Oil migration in the Vulcan Sub-basin, Timor Sea, investigated using GOI and FIS Data

Oil migration in the Vulcan Sub-basin from the Swan and Paqualin depocentres to the Montara and Jabiru terraces and Ashmore Platform has been investigated using an integrated approach called Oil Migration Interval (OMI) analysis. OMI analysis is a tool for evaluating the depth intervals where migrating oil is concentrated by buoyancy and capillary forces, and for comparing profiles of measured palaeo-oil indicators, such as GOI™, Fluid Inclusion Stratigraphy (FIS), and conventional oil shows, for consistency with the expected migration profile. Where oil shows occur below intra-formational seals, GOI values are <0.5% and FIS values are m/z 57 <500 ppm and m/z 97 <3,000 ppm. In oil zones, GOI values are typically >5% and FIS values are m/z 57 >50,000 and m/z 97 >15,000 ppm. In the Swan and Paqualin depocentres, palaeo-oil zones at Champagny-1 and Maple-1, below LowerVulcan Formation shale, confirm this formation as a regional seal for oil accumulation, as documented elsewhere in theVulcan Subbasin. On the Skua Trend and Montara Terrace, testing of sandstone below LowerVulcan Formation shale yielded no evidence (Birch-1) or weak evidence (Longleat-1) for migratory oil. These wells are outside the regions of oil migration predicted by orthocontour modelling on a mid- Callovian surface. Evidence for migratory oil was detected below intra-formation capillary barriers at Birch-1, Longleat-1 and Rainier-1. MCI analysis of a sample from the Montara Formation at Longleat-1 indicates source affinities with Late Jurassic marine shale.