Summary: During the process of cementing, MgO-based expansive additives are widely used to increase bond and adhesion of the cement stone annulus with the wellbore and casing. Under the high-temperature condition of the bottom hole area, the additives help prevent gas channelling and migration in the well. The paper presents the results of a study on the preparation of the PVChem MgO expansion additive based on the magnesite ore from Kong Queng mine (Gia Lai province). The analyses of density, water separation, water discharge, rheological properties, thickening time and strength of cement stone then showed that adding 0.75% PVChem MgO expansion additive into the cement slurry mixture prevents gas ingress and migration effectively.

Key words: Expansion additive, MgO, cementing, gas channelling, gas migration.