Oil Shale - An Impending Energy Source

Abstract

Recent political, technological, and economic developments lead to optimism for the commercial exploitation of oil slide as a source of energy. Although presently the production of oil by mining or aboveground retorting seems feasible, the production of oil by in-situ techniques or of pipeline gas by either aboveground or underground gasification is less probable for a while. Introduction Where is oil shale going now? After many years of research, during which enthusiasm for development has periodically waxed and waned, the climate for development seems once again favorable. This report attempts to tell why. It includes a review of the size, location, and characteristics of the deposits, an assessment of the status of the processing technology, and a description of a planning program for oil-shale development. An attempt to weigh positive and negative factors to develop a current outlook results in a moderate optimism for the near-term development of an oil-shale industry. The Oil-Shale Deposits Oil shales are widely distributed throughout the U. S., but only those of the Green River formation of Colorado, Utah, and Wyoming have received appreciable attention as a possible source of fuels and chemicals. The location of the Green River deposits is indicated on Fig. 1. They underlie an area of about 17,000 sq miles in four principal basins: the Piceance Creek basin of Colorado, the Uinta basin Piceance Creek basin of Colorado, the Uinta basin of Utah, and the Washakie and Green River basins of Wyoming. Their energy potential has been estimated at more than 1 trillion bbl of oil, with about 600 billion bbl represented by the richer deposits those that assay greater than 25 gal of oil per ton in continuous sections of shale 10 ft or greater in thickness. The shale deposits vary in accessibility from those with no overburden (outcrops) to very deeply buried shales in the western Uinta basin. The outcrop (called the Mahogany ledge because of its color) along the cliffs above the Colorado River at the southern edge of the Piceance Creek basin has been utilized to study mining and retorting processes. In this Colorado basin, continuous sections of shale several hundred feet thick occur. Oil-yield assays average more than 25 gal/ton.: In Utah and Wyoming the sections of rich shale are not so thick, and in Wyoming they are often interspersed with alternating beds of lean shale. Mineralogically, the oil shales vary in composition from rocks composed of illite clay to those containing dawsonite, nahcolite, and potash feldspar as the principal minerals or to those made up of calcite and principal minerals or to those made up of calcite and dolomite. The minerals often occur as small crystals. When the organic material is present in significant quantity, it seems to be the cementing agent that holds the rock together, so that removal of the organic material from a rich shale leaves a residue with little structural stability. A typical oil shale from the stratum called the Mahogany zone in Utah and Colorado has the following composition: Organic matter, percent of shale: 13.9 Elemental composition, weight percent Carbon 80.5 Hydrogen 10.3 Nitrogen 2.4 Sulfur 1.0 Oxygen 5.8.