THE CAROLINE CARBON DIOXIDE FIELD AND ASSOCIATED CARBON DIOXIDE OCCURRENCES, GAMBIER EMBAYMENT, SOUTH AUSTRALIA

Abstract

Subsurface occurrences of high purity carbon dioxide are comparatively rare although widespread geographically. Within the Gambier embayment of the Otway Basin two substantial examples of carbon dioxide entrapment have been encountered, at Kalangadoo No. 1 with 147 tonnes/day (2.8 mmcf/day) and Caroline No. 1 with 142 tonnes/day (2.7 mmcf/day). Australia's only commercial production of subsurface CO2 is the Alliance Caroline well which produces at an annual rate of around 15 000 tonnes (0.3 BCF) per annum of liquid CO2. Treatment is limited to removal of the 1% hydrocarbon content of the well-head stream by simple fractionation.

At Kalangadoo No. 1 the CO2 is found in steeply dipping (?) Palaeozoic arenaceous sediments (unconformity trap), with porosity coming from secondary fractures. By contrast, at Caroline No. 1 the host sediments are sands of the Cretaceous Waarre Formation (fault trap) with primary porosity.

Throughout the world several diverse sources of subsurface C02 have been established. The most significant occurrences are in regions with vulcanism in close proximity to carbonate sediments. These show a random distribution with regard to age and nature of host sediments. Isotopic studies (for both carbon and oxygen) have been employed in an attempt to further clarify the source of subsurface CO2 at the Caroline Field. Although not conclusive the evidence to date suggests that a volcanic origin would seem the most likely.