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The Helium System: A Modification of the Petroleum System for Inert Gases


Helium is a naturally occurring inert gas commonly associated with oil and gas accumulations. Although it generally constitutes less than two percent of the total gas stream, its occurrence within specific stratigraphic intervals and geographic areas can shed light on gas migration pathways within a basin. Moreover, the recent rise in helium prices and contemporaneous drop in oil and gas commodities has piqued commercial interests where oil and gas infrastructure, insight, and expertise is readily available. Most petroleum explorationists are not familiar with helium exploration; however, a widespread and common method may be easily modified for our purposes: the petroleum system. The petroleum system concept has been used successfully for decades to high-grade plays and de-risk oil and gas prospects around the world. We propose a modification of the petroleum system approach to aid exploration for helium resources and other inert gases. In order to provide a proof-of-concept, a case study was undertaken in the Uinta basin of eastern Utah and Piceance basins of northwestern Colorado. These basins produce nearly three percent of the total natural gas in the United States and also contribute appreciable amounts of helium from various geologic formations. Like a petroleum system, the helium system is identified by its source rock, reservoir, trap, seal, and migration pathway. Two helium systems are identified and tentatively called the Uncompahgre and Uinta systems; named after their interpreted source rock intervals. The helium gas, as well as nitrogen and carbon dioxide, are believed to migrate through basinal brine systems until trapped in conventional petroleum traps. These gases are found primarily in the Entrada, Morrison, Dakota, Frontier, and Prairie Canyon Member of the Mancos formations. The Mancos Shale provides a basin-wide seal for both helium systems and prevents significant leakage to the younger Mesaverde, Wasatch, and Green River gas-productive intervals. We used common risk segment (CRS) approach and mapped areas of low, moderate, or high risk for the occurrence of pools with significant helium content.