ACCESSING THE SOURCES, MIGRATION AND COMPOSITIONAL VARIABILITY OF NATURAL GAS IN THE TEXAS PANHANDLE FIELD - A NOBLE GAS STUDY

The Panhandle-Hugoton field in Texas-Oklahoma-Kansas is the largest conventional gas field in North America and also a primary commercial helium producer in the world. Despite years of exploitation, many aspects of the field require clarification. These include the sources of helium and extremely subnormal reservoir pressures. In this study, twelve natural gas samples were collected from twelve production wells in the Texas Panhandle for the analysis of the complete set of stable noble gases (He, Ne, Ar, Kr and Xe) to investigate the composition, source and migration of natural gas within the reservoir. These twelve wells belong to two groups, with six wells located in Potter County on the west side of the study area, and the six others in Gray County, to the east.

Results show that in all samples, over 99.9% of the ⁴He is crustally produced. Samples collected from the west side display higher R/Ra ratios of 0.10-0.11 (where R is the measured ³He/⁴He ratio and Ra is the atmospheric ratio) compared to those in the east side, with R/Ra ratios between 0.03-0.04. Crustal production of ²¹Ne, ⁴⁰Ar and ¹³⁶Xe are also significant as evidenced by ²¹Ne/²²Ne, ⁴⁰Ar/³⁶Ar and ¹³⁶Xe/¹³⁰Xe ratios of up to 0.046, 1481.8 and 2.223 respectively. Samples located in Potter County, to the west, display significantly higher crustal ⁴He*, ²¹Ne*, ⁴⁰Ar and ¹³⁶Xe* volume fractions, compared to those in Gray County to the east, with values up to 4.8×10^-3, 2.4×10^-10, 6.4×10^-4 and 1.4×10^-11, respectively. A small mantle Ne component is also present.

A strong positive correlation is observed between CH₄ and crustal ⁴He* and ²¹Ne* in samples located in Potter County, possibly suggesting a common origin and transport of both CH₄ and radiogenic noble gases. No correlation between noble gases and CH₄ is observed in Gray County. The origin of noble gases in the Texas Panhandle field, as well as the reasons behind the significantly different noble gas signatures in the two groups remain unclear at this time. It may be related either to gases originating from different formations or with different levels of interaction between groundwater and these natural gas reservoirs, or both. Further analysis and additional sampling will be required to characterize the various behaviors within the reservoirs.