Diagenetic Mineral Reactions Influenced by Hydrocarbon Fluids: Evidence from Deeply Buried Red Bed Reservoirs of the Central European Basin System

Robert Schöner¹ and Reinhard Gaupp^2
1 Friedrich-Schiller-University Jena, 07749 Jena, Germany
² Friedrich-Schiller-University Jena, Jena, Germany

Red bed sandstones are important hydrocarbon reservoirs worldwide. Focussing on sedimentary facies types with high primary porosity and permeability, diagenetic processes are controlling reservoir properties during burial. Organic rich fluids, which may have positive and negative effects on reservoir properties, are omnipresent in areas where we prospect for oil and gas reservoirs. To evaluate the importance of organic maturation products during clastic diagenesis, we compared the diagenetic evolution of deeply buried Permian red bed sandstones from areas with and without hydraulic contact to hydrocarbon source rocks in the German part of the Central European Basin System. The comparative study of petrography, authigenic mineral chemistry, burial and thermal evolution of reservoir and source rocks suggests that major diagenetic processes are controlled or at least influenced by organic maturation products. Important diagenetic features are spatially related to the presence of maturing hydrocarbon source rocks: the bleaching of red beds, major dissolution events, pervasive illite formation, impregnation of pore surfaces with bitumen and formation of late Fe-rich cements. The spatial coincidence of these processes, their timing with respect to organic maturation and the presence of paleo oil (bitumen) suggests that they trace paleo hydrocarbon migration pathways. Cementation patterns can be strongly reorganized in areas affected by hydrocarbon fluids. Other deep basinal compartments, which are not in hydraulic contact to organic rich source rocks, often preserve relatively early burial cements. This study was financed by German Science Foundation (DFG). Core and data material was provided by ExxonMobil (EMPG) and Gaz de France.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005