Barite sag is a well recognized, but poorly understood phenomenon in the drilling industry. Historically it has been associated with a static well environment; consequently test devices and rheological measurements were originally based on static conditions. Dynamic barite sag is now recognized as the major contributor to sag-related drilling problems. There are two prominent variables conducive to creating dynamic sag; 1) low shear rate conditions (drilling process-related) and 2) insufficient ultra-low shear rate viscosity (drilling fluid-related). Dynamic sag is not entirely a mud-related problem and, under certain conditions, will occur despite appropriate control of drilling fluid viscosity.
Barite sag is typically attributed to the mud system and the traditional approach to manage barite sag is to modify (increase) certain rheological properties of the mud system. These efforts are often frustrating because; 1) the proposed solution is ineffective, 2) the solution creates a new problem such as ECD management and 3) expectations are not met. This paper proposes that dynamic sag is related to both the drilling process and drilling fluid, and that these two variables cannot be treated independently from one another.