Evaluation method for tectonic genesis of natural fractures in disturbed geostress field environment

Abstract

Disclosed is an evaluation method for tectonic genesis of natural fractures in a disturbed geostress field environment, including the following steps: S1, data collection; S2, separation of a natural fracture subsystem dominated by a regional tectonic stress field; S3, separation of a natural fracture subsystem dominated by a fault-induced disturbed stress field; S4, separation of a natural fracture subsystem dominated by a fold deformation disturbed stress field; SS, partitioning of ordered natural fracture subsystems in tight sandstone; and S6, clarification of developmental distribution characteristics of natural fracture subsystems in tight sandstone. In the present application, the relationship between geostress disturbance and fracture development characteristics is considered. Progressive isolation and comparative analysis of developmental features for tectonically induced fractures of different origins are conducted, and an evaluation method for tectonic genesis of natural fractures in a disturbed geostress field environment is formed. FIG. 1

Description

TECHNICAL FIELD The present application relates to the technical eld of exploration and development of an oil and gas eld, and specically to an evaluation method for tectonic genesis of natural fractures in a disturbed geostress eld environment. BACKGROUND With the continuous growth of global demand for oil and gas resources and the ongoing decline in conventional oil and gas production, unconventional oil and gas resources have demonstrated tremendous potential under the current economic and technological conditions. Among them, tight sandstone oil and gas resources are abundant, widely distributed, and are a key area for increasing reserves and production of oil and gas resources worldwide. Under the combined effects of diagenetic evolution and tectonic compression, the matrix porosity and permeability of tight sandstone reservoirs continuously decrease while developing abundant natural fractures. As crucial migration pathways and storage spaces for tight sandstone oil and gas, the investigation of natural fracture development and distribution characteristics constitutes a key focus in tight reservoir research. Geostress represents a critical factor inuencing the development and distribution patterns of natural fractures in tight sandstone reservoirs. Natural fractures are direct manifestations of stressstrain responses and serve as the most direct indicators of stress eld perturbations. Generally, stress elds can be categorized into regional stress elds and disturbed stress elds, in which regional stress eld refers to the distribution of crustal stresses within a specic spatial domain of a particular crustal region, and the disturbed stress eld refers to the stress eld in a region that has been decoupled due to pre-existing structural deformation, resulting in a disturbed stress eld in localized areas that differs signicantly from the regional stress state. In tight sandstone reservoirs, there mainly develop two types of disturbed stress elds: fold deformation-induced disturbed stress eld and faultinduced disturbed stress eld. The presence of these disturbed stress elds can lead to strong heterogeneity in fracture distribution within tight sandstone reservoirs, potentially causing intersecting, overlapping, and propagating of fractures, ultimately resulting in a more complex fracture network system. In the formation process, tight hydrocarbon reservoirs have typically undergone complex tectonic evolution, leading to the superimposed distribution of regional and disturbed stress elds. Under current complex structural conditions, the dominant controlling factors of natural fractures are not easily discernible, making it difcult to differentiate characteristics and distribution patterns of natural fractures with distinct tectonic origins. Therefore, it is imperative to conduct research on classication of tectonic genesis of natural fractures in a disturbed geostress eld environment, which will provide critical guidance for the analysis, evaluation, and prediction of natural fractures in tight hydrocarbon reservoirs. In terms of the relationship between geostress and fractures, an existing patent primarily considers the mutual inuence between fractures and stress from two aspects. Firstly, fracture network zones and directional fracture zones are determined based on horizontal differential stress values, in which the directional fracture zones are irther subdivided into fracture-developed and fracture-underdeveloped zones. Subsequently, in fracturedeveloped zones, the hydraulic fracture initiation direction is determined based on the angular relationship between pre-existing fractures and the maximum horizontal principal stress orientation, whereas in fractureunderdeveloped zones, the maximum horizontal principal stress orientation is selected as the preferred fracture initiation direction. This methodology primarily utilizes two key parameters: a horizontal differential stress magnitude and an angular relationship between maximum horizontal principal stress orientation and natural fractures, to determine optimal hydraulic fracture orientations. Currently published literature presents various classications of fractures. Some divide fractures into two major categories: nontectonic fractures and tectonic fractures, while others categorize them as tectonic fractures, diagenetic fractures, and drillinginduced fractures, without irther subdividing tectonic fractures based on the tectonic genesis. A minor portion of tectonic fractures is classied based on developmental characteristics of fractures themselves, categorizing them into regional tectonic fractures, tectonic deformation fractures, and fault-associated fractures. Specically: regional tectonic fractures are straight, strongly penetrating through layers, and extensively extending, generally perpendicular to bedding planes or intersecting with them at high angles, formed under regional stress over a large area. Fault-derived fractures, developing on both sides of fault cores, include two sets of conjugate shear fractures intersecting at small angles and high-angle extension fractures, whereas the fault-associated fractures developed in fault cores are characterized by disordered, highdensity network fractures. Tectonic deformation-related fractures are fractures derived from local compression and bending of rock strata. Current studies on the coupling relationships between geostress and fractures have failed to denitively establish the genetic mechanisms of natural fractures. The relationship between different genetic types of fractures and geostress elds exhibit is different, and considering natural fracture density solely based on stress orientation, without analyzing the controlling factors of fractures from different origins, may result in low accuracy of ndings. Furthermore, the inuence of geostress on the geometric parameters and mechanical properties of natural fractures has not been investigated. Essentially, fracture zoning is only based on natural fracture density and stress magnitude, without considering the control ranges of different types of dominant