Variable Characteristics of the Oil in the Tensleep Sandstone Reservoir, Elk Basin Field, Wyoming and Montana

Abstract

Abstract In the spring of 1943, when it was evident that the Tensleep sandstone inthe Elk Basin Field, Wyoming and Montana, held a large reserve of petroleum, Bureau of Mines engineers obtained samples of oil from the bottom of nine wellsand analyzed them for such physical characteristics as the volumes of gas insolution, saturation pressures or bubble points, shrinkage in volume caused bythe release of gas from solution, expansion of the oil with decrease inpressure, and other related properties. The composition of the gas in solutionin the oil was studied. The pressures and temperatures existing in thereservoir and the productivity characteristics of the oil wells weredetermined. The data obtained indicate that the oil in the Tensleep Reservoir of the ElkBasin Field has unusually varying physical characteristics, such as asaturation pressure of 1,250 psia and 490 cu ft of gas in solution in a barrelof oil at the crest of the structure and a saturation pressure of 530 psia and134 cu ft of gas in solution in a barrel of oil low on the flanks. The hydrogensulfide content of the gas in solution in the oil varies from 18 per cent foroil on the crest to 5 per cent for oil low on the flanks of the structure. Ofeven greater significance is the fact that these and other variablecharacteristics of the reservoir oil are related to the position of the oil inthe structure. Many geologists and petroleum engineers have considered that allthe oil in a petroleum reservoir has rather uniform physical characteristicsand that equilibrium conditions prevailed in all underground accumulations ofoil and gas; that such is not always so is borne out by the results of thestudy by the writers. T.P. 3018