Drilling muds are a sophisticated mixture of many additives that alter the fluid density, rheology, and pH. Some of the uses for magnesium oxide are:
- It is used in brine drilling mud to act as a scouring agent in order to keep the annulus clean as well as to neutralize acid gases released from the formation during the drilling operation.
- It is also used to control fluid alkalinity, particularly in clay-free polymerbased fluids.
- Attapulgite clay is also used as a rheology modifier in drilling mud, and the addition of small quantities (approximately 2% by weight) of MgO helps to increase fluid viscosity.
- Dead-burned magnesia has been employed in expansive cement to seal a steel casing to the bore-hole walls. The dead-burned magnesia slowly hydrates and expands the cement to compensate for any shrinkage that the cement should undergo during curing.
- Sorel cement has been reported to be useful as a bridging agent in drilling and servicing fluids. A bridging agent deposits as a filter cake on the walls of the well bores within the producing formations. This prevents the drilling or servicing fluid from being lost into the formation and also prevents solids from entering the porosity of the formation and causing blockage. The Sorel cement bridging agent can be removed by dissolving with an organic acid, once drilling is complete, to allow the production of hydrocarbons.