Abstract: A casing or liner in a wellbore penetrating a zone having high formation gas pressure is cemented with a cementitious slurry comprising blast furnace slag. In one embodiment the cementitious slurry is made by combining blast furnace slag and a drilling fluid. Also, a method for plugging or setting sidetracking plugs and other secondary cementing operations in a wellbore penetrating a zone having high gas formation pressure comprising placing a mass of blast furnace slag cementitious slurry at a preselected location and allowing the slurry to set.

Abstract: A wellbore is drilled utilizing a conventional drilling fluid or a drilling fluid such as one containing a cementitious component selected from blast furnace slag, a metal oxide component of an ionomer or a metal oxide component of a phosphate salt. A compatible cementitious slurry such as one containing blast furnace slag and an activator system is then introduced into the borehole and displaced up into an annulus by direct contact with a displacement fluid. Generally, in the case of the slag-containing drilling fluid the cementitious slurry is prepared by adding additional blast furnace slag and an activator such as a sodium hydroxide/sodium carbonate mixture to the used drilling fluid. Similarly, in the case of the ionomers or phosphates, additional metal oxide component and the reactive second component can be added to the used drilling fluid to produce the cementitious slurry.