Petrophysical Interpretation of Electromagnetic Measurements in Clay and Pyrite Bearing Formations
Speaker: Siddharth Misra, University of Oklahoma
Date: April 20, 2016
Meeting: 11:30AM – 12:30PM
Location: Crown Plaza - Downtown
1700 Smith Street, Houston, TX 77002
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Abstract: Subsurface electromagnetic (EM) measurements, namely galvanic resistivity, EM induction, EM propagation, and dielectric dispersion measurements, in shaly sands, sand-shale laminations, conductive-mineral-rich shales, and organic-rich mudrocks exhibit directional and frequency dispersive characteristics, primarily due to the effects of electrical conductivity anisotropy and interfacial polarization phenomena. Existing petrophysical interpretation techniques for laboratory and subsurface EM measurements do not account for the effects of dielectric permittivity, dielectric dispersion, and dielectric permittivity anisotropy arising from the interfacial polarization of clay minerals, clay-sized particles, and conductive minerals.
A non-contact and non-invasive, laboratory-based EM induction apparatus was developed and employed to study the effects of interfacial polarization of conductive minerals on the effective conductivity and permittivity. A newly developed electrochemical model, referred to as the PS model, processed the measured effective EM properties of geological formations to estimate the true conductivity and permittivity of hydrocarbon-bearing host media free from the effects of clay minerals, clay-sized particles, and conductive minerals. The PS model predictions successfully reproduced several laboratory measurements of multi-frequency complex electrical conductivity of fluid-saturated mixtures in the frequency range of 100 Hz to 10 MHz. The model indicates high sensitivity of subsurface EM measurements to the electrical properties, shape, volumetric concentration, and size of the inclusion phase, and to the conductivity of pore-filling electrolyte.
A recently published well log shows that the conventional interpretation of a single frequency EM measurement in pyrite-bearing mudrock and shale formations, containing clays and conductive minerals, doesn’t lead to accurate water saturation values due to the effects of frequency dispersion and interfacial polarization. However, a joint interpretation of EM induction, EM propagation, and dielectric dispersion logs generated the true conductivity and true permittivity, which can then be interpreted using conventional interpretation techniques to obtain improved water saturation estimates.
Biography: Siddharth Misra is Assistant Professor in Mewbourne School of Petroleum and Geological Engineering. He holds Ph.D. and M.S.E. in Petroleum Engineering from the University of Texas at Austin. Dr. Misra completed his B.Tech. degree in Electrical Engineering from the Indian Institute of Technology Bombay, India. From 2007 to 2010, he worked for Halliburton Energy Services as a Wireline Field Engineer. In his doctoral research, Dr. Misra collaborated with Schlumberger to develop a multi-frequency inductive conductivity tensor apparatus to estimate the electromagnetic properties of geological whole core samples. Using that laboratory apparatus, he investigated the effects of pyrite and graphite on electromagnetic induction measurements. He also developed a wideband mechanistic model for electrical conductivity and dielectric permittivity interpretation in formations containing clays, inclusions, and conductive minerals.