Study On Fracture Mechanical Model Of Horizontal Well Cementing Second Interface In Fracturing Process

Good zonal isolation was the precondition to achieve horizontal staged fracturing effect,the second interface was the weakest part for the whole cementing system,if fracturing parameter designed unreasonably,and channeling-path was formed easily in the second interface.At present,few studies had been done on second interface failure problem of fractured horizontal well.Therefore,it was necessary to research the failure mechanism and mechanical problems of second interface in horizontal staged fracturing.Firstly,the failure mechanism in second interface was proposed during horizontal well fracturing.The failure process of second interface was that:interface slippage first occurred because of characteristics difference between cement sheath and formation.On the basis of deboning length,fractures continue to expansion along second interface.And the failure length of second interface included debonding length and expansion length.According to interface bond-slip mechanics,beginning with the existence of false filter cake,compressor and expander phenomenon of formation and cement sheath was considered.The debonding mechanics model of second interface was established under non-uniform in-situ stress.The stress distribution of formation and cement sheath in debongding area and viscoelastic area and bond shear stress formula of second interface were obtained respectively.Combined with interface cementing strength and boundary conditions,debongding pressure and length of second interface were calculated.By applying the fracture mechanics and analyzing the fracture area friction,fracture expansion mechanics model alone second interface was established.At last,second interface failure lengths under different fracturing conditions were calculated.According to the failure length of second interface,the discriminant condition of second interface sealing failure could be achieved.Finally,choosing one horizontal well in Jilin Fuyu oilfield to perform the demonstration calculation and analyze the fracturing integrity of its second interface,meanwhile,the packers interval under different fracturing pressure could be determined.The above research results could not only evaluate the pressure resisting capability of horizontal well second interface,but could guide the parameter design of horizontal well fracturing.