High Nitrogen Gas Wells - A Mid-Continent Mystery

Robert Ehinger1

¹ Consultant

High-Nitrogen gas wells (> 10 mole % N2) occur sporadically throughout the Mid-Continent and are a bane to explorationists. In many cases the high nitrogen content makes these wells non-commercial. These isolated, high-nitrogen wells occur at relatively shallow depths (<6000’), may be associated with red beds, structurally positive areas (arches), and/or deep, through-going fault systems. This talk will explore several possible origins for these wells. One group of these high-nitrogen wells is particularly intriguing as their BTU content is higher than expected, due to the presence of higher values of C2 through C5+. One specific example is a well from Noble County OK, which contained 53% mole percent N2, 38% methane (C1), 3.5% ethane (C2), 2% propane (C3), and 2.5% butane/pentane+ (C4-C5+). This well had a BTU content of 591! It is interesting to note that high nitrogen gases are not reported from coal bed methane wells or from wells in the horizontal shale plays. These plugged and abandoned high-nitrogen wells can be alluring to the unwary geologist as they will show good “gas effect” on the neutron/density logs, acceptable porosity and resistivity values, reasonable initial bottom hole pressures, and encouraging initial flow tests, but no production history! The same formation may be highly productive a few miles away. Without the gas analyses, one may be lured into using the “should have been a productive well” as the basis for part of a prospect play!

AAPG Search and Discover Article #90097 © 2009 Tulsa Geological Society, Tulsa, Oklahoma

 

 

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