The Relationship of Faulting to Hydrocarbon Accumulations in the Barrow and Exmouth Sub-Basins.
Honours Degree, 1996
University of Adelaide
This study seeks to quantify the factors that control a number of the hydrocarbon accumulations that occur on the eastern edge of the Barrow and Exmouth Sub-basins of the Carnarvon Basin in terms of their present and past hydrocarbon columns and their fault-dependency. Structurally-dependent hydrocarbon accumulations in these sub-basins occur in reservoirs which range from the Middle to Late Triassic Mungaroo Formation to the Late Jurassic Dupuy Formation and the Early Cretaeeous Barrow Group, Flag Sandstone and Birdrong Sandstone.
There is good circumstantial evidence that hydrocarbon accumulations in the Barrow and Exmouth Sub-basins which are directly fault-dependent are predominantly oil. Accumulations which are trapped by four-way-dip closures contain predominantly gas.
Leakage of hydrocarbons and the formation of residual hydrocarbon columns in fault-dependent structural traps have been attributed to fault movement. This study seeks to find a relationship between the occurrence of residual hydrocarbon columns in the Barrow and Exmouth Sub-basins and the orientation of the present stress field in the Carnarvon Basin which is thought to have been active since the Middle Miocene, and to have caused fault reactivation and the leakage of hydrocarbons from some fault-dependent structural traps. This could not be statistically proven. It appears that there are factors other than orientation, specific to each structural trap, which influence hydrocarbon leakage and the formation of residual oil columns. Such factors might include the reliability of the top seal, rugosity and character of the fault surface, variation in displacement along the fault surface, pressure within the reservoir and also tilting of the reservoir to give an apparent residual hydrocarbon column.