Offshore Production and Onshore Falling Water Levels in the Gippsland Basin Australia

James Underschultz¹, Claus Otto¹, and Tom Hatton^2
1 CSIRO Petroleum (ARRC), Perth, Australia
² CSIRO Land and Water, Wembley WA, Australia

The Late Cretaceous to Early Tertiary Latrobe Group supports a number of water related industries across a large region (~20,000km2) of the Gippsland Basin in southeast Australia. Offshore, hydrocarbons have been produced since the late 1960's in volumes equivalent to between 40,000 and 90,000Mega litres/yr. Onshore, dewatering of between 20,000 and 30,000Mega litres/yr has occurred since 1960 in association with coal mine development, and abstraction for agricultural and municipal purposes has traditionally been between 5,000 and 10,000Mega litres/yr.

Water levels in the aquifer onshore have been falling at the rate of about 1m/yr for decades, resulting in irrigators incurring significant costs for lowering pumps and re-completing extraction wells. There is an added impact on the wider community with concerns of land subsidence. Community perception was that hydrocarbon extraction was the primary cause of falling water levels and pressure was applied to regulators and oil companies for compensation.

The CSIRO undertook a hydrodynamic evaluation of the Latrobe Group Aquifer system (onshore and offshore) to better constrain the cause of falling water levels and to recommend mitigation strategies. The study indicated that a combination of basin-scale structural elements and the geographic location of various extractors resulted in a geographically variable impact of individual extractors on water level decline. This allowed for mitigation strategies to be geographically targeted rather than requiring a regional solution.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005