| abstract |
A method of controlling the pressure of a casing annulus in a subterranean well that includes injecting into the casing annulus a composition including a base fluid and a polymer coated colloidal solid material. The polymer coated colloidal solid material includes: a solid particle having an weight average particle diameter (d50) of less than two microns, and a polymeric dispersing agent coated onto the surface of the solid particle during the cominution (i.e. grinding) process utilized to make the colloidal particles. The polymeric dispersing agent to may be a water soluble polymer having a molecular weight of at least 2000 Daltons. The solid particulate material ma y be selected from materials having of specific gravity of at least 2.68 and preferably the solid particulate material may be selected from barium sulfat e (barite), calcium carbonate, dolomite, ilmenite, hematite, olivine, siderite , strontium sulfate, combinations and mixtures of these and other similar soli ds that should be apparent to one of skill in the art. |