Reservoir architectures of interlava systems – a 3D photogrammetrical study of Eocene cliff sections, Faroe Islands

A need for suitable intra-volcanic analogues to elucidate, for example, reservoir architectures has arisen following the Rosebank discovery in the Faroe-Shetland Basin, NE Atlantic. The Faroe Islands, situated ~160-190 km NW of this discovery, are an exposed remnant of the Palaeogene lava field host. The near-vertical cliff sections of the archipelago afford the opportunity to map lateral variations over many kilometres and delineate potential reservoir architectures. This was achieved by acquiring high-resolution photographs taken from a helicopter and then analysed using a 3D stereo-plotter coupled with stereo-mirror technology in a geographic information system (GIS). The study focussed on the interval spanning the <6 m thick Argir Beds, a volcaniclastic overbank-fluvial sequence and stratigraphic marker unit within the Enni Formation. The formation is dominated by a mixture of simple and compound lava flows commonly separated by minor volcaniclastic units. The decimetre scale analysis of the cliff sections record important information for the estimation of reservoir geometry, connectivity and compartmentalisation of intra-volcanic reservoirs. This includes the wedging out of lava flows over several kilometres and the merging of interlava units. The identification of major channels, up to 45 m deep and 180 m wide, filled with volcaniclastic conglomerates and/or lava flows has implications for the role of sedimentation across the lava field. The vertical connectivity of the interlava units is inferred by the presence of dykes, fractures and reverse faults. All these features are superbly shown through videos created from the overlapping photographs. In addition, more than 70 km of mapped horizons are stored in a GIS database that can be used for 3D modelling using, for example, Petrel reservoir engineering software.