Reservoir heterogeneity plays an important role in oil field economics and completion strategies. We herein characterize the reservoir heterogeneity of the Early Jurassic Navajo Sandstone in the Justensen Flat/Devils Canyon area of the San Rafael Swell, Utah. These outcrops are located approximately 60 kilometers (45 mi) east of the recently discovered Covenant oil field which is located in the central Utah thrust belt exploration play. The reservoir for the Covenant field is the Navajo Sandstone. This study can serve as an outcrop analogue for this developing play and other eolian reservoirs worldwide. There are eight facies within the Navajo Sandstone in the Justensen Flat/Devils Canyon area based on differences in primary and secondary sedimentary structures, sedimentary texture, petrology, porosity/permeability, and other macro-scale features of the outcrop. Three facies were deposited by eolian dunes. These serve as the primary reservoir facies of the Navajo in the Justensen Flat/Devils Canyon area, displaying relatively high porosity and permeability (approximately 28 percent porosity and 100 mD of permeability). Five interdune facies display finer grain size, more abundant cement, and relatively lower porosity and permeability (approximately 18 percent porosity and 29 mD of permeability). Four of the five inderdune facies have variable porosity and permeability or are not laterally extensive (tens of meters). These four facies act as baffles to fluid flow within the reservoir. One interdune facies, the Wavy Algal Matted facies (WAM), displays very low porosity (10 percent) and permeability (0.265 mD) based on 4 samples, and is laterally extensive in the field area (greater than 1 km2). There are nine facies in the Wolverine Federal 17-3 core from the Covenant Field, four of which are tidally influenced. This is unique compare to the Justensen Flat/Devils Canyon outcrop. Tidal influence was apparently present in western Utah but did not have a direct influence on sedimentation 60 kilometers (45 mi) to the east. The Large Trough Cross-stratified (LTC) facies, which serves as the primary reservoir of the Navajo Sandstone, was observed in both outcrop and core. The laterally extensive, low permeability WAM facies was also present in both core and outcrop, suggesting the possibility of reservoir partitioning within oil fields having eolian reservoirs similar to the Navajo Sandstone.



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Physical and Mathematical Sciences; Geological Sciences



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reservoir characterization, Navajo Sandstone, geology, Covenant Field, oil reservoir, erg, dune, interdune, eolian, sedimentary facies



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