The Use of Graphic Correlation for Reservoir Scale Stratigraphic Resolution

Donald S. Van Nieuwenhuise
University of Houston, Houston, TX

An important aspect of reservoir characterization is reservoir continuity. Flow units are often confined to a single porous and permeable stratigraphic or genetic unit that is bound stratigraphically above and below by impermeable layers that separate the flow unit from others. Flow units may also include multiple cross-cutting stratigraphic units of differing ages or genesis but that can only occur when porous and permeable portions of each unit are in open stratigraphic contact with one another. In either case, high-resolution biostratigraphy can help determine the stratigraphic architecture to a degree that allows interpretating the lateral continuity of a flow unit or if it is rather more likely to be truncated by an impermeable unit, a sealing fault, or an unconformity.

This is particularly useful when seismic events appear to be slightly discontinuous. Often high-resolution biostratigraphy can resolve elements of the stratigraphic architecture causing the seismic discontinuity which turns out to be an important signal rather than noise.

Several examples from the Gulf of Mexico and the North Sea are presented. In most cases with adequate biostratigraphic data, reservoir continuity or discontinuities due to multiple reservoirs can be determined using graphic correlation. Further, models are presented to explain the various graphic correlation patterns expected to occur when wells penetrate flow units that are truncated by various stratigraphic architectures including stratigraphic onlap or transgression, downlap and progradation, fault cuts, regional thinning or thickening, and truncation by unconformities.