| abstract |
A method of controlling the pressure of a casing annulus in a subterranean well is disclosed, wherein the method includes injecting into the casing annulus a composition including a base fluid and a polymer coated colloidal solid material, wherein the polymer coated colloidal solid material includes: a solid particle having an weight average particle diameter (d50) of less than 2 microns but not more than 5% of the d50 particles are less than 0.1 micron in diameter, and a polymeric dispersing agent coated onto the surface of the solid particle during the comminution (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 may be selected from materials having of specific gravity of at least 2.68 and preferably the solid particulate material may be selected from barium sulfate (barite), calcium carbonate, dolomite, ilmenite, hematite, olivine, siderite, strontium sulfate, combinations and mixtures of these and other similar solids that should be apparent to one of skill in the art. The base fluid may be selected from, water, brine, diesel oil, mineral oil, white oil, n-alkanes, synthetic oils, saturated and unsaturated poly(alpha-olefins), esters of fatty acid carboxylic acids and combinations thereof. |