Burial History and Maturation Analysis of the Munyarai-1 and Karlaya-1 Wells with Focus on the Alinya and Pindyin Petroleum System, Officer Basin, South Australia
Keith T. Weatherley, 2013
Honours Bachelor of Science (Petroleum Geoscience)
Australian School of Petroleum
University of Adelaide
A new evaluation of the tectonic and thermal history of the Officer Basin in South Australia, based upon tectonic modelling constrained by thermal, stratigraphical and seismic data from well intersections has resulted in the reassessment in the maturation potential of deeply buried sediments and the erosional variance of tectonic phases. Previous research was primarily based on younger stratigraphic sequences and well data, which indicated that the maturation of all sediments within the eastern Officer Basin in areas around the Munyarai Trough as over mature. Thickness estimates for the Munyarai trough are >10,000m of sediments at the deepest point.
Results on the sediment thicknesses from seismic interpretation using seismic lines within the Munyarai trough indicate a thickness of only 8,000m. This impacts on the maturation potential of the source rocks at depth, as well as the timing hydrocarbon potential of the entire stratigraphic sequence. Thickness variations impact directly on the maturation and palaeo-heat flow of the basin.
Palaeo-heat flow results derived from Tmax and WCR's indicate the highest heat flow observed during the Petermann Ranges Orogeny. Heat flow indicates the generation potential of the basin sediments is high. Indications show the heat flow higher during tectonic events. Higher heat flow is also observed during the Alice Springs Orogeny as a result of high compressional stress and uplift of sediments which have higher thermal conductivity and heat retention properties . Heat flow is fundamentally linked to the maturation and preservation of hydrocarbons.
Maturation analysis has indicated the maturation model for the Officer Basin proposed by Gravestock and Hill (1997) as correct for the Munyarai trough, but not the study area as a whole.
The models depicting the Munyarai-1 well confirm the prediction of over-maturation. Inversely the maturation of the Karlaya-1 well was previously interpreted as over-mature. This is shown to be
incorrect. The 2D models formulated as part of the study, indicate the maturation of the Alinya (780Ma) and Pindyin (800Ma) formations as peak-oil with the majority of sediments either early-oil or immature. This indicates the possibility of hydrocarbon generation is currently occurring within source rocks in regions surrounding the Karlaya-1 well. Maturation indicates the possibility of deep reservoirs and accumulations associated with the Alinya and Pindyin petroleum system.
The Alinya and Pindyin system is the final unexplored hydrocarbon system within the basin. The 2D and subsequent 3D analysis of this system indicate the probability of hydrocarbon accumulations within the study area. The accumulations are the result of downward migration of hydrocarbons from the overlying Alinya formation to the Pindyin Sandstone. Large accumulations are present within the 2D models of the Munyarai-1 well simulation as a result of this downwards migration. The associated accumulations indicate the preservation potential of the overlying strata and the potential reserves that are below the TD of the Munyarai-1 well. Reserves in the Karlaya-1 well region are lower as a result of fault migration of fluids and no anticlinal traps. Analysis indicates the probability of small hydrocarbon traps in the Karlaya-1 well region but not as expansive as in the Munyarai trough.