Status Quo of Research on and Prospect of MgO as Oil Well Cement Expansion Agent

As petroleum production is moving forward to the production of heavy oil and oils from ultra-deep wells, conventional oil well cement expansion agents, such as CaO and ettringite are no longer able to satisfy the needs of well cementing because of their deficiency in high temperature performance. Oil well cement expansion agents with MgO as the main component, is expected to find wide application in oil well cementing. This paper listed the research findings made abroad in the application of MgO in oil well cement. From these researches it was found that there must be a matching between the calcination temperature of MgO and the operation temperature. High concentration (12%) of MgO can be used to optimize the pore sizes of set cement with 3D constrained state at 80℃ and to enhance the compressive strength of the set cement. At concentrations between 5%-10%, MgO would reduce the compressive strength of sand-contained set cement at 135℃-150℃. The existence of MgO in set cement helps improve the bonding between the interfaces between cement sheath and borehole wall because of the radial expansion of the set cement caused by MgO. The quality of sealing of the annular space is thus improved and interfaces between cement sheath and borehole wall in which mud cakes of poor quality also has its strength enhanced. This paper is of guidance in the study, application and popularization of high temperature compound anti-channeling agents with MgO as the main component.