Abstract

The relationship between low-frequency electrical properties and hydraulic permeability of rocks has been the focus of geophysical investigations for a long time because it offers a possibility for an in situ and noninvasive permeability estimation of rocks. We examined the hydraulic and low-frequency (10mHzto100Hz) electrical properties as well as the anisotropic properties of low-permeability sandstones from a tight gas reservoir. Single-frequency electrical properties were found to be of low value for the determination of permeability for the studied samples, whereas a strong link between the spectral-induced polarization (SIP) response and permeability was found. The SIP response was transformed into a relaxation-time distribution using a Debye decomposition procedure. We observed a strong positive correlation in form of a power law between median relaxation time of the distribution and permeability, suggesting that relaxation time is a good measure of the effective hydraulic length scale. From a comparison of our results with published relationships between relaxation time and permeability, it becomes evident that the corresponding function is formation specific, requiring a separate calibration for each formation. Nevertheless, SIP offers a high potential for in situ permeability determination because estimation of permeability from relaxation time seems to be applicable for very different lithologies.

You do not currently have access to this article.