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Role of the Base Permian Unconformity in controlling Carboniferous reservoir prospectivity, Southern North Sea


Marta Swierczek

Institute of Petroleum Engineering, The Heriot-Watt University, Edinburgh, Scotland, UK

Grant Institute of Earth Science, School of Geosciences, The University of Edinburgh, Edinburgh, Scotland, UK

[email protected]


Unconformity surfaces in sedimentary basins may either be highly cemented and therefore form low permeability zones, or they may be associated with coarse-grained sediments that offer high permeability pathways for fluid flow.

The research project is investigating the effects that unconformities have on fluid flow processes and hence, on sub-unconformity reservoir prospectivity in sedimentary basins. The project places emphasis on the effects that the Base Permian Unconformity (BPU) has on highly prospective Carboniferous gas-reservoirs found beneath it in the Southern North Sea (SNS). It is investigating if the weathered zone beneath the BPU might enhance development of secondary porosity and consequently improvement of permeable horizons. However, conventional wisdom has polarised views and has been a part of an on-going debate with an opinion divided as to whether reservoir properties are enhanced or not by the unconformity. Given the significance for exploration, appraisal and development of the prospective Carboniferous play fairway in the SNS, it is now the main purpose of the research to try and resolve this issue through stratigraphic determination of the erosional surface, seismic interpretation of the truncated subcropping clastic reservoirs and systematic sampling and analysis of field exposures and cored sections.

High-resolution 3D seismic data have also permitted the identification of major WNW-ESE striking Tertiary intrusive dykes which transect the Carboniferous sediments and the Base Permian Unconformity into the higher horizons. The intrusive, igneous bodies might further affect the reservoir quality by not only instigating diagenetic changes but also compartmentalisation of the reservoir.


AAPG Search and Discovery Article #90094 © 2009 AAPG Foundation Grants in Aid