Dynamic Barite Sag in Oil Based Drilling Fluids

Abstract

A rheological technique is described which utilises flat parallel plate geometry. The technique is sensitive enough to pick up the effect of syneresis and resulting movement of denser materials from the surface layers into the bulk of the drilling mud samples over time. Examples of down flow curves are given which demonstrate that dynamic sag while in flow is represented by a dip in this curve depending flow on particular samples, when expressed as log/log plots of viscosity vsshear rate. The up curves illustrate the degree of syneresis and static sag in the samples. Log/log plots of viscosity vs shear rate for both up and down flow curves exhibit one or two crossover points. The lower crossover points can be plotted on a 3D graph for easy visualisation of the sagging tendencies of various oil mud samples.