Exhumation of Irish Sedimentary Basins and Implications for Petroleum Exploration Offshore Ireland

D. V. Corcoran¹ and Anthony G. Dore^2
1 Statoil Exploration (Ireland) Ltd, Dublin, Ireland
² Statoil U.K. Ltd, London, England

Exhumation, the removal of overburden resulting from the vertical displacement of rocks from maximum burial depth, has important implications for the prospectivity of petroliferous basins. In these basins, issues to be addressed by the petroleum geologist include, the timing of thermal ‘switch-off' of source rock units, the compactional and diagenetic constraints imposed by the maximum burial depth of reservoirs (prior to uplift), the physical and mechanical characteristics of cap-rocks during and post-exhumation, the structural evolution of traps and the hydrocarbon emplacement history.

Three decades of exploration offshore Ireland and the drilling of 150 wildcat and appraisal wells has yielded only 4 commercial gas accumulations and a number of oil and gas discoveries which have disappointed upon appraisal. Nevertheless the key elements of source, reservoir and trap/seal have long been recognized or postulated to be present in Ireland's offshore basins. However, it is the evolution of the petroleum systems within these basins that is less well understood, in particular the impact on prospectivity of multiple exhumation events. A variety of techniques including vitrinite reflectance, apatite fission tracks, fluid inclusions and sonic interval transit times, have been utilized to elucidate thermal and burial history and quantify the magnitude of exhumation in some of these offshore basins. Seismic interpretation and stratigraphic restoration are employed to help rationalise the range of exhumation estimates derived from these techniques. Implications for future exploration offshore Ireland are discussed in the context of these empirical observations.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005