Using Formation Micro Imaging (FMI) as a Powerful Tool in the Identification of Volcanic Lithofacies in Igneous Affected Basins: A Case Study from the Faroe-Shetland Basin

Timothy Watton

The North Atlantic Igneous Province (NAIP) and Siberian Trapps are two large volcanic events that cover much of the arctic and associated regions. Sub-Palaeogene exploration in the North Atlantic (E & W Greenland, Jan Mayan, Norwegian Shelf), for example, will often require drilling through significant quantities of volcanic rocks. With increasing exploration in such volcanic margins, and with appraisal/development of discovered fields associated with volcanic successions, clear methodologies for dealing with the sub-surface data within and around volcanic packages, e.g. wireline logs and down borehole imaging etc. is an important requirement for effective exploration. During the onset of flood basalt volcanism the initial volcanic sequences can bury and interact with the sedimentary environments leading to un-usual or little understood hydrocarbon plays. Recognition of specific volcanic facies (e.g. hyaloclastite or hydromagmatic deposits) can indicate if significant water was present during emplacement providing additional palaeo-environmental information. As exploration continues in volcanic effected basins, volcanic rich sequences are being drilled and imaged using Formation Micro Imaging (FMI), a tool that produces micro resistivity images of the side wall of the well bore. Down borehole FMI used in conjunction with conventional well logging techniques (GR/RES/Density/Vp) allows unrivalled analysis of volcanic lithofacies variation. In this contribution we show how FMI data can be linked to volcanic facies analysis, and using the existing array of down borehole tools, provide a robust interpretation of the volcanic sequences. This methodology is of particular use where core data are limited/not present. Using examples from the Faroe-Shetland Basin where the re-establishment of fluvial activity between phases of effusive volcanism leads to a complex arrangement of siliciclastic sediment and basaltic lava, we present examples of lithofacies variation from a mixed volcanic and siliciclastic system (the Rosebank Field, West of Shetland, UKCS). FMI images are shown to be useful in differentiating internal basalt lava flow features, identifying flow type and characterizing joint/fracture networks. If FMI data exists through volcanic packages and if assessed properly, it can provide additional valuable exploration information. In new frontier exploration targets, FMI analysis through volcanic successions, which are rarely cored, may be a relatively cost effective way of maximising the information returned from the planned well. Acknowledgments All well log data and FMI is sourced from the Rosebank discovery has been kindly supplied by the Rosebank partnership (Chevron North Sea Limited (U.K), DONG E&P (U.K) Limited, Statoil (U.K) Limited and OMV (U.K) Limited)

AAPG Search and Discovery Article #90177©3P Arctic, Polar Petroleum Potential Conference & Exhibition, Stavanger, Norway, October 15-18, 2013