Metodologia para preparação de amostras em testes reológicos e determinação da tensão limite de escoamento de fluidos de perfuração

Abstract

In this work, a sampling methodology for oil based drilling muds is proposed, which is later used to evaluate the dynamic and static yield stress of the BR-MUL 117 drilling fluid. The methodology is validated using experimental data, aiming to select the best measuring geometry and the optimal resting time. Thereafter, the influence of the measuring geometry, the sample insertion method and several pre-shearing conditions in the yield stress and in the steady state stress is studied, using statistical methods to validate the methodology. It is shown that the best measuring geometry is the roughened parallel plates, that the sample insertion method does not induce significant statistical changes in the rheological behavior and that the pre-shearing induces irreversible changes in the sample, which leads to changes in the rheological behavior. The dynamic yield stress is determined from equilibrium curves fitted with the Bingham and Herschel-Bulkley equations, while the static yield stress is evaluated trough creep tests. It is shown that the static and dynamic yield stresses are different for the drilling fluid BR-MUL 117.