HARRIS, P. M., D. J. COGGIN, and C. W. GRANT, Chevron Petroleum Technology Company, La Habra, CA

ABSTRACT: Permeability Distribution and Fluid Flow within Carbonate Cycles -- An Example from the Permian Basin

Vertical and horizontal permeability (k) transects were collected from core and outcrop of the upper San Andres Formation at Lawyer Canyon, Guadalupe Mountains, New Mexico, to assess the lithofacies and k variation in and between ramp-crest carbonate cycles and to determine what affect these variations have on waterflood-flow simulations.

A typical cycle (10-45-ft thick) consists of an upward shallowing facies succession with a basal dolomudstone (geometric mean permeability kg = 2.3 md), overlain by burrowed dolopackstone (kg = 6.1 md) and bar-flank ooid-peloid dolograinstone (kg = 8.1 md). Thicker, better developed cycles have a capping (10-20-ft thick) bar-crest ooid grainstone (kg = 13.0 md). Therefore, an upward increasing k trend occurs within a cycle. Vertical correlation lengths of k derived from semi-variogram

analysis support that such depositional cycles may be the fundamental fluid-flow unit in such shelf-carbonate settings.

Three basic k fields are generated for a cross-sectional model of three cycles, and each field is input into a waterflood-flow simulator to test the significance of the observed geologic variation. These fields are (1) a simple "layer cake" k field distributed according to the vertical succession of facies, (2) a geostatistical approach for distributing k across the panel, honoring vertical transect data, geologic markers, and spatial correlation data, and (3) a model incorporating additional geologic information and core data to guide the geostatistical approach for the most realistic distribution of k. These simulations show that viscous-dominated flow behavior appears to be compartmentalized by individual cycle, and that both basal dolomudstones and poorly developed cycles are pote tial barriers to fluid crossflow. In addition, sets of poorly developed cycles (i.e., those lacking well developed bar-crest facies) have the highest potential for bypassed or remaining mobile oil. The three different models of k have similar overall recovery efficiencies; however, each model exhibits a different processing rate, directly affecting the timing of recovery.

AAPG Search and Discovery Article #90994©1993 AAPG Southwest Section Meeting, Fort Worth, Texas, February 21-23, 1993.