fax 01-972-952-9435. AbstractIn mature fields the difference between the pore pressure and fracture pressure, expressed as the hydraulic window, is reduced. Underbalanced drilling and the use of low-viscosity drilling fluids are but a few of the many approaches that have addressed this challenge. While low-viscosity fluids severely reduce frictional pressure loss when compared to more viscous fluids, there is a limit to how much viscosity can be reduced before conventional weight material begins to settle. This paper describes the development and application of novel technology that has resulted in a ten-fold reduction in the particle size of the weighting agent. With this development, invert emulsion drilling fluids can be designed with low viscosity with minimal settling potential of the weight material.The authors will explain in detail the first field applications of this polymer-coated, micron-sized weighting agent in an oil-based drilling fluid. The system was used to drill two wells offshore Norway. These reservoir wells included an 8½-in. section and a 5⅞-in. thru-tubing section.This novel drilling fluid technology delivers a lowrheology, low-sag fluid offering a number of performance benefits over conventional technology. Performance data from offset wells will be presented that show the benefits of this unique approach. Equivalent circulating densities (ECD) and torque values were significantly lower than comparable wells and no instances of particle settlement were observed.
fax 01-972-952-9435. AbstractOne 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.
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