Distribution Characteristics And Formation Mechanism Of Fractures Related To Reverse Fault

Fractures related to reverse fault have a profound impact on the development of fossil energy such as petroleum and natural gas,and the construction of large-scale geotechnical engineering such as water conservancy and hydropower,bridges and tunnels,and also have an important impact on the prediction of geological disasters such as earthquakes,landslides,and mudslides.The distribution characteristics of the cracks related to reverse faults often affect the further evolution of reverse faults,control the formation of fractured oil and gas reservoirs,the distribution law of reservoir oil and gas,and ultimately affect the oil and gas recovery rate of oil and gas reservoirs.Studying the genesis mechanism of reverse fault-related fractures will help to understand the distribution characteristics and formation and evolution rules of reverse fault-related fractures in essence,and protect my country from deep energy resource development and utilization,such as oil and gas reservoir exploration and development,dry hot rock reservoir transformation,etc.Energy security and the prevention of geological disasters are of great significance.Based on field outcrops,seismic interpretation,drilling cores,logging data,etc.,this paper studies the distribution characteristics and control factors of reverse faultrelated fractures;based on the transparent standard cylindrical sample compression test,studies the formation process of reverse fault-related fractures,combined with rock triaxial The stress-strain test establishes a constitutive equation suitable for the formation of reverse fault-related cracks;based on the physical simulation test and numerical simulation test of the geological structure,the genetic mechanism of reverse fault-related cracks is studied from the perspective of strain energy and numerical simulation;finally,analysis The relationship between related cracks and hydrocarbon accumulation in reverse faults in Pengzhou area,as well as the influence of in-situ stress disturbances near reverse faults in Yongchuan area on engineering renovation.The knowledge gained in this article has the following 6 points.(1)Relevant fractures of reverse faults develop along the reverse fault plane,and the spatial distribution positions of the two have the phenomenon of "interlacing and overlapping".The mechanical properties of the fractures related to reverse faults are mostly tensile or tensile-torsion,and mainly tensile fractures and shear fractures are developed.The strikes of the related fractures of reverse faults are consistent with the strikes of reverse faults.The reverse fault-related fracture development index in the footwall area of reverse faults is smaller than that in the hanging wall area.When far away from the reverse fault plane,the development index of reverse fault-related fractures gradually decreases,the dip angle gradually increases,and the fractures gradually evolve into high-angle oblique fractures.The nature of reverse faults,the scale of reverse faults,the lithology of the formation,and the thickness of the formation are all key factors that affect the development index of reverse faults.(2)The in-situ stress state is the core factor that controls the distribution characteristics of reverse fault-related fractures,and reverse faults control the distribution characteristics of reverse-fault-related fractures by influencing the in-situ stress field in their vicinity.That is,the reverse fault affects the distribution of the direction of the in-situ stress in its vicinity.The absolute value of the in-situ stress on the reverse fault is lower than that in the area near the reverse fault,which is a lowvalue area of the in-situ stress.The middle area of the reverse fault is a relatively lowvalue area of the in-situ stress;the tip(end)end of the reverse fault and the reverse fault surface Structural parts such as curved convex parts have the effect of in-situ stress concentration,which often exhibits abnormal stress field distribution and disturbance of the in-situ stress direction.These areas are prone to develop reverse fault-related fractures;the in-situ stress concentration effect of reverse faults determines the correlation of local reverse faults.The direction in which the crack extends.(3)Under the same in-situ stress state,the spatial distribution of micro-cracks is the main reason for the differentiation and development of micro-cracks in the formation of rock into reverse fault planes and reverse fault-related cracks.In the time sequence of the formation of reverse faults,before each stage,the micro-cracks generated by the stress concentration effect at the tip(end)end of the reverse fault will serve as the "initial" micro-cracks in the next stage of the evolution of the reverse fault.Since most of the micro-fissures are not in the expected direction of extension and expansion of the reverse fault plane,the micro-fissures that failed to develop into the fault plane will continue to extend and expand under the action of the load to form reverse fault-related fractures.(4)From the energy point of view,the accumulation and release of formation strain energy is the main internal cause of the formation of reverse fault-related fractures.The accumulation and release of strain energy are consistent in time with the formation of reverse faults;the magnitude and release rate of strain energy determine the scale of reverse fault-related fractures,and the spatial location of strain energy release determines the distribution characteristics of reverse fault-related fractures;The continuous change of energy points is the reason that reverses fault-related fractures have both tensile fractures and shear fractures;reverse fault-related fractures are dynamic,regional,and multi-stage structural fractures.(5)The generation and development of micro-cracks are the internal genetic mechanism of reverse fault-related cracks.The micro-fracture process of reverse faultrelated cracks follows the following rules: at the beginning of loading,micro-cracks first start to form inside the rock sample,and the location of micro-crack initiation Mainly at the tip(end)end of the original crack;continue to load,the microcracks continue to grow and expand,and the number of microcracks also increases significantly.The area near the original cracks in turn sprouted secondary inclined cracks and secondary coplanar cracks;continue to increase Load,the length and number of micro-cracks in the formation rock are increasing.Numerous micro-cracks in the rock rapidly expand and penetrate to form reverse fault-related cracks;as the degree of internal damage in the rock continues to increase,a macroscopic and visible throughfracture phenomenon is finally formed-Reverse fault.(6)The included angle(approaching angle)between reverse faults and related cracks affects the strike and initiation stress of reverse faults-related cracks.When the approach angle is small(?<45°),wing cracks are easy to initiate in the formation,and the micro-cracks spread uniformly throughout the compression process.The failure mode of the formation rock is mainly the tensile mode;when the approach angle is large(?> 45°),wing cracks are difficult to initiate in the formation rocks;after the local stress reaches a certain critical value,the formation rocks gradually form secondary inclined cracks and secondary coplanar cracks.The main results obtained in this paper:(1)Based on the compression test of transparent standard cylindrical specimens and the triaxial stress-strain test of rock,a constitutive equation suitable for the formation of reverse fault-related cracks has been established.(2)Through physical simulation experiments,the genetic mechanism of reverse fault-related fractures were analyzed from the perspective of strain energy,and physical simulation experiment methods and data analysis methods for the formation and evolution of reverse faults were established.(3)The particle flow program is used to simulate rock microcrack initiation and microcrack propagation process,quantitatively analyze the influence of cracks with different inclination angles on microcrack initiation and crack initiation stress in the rock,and establish a dynamic simulation method for the development of reverse fault-related cracks,revealing the inverse The influence mechanism of fault geometric characteristics on the process of initiation,initiation,propagation,and extension of related fractures.In addition,the control effect of the related cracks of reverse faults in the Pengzhou area on hydrocarbon accumulation,and the influence of in-situ stress disturbances near reverse faults in the Yongchuan area on engineering renovation are analyzed.This paper studies the distribution characteristics and genetic mechanisms of reverse fault-related fractures,which can provide a certain theoretical basis for oil and gas field exploration and development and geological disaster prevention,and also have a certain significance for hydraulic fracturing and drilling well design.