For example, a cement-gilsonite ration of 1:4, using the coarse aggregate specified above, is difficult to pump and is likely to plug restricted passages in the system, whereas the same mix, using the fine aggregate specified above, will never plug if the water-cement ratio is high enough.

An amount of a petroleum solvent which depends upon the amount of gilsonite present, may be added to the wet or dry mix for wetting the surface of the gilsonite particles and causing them to form an intimate bond with casing and earth formations of the bore hole, thus preventing corrosion and minimizing pulling away of the cement from the casing and/or bore hole wall by reason of the shrinkage normal to setting of the cement.

Instead of adding the solvent directly to the mix, it may be pumped through the casing and into the cementing zone in advance of the gilsonite-cement slurry.