LETC tar sand research - North Asphalt Ridge

This report describes work done by the United States Department of Energy's Laramie Energy Technology Center (LETC) from 1971 through 1982 to develop technology for future recovery of U.S. tar sands. The objectives of the program are: 1. To determine the feasibility of in situ recovery methods applied to tar sand. 2. To establish a system for classifying tar sand deposits relative to those characteristics that would affect the design and operation of in situ recovery processes. Work was centered on the major U.S. tar sand deposits, which are found in Utah. Most of the world's supply of tar sand is found in the Western Hamisphere. Deposits in Venezuela and Columbia are estimated to exceed 1 trillion barrels. Canadian deposits are estimated at 967 billion barrels in Alberta. The U.S. tar sand deposits are estimated at over 36 billion barrels, with 25 billion barrels in Utah. Estimates have been made that 10% of the U.S. tar sand can be recovered by surface mining and 90% will entail the use of in situ processes for recovery. Early work at LETC centered on the characterization of Utah tar sand. Tar sands are bitumen bearing rock with an in-place viscosity of the benzene soluble bitumen exceeding 10,000 centipoises at reservoir temperature. Athabasca tar sand is a water wetted sand which is amenable to water based extraction processes, while many U.S. tar sand deposits are oil wetted sand which require different approaches to recovery. The U.S. tar sand typically contains 5 to 10 weight % bitumen. Uinta Basin bitumen, with less than 1% sulfur, is low in sulfur content compared to Athabasca and other U.S. bitumens. The heavy oil recovered from tar sand presents a difficult challenge in refining. Laboratory work was conducted to gain insight into the reduction of viscosity necessary for recovery of bitumen from Utah tar sand. These experiments showed that reverse combustion could be used to open and heat a flow path from a well bore into a tar sand deposit. Air flux rates necessary to sustain combustion were determined and oil yields were shown to be encouraging. A mathematical model of the reverse combustion process was developed and was used to design field experiments. Later laboratory work was conducted with steam injection into Utah tar sand. This work showed that the mechanisms associated with a hot water flood are part of the steam drive recovery mechanism. Steam drive recovery of oil was also shown to have the added advantage of a solvent extraction mechanism working to increase the recovery of oil over that which would be expected from a hot water flood. This work, combined with a steam drive simulator, was used to design and operate a field experiment described in this report.