--> --> Geologic characterization of new Cane Creek cores from the northern part of the Paradox Basin, Utah

AAPG Rocky Mountain Section Meeting

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Geologic characterization of new Cane Creek cores from the northern part of the Paradox Basin, Utah

Abstract

The Cane Creek (CC) shale of the lower Pennsylvanian Paradox Formation is a productive, but still emerging oil and gas play in the Fold and Fault Belt of the northern Paradox Basin, Utah. Oil production has been most successful from horizontal wells at the Big Flat field in the central play area, whereas areas to the north (Greentown and Gunnison Valley) are currently unproductive but limited historic drilling has shown significant promise. The lack of core data in the northern part of the basin has made it difficult to determine reservoir quality and facies heterogeneity. However, several cores were recently drilled along the Salt Valley Anticline near Crescent Junction which provide new sedimentological data, reservoir properties, and source rock quality of the northern CC play area. The CC is a heterolithic unit comprised of meter-scale cycles of anhydrite, anhydritic dolomitic mudstone, silty dolomite, very fine-grained sandstone to siltstone, and organic-rich calcareous mudstones. Thick beds of overlying and underlying halite provide regional seals and overpressure to the reservoir, and naturally occurring fractures are important for system permeability. Siliciclastic deposits are predominantly bioturbated and contain climbing current ripples, bidirectional cross-stratification, and mud drapes along ripple foresets, all suggestive of tidal depositional processes. Anhydrite pseudomorphs after bottom growth gypsum, invasive displacive nodular anhydrite, dolomite, laminated organic-rich mudstones with Type I & II kerogen, as well as the paucity of burrows, indicate periods of restrictedevaporative sea waters in a sabkha environment. Source rock analyses indicate the northern CC is within the oil window (VRo ~0.80) with up to 20 wt% TOC in several thin shale beds. Siliciclastic reservoir rocks have low permeabilities (0.009-0.202 mD) and variable porosities (6.0-17.0 %) due to dolomiteanhydrite cements, and thus naturally occurring and possibly stimulated fractures are essential. Although total oil production from the CC is only about 8 MMBO, current estimates of the undiscovered resource is about 215 MMBO. With advancements in horizontal drilling, reservoir characterization, and reduction of structure related risks, the CC has the potential to become a significant resource play.