Study On Fracture Mechanism Of Hard Brittle Rock Under Vibration

With the development of oil and gas exploration,the difficulty of drilling is increasing.The depth of the well slowly extends from the shallow layer to the deep layer and even the deep layer.The difficulty of rock fragmentation is gradually increasing.The rock crushing efficiency is getting lower and lower,the drilling cycle is lengthened and the drilling cost is increasing.It is urgent to improve the rock breaking efficiency and improve drilling speed?Therefore,the technology of high efficient drilling and rock breaking highlight its importance in various kinds of drilling technology.At present,the domestic and foreign scholars have carried on the research to the impact vibration drilling technology.However,the research on the theoretical mechanism of vibration impact is less.In this paper,based on the consideration of the rock gravity,the vibration response and the mechanism of the rock under the high frequency impact drill bit are studied.Based on the theory of vibration,considering the actual situation of percussion drilling,the physical model of rock with gravity is established.And the mathematical model is solved by using the renormalization method.At the same time,the dynamic fracture model of brittle rock is established and the direct relation between the response and the crushing of rock is established.Through the analysis and comparison of the parameters to determine the impact of various parameters on the rock broken fruit,which provides a theoretical basis for the field of rock breaking.The following conclusions are obtained:(1)Considering the gravity of rock,the rock is assumed to be ideal multiple spring with the weight to establish the rock vibration model.With the application of renormalization method,the calculation model of rock natural frequency is solved and the calculation model of vibration displacement of rock are presented.(2)Based on the calculation model of rock vibration displacement and the dynamic fracture criterion of rock,the ultimate displacement of rock fracture is presented.The limit displacement is a range,which is composed of the upper and lower limits,which indicates the crack opening and closing degree of the rock crack under the two conditions of tension and compression.(3)The vibration impact response of rock and numerical analysis of impact vibration under the action of rock breaking experiment research done: analysis of the influence of rock density,elastic modulus of rock rock vibration frequency;analysis of the impact of the maximum displacement amplitude of vibration impact load of rock under impact and the maximum equivalent stress analysis;the effect of maximum displacement of the rock vibration frequency of different impact under the impact,and compared with the natural frequency values of rock.(4)The density of the rocks,the rock drill stiffness,the magnitude of the impact force and impact frequency on the vibration effect of rock drill The smaller the density of rock is,the smaller the stiffness is,the higher the impact force is,the larger the vibration amplitude and vibration speed are.(5)There is a natural frequency of rock,which is positively correlated with rock stiffness and negatively correlated with rock density.The vibration frequency of the drill bit is closer to the natural frequency of the rock.When the high frequency and the natural frequency of the drill are equal,the amplitude and the vibration velocity of the rock are the largest,which is the resonance.The research has important realistic significance and certain practical value on the field application of resonance impact drilling.