title: Secondary migration and leakage of methane from a major tight-gas system.
abstract: Tight-gas and shale-gas systems can undergo significant depressurization during basin uplift and erosion of overburden due primarily to the natural leakage of hydrocarbon fluids. To date, geologic factors governing hydrocarbon leakage from such systems are poorly documented and understood. Here we show, in a study of produced natural gas from 1,907 petroleum wells drilled into a Triassic tight-gas system in western Canada, that hydrocarbon fluid loss is focused along distinct curvilinear pathways controlled by stratigraphic trends with superior matrix permeability and likely also structural trends with enhanced fracture permeability. Natural gas along these pathways is preferentially enriched in methane because of selective secondary migration and phase separation processes. The leakage and secondary migration of thermogenic methane to surficial strata is part of an ongoing carbon cycle in which organic carbon in the deep sedimentary basin transforms into methane, and ultimately reaches the near-surface groundwater and atmosphere.
authors.affiliation: Encana Corporation, 500 Centre Street SE, Calgary, Alberta, Canada T2P 2S5.
authors.forename: James M
authors.initials: JM
authors.lastname: Wood
authors.affiliation: Geological Survey of Canada, 3303 33rd Street NW, Calgary, Alberta, Canada T2L 2A7.
authors.forename: Hamed
authors.initials: H
authors.lastname: Sanei