Development of the thin Oil Zone Underlying the Snapper Gas Field

Abstract

ABSTRACT This paper describes the successful development by Esso Australia Ltd (Operator) and BHP Petroleum Pty Ltd of the Snapper field which is located in the Gippsland Basin beneath the waters of Bass Strait off south-eastern Australia. Discussion is focussed on the development of a thin, "pancake" type oil column of 4 to 8 metres thickness which underlies the Snapper N-1 gas reservoir. The gas reservoir, which has a maximum gross thickness of 208 metres, comprises very high quality sandstones with interbedded shales, siltstones and coals. A 27 conductor production platform has been installed in 55 metres of water with facilities for concurrent production of gas and oil. The timing of the development has permitted successful development of the thin oil column before major withdrawal of gas takes place. Development of the oil zone was complicated by the presence of interbedded non-net sections which, combined with the varying thickness of the oil column provided significant well targeting challenges. Several high angle wells were required for oil production which presented drilling and logging problems. However, 16 of the 21 wells drilled succeeded in intersecting oil columns suitable for production. Performance of the oil wells has been very encouraging, but also variable with a wide range of producing GOR's, water cuts and wellhead pressures. Thin oil columns of 2 to 15 metres overlying water and underlying a large gas cap are common within the Gippsland Basin and elsewhere. Snapper, the first development of one of these oil zones in the Gippsland Basin, has provided valuable and encouraging experience in performance of the wells, completions and surface equipment. This will assist economic assessment and facilities design for other with thin oil column development prospects.