Abstract An extensive experimental study on friction pressure drop for nonNewtonian drilling fluids in pipe and annular flow was conducted. A fully instrumented 350 feet flow loop, consisting of two pipes and two annular flow test sections, was used in the test program. Five different muds were tested, which included: Bentonite mud, MMH mud, polymer mud, Glycol mud and Petrofree vegetable oil mud.
The experimental data obtained were used to generate very useful plots of "friction factor" versus "generalized Reynolds number". For each of the mud systems, the plots offer a practical and accurate means in determining needed friction factors for the calculation of pressure drops in pipe and annular flow. In addition, a comparative discussion is presented on measured friction pressure drop data, predicted by correlations such as the power law, Bingham plastic and yield power law. The importance of wall roughness on turbulent flow friction pressure drop calculations is also investigated.
Introduction The prediction of friction pressure losses is very important during drilling operations. The concern is that inaccurate prediction of the friction pressure loss can cause inaccurate engineering decisions that may cause drilling problems such as loss of circulation, kicks, improper rig power selection, etc. These problems become more significant in the area of slim hole drilling. Generally, when a drilling fluid flow behavior deviates from the simple Newtonian, friction pressure loss predictive equations become more complex and less accurate due to many simplifying assumptions. It is believed that one factor that may contribute to the inaccuracies in friction pressure loss calculation in drilling is the particular rheological model used in the development of a given empirical correlation or theoretical expression. The rheological models that are thought to represent the flow behavior of drilling muds are the Bingham Plastic, the power law and yield power law. Not knowing which model may best represent a given drilling mud type in the prediction of friction pressure loss motivated this study.
Literature Review Many publications appear in the literature that deal with the flow of nonNewtonian fluids through pipes and annuli. However, experimental data in regard to these fluids are almost non-existing. Drilling muds are nonNewtonian fluids and thus several rheological models have been proposed to describe their flow behavior. The most commonly used in the drilling industry are the Bingham plastic model and the power law model. Due to its complexity, the yield power law model did not receive as much use. Hanks et.al. (1963) have published a paper on flow of fluids with yield stress. He used the Bingham plastic model to predict laminar and turbulent transition for fluids with yield stress. They proposed a general criterion for the onset of turbulence. Hanks has also published a number of papers on concentric annular flow of fluids. Langlinais et. al. (1985) studied friction pressure losses for gas and drilling mud. They have used different equivalent diameters and their effects on single phase flow of drilling mud in concentric annulus.