Prediction of deep-water stratigraphic traps developed across the syn-rift to post-rift transition in Atlantic margin basins

 

PhD Candidate: Lewis Whiting

Supervisor: Professor Peter D. W. Haughton, Professor Patrick M. Shannon

Funded by: Science Foundation Ireland (SFI) through iCRAG

Abstract:

Atlantic margin basins west of Ireland have significant potential for hydrocarbons in stratigraphic and combination traps comprising deep-water sandstones that pinch out laterally against draped structural highs and unconformities. The project will focus on the Porcupine and Rockall basins which developed in response to multi-phase Mesozoic rifting interspersed with periods of thermal subsidence (Shannon et al., 2003). Several wells have proved the presence of a petroleum system in these frontier regions, including the discovery wells 26/28-1 (Connemara), 35/8-1 (Burren) and 35/8-2 (Spanish Point) but vast areas remain underexplored and poorly understood.

In the Porcupine Basin, rifting in the Middle and Late Jurassic represented a period of major crustal extension (Shannon 1991). The crust became severely stretched or completely attenuated at the central regions (O’Reilly et al., 2006) where beta factors reached as high as 6. While the basin margins experienced less extension (β = <2) and are characterised by rotated Jurassic fault blocks bounded by large high-angle faults, the main basin depocentre facilitated the accumulation of up to 4 km of Cretaceous marine sediments.

During the early Cretaceous, steep-side slopes connected the main basin trough to the proximal shelves, interspersed with several localised intra-slope platform areas. Several prominent ridges of unknown composition formed topographic highs in the distal basin upon which Lower Cretaceous sediments onlapped. Moore & Shannon (1995) recognised that clastic fans and turbidite deposits within the mud-dominate Lower Cretaceous sequences offer good reservoir potential. The combination of high-angle slopes with large drop-off points and intra-basin highs provide the potential for large-volume flows that bypassed proximal slopes and deposited in deeper areas to form pinch-out reservoirs. To date, since drilling has focused towards the margins or on major topographic highs, no exploration wells have penetrated earliest Cretaceous sediments in the distal basin areas.

The project will firstly study the better understood Porcupine Basin before turning attention to largest of the Irish sedimentary basins - the Rockall Basin. Separated from the Porcupine Basin by the Porcupine High, the Rockall Basin contains large volumes of igneous material which coincided with the onset of the North Atlantic Igneous Province, reducing the quality of seismic reflection data.

By combining 2D and 3D seismic reflection data with well studies in the Porcupine and Rockall basins, and by studying cored examples in the North Sea, the project aims to:

•Characterise the stratigraphic architecture of the syn-rift to post-rift transitional sequences in hyper-extended basins.

•Analyse the deep-water slope onlap styles present in the Irish basins and develop tools that help characterise sand presence, character and reservoir quality trends in base-of-slope settings.

•Identify deep-water stratigraphic traps and assess the likelihood of trap integrity.

The primary focus is to understand the relationship between hyper-extension and sedimentary response, and determine the reservoir potential in hyper-extended areas.

 

References:

Moore, J, G., and Shannon, P. M., 1995, The Cretaceous succession in the Porcupine Basin, offshore Ireland: facies distribution and hydrocarbon potential, The Petroleum Geology of Ireland’s Offshore Basins, Geological Society Special Publication, v. 93, p. 345-370

O’Reilly, B. M., Hauser,F., Ravaut, C., Shannon, P. M., and Readman, P. W., Crustal thinning, mantle exhumation and serpentinization in the Porcupine Basin, offshore Ireland: evidence from wide-angle seismic data, 2006, Journal of the Geological Society, London, V. 163, P. 775 – 787

Shannon, P. M., 1991, The development of Irish offshore sedimentary basins. Journal of the Geological Society, London, V. 148, P 181 – 189

Shannon, P. M., McDonnell, A., and Bailey, W. R., 2006, The evolution of the Porcupine and Rockall basins, offshore Ireland: the geological template for carbonate mound development, Int J Earth Sci (Geol Rundsch), v. 96, p. 21-35