Abstract
One important issue for drilling operations is control of down hole pressures. When drilling with synthetic or oil-based drilling fluids, the ability to maintain all the weighting agents in suspension is particularly difficult since these fluids are more vulnerable for sag than water-based drilling fluids.
In the current study, it has been shown that the ability to keep barite in suspension also depends on the chemical composition of the water phase. The sag tendency of a mineral oil-based drilling fluid, a linear paraffin-based drilling fluid and both an ester and a LAO-based synthetic drilling fluid has been evaluated. For comparison, all fluids were formulated with equivalent water activity in the internal brine phase. The results show that for all these fluids, improved performance was observed if the traditional calcium chloride salt was replaced with a selection of other salts. Formates as the internal salt, gave generally better performance than if calcium chloride was used. The best performance with respect to sag stability in the tests was observed using an ammonium calcium nitrate as the internal salt phase.
The paper describes in detail the effect that different salts in the internal brine phases in synthetic and oil-based drilling fluids was found to have on sag performance in a series of tests.
