Kinematic interaction between stratigraphically discrete salt layers; the structural evolution of the Corrib gas field, offshore NW Ireland

Abstract

The kinematic interaction of thin salt layers during basin evolution has received little attention to date, despite there being several basins which contain multiple thin salt layers across NW Europe. This study utilises high-quality 3D seismic reflection data coupled with borehole data to investigate the evolution of the structure containing the Corrib gas field which is composed of two distinct salt structures. Located in the Slyne Basin offshore NW Ireland, the structure consists of a NE-SW oriented Permian salt pillow which folds the overlying Mesozoic stratigraphy. Upper Triassic salt acts as a second mechanical detachment and forms an elongate salt roller parallel to the crest of the Permian salt pillow. The Upper Triassic salt roller forms the footwall of a delamination fault which downthrows the anticlinal crest of the folded Jurassic section to the SE. The Permian salt pillow began rising during the Late Triassic and Early Jurassic driven by low-strain regional extension. During the main phase of rifting, a combination of basement tilting, gravity gliding, and salt welding resulted in a steep increase in the amplitude of the Permian salt pillow. The relief on the salt-cored fold resulted in gravity gliding on the Triassic salt, forming the parallel salt roller and delamination fault. The throw distribution on the delamination fault is driven by the combined mechanisms of gravity sliding on the Triassic salt and by inflation of Triassic salt in the footwall of the fault. The delamination fault is reactivated post-rift, suggesting modification of the Permian and Triassic salt structures. This study improves the understanding of the kinematic interaction of thin salt layers during syn-rift and post-rift deformation, with implications for hydrocarbon exploration on the Irish Atlantic margin and further afield. This research is funded in part by a research grant from Science Foundation Ireland (SFI) under Grant Number 13/RC/2092 and is co-funded under the European Regional Development Fund, and by the Petroleum Infrastructure Programme (PIP) and its member companies. The authors would like to thank the Petroleum Affairs Division (PAD) of the Department of Communications, Climate Action and Environment (DCCAE), Ireland, for providing access to released well and seismic reflection datasets. Shell Exploration & Production Ireland Ltd. are thanked for providing access to reprocessed volumes of the 1997 Corrib seismic. Europa Oil & Gas are thanked for providing access to the Inishkea 2018 reprocessed seismic volume and allowing a section from the volume to be shown. The authors thank Schlumberger for providing academic licenses of Petrel to University College Dublin. The authors also thank Petroleum Experts for providing academic licenses of Move to University College Dublin.