REVIEW: North Sea Petroleum Geology Course
Review by Rachael Hunter – PhD student, Heriot-Watt University/NERC CDT in Oil and Gas
On the 9th -11th of May, a group of 27 geoscientists gathered at the PESGB Croydon Office to participate in the 3-day intensive PESGB North Sea Petroleum Geology Course led by Professor John Underhill and esteemed colleagues. The participants came from across the petroleum sector, representing operating companies, spec seismic companies, contractors and postgraduate students.
The North Sea Course is one of PESGB’s longest running and well renowned and is led by some of the most experienced geoscientists from academia and industry working within the North Sea Basin. The aims of the course were to deliver a comprehensive and in-depth review of the North Sea’s structural, stratigraphic and sedimentological development and the consequent implications for its petroleum prospectivity, a huge task given its multi-phase tectonic evolution and numerous plays.
The course commenced with John Underhill (Heriot-Watt University) providing insights into the basin’s exploration and production over its 50 year history before giving a comprehensive review of its structural development. Following this introduction, the course was structured so that over the three days experts in North Sea Geology took the podium to discuss each stage of the basin’s stratigraphic development in turn, highlighting the implications for prospectivity of each interval. Their overview of the main play fairways was supplemented by numerous bespoke field case studies aptly exemplified the points made and helped to stimulate thought and discussion.
The Palaeozoic focus of day 1 included a review of the Devono-Carboniferous by Dr Bernard Besly (Besly Earth Science). This forms the oldest prospective sedimentary unit within the North Sea and is poorly understood in many areas due to deep burial. Bernard showed how analogues from onshore areas and the comparison between structural horsts and adjacent troughs can not only aid the definition of depositional systems and structures but also provide important information on potential prospectivity.
Dr Richard Steele (Tullow) then presented on the highly prospective Rotliegend Group, which includes the Leman Sandstone Formation which forms many of the gas reservoirs of the Southern North Sea.
Professor John Underhill then followed with a presentation on the Upper Permian Zechstein Group, a carbonate-evaporitic unit that was deposited over much of the Southern and Central North Sea. John showed how the evaporites have had a huge effect on structural systems in the North Sea due to subsequent halokinesis and also discussed the impact of this robust seal on underlying petroleum systems.
Day 2 began with Dr Neil Meadows (Red Rock international) reviewing the prospectivity of the Triassic, a poorly understood unit in parts of the North Sea due to its deep burial beneath the subsequent Jurassic rift system. He extended the focus to include examples from the Irish Sea and Wessex Basin, both of which complimented the North Sea ones.
The Jurassic system is the most recognisable in the North Sea due to the formation of the North Sea Trilete Rift System and deposition of the world-renowned Kimmeridge Clay source rock. John Underhill gave a scene-setting overview of the Jurassic, explained the use of sequence stratigraphic methods in developing BP’s J-scheme for correlation and discussed the driving mechanism for North sea doming its consequences for the Upper Jurassic rifting event and the implications for prospectivity.
Professor Gary Hampson (Imperial College) discussed the Lower and Middle Jurassic reservoirs of the Statfjord Formation and Brent Group and provided a welcomed opportunity for class interaction by means of a Brent Group well correlation exercise enabling attendees to practically address the complexity in reservoir architecture of these deltaic sequences within arguably the basins most prospective stratigraphic interval.
The final day focused on the prospectivity of the North Sea’s Cretaceous and Cenozoic post-rift sequences. John Underhill began the day with a presentation on the Lower Cretaceous, a unit often forgotten in favour of the more prospective stratigraphic intervals but one during which a surprising amount of tectonism occurred.
Remaining in the Cretaceous, Professor Andy Gale (Portsmouth University) outlined the controls on the Upper Cretaceous Chalk Group and its transition into the mud-dominated Shetland Group equivalent to the north. This sequence is often considered homogeneous ‘overburden’ but is of great significance due to the effects of high sedimentation rates on controlling the timing of maturation. It also provides an, often highly complex, reservoir in some fields.
Howard Johnson (Imperial College) continued with the Tertiary and focused on Paleogene Plays. He discussed the effects of hinterland rejuvenation in depositing the highly prospective Palaeocene and Early Eocene reservoirs and highlighted the importance of clastic sedimentology in the reservoir engineering of fields.
To close off the course, John Underhill returned with a summary of the petroleum systems discussed and additionally delivered a hopeful message for the longevity of North Sea through discussing recent discoveries, current frontier exploration and the potential to rejuvenate old play fairways via seeking new uses such as carbon capture and storage opportunities.
Participants left armed with a supporting catalogue of field case studies and a thorough understanding of the extent to which the North Sea’s geological development and evolution has controlled its petroleum prospectivity. Together, the collective contribution by the presenters conveyed that, despite being a mature basin, application of forensic geoscience coupled with technological advancement continues to increase our understanding of the North Sea hydrocarbon province and contribute to exploration success.
Thanks are extended to all of the presenters for their contributions to this fantastically insightful course and one which can be thoroughly recommended for fellow geoscientists with interests in history and future of North Sea petroleum systems.