Using formation micro-imaging, wireline logs and onshore analogues to distinguish volcanic lithofacies in boreholes: examples from Palaeogene successions in the Faroe–Shetland Basin, NE Atlantic
Tim J. Watton, Steve Cannon, Richard J. Brown, Dougal A. Jerram, Breno L. Waichel, 2014. "Using formation micro-imaging, wireline logs and onshore analogues to distinguish volcanic lithofacies in boreholes: examples from Palaeogene successions in the Faroe–Shetland Basin, NE Atlantic", Hydrocarbon Exploration to Exploitation West of Shetlands, S. J. C. Cannon, D. Ellis
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Formation micro-imaging (FMI) is a tool that produces micro-resistivity images of the sidewall of the well bore. FMI logging used in conjunction with conventional well logging techniques (e.g. GR, Gamma Ray/RES, Resistivity/NPHI, Neutron Porosity/SONIC, Velocity tools) allows detailed analysis of volcanic lithofacies variation and informs a robust interpretation of volcanic sequences. This methodology is of particular use where rock core data are limited or not present. Examples are presented from the Rosebank Field in the Faroe–Shetland Basin (West of Shetland, UK continental shelf) where the re-establishment of fluvial activity between phases of effusive volcanism resulted in a complex sequence of siliciclastic sedimentary rocks and basaltic lavas. We demonstrate how high-resolution FMI images through this sequence can differentiate internal basalt lava flow features, such as vesicular zones, brecciated intervals, sediment–lava contact relationships and joint/fracture networks. If FMI data exist through volcanic packages and if assessed and calibrated properly via core, sidewall core and field analogue comparisons, it can provide additional constraints on the interpretation and classification of reservoir (siliciclastic) and non-reservoir (volcanic) rocks.
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This volume addresses the challenges facing explorers and developers alike in a region that is becoming a major focus of the petroleum industry in the United Kingdom, Faroes and North Norway. Several West of Shetland fields are still in the appraisal phase almost a decade after discovery. Sub-volcanic exploration risks remain high: sub-volcanic structural traps are imaged poorly, and so the geophysical community is responding with the application of latest technology. The more simple reservoirs might not be large enough to prompt informed and speedy development decisions; larger fields might have a combination of complexities, requiring a phased approach to the development. Infrastructure has been slow to arrive and planned developments have been subject to dramatic swings in fiscal regime ranging from special allowances to unexpected tax increases.
Environmental challenges are significant when moving into more remote, deeper water. The perception of these challenges by the third parties has become much more acute. To sustain its right to operate, the industry has to demonstrate safe drilling operations and appropriate response capability with government agencies.