Measuring Permeability Trends and Correlation Structures in Heterogeneous Carbonates, San Andres Formation, New Mexico

Abstract

Detailed permeability measurements were obtained using a mechanical field permeameter (MFP) on a 210-ft core of the upper San Andres Formation. Analyses of these measurements were used to arrive at an optimal combination of sampling method, number of measurements, and measurement spacing. Parasequences are considered to be a fundamental geologic unit in the shelf carbonate depositional setting. In this case, the parasequences typically are composed of a thin mudstone base, overlain by bar-flank, burrowed wackestones-packstones, and capped by thick barcrest planar- to cross-bedded oolitic packstones-grainstones. The presence and physical scale of vugs, burrows, cemented zones, and moldic porosity makes the task of obtaining representative petrophysical measurements, such as permeability, difficult at best in these facies. To address this complexity, two basic sampling strategies were applied to the core for MFP-scale measurements. The first approach use a vertical transect of closely spaced (1.2 in) measurement points along the length of the core. The second approach used clusters of five points (pads) located at less frequent 6-in intervals. In a comparison of sampling schemes, closely spaced transects and pads yield similar local estimates of the mean; however, the closely spaced transect yields more correlation information because of its superior vertical coverage formore » a fixed overall number of measurements. Therefore, the authors recommend using closely spaced, vertical transects of measurements over pad sampling schemes.« less