Improving Petrophysical Interpretation With Wide-Band Electromagnetic Measurements
- Emmanuel Toumelin (Chevron North American E&P) | Carlos Torres-Verdin (U. of Texas at Austin) | Nicola Bona (Eni E&P)
- Document ID
- Society of Petroleum Engineers
- SPE Journal
- Publication Date
- June 2008
- Document Type
- Journal Paper
- 205 - 215
- 2008. Society of Petroleum Engineers
- 5.5.3 Scaling Methods, 4.3.1 Hydrates, 1.6.9 Coring, Fishing, 1.2.3 Rock properties, 5.6.1 Open hole/cased hole log analysis, 5.1 Reservoir Characterisation, 4.3.4 Scale
- 3 in the last 30 days
- 672 since 2007
- Show more detail
- View rights & permissions
|SPE Member Price:||USD 12.00|
|SPE Non-Member Price:||USD 35.00|
Because of their sensitivity to ionic content and surface texture, wide-band electromagnetic (WBEM) measurements of saturated rocks exhibit frequency dispersions of electrical conductivity and dielectric constant that are influenced by a variety of petrophysical properties. Factors as diverse as fluid saturation, porosity, pore morphology, thin wetting films, and electrically charged clays affect the WBEM response of rocks. Traditional dielectric mixing laws fail to quantitatively and practically integrate these factors to quantify petrophysical information from WBEM measurements. This paper advances a numerical proof of concept for useful petrophysical WBEM measurements. A comprehensive pore-scale numerical framework is introduced that incorporates explicit geometrical distributions of grains, fluids and clays constructed from core pictures, and that reproduces the WBEM saturated-rock response on the entire kHz-GHz frequency range. WBEM measurements are verified to be primarily sensitive (a) in the kHz range to clay amounts and wettability; (b) in the MHz range to pore morphology (i.e., connectivity and eccentricity), fluid distribution, salinity, and clay presence; and (c) in the GHz range to porosity, pore morphology and fluid saturation. Our simulations emphasize the need to measure dielectric dispersion in the entire frequency spectrum to capture the complexity of the different polarization effects. In particular, it is crucial to accurately quantify the phenomena occurring in the MHz range where pore connectivity effects are confounded with clay polarization and pore/grain shape effects usually considered in dielectric phenomena. These different sensitivities suggest a strong complementarity between WBEM and NMR measurements for improved assessments of pore-size distribution, hydraulic permeability, wettability, and fluid saturation.
A number of experimental and theoretical studies suggest the measurable sensitivity of WBEM to various petrophysical factors, including porosity, brine salinity, fluid saturation and wettability, clay content, surface roughness, and even pore surface-to-volume ratio. Given the complexity of the different phenomena under consideration, practical models are designed to fit measured dielectric dispersions to ad-hoc models whose parameters are marginally supported by quantitative petrophysical concepts.
Therefore, to assess whether accurate and reliable petrophysical interpretations are possible with WBEM measurements requires an analysis that (a) incorporates pore structure, pore connectivity, multiphase saturation and electrochemical effects; and (b) quantifies the contributions of each factor in the measured WBEM dispersions. However, extracting explicit petrophysical information from WBEM responses is a difficult task. Myers (1991), for instance, illustrated the non-uniqueness of WBEM measurements when a decrease of water saturation, porosity, or brine salinity yielded similar responses. Recent advances in NMR logging and interpretation (Freedman et al. 1990) can eliminate some of these ambiguities with adequate experimental conditions, and if rock wettability is known. Conversely, WBEM measurements could provide independent wettability assessment in the cases where NMR measurements alone reach their limits of sensitivity [for instance, the impact of fluid saturation history on wettability determination was studied by Toumelin et al. (2006)]. Likewise, the interpretation of NMR measurements can be biased by unaccounted rock morphology (Ramakrishnan et al. 1999) or by internal magnetic fields in shaly or iron-rich sands (Zhang et al. 2003), whereas WBEM measurements provide independent information on overall rock morphology. It is therefore timely to consider integrating both technologies for improving petrophysical analysis.
The objectives of this paper are twofold: (1) Review existing results on the extraction of petrophysical information from rock WBEM measurements, and (2) establish a proof of concept for the necessity to integrate electromagnetic measurements on the wide-frequency band from the kHz range to the GHz range, and study how WBEM techniques may yield petrophysical information unavailable from other in-situ measurements. To reach the second objective, we introduce a generalized pore-scale simulation framework that allows incorporating arbitrary rock morphology and multiphase fluid distribution.
|File Size||2 MB||Number of Pages||11|
Arns, C.H. et al. 2005. Pore-Scale Characterization ofCarbonates Using X-Ray Microtomography. SPEJ 10 (4): 475-484.SPE-90368-PA doi: 10.2118/90368-PA
Bona, N. et al. 1998. Characterization of rock wettability throughdielectric measurements. Revue de l'Institut Français du Pétrole53 (6): 771-783.
