Abstract
In 1971, the Bluewater III semi-submersible rig drilled the first wildcat well, KK6-1, some 40km north west of Tobago's Buccoo Reef, in the Paria Sub-Basin of the North Coast Marine Area, resulting in the Orchid discovery. The subsequent appraisal well, KK6-2 discovered gas in a series of stacked Late Miocene (NC30) – Pliocene (NC80) sandstones. The lowermost and thickest of these gas charged sandstones was found unconformably overlying Cretaceous metamorphic basement, and has since been termed the Basal Sand.
In 2011 a 4370sqkm 3D seismic survey was jointly acquired over NCMA and Block-22 by Niko Resources and Centrica Energy, allowing for extensive regional mapping and the potential to resolve the Orchid Basal Sand gas discovery. Detailed mapping on basement revealed extensive areas with pronounced dendritic drainage, potential islands and shelfal platforms. Seismic amplitude extractions at this interval point to a number of low impedance anomalies, one of which ties very well to the KK6-2 gas discovery.
In the absence of Basal Sand core at Orchid, present day analogues were selected for reservoir sampling and analysis. Integration of regional well data, sea bed samples, ocean current data, seismic impedance volumes, thin sections from side wall cores and cuttings as well as palinspastic restorations resulted in the generation of a regional NC30 Basal Sand gross depositional map, depicting the drowned mountain ridge of ‘Isla de la Asumpción', carbonate mounds and potential Orchid Basal Sand look-alike plays within the Paria Sub-Basin.
