NON-VOLATILE HYDROCARBON CHEMISTRY STUDIES AROUND A PRODUCTION PLATFORM ON AUSTRALIA'S NORTH WEST SHELF

Abstract

In September 1994 and 1995, scientists from the Australian Institute of Marine Science (AIMS) and the Australian Geological Survey Organisation (AGSO) conducted surveys aboard the Research Vessel Lady Basten to determine the dispersion, fates and effects of Produced Formation Water (PFW) discharged from the Harriet A production platform near the Montebello Islands, on the North West Shelf of Australia. This report describes the non-volatile hydrocarbon chemistry studies.

We measured the dispersion of the PFW into dissolved and particulate fractions of seawater using moored high volume water samplers, surface screen samplers and moored and drifting sediment traps. We studied bioaccumulation using transplanted oysters, and we measured dispersion into sediment with benthic grabs. Samples were analysed for total non-volatile hydrocarbons and individual hydrocarbon components using ultraviolet fluorescence spectroscopy (UVF), gas chromatography with flame ionisation detection (GC-FID), and GC with mass selective detection (GC/MS). The hydrocarbon concentrations were used to calculate vertical fluxes and the total concentrations of hydrocarbons in the various ecosystem compartments. A mass balance model was then used to calculate the rates of other important dispersion and degradation processes.

We estimate the potential zone of biological impact in the water column extends to a distance of approximately 0.5 nmile (900 m). Concentrations of oil in sediments were too low to indicate potential toxicity. By the collaborative application of oceanographic and geochemical techniques to marine environmental problems, we endeavour to provide effective feedback to the oil industry to gauge the effectiveness of their operational strategies in minimising impact in these pristine regions.