Prediction of Cement Slurry Laminar Pressure Drops by Rotational Viscometry

Abstract

Abstract The flow behaviour of cement slurries, as measured with different types of equipment – a pilot-scale pipe viscometer, a Searl and a Couette coaxial cylinder viscometer – is analyzed. The dimension of the flow geometries, respectively pipe diameter and annular gap size, was varied to detect the presence of an apparent slippage at the wall. Different cement formulations were tested including a wide range of specific gravity from 1.7 to 2.2. Experimental flow curves were also compared for a polymer solution, and two water-base bentonitic muds. For cement slurries, experimental results show that the flow curves obtained with the pipe and the Searl viscometer are very similar. The abrupt increase in viscosity at low shear-rates is attributed to the existence of a yield stress (τy), For stresses lower than τy, flow is still observed in both cases. The size dependence of the flow curves indicates that such a behaviour can be attributed to an apparent slippage at the wall. For stresses higher than τy little or no slippage is observable, and slurries exhibit a shear thinning behaviour that can be well fitted to a power law model from 30 to 500 s−1. Different methods of calculating pressure drops in pipe flow from rotational viscometer data are presented. Their precision and limitations are compared. As a conclusion, it is established that laminar pipe flow pressure losses can reliably be predicted from rotational viscometer measurements if made on representative samples using equipment which minimizes particle centrifugation e.g. Searl systems instead of Couette systems.