ABSTRACT: Well Log Patterns and the Micro-Stratigraphic Framework of Important Clastic Reservoirs

SWANSON, DONALD C.

The ability to predict the location, distribution, trend, and quality of undrained reservoir segments has become an increasingly vital part of the world-wide effort to increase the reserves and deliverability of old fields. This is particularly true where clastic reservoirs are present. Regardless of diagenetic change, the nature of clastic reservoirs is mostly the result of depositional environments and the processes operating there. It therefore follows that the existence and location of untapped clastic reservoir segments can be better predicted by using biased interpretations based upon environmental facies knowledge, paleogeography and the microstratigraphic framework.

Well log shape has been used and misused for years (with, varying success) as a facies indicator of various subsurface clastic deposits. Log curve patterns can often provide diagnostic features, such as vertical porosity-texture changes, nature of textural mixing, and the relative thicknesses of facies units, all useful in identifying various clastic reservoir types.

Well log facies placed within their enveloping, three dimensional micro-stratigraphic setting can provide operators with the best method for predicting the existence, location, and extent of undrained and/or untapped clastic reservoir segments. Fluvial, deltaic, and deep water deposits, besides being the most important reservoir facies, are subject to a reliable and predictive influence by their depositional processes and paleogeography.

Examples of the relationship between clastic well log facies, and their microstratigraphic framework can be used as guides to their applications.

AAPG Search and Discovery Article #90947©1997 AAPG Southwest Section Meeting, San Angelo, Texas