| hydraulic fracturing technology of rock mass has been widely used in engineering field.However,as an inhomogeneous,anisotropic brittle structure rich in structural planes,the fracturing process of rock mass is an extremely complex nonlinear and irreversible fracture evolution process.Under the action of external forces,the occurrence and accumulation of fracture events with different failure mechanisms in the rock mass lead to fracturing fractures,which may be extended,turned,bifurcated,intersected and connected.A large number of studies have shown that it is the most direct and effective method to study the extremely complex nonlinear fracture evolution process,such as rock mass hydraulic fracture,and to track and monitor the fracture events in the fracturing process in real time.The fracturing process of rock mass releases a large number of stress waves.According to the stress wave signals received by acoustic emission probes and related algorithms,the real-time fracture event location information in fracturing can be obtained,which can provide tracking and location information for the study of fracture evolution of rock mass fracturing.However,the existing acoustic emission monitoring technology of rock mass can only obtain a series of independent locating points,which cannot effectively reflect the regional scope of rupture events.This article in the existing rock mechanics,seismology,elastic-plastic mechanics and fracture mechanics on the basis of relevant theories put forward four assumptions,the acoustic emission anchor point as the center coordinates of burst events inversion calculation rupture event corresponding to the area of the location,shape and size of accumulative fracturing process of fracture zone can be obtained,called real-time location monitoring acoustic emission inversion of rock mass fracture evolution method,is first proposed in this paper.In with the effective methods on the basis of the rock burst monitoring,this article selects hard primary pore fissure development shandong grey granite and native bedding fracture of fushun shale as the research sample,in the lab for large scale hydraulic fracturing of rock specimen experiment,using a high sampling frequency of the acoustic emission and high sensitivity of the acoustic emission probe observation records in the fracturing process acoustic emission phenomenon,the inversion process of fracturing fracture have regional characteristics,so as to study the fracture evolution characteristics in the process of different lithology rock mass fracturing.The main research of this paper can be divided into three main parts,as follows:(1)Research on methods of acoustic emission real-time positioning monitoring and inversion of rock fracture evolution.In similar seismology,the source is regarded as a point with a certain scale,and acoustic emission positioning signals during rock fracturing are regarded as the center of the fracture area.Put forward four assumptions: 1)the rock mass damage obey the rule of maximum elastic energy density;2)for any specific rock mass,the damage can consists of two parts,the elastic energy and the plastic can,this ratio is related to rock types;3)rock rupture area flat in elliptic ball;4)and acoustic emission energy rock failure of elastic energy is required;Based on the hypothesis and the interpolation average,the rupture region corresponding to the ae locating point can be inverted,and then the orientation and corresponding failure type of the rupture region can be obtained according to the simplified source function and measured AE information.(2)Study on the fracture evolution characteristics in the process of fracture initiation,fracture initiation and fracture propagation and extension in large-scale granite laboratory hydraulic fracturing.Choose 1 m scale of shandong grey granite specimen,at the center of the specimen on both sides of drill hole and drilling with mixed abrasive two-phase flow after 60 mpa prefabricated crack rock cutting equipment,using a large exert confining pressure true triaxial testing machine,precision servo pump constant lingers on water pressure,for different levels of stress difference under the condition of hydraulic fracturing experiments,observation records during the process of fracturing confining pressure,drilling pressure and acoustic emission signal;According to the experimental results the fracturing process is divided into three stages: crack breeding stage,stage of crack and fracture extension stage,combined with the new burst segmentation time areas in the stages form,cumulative failure form,failure type and largest connected group studies the changes of fracturing process bursts evolution characteristics,crack analysis of hydraulic fracture,the rupture characteristics of extension,steering,extension process.The new fracture events were divided into four categories according to the distribution location,and the fracture evolution patterns in different fracturing processes were studied.The ratio of the maximum fractured connected group(n)to the cumulative fracture region(N)and the fracture concentration degree were used to study the fracture evolution process.(3)Study on fracture evolution characteristics of large-scale hydraulic fracturing in laboratory of oil shale.Shale specimens taken from liaoning fushun open-pit mine,the size of 1400 mm,after filling cement package made appearance is 1400 mm in diameter,800 mm cylindrical specimens,set up 13 drilling,from the central area of 7 # hole water injection rate is 100 m L/min pressure,the pressure inside the observation records various drilling fracturing and acoustic emission signal,the research level of bedding structure fracture evolution characteristics in the process of development of rock mass fracturing.After the appeal study,the main conclusions of this paper are as follows:(1)Acoustic emission real-time positioning monitoring and inversion method for rock fracture evolution is a feasible and effective method for studying rock fracture evolution,which can carry out real-time monitoring of the fracture area during fracturing.(2)through the study of hydraulic fracturing process of large scale granite found that with the increase of the horizontal stress difference crack granite pressure decreases,and eventually produce along the prefabricated crack propagation in the hydraulic fracture of the shorter the straight line segment,crack,crack in the process of rupture strength,fracture extension phase within the rupture strength increases,the fracture surface formation development increasingly after the stage of crack occurring in the fracture extension stage.(3)In the process of pressure rise,most of the large-range connectivity in the fracture region occurs,accompanied by a decrease in the tensile proportion and an increase in the shear proportion.The shear fracture is more reflective of the fracture surface expansion,and the tensile/shear ratio is the highest at the initiation stage.(4)The fracture evolution of rock mass is the result of the combined action of four types of events,D types of events are the main reason for the increase of the cumulative fracture region,And B types of events and C types of events cause the increase of the fractured connected group region to which they belong,and the fracture evolution mode can be divided into five types.(5)Under the condition of low stress,the fracture events are mainly of Type A.When the local stress is concentrated,the probability of occurrence of the fracture events in this region increases,the degree of fracture concentration of new fracture events in this region increases,and the fracture region is connected.Later,with the transfer of partial stress to the surrounding rock bridge,more scattered fracture events began to occur outside the local area.With the accumulation of rupture events,the newly increased rupture concentration began to rise again,and the connected broken groups formed in local areas expanded to surrounding areas.(6)Four combinations can be obtained from the changing trend of joint/N and fracture concentration degree,and the characteristics of fracture evolution corresponding to each combination are different,respectively: the development of primary fracture region is dominant,the development of non-primary fracture region is dominant,the development of primary fracture region,the rupture events in external region are scattered,and the rupture is scattered. |
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