Abstract: Use of Quantitatively Calibrated Depositional Models in Constructing High-Resolution Sequence Stratigraphic Frameworks for Reservoir Characterization

Charles Kerans, S. W. Tinker

High-resolution sequence stratigraphic reservoir descriptions can yield superior models for assessing remaining hydrocarbon potential and guiding fluid-flow simulation studies. These descriptions differ from most existing carbonate reservoir descriptions that remain biased toward lithostratigraphy rather than chronostratigraphy. Lithostratigraphically biased models give an unrealistically high prediction of reservoir continuity because high-frequency time lines are ignored in order to match constant well-log (lithologic) responses. Construction of high-resolution sequence interpretations that honor chronostratigraphic relationships requires the geologist to push the limits of conventional subsurface well-log and core data, but important support from a commonly overlooked source, the c cle-specific depositional model, can provide critical constraints on the configuration of time lines for constructing a high-resolution sequence stratigraphic correlation.

Permian carbonate ramp outcrops of the Guadalupe Mountains, west Texas, and their subsurface counterparts provide an example of the predictive value of depositional models for aiding correlation at the scale of individual cycles. The outcrops allow quantitative calibration of the cycle-scale depositional model in terms of facies dimensions and their associated depositional topography. Inner ramp grain-dominated packstones are typically less than 5 ft thick, extend for less than 500 ft laterally, and were deposited on a flat surface. Ramp-crest grainstones are 0-25 ft thick, up to 6000 ft in dip dimension, and have highly variable upper surfaces that may be channelized or truncated sharply in strike and dip directions. Outer ramp fusulinid packstones are laterally continuous for more t an 10,000 ft at near-constant thickness, but have depositional dips of 1-17°. This calibrated ramp model can then be used to test confidence levels of subsurface reservoir descriptions.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994