The Middle Jurassic Brent Group of the northern North Sea presents a mature and highly productive reservoir play fairway where a combination of effective facies analysis and depositional sequence stratigraphy offers real potential to optimize exploitation. The north of the Brent province differs from classically studied southern areas in being dominated by marginal-marine delta-front facies. A core- and log-based study of 37 wells around the Don fields was performed to establish a sequence stratigraphic framework, map facies and thereby describe facies architecture. The results demonstrate that reservoir quality and productivity are regionally and locally controlled by facies. Of particular interest are intervals of fluvio-estuarine channel to sharp-based shoreface sandstone that formed during sea-level lowstands, since it is these packages that boost well productivity but, conversely, also increase the risk of early water breakthrough on production. Analogy with the Saloum Delta of Senegal highlights the importance of rapid and continuous barrier migration and destruction in controlling the deflection and switching of fluvio-estuarine channels, explaining also the preferential preservation of channel-floor deposits over continuously eroded barrier and delta-top facies. Interpretations suggest that deposition in the study area was dominated by punctuated progradation of the Brent Delta, as periods of delta plain incision alternated with episodes of base-level rise and delta aggradation/progradation. A model of regression for the Brent Delta is presented, where the Rannoch, Etive and Ness formations are an amalgam of highstand, falling stage and lowstand systems tract deposits, and the Tarbert Formation is a transgressive systems tract deposit, with the delta responding to regional relative sea-level changes driven by uplift and deflation of the mid North Sea dome. The prograding Brent Delta is characterized as a succession of attached shorefaces formed by alternating periods of normal and forced regression. Significantly, this explains the long distance (>200 km) build out of the Brent Delta and the continued presence of coarse-sandstone packages, as well as the potential for high-quality reservoirs even in the distal reaches of the system. It also suggests that there is limited potential for lowstand fan plays beyond the northernmost tip of the delta.

The influence of igneous intrusions and their associated vent complexes on hydrocarbon migration is poorly understood, yet may be significant in the exploration of petroleum basins located on passive margins. A regional review of the northeasternmost frontier sector of the UK Continental Shelf (UKCS) encompassing the southern extent of the Møre Basin has revealed evidence of extensive vent formation during the Late Paleocene. Anomalous seismic amplitude events that have not been previously described in this area are identified above and clearly related to several of the vent complexes, and a number of scenarios are postulated to explain their presence. Integrating existing geological studies and regional seismic interpretation with a new 3D seismic dataset reveals a close relationship between sills, vents and seismic anomalies which may be related to the presence of gas/fluid. Recognition of the vent complexes as potential fluid conduits long after initial formation may be important in focusing migration to younger stratigraphic levels. Important observations are made regarding a link to possible hydrocarbon migration mechanisms within the study area and the associated implications for hydrocarbon exploration and risking within this petroleum basin are investigated.

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