Quemada model approach to oil or synthetic oil based drilling fluids rheological modelling

Abstract Understanding and modelling the deviations from Newtonian behavior of synthetic-based drilling fluids (SBFs) is essential to design optimal flow systems and efficient cuttings transport. This research develops a better insight into synthetic fluid rheology based on the theory of internal structural units (SUs) suspensions. Although different studies have been proposed to characterize SBF rheology, yield stress and time dependency proved difficult to determine. This study explains how most difficulties disappear when taking thixotropy into account. The behavior of structural units and effective volume fractions as a function of shear rate, has been analyzed by Qemada (1998) to develop a rheological model for particles suspension. This rheological model has been modified to describe the behavior of SBFs. For validation purposes, an industrial SBF used for drilling in a shale reservoir is analyzed. A novel experimental procedure is proposed that makes extensive use of rotational rheometers to estimate the parameters of the model. Various combinations of temperatures and resting times have been tested to develop semi-empirical correlations for the model parameters. In addition, a practical use of the model is demonstrated by accurately estimating the settling of retrieved shale cuttings through the analyzed synthetic fluid. The experimental protocol represents a design tool for onshore and offshore drilling operations that involve SBFs, with potential improvements on optimization of flow systems and cuttings transport efficiency.