--> Stratigraphic Architecture and Reservoir Characteristics of Slumped Distributary Mouth Bar Deposits, Cretaceous Ferron Sandstone, Utah: An Analysis of Sedimentary Fabric and Facies Utilizing Outcrop and Core Data

AAPG ACE 2018

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Stratigraphic Architecture and Reservoir Characteristics of Slumped Distributary Mouth Bar Deposits, Cretaceous Ferron Sandstone, Utah: An Analysis of Sedimentary Fabric and Facies Utilizing Outcrop and Core Data

Abstract

Deltaic systems are the staging area for sands that move into deeper water environments and account for a significant portion of petroleum reservoirs worldwide. A common process in fluvial-dominated deltas is sediment failure derived from gravitational instabilities that occur at the seaward extent of rapidly prograded delta front environments. These slumps may (1) cause a reorganization of depositional facies, (2) negatively impact reservoir quality, (3) result in heterogeneous or compartmentalized reservoirs that contain internal barriers to hydrocarbon flow. In order to understand potential production challenges associated with slumped delta-front deposits, we characterized delta-front sediment failures from an outcrop evaluation of well-preserved, slump-rotated distributary mouth bar deposits and growth-faulted distributary mouth bar/channel deposits along with behind outcrop cores in exposed Cretaceous strata of the Ferron Sandstone, east-central Utah.

Remobilized, slump-rotated deposits are associated with the third stratigraphic cycle of the upper Ferron Sandstone and traveled < 5 miles from their equivalent delta-front. These features are characterized by a coarsening upwards facies succession, representing distal bar, distributary mouth bar, and subaqueous terminal distributary channel environments, as well as abundant micro-faults and deformation banding indicative of secondary transport downslope. The geometry of the slump blocks is characterized by two distinct, arcuate groups of isolated sandstone deposits that range in stratigraphic thicknesses from 20-82’, have maximum lengths along strike from 46-290’, and have rotated bed set dips ranging from 55-80°. We suggest that up-dip growth faulting occurring at the proximal delta-front may initiate the formation and transportation of rotated slump blocks downslope. The prodelta shale underlying the slump deposits is similar to the growth fault décollement and likely functioned as the glide plane upon which remobilization occurred. A consistency of sedimentological features in slump block deposits, core, and growth-faulted outcrop offered an opportunity to calibrate subsurface and field observations as well as tie sedimentary processes to various positions along the depositional profile. Remobilized slump deposits are likely preserved as isolated sandstone bodies that are not connected to neighboring sands, which may lead to potential challenges during hydrocarbon production.