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
SUMMARYA seismic attribute study was conducted over a subset of data located in the onshore area of the Otway Basin, Victoria. Attributes were developed from the original legacy processed seismic data including energy and frequency attributes. With investigation and analysis it was possible to identify an amplitude anomaly with multiple stacked attribute anomalies directly related to reservoir levels with observed hydrocarbon shows from legacy well data close to the structure. This study combined with a new independent evaluation of the exploration potential revealing thickening and extension of an excellent reservoir and indications of trapped hydrocarbons that have previously gone unnoticed on data acquired in the 1980's.Evaluation of the well data identified a thick sequence of stacked sandstones representing a facies change of the lower Eumeralla Fm. Identification of anomalous energy and frequency and combined with a neural network chimney model that demonstrates a gas cloud overlying the reservoir interval; presents a clear target for further evaluation.Seismic mapping identified potential closure from a coarse 2D seismic grid. The nearby Greenslopes-1 well, located in a highly structured zone, represents high risk leak potential from migrated hydrocarbons and was drilled in a zone of low seal potential. This well however, provides an excellent test of the good quality reservoir potential at the level of the interpreted anomalous energy and frequency attributes.Deterministic volumetrics of the prospect assuming a 70% recovery factor estimate recoverable gas volumes of 108 BCF. If a 10 barrel/MMCF ratio is assumed for condensate then the estimated recoverable condensate volume is estimated at 1.08 MMBBL. The overlying gas cloud potentially indicates significant liquids enrichment and it is likely the reservoir contains a fully saturated hydrocarbon charge.Due to the current moratorium for onshore oil and gas drilling in Victoria the target will undergo further evaluation to assess the oil potential.
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