Generation and Accumulation of Nitrogen-Rich Natural Gases in Deeply Buried Permian Reservoirs of Northern Germany

Gregor H. Neunzert, Ralf Littke, and Bernd M. Krooss

Natural gases rich in molecular nitrogen commonly occur in the major gas province of northern Germany. During the last years detailed geological and geochemical studies were performed in collaboration with the gas industry, in order to evaluate the origin of the nitrogen gas and to find tools, which allow explorationists to predict nitrogen/methane ratios for target structures in the deep subsurface. Major results of this investigation were that i) total gas generation potential exceeds the volume of potential gas structures by at least 2 orders of magnitude, ii) if the nitrogen generation potential is assumed to correspond to about one tenth of the methane generation potential, it will be sufficient to fill the available reservoir structures, iii) most nitrogen is genera ed at high temperatures, at which methane generation has ceased iiii) based on kinetic data derived from laboratory experiments the methane/nitrogen ratio of gas generated from coals was predicted.

The geochemical concepts and the kinetic data were tested along two 100 km long seismic lines in northern Germany, for which a detailed stratigraphic, lithologic, and tectonic interpretation was established. Comparisons of calculated and real methane/nitrogen ratios along the profiles provide a clue towards an understanding of the effective source rocks, the timing of gas accumulations, and the migration pathways.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California