EFFECTS ON THE MARINE ENVIRONMENT OF PRODUCED FORMATION WATER DISCHARGES FROM OFFSHORE DEVELOPMENT IN BASS STRAIT, AUSTRALIA

Abstract

An environmental effects study was undertaken to assess the potential environmental effect of discharged produced formation water from offshore oil and gas platforms in Bass Strait. The focus was on potential effects on the fisheries of Bass Strait. Produced formation water discharged to the ocean from the Halibut platform, one of the largest Australian oil fields and now the most prolific produced formation water field, was modelled for dilution versus distance from the platform. Characterisation of produced formation water from 10 Bass Strait platforms for chemical constituents and toxicity to local marine organisms was performed.

It was found that produced formation water discharged into Bass Strait presents a very low risk to marine organisms due to very low toxicity and very high dilution rates. For the Halibut platform, acceptable acute toxicity concentration can be obtained with dilution of less than 2:1. Actual dilution rates are approximately 30:1 within 10m of the discharge point, and concentrations reach an indicative 'no chronic' toxicity effect within 25m of the discharge point. The plume is also spatially limited and mobile and any organism would be exposed to potentially lethal concentrations of produced formation water for less than about 30 seconds for median current condition.