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Department of Geology & Petroleum Geology, University of Aberdeen, Meston Building, King’s College, Aberdeen AB9 2UE, UK
Sedimentological research has traditionally produced geologic models primarily relevant to hydrocarbon exploration, focusing predominantly on location and external geometry of sediment bodies, be they clastic or carbonate, and underplaying the importance of the internal reservoir framework. For example, it has been estimated that geological heterogeneity traps up to 40% of moveable oil reserves in fluvial reservoirs (Tyler & Finley 1991). This failure severely inhibits the application of new and sophisticated technologies to improving recovery efficiencies which are lamentably low in far too many cases, efficiencies less than 25% being common (Tyler & Finley 1991). It is reservoir architecture, the internal fabric and structure of a reservoir, that ultimately controls the paths of fluid migration during oil and gas emplacement and subsequent extraction. This architecture is, in turn, the product of the depositional and diagenetic processes which created the reservoir. If an understanding of the origin of the reservoir is developed, reservoir architecture, and hence fluid flow paths, become predictable. The task for the geologist, then, is to locate and describe this heterogeneity, so that the trapped hydrocarbons may be liberated.
In the past few years, much more emphasis has been placed by reservoir geologists on elucidating the nature of geological heterogeneity, and developing predictive models for use by engineers. However, in geologically complex reservoirs, and those composed of sediments deposited in continental settings almost invariably come into this category, the rate of change of lithology and petrophysical properties is usually very high, making subsurface geological prediction extremely difficult. Indeed for
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