Enhanced dispersive stability of bentonite suspension in saline water-based mud

Developing drilling fluids with good bentonite suspension stabilities in saline water-based muds are preferred for sufficient cutting carrying capacities, lower filtration loss, and better shear-thinning behavior. In this work, the salt-tolerant bentonite (STB) was prepared by bentonite, composite fiber materials, and other additives. The results indicated that the drilling fluids of STB had excellent rheological and filtration properties in brine compared with drilling fluids of attapulgite. The ratio of yield point to plastic viscosity (RYP) of 6.4% STB in brine was suitable for drilling operation, while the RYP of 6.4% bentonite was almost 0 Pa/(mPa.s). The salt-tolerant properties of different materials including fiber materials, polyanionic cellulose, and so on were investigated. The fiber materials played an essential role in improving the stability of bentonite particles. Aiming to improve cost-efficiency, the cotton fibers were investigated to replace a certain dosage of asbestos fibers. The cotton was modified by 10wt% NaOH solution to resolve the compatibility problem with asbestos. The rheological modifier prepared from composite fibers has been successfully used in Dagang Oilfield, China. The rheological modifier increased the viscometer dial reading of theta(6) and theta(3) of drilling mud from 5 dia and 4 dia to 8 dia and 6 dia, which could significantly improve the suspension capacities of the mud.