Revised Structural Evolution of the North Celtic Sea Basin, Offshore Ireland, Based on Modern 2D and 3D Seismic Data.

Abstract

Previous authors have described the North Celtic Sea Basin (NCSB) as having a conventional steers head geometry or alternatively a half graben geometry. Seismic acquisition and processing improvements in the last decade have assisted in providing new insights into the structural evolution of the NCSB. The 2011 Barryroe 3D seismic survey provided the first 3D view of the Triassic section showing significant fault surfaces that demonstrate the importance of intra-basinal faulting. Interpretation from the Providence Resources Plc operated Barryroe 3D seismic dataset has been extended using a modern 2D long-offset regional seismic survey acquired by TGS/Fugro in 2006 and a Merlin Profilers 1981 2D regional seismic dataset reprocessed by Schlumberger Multiclient in 2014. The improved seismic imaging allows for a more robust regional interpretation of the structural evolution of both the North Celtic Sea Basin and adjacent South Celtic Sea Basin. Three distinct rifting events have been recognised regionally across the NCSB and adjacent basins.

Initially, rifting commenced in the Triassic with half graben geometry associated with extension primarily accommodated along the main northern basin bounding fault. Later Upper Jurassic and Lower Cretaceous rifting was accommodated predominantly by large mid-basinal faults, antithetic to the main northern basin bounding fault. Minor localised halokinesis has been identified on seismic data which supports the presence of mobile halite within the Triassic section. It is postulated that this evaporitic sequence, which had been highly rotated in the previous rifting event, became a detachment zone for these normal faults in the Upper Jurassic. These normal faults were subsequently preferentially reactivated during Cenozoic compression with significant reverse movement creating either broad mid-basinal anticlines, such as the Kinsale Head and Seven Heads structures, or smaller inversion flower structures. Recognition and understanding of the structural evolution of the NCSB is critical to de-risking hydrocarbon prospectivity, particularly in areas of poor or vintage seismic datasets.

AAPG Datapages/Search and Discovery Article #90226 © 2015 European Regional Conference and Exhibition, Lisbon, Portugal, May 18-19, 2015