--> ABSTRACT: Nitrogen and Helium in Natural Gases: Identifying the Risk Factors from a Noble Gas Study of the Hugoton Panhandle Giant Gas Field, by Chris J. Ballentine and Barbara Sherwood Lollar; #90906(2001)

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Chris J. Ballentine1, Barbara Sherwood Lollar2

(1) IGMR, Zuerich, Switzerland
(2) University of Toronto, N/A

ABSTRACT: Nitrogen and Helium in Natural Gases: Identifying the Risk Factors from a Noble Gas Study of the Hugoton Panhandle Giant gas Field

The most abundant non-hydrocarbon gas within most sedimentary basins is nitrogen, with 10% of natural gases in the US containing >25% N2. Helium rich natural gases contain high nitrogen concentrations. Although the inverse is not true, this simply reflects the multiple nature of N2 sources within natural gases, which may include air dissolved in water, organic, inorganic and magmatic sources. Noble gases provide a way of unambiguously resolving these components and allows us to identify the transport mechanism from source to trap. The case type example is the Hugoton-Panhandle giant gas field with a N2 content averaging ~15% and He/N2 ratios ranging from ~0.025 in the Kansas Hugoton to ~0.05 in the Texas Panhandle. We present noble gas and nitrogen isotope results from 31 samples taken across a 350km north-south traverse across this field. 3He/N2 and 20Ne/N2 are used to rule out a magmatic or air source for this nitrogen. 4He is derived from the radioactivity in the crust. Simple mass balance requires this to be from a regional diffuse flux from the crystalline basement. In a plot of 4He/N2 vs. 20Ne/4He all data lie on a single mixing line between two nitrogen endmembers, one that has neither 4He nor 20Ne and a nitrogen component with a near constant 4He/20Ne/N2 value. The mixing between these endmember components is also reflected in the N2 isotopes, which vary between +10o/oo and +3o/oo respectively. 20Ne is an unambiguous tracer of groundwater involvement and shows that between 26-41% of the nitrogen in the gas field has been transported to the gas field in solution by the regional groundwater system.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado