Abstract: Characterization of Reservoir Heterogeneity in Carbonate Ramp Reservoirs for Simulation Studies

F. Jerry Lucia, C. Kerans, R. K. Senger, F. P. Wang, Anil Mishra

Three-dimensional arrays of rock properties are essential for reservoir simulation studies for improved recovery. In carbonate reservoirs, stacking of rock-fabric bodies within a high-frequency sequence stratigraphic framework provides the most accurate framework for displaying the distribution of petrophysical rock properties of porosity, permeability, relative permeability, and capillarity. The sequence stratigraphy of a major carbonate ramp system exposed along the Algerita escarpment, Guadalupe Mountains, Texas and New Mexico, has been described, and the high-frequency cyclicity and petrophysics of interwell-scale reservoir windows from the outer ramp, ramp crest, and inner ramp have been studied in detail. Each window is characterized by (1) unique stacking of rock-fabric bodies haracteristic of the depositional and diagenetic setting and (2) unique performance characteristics related to the stacking patterns.

The outer-ramp window is characterized by gently dipping clinoforms composed of subtidal cycles of fusulinid wackestones/mud-dominated packstones and fusulinid grain-dominated packstones. There are few barriers to flow, and waterflood recovery efficiency decreases with increasing connection of discontinuous grain-dominated units by wells. The ramp-crest window is characterized by flat-bedded upward-shoaling cycles of mud-dominated fabrics to grainstones. Grainstone flow units dominate the flow characteristics and are laterally continuous on a scale of thousands of feet. Numerous thin discontinuous mudstone layers form vertical flow barriers. The inner ramp window is characterized by flat-bedded cycles that contain mud-dominated fabrics and grain-dominated packstones. Cycles capped by rainstones contain large volumes of moldic porosity. Numerous thin to thick flow barriers are present, and flow characteristics are dominated by the high degree of heterogeneity.

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