A combine of Exoma Energy Ltd., Brisbane, and an onshore unit of China National Offshore Oil Corp. have a large indicated oil discovery in the Galilee basin of central Queensland, Australia.
Independent well log and petrophysical evaluation has confirmed that the Katherine West structure may contain as much as 177 million bbl of oil in place and that the adjacent, undrilled Katherine East prospect may contain up to 458 million bbl of oil in place. Katherine East is to be drilled in 2012.
Exoma and CNOOC Galilee Gas Co. Pty. Ltd. hold 50-50 interests in five exploration permits that total 27,000 sq km near Longreach, Queensland. They are ATPs 991, 996, 999-P, 1005, and 1008. The lands are also prospective for coalbed methane.
CNOOC farmed into its 50% interest in late 2010 as the company’s first relatively
large-scale exploration of overseas onshore unconventional gas. Consulting engineers found that the permits could contain as much as 2.83 trillion cu m of CBM and shale gas resources, including 56 bcm of CBM.
The Katherine West resource estimates are based on independent analysis of log results from Exoma’s Katherine-1 well drilled in August-September 2011, Ampolex’s 1985 Toobrac-1 well, and Exoma’s reinterpretation of seismic data over the structure.
Katherine-1 was drilled to 1,207 m in ATP-999-P to test Exoma’s modeled extension of the Toobrac-1 oil show. The well intersected a number of oil zones totaling 10 m of potential oil pay. Log analysis indicates that the well intersected oil columns of 4 m in the Adori sandstone and 6 m in the Lower Hutton sandstone, both of Jurassic age.
Exoma was unable to recover a representative sample from Katherine-1 due to adverse well conditions, but oil shows were observed and tested in the drill cuttings through the Adori and Hutton sandstones and a sample of crude oil was recovered from the drilling fluid. Interpretation of the Katherine-1 logs confirms Exoma’s model of the Hutton sandstone as an oil-filled stratigraphic trap against a granite basement high.
The log analysis shows that the Hutton oil column is in a permeable reservoir zone and contains free oil able to be flowed. Log interpretations of the Adori at Katherine-1 and Toobrac-1 are less conclusive than those for the Hutton but indicate that the Adori contains oil and that potentially this oil may extend over the entire Katherine West structure.
The mean estimate of the total oil resource at Katherine West is 79 million bbl of oil. Reservoir properties and deliverability are yet to be established, and one of the objectives of the next well will be to move some of the above resource estimates for Katherine West into the reserves category.
Exoma will drill a core well, Katherine-2, in early 2012 to improve its understanding of reservoir quality and the extent of the oil fill in the Adori and to test Hutton deliverability.
Exoma said the discovery validates its stratigraphic oil play concept in its Galilee basin tenements and “forms the basis of our exploration planning for other oil targets in ATP 999 and ATP 1005.”
Mapping based on seismic data shows the Adori and Hutton sandstone closures at Katherine East each cover 25 sq km if those sandstones are in place.