stress elds. The above methods for classifying natural fracture systems in tight sandstone reservoirs are all based on the study of all single-well fractures, without selecting wells dominated by different stress elds or employing a stepwise decoupling method to investigate the development characteristics of natural fractures under the control of different stress elds. Meanwhile, the inuence of geostress on fracture development has been overlooked. Geostress is the primary force driving the formation and evolution of natural fractures, and natural fractures are important responses to geostress disturbances. Furthermore, the tectonic genesis classication of fractures has not been conducted within a clearly dened geostress disturbance environment. The relationships between different stress elds and fractures have not been clearly dened, which can easily lead to insufcient understanding of tight oil and gas accumulation, affecting the efciency, safety, and economics of drilling, completion, and hydraulic fracturing operations, as well as the highyield and stable production of tight oil and gas wells. SUMMARY In view of this, the present application provides an evaluation method for tectonic genesis of natural fractures in a disturbed geostress eld environment, which can analyze inuencing factors of fracture control with different genetic factors, clarify control scopes of different types of dominate stress elds, and determine dominant zoning distribution characteristics of natural fracture subsystems in complex structural areas. To realize the above objective, the present application employs the following technical solutions. An evaluation method for tectonic genesis of natural fractures in a disturbed geostress eld environment includes the following steps: S 1, data collection; S2, separation of a natural fracture subsystem dominated by a regional tectonic stress eld; S3, separation of a natural fracture subsystem dominated by a faultinduced disturbed stress eld; S4, separation of a natural fracture subsystem dominated by a fold deformation disturbed stress eld; S5, partitioning of ordered natural fracture subsystems in tight sandstone; and S6, clarication of developmental distribution characteristics of natural fracture subsystems in tight sandstone. In a further description, S1 specically includes the steps of: collecting the data on structural maximum curvature of the target formation, stress eld magnitude and direction, distance-to-fault, core-photograph fracture identication, and imaging logging identication of natural fracture strike and dip from a single well. In a further description, S2 specically includes the following steps: S2.l, screening out a well dominated by a regional tectonic stress eld; and 82.2, obtaining natural fracture features dominated by the regional tectonic stress eld, and dening an average density po of natural fractures dominated by the regional tectonic stress eld. In a irther description, S3 specically includes the following steps: S3.1: calculating the distances between each single well and the nearest faults, differentiating between a primary fault and secondary and tertiary faults, performing statistical analysis on the correlation between the natural fracture density in the single wells and distances from the primary fault, as well as the correlation between the natural fracture density in the single wells and distances from the secondary and tertiary faults, and establishing a rst linear regression equation and a second linear regression equation based on these analyses. 83.2: using the average density po of natural fracture dominated by the regional tectonic stress eld as a constraint, and substituting the po and 2p0 into the rst linear regression equation to calculate corresponding distances to the primary fault, with these distances as an initiation critical distance for development Dl and a dominance critical distance D1 of natural fracture dominated by the primary faultinduced disturbed stress eld in the single well; or and substituting the po and 2p0 into the second linear regression equation to calculate corresponding distances to the secondary and tertiary faults, with these distances as an initiation critical distance for development DZ and a dominance critical distance D2 of natural fracture dominated by the secondary and tertiary faults-induced disturbed stress eld in the single well. 83.3: screening out a well dominated by the faultinduced disturbed stress eld based on the dominance critical distances D1 and D2 , and removing a natural fracture dominated by the regional tectonic stress eld based on the separation of a natural fracture subsystem dominated by a regional tectonic stress eld; and 83.4: characterizing natural fracture features dominated by the fault-induced disturbed stress eld, including dip angle, dip direction, fracture surface morphology, and angular relationships with the maximum horizontal principal stress. In a further description, 83.1 includes the steps of: performing hierarchical analysis on the relationship between distancetofault and natural fracture density in the single well, to obtain a linear regression equation between distance to a primary fault and average natural fracture density of single well: p = 0.099 ln Dl + 0.8009, R1 = 0.6510 (1) in which p is an average natural fracture density of single well, with a unit: fracture / m; Dl is a distance form a single well to a primary fault, With a unit: m; and R1 is a correlation coefcient between the average natural fracture density of single well and the distance from the single well to the primary fault; and a linear regression equation between distance to secondary and tertiary faults and average natural fracture density of single well is: p = 0.0921n DZ + 0.7127, R2 = 0.7620 (2) in which p is an average natural fracture density of single well, with a unit: fracture / m, DZ is a distance form a single well to secondary and tertiary faults, with a unit: m, and R2 is a correlation coefcient between the average natural fracture density of single well and the distance from the single well to the secondary and tertiary faults. In a further description, 83.2 includes the steps of: using the average density po of natural fracture dominated by the regional tectonic stress eld as a constraint, and substituting the pO and 2p0 into a linear regression equation (1) to calculate corresponding distances to the primary fault, with these distances as an initiation critical distance for development Dl and a dominance critical distance D1 of natural fracture dominated by the primary faultinduced disturbed stress eld in the single well; or using the average density po of natural fracture dominated by the regional tectonic stress eld as a constraint, and substituting the pO and 2p0 into a linear regression equation (2) to calculate corresponding distances to the secondary and tertiary faults, with these distances as an initiation critical distance for development D2 and a dominance critical distance D2 of natural fracture dominated by the secondary and tertiary faultsinduced disturbed stress eld in the single well. In a further description, S3.3 includes the steps of: screening out a well dominated by the primary faultinduced disturbed stress eld based on the dominance critical distance