Comparison between outcrop-spectral gamma ray logging and whole rock geochemistry: implications for quantitative reservoir characterisation in continental sequences

Abstract

A high-resolution spectral gamma-ray (SGR) log is compared to elemental whole rock geochemical data in a reservoir scale outcrop analogue, the Otter Sandstone Formation (Sherwood Sandstone Group), east Devon. SGR data compare closely to those generated for point samples by inductively coupled plasma (ICP) techniques, with disparities attributable to the different sample volumes. ICP data reveal separate mineralogical sources for radio-elements, which enable three lithotypes to be discriminated using Th/U ratio and K 2O data. Once established, the discriminants are applied to the SGR log enabling three lithotypes to be dicriminated. These conclusions suggests that SGR logs have significant potential for real-time lithotype prediction in continental sequences, which in turn enable predictions of reservoir quality, and increase confidence in the interpretation of sedimentary architecture.