Reservoir Facies Characterization and LiDAR Model of a Mixed-Energy Estuarine-Tidal Succession, Cretaceous Straight Cliffs Formation, Southern Utah

Abstract

Depositional architectures in tidal successions reflect a complex mixture of fluvial, tidal, and marine environments, making their recognition and interpretation difficult. Because tide-dominated and tidally-influenced reservoirs account for a significant portion of petroleum reserves, predictive facies models derived from outcrops are invaluable. Outcrops of Cretaceous strata in Tibbet Canyon, southern Kaiparowits Plateau of southern Utah, offer insight into the regional extent and internal complexity of tidal processes. This study captures the architecture of a mixed-energy estuarine succession preserved as part of the John Henry Member fluvial to marine transition of the Upper Cretaceous (Santonian-Campanian) Straight Cliffs Formation. A detailed interpretation of an 8 m by 500 m bayhead delta is presented, highlighting its internal architecture as well as its relationship to underlying tidal bars and overlying coastal plain strata. Superficially, bayhead deltas and tidally influenced point bars have similar, IHS-dominated architectures, but they form by different processes and have different architectural expressions (progradational and coarsening upward vs. lateral accretion and fining upward, respectively). As such, they behave quite differently as reservoirs. Terrestrial LiDAR, outcrop photomosaics, detailed measured sections, and paleocurrents were used to describe facies and facies associations and interpret architectural elements. LiDAR scans provide point clouds tied to RGB values for a photo-realistic geospatial outcrop reconstruction of a complex vertical succession. The ~65 m thick interval is an excellent example of inner-middle estuary succession consisting of elongate, sigmoidal tidal bars, estuarine point bars, bayhead deltas, and tidal flat deposits. The stratigraphic evolution of an estuarine succession from tidal bars to a bayhead delta overlain by coastal plain deposits was captured in a conceptual model. Within the bayhead delta, beds thicken and coarsen vertically, and are composed of very fine- to medium-grained trough cross-stratified, rippled (some climbing), planar laminated, and planar cross-stratified sandstones and interbedded mudstone/siltstone. Modeling results are compared to published studies of IHS point bar models to demonstrate the impact of distinct stacking patterns and geometric relations of different IHS deposits on reservoir character.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015