Application of Amphoteric Cellulose Ethers in Drilling Fluids

Abstract Anionically charged cellulosic ethers have been used for many years in water-based drilling fluids. While the anionic charge imparts a benefit in the filter-cake properties of bentonite containing drilling fluids, this same charge deflocculates (thins) the viscosifying ability of this same bentonite. As a result, additional bentonite is often required in the drilling fluid to maintain an adequate rheological profile. Also, it is well known that cations are viscosity enhancers to bentonite drilling fluids by virtue of the flocculation effect of the cation. This has been used for many years in the potassium chloride (and similar salts) based drilling fluids. Amphoteric Cellulose Ethers represent a new class of drilling fluid additives which combine an anionic and cationic charge onto the same cellulose backbone. The result is a drilling fluid additive having both desirable filter-cake enhancement and partial flocculation properties. Discussion will include the effects of degree of substitution for the anionic and cationic species, as well as the influence of molecular weight on the properties of the Amphoteric Cellulose Ethers.