Sedimentology of the Lower Cretaceous reservoirs of the Sea Lion Field, North Falkland Basin

The Sea Lion Field in the North Falkland Basin was discovered in 2010 by Well 14/10-2, which tested oil from Lower Cretaceous sands of the Sea Lion fan complex. Appraisal of the field involved the drilling of a further eight wells from which an extensive wireline-log data set and 455 m of core were acquired. This unique data set has allowed detailed study of the reservoir sedimentology and has significantly benefited reservoir characterization. The reservoirs are interpreted to be deposited in a deep-water lacustrine basin as base-of-slope to basin-floor fans fed by canyons or channel-feeder systems from the east. Deposition is considered to have been affected both by turbidity currents and by liquefied sediment gravity flows, such that reservoir facies are dominated by those associated with high- and low-density turbidites, mass-flow deposits, and, to a lesser extent, hybrid-event beds. In the absence of significant chronostratigraphic control, the description of the first-order reservoir architecture is primarily driven by seismic interpretation, whilst the core affords significant control of the internal architecture of individual fans. Several lines of evidence point towards the Sea Lion sands being derived from a coexisting, shallow-water system on the eastern margin of the basin. Palaeogeographical reconstruction links this shoreface system to a large, contemporaneous, southerly-prograding delta via wave reworking and longshore drift of delta-front sands. Evolution of this delta has played a significant role in the timing, positioning and emplacement of fans along the eastern margin of the North Falkland Basin. The overall impact of the core data set has been to improve confidence in the reservoir characterization and spatial distribution of facies within the reservoir model, and to narrow significantly the range of uncertainty, which has direct implications for field development planning.