In 1999, in response to its escalating number of wells requiring abandonment, ChevronTexaco initiated research into the use of compressed sodium bentonite as an alternative to cement for permanent well plugging. The objective of this research was to identify a process to reduce plugging costs by at least 30% to encourage the expeditious abandonment of the growing back-log of wells. A subsidiary company, Benterra Corporation, was established to manage ChevronTexaco's research and subsequent implementation of any proposed new processes. Following pilot studies in California, Benterra has so far abandoned over 500 wells across the USA using highly compressed sodium bentonite, marketed as "ZoniteTM".

The Barrow Island oil field is located on an A-class nature reserve and is operated by ChevronTexaco Australia Pty Limited on behalf of Joint Venture Participants, Mobil Australia Resources Company Pty Limited and Santos Offshore Pty Limited. Approximately 100 wells have been identified as possible abandonment candidates on Barrow Island. The Zonite plugging process could reduce the cost to abandon these wells by up to 50%. With the close involvement of the Western Australian Department of Minerals and Petroleum Resources (DMPR), ChevronTexaco undertook a Zonite plugging trial in October 2002. This was the first application of Zonite outside the USA.

This paper discusses the Barrow Island trial and the potential environmental and economic benefits of future Zonite abandonments.

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