A Study on the Effect of Electrolytes, Shalehib Ultra Amine, pH and Temperature on the Clay Hydration and Rheological Properties of Water-Based Drilling FluidsBenjamin Crichton and Ben Thomson - 2014
Australian School of Petroleum
University of Adelaide
The objective of this study was to investigate the effect of electrolytes, Shalehib Ultra, pH and temperature on the clay hydration and rheological properties of Aus-Ben, an API 13A standard viscosifier distributed by the Australian Mud Company (AMC) typically used in water-based drilling applications. Clay hydration and rheological properties of drilling fluids are significant because of the influence they exert on factors such as wellbore stability, hole cleaning capacity, cuttings transport and several other crucial drilling functions. In this study, aqueous bentonite dispersions were prepared using AMC's Aus-Ben product and rheological properties were measured using an Anton Paar Physica MCR 301 rheometer in a Couette-type, concentric cylinder geometry. Rheological data was fitted and interpreted according to the Bingham plastic and Herschel-Bulkley fluid models. Results indicated that at 100 to 500 ppm inhibitor concentrations, net attractive forces developed between clay particles resulted in the formation of internal network structures, producing an increase in plastic viscosity, yield point and psuedoplastic behaviour.
Further increase in inhibitor concentration resulted in the collapse of network structures, leading to aggregation, destabilisation and loss of non-Newtonian fluid properties. The inhibition performance of Shalehib Ultra was found to follow a similar trend to that observed for NaCl and KCl. At pH values between 8.5 and 10, typically maintained for bentonite mud systems, negative edge charges develop, altering the dominant mode of particle association causing a reduction in plastic viscosity and yield point.
Positive edge to negative face associations at pH values less than the isoelectric point (IEP) of the edges, estimated to lie between pH 7 and 8, was observed to cause flocculation, leading to an increase in yield point. Addition of KCl across alkaline pH conditions from ~5.0 to 12.0 was found to increase the magnitude of all rheological parameters except flow consistency index, which decreased. This was due to compression of the electrostatic double layers surrounding clay particles, increasing the strength of particle interactions. Experiments were also performed to investigate the effect of elevated temperatures, up to 70C, on the rheological properties of water-based drilling fluids. Elevated temperatures were observed to have no effect on the Herschel-Bulkley yield point for muds with ≤100ppm NaCl concentrations. NaCl concentration between 100 and 2500ppm was observed to aid flocculation, causing an increase in yield point. These findings are significant because they present quantitative data for the performance of AMC's Aus-Ben and Shalehib Ultra products under varying conditions relevant to typical drilling operations.