Research On Mechanics Mechanism Of Cement Sheath Integrity In Reservoir Stimulation Process

During well cementing operation,cement hardens to form cement sheath,and then form the casing/cement/formation system.Cement sheath is mainly used to support casing and seal off annulus.During the production,the integrity of cement sheath is generally damaged by reservoir stimulation processes,can't continue to provide zonal isolation.Therefore,research on cement sheath integrity has important guiding significance to well cementing operation and reservoir stimulation.Be aimed at cement sheath integrity in reservoir stimulation,this paper mainly focuses on the following:(1)This paper formulated relevant experiment scheme,completed the test of cement compressive strength and tensile strength,and suggested that cement sheath compressive strength is 30~45MPa,Elastic modulus is 5 ~ 8 GPa,Poisson's ratio is 0.101 ~ 0.171.(2)This paper built a casing/cement/formation mechanical model under uniform and non-uniform in-situ stress field,getting the analytical solution of stress distributing state.It suggested that radial and tangential stresses decreased with the increase of cement sheath radius.(3)Be aimed at the stress distributing state of cement sheath under non-uniform in-situ stress field,this paper built a coupled numerical model for reservoir stimulation,to analyze the effect of formation and cement sheath on the integrity of casing/cement/formation system.It suggested that cement with lower Young's modulus and higher Poisson's ratio is advantageous to maintain cement sheath integrity during the reservoir stimulation operations.(4)In order to verify the accuracy of the finite element program,this paper used the analytical model to simulate and analyze the fracturing operation of H4 in Well XXX and cement sheath failure problem in Well Longgang-001.It suggested that the maximum wellbore pressures in Well XXX and Longgang-001 are 105 and 90 MPa respectively,The results are consistent with the actual working condition.