Relationship Between Seismic Signals and Reservoir Properties of Tight Gas Reservoirs in Northwest Germany (Permian Rotliegend Sandstones)

Abram, Peter, Reinhard Gaupp, Friedrich-Schiller-University, Jena, Germany

Tight Gas Reservoirs in Northwest-Germany consist of aeolian and lacustrine sand­stones in 3,5-5 km depth with moderate porosities but strongly varying permeabilities. Samples of comparable lithology with 10% porosity provide permeabilities in the range of 0,05-100 mD due to different mechanical compaction, mineral authigenesis and cement dis­solution. These processes resulted in good and poor reservoir qualities in proximate areas. Therefore deep gas exploration is highly dependent on reservoir property information from 3D-seismic signals. In this study geophysical, petrophysical and petrological data are gained and evaluated to investigate the potential calibration of 3D-seismic signals with core and log data.

The relations between seismic and lithological properties have been investigated by tri­axial measurements of travel times, image analysis of thin sections, NMR-measurements, Scanning Acoustic Microscopy and mercury-injection to derive pore parameters (e.g. aspect-ratio), compiling sedimentological features (e.g. sand-shale-interbeddings) and eval­uating the influence of different water saturations on seismic signals. Until now the non lin­ear behaviour of porosity and permeability, the clear relation between permeability and impedance and the correlation between impedance and cement types suggest a dependence of seismic signals and reservoir properties based on pore- and matrix geometries. These preliminary results correspond to pore parameters derived from image analysis of thins sec­tions and to pore radii distributions from capillary pressure curves and NMR-measure-ments. We intend to visualize impedance contrasts by means of synthetic seismograms rep­resenting the extreme cases of different permeabilities.