Abstract
The cuttings transport efficiency of a drilling fluid is a combination of the ability to keep particles in suspension and the ability to entrain particles which have settled onto a cuttings bed. The rheological properties of the drilling fluid are important for both these cuttings transport mechanisms. While weight materials are added to a drilling fluid to increase its density, such materials will also affect the rheological properties in various ways. In this work we compare the cuttings transport efficiency of two similar oil-based drilling fluids from the same vendor, where one drilling fluid contains barite particles (a common weight material) with a standard particle size distribution, and the other drilling fluid contains micronized barite particles, i.e. with a much smaller average particle size. While a motivation for using micronized barite is to reduce the risk of barite sag (alternatively to allow using a less viscous fluid), the smaller particle size and larger total particle surface area may also affect the rheological properties and thereby the cuttings transport mechanisms mentioned above. We present results from flow loop experiments using these two drilling fluids, comparing and discussing the performance of these fluids with respect to hydraulics and cuttings transport for horizontal and inclined wellbore and both at room temperature and elevated temperature. We argue that the differences observed can be explained in part by the effect of the barite particles on the fluid transport properties.