D1 , and removing a natural fracture dominated by the regional tectonic stress eld based on the separation of a natural fracture subsystem dominated by a regional tectonic stress eld; or screening out wells dominated by the secondary and tertiary fault-induced disturbed stress eld based on the dominance critical distance D2 , and removing a natural fracture dominated by the regional tectonic stress eld based on the separation of a natural fracture subsystem dominated by a regional tectonic stress eld. In a irther description, S4 specically includes the following steps: S4.1: establishing a third linear regression equation by investigating a relationship between the structural maximum curvature of the target formation and residual natural fracture density of single well, with the third linear regression equation being shown in equation (3): = 0.0205 4-30 3 = 0.7683 (3) in which p is an average natural fracture density of single well, with a unit: fracture / m; K is a structural maximum curvature of the target formation, with a unit: l / km; and R3 is a correlation coefcient between the average natural fracture density of single well and the structural maximum curvature of the target formation; 84.2: substituting the po and 2p0 into the third linear regression equation to calculate corresponding data of structural maximum curvature of the target formation, with these data as an initiation critical curvature for development K and a dominance critical curvature K of natural fracture dominated by a fold deformation disturbed stress eld in the single well; 84.3: screening out a well dominated by the fold deformation disturbed stress eld based on the dominance critical curvature K', and removing a natural fracture dominated by the regional tectonic stress eld based on the separation of a natural fracture subsystem dominated by a regional tectonic stress eld; and S4.4: characterizing natural fracture features dominated by the fold deformation disturbed stress eld, including dip angle, dip direction, fracture surface morphology, and angular relationships with the maximum horizontal principal stress. In a irther description, 85 specically includes the steps of: forming an identication parameter table and a classication criteria template based on three natural fracture subsystems separated from disturbed geostress eld, initiation critical distances for development, dominance critical distances, initiation critical curvatures for development from the target formation as well as dominance critical curvatures, obtaining a dimensional-reduction-based zoning map of ordered natural fracture subsystems in complex structural zones, and classifying a study area into a regional tectonic stress eld-dominated zone, a fold deformation disturbed stress eld-dominated zone, and a faultinduced disturbed stress elddominated zone, the three natural fracture subsystems including a natural fracture subsystem dominated by a regional tectonic stress eld, a natural fracture subsystem dominated by a faultinduced disturbed stress eld and a natural fracture subsystem dominated by a fold deformation disturbed stress eld. Compared to the related art, the present application has the following benecial effects. According to the present application, the relationship between geostress disturbance and fracture development characteristics is considered. Under geostress eld disturbance conditions, progressive isolation and comparative analysis of developmental features for tectonically induced fractures of different origins are conducted, and an evaluation method for tectonic genesis of natural fractures in a disturbed geostress eld environment is formed, which can enhance the accuracy of research on fracture developmental patterns, and provide a more powerful basis for fracture studies. BRIEF DESCRIPTION OF THE DRAWINGS To more clearly illustrate the technical solution in the example of the present application, a brief description of the drawings required to be used in the example is presented below. It is to be understood that the drawings described below are only certain examples of the present application and shall not be regarded as limiting the scope. For those ordinary skilled in the art, other related drawings may be obtained based on these drawings without creative efforts. FIG. 1 is a ow chart of an evaluation method for tectonic genesis of natural fractures in a disturbed geostress eld environment; FIG. 2 is a fracture characterization map of a well dominated by a regional tectonic stress eld; FIG. 3 is a relational graph between an average fracture density of single well and a distance form a single well to a primary fault; FIG. 4 is a relational graph between an average fracture density of single well and a distance form a single well to secondary and tertiary faults; FIG. 5 is a fracture characterization map of a well dominated by a fault-induced disturbed stress eld; FIG. 6 is a relational graph between an average fracture density of single well and a structural maximum curvature of target formation; FIG. 7 is a fracture characterization map of a well dominated by a fold deformation disturbed stress eld; FIG. 8 is a tectonic genetic zoning map of single well fractures in a disturbed geostress eld environment; and FIG. 9 is a dimensional-reduction-based zoning map of ordered natural fracture subsystems in complex structural zones. DETAILED DESCRIPTION In order to make the purpose, technical solutions and advantages of the examples in the present application more clear, the technical solutions in the examples of the present application is further described clearly and completely below in combination with the accompanying drawings. Obviously, the examples described are only some, rather than all examples of the present application. Referring to FIG. 1, an evaluation method for tectonic genesis of natural fractures in a disturbed geostress eld environment includes the following steps: In Sl, data collection: the data on structural maximum curvature of the target formation, stress eld magnitude and direction, distancetofault, corephotograph fracture identication, and imaging logging identication of natural fracture strike and dip from a single well are collected. The distance-to-fault is a distance between a single well target formation and the fault. In 82, separation of a natural fracture subsystem dominated by a regional tectonic stress eld specically includes the following steps: In 82.1, a well dominated by a regional tectonic stress eld is screened out. In 82.2, natural fracture features dominated by the regional tectonic stress eld are obtained, and an natural fracture density po of natural fracture dominated by the regional tectonic stress eld is dened. The screening conditions are as follows: the well located at a relatively large distance from the fault and with a small structural maximum curvature of the target formation (specic numerical thresholds are provided in subsequent Table l). Such well is far from the fault, exhibiting relatively weak structural deformation, and are situated within a dominant regional tectonic stress eld environment. By characterizing natural fracture features dominated by the regional tectonic stress eld, such as dip angle, dip direction, fracture surface morphology, and angular