William M. Dye

Correlation of Ultra-low Shear Rate Viscosity and Dynamic Barite Sag in Invert-Emulsion Drilling Fluids

The occurrence of barite sag has been a well recognized, but poorly understood phenomenon in the drilling industry. Problems such as lost circulation, well control and stuck pipe have resulted from, the occurrence of barite sag. The financial impact of barite sag on drilling costs, usually resulting from rig-time lost while circulating and conditioning the mud system, is not trivial. There are reported incidences where recurring barite sag problems have resulted in the loss of drilling projects. Although originally thought to occur under static conditions, barite sag is now recognized to occur more readily under dynamic, low shear rate conditions. Industry experts have offered a variety of measuring parameters, based upon empirical data, that only partially correlate with the occurrence of barite sag. The prediction of barite sag in dynamic flow has created an engineering challenge. The effect of shear rate on dynamic barite sag, for invert-emulsion muds, has been studied and quantified using new and advanced technology. A new field viscometer, capable of measuring viscosity at shear rates of 0.0017 s -1 , and an eccentric well-bore hydraulics model were used to develop and understand this relationship. Changes in mud weight as a function of shear rate, hole angle, annular velocity and eccentricity correlate with ultra-low shear rate viscosity. Based upon experimental results, field technology has been developed to predict the potential for barite sag of invert-emulsion muds and to provide remedial measures through ultra-low shear rate viscosity modification. The efficacy of using traditional rheological measurements as indicators of barite sag potential are addressed.

An Environmentally Safe Water-Based Alternative to Oil Muds

In this paper, a mechanism describing the onset of bit balling is given. On the basis of this mechanism, a new copolymer/polypropylene glycol (COP/PPG) water-based drilling fluid was developed. The properties of this fluid are described, and field test comparisons are made with water- and oil-based fluids.

Recent Advances in Barite Sag Technology

The occurrence of barite sag is a well recognized but poorly understood phenomenon in the drilling industry. Industry experts have offered a variety of measuring parameters, based upon empirical data, that only partially correlate with the occurrence of barite sag. The industry’s lack of understanding of the mechanisms and types of barite sag generally result in a poor correlation between laboratory results and field observations of barite sag. The financial impact of barite sag on drilling costs, usually resulting from rig-time lost while circulating and conditioning the mud system, is not trivial. There are reported incidences where recurring barite sag problems have resulted in the loss of drilling projects. The accuracy and relevance of technology utilized to manage barite sag can help reduce drilling costs. In the field barite sag frequently occurs in deviated wells where pipe eccentricity creates conditions conducive to dynamic sag. With the exception of a flow loop, laboratory tests do not simulate field conditions. Historically, laboratory tests characterize density variations arising from a vertical fluid column as static or dynamic sag without proper consideration to angle, pipe eccentricity, annular shear rates and annular flow. This paper reviews traditional and newly-emerging barite sag technology and compares their ability to predict barite sag potential. This potential will be determined under dynamic and static conditions in a sophisticated flow loop configured to match certain field conditions.Copyright