Facies Architecture and Controls on Reservoir Behavior in the Turonian Wall Creek Member of the Frontier Formation in the Powder River Basin, Wyoming

Abstract

Inter-well heterogeneities influencing fluid migration in deltaic reservoirs are controlled by lateral lithofacies changes and vertical complexities such as low permeability thin-beds. Subsurface wireline tools often cannot sufficiently predict the spatial and stratigraphic organization of these architectural elements and their influence on effective reservoir properties and connectivity.

Here we present results from an integrated sedimentological, stratigraphic, and geocellular modelling approach, that quantifies the stratigraphic multi-scale heterogeneity observed from outcrops in the Wall Creek Member (WCM) of the Turonian Frontier Formation, and provides a detailed 3D model for subsurface application in time equivalent strata in the Powder River Basin (PRB). Exposures of the WCM in the Tisdale Anticline, on the western limb of the PRB, are crosscut by a series of intersecting canyons, providing the 3D control necessary to quantify parameters for a 1km² geocellular model. Lithologic facies constraint from 13 tightly spaced stratigraphic sections and digital outcrop model (DOM) interpretations condition the geocellular model framework and model facies. Key surfaces recognized across the study area separate the WCM into two distinct depositional sequences. Sequence 1 consists of river-dominated deltaic deposits, interpreted as a lowstand delta (LST1), overlain by storm-dominated shoreface sandstones interpreted as highstand deposits (HST1). Sequence 2 consists of heterolithic deposits interpreted as tidal bars associated with a lowstand delta (LST2). In all instances lowstand deposits show higher facies and architectural heterogeneity compared to the highstand deposits.

To capture this stratigraphic complexity and to provide accurate reservoir parameters for the 1km² geocellular model, multiple small-scale, high resolution facies models were created for each systems tract. Fluid simulation on the facies models captures the geometric arrangement of bedding heterogeneities on a sub-centimeter scale and provides accurate representations of resulting permeability anisotropy when upscaling to the full gridded 1km² model. Sensitivity testing of variable lithologic conditions reveal pore-scale controls on fluid migration within outcrop- constrained facies models. Integration of this data with upscaled model simulation results discerns the importance of pore-, bed-, and architectural element scale heterogeneities on fluid flow in a tight oil reservoir.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018