Developing an Exploration Strategy for Upper Carboniferous Tight Gas Sandstone Reservoirs
Becker I, Wüstefeld P, Koehrer B, Busch B, Hilgers C
Understanding reservoir quality variations in tight gas sandstones is key to improve their exploration potential. This study focuses on the integration of outcrop and subsurface data of Upper Carboniferous sandstones in the Lower Saxony Basin, NW Germany, to derive lateral and vertical porosity and permeability trends on different scales. Linking petrophysical data sets to the diagenetic and structural evolution of tight sandstone reservoirs allows to define control factors on reservoir heterogeneity. Results indicate similar matrix permeabilities for surface and subsurface rocks, but porosities are generally enhanced in outcrop samples due to late uplift-related dissolution processes of mainly unstable carbonate cements. Variations in the intensity of authigenic clay phases and quartz cementation control the permeability evolution. The original composition related to the depositional setting and temperature anomalies in the vicinity of faults control diagenesis and thus, reservoir quality. Intense natural fracturing or faulting may act as potential migration pathway for leaching fluids enhancing reservoir characteristics in those structurally affected reservoirs. This complex interplay of depositional setting, burial history, and structural inventory of each setting needs to be understood to support future exploration and appraisal efforts in tight gas sandstones.