Harm of bypassing flow in laminar flow well cementation and its prevention and cure

Bypassing flow is apt to happen when the cement milk bypasses the thick drilling fluid on the in the process of laminar flow cementation.This phenomenon will cause the mixture of cement milk and drill fluid which results in the weak bond of cement mantle.There is not a universal idea of optimization design method of cementing displacement though a lot of work has been done for bypassing flow prevention.Through the bypassing flow experiments in house and quantities of field well cementation practice,it was found "priority centering" of casing,"negative density gradient structure" of cement milk,"high efficiency viscosity break" of circulation fluid,"intensive draw" of isolation fluid and "thick displacement slow" of cement milk,all these were effective measures to decrease bypassing flow and improve the displacement efficiency.Cement jobs of more than 10 wells in South China Sea zone were all big success and the cement quality came to fineness level.