Unconventional Gas Reservoir Productivity in Australian Proterozoic Rocks — Studies From the McArthur, Beetaloo, Mount Isa and Amadeus

Abstract

A large amount of available exploration data is readily available for many Proterozoic areas in Australia. The data ranges from seismic and conventional well data to cored and mineral bores not specifically focused on the search for hydrocarbons. Both Commonwealth-and State-based programs have also been focused on these rocks. Many Proterozoic basins occur in Australia; however, the Paleo-MesoProterozoic sequences of the McArthur and Mount Isa areas have been an important focus over the past few years. In the McArthur Basin the key organic-rich sequences comprise the Barney Creek and the Velkerri formations. At Mount Isa the Riversleigh and Lawn Hill formations have been the main targets assessed. Despite this activity, several units in the Proterozoic remain little tested, particularly the Wollogorang Formation of the Tawallah Group in the McArthur Basin with known vuggy oil and the organic-rich units of the Bowthorn Siltstone of the Mount Isa area. In the Amadeus Basin, Upper Proterozoic sequences containing organic-rich rocks are interpreted conventional source rocks for gas fields, such as Dingo. These source rocks are interpreted to have unconventional gas potential, and efforts are progressing to better understand the key focus criteria to recognise potential sweet spots to enable exploration focus. The key reservoir shales are commonly carbonaterich with good fracture stimulation potential. The nature of unconventional reservoirs varies according to the contained gas characteristics and the reservoir conditions. Many situations can combine to provide higher gas production potential and increased wet gas components that can improve the financial returns for individual field areas. In the Proterozoic, one key factor is to target lower maturity rocks as all reservoirs leak, and older rocks have less chance of maintaining preservation conditions and higher formation pressures. Organic content and saturation plus structural controls are additional important factors that can influence hydrocarbon volumes accessible from an individual well bore. From a financial perspective, the main criterion for