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Tectonic and Stratigraphic Mapping Framework of the Lower Arthur Creek, South Georgina Basin, Northern Territory, Australia

Boult, Peter¹; Bennett, Paul J.²
¹Ginkgo Resources, Npsp, SA, Australia.
²PetroFrontier, Calgary, AB, Canada.

Potential economic hydrocarbon resources of the South Georgina Basin have been identified by using tectonic/stratigraphic studies and horizontal drilling.

The distribution of the Middle Cambrian Lower Arthur Creek Fm. (LAC) in the South Georgina Basin (SGB), NT, Australia contains sediments that range from Neoproterozoic to Devonian. The major tectonic events that have deformed the area are: the late Neoproterozoic Petermann Ranges Orogeny , Middle Cambrian extension followed by mild compression and the Devonian/Carboniferous Alice Springs Orogeny (ASO).

Middle Cambrian to Devonian sediments were deposited in several sub depo-centres: the Marqua, Arganargada, Manners, Dulcie & Toko Troughs. Up to 1500 m & 4000 m of post Neoproterozoic section is interpreted in the Dulcie and Toko Troughs, however, the others remain mostly unexplored. Within these depo-centres Lower to Middle Cambrian, south facing mixed clastic / carbonate, but primarily carbonate platforms developed. These supplied carbonate rich sediment into the deeper anoxic parts of the basins where background, black, high TOC carbonaceous rich silts and shales of the LAC accumulated. Deposits from the shelf inter-fingered with the high TOC units and diagenetic scavenging of radioactive isotopes occurred to create what is today called the LAC or "hot shale" zone.

The "hot shale" is the target of active unconventional hydrocarbon exploration in the SGB. Two recent horizontal wells in the Dulcie Trough (Baldwin-2H ST1 and MacIntyre-2H) have encountered elevated "heavy" gas readings over their horizontal lengths, and demonstrated the potential for unconventional hydrocarbon recoveries. The feasibility of exploiting the "hot shale" is dependent on lithology, geomechanical properties, TOC% and source maturity, as well as there being sufficient depth to allow for environmentally sensitive fracture stimulation completions.

New seismic studies have refined the understanding of the SGB tectonic setting first established by potential field mapping. In addition to using conventional isopach maps, areas where the "hot shale" has been uplifted close to the surface need to be identified. Uplift has occurred along ASO reactivated pre-existing fault trends and has resulted in bringing parts of the "hot shale" to depths of less than 500m. However, only when deeper than ~500m it is possible to use controlled fracture stimulation and horizontal drilling to stimulate hydrocarbon production from the "hot shale".

 

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012