ h / σ H less than 0.1 and greater than 0.9, the corresponding constant terms a, b and c are obtained by linear trend extrapolation. The conversion model 3 of L(D h = 0) and D H / D V is specified by equation group (8) with parameter σ V-MAX / σ V-MIN :

[0155]

[0156] Where X represents D V-MAX / D V-MIN , and Y represents L(D V = 0). The curves of constant terms a, b and c about parameter σ h / σ H are shown in the appendix Figure 12 .

[0157] Step S4, obtain the D V curve of the vertical fracture as the research object in step S1, and the corresponding L(D V = 0) and D V-MAX / D V-MIN .

[0158] Step S41, obtain the D V curve of the vertical fracture as the research object in step S1.

[0159] The calculation of vertical fracture D is described in step S24. V The curve method is used to obtain the D of the vertical fracture of the research object. V The curve represents the distance from the displacement data point to the southernmost side of the fracture. The minimum value of the horizontal axis is 0, and the maximum value is the total length of the fracture.

[0160] In one embodiment of this application, the vertical fracture F1, which is the subject of study, has a D V The curve is attached. Figure 13 As shown in Figure A, the horizontal axis of the curve represents the distance from the displacement data point to the southernmost side of fracture F1. The minimum value of the horizontal axis is 0, and the maximum value is the total length of fracture F1, which is 6.834 km.

[0161] Step S42, based on the vertical fracture D of the research object V L(D) is calculated from the curve. V =0) and D V-MAX / D V-MIN .

[0162] Based on the vertical fracture D obtained from step S41, which is the object of study... V The curve is then used to solve for the corresponding L(D) according to the method mentioned in step S25. V =0) and D V-MAX / D V-MIN .

[0163] In one embodiment of this application, based on the D of the upright fracture F1 obtained from step S41 V The curve is attached. Figure 13 As shown by the red line in A. Solve for the corresponding L(D) using the method mentioned in step S25. V =0) equals -0.736, the solution D V-MAX / D V-MIN The values ​​are equal to 0.308, all of which are marked in the appendix. Figure 13 In A.

[0164] Step S5, based on the vertical fracture L(D) obtained from step S42, which is the object of study... V =0) and D V-MAX / D V-MIN And the three transformation models proposed in step S3, to obtain the corresponding σ H / σ V σ h / σ H And θ, and based on this, reconstruct the regional paleotectonic stress field related to the strike-direction activity of fault F1.

[0165] Step S51, respectively with σ H / σ V σh / σ H With θ as the horizontal axis, and L(D) as the horizontal axis... V Plot three function curves with =0) as the vertical axis.

[0166] Firstly, with σ H / σ V Using L(D) as the horizontal axis, V Plot the discriminant curve with σ = 0 on the vertical axis. Equation (6) gives the result when σ = 0. H / σ V L(D) takes any value V =0) and D V-MAX / D V-MIN The transformation model 1 will take the vertical fracture D obtained in step S42 as the research object. V-MAX / D V-MIN Substituting the variable X into equation (6), we can obtain L(D) V =0) Regarding σ H / σ V The functional relationship between the two equations can be used to plot the corresponding function curve. Similarly, L(D) can be plotted sequentially based on equations (7) and (8). V =0) Regarding σ h / σ H The function curve of θ.

[0167] In one embodiment of this application, D V-MAX / D V-MIN Substituting 0.308 into equations (6) to (8), we can obtain L(D) respectively. V =0) Regarding σ H / σ V σ h / σ H The functional relationship between θ and θ can be used to plot the corresponding function curves, as shown in the appendix. Figure 13 B is indicated by the thick solid black, red, and blue lines.

[0168] Step S52, based on the vertical fracture L(D) obtained from step S42 as the object of study... V =0), and plot a line on the function curve obtained from step S51 with the ordinate always equal to this L(D). V =0), and based on the intersection of this horizontal line and the function curve obtained from step S51, reconstruct the regional paleotectonic stress field related to the strike-direction activity of fracture F1.

