Effects of carbon ash on rheological properties of water-based drilling fluids

The rheological properties of drilling fluid play a fundamental role in drilling operations, and the water-based drilling fluid is based on bentonite dispersion. According to Bingham-plastic model, the influences of carbon ash and commercial rheological modifier (RM) on rheological properties of bentonite dispersion are investigated systematically from apparent viscosity (AV), plastic viscosity (PV), yield point (YP) as well as the ratio of yield point and plastic viscosity (RYP). The results indicate that the theological properties of bentonite dispersion with carbon ash are improved markedly in YP, and especially for the low solid content of bentonite dispersion. The filtration and density test are also carried out using an API Filter Press and mud balancer respectively. From the results, it could be observed that the filtrate loss and filter cake thickness increase dramatically whereas the density of bentonite dispersion decreases slightly as the addition of carbon ash increases. Furthermore, the stability of bentonite dispersion incorporated with carbon ash is evaluated. The experimental results indicate that carbon ash is better than RM in stability. Through this study, carbon ash is an excellent potential additive for improving the rheological properties of water-based drilling fluids. (C) 2012 Elsevier B.V. All rights reserved.