relationships with the maximum horizontal principal stress, the natural fracture features dominated by the regional tectonic stress eld are obtained; and the average density po of natural fracture dominated by the regional tectonic stress eld is dened based on outcrop fracture data. Through the analysis of the development characteristics of natural fractures of well in the target formation dominated by the regional tectonic stress eld and the data analysis of the stress eld, it is found that the direction of the tectonic stress eld is nearly north-south (as indicated by a central arrow in FIG. 2). The core samples from the single well are predominantly characterized by NNW- and NNE-striking shear fractures with planar surfaces, accompanied by a minor occurrence of NSoriented tensile fractures exhibiting rough surfaces, which are primarily vertical. The NNW and NNE shear fractures intersect the in-situ stress eld at acute angles, whereas the NS tensile fractures are subparallel to the geostress orientation. Based on the statistical analysis of outcrop fractures in the study area, the average density pO of natural fractures dominated by the regional tectonic stress eld is approximately 0.08 fractures / m. In S3, separation of a natural fracture subsystem dominated by a fault-induced disturbed stress eld specically includes the following steps: In 83.1, the distances between each single well and the nearest faults are calculated, a primary fault and secondary and tertiary faults are differentiated, statistical analysis is performed on the correlation between the natural fracture density in the single wells and distances from the primary fault, as well as the correlation between the natural fracture density in the single wells and distances from the secondary and tertiary faults, and a rst linear regression equation and a second linear regression equation are established based on these analyses. In 83.2, the average density po of natural fracture dominated by the regional tectonic stress eld is used as a constraint, and the pO and 2p0 are substituted into the rst linear regression equation to calculate corresponding distances to the primary fault, with these distances as an initiation critical distance for development Dl and a dominance critical distance D1 of natural fracture dominated by the primary faultinduced disturbed stress eld in the single well; or and the po and 2p0 are substituted into the second linear regression equation to calculate corresponding distances to the secondary and tertiary faults, with these distances as an initiation critical distance for development DZ and a dominance critical distance D2 of natural fracture dominated by the secondary and tertiary faults-induced disturbed stress eld in the single well. In S3.3, a well dominated by the faultinduced disturbed stress eld is screened out based on the dominance critical distances D1 and D2 , and a natural fracture dominated by the regional tectonic stress eld is removed based on the separation of a natural fracture subsystem dominated by a regional tectonic stress eld. The screening condition is as follows: the distance to the primary fault is less than the D'1 , or the distances to the secondary and tertiary faults are less than the D2 . In 83.4, natural fracture features dominated by the faultinduced disturbed stress eld are characterized, such as dip angle, dip direction, fracture surface morphology, and angular relationships with the maximum horizontal principal stress. The rst linear regression equation is established by investigating the relationship between the distance from the single well to the primary fault and the natural fracture density in the single well, and the average density pO of natural fracture dominated by the regional tectonic stress eld is used as a constraint. Under the inuence of faultinduced disturbed stress eld, when an average natural fracture density of single well is greater than po, the average natural fracture density of single well is greater than the average density of natural fracture dominated by the regional tectonic stress eld, indicating an initiation of faultrelated natural fracture. Similarly, under the inuence of faultinduced disturbed stress eld, when an average natural fracture density of single well is greater than 2p0, an average density of natural fractures dominated by the faultinduced disturbed stress eld developed in the single well will be higher than that of natural fractures dominated by the regional tectonic stress eld, dominating in the single well fractures. At this time, the single well fractures are primarily attributed to the natural fractures dominated by the fault-induced disturbed stress eld. The po and 2p0 are substituted into the rst linear regression equation to calculate corresponding distances to the primary fault, with these distances as an initiation critical distance for development Dl and a dominance critical distance D1 of natural fracture dominated by the primary fault-induced disturbed stress eld in the single well. Based on the dominance critical distance D1 , the well dominated by the primary fault-induced disturbed stress eld is screened out, and a natural fracture dominated by the regional tectonic stress eld is removed based on the separation of a natural fracture subsystem dominated by a regional tectonic stress eld. Moreover, the natural fracture features dominated by the primary faultinduced disturbed stress eld are characterized, such as dip angle, dip direction, fracture surface morphology, and angular relationships with the maximum horizontal principal stress. When faults exhibit signicant differences in development scales, the faults may be hierarchically classied into secondary or tertiary structures for systematic analysis. By repeating the above steps, the second linear regression equation can be obtained, and the critical distances to the secondary and tertiary faults DZ and D'2 are obtained. Research indicates that while faults of different orders have varying disturbance ranges, the distance from faults of any order has a pronounced effect on the natural fracture density of single well. Referring to FIGS. 34, the closer the distance to the fault, the greater the average natural fracture density of single well. At this time, 83.1 includes the following steps that: hierarchical analysis is performed on the relationship between distance-to-fault and natural fracture density in the single well, to obtain a linear regression equation between distance to a primary fault and average natural fracture density of single well: p = 0.099 ln Dl + 0.8009, R1 = 0.6510 (1) in which p is an average natural fracture density of single well, with a unit: fracture / m; Dl is a distance form a single well to a primary fault, with a unit: m; and R1 is a correlation coefcient between the average natural fracture density of single well and the distance from the single well to the primary fault, which is automatically generated from a scatter plot. A linear regression equation between distance to secondary and tertiary faults and average natural fracture density of single well is: p = 0.092 ln DZ + 0.7127, RZ = 0.7620 (2) in which p is an average natural fracture density of single well, with a unit: fracture / m; DZ is a distance form a single well to