--> --> A Sequence Stratigraphic Approach to Identifying Plays and Reducing Risk in the Porcupine and Rockall Basins

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A Sequence Stratigraphic Approach to Identifying Plays and Reducing Risk in the Porcupine and Rockall Basins

Abstract

The Irish Atlantic margin is a relatively frontier area but success elsewhere on the European Atlantic margin and on the Canadian conjugate margin, most notably the recent Bay du Nord discovery, highlights the prospect of analogous plays offshore Ireland. In order to accurately predict key play elements in the Porcupine and Rockall basins it is necessary to understand the development of regionally significant source rocks and reservoirs in the context of the palinspastic evolution of the North Atlantic margin. This provides an understanding of sediment provenance and identifies appropriate analogues and possible plays. Widespread organic enrichment, enhanced by restriction, occurred in the Kimmeridgian throughout the North Atlantic margin, resulting in the development of important source rocks in the Norwegian Sea (Spekk Formation) and in the Jeanne d'Arc Basin (Egret Member). While a similar source rock exists in the Porcupine Basin its probable burial depth in the south creates overmaturity and timing issues, analogous to the Faroe-Shetland Basin. Organic enrichment associated with the Aptian Oceanic Anoxic Event 1a is noted elsewhere on the North Atlantic margin and the potential for a Cretaceous source rock in the deeper parts of the Porcupine and Rockall basins will be discussed. Predicting reservoir presence and quality can be enhanced by understanding the regional context and sequence stratigraphy of the basin. For example, the Early Cretaceous transgressive sands of the Wealden Formation and the Greensand Group (reservoirs within the North Celtic Sea Basin) provide a clue to predicting the distribution of Early and Middle Cretaceous shallow marine and LST fan sands that may lie down systems tract in the Porcupine Basin. Age equivalent reservoirs are known from the Canadian margin, resulting from the break-up of the Canadian and Irish conjugate margins and associated uplift. The Cretaceous may be of particular interest in light of reservoir quality issues of Jurassic sands previously drilled in the Porcupine Basin. Cenozoic sands are also a potential reservoir in the Porcupine Basin. A preliminary assessment of both their likely quality and the quality of Cretaceous sands predicted in the southern part of the Porcupine Basin can be undertaken by assessing the depositional history of the Irish margin and the resulting provenance of sediments.