SCHOFIELD, KEVIN, Conoco Inc., Houston,TX

Abstract: From Sequence Stratigraphy to Laser Grain Size Analysis: A Holistic Look at Reservoir Quality Variation in the Gulf of Mexico

Data from two cored reservoir sands from a single well in the Gulf of Mexico are presented. Although both are characterized by the somewhat serrate cylindrical log character and laterally extensive trough-dominated seismic signature often associated with the so-called "high performance reservoir" sands (HPR), there is a considerable difference in their reservoir quality.

The two sands occur at the base (the Lower sand) and towards the top (the Upper sand) of a sand-prone interval some 2500 feet thick. Each is composite (i.e., comprises two or more stacked sandbodies) and is 100 - 200 feet in thickness.They are separated by a heterolithic interval of approximately 1400 feet. The Lower sand has measured porosities in the range 30-33%, and permeabilities of 1.8 - 3.3D.The Upper sand, by contrast, has porosities in the range 25-32%, and permeabilities from 0.034 to 1.7D.

These variations in reservoir quality are explained in terms of the petrographic character of the sands, linked in turn to mechanisms of sediment transport/deposition and the sequence stratigraphic context.

Some thoughts are shared, inter alia, on the methodology and results of laser grain-size analysis, which has proven to be an accurate method, yielding results which go a long way towards explaining the differences in measured reservoir quality, and also may furnish clues to the rheology of the flows responsible for deposition of the sands.

AAPG Search and Discovery Article #90923@1999 International Conference and Exhibition, Birmingham, England