Siddharth Misra, University of Oklahoma
Improved Estimation of Water Saturation in Clay- and Pyrite-Bearing Formations
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 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 phenomena.
The effects of interfacial polarization of conductive minerals the effective conductivity and effective permittivity was studied using a non-contact and non-invasive, laboratory-based EM induction apparatus. EM response of brine-filled pyrite- and graphite-bearing glass-bead packs were measured at multiple frequencies in the range of 10 kHz to 300 kHz. At an operating frequency of 59 kHz, the estimated values of effective relative permittivity of samples containing uniformly distributed pyrite and graphite inclusions were 104 and 105, respectively. At the same operating frequency, samples containing 1.5-vol% of graphite and pyrite inclusions exhibited effective conductivity values that were 200% and 90%, respectively, of the host conductivity. The estimates of effective conductivity and permittivity of the samples also exhibited significant frequency dispersion in the range of 10 kHz to 300 kHz.
True conductivity and true permittivity of hydrocarbon-bearing host medium, which free from the effects of clay minerals, clay-sized particles, and conductive minerals, can be determined by processing the estimated effective conductivity and permittivity of the geological mixtures (formation) using a newly developed electrochemical model, referred to as the PS model. The developed model quantifies the effective directional electrical conductivity and dielectric permittivity of geomaterials containing electrically conductive mineral inclusions, such as pyrite and magnetite, that are uniformly distributed in a fluid-filled, porous matrix made of non-conductive grains, such as silica, clay-sized particles, and clay minerals,that possess surface conductance. The PS model predictions successfully reproduced several laboratory measurements of multi-frequency complex electrical conductivity of mixtures in the frequency range of 100 Hz to 10 MHz.
The PS model predicts that the low-frequency effective electrical conductivity of geomaterials containing 5% volume fraction of disseminated conductive inclusions will vary in the range of 70% to 200% of the host conductivity for operating frequencies between 100 Hz to 100 kHz, where as its high-frequency effective relative permittivity will vary in the range of 190% to 90% of the host relative permittivity for operating frequencies between 100 kHz and 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. Two sets of recently published logs show that conventional interpretation of a single frequency EM measurement in mudrock and shale formations, containing clays and conductive minerals, doesn’t lead to accurate water saturation estimation due to frequency dispersion and polarization effects. A joint interpretation of EM induction, EM propagation, and dielectric dispersion logs generated the true conductivity and true permittivity that was then interpreted using conventional interpretation techniques to obtain accurate water saturation.
Siddharth Misra is Assistant Professor in Mewbourne School of Petroleum and Geological Engineering. He holds a 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 experimental apparatus to measure 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 resistivity and dielectric permittivity interpretation in formations containing clays, inclusions, and conductive minerals.
October2015 Technical Lunch
Tuesday, October 13, 2015
11:30 AM Lunch, 12:00 PM Talk
2nd floor, King Kolsch Room
1 North Oklahoma Ave.
Oklahoma City, OK 73104
Before 10 AM, Monday, October 12
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