Detailed internal architecture of a fluvial channel sandstone determined from outcrop, cores, and 3-D ground-penetrating radar: Example from the middle Cretaceous Ferron Sandstone, east-central Utah

Ideally, characterization of hydrocarbon reservoirs requires information ab out heterogeneity at a submeter scale in three dimensions. Detailed geologi c information and permeability data from surface and cliff face outcrops an d boreholes in the alluvial part of the Ferron Sandstone are integrated her e with three-dimensional (3-D) ground-penetrating radar (GPR) data for anal ysis of a near-surface sandstone reservoir analog in fluvial channel deposi ts. The GPR survey covers a volume with a surface area of 40 x 16.5 m and a depth of 12 m. Five architectural elements are identified and described in outcrop and well cores, using a sixfold hierarchy of bounding surfaces. In ternally, the lower four units consist of fine-grained, parallel-laminated sandstone, and the upper unit consists of medium-grained, trough cross-bedd ed sandstone. The same sedimentary architectural elements and associated bo unding surfaces are distinguished in the GPR data by making use of principl es developed in seismic stratigraphic analysis. To facilitate comparison of geologic features in the depth domain and radar reflectors in the time domain, the radar data are depth migrated. The GPR interpretation is carried out mainly on migrated 100 MHz data with a vertic al resolution of about 0.5 m. Measures of the spatial continuity and variat ion of the first- and second-order bounding surfaces are obtained by comput ing 3-D experimental variograms for each architectural element (each radar facies). The maximum correlation length of the dominant internal features r anges between 4 and 6 m, and the anisotropy factor ranges between 0.6 and 0 .95.