[0169] Based on the vertical fracture L(D) obtained from step S42, which is the object of study... V =0), and plot a line on the function curve obtained from step S51 with the ordinate always equal to this L(D).V Line L with a horizontal line of 0 and perform the following operations:

[0170] Operation 1: If the horizontal line L is the same as the L(D) obtained from step S51 V =0) Regarding σ H / σ V If the graphs of the functions intersect at a point, then the x-coordinate of that intersection point is considered to be σ. H / σ V The numerical value represents σ, which is related to the strike-slip of the upright fracture under study. H / σ V Numerical value. If the horizontal line L is the same as L(D) obtained from step S51. V =0) Regarding σ H / σ V If the function curves do not intersect, then in L(D) V =0) Regarding σ H / σ V Find the point on the function curve that is closest to the horizontal line L, and identify it as the intersection point 1.

[0171] Operation 2: If the horizontal line L is the same as the L(D) obtained from step S51 V =0) Regarding σ h / σ H If the graphs of the functions intersect at a point, then the x-coordinate of that intersection point is considered to be σ. h / σ H The numerical value represents σ, which is related to the strike-slip of the upright fracture under study. h / σ H Numerical value. If the horizontal line L is the same as L(D) obtained from step S51. V =0) Regarding σ h / σ H If the function curves do not intersect, then in L(D) V =0) Regarding σ h / σ H Find the point on the function curve that is closest to the horizontal line L, and identify it as the intersection point 2.

[0172] Operation 3: If the horizontal line L is the same as the L(D) obtained from step S51 V =0) The function curve of θ intersects at a point, then the x-coordinate of the intersection point, i.e., the value of θ, is considered to represent the value of θ related to the strike-slip of the upright fracture as the object of study. If the horizontal line L intersects with L(D) obtained from step S51, then the horizontal line L intersects with the horizontal line L(D) obtained from step S51. V =0) The function curves of the function with respect to θ have no intersection points, then in L(D V =0) Find the point on the graph of the function of θ that is closest to the horizontal line L, and identify it as the intersection point 3.

[0173] The x-coordinates of the intersection points 1, 2, and 3 above represent the σ values ​​of the corresponding regional tectonic stress fields when the vertical fracture under study undergoes sliding along its strike. H / σ V σ h / σ H and θ, where σ H / σ V and σ h / σ H It can reflect the relative magnitudes of the regional horizontal maximum principal stress, regional horizontal minimum principal stress, and vertical stress, and can be used to reflect the type of tectonic stress (Anderson, EM, 1951. The Dynamics of Faulting and Dyke Formation with Application to Britain, The Journal of Geology, 51(2), 140-140). The parameter θ reflects the angle between the regional horizontal maximum principal stress and the vertical fracture. Combined with the direction of the vertical fracture's strike-slip, the precise azimuth of the regional horizontal maximum principal stress can be quantitatively determined. The reconstruction of the paleotectonic stress field is now complete.

[0174] In one embodiment of this application, the L(D) of the vertical fracture F1 is solved from step S42. V =0) equals -0.736, in the appendix Figure 13 Draw a horizontal line L with a ordinate of -0.736 in B, and perform the following operations:

[0175] Operation 1: The horizontal line L and the attached Figure 13 B in L(D) V =0) Regarding σ H / σ V The function curves have one intersection point, and the x-coordinate of this intersection point is 1.863. Therefore, it is assumed that σ is related to the strike-slip of the vertical fracture F1. H / σ V It is 1.863.

[0176] Operation 2: The horizontal line L and the attached Figure 13 B in L(D) V =0) Regarding σ h / σ H The function curves have one intersection point, and the x-coordinate of this intersection point is 0.065. Therefore, the σ value associated with the strike-slip of the vertical fracture F1 is considered to be related to this intersection point. h / σ H It is 0.065.

