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Dispersive and directional electrical conductivity and dielectric permittivity of conductive-mineral-bearing samples derived from multifrequency tensor electromagnetic induction measurements

Siddharth Misra, Carlos Torres-Verdin, Dean Homan and John Rasmus
Dispersive and directional electrical conductivity and dielectric permittivity of conductive-mineral-bearing samples derived from multifrequency tensor electromagnetic induction measurements
Geophysics (July 2017) 82 (4): D211-D223

Abstract

Organic-rich mudrocks, hydrocarbon-bearing conventional formations, and source rocks generally contain pyrite, rutile, graphite, graphitic precursors, and other electrically conductive minerals in the form of veins, laminations, flakes, and grains. Under redox-inactive subsurface conditions, when an external electromagnetic (EM) field is applied to geomaterials containing conductive mineral inclusions, ions in pore-filling brine and charge carriers (electrons and holes) in electrically conductive mineral inclusions migrate, accumulate/deplete, and diffuse around impermeable host-inclusion interfaces. These EM-field-induced phenomena are referred to as perfectly polarized interfacial polarization (PPIP) phenomena, and they alter the effective electrical conductivity sigma (sub eff) and effective relative dielectric permittivity epsilon (sub r,eff) of geomaterials. In addition, the relaxation process associated with such polarization phenomena and the time required to fully develop and dissipate the EM-field-induced polarization gives rise to frequency dispersion of sigma (sub eff) and epsilon (sub r,eff) of geomaterials containing conductive mineral inclusions. A laboratory-based EM apparatus, referred to as a whole-core EM induction tool, was used to measure the directional, multifrequency EM response of brine-saturated 4 in diameter (10.16 cm diameter), 2 ft long (0.61 m long), glass-bead packs containing uniformly distributed pyrite and graphite inclusions. We then implemented a semianalytic (SA) EM forward model, referred to as the SA model, to compute the sigma (sub eff) and epsilon (sub r,eff) of these conductive-mineral-bearing glass-bead packs. The estimated sigma (sub eff) and epsilon (sub r,eff) of conductive-mineral-bearing packs exhibit directional and frequency dispersive characteristics, which can be explained using the theory of PPIP phenomena. Relative variations in sigma (sub eff) and epsilon (sub r,eff) due to frequency dispersion were as large as +50% and -80%, respectively, between the values estimated at 20 and 260 kHz. Computed values of epsilon (sub r,eff) of conductive-mineral-bearing packs were unusually large in the range of 10 (super 3) -10 (super 6) , whereas the corresponding values of sigma (sub eff) exhibited strong dependence on volume content, size, and metallic nature of conductive mineral inclusions, brine salinity, and frequency. Furthermore, packs containing uniformly distributed pyrite and graphite inclusions exhibited conductivity and permittivity anisotropy in the range of one to two.


ISSN: 0016-8033
EISSN: 1942-2156
Coden: GPYSA7
Serial Title: Geophysics
Serial Volume: 82
Serial Issue: 4
Title: Dispersive and directional electrical conductivity and dielectric permittivity of conductive-mineral-bearing samples derived from multifrequency tensor electromagnetic induction measurements
Affiliation: University of Oklahoma, Mewbourne School of Petroleum Engineering, Norman, OK, United States
Pages: D211-D223
Published: 201707
Text Language: English
Publisher: Society of Exploration Geophysicists, Tulsa, OK, United States
References: 27
Accession Number: 2017-077383
Categories: Applied geophysics
Document Type: Serial
Bibliographic Level: Analytic
Annotation: Includes appendices
Illustration Description: illus.
Secondary Affiliation: University of Texas at Austin, USA, United StatesSchlumberger Technology Corporation, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by Society of Exploration Geophysicists, Tulsa, OK, United States
Update Code: 201741
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