COOPERATIVE INDUSTRY APPROACH TO ENVIRONMENTAL INVESTIGATIONS IN THE TIMOR SEA

Abstract

For more than 20 years, oil and gas exploration and production activities have been conducted in the Timor Sea region, including the Sahul Shelf. The Shelf is a large, shallow platform off the Northern Australian Coast, considered to be a recently drowned part of the Australian Platform. Seismic surveys have indicated submerged banks on the edge of this Shelf. Until recently, little was known of the physical nature of these banks, or their ecology.

Environmental management of petroleum exploration and development activities in the area is required to avoid potentially impacting the surrounding environment. Accurate information on ecological systems is therefore required in order to design detailed Environmental Management Plans which aim to minimise impacts and protect the environment.

BHP Petroleum and Woodside Offshore Petroleum, as operators of permits in the area, independently conducted baseline environmental investigations. This information was exchanged, and the cooperative effort between BHPP and Woodside resulted in a significantly improved environmental resource database, which will aid in the planning and implementation of effective environmental management of petroleum operations.

The studies included:

Accurate bathymetric surveys to determine the geomorphology of the banks.Acquisition of side-scan sonar for interpretation of substrate features and the preparation of preliminary habitat maps.Remotely Operated Vehicle (ROV) surveys to ground truth habitats, and to determine their distribution and species composition.Grab and drop-core sampling to validate ROV film and provide material for chemical and physical analysis.Collecting current data, to aid in the formulation of management strategies for the disposal of drilling discharges and for oil-spill contingency planning.Deep-water benthic trawling to determine the abundance and composition of epi-benthic macrofauna.

The main conclusions were that submerged banks are reef-systems that have variable density of coral cover, which are dependant on depth (light intensity), and substrate type. Thirty metres is assumed to be the maximum depth for reef-flat coral growth. The outer rims of the banks support the highest density of coral growth, probably due to the prevailing strong currents which provide greater feeding opportunities and which maintain bare substrate suitable for colonisation. Bank slopes may support a moderate density of coral cover to 60 m. Where conditions are less favourable for coral growth, reef-flats support the macro-algae assemblages dominated by the coralline alga Halimeda, which contributes between 10–60 per cent substrate cover.

Deep-water benthic habitats (>300m) support a low-abundance epi-benthic macrofauna.