--> Abstract: Isotope Study of Nitrogen in Carboniferous, Zechstein And Buntsandstein Reservoirs in Northwest Germany - The Role of Structural Inversion Combined With a Major Heat Event, by P. Gerling, E. Sohns, S. Brueckner-Roehling, G. Everlien, and E. Idiz; #90956 (1995).

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Abstract: Isotope Study of Nitrogen in Carboniferous, Zechstein And Buntsandstein Reservoirs in Northwest Germany - The Role of Structural Inversion Combined With a Major Heat Event

Peter Gerling, Eberhard Sohns, Simone Brueckner-Roehling, Georg Everlien, Erdem Idiz

More than 50% of the annual production of natural gas (ca. 20 × 109 m3) in Germany (1993) derives from Carboniferous, Zechstein and Buntsandstein deposits. Nitrogen contents of these gases vary from 1% to 74%, with ^dgr15N-values ranging from -2.7 ^pmil to +15.5 ^pmil. Based on geological and geochemical coincidences, two main groups of gases can be distinguished:

Nitrogen from gas fields with a continuous subsidence history can easily be explained by a generation either from Westphalian coal seams, or from marine precursors in Devonian through Zechstein sediments, or as a gas mixture from both sources. Such gases contain usually less than 10% of nitrogen with ^dgr15N-values > +4 ^pmil.

However, many gas deposits are influenced by an Upper Cretaceous structural inversion, accompanied by a large laccolithic intrusion. This event has lead to the loss of early formed and trapped gases. At the same time an extraordinary, short-time maturation of the source rocks has occurred. Hereafter accumulated nitrogen gases are characterized by ^dgr15N-values < +3 ^pmil. Although intrusion-related abiogenic nitrogen cannot totally be excluded, we assume that Westphalian coal measures are the precursors of this nitrogen. The variations in nitrogen isotopes in this area may be reflecting the release of nitrogen from different functional groups (pyridinic vs. pyrrolic).

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France