fax 01-972-952-9435. AbstractExtended reach wells drilled from the Goodwyn Alpha platform are highly aggressive and have been drilled with a variety of invert-emulsion mud systems. Historically, mud system selection for these wells was based on compliance to environmental regulations and satisfaction of technical criteria. In order to take a more proactive approach to mud system selection and to raise environmental standards to new levels, an initiative was undertaken to replace the environmentally acceptable, and technically competent mud system being used on Goodwyn with a new ester-based system. Ester-based mud systems are considered the "systemof-choice" in terms of environmental acceptability and possess inherent lubricating qualities for torque and drag reduction. This paper describes the development process and 4 successful field applications of the new ester-based mud system. A new ester, which exhibits the lowest kinematic viscosity of commercially available esters, was identified and selected for use. New and innovative technologies were introduced in the laboratory development and field applications to address barite sag, hole cleaning efficiency and hydrolytic stability.The system development and field testing processes were enhanced by daily communication with the development teams in Aberdeen, Houston and Perth. Down-hole friction factors were significantly lower than modeled predictions. Barite sag problems encountered on previous wells were eliminated, and hole cleaning efficiency was optimized.