| Abstrakt: |
Esso Australia Pty Ltd (Esso), in a joint venture with BHP Petroleum Pty Ltd, operates 23 oil and gas production platforms and subsea facilities off the Victorian coast near Gippsland, Australia. The underlying reservoirs have multi-darcy sands and a strong aquifer water drive, so in addition to oil and gas, the extraction activities result in substantial amounts of produced formation water (PFW). Following on-platform treatment, PFW containing a variety of hydrocarbons, ions and inorganics, such as calcium, ammonia, sulfate and trace metals, is discharged into the receiving environment. This paper reports on a study undertaken to investigate the potential effects of PFW discharges from two platforms (Tuna (TNA) and West Kingfish (WKF)) on the receiving environment. Four complementary sampling approaches were used to address the objectives of the study: (1) measure and estimate the dilution of Rhodamine FWT dye solution in the receiving environment following injection into the PFW discharge line, (2) collect and analyse undiluted PFW samples before discharge, (3) collect and analyse marine water samples from within the discharge plume and (4) collect and analyse sediment and benthic infauna samples at various distances away from platforms and at reference locations. Results indicate the rate of PFW dilution within the receiving environment is more rapid than predicted by existing numerical models and that the concentration of all analytes present in PFW were below Australian and New Zealand Environment Conservation Council (ANZECC) 2000 guideline trigger values for 80% protection; moreover, with one exception, analytes were not detected above background levels more than 59 m from the platform. With the exception of a few samples containing metals, specifically arsenic, copper, lead, zinc and nickel, concentrations of analytes in the majority of sediment samples collected were below the ANZECC 2000 and revised 2013 sediment quality guidelines. A diverse range of benthic infauna were sampled, with the abundance of a limited number of taxa influenced by distance from individual platforms. No substantial differences in abundances of benthic infauna were detected at distances greater than 1.3 km from TNA and 1.0 km from WKF, compared with reference locations. These results indicate that PFW discharges from TNA and WKF likely represent a low risk to the receiving environment. |
