A conventional oil-based drilling fluid was determined not to be applicable for drilling narrow hole annuli in a mature field offshore Norway. Drilling these wells with a very narrow hydraulic window required an oil-based drilling fluid with reduced viscosity and improved sag stability.

A totally reformulated drilling fluid system was developed. The combination of base oil and selected products produced a fluid with a flatter rheological profile, resulting in reduced plastic viscosity (PV) and increased low shear rate viscosity (LSRV). This rheological profile reduced equivalent circulating density (ECD) and improved sag stability. This rheological profile also directly impacted pump pressure and hole cleaning capabilities, delivering lower pump pressure and allowing for higher pump rates and improved hole cleaning.

This paper presents the experimental work performed when developing the system for this specific application. The authors also will present field data and compare the performance of the new drilling fluid system with that of conventional systems.

Keywords:
drilling fluid chemistry, rheology, fluid loss control, drilling fluids and materials, weight material, application, emulsifier, drilling fluid property, sag stability, linear paraffin system
Subjects:
Drilling Fluids and Materials, Drilling fluid selection and formulation (chemistry, properties)
Copyright 2004, IADC/SPE Drilling Conference
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