NEUNZERT, GREGOR H.¹, RALF LITTKE^2, and DIETRICH H. WELTE^3
1RWE-DEA AG, Hamburg, Germany
²Aachen University of Technology, Aachen, Germany
³Integrated Exploration Systems GmbH, Juelich, Germany

Abstract: Gas Potential below Salt Domes in Overcooked Regions

In the Northwest German Rotliegend Gas Play Area a 2D basin modelling study was performed. According to our seismic interpretations, the subsidence of the Basin can be subdivided into four major phases: During Phase I, the Upper Carboniferous source rocks were deposited. Phase II (Rotliegend) was an interval of enhanced heat flow and significant tectonic motions. During Phase III (Cretaceous), subsidence of the basin was renewed after a period of erosion. During Tertiary (Phase IV) the strata reached their deepest burial and were exposed to maximum temperatures.

Based on this geological model the 2D simulation of the methane and nitrogen generation, migration and accumulation was performed. Nitrogen is generated from organic matter at very high temperatures, when almost no potential for methane generation is left. Methane is still generated at the basin edges. In the basin center only potential for nitrogen is left.

Beneath salt domes temperatures are significantly lowered. This is caused by the enhanced heat conductivity of evaporites compared to other rocks. To quantify this effect, the dynamic evolution of a salt dome, situated in the basin center, was reconstructed. It can be shown that underneath the salt dome the temperatures were lowered by more than 10°C. Therefore below the salt structure an additional potential of methane generation of up to 44 billion m³ CH₄ may be left. In neighbouring regions no potential for methane is left and only nitrogen can be generated.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas