Research Taps into Hydrocarbon Exploration of Volcanic Passive Margin Basins
Global hydrocarbon exploration is increasingly focussed on passive margin basins. However exploration of continental margins poses major risks due to the significant geological uncertainties from sparse data coverage and their poorly understood formation and evolution.
An important geological risk associated with exploration in almost all passive margins is the presence of volcanic rocks. Volcanic activity is a key outcome of lithospheric stretching processes and thus all extensional sedimentary basins located along passive margins witness some degree of intrusive and extrusive activity during their life spans.
Evidence for past intrusive and extrusive igneous activity can constrain the distribution, timing and pathways of magmatism in these basins, which offers a means of reducing exploration risk.
Research by TRaX deputy director Dr Simon Holford; PhD student Justin MacDonald; plus personnel from the University of Birmingham and Geotrack International Pty Ltd; sheds light on the impacts of volcanic activity on sedimentary basin hydrocarbon prospectivity through the use of 3D seismic datasets.
In the past, difficulties with seismic imaging of sedimentary sequences beneath basalt lava flows and the detrimental short- and long-term impacts on petroleum systems -- such as reservoir degradation and compartmentalisation - have meant explorers avoided basins containing igneous rocks.
However the depletion of reserves in traditional hydrocarbon provinces, coupled with improvements in seismic acquisition and processing methods in basins, has led to increased exploration activity and success.
Some global basins which have proved successful include the Faroe Shetland Basin located along the northwest European Atlantic margin, and the Browse Basin of the Australian North West Shelf.
In this study, the researchers provide the first margin-wide synthesis of the distribution of volcanic rocks along the offshore basins of the southern Australian margin. Producing and prospective Australian passive margin basis where igneous systems have been identified include the Bight, Otway, Bass, Gippsland and Sorell basins of the southern margin.
The researchers applied new interpretation tools and workflows for characterising both extrusive and intrusive igneous rocks, providing new insights into sill morphologies and emplacement mechanisms and their role in the transport of magma through the crust. They also found widespread recognition of hydrothermal vents that witness the interaction between basinal fluids and volcanic activity.
Igneous activity has both positive and negative impacts on the petroleum systems of these basins.
Generic processes relevant to other volcanic basins include the compartimentalisation and degradation of reservoirs by intrusions and hydrothermal fluids and the flooding of reservoirs by CO2 from degassing magmas. On the other hand, the impermeable properties of some volcanic rocks provide them with excellent sealing qualities which prevent the escape of hydrocarbons from subsurface traps.
The researchers acknowledge the support of the Australian Research Council and research funding from STATOIL FÆRØYENE As, Chevron North Sea limited and Hess Limited.
Figure 5 :
"3D seismic visualisation of a Miocene volcano in the Bass Basin. This volcano overlies the Yolla gas field which will meet ~10% of Victoria's current demand for the next 15 years through the $750M BassGas project".
• Summarised excerpt from Holford S. P, Schofield N, MacDonald J. D, Duddy I. R and Green P. F, 2012, "Seismic Analysis of Igneous Systems in Sedimentary Basins and their Impacts on Hydrocarbon Prospectivity: Examples from the Southern Australian Margin', APPEA Journal, 2012, pp229 to 252.
