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The Laramie Energy Technology Center completed three in-situ oil-recovery experiments from tar sands at N.W. Asphalt Ridge, Utah. The 10-acre (4 ha.) tract is part of the Sohio Shale Oil Co. "D" tract located west of Vernal, in Uintah County. Asphalt Ridge, lying on the northern boundary of the Uinta basin, is a northwest-southeast-trending ridge. The area on the northwest is structurally a monocline dipping southwest. The 3.28 to 14.75 m thick experimental tar-sand zones are in the Rim Rock Sandstone Member of the Mesaverde Formation of Cretaceous age. The beds dip 28°SW, and overburden thicknesses range from 89 to 164 m. Two known faults, with throws up to 66 m, bound the tract.

Three experiments were performed at the tract on varying partial acreages from 1975 to 1980. Two combustion tests using reverse combustion and a combination reverse and forward combustion were completed in a tar-sand bed 3.28 to 3.93 m thick. Recovered oil and water for the experiments ranged from 65 to 580 bbl and 167 to 600 bbl, respectively. The third test used steam injection on a 14.75 m thick bed. Production was 1,150 bbl of oil and 6,250 bbl of water. Tar-sand analyses yielded the following range of data for the three tests: extracted porosity, 26.1 to 31.1%; absolute air permeability, 651 to 2,175 md; oil saturation, 62 to 75% pore volume; water saturation, 2.4 to 7.9% pore volume. Various geologic controls can determine the effectiveness of the extraction process. These inclu e the dip of the beds, reservoir thickness, water and oil saturation, porosity, permeability, vertical and horizontal continuity of section, confinement of zone, and potential fractures and faulting in area.

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