secondary and tertiary faults, with a unit: m; and R2 is a correlation coefcient between the average natural fracture density of single well and the distance from the single well to the secondary and tertiary faults, which is automatically generated from a scatter plot. 83.2 includes the following steps that: the average density po of natural fracture dominated by the regional tectonic stress eld is used as a constraint, and the pO and 2p0 are substituted into a linear regression equation (1) to calculate corresponding distances to the primary fault, with these distances as an initiation critical distance for development Dl and a dominance critical distance D1 of natural fracture dominated by the primary faultinduced disturbed stress eld in the single well; or the average density po of natural fracture dominated by the regional tectonic stress eld is used as a constraint, and the pO and 2p0 are substituted into a linear regression equation (2) to calculate corresponding distances to the secondary and tertiary faults, with these distances as an initiation critical distance for development Dz and a dominance critical distance D2 of natural fracture dominated by the secondary and tertiary faultsinduced disturbed stress eld in the single well. S3.3 includes the following steps that: based on the dominance critical distance D'1 , a well dominated by the primary faultinduced disturbed stress eld is screened out, with a distance from the primary fault being less than the D1 , and a natural fracture dominated by the regional tectonic stress eld is removed based on the separation of a natural fracture subsystem dominated by a regional tectonic stress eld; or wells dominated by the secondary and tertiary fault-induced disturbed stress eld are screened out based on the dominance critical distance D2 , with distances from the secondary and tertiary faults being less than the D'2 , and a natural fracture dominated by the regional tectonic stress eld is removed based on the separation of a natural fracture subsystem dominated by a regional tectonic stress eld. The screening conditions are as follows: the distance to the primary fault is less than the dominance critical distance D1 ; or the distances to the secondary and tertiary faults are less than the dominant critical distance D2 . Field statistics indicate that the pO is approximately 0.08 fractures / m. When the average natural fracture density of a single well under the inuence of the primary faultinduced disturbed stress eld exceeds the po , it signies that this density surpasses the average density of natural fractures dominated by the regional tectonic stress eld, thereby marking the initiation of natural fractures dominated by the primary fault-induced disturbed stress eld. The p = pO = 0.08 is substituted into the equation (1) to obtain: 0.08 = 0.099 ln Dl + 0.8009 Dl z 1453.63 Similarly, when the average natural fracture density of a single well under the inuence of the primary faultinduced disturbed stress eld exceeds 2p0 , the density of natural fractures dominated by primary faultinduced disturbed stress eld within the well will surpass the average density po of natural fractures dominated by the regional tectonic stress eld , thereby becoming predominant in the single well fractures. At this time, the natural fractures within the well are dominated by the primary fault-induced disturbed stress eld. The p = 2p0 = 0.16 is substituted into the equation ( 1) to obtain: 0.16 = 0.099 ln D1 + 0.8009 D1 = 647.90 The computational results above indicate that when the distance from the primary fault is less than 1453.63 m, natural fractures dominated by the primary fault-induced disturbed stress eld begin to develop in the single well. When the distance is irther reduced below 647.90 m, these natural fractures dominated by the primary fault-induced disturbed stress eld become predominant in the single fracture system, as illustrated in FIG. 3. When the average natural fracture density of a single well under the inuence of the secondary and tertiary faultinduced disturbed stress eld exceeds the pO, it signies that this density surpasses the average density of natural fractures dominated by the regional tectonic stress eld, thereby marking the initiation of natural fractures dominated by the secondary and tertiary faultinduced disturbed stress eld. The p = po = 0.08 is substituted into the equation (2) to obtain: 0.08 = 0.092 ln DZ + 0.7127 Dz = 969.88 Similarly, when a single well fracture under the inuence of the secondary and tertiary fault-induced disturbed stress eld exceeds 2p0, the density of natural fractures dominated by the secondary and tertiary fault-induced disturbed stress eld Within the well will surpass the average density po of natural fractures dominated by the regional tectonic stress eld, thereby becoming predominant in the single well fractures. At this time, the natural fractures within the well are predominantly governed by the secondary and tertiary fault-induced disturbed stress eld. The p = 2p0 = 0.16 is substituted into the equation (2) to obtain: 0.16 = 0.0921n D2 + 0.7127 D2 % 406.51 The computational results above indicate that when the distances from the secondary and tertiary faults are less than 969.88 m, natural fractures dominated by the secondary and tertiary fault-induced disturbed stress eld begin to develop in the single well. When the distances are irther reduced below 406.51 m, these natural fractures dominated by the secondary and tertiary fault-induced disturbed stress eld become predominant in the single fracture system, as illustrated in FIG. 4. Based on the dened critical distances D1 and D2 , single wells located either within D1 of primary fault or within D2 of secondary and tertiary faults are screened out as wells dominated by the fracture disturbance stress eld. Based on the separation of a natural fracture subsystem dominated by a regional tectonic stress eld, a natural fracture dominated by the regional tectonic stress eld is removed. Analysis of the developmental characteristics of natural fractures in the target formation of the well dominated by fault-induced disturbed stress eld, combined with stress eld data, the regional tectonic stress eld orientation is approximately northsouth is revealed. However, inuenced by the fault-induced disturbed stress eld, the geostress direction deects near the fault (as indicated by a central arrow in FIG. 5), thereby governing the development orientation of the natural fracture subsystems dominated by fault-induced disturbed stress eld. The core from a single well shows the development of one set of conjugate shear fractures intersecting with the insitu stress direction at a small angle, and another set intersecting at a large angle. The fractures are dominated by high-angle to vertical shear fractures oriented in the NNE and NNW directions. In the fault core, the fracture orientations are chaotic, forming a network of fractures or resulting in a broken core appearance. The fracture surfaces are straight, with visible slickensides and steplike features (as shown in FIG. 5). In 84, separation of a natural fracture subsystem dominated by a fold deformation disturbed stress eld specically includes the following steps: In 84.1, a third linear regression equation