Reservoir Characterization and Comparisons of Permian and Jurassic Eolian Sandstones From Central Utah

Abstract

Eolian sandstones are often considered homogeneous units in reservoir modeling. However, numerous internal small-scale (mm- to cm-scale) heterogeneities can act as fluid flow baffles and affect reservoir performance. In the San Rafael Swell, Utah, the eolian Permian White Rim Sandstone, Jurassic Wingate Sandstone, and the Jurassic Navajo Sandstone are considered as potential carbon capture and sequestration (CCS) reservoirs. These deposits demonstrate a wide range in eolian expressions and provide an ideal site to understand how eolian heterogeneities affect reservoir properties. Bed-scale measured sections and architectural observations provide a stratigraphic and sedimentological framework for petrographic porosity and Tinyperm II permeability measurements.

Eolian bounding surfaces have low transmissibility and can act as fluid flow baffles across millimeter laminae scales to decameter bedset scales. Extensive horizontal boundaries, related to paleo-hydrological conditions, create discrete “zones” within the formations. Horizontal permeability is two to six times greater than vertical permeability due to low transmissibility across bounding surfaces. Internally within bedsets, lithofacies are the dominant control on reservoir properties with dune facies permeability exceeding that of interdune deposits. Grainflow laminae are internally massive and coarser-grained than the lower permeability wind ripple laminae. Any textural disruption such as bioturbation or soft-sediment deformation can also increase reservoir quality.

Eolian unit comparisons reveal several strategies that can improve the accuracy and predictability of simulation models. Model cells should incorporate anisotropy to reflect the difference in horizontal and vertical permeability from internal laminae. Major bounding surfaces typically define breaks in deposition and tend to express low vertical transmissibility. Comparatively, the Navajo Sandstone has superior reservoir quality in both outcrop and core. Although the Wingate and White Rim formations have similar reservoir quality in outcrop, low White Rim permeability in core makes it a poor CCS reservoir. Overall, eolian deposits have heterogeneities that should be incorporated into reservoir models in order to accurately predict reservoir performance particularly for CCS and late-stage oil field development.

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