Chemostratigraphy and Its Role in a Multi-Disciplinary Stratigraphic Approach to the Exploration and Development of Upper Carboniferous (Pennsylvanian) Gas Fields in Southern North Sea

Timothy J. Pearce¹, Duncan McLean², John H. Martin¹, Georgina Doughty³, and David Wray^4
1 Chemostrat Ltd, Llanfyllin, United Kingdom
² Sheffield University, Sheffield, United Kingdom
³ ConocoPhillips (UK) Ltd, Aberdeen, United Kingdom
⁴ University of Greenwich, Chatham Maritime, United Kingdom

Important gas reservoirs lie in the Upper Carboniferous Coal Measures and red beds of the Southern North Sea. The red beds of the Boulton/Ketch Formations and the underlying Coal Measures of the Westoe Coal and Cleaver Formations. These represent a 2000ft-3000ft thick sequence that is notoriously difficult to correlate, with poor internal seismic definition, repetitive e-log signatures and in places poor palynological preservation.

These sequences have been re-evaluated by applying a multidisciplinary approach, which includes chemostratigraphy, mineralogy, palynology, Sm-Nd isotopes, petrophysics, sedimentology and seismic data that focuses on a series of type wells in the northern area of Quadrant 44. The sequence is divided into seven age dated chemostratigraphic packages WC, LCF, UCF, LK1, LK2, UK, BF on the basis of variations in the mudstone and sandstone data, these variations being linked to changes in provenance, depositional environment and climate. The chemostratigraphic zonation is compared with the biostratigraphic zonation of the same section. Heavy mineral data confirm the sediment source and Sm-Nd isotope data provide a provenance age for the succession. These packages can sometimes be tied to seismic data and form the basis for field-subregional stratigraphic modelling In addition, a higher resolution stratigraphic zonation scheme is used to enhance reservoir correlation and connectivity modelling, and provides a dataset to aid in wellsite geosteering using chemostratigraphy.