is established by investigating a relationship between the structural maximum curvature of the target formation and residual natural fracture density of single well. The remaining single wells are those located at distances greater than D1 from the primary fault and greater than D2 from secondary and tertiary faults, exhibiting relatively high structural curvature in the target formation (specic threshold values are detailed in Table 1), and the third linear regression equation is shown in equation (3): = 0.0205 43029 , 3 = 0.7683 (3) in which p is an average natural fracture density of single well, with a unit: fracture / m; K is a structural maximum curvature of the target formation, with a unit: l / km; and R3 is a correlation coefcient between the average natural fracture density of single well and the structural maximum curvature of the target formation, which is automatically generated from a scatter plot. In 84.2, the po and 2p0 are substituted into the third linear regression equation to calculate corresponding data of structural maximum curvature of the target formation, with these data as an initiation critical curvature for development K and a dominance critical curvature K of natural fracture dominated by a fold deformation disturbed stress eld in the single well. In 84.3, a well dominated by the fold deformation disturbed stress eld is screened out based on the dominance critical curvature K , and a natural fracture dominated by the regional tectonic stress eld is removed based on the separation of a natural fracture subsystem dominated by a regional tectonic stress eld. In 84.4, natural fracture features dominated by the fold deformation disturbed stress eld are characterized, such as dip angle, dip direction, fracture surface morphology, and angular relationships with the maximum horizontal principal stress. The maximum structural curvature can reect the degree of stratigraphic deformation and serves as an important indicator of the intensity of the fold deformation disturbed stress eld. After excluding the well dominated by the faultinduced stress eld, a third linear regression equation is obtained by studying the relationship between the maximum structural curvature of the target formation and the remaining singlewell natural fracture density. Research shows that the maximum structural curvature of the target formation has a signicant inuence on the singlewell fracture development, where greater maximum structural curvature corresponds to higher average natural fracture density of single well (as shown in FIG. 6). The average density pO of natural fracture dominated by the regional tectonic stress eld is used as a constraint. Under the inuence of fold deformation disturbed stress eld, when an average natural fracture density of single well is greater than pO , the average natural fracture density of single well is greater than the average density of natural fracture dominated by the regional tectonic stress eld, indicating an initiation of fold deformationrelated natural fracture. Similarly, under the inuence of fold deformation disturbed stress eld, when an average natural fracture density of single well is greater than 2p0, an average density of natural fractures dominated by the fold deformation disturbed stress eld developed in the single well will be higher than that of natural fractures dominated by the regional tectonic stress eld, dominating in the single well fractures. At this time, the single well fractures are primarily attributed to the natural fractures dominated by the fold deformation disturbed stress eld. The po and 2p0 are substituted into the third linear regression equation to calculate corresponding data of structural maximum curvature of the target formation, with these data as an initiation critical curvature for development K and a dominance critical curvature K' of natural fracture l9 dominated by a fold deformation disturbed stress eld in the single well. Based on the dominance critical curvature K, the well dominated by the fold deformation disturbed stress eld is screened out, and a natural fracture dominated by the regional tectonic stress eld is removed based on the separation of a natural fracture subsystem dominated by a regional tectonic stress eld. Moreover, the natural fracture features dominated by the fold deformation disturbed stress eld are characterized, such as dip angle, dip direction, fracture surface morphology, and angular relationships with the maximum horizontal principal stress. Field statistics indicate that the pO is approximately 0.08 fractures / m. When the average natural fracture density of a single well under the inuence of the fold deformation disturbed stress eld exceeds the po , it signies that this density surpasses the average density of natural fractures dominated by the regional tectonic stress eld, thereby marking the initiation of natural fractures dominated by the fold deformation disturbed stress eld. The p = p0 = 0.08 is substituted into the equation (3) to obtain: 0.08 = 0.0205e4'3029K K % 0.32 Similarly, when the average natural fracture density of a single well under the inuence of the fold deformation disturbed stress eld exceeds 2p0, the density of natural fractures dominated by the fold deformation disturbed stress eld within the well will surpass the average density po of natural fractures dominated by the regional tectonic stress eld , thereby becoming predominant in the single well fractures. At this time, the natural fractures within the well are dominated by the fold deformation disturbed stress eld. The p = 2p0 = 0.16 is substituted into the equation (3) to obtain: 0.16 = 0.0205e4-3029K' K = 0.48 The computational results above indicate that when the structural maximum curvature of the target formation is greater than 0.32, natural fractures dominated by the fold deformation disturbed stress eld begin to develop in the single well. When the structural maximum curvature of the target formation is greater than 0.48, these natural fractures dominated by the fold deformation disturbed stress eld become predominant in the single fracture system. Based on the determined critical curvature K , the well dominated by the fold deformation disturbed stress eld with maximum structural curvature of the target formation exceeding K is screened out. Based on the separation of a natural fracture subsystem dominated by a regional tectonic stress eld, a natural fracture dominated by the regional tectonic stress eld is removed. Through analysis of natural fracture development characteristics and stress eld data in the well dominated by the fold deformation disturbed stress eld of the target formation, the structural stress eld orientation is determined to be approximately northsouth (as indicated by a central arrow in FIG. 7). Core analysis revealed dominant east-west trending tensional vertical fractures with rough fracture surfaces (as shown in in FIG. 7), demonstrating fracture strikes approximately perpendicular to the geostress direction. In 85, partitioning of ordered natural fracture subsystems in tight sandstone specically includes the following steps that: an identication parameter table (Table 1) and a classication criteria template (as shown in FIG. 8) are formed based on three natural fracture