Physical Reservoir Models : From Pictures to Properties

Petrophysics and Geophysics have not always worked in the past as closely together as one might expect. This paper discusses current advances, and sketches future developments. The major objective of Geophysical Research was to obtain sharper pictures. With the advent of 3-D seismic, there is a strong trend to make displays both in time and depth, and to convert seismic attributes into rock properties. Conversions based on seismic data alone give nonunique results. Further progress hinges on calibration of acoustic attributes with parameters measured on cores. For time lapse seismic, the situation is even more complicated, due changing effects of temperature, pressure, and compaction. All these effects have to be properly quantified if we want to couple 4-D seismic interpretations to dynamic reservoir models and realize the situation where all geoscientists work on one “unified” 3-D earth model. Biot Gassman fluid substitution algorithms were successfully applied for decades, but suffer like all mixing laws from non-uniqueness. Recent investigations demonstrate that dispersion in the low frequency band could have strong implications on seismic attribute analysis. Further experimental work is warranted to find out which relations measured at high frequencies can be used for seismic, and which require additional laboratory work. The shock-tube is well suited for this task, because it handles large rock samples, and obtains acoustic responses down to a few hundred Hz.