T92 Geology and Geochemistry of Carbon Dioxide, Helium, and Other Low-BTU Natural Gas Systems

Monday, 26 September 2016
8:00 AM - 12:00 PM
Room 506

GEOCHEMICAL AND NOBLE GAS INDICATORS OF THE ORIGIN OF CARBON DIOXIDE GAS ACCUMULATIONS IN THE GREATER PERMIAN BASIN

Paper number: T92-8
Program: Technical Sessions
Time: 9:35 AM – 9:50 AM

Authors

Abstract

The Permian Basin of west Texas and southeastern New Mexico has numerous Paleozoic natural gas reservoirs with high concentrations (> 5 mol%) of natural carbon dioxide (CO2). These high-CO2 gas fields are the focus of a U.S. Geological Survey research initiative on CO2-enhanced oil recovery, natural CO2 resources, and analogues for anthropogenic CO2 storage. To better understand the source of the CO2 in these reservoirs, compositional and isotopic analysis of free and dissolved gases, including noble gas isotopes, were conducted on gas samples collected from 23 producing petroleum wells located across a four-county area, as well as water and gas samples collected from hot springs located along the southwestern outer perimeter of the Permian Basin in the Rio Grande River valley.

Results indicate that CO2 concentration in the sampled reservoirs and hot springs ranges from 0.4 to 90.6 percent with the highest concentrations occurring in the southwestern basin near the Marathon-Ouachita Thrust Belt. Values of δ13C-CH4 (methane) for the gas reservoirs range from -43.5 to -35.3 ‰, while the hot spring values range from +16.3 to +24.3 ‰. These data suggest two active CH4 systems; CH4 in gas reservoirs is of thermogenic-organic origin whereas CH4 in hot springs is complex and may be partially magmatic (abiogenic) sourced. Values of δ13C-CO2 for all samples range from -10.3 to -1.96 ‰, with hot springs generally associated with more negative values of δ13C-CO2 than reservoir samples. 3He/4He ratios of collected gases and dissolved water samples range from 0.018 to 0.87 R/Ra (relative to 3He/4He ratio in air), indicating a mix of sources: crustal-sourced He (< 0.02 R/Ra) and associated CO2 for samples collected in more interior parts of the basin, and magmatic-sourced He (> 0.8 R/Ra) and CO2 in southwestern regions of the basin and at hot spring locations. The CO2/3He ratios are variable and range from 2.04 x 107 to 4.12 x 1010. These initial results and interpretations differ from previous studies, and suggest a complex mix of magmatic and crustal sources for the CO2 in the sampled areas. Likely sources of the magmatic gases may be related to post-Paleozoic volcanism and subsequent gas migration along deep-seated faults and lineaments.

Geological Society of America Abstracts with Programs. Vol. 48, No. 7

doi: 10.1130/abs/2016AM-285650

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