subsystems separated from disturbed geostress eld, initiation critical distances for development, dominance critical distances, initiation critical curvatures for development from the target formation as well as dominance critical curvatures, a dimensionalreductionbased zoning map of ordered natural fracture subsystems in complex structural zones is obtained, a study area is classied into a regional tectonic stress elddominated zone, a fold deformation disturbed stress eld-dominated zone, and a fault-induced disturbed stress eld-dominated zone (as shown in FIG. 9), and the three natural fracture subsystems include a natural fracture subsystem dominated by a regional tectonic stress eld, a natural fracture subsystem dominated by a faultinduced disturbed stress eld and a natural fracture subsystem dominated by a fold deformation disturbed stress eld. Table l Identication parameter table of sandstone natural fractures ordered subsystem zonation Natural fracture Natural fracture Natural fracture _ _ distribution zone distribution zone distribution zone Identication _ _ _ domlnated by dominated by domlnated by fold parameter _ _ _ _ _ _ regional tectonlc fault-Induced dlsturbed deformation disturbed stress eld stress field stress eld Curvature (km'l) < 0.48 - > 0.48 Distance to _ > 647.90 < 647.90 > 647.90 primary fault Distance to secondary and > 406.51 < 406.51 > 406.51 tertiary faults In 86, clarication of developmental distribution characteristics of natural fracture subsystems in tight sandstone. Ultimately, an evaluation method for tectonic genesis of natural fractures in a disturbed geostress eld environment is established, which claries the developmental distribution characteristics of natural fracture subsystems in target formations within the study area under disturbed geostress conditions (as shown in Table 2). Table 2 Developmental distribution characteristics of natural fracture subsystem under geostress eld disturbance Natural fracture Natural fracture subsystem subsystem Natural fracture subsystem _ _ _ _ _ _ dominated by dominated by Main parameter domlnated by regional tectonlc _ _ fault-1nduced fold deformation stress eld disturbed stress disturbed stress eld eld Mechanical _ _ _ _ Shear fracture Tens1le fracture Shear fracture Tens11e fracture characteristics One set Geostress and Intersecting at intersecting at a fracture a small angle Approximately small angle, and Approximately angular (approximatel parallel another set perpendicular relationship y 30°) intersecting at a large angle Vertical fractures with Vertical fractures Fractures with a Vertical fractures Dip angle a dip angle with a dip angle dip angle greater with a dip angle greater than greater than 75° than 60° greater than 75° 75° _ Curved and _ Curved and rough Straight fracture Straight _ rough fracture Fracture surface fracture surfaces surfaces w1th _ fracture _ _ _ _ _ _ _ surfaces With no morphology w1th no str1at10ns v1s1ble str1at10ns _ _ surfaces _ _ str1at10ns or steps or steps v1s1ble and steps _ _ v1s1ble According to the present application, the relationship between geostress disturbance and fracture development characteristics is considered. By analyzing the geostress characteristics and fracture development features of single wells dominated by different stress elds, the natural fracture characteristics of the dominant wells are matched with the mechanical conditions. Under geostress eld disturbance conditions, progressive isolation and comparative analysis of developmental features for tectonically induced fractures of different origins are conducted. By analyzing the inuencing factors of natural fractures, the dominant zoning distribution characteristics of natural fracture subsystems in complex structural areas are identied, and an evaluation method for tectonic genesis of natural fractures in a disturbed geostress eld environment is formed, which can provide a more powerful basis for fracture studies, and enhance the accuracy of research on fracture developmental patterns. The foregoing is only the specic example of the present application, but the scope of protection of the present application is not limited thereto. Within the scope of the technology disclosed in the present application, any person skilled in the art may readily think of changes or substitutions, and these changes or substitutions shall be covered by the scope of protection of the present application. Therefore, the scope of protection shall be determined by the scope of protection of the claims. CLAIMS 1. Evaluatiemethode voor tektonische genese van natuurlijke breuken in een verstoorde geostressveldomgeving, bestaande uit de volgende stappen: S 1, verzamelen van gegevens; 82, separation of a natural fault subsystem dominated by a regional tectonic stress field; S3, separation of a natural fault subsystem dominated by a fault-dominated causes disturbed tension field; S4, separation of a natural fault subsystem dominated by a fold formation disturbed tension field; S5, partitioning of ordered natural fracture subsystems in dense sandstone; and S6, clarification of the development distribution characteristics of natural fracture subsystems in solid sandstone. 2. Evaluation method for tectonic genesis of natural faults in a disturbed geostress field environment according to requirement 1, in which Sl specifically includes the steps of: collecting the data on the structural maximum curvature of the target formation, the magnitude and direction of the stress field, the distance to the fracture, core photo fracture identification and imaging logging identification of the natural fracture strike and dip from a single well. 3. Evaluation method for tectonic genesis of natural faults in an environment with disturbed geostress field according to requirement 2, where 82 specifically includes the following steps: S2.l, selecting a well dominated by a regional tectonic tension field; and 82.2, obtaining natural fractures dominated by the regional tectonic stress field and the definition of an average density p 0 of natural fractures dominated by the regional tectonic stress field. 4. Evaluation method for tectonic genesis of natural faults in a disturbed geostress field environment according to requirement 3, where S3 specifically includes the following steps: 83.1: Calculating the distances between each individual well and the nearest fractures, with a distinction being made between a primary fracture and secondary and tertiary fractures, performing statistical analyses on the correlation between the natural fracture density in the individual wells and the distances to the primary fracture, as well as the correlation between the natural fracture density in the individual wells and the distances to the secondary and tertiary faults, and the preparation of an initial linear regression equation and a second linear regression equation based on this analyses; 83.2: using the average density p 0 of the natural fracture that is dominated by the regional tectonic stress field as a constraint, and substitution of the p 0 and 2p 0 into the first linear regression equation to get the to calculate corresponding distances to the primary fault, with these distances as critical initiation distance for development D1 and a critical dominance distance D1 , of the natural fault dominated by the primary fault caused disturbed voltage field in the single well; or and substitution of the p 0 and 2 p 0 in the second linear regression equation to find the corresponding distances to the secondary and tertiary fractures, using these distances as the critical initiation distance for development DZ and a critical dominance distance D2 , of the natural fracture that is dominated by the secondary and tertiary fault induced disturbance tension field in the single well; S3.3: Excluding a well dominated by a fault induced disturbed stress field based on the dominance critical distances D1 and D2 , and removing a natural fracture dominated by the regional tectonic stress field based on the separation of a natural fault subsystem dominated by a regional tectonic stress field; and 83.4: Characterize natural faults dominated by the fracture caused disturbed stress field, including dip angle, dip direction, fracture surface morphology and angular relationships with the maximum horizontal principal stress. 