[0177] Operation 3: The horizontal line L and the attached Figure 13 B in L(D)V If the function curve of θ has two intersection points with the horizontal axis, the horizontal maximum principal stress is equal to 27.14° or 35.98°.

[0178] σ H / σ V and σ h / σ H are equal to 1.863 and 0.065 respectively, corresponding to a type III stress field (σ H > σ V > σ h ). θ is equal to 27.14° or 35.98°, which means that the angle between the regional horizontal maximum principal stress and the vertical fault F1 is 27.14° or 35.98°. From step S1, it is known that the vertical fault F1 is left-lateral strike-slip, so the direction of the regional horizontal maximum principal stress is parallel to the trace of the vertical fault F1 after a clockwise rotation of 27.14° or 35.98°. Fig. 2A shows the trace of the vertical fault F1 in the plane, and its strike is NW-56.68°, so the direction of the regional horizontal maximum principal stress is NWW-83.82° or SWW-92.66°, as shown in Fig. 2B. Thus, the reconstruction of the paleo-tectonic stress field is completed. Figure 13 C shows the trace of the vertical fault F1 in the plane, and its strike is NW-56.68°, so the direction of the regional horizontal maximum principal stress is NWW-83.82° or SWW-92.66°, as shown in Fig. 2B. Thus, the reconstruction of the paleo-tectonic stress field is completed. Figure 13 C shows the trace of the vertical fault F1 in the plane, and its strike is NW-56.68°, so the direction of the regional horizontal maximum principal stress is NWW-83.82° or SWW-92.66°, as shown in Fig. 2B. Thus, the reconstruction of the paleo-tectonic stress field is completed.

[0179] Any technical features in the above embodiments can be combined, and for the sake of brevity, not all possible combinations of the technical features in the above embodiments are described, however, as long as the combinations of the technical features do not contradict each other, they shall be considered within the scope of the present disclosure.

Claims

1. A method for reconstructing paleotectonic stress fields based on vertical displacement of vertical fractures, characterized in that, include: Step S1: Determine the study area, target strata, and vertical fractures as the research object; obtain core data, conventional logging data, and array sonic logging data of the target strata; and solve for the static rock mechanics parameters of the target strata. Step S2 involves constructing geomechanical and mathematical models related to the strike-slip movement of the vertical fracture, conducting numerical simulation experiments on the tectonic stress field, obtaining the vertical deformation characteristics of the strata on both sides of the vertical fracture from the experimental results, and plotting the vertical displacement of the vertical fracture corresponding to different models. Curves, and statistically analyze the results for each model. Maximum value and minimum value ratio ,as well as zero position ; Step S3, Build and The conversion model between them; step S3 includes: When the ratio of the maximum horizontal principal stress to the vertical stress in the region When taking different values, the zero-value location of the vertical displacement obtained from all models in step S2 is determined. The ratio of the maximum value to the minimum value Fit the effective data to obtain and The first conversion model; When vertical fracture occurs and the maximum principal stress in the region is equal to the horizontal stress Angle of direction When taking different values, the values ​​obtained from all models in step S2 are... and Fit the effective data to obtain and The second conversion model; When the ratio of the minimum principal stress to the maximum principal stress in the region is When taking different values, the values ​​obtained from all models in step S2 are... and Fit the effective data to obtain and The third transformation model; The construction of the first, second, and third transformation models also includes: When σ H / σ V When taking different values, for and The effective data is fitted using the following formula: ； Where X represents Y represents a, b, and c all represent constant coefficients; using parameters The exponential function model between parameters X and Y is concretized into the first transformation model: ； In the formula, X represents Y represents ; , and These represent the constant coefficients of the first transformation model; when When taking different values, the fitting formula is used to... and Fit the valid data; Using parameters The fitting formula is then concretized into a second transformation model: ； Where X represents Y represents ; , and Indicates the constant coefficients of the second transformation model; when When taking different values, the fitting formula is used to... and Fit the valid data; Using parameters The fitting formula is then concretized into a third transformation model: ； Where X represents Y represents ; , and Represents the constant coefficients of the third transformation model; Step S4, according to the Curve calculation and ; Step S5, based on the vertical fracture obtained from step S4 and And the conversion model proposed in step S3, to obtain the corresponding , and Based on this, the regional paleotectonic stress field associated with the strike-direction activity of vertical faults can be reconstructed.

