Evaluation of Rheology and Pressure Losses for Oil-based Drilling Fluids in a Simulated Drilling Process

Abstract

The advancements in the field of hydraulics have indicated that eccentricity in the well greatly reduces the pressure losses. This knowledge has been readily adopted in the industry practice, but the theoretical approximations of the pressure losses regarding the eccentricity have not been fully modified. The existing approximations are based on the older solutions from the concentric annulus case and suggest use of correction factors. The flow loop experimental rig of SINTEF Petroleum Research has allowed conducting experiments on eccentric annulus, allowing us to evaluate and verify the theoretical estimation method that was derived, and it has proved to give good predictions of pressure drop in eccentric annulus.

Herschel-Bulkley rheology model was found to be the model that provides the best mathematical description of the rheology of the tested oil-based fluids for the pressure loss calculations, among several other models. However, during the comparison of the experimental data with the theoretical predictions and subsequent evaluation of these some questions were raised about the quality of the rheological measurements and the methodology used for performing these. Additional experiments were conducted with both Fann 35 viscometer and Anton Paar Physica rheometer in order to find out how pre-treatment of samples and other relevant measuring factors can affect the quality of the measurements. The result of this work has provided both quantification of the effects of these factors and suggestions for improvement of the measurement methodology, and the findings are submitted and accepted in a paper for the Nordic Rheology Society.