Abstract
Outcrop studies provide high-resolution information about facies architectural controls on the spatial distribution of petrophysical attributes in reservoir analogs. One of the sandstones in the Ferron delta system in central Utah has been selected for detailed analysis as an analog of Gulf Coast deltaic reservoirs. Unit 5 of the Ferron, a wave-modified deltaic sandstone, consists of a meandering distributary system that fed stratified delta-front deposits. Lateral migration, coupled with rising base level, resulted in horizontally and vertically heterogeneous distributary sandstones, in contrast to the delta front where vertical heterogeneity is dominant and lateral complexity minimal.
Permeability distribution and structure are strongly related to facies composition, stratal type, and grain size. Thus, distributary-channel sandstones have the highest mean permeability, delta-front sandstones the lowest. Within the distributary system the trough-crossbedded stratal type has the highest mean permeability. Variogram analysis indicates correlation at several scales—largest correlation lengths are 182 m in the distributary-channel sandstones. At the stratal level horizontal correlation lengths are less than 6 m and relate to erosional discontinuities and bed size. Quantification of permeability characteristics suggests a hierarchy of bounding-surface types that have attendant geometric and permeability characteristics. Such characteristics can be critical input to reservoir simulation studies of analogous reservoirs in the Gulf Coast Basin, many of which are major natural gas producers.