2. The method for reconstructing paleotectonic stress fields based on vertical displacement of vertical fractures according to claim 1, characterized in that, Step S1 includes: For study areas with core data but lacking array sonic logging data, rock mechanics tests are conducted on core samples to obtain static rock mechanics parameters. Each static rock mechanics parameter is the average of the corresponding parameters from all samples. The static rock mechanics parameters include static Young's modulus, static Poisson's ratio, and density. For study areas lacking core data, static rock mechanics parameters of the corresponding lithology in the nearby area are obtained by consulting literature after identifying the main lithology of the target stratigraphy. For study areas with core, conventional logging, and array sonic logging data, dynamic rock mechanics parameters are first calculated based on conventional logging and array sonic logging data, using the following formula: ； ； in, This represents the dynamic Young's modulus, expressed in GPa. Indicates the dynamic Poisson's ratio; This represents the longitudinal wave time difference (DTC), with units of μs / ft. The transverse wave time difference (DTS) is expressed in μs / ft; ρ represents density, expressed in g / cm³. 3 The dynamic rock mechanics parameters include dynamic Young's modulus and dynamic Poisson's ratio. Based on the static rock mechanics parameters obtained from the rock mechanics tests of the core samples, a fitting process is performed on the dynamic and static rock mechanics parameters to obtain a conversion model for the dynamic and static rock mechanics parameters of the target strata. The dynamic rock mechanics parameters are then converted to static rock mechanics parameters using the conversion model. The conversion formula is as follows: ； ； In the formula, This represents the dynamic Young's modulus, expressed in GPa. Indicates the dynamic Poisson's ratio; This represents the static Young's modulus, with units of GPa. This represents the static Poisson's ratio.

3. The method for reconstructing paleotectonic stress fields based on vertical displacement of vertical fractures according to claim 1, characterized in that, Step S2 includes: Based on the geological characteristics of the study area, a three-dimensional geomechanical model was constructed, which includes the location, strike, and extension length of the vertical fracture, as well as the geometric characteristics of the target strata. The vertical fracture was set as a discontinuity with a certain friction coefficient to simulate the relative sliding of the strata on both sides of the fracture. The geomechanical model is transformed into a mathematical model, and the model is divided into several elements and nodes by meshing using finite element analysis software. The static rock mechanics parameters obtained from step S1 are assigned to each element in the mathematical model; the boundary conditions and constraints of the mathematical model are set according to the requirements of research accuracy; numerical simulation experiments of tectonic stress field are carried out to obtain the simulation results corresponding to each experiment; The vertical displacement of the vertical fracture corresponding to each set of tectonic stress field numerical simulation experiments is obtained based on the vertical displacement of the top interface of the model. Curves were used to establish the boundary conditions and vertical displacement curves for numerical simulation of the structural stress field. One-to-one correspondence; Based on vertical displacement The curve was used to calculate the vertical displacement of each model. maximum value and minimum value ratio and vertical displacement zero position .

