FLUVIAL ARCHITECTURE AND FACIES DISTRIBUTION OF THE CUTLER FORMATION WITHIN FISHER MINIBASIN, PARADOX BASIN, UTAH: SPATIAL TRENDS AND RESERVOIR CONNECTIVITY IN A SALT-INFLUENCED, SOURCE-PROXIMAL FLUVIAL SYSTEM

The Paradox basin formed on the southwest flank of the Uncompahgre uplift, a mountain range that shed the arkosic facies of the Cutler Formation into the basin. The thickness and coarse grain size of the terrigenous detritus indicate that the source terrain had high relief, and arkosic composition reflects derivation from uplifts cored by crystalline rocks. Outcrops of the Cutler Formation in the Fisher minibasin represent the deposition of fluvial strata proximal to the Uncompahgre uplift. The Fisher minibasin study area (from Richardson Amphitheater to Fisher Towers) records the shift from medial braided to distal braided stream deposits (Campbell, 1980) in a 10-16 km interval away from the sediment source. This area is an important end-member in a broad spectrum of fluvial depositional environments. The goal of this research is to add further insight into reservoir interconnectedness and spatial variability, fluvial architecture, and facies of this proximal fluvial system.

A series of cyclic stratal units are present in the Cutler Formation at this locality which subdivide the outcrop into several laterally correlative packages. These cycles are interpreted to be the result of increased uplift of the Uncompahgre orogeny, flooding events due to base level change, climate change resulting in changes in sediment concentrations, or a combination of these drivers. These packages are bounded by major erosional surfaces. Differential GPS mapping of major erosional surfaces in the Cutler Formation will help construct static 3D reservoir models in Petrel that can serve as quantitative analogs for similar systems elsewhere. In addition, preliminary observations indicate that growth strata are present in the study area, and these are interpreted to be the result of salt deformation due to evacuation and salt diapirism associated with the underlying Paradox evaporites. The reaction of the Cutler fluvial system to syndepositional salt tectonics leads to very different fluvial architectures which are well-preserved in the study area.