Depositional Cyclicity and Scaling Petrophysical Parameters for Characterization of Fluid Flow in Carbonate Platform Reservoirs: San Andres Outcrop, Algerita Escarpment, New Mexico

Abstract

San Andres outcrops along the Algerita escarpment in the Guadalupe Mountains of New Mexico are composed of five sequences: a lower to middle San Andres sequence and four upper San Andres sequences. Within a sequence the predictable stacking patterns of cycles in different systems tracts, and of facies and rock-fabric successions within cycles, provide the necessary geologic framework for petrophysical quantification of geologic models. Rock fabric is a fundamental scale controlling the petrophysical properties of porosity, permeability, and capillarity. Four basic rock fabrics are present in the upper San Andres at Lawyer Canyon: dolograinstone, dolograin-dominated packstone, finely crystalline mud-dominated dolostone, and separate-vug dolograinstone. These four rock fabrics have unique average permeability values and porosity-permeability transforms. Permeability distribution was determined in the grainstone facies of cycle 1 at scales ranging from 1 in. to 100 ft. Variogram analysis of spatial permeability distribution indicates short-range correlation with a relatively high nugget, suggesting that permeability heterogeneity is largely random within a rock-fabric facies. A detailed cross section showing the nine cycles and the vertical and lateral distribution of rock fabrics within the cycles was converted to a permeability flow model using geometric mean permeabilities. The resulting rock-fabric flow model is suitable for inputmore » into reservoir simulators for performance prediction studies.« less