Thin-bedded reservoir analogs in an ancient delta using terrestrial laser scanner and high-resolution ground-based hyperspectral cameras

Abstract

Ground-based terrestrial laser scanning and hyperspectral sensors were used to image fine-scale heterogeneity in outcrops of prodeltaic heterolithic facies of Parasequence 6 of the Cretaceous Ferron Notom delta in Southern Utah. Previous work shows that Parasequence 6 is an upward coarsening fluvial-dominated, wave-influenced deltaic deposit containing heterolithic thin-bedded facies representing distal delta front and proximal prodelta environments. Primarily, the thin beds have been interpreted as turbidites, storm beds (tempestites), and hyperpycnites. These deposits represent analogs for thin-bedded unconventional pay zones that lie at the margins of conventional deltaic sandstone reservoirs.The terrestrial laser scanner was used to create a centimeter- to decimeter-scale, digital representation of the outcrops in three dimensions. Hyperspectral sensors record electromagnetic radiation reflected off the outcrops in 840 contiguous bands, which were then used to generate a spectral signature for each pixel sampled. The spectral signatures are a function of mineralogy, chemistry, surface alteration, grain-size, and cements, and were used to distinguish thin mudstones from sandstones within an interbedded succession at the base of a deltaic parasequence. Comparison between the spectral signatures recorded from the outcrop and those of reference materials, and with previous facies architecture studies, enables lithofacies to be identified and subsequently accurately mapped. Hyperspectral data are then draped over the terrestrial laser scanner model to generate a spatially-accurate detailed three-dimensional (3D) geologic map of the heterogeneity.Approximately 100m of outcrop was imaged laterally with the hyperspectral camera and terrestrial laser scanner on the previously mapped distal delta front and prodeltaic facies of Parasequence 6. Bed thickness data, based on measurements made along depositional dip versus strike, show that bed geometries are anisotropic. Reconstruction of the plan-view geometry shows that the thin-beds are lobate to elongate in plan-view profile and extend over distances of about 1km, indicative of the dispersive waning sediment transport processes found in storm-influenced fluvial-dominated deltas. The lobate geometry suggests that beds are laterally discontinuous, with a width to thickness ratio on the order of <10,000 (i.e. a 10cm bed extends for <1km). The combined terrestrial laser scanner and hyperspectral data provide continuous 3D maps of grain-size and lithology. The maps which emphasize the continuity and dimensions of thin beds are among important factors which impact reservoir behavior.