Complex Electrical Permittivity of Shale as a Function of Frequency

by
Paulus Suryono Adisoemarta, M.S.E.

University of Texas at Austin, 1995
Supervisors: Dr. Steven L. Morriss
Augusto L. Podio

The objective of this study is to analyze the change in complex electrical permittivity of shale as a function of water content. An experimental research program has been initiated to investigate the electrical properties of swelling shales, shales that have been exposed to water and are therefore expanding, across a wide frequency range, 5 Hz to 1.3 GHz. This range spans the spectrum of the commonly used downhole logging measurements, from the deep laterologs to the microwave dielectric tools. Two distinct measurement techniques have been utilized to span the range: two-electrode with balanced bridge for the low frequencies, and open-ended coaxial probe with network analyzer at the high end. The probe technique is simple to use, potentially enabling field measurements of complex permittivity to be taken, although some accuracy is sacrificed. The effects of swelling are most pronounced at the lowest frequencies. This investigation discovered a phenomenon of shale, that it will generate a direct electrical current under stress that has potential for a wellbore diagnostic tool. Also the best fluid for shale preservation was found to be Isopar M^tm, a mineral oil, saturated with deionized water.

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