P. R. spring oil-impregnated sandstone deposit Uintah and Grand Counties, Utah

Oil-impregnated sandstone beds underlie at least 214 square miles in the southeastern Uinta Basin and may extend northward beneath cover. One to as many as five principal saturated zones, 3 to 75 feet thick, occur in a 250-foot interval that dips gently northward. The northernmost outcrops are overlain by 250 feet of overburden. Average porosity obtained from 33 outcrop samples is 30.5 percent, and from four core holes drilled by Skyline Oil Co., 2 6.6 percent. Calculations by triangle method indicate approximately 3,700, 000, 000 barrels of oil in place. Oil impregnation occurs in lenticular sandstone and siltstone in the uppermost Douglas Creek member of the Green River Formation 600 feet above the base. The top of the oil-impregnated zone is a few to 50 feet below the oil shale zone in the overlying Parachute Creek member. These lenticular sandstones and siltstones were deposited around the periphery of the basin in a fluvial-deltaic environment. Mesozoic rocks at depth are draped over displacements on normal fault blocks in the Precambrian basement rocks of the Uncompahgre uplift. These folds, weakly reflected in the beds of the Green River Formation at the surface, have funneled the bituminous saturation to the area around P.R. Spring where it seeps onto the surface. A Fortran IV computer program for cross-association of nonnumeric sequences was used to help correlate the lenticular stratigraphy in the study area. The program was used to find similarities, deletions, insertions, or inversions difficult to detect by visual methods. Cross sections illustrate the lenticular nature of the sands and facies changes in the upper Douglas Creek member.