Ground-water flow and migration of hydrocarbons to the Lower Permian White Rim Sandstone, Tar Sand Triangle, southeastern Utah

The Lower Permian White Rim Sandstone in the Tar Sand Triangle of southeastern Utah contains an estimated 12.5-16 billion barrels of heavy oil. Despite the large size of the deposit, the source of its oil is unknown. This paper systematically discusses source rocks for this petroleum from the standpoint of hydrocarbon abundance and maturity and ground-water flow history. Ground-water flow through the White Rim Sandstone was governed by six periods, each characterized by distinct paleotopographic conditions and directions of horizontal flow. Analysis of the transmissivity and thickness of the hydrostratigraphic units indicates that flow was mainly horizontal and had no major vertical component. Long-range transport of petroleum through Pennsylvanian and Permian sandstone aquifers that were hydrologically continuous with the White Rim was possible until Late Cretaceous to Paleocene Sevier thrusting. After thrusting, long-range migration would have been impeded or diverted by the thrust faults. Ten potential source-rock units are identified in the area. Some are unfavorable because they lack sufficient organic matter to account for the hydrocarbons in the Tar Sand Triangle. Others, particularly those in northern Utah, are unfavorable because ground water never flowed in the required direction. Sources to the southwest and southeast are hydrologically favorable. The Paradox Formation of the Hermosa Group is hydrologically favorable, but the pattern of bleaching of the Cutler Group redbeds and the eastward thinning of the White Rim are unfavorable. The Chainman Shale and other formations in Nevada are consistent with east- and northeast-flowing ground water, but migration across the thrust belt is problematic. The most likely source is the Late Proterozoic Chuar Group in west-central Utah. It is compatible with eastward and northeastward ground-water flow, with bleaching of the Permian aquifers, and with continuous sandstone aquifers east of the thrust belt, and it probably has sufficient mature organic matter to account for the oil in the Tar Sand Triangle.