Invert Emulsion Fluids for Drilling Through Narrow Hydraulic Windows

Abstract

Abstract In 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 low-rheology, 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.