5. Evaluation method for tectonic genesis of natural faults in a disturbed geostress field environment according to requirement 4, where 83.1 specifically includes the steps of: Performing hierarchical analysis on the relationship between the distance to the fault and the natural fracture density in the single well to fit a linear regression equation obtain between the distance to a primary fault and the average natural fracture density of the single well: p = 0.0991n Dl + 0.8009, R1 = 0.6510 (1) where p is an average natural fracture density of a single well, with a unit: fracture / m; D1 is a distance from a single well to a primary fracture, with a unit: m; and R1 is a correlation coefficient between the average natural fracture density of a single well and the distance from the single well to the primary fracture; and a linear regression equation between the distance to secondary and tertiary faults and the average natural fracture density of a single well is: p = 0.092 ln D2 + 0.7127, R2 = 0.7620 (2) where p is an average natural fracture density of a single well, with unity: fracture / m, DZ a distance from a single well to secondary and tertiary fractures, with a unit: m, and R2 a correlation coefficient between the average natural Single well fracture density and the distance from the single well to the secondary and tertiary fractures. 6. Evaluation method for tectonic genesis of natural faults in a disturbed geostress field environment according to requirement 5, in which 83.2 specifically includes the steps of: using the average density p 0 of natural fractures dominated by the regional tectonic stress field as a constraint, and by the p 0 and 2 p 0 to substitute into a linear regression equation (1) to get the corresponding distances to calculate the primary fracture, using these distances as the critical initiation distance for development D1 and a critical dominance distance D1 of the natural fault that is dominated by the disturbed stress field caused by the primary fracture in the single well; or by using the average density p 0 of natural fractures dominated by the regional tectonic stress field as a constraint, and to substitute p 0 and 2p 0 into a linear regression equation (2) to get the to calculate corresponding distances to the secondary and tertiary faults, using these distances as critical initiation distance for DZ development and a critical dominance distance D2 of natural faults dominated by the secondary and tertiary fractures induced disturbed stress field in the single well. 7. Evaluation method for tectonic genesis of natural faults in a disturbed geostress field environment according to requirement 6, in which 83.3 specifically includes the steps of: selecting wells dominated by the primary fault caused disturbed stress field based on the dominance critical distance D1 , and removing a natural fault dominated by the regional tectonic stress field based on the separation of a natural fault subsystem that is dominated by a regional tectonic stress field; or the exclusion of wells dominated by the secondary and tertiary fault-induced disturbed voltage field based on the critical dominance distance D2 , and the removing a natural fault dominated by the regional tectonic stress field based on the separation of a subsystem of natural faults dominated by a regional tectonic stress field. 8. Evaluation method for tectonic genesis of natural faults in a disturbed geostress field environment according to requirement 7, where S4 specifically includes the following steps: 84.1: Establishing a third linear regression equation by relating investigate between the structural maximum curvature of the target formation and the residual natural fracture density of some wells, where the third linear regression equation is shown in equation (3): = 0.0205 4'3029 3 = 0.7683 (3) where p is an average fracture development density of individual wells, with a unit: fraction / m; K is a structural maximum curvature of the target formation, with a unit: l / km; and R3 is a correlation coefficient between the average Single well fracture development density and the structural maximum curvature of the target formation; S4.2: Substitute the p 0 and 2p 0 into the third linear regression equation to corresponding data of structural maximum curvature of the target formation calculate, using this data as an initiating critical curve for development K and a dominance critical curvature K' of natural fracture dominated by a folding deformation disturbed stress field in the single pit; 84.3: Excluding a well dominated by the fold deformation disturbance stress field based on the dominance critical curvature K', and removing a natural fault dominated by the regional tectonic stress field based on the separation of a natural fault subsystem dominated by a regional tectonic stress field; and S4.4: Characterize natural fault features dominated by the stress field disturbed by wrinkle formation, including dip angle, dip direction, fracture surface morphology and angular relationships with the maximum horizontal principal stress. 9. Evaluation method for tectonic genesis of natural faults in a disturbed geostress field environment according to requirement 8, in which S5 specifically includes the steps of: creating an identification parameter table and a classification criteria template based on three natural fracture subsystems separated from disturbed geostress field, initiation critical distances for development, dominance critical distances, initiation critical curves for target formation development as well as critical dominance curvatures, obtaining a dimensional reduction based zoning map of ordered natural fracture subsystems in complex structural zones, and the classicizing a study area in a regional tectonic stress field dominated zone, a fold deformation disturbed stress field dominated zone and a fault- induced disturbed stress field dominated zone, the three natural fractures subsystems consisting of a natural fracture subsystem dominated by a regional tectonic stress field, a natural fault subsystem dominated by a fracture-induced disturbed stress field and a natural fracture subsystem dominated by a fold deformation disturbed stress field. 1 / 4FIG.1FIG.2