Abstract: Gas, oil or water breakthrough caused by weightlessness during cement slurry coagulation is one of the most important factors, which influences cementing quality. In connection with characteristics of high temperature, high pressure and active oil gas and water in deep well, and combining mechanism study and field application, the factors affecting cement slurry weightlessness and gas breakthrough, and the mechanism and method of preventing gas breakthrough is studied, and presents the measures of monitoring cement slurry’s resistance, stability, and water loss, and assuring the pressure balance in the procedure of cement slurry coagulation is presented, so as to reach the goal of preventing oil, gas and water breakthrough. Tests
shows that six types of cement slurry compounding are capable of preventing gas breakthrough, and are separately suitably for hole depth of various pressure gradients, of which 3-S slurry is of the best capability for preventing gas breakthrough.

Key words: Cementing, Cement Slurry Gel, Cement Slurry Property, Cement Additive, Cement Composition, Channeling, Gas Channeling