THE TUNA FIELD, A RECENT GIPPSLAND DEVELOPMENT

Abstract

The Tuna field, 42 km offshore from the Victorian coast, was contributing approximately four percent of Australia's total crude oil production by the time development was successfully completed in 1982. The field was the most complex of the seven Gippsland Basin fields developed by the Esso/BHP joint venture up to that time. Commercial reserves are contained in four sets of reservoirs, featuring both structural and stratigraphic traps.

The field has been developed with an 18 well platform, initially as an oil producer and later to be converted for gas production. Development drilling commenced in October 1978, with production start-up 11 months later when the first four wells were brought on-line. Several oil accumulations were discovered during development drilling. Two of the development wells were used also as deep exploration wells, requiring the drilling of "S" shaped wells.

The complexity of the reservoirs was revealed during simultaneous drilling and production operations. Crucial reservoir production performance data were obtained sufficiently early for optimum well targetting and completions. Reservoir pressure profiles, collected using the Repeat Formation Tester (RFT)*, and the performance of producing wells showed that the major oil reservoir was far more complex than the original exploration wells had indicated. This, plus the additional discoveries, led to the installation of 13 multiple completions, including one dual/tandem completion. Development drilling was completed in March, 1982. Satisfactory development of the field was greatly assisted by extensive performance monitoring during development.