Fluid inclusion and scanning electron microscope-cathodoluminescence evidence indicates focused hot, saline, diagenetic £uid £ow within the Eastern Flank of the Britannia Field, o¡shore Scotland, UK.The £uid was sourced from the Andrew Salt Dome,10 km to the east.The £uids, which promoted quartz cementation of the upper zones within the ¢eld, were up to $30 1C hotter and had salinities up to $10 wt% NaCl equivalent higher than £uids from lower in the reservoir section. During diagenesis hot saline £uids migrated westwards as part of a radiating 'diagenetic front' from the Andrew Salt Dome. Structural dip associated with the Eastern Flank of the Fladen Ground Spur impeded the westward movement of the diagenetic £uid.The quartz cements from the upper and lower reservoir zones can be distinguished by morphology. In the upper zones the quartz cements have well-developed macro -crystalline zoning and heterogeneous luminescence across the grain. In the lower zones, the cements are much less developed, unzoned and very weakly luminescent.The diagenetic £uids were primarily focused into Zone 45 within the upper reservoir. Furthermore, within the Main Platform Area the most proli¢c producing zone is Zone 45, indicating the importance of this interval as a permeable £ow unit during both diagenetic and production timescales.Within the Eastern Flank, the quartz overgrowths have a major impact on reservoir permeability and thus well productivity.The overgrowths are most extensive in the originally clean sandstones with low clay content. Clay in optimum volumes (5^10%) can inhibit nucleation of the damaging quartz overgrowths without having a detrimental e¡ect on pore connectivity.These observations provide a predictive concept for use in the search for relative reservoir sweetspots within the degraded Eastern Flank.
Sedimentary basins developed along the European margin during the earliest, Permian, stage of protoAtlantic rifting, during a phase of high heat flow. The proximity of some basins to Caledonian thrusts has implied that rifts locally utilized the basement fabric. New mineralogical and palaeomagnetic data show that thrust planes in the Moine Thrust Zone channelled a pulse of hot fluid in Permian time. The fluids precipitated kaolin in fractures in the thrust zone, and with decreasing intensity away from the zone. The high-temperature polytype dickite is largely confined to major thrust planes. Stable H and O isotope analyses indicate that the parent fluid included meteoric water involved in a hydrothermal system. Coeval hydrothermal hematite has a chemical remanence that dates the fluid pulse as Permian. This is direct evidence for post-orogenic activity in the thrust zone, in which the thrusts vented excess heat during regional crustal extension. The example from the European margin exemplifies the importance of deep-seated structures in the release of heat, and the value of kaolinite polytype mapping as a tool to record anomalous palaeo-heat flow.
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