J. Naeth1,2 *, R. di Primio2,5, B. Horsfield2, R.G. Schaefer1, P.M. Shannon3, W.R. Bailey3 and J.P. Henriet4

1 Forschungszentrum Jülich GmbH, ICG-4 D-52425 Jülich, Germany.

2 GeoForschungsZentrum Potsdam, Telegrafenberg, D-14473 Potsdam, Germany.

3 University College Dublin, Department of Geology, Dublin 4, Ireland.

4 Renard Centre of Marine Geology, University of Gent, B9000 Gent, Belgium.

5 author for correspondence, dipri@gfz-potsdam.de

* Present Address: Fugro Robertson Limited, Tyn-y-coed Site, Llanrhos, Llandudno, North Wales, LL30 1SA. jochen.naeth@fugro-robertson.com

This study assesses whether the growth of deep water carbonate mounds on the continental slope of the north Atlantic may be associated with active hydrocarbon leakage. The carbonate mounds studied occur in two distinct areas of the Porcupine Basin, 200 km offshore Ireland, known as the Hovland-Magellan and the Belgica areas.

To evaluate the possible link between hydrocarbon leakage and mound growth, we used two dimensional cross-section and map-based basin modelling. Geological information was derived from interpretation of four seismic lines across the province as well as the Connemara oilfield. Calibration data was available from the northern part of the study area and included vitrinite reflectance, temperature and apatite fission track data.

Modelling results indicate that the main Jurassic source rocks are mature to overmature for hydrocarbon generation throughout the basin. Hydrocarbon generation and migration started in the Late Cretaceous. Based on our stratigraphic and lithologic model definitions, hydrocarbon migration is modelled to be mainly vertical, with only Aptian and Tertiary deltaic strata directing hydrocarbon flow laterally out of the basin. Gas chimneys observed in the Connemara field were reproduced using flow modelling and are related to leakage at the apices of rotated Jurassic fault blocks. The model predicts significant focussing of gas migration towards the Belgica mounds, where Cretaceous and Tertiary carrier layers pinch out. In the Hovland-Magellan area, no obvious focus of hydrocarbon flow was modelled from the 2D section, but drainage area analysis of Tertiary maps indicates a link between mound position and shallow Tertiary closures which may focus hydrocarbon flow towards the mounds.

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