Patent ID: 7939469
Filing Date: 2011-05-10
Classification: C09K

Abstract:
1. A water-based drilling fluid composition comprising: water, a smectite type of clay, and a carboxymethyl cellulose (CMC), wherein the CMC is characterized by forming a shear-thinning gel at 25° C. after high-shear dissolution in a 0.3 wt % aqueous sodium chloride solution, the final content of the CMC in the aqueous sodium chloride solution being 1 wt % for a CMC having a degree of polymerization (DP) of more than 4000, 1.5 wt % for a CMC having a DP of 3,000 to 4,000, 2 wt % for a CMC having a DP of 1,500 to less than 3,000, and 4 wt % for a CMC having a DP of less than 1,500, the gel being a fluid having a storage modulus (G′) which exceeds the loss modulus (G″) over the entire frequency region of 0.01-10 Hz when measured on an oscillatory rheometer operating at a strain of 0.2, and wherein the gel reaches at least 60% of its gel strength within ten seconds of cessation of shear, wherein the drilling fluid composition has sufficient rheology properties for carrying cuttings.