Application of Noble Gases to Understanding Migration and Filling History in Large Tight Gas Sand Reservoirs, Rocky Mountains, U.S.A

We have applied noble gas geochemistry to three large tight gas sandstone reservoirs in the Rocky Mountains: Jonah Field, Green River Basin; Greater Natural Buttes, Uinta Basin; and the Mamm Creek-Rulison-Parachute-Grand Valley complex, Piceance Basin, Colorado. Production in these fields is from Upper Cretaceous discontinuous fluvial sandstones that interfinger with overbank siltstones and mudstones. Although these reservoirs comprise a major natural gas resource, the migration processes by which gas fills these reservoirs and the extent to which these reservoirs are compartmentalized are largely unknown. Noble gases have been proven to be a powerful tool in the study of natural gas origin, migration and filling in conventional reservoirs, where gases from the atmosphere can be distinguished from crustal and volcanic sources.

In the tight gas sandstone fields, various isotope ratios (3He/4He, 4He/20Ne, 20Ne/22Ne, 21Ne/22Ne, 40Ar/36Ar, 38Ar/36Ar, 20Ne/36Ar) indicate noble gas contributions from both crustal and atmospheric sources, with additional complexities introduced by diffusion and gas stripping from water. Although the samples come from different basins, both the air-derived and crustal radiogenic noble gas data ranges overlap, pointing to similar processes operating in all systems. In detail, the Piceance basin data appear to show consistent changes in air-derived composition gases related to in-reservoir faults, suggesting measurable control of water contact with the gas exerted by the fault system.

Although we are at an early stage in investigating this complex data set, developing a model that describes gas/water phase relationships will enable us to quantify the volume of water involved in the gas emplacement process, reservoir compartmentalization, identify spatial relationships with groundwater systems and fluid residence time.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California