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Quantifying Previous HitStratigraphicNext Hit and Structural Controls on Reservoir Connectivity: A 3-D Modelling Approach from the Grassy Member Blackhawk Formation, Previous HitBookNext Hit Cliffs, Utah, USA


A quantitative study of reservoir heterogeneity has been achieved by adopting three techniques; i) high resolution sequence stratigraphy to predict 3-D reservoir architecture, ii) the introduction of seismic and sub-seismic fault populations into the reservoir volume and, iii) subsequent output to fluid flow simulation allowing quantification and assessment of the effects of fault-related and sedimentary compartmentalization.

A high resolution time-Previous HitstratigraphicNext Hit correlation of complex Cretaceous shallow marine clastic strata (Previous HitBookNext Hit Cliffs outcrops, Utah) has identified flooding surfaces and widespread lowstand erosion surfaces which provide a robust framework for confident correlation of reservoir units. Predictably, differences in sandbody geometries and shale pemmeability barrier distributions are controlled by facies partitioning through systems tracts. Incised valley fills have been recognized, which although characterized by complex lateral and vertical facies stacking patterns, contain sandstones with pemmeabilities up to an order of magnitude higher than the bay fill/swamp/shoreface strata they incise into. The valleys represent an important element of the reservoir architecture; valley sandstones may contain considerable hydrocarbon reserves and may increase overall reservoir connectivity.

The single phase flow results derived from testing model sensitivities to Previous HitstratigraphicTop parameters and faulting have shown that, i) high permeability valley fills provide the main conduits for fluid flow through the reservoir, ii) neutral (non-sealing) sub-seismic faults have little effect on flow through the reservoir models tested.

The fluid flow is mainly controlled by sedimentology and stratigraphy, except in cases where the faults have fault rock permeabilities more than three orders of magnitude less than those of host rock sandstones.

AAPG Search and Discovery Article #91021©1997 AAPG Annual Convention, Dallas, Texas.