Elastic and Petrophysical Properties of Shales

Abstract

Although shales comprise a large proportion of the sedimentary pile in many hydrocarbon-rich regions, their behaviour is not well understood from basin scales right down to the microscopic physics of particle interactions. Shale properties impact significantly on exploration, development and production costs through the effect of seismic anisotropy on imaging and depth conversion, the role of shales in 4D seismic response, in addition to associated issues such as pore pressure prediction and prediction of dynamic Poisson?s ratio. Tests were performed on shales from the North Sea and Officer Basins with a view to measuring their petrophysical and ultrasonic properties. Ultrasonic tests were carried out to evaluate the full elastic tensor and its variation with stress. Variability in dielectric properties could be explained from fabric studies using both SEM and CT scanning. Ultrasonic tests evaluating the full elastic tensor on single shale core plugs show smooth responses in terms of velocity, elastic coefficients and anisotropy over a large stress range and are interpretable in terms of composition and the orientation of micro-fabric anisotropy with respect to stress anisotropy.