The Forties field was discovered in 1970 and at its peak produced 500,000 bbl of oil per day (bopd). To re-start major drilling operations using oil-based drilling fluids on some of the field's old platforms would have required significant capital expenditure (CAPEX) to ensure total containment of both the fluid and cuttings. An alternative approach on three of the field's platforms has been successfully employed. The first utilisation in the North Sea of a high-performance, environmentally friendly, water-based drilling fluid has helped the operator achieve early oil with much lower CAPEX. It has also proved possible to drill side-track wells through the Eocene overburden and through the reservoir in one hole section. This was not previously considered possible - historically intermediate casing was set and the reservoir drilled with a smaller hole size. Expensive retrofitting of aging platforms to meet environmental obligations for total containment may be unnecessary when a high-performance, water-based fluid is utilised.

This paper describes the characteristics and field performance of this innovative drilling fluid system. Six wells have been drilled from three different platforms during 2004 and early 2005. This paper describes how the fluid performed drilling reactive formations that have only been successfully drilled in the past using oil-based muds. The paper presents a cost model of the alternative approaches to developing Forties using either oil-based muds with total containment or high-performance, water-based fluids with cuttings discharge. This paper will be of interest to Operator's of aging assets looking to continue drilling without heavy CAPEX investment for Total Containment.

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