4. The method for reconstructing paleotectonic stress fields based on vertical displacement of vertical fractures according to claim 1, characterized in that, The construction of the first, second, and third transformation models also includes: when When taking different values, for and Fitting to valid data, if multiple different settings are used. The numerical values ​​are then fitted to obtain multiple corresponding fitting functions, which are denoted as the first transformation model. In the first transformation model, all fitted functions belong to the same type, but their constant coefficients differ; the constant coefficients in each fitted function are compared with... The functional relationship, if the fitted function is unclear, is determined based on the constant coefficients and... Based on the one-to-one correspondence, a first correlation curve is plotted as a discrimination chart, wherein the horizontal axis of the first correlation curve is... The vertical axis represents the constant coefficients of each term. A curve is plotted for each undetermined constant coefficient. when When taking different values, for and Fitting to valid data, if multiple different settings are used. The numerical values ​​are then fitted to obtain multiple corresponding fitting functions, which are denoted as the second transformation model. In the second transformation model, all fitted functions belong to the same type, but their constant coefficients differ; the constant coefficients in each fitted function are compared with... The functional relationship, if the fitted function is unclear, is determined based on the constant coefficients and... A second correlation curve is plotted based on the one-to-one correspondence, serving as a discrimination chart. The horizontal axis of the second correlation curve is... The vertical axis represents the constant coefficients of each term; a curve is plotted for each undetermined constant coefficient. when When taking different values, for and Fitting to valid data, if multiple different settings are used. The numerical values ​​are then fitted to obtain multiple corresponding fitting functions, which are denoted as the third transformation model. In the third transformation model, all fitted functions belong to the same type, but their constant coefficients differ. The constant coefficients in each fitted function are compared with... The functional relationship, if the fitted function is unclear, is determined based on the constant coefficients and... Based on the one-to-one correspondence, a third correlation curve is plotted as a discrimination chart, wherein the horizontal axis of the third correlation curve is... The vertical axis represents the constant coefficients of each term. A curve is plotted for each undetermined constant coefficient.

5. The method for reconstructing paleotectonic stress fields based on vertical displacement of vertical fractures according to claim 1, characterized in that, Step S5 includes: respectively , and With the horizontal axis as the base, Plot the corresponding discrimination curve for the vertical axis; According to the information obtained from step S4 Plot the vertical axis on the corresponding discrimination curve, which is always equal to... The horizontal line is used to reconstruct the regional paleotectonic stress field related to the strike-direction activity of the vertical fault, based on the intersection of the horizontal line and the discrimination curve.

6. The method for reconstructing paleotectonic stress fields based on vertical displacement of vertical fractures according to claim 5, characterized in that, Step S5 further includes: by With the horizontal axis as the base, Plot the first discriminant curve on the vertical axis; if the horizontal line If the horizontal line intersects with the first discrimination curve, then that intersection point is recorded as the first intersection point; if the horizontal line... If there is no intersection with the first discrimination curve, then in about Find the horizontal line on the function curve graph. The point that is closest to the first intersection is then identified. by With the horizontal axis as the base, Plot the second discriminant curve on the vertical axis; if the horizontal line If the horizontal line intersects with the second discrimination curve, it is recorded as the second intersection point; if the horizontal line... If there is no intersection with the second discrimination curve, then... about Find the horizontal line on the function curve graph. The point closest to the intersection is designated as the second intersection point. by With the horizontal axis as the base, Plot the third discriminant curve on the vertical axis; if the horizontal line If the horizontal line intersects with the third discrimination curve, it is recorded as the third intersection point; if the horizontal line... If there is no intersection with the third discrimination curve, then in about Find the point on the function curve that is closest to the horizontal line L, and mark it as the third intersection point; The abscissas of the first, second, and third intersection points represent the corresponding regional tectonic stress fields when the vertical fracture under study undergoes sliding along its strike. , and ,in, and It reflects the relative magnitudes of the maximum horizontal principal stress, the minimum horizontal principal stress, and the vertical stress in the region, and reflects the type of tectonic stress. By reflecting the angle between the maximum horizontal principal stress in the region and the vertical fracture, and combining this with the direction of sliding along the strike of the vertical fracture, the precise azimuth of the maximum horizontal principal stress in the region can be quantitatively determined, thus completing the reconstruction of the paleotectonic stress field.

Images