Reservoir Heterogeneities of Storm-Generated Shelf Sandstone Bodies: Implications for Reservoir Management

Mark H. Scheihing, Gerard C. Gaynor

Examination of a number of examples of storm-generated shelf sandstones, including part of the Kuparuk River formation (Cretaceous, North Slope of Alaska) and examples from the Cretaceous Western Interior seaway, suggests that these reservoirs differ in their geometries, internal facies architectures, and heterogeneities from continental, shoreline, and deep-water reservoirs. Heterogeneities inherent in such shelf sandstone reservoirs control the distribution of permeability and porosity and influence the effectiveness of recovery techniques.

Sandstone bodies produced by storm-driven processes generally exhibit sheet-like geometries and upward-coarsening vertical profiles. These bodies are typically composed of individual event beds of very fine- to fine-grained sandstone and exhibit wave-generated and combined flow structures with laterally persistent mud drapes at their tops. The event nature of deposition of these sandstones produces a highly stratified reservoir. Vertical to horizontal permeability ratios are very low and individual sandstone beds may behave as separate conduits of flow during production. Hummocky cross-stratified beds at the tops of upward-coarsening sequences constitute the most permeable, porous, and laterally continuous parts of these reservoirs.

The contribution of interbedded sandstones to primary production will be relatively limited due to their poor interconnectedness. Under secondary recovery, only amalgamated hummocky cross-stratified beds are likely to waterflood. The vertically heterogeneous nature of permeability distribution and lateral continuity of these sandstone bodies must be considered in modeling of reservoir performance and in recovery technology.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.