Sandstone reservoir zonation of the north-western Bredasdorp Basin South Africa using core data

Abstract

This study delineates sandstone reservoir flow zones in the north-western Bredasdorp Basin, offshore South Africa, using conventional core porosity and permeability data. The workflow begins by integrating sedimentology reports and logs to identify lithofacies before evaluating petrophysical flow zones. Three lithofacies were classified as lithofacies 1, 2, and 3. Lithofacies 1 is a silty shale and bioturbated sandstone, lithofacies 2 is an interbedded sandstone and shale, with very fine sandstone with well-sorted grains, and is heavily cemented. Conversely, lithofacies 3 is a fine-to medium-grained sandstone with minor shale that is moderately cementation. Lithofacies 3 is ranked as the best reservoir rock, followed by lithofacies 2 and 1.Four independent reservoir zonation methods (permeability anisotropy, Winland r35 pore throat, flow zone indicator (FZI), and stratigraphic modified Lorenz lot (SMLP)) were applied to core samples from three wells (MO4, MO5, and MO6). The core samples predominantly had slight anisotropic permeability (0.5–1.1). The reservoir units were ranked into four flow zone categories as tight, very low, low, and moderate, based on porosity and permeability, and calculated parameters. Owing to the reservoir unit heterogeneity, the classification was based on average values. The moderate zone exhibits the best reservoir quality, which is associated with lithofacies 3. The very-low flow zone extends laterally to all wells. The tight zones showed fluid storage potential but no flow capacity. In general, the lithofacies do not always correspond to petrophysical flow zones. The moderate and low flow zones identified in well MO5 are comparable to previously identified flow zones (MO2, MO3, and MO1) in the Western Bredasdorp Basin.