煤层气井固井水泥冲击断裂特征与破坏模式

he fracture behavior and failure modes of oil-well cement under perforation impact are the key problems that need to be solved urgently in the maintenance of the annulus sealing capacity of deep gas wells and the protection of oil-well cement annulus.In this paper,polyvinyl alcohol(PVA)fiber oil-well cement was taken as the object,and high strain rates impact loading was carried out on samples of oil-well cement by using Split-Hopkinson Pressure Bar device combined with high-speed camera,so as to obtain the time history information of fracture propagation and failure modes of the oil-well cement under the strain rates of level 4.The results show that the impact fracture process of oil-well cement includes four stages:materials compression deformation,fractures initiation,fractures propagation and fractures penetration and overlapping.With the increase of strain rates,the fracture rates oil-well cement accelerates,and the fracture rates range from 137.93 to 513.37m?s-1. The failure modes of oil-well cement include tensile splitting failure(TF),shear failure(SF)and mixed failure.With the increase of strain rate,the impact failure modes of oil-well cement change from tensile splitting mode and shear mode to mixed mode,and the particle size of material becomes finer and the degree of failure intensifies. With the increase of strain rates,the impact failure mechanisms of oil-well cement gradually changes from plastic failure to quasi-brittle failure.It can provide reference for oil-well cement integrity evaluation and material property modification of deep gas wells.