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Reservoir Quality of the Cretaceous Dakota Formation, Uinta Basin, Utah

Homan, Mindy B.*1; Hokanson, William 1; Currie, Brian S.1
(1) Deparment of Geology and Environmental Earth Sciences, Miami University, Oxford, OH.

The Cretaceous Dakota Formation in the Uinta Basin of Utah, produces natural gas from fluvial and estuarine sandstones. However, the risk of drilling a non-productive well in the basin is high due to the effects of compositional and morphological variations of pore-filling cements within reservoirs. While the relationships between cements and Dakota reservoir quality has been previously documented, the factors controlling observed variations are unknown.

The purpose of this research is to characterize the composition and paragenesis of Dakota Formation sandstone cements in order to identify the controls influencing overall reservoir quality. Over 100 sandstone thin sections from cores and outcrops have been analyzed using optical microscopy, cathodoluminescence, and scanning electron microscopy. Results from core samples indicate that pervasive quartz overgrowths fill most of the porosity in non-productive wells, but are rare in producers. Observed relationships indicate that early clays coats prevented the formation of quartz overgrowths and helped maintain open pore systems. In addition, similarities between core and outcrop sample porosity and permeability values indicate outcrop data can be used as an analogue for the subsurface. Currently, I am analyzing a suite of 24 samples from a Dakota channel sandstone to evaluate the vertical and lateral variability in reservoir quality.

In conjunction with the Dakota Formation composition and paragenesis, a comparison of the petrographic results with the current sequence stratigraphic model for the Dakota will be done. From this, stratigraphic or paleoenvironmental controls on Dakota reservoir quality can be identified that will be used to assist future gas exploration and development in the Uinta Basin.


AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California