ABSTRACT: Potential Methane Resources in Nahcolitic Oil Shale: Green River Formation (Eocene), Piceance Creek Basin, Colorado

COLE, R. D., Unocal Corporation, Brea, CA, and G. J. DAUB, Daub and Associates, Grand Junction, CO

The saline zone of the Parachute Creek Member of the Green River Formation in the north-central Piceance Creek basin contains abundant methane plus associated carbon dioxide, nitrogen, and oxygen at depths ranging from 1400 to 1800 ft (427-549 m). This gas mixture occurs primarily in unfractured oil shale and nahcolitic oil shale, and within seams of nahcolite and halite. Gas-desorption tests (N = 274) of 2795 ft (852 m) of core from three closely spaced wells indicate gas concentrations ranging from near zero to 103.3 cubic feet/ton (3.2 cubic centimeters /g). The lower half of the saline zone, which is approximately 625 ft (191 m) thick, averages 43.8 cubic feet/ton (1.4 cubic centimeters /g), whereas the upper saline zone, which is about 475 ft (145 m) thick in the study area, aver ges about 25 cubic feet/ton (0.8 cubic centimeters /g). Analyses of gas samples indicate average CH4, CO2, N2, and O2 values of 77.2%, 17.3%, 4.3%, and 0.3%, respectively.

The gas-concentration data suggest that the lower saline zone has an estimated resource content of 80.3 million cubic feet/ac (561.5 million cubic centimeters /sq. meters), whereas the upper saline zone has a possible resource content of 34.5 million cubic feet/ac (241.3 million cubic centimeters /sq. meters). Using the known areal distribution of the saline zone, these resource values suggest that the lower saline zone may contain 4.5 tcf (1.3 x 1017 cubic centimeters ) of gas, whereas the upper saline zone may hold an additional 0.7 tcf (2.0 x 1016 cubic centimeters ).

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)