P. C. Lysne, J. S. Yu, C. N. Vittitoe and L. E. Duda
Sandia National Laboratories
P. C. Reardon
Science Applications, Inc.
ABSTRACT
Two processes involved in dielectric log interpretation are considered in this investigation: the inversion of probe responses to obtain dielectric data and the subsequent conversion of these
data into hydrocarbon production information.
First consider the class of dielectric probes which consists of transmitter and receiver coils located along the borehole axis. The investigated problem assumes the coils and the earth to be symmetric about the borehole. Variable quantities include coil, hole and invasion zone radii, coil separations and the electrical properties of all zones. Two codes, based on analytic and on finite-difference techniques, have been developed to calculate the open circuit voltage induced in the receiver coils. These forward solutions generated a set of charts that predict the probe response for various formation parameters. In simple cases, these charts are sufficient to evaluate the formation dielectric properties from measured probe responses. However, if the formation is complicated the inversion charts may not be adequate and other inversion techniques need to be investigated.
Next consider the dielectric properties of a reservoir rock. The bulk dielectric properties of an insulator containing conducting inclusions depends upon the shape of the inclusions. Thus, the geometry assumed by the water within the pore structure is important. we have followed Sillars’ model of an inhomogeneous material by assuming that the water geometries may be approximated as an assemblage of spheroids with different orientations and aspect ratios. While simplistic, this model provides a method of calculating pore shapes from multiple frequency data. Permeability and rock wettability information may be contained in these geometric data.