Cao, Q.-Z., Wong, P.-Z., and Schwartz, L.M. 1994. Numerical studies of theimpedance of blocking electrodes with fractal surfaces. Physical ReviewB 50 (8): 5771-5774. doi: 10.1103/PhysRevB.50.5771.
Chew, W.C. and Sen, P.N. 1982. Dielectric enhancement due toelectrochemical double layer: thin double layer approximation. J. ofChemical Physics 77 (9): 4683-4693. doi: 10.1063/1.444369.
DeLacey, E.H.B. and White, L.R. 1981. Dielectric response andconductivity of dilute suspensions of colloidal particles. J. of theChemical Society, Faraday Transactions 2 (77): 2007-2039. doi:10.1039/f29817702007.
Fixman, M. 1980. Chargedmacromolecule in external fields. I. The sphere. J. of ChemicalPhysics 72 (9): 5177-5186. doi: 10.1063/1.439753.
Freedman, R. et al. 1990. Wettability, Saturation, andViscosity From NMR Measurements. SPEJ 8 (4): 317-327.SPE-87340-PA doi: 10.2118/87340-PA
Glover, P.W.J., Meredith, P.G., Sammonds, P.R., and Murrell, S.A.F. 1994. Ionic surface electricalconductivity in sandstones. J. of Geophysical Research 99(B11): 21635-21650. doi: 10.1029/94JB01474.
Kanket, W., Suddhiprakarn, A., Kheoruenromne, I., and Gilkes, R.J. 2005. Chemical andcrystallographic properties of Kaolin from Ultisols in Thailand. Claysand Clay Minerals 53 (5): 478-489. doi:10.1346/CCMN.2005.0530505.
Kenyon, W.E. 1984. Textureeffects on megahertz dielectric properties of calcite rock samples. J.of Applied Physics 55 (8): 3153-3159. doi: 10.1063/1.333315.
Knight, R.J. and Nur, A. 1987. The dielectric constant ofsandstones, 60 kHz to 4 MHz. Geophysics 52 (5): 644-654. doi:10.1190/1.1442332.
Landau, L.D. and Lifschitz, E.M. 1960. Electrodynamics of continuousmedia. Oxford, UK: Pergamon Press.
Lesmes, D.P. and Frye, K.M. 2001. Influence of pore fluid chemistryon the complex conductivity and induced polarization responses of Bereasandstone. J. of Geophysical Research 106 (B3): 4079-4090.doi: 10.1029/2000JB900392.
Lima, O.A. and Sharma, M.M. 1992. A generalized Maxwell-Wagner theoryfor membrane polarization in shaly sands. Geophysics 57 (3):431-440. doi: 10.1190/1.1443257.
Milton, G.W., Eyre, D.J., and Mantese, J.V. 1997. Finite Frequency RangeKramers-Kronig Relations: Bounds on the Dispersion. Physical ReviewLetters 79 (16): 3062-3065. doi: 10.1103/PhysRevLett.79.3062.
Myers, M.T. 1991. A saturation interpretation model for the dielectricconstant of shaly sands. Paper 9118. SCA International Symposium, San Antonio,Texas, 21-22 August.
Myers, M.T. 1996. A pore geometry dispersion model for the dispersion of thedielectric constant. Paper 9626. SCA International Symposium, Montpellier,France, 8-10 September.
Olhoeft, G.R. 1985. Low-frequency electricalproperties. Geophysics 50 (12): 2492-2503. doi:10.1190/1.1441880.
Ramakrishnan, T.S., Schwartz, L.M., Fordham, E.J., Kenyon, W.E., andWilkinson, D.J. 1999. Forward models for nuclear magnetic resonance incarbonate rocks. The Log Analyst 40 (4): 260-270.
Seleznev, N., Habashy, T., Boyd, A., and Hizem, M. 2006. Formationproperties derived from a multi-frequency dielectric measurement. Paper VVV.SPWLA Annual Logging Symposium, Veracruz, Mexico, 4-7 June.
Sen, P.N. and Chew, W.C. 1983. The frequency dependent dielectric andconductivity response of sedimentary rocks. J. of Microwave Power18 (1): 95-104.
Sen, P.N., Scala, C., and Cohen, M.H. 1981. A self-similar model for sedimentaryrocks with application to the dielectric of fused glass beads.Geophysics 46 (5): 781-795. doi: 10.1190/1.1441215.
Sonon, L.S. and Thompson, M.L. 2005. Sorption of a nonionicpolyoxyethylene lauryl ether surfactant by 2:1 layer silicates. Claysand Clay Minerals 53 (1): 45-54. doi: 10.1346/CCMN.2005.0530106.
Stroud, D., Milton, G.W., and De, B.R. 1986. Analytical model for thