A SEDIMENTOLOGICAL PROCESS-BASED APPROACH TO DEPOSITIONAL RESERVOIR QUALITY OF DEEP-MARINE SANDSTONES: AN EXAMPLE FROM THE SPRINGAR FORMATION, NORTHWESTERN VORING BASIN, NORWEGIAN SEA

Reservoir properties of deep-marine sandstones deposited by various sediment-gravity-flow types in the northwestern Voring Basin (Norwegian Sea) are characterized using detailed sedimentological and petrographic analyses. The sandstones are quartz arenites and subarkoses, having similar mineralogical compositions, a low degree of diagenetic modification, and low to moderate volumes of quartz cement (up to 6%). However, significant textural variability is observed for the various sandstone types, which were subdivided based upon their interpreted processes of deposition. In the studied wells there is a predominance of turbidites deposited by high-density turbidity currents (HDTs) and a range of hybrid event beds (HEBs). HDTs are coarser grained and contain less detrital clay than the various HEBs. In addition, the dominant grain size of HEBs decreases down the depositional profile whilst the content of detrital clay increases. Porosities of the various bed types span the same interval, but overall the HDTs and proximal HEBs have a higher proportion of samples with porosities higher than 20%, compared to distal HEBs. Permeabilities, in contrast, are significantly different, with the HDTs having permeabilities approximately two orders of magnitude higher than clay-rich HEBs. A comparison of the observed variability in composition and textural parameters with porosity and permeability indicates that sedimentological flow processes control the depositional reservoir quality of deep-marine sandstones; understanding these processes therefore enhances our ability to predict distribution of reservoir quality in deep-marine systems.