Integrated petroleum systems analysis to understand the source of fluids in the Browse Basin, Australia

Abstract

Abstract. The Browse Basin is located offshore on Australia's North West Shelf and is a proven hydrocarbon province, hosting gas with associated condensate in an area where oil reserves are typically small. The assessment of a basin's oil potential traditionally focuses on the presence or absence of oil-prone source rocks. However, light oil can be found in basins where source rocks are gas-prone and the primary hydrocarbon type is gas-condensate. Oil rims form whenever such fluids migrate into reservoirs at pressures less than their dew point (saturation) pressure. By combining petroleum systems analysis with geochemical studies of source rocks and fluids (gases and liquids), four Mesozoic petroleum systems have been identified in the basin.This study applies petroleum systems analysis to understand the source of fluids and their phase behaviour in the Browse Basin. Source rock richness, thickness and quality are mapped from well control. Petroleum systems modelling that integrates source rock property maps, basin-specific kinetics, 1D burial history models and regional 3D surfaces, provides new insights into source rock maturity, generation and expelled fluid composition.The principal source rocks are Early-Middle Jurassic fluvio-deltaic coaly shales and shales within the J10-J20 supersequences (Plover Formation), Middle-Late Jurassic to Early Cretaceous sub-oxic marine shales within the J30-K10 supersequences (Vulcan and Montara formations) and K20-K30 supersequences (Echuca Shoals Formation). These source rocks contain significant contributions of terrestrial organic matter, and within the Caswell Sub-basin, have reached sufficient maturities to have transformed most of the kerogen into hydrocarbons, with the majority of expulsion occurring from the Late Cretaceous until present.

Regional Jurassic sediment depositional architecture, Browse Basin: Implications for petroleum systems

“…Seismic mapping based on regional 2D and some 3D seismic survey data was tied to 60 key wells ( Figure 1) using a revised tectonostratigraphic framework ( Figure 2) for the basin. Recent seismic and well interpretations (Rollet et al, 2016a) are used to produce palaeogeographic maps ( Figure 3) and develop a regional 3D geological model of the Browse Basin (Palu et al, 2017). The model is used to map the gross thickness of each set of supersequences containing source rock facies; i.e.…”

“…Integration of the palaeogeography with geochemical analyses has enabled a better understanding of the spatial and temporal distribution of the source rocks. The role of these Jurassic to earliest Cretaceous source rock pods is demonstrated in a petroleum systems model that aims to clarify the charge history of the basin and determine which active source kitchens may have generated the fluids in the known hydrocarbon accumulations (Palu et al, 2017).…”

“…Hydrocarbon expulsion modelling (Palu et al, 2017) shows that the J10-J20 and J30-K10 source rocks within the Caswell Sub-basin have reached sufficient maturities to have transformed most of the kerogen into hydrocarbons, with the majority of expulsion occurring from the Late Cretaceous until present. Within the Barcoo Sub-basin, source rocks of the J10-J20 supersequences have reached sufficient maturity for generation, where the better-quality source rocks within this supersequence are modelled to have expelled hydrocarbons.…”

“…Oil sampled from a thin shallow porous/fractured zone (~2150 mRT) in Torosa 4 is geochemically similar to the condensate recovered from the J10-J20 supersequences (Woodside Energy Ltd, 2008b), indicating a common (Plover Formation) source for these hydrocarbons. This oil may have formed by liquids dropping out of a Plover-derived gas-condensate as it migrated into a zone of reduced pressure with the associated gas not being retained (Palu et al, 2017).…”

Validation of Fault Seal Mechanisms in the Timor Sea: An Outcrop and Subsurface Perspective

“…In these data we found that prominent gas kick started in the Echuca Shoals Formation and/or the Darwin Formation. Although the Echuca Shoals Formation has a high Gamma Ray response, it is a source rock (Palu et al 2017). The observed prolific mud gases show that the unit is transmissive, thus we inferred that this unit could act as a thief zone for the purposes of exploration time scale fault seal analysis.…”