A study of the hydrocarbon distribution and Lower Cretaceous Greensand prospectivity in Blocks 48/15, 48/17, 48/18 and 48/19, North Celtic Sea Basin

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Abstract
Well 48/19-2 was drilled in the North Celtic Sea in 1992 to test the Lower Cretaceous Greensand fairway along trend from the Kinsale Head and Ballycotton gas fields. The mapping of the 48/19-2 prospect is discussed and the results of the well are detailed. The discovery of a heavy oil accumulation in the well along this gas trend led to a comprehensive multi-disciplinary reappraisal of the 48/15, 48/17, 48/18 and 48/19 area. The results of this study highlight the adequacy of available source rocks, and suggest a possible Portlandian-Purbeck origin for the oils found in boreholes 48/24-1, 48/24-2 and 48/28-1. Maturation modelling in the study area pointed to a principal pulse of hydrocarbon generation and expulsion during the Late Cretaceous to early Tertiary. It was concluded that the Kinsale Head, Ballycotton and 48/18-1 gas accumulations could have been trapped in closures created after Miocene inversion. Earlier traps, which were pre-Miocene inversion in age, could have received oil which later became subjected to incursions of meteoric water and suffered biodegradation.