Potential Upside Reserves of Shallow Gas Discovered Within the Early Triassic Mount Goodwin Sub-Group and the Early Permian Torrens and Fossil Head Formations in the Blacktip Gas Field, Bonaparte Basin, Australia

Abstract

The Blacktip Gas Field is located offshore in the southern Bonaparte Basin, Australia. The main reservoirs are the Early Permian Keyling and Treachery Formations. The field supplies gas to the Northern Territory utility Power and Water Corporation from two deviated gas production wells via an unmanned well-head platform to shore at Yelcherr near Wadeye in the Northern Territory. The field will deliver gas to the Northern Territory's Power and Water Corporation over a period of 25 years. One of the potential upsides of the gas field is the shallow and previously overlooked Early Triassic Mount Goodwin Sub-Group sandstones and also the Early Permian Torrens and Fossil Head Formations. Eni successfully acquired more data from the drilling of the development wells over these sections, with the objective being to fully assess minor gas shows observed in the original Blacktip-1 discovery well. The Mount Goodwin Sub-Group Sandstones, Torrens Formation and Fossil Head Formation are a thick sequence of inter-bedded shale, siltstone and very fine sandstones. The intervals are thinly bedded, and this makes conventional wireline difficult to interpret. Acquiring a wireline image log and performing a petrophysical thin-bed analysis has helped define the net sandstone thickness and net pay thickness of these formations. Performing geochemical analyses on mud gas samples collected in isotubes has helped to characterise the gas composition throughout the formations. In addition, the identification of moveable gas and verification of the extent of the gas columns has been achieved through the acquisition of formation pressure points and bottom- hole samples by Modular Formation Dynamic Tester (MDT). The conclusion is that from review of recently acquired data the Mount Goodwin Sub-Group Sandstone, Torrens Formation and Fossil Head Formations show good potential for future development in the Blacktip Field. A comparison between conventional log analysis and thin bed analysis is also discussed, with estimates of net sand and net pay thickness contrasted. Blacktip Field is 100% owned and operated by Eni Australia.