In-Place Oil Shale Resources in the Saline Mineral and Saline-Leached Intervals, Piceance Basin, Colorado
The Eocene Green River Formation of the Piceance Basin in western Colorado contains most of the high-quality oil shale resource in the western United States. According to a recent analysis by the U.S. Geological Survey of the potentially recoverable resource as a function of oil-shale grade, the basin contains about 920 and 352 billion barrels of potential oil resource using oil-yield cutoffs of 15- and 25-gallons per ton (GPT), respectively. Much of this rich oil shale is associated with the saline minerals nahcolite and halite or intervals in which these minerals have been leached by groundwater. This impacts the potential for oil shale resource extraction as nahcolite must be co-produced or preserved. Furthermore, the presence of vugs and breccias in the leached zones can effect groundwater movement and potentially affect the implementation of in-situ oil shale extraction technologies. To facilitate the assessment of potentially recoverable resources associated with the major mineral facies of the Piceance Basin, oil-shale zones were delineated into mineralogical-stratigraphic intervals, specifically: (1) the illitic zone, which predates the deposition of saline minerals; (2) the saline zone; (3) the leached zone; and (4) other overlying oil shale zones. The oil shale resources in each interval were further sorted according to oil-shale grade. Of the 352 billion barrels of potentially recoverable oil resources associated with high-grade (≥ 25-GPT) oil shale, the amounts present in the illitic, saline and leached intervals were 11%, 33% and 54%, respectively. Very little high-grade oil shale was associated with the overlying oil shale zones. These results highlight the importance of investigating the association between saline minerals and organic richness in the Piceance Basin oil shale, both to understand the geological setting and to facilitate resource development.
AAPG Datapages/Search and Discovery Article #90193 © 2014 Rocky Mountain Section AAPG Annual Meeting, Denver, Colorado, July 20-22, 2014