RESERVOIR CHARACTERIZATION OF THE NAVAJO SANDSTONE AT EAGLE CREEK CANYON AND DEVIL'S CANYON, SAN RAFAEL SWELL, UTAH: AN ANALOGUE TO HYDROCARBON RESERVOIRS OF THE CENTRAL UTAH THRUST BELT

Outcrop studies of the Navajo Sandstone were conducted to better understand and characterize potential hydrocarbon reservoirs yet undiscovered in the central Utah thrust belt. The Navajo Sandstone is the producing reservoir rock for the recently discovered (2004), 250MBbl, Covenant oil field in the central Utah thrust belt. The Navajo erg system, deposited during the Early Jurassic over much of Utah, Wyoming, and Arizona, consists of dune and interdune facies that may be reservoirs or baffles or barriers to fluid flow at depth. Our study focused on the Navajo Sandstone exposed on the west flank of the San Rafael Swell, just east of the central Utah thrust belt. An analysis of the quality and facies heterogeneity of the rock as a potential reservoir was done by completing two measured sections (~¼ mile apart) in Devil's and Eagle Creek Canyons where complete sections of the Navajo are exposed. Petrographic, porosity, and permeability analyses, as well as gamma-ray scintillometer measurements of the outcrop, were also completed. Eight facies, three dune and five interdune, have been identified based on detailed analyses in the study area. The upper 2/3 of each measured section is composed mostly of high porosity (20% to 30%) and permeability (average 122 mD) dune facies. Interdune facies are dominant in the lower 1/3 of each measured section. These facies have low porosity and permeability (some less than 0.1 mD). Most are baffles to fluid flow and one is likely a barrier. The lateral extent of each facies varies greatly, ranging from a few meters to kilometers. Only one interdune facies could potentially be correlated between the two measured sections. This facies has the lowest permeability and potentially compartmentalizes the Navajo Sandstone reservoir into an upper, dune-dominated unit and lower, interdune-dominated unit. This compartmentalization could impact drilling and completion strategies within a potential reservoir of the Navajo Sandstone.