Subsurface reservoir models are typically limited by a lack of spatially accurate geometric data on bedform architecture and geometry. These factors are key controls on fluid flow. Outcrop analogs have long been used as a source of such data, but the capture of sufficiently precise outcrop data is a challenge. The study presented in this article used highly accurate geometrical digital geological outcrop data collected using ground-based laser scanning (light detection and ranging [LIDAR]) to build and test three-dimensional geocellular models of deltaic reservoir analogs.
Two well-exposed ancient river-dominated delta systems, the Panther Tongue and the Ferron Sandstone Member, which both crop out in central Utah, were digitally mapped to precisely recreate their clinothem and clinoform geometries in geocellular reservoir modeling software. Such clinoforms are commonly draped with low-permeability mudstones that produce reservoir heterogeneity by subdividing the deltaic sand body into a series of dipping sandstone beds (clinothems). A key aspect of the modeling was to accurately capture these geometries and their effect on simulated fluid flow.
Portions of the two deltaic systems were dynamically analyzed in a reservoir modeling software by simulating production in 41 models. These models tested a range of mudstone barrier continuities and permeabilities. Results quantify how the continuation of the heterogeneities governed the production rate and recovery factor in the Panther Tongue models. Mudstone permeability values were more important in the Ferron Sandstone models with steeper dipping and closer spaced clinothems, although production was still influenced by the continuation of the heterogeneities.