Woollybutt title relinquishment

The Woollybutt Field, located approximately 50km west of Barrow Island in the Barrow Sub-basin of the Northern Carnarvon Basin in Western Australia, is the first title to be successfully handed back to the government post decommissioning in Commonwealth waters.

The field was discovered in 1997 and further appraisal drilling delineated two separate oil accumulations in the Early Cretaceous Barrow Group Sandstone; the Woollybutt North and South Fields.

The Woollybutt project was a joint venture operated by Eni (76.5%) and MARC (23.5%) and was designed as a short life, leased Floating Production, Storage and Offloading (FPSO) development utilising the Four Vanguard, a converted oil tanker, designed for holding 40 thousand barrels of oil per day.

The North Field came into production in April 2003 with the initial development of two producing wells. In 2005, further development drilling extended the life of the field by another three years.

Ashley Duckett, Senior Geoscience Principal, was one of the geoscientists who helped identify Woollybutt as a prospect.  

“My involvement in this project started right from the beginning when I was tasked with completing the depth conversion of the interpretation. This took the idea of a lead to a viable prospect once we identified the structure as having potential to be of material volume.”

“Since then, the work continued to evolve with the integration of additional drill well data, further refinement of the velocity model and resultant depth structure to recognise multiple closures which were targeted by the development drilling. From small things grew bigger things and Woollybutt has proven a success as it was initially developed to produce 20 million barrels of oil but has ultimately produced gross 34.2 million barrels,” he added.

Production ceased in 2012 and in 2022, Eni Australia committed to full decommissioning of the offshore oil field which included the plug and abandonment of 4 wells and the removal of the 450 tonne Disconnectable Riser Turret Mooring (DSPM), 9 wellheads, 30 kilometres of flexible flowlines and umbilicals and associated subsea infrastructure.

Suzanne Borrett, Joint Interest Asset Manager, and joint venture representative for the project highlighted, “MARC has contributed valuable input and expertise and received learnings throughout the full lifecycle of the Woollybutt asset from exploration and development, operations and decommissioning phases. We are immensely proud to have been involved in this project from start to finish, with title relinquishment a milestone worth celebrating!”