Formation of
Nitrogen-rich Accumulations in the Central
European
Basin. II: Fluid
Evolution and Migration
Lüders, Volker1,
Peer Hoth2, Birgit Plessen3, David A. Banks4
(1) GeoForschungsZentrum Potsdam, Potsdam, Germany
(2) Bundesanstalt für Geowissenschaften und Rohstoffe,
Berlin, Germany (3) GeoForschungsZenrum Potsdam,
Potsdam, Germany (4) School of Earth Sciences, University of Leeds, Leeds,
United Kingdom
Fluid inclusions in diagenetically
formed minerals and in fissure minerals from wells that have penetrated into
Paleozoic strata have been studied in order to reconstruct the thermal history
through time within the North German Basin. Locally, early
hydrothermal activity is related to the intrusion of Permian volcanic rocks.
The subsequent main stage of subsidence is characterized by the migration of
H2O-NaCl±KCl brines and CH4-CO2-rich gases. During further burial the fluid
system evolved to a H2O-CaCl2-NaCl type fluid by intensive interaction of the
brines with Paleozoic rocks as indicated by newly-formed illites
in Carboniferous shales, light 34 values of
fissure anhydrite (oxidation and redeposition of
biogenic sulfur), local dissolution of halite, and highly variable cation ratios of fluid inclusions hosted in fissure
minerals. Further main stages of fluid migration can be related to stages of
extension (Triassic-Jurassic) and the main stage of basin inversion at late
Cretaceous/Tertiary times. Inversional tectonics also
let to the migration of distinctly different composed gases in various parts of
the basin. In the western part of the North German Basin the migration of
almost CH4-rich gases let to the accumulation of high-quality gas fields
whereas in the eastern part of the basin N2-rich gases where trapped under
low-pressure (i.e., hydrostatic) pressure conditions. The origin of N2-rich
gases is assumed to be derived by water/rock interaction of brines with
Carboniferous shales and connected release of fixed
ammonia from the sedimentary rocks.
Print this page