The Law Of Fractures Space-time Initiation And Propagation Along Radial And Axial Direction Of Rock Hydraulic Fracturing Drilling

The paper is based on the phenomenon of space-time initiation along radial and axial direction of rock hydraulic fracturing drilling by the tutor Professor Huang Bingxiang during the true triaxial fracture experiment.Physical model tests were conducted using the true triaxial test system of the research group.These experiments include regular exploration experiments(initiation sequence of radial and axial cracks and crack space morphology)and influencing factors analysis experiments(three-dimensional stress field and pump displacement).Using COMSOL Multiphysics numerical simulation software to analyze the change of the axial stress field of the borehole after the radial crack initiation.Based on elastic mechanics and other related knowledge,the model of space-time initiation along radial and axial direction of rock hydraulic fracturing drilling was established,and the criterion of space-time initiation and propagation along radial and axial direction of rock hydraulic fracturing was established.The following main conclusions were reached:(1)After the induced stress in radial cracks reaches a certain level,the direction of the new stress field changes,and the direction of the minimum principal stress changes.After the axial crack initiation conditions are satisfied,the axial crack initiates perpendicular to the direction of the present minimum principal stress.(2)The induced stress field formed by the appearance of radial cracks has a certain range of influence.When the stress isotropy of the new stress field is reached,the axial cracks turn.After exceeding the stress isotropy point,the axial crack gradually turned into a radial crack and continued to expand in the radial direction.(3)The radial cracks and axial cracks are expanding to the surroundings,and the length of the line of intersection of two crack surfaces is also increasing,and the radial cracks and axial cracks are continuously passing through.(4)When the pump displacement is small,the the hydrostatic pressure formed in the radial crack is small,and the axial crack cannot be induced.When the pump injection volume increases to a certain extent,axial cracks began to be induced.As the pump displacement increases,the intensity and range of the induced stress increase,and the less likely it is that the axial cracks will turn in the same range.(5)When the difference between the intermediate principal stress and the minimum principal stress is large,radial cracks cannot induce axial cracks;as the difference between the intermediate principal stress and the minimum principal stress becomes smaller,the original The direction of the stress field is more easily changed by the induced stress,so that the radial and axial cracks are more easily formed.(6)Considering the stress concentration at the crack tip,the model of space-time initiation and propagation along radial and axial direction of rock hydraulic fracturing drilling was established.The criterion of space-time crack initiation and propagation along radial and axial direction of rock hydraulic fracturing was established.The relationship between the formation of radial and axial cracks and the pump displacement and main stress difference is given.The turning position of axial crack is proposed Finally,an example verification was carried out to verify the accuracy of criteria for the radial and axial cracks spatiotemporal initiation and propagation.(7)Did a field test at 3251 South Coal Face in Lushuidong Coal Mine.The effect of the pumping displacement on the formation of radial and axial fractures was analyzed.The greater the pump displacement,the easier it is to form radial and axial space cracks.Because the on-site rock mass is heterogeneous and anisotropic,there are layers,bedding,joints,etc.,which can form multiple radial and axial cracks,and some radial and axial cracks can develop into radial and axial crack network.This paper have 69 figures,10 tables and 90 references.