Lithofacies architecture and facies models of volcanic, volcaniclastic and sedimentary rocks in the Hreppar Formation, Iceland : understanding hydrocarbon prospects in volcanic rifted margins

• Main Author: Dietz, Jonathan David
• Published: University of Glasgow 2018
• Subjects: QE Geology
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.761894

Predicting the geometry and continuity of clastic units within lava-dominated sequences in volcanic margin settings is problematic as they are typically laterally discontinuous, relatively thin and often poorly imaged in the subsurface. Although such sequences are well known, detailed studies of their lithofacies architecture are rare and poorly constrained, which can result in major challenges to hydrocarbon exploration in these settings. As the demand for hydrocarbons increases, exploration is being focussed on more challenging stratigraphic and tectonic settings, such as volcanic margins. Consequently, it is necessary we enhance our understanding of how petroleum systems interact with volcanic-prone sequences, in order to maximise recovery of hydrocarbons. Using a field analogue in conjunction with remote sensing datasets is fundamental to understanding these complicated systems. This study utilises the Hreppar Formation (HF) in SW Iceland as an analogue to understand elements of petroleum systems to reduce the challenges and risk associated with hydrocarbon exploration within volcanic-dominated basins. The HF at Flúðir, comprises basaltic lavas and interbasaltic sedimentary rocks of Plio-Pleistocene age (3.3-0.7Ma) and provides excellent 3D exposure. This study provides a comprehensive evaluation of the geology in this area and its relevance and importance to hydrocarbon exploration. Detailed field mapping and graphic logging have been combined with field panoramas and photogrammetry to characterise the sequence in detail and to identify the lateral (dis)connectivity of the clastic units, the main lithofacies, the different facies architectures, structural elements and drainage pathways within the HF. The detailed field data presented here are generally all below seismic resolution. In an offshore setting, with currently available technology, it is highly unlikely this level of detail can be captured using remote sensing tools alone. The advantage of using a field analogue such as that of the HF is the level of detail which can be captured. This enables the gap in scale, between field-scale and seismic¬/well-scale to be bridged. It allows models to be ground truthed, which reduces uncertainty and risk, essential to hydrocarbon exploration. This research identifies complex interaction between volcanic, glacial and fluvial systems, underpinned by a strong tectonic influence. >60% of the HF is dominated by sub-aerial basaltic lavas and predicting where lithofacies occur in these types of environments is challenging, however, through initial quantitative analysis of volcanic and sedimentary units in the HF, basic prediction in similar settings is possible. The field data collected in the HF can inform every stage of the development of a hydrocarbon field in a volcanic margin, from determining the architecture of a potential reservoir to defining the main structures and potential fluid pathways as well as deciding how to produce the field.