High Resolution Sequence Stratigraphy of the Late Namurian, Onshore Northern England: Implications for Silesian Reservoir Development

Kevin D. Church, Robert L. Gawthorpe

Synthesis of data from outcrop and oil and coal exploration wells from the late Namurian in northern England has allowed the development of a regional, high resolution sequence stratigraphic scheme. This stratigraphic framework has been used to evaluate the geometry and continuity of the main reservoir intervals and assess the factors controlling reservoir development.

Thick fluvial sandbodies in the Namurian have traditionally been assigned to a delta top, distributary channel environment. In the model presented here, many are re-interpreted to have formed during subaerial exposure and incision of the underlying highstand delta system, during relative sea-level falls. The cutting out of marine bands by these incision events has important implications for the potential miscorrelation of sandbodies. The correlations also indicate that sequence set stacking patterns control the distribution of reservoir sandstones. In particular, incised valley fills, by cutting out permeability barriers and connecting sandstones of successive delta systems, produce complicated reservoir geometries and interconnect what would otherwise have been separate flow units.

Mapping of thickness and facies variations for individual systems tracts and sequences allows the controls on reservoir development to be constrained. The recognition of most of the sequences across northern England suggests a regional sea-level control. However, there is significant spatial variation in the sequence and sequence set stacking patterns, indicating reservoir development was heavily influenced by fluctuations in sediment supply. In particular, long-lived sediment transport pathways tend to be the sites of exceptionally thick reservoirs with a high net:gross.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995