Low Equivalent Circulating Density Organoclay-Free Invert Emulsion Drilling Fluids

Abstract

High pressure and high temperature (HTHP) wells especially those with narrow pore / fracture pressure gradient margins present challenges in drilling. Maintaining optimum and low rheology for such wells becomes a challenge where a slight change in the bottom-hole pressure conditions can lead to non-productive time. However, maintaining low viscosity profile for a drilling fluid can pose a dual challenge in terms of maintaining effective hole-cleaning and barite-sag resistance. This paper describes the formulation of 95pcf medium-density organoclay-free invert emulsion drilling fluids (OCIEF) with a low viscosity profile. The fluids gave lower plastic viscosity (PV), which ensured that the fluid presents low equivalent circulation density (ECD) contribution while drilling/circulating. These fluids were formulated with acid-soluble manganese tetroxide as weighting agent and specially designed bridging-agent package. The fluids were hot rolled at 300oF and their filtration and rheological properties were measured. The paper describes the static-aging, contamination and high pressure/high temperature rheology measurements of the fluids at 300oF. Particle plugging experiments were performed on the fluids to determine the invasion characteristics and the non-damaging nature of the fluids. These organoclay-free invert emulsion fluids were then field-trialed in different wells with good results. Field deployment of the 95pcf organoclay-free invert emulsion fluid helped to maintain the required hole stability in the HTHP well. The paper demonstrates the superior performance of the developed fluid in achieving the desired lab and field performance.