
TY  - JOUR
A1  - Oliver, G.A. 
A1  - Fisher, S.J. 
T1  - THE PERSISTENCE AND EFFECTS OF NON-WATER-BASED DRILLING FLUIDS ON AUSTRALIA'S NORTH WEST SHELF: PROGRESS FINDINGS FROM THREE SEABED SURVEYS
JF  - The APPEA Journal
JO  - The APPEA Journal
Y1  - 1999
VL  - 39
IS  - 1
SP  - 647
EP  - 662
KW  - 
UR  - https://doi.org/10.1071/AJ98044 
N2  - The effects and persistence of non-water-based drilling fluids discharged into the marine environment were investigated at three locations on Western Australia's North West Shelf (NWS), namely the North Rankin 4A' (NRA) drilling platform, the Wanaea&#x2013;6 production well and the Lynx&#x2013;la exploration well. For the multiple-well drilling operation at NRA, acute biological effects at the completion of drilling were restricted to within 400 m in the direction of the prevailing current. High total petroleum hydrocarbon (TPH) concentrations within the NRA cuttings pile persisted between 1991 and 1993. Away from the cuttings pile itself, a consistent downward trend in TPH concentrations was evident, indicating an approximate half-life of one year for surface sediments. Three years after the completion of drilling at Wanaea&#x2013;6, biological effects appeared to be limited to within 100 m of the cuttings discharge point, with background concentrations of TPH and trace metals occurring near 1,200 m in the direction of the prevailing current. Sediment hydrocarbon concentrations greater than 1 mg/kg were found to be restricted to within 200 m of the cuttings discharge point. Dramatic reductions in TPH and barium concentrations occurred in the 12-month period between the completion of drilling and the follow- up survey at Lynx&#x2013;la. The reductions are attributed to sediment dispersal mechanisms which appear to play a major role in reducing sediment TPH and trace metal concentrations in mid-shelf water depths (70&#x2013;80 m) on the NWS. The installation and presence of subsea production facilities may result in sediment redistribution and changed dispersal mechanisms, complicating the interpretation of the presence of contaminants within sediments. 
ER  -

