SPATIAL AND STRATIGRAPHIC DISTRIBUTION OF WATER IN OIL SHALE OF THE GREEN RIVER FORMATION USING FISCHER ASSAY, PICEANCE BASIN, NORTHWESTERN COLORADO

The spatial and stratigraphic distribution of water in oil shale of the Eocene Green River Formation in the Piceance Basin of western Colorado was studied in detail using the more than 321,000 Fischer assay analyses in the U.S. Geological Survey oil shale database. The oil shale section was subdivided into 17 roughly time-stratigraphic intervals, and the distribution of water in each interval was assessed separately. This study was conducted in part to determine if water in oil shale could provide a significant amount of the water needed for an oil shale industry. Recent estimates of water requirements vary from 1-10 barrels of water per barrel of oil produced, depending on the type of retort process used. Sources of water in Green River oil shale include: 1) free water within clay minerals; 2) water from the hydrated minerals nahcolite (NaHCO₃); dawsonite (NaAl(OH)₂CO₃); and analcime (NaAlSi₂O₆^.H₂0), and 3) water produced from the breakdown of organic matter in oil shale during retorting. The potential contribution from each of these sources varies both stratigraphically and aerially in the basin. Clay is the most important source of water in the lower part of the oil shale interval and in many basin margin areas. Nahcolite and dawsonite are the dominant sources of water in the oil shale and saline mineral depocenter, and analcime is important in the upper part of the formation. Organic matter does not appear to be a major source of water. The ratio of water to oil generated with retorting is significantly less than one for most areas of the basin and for most stratigraphic intervals, thus water within oil shale can provide only a fraction of the water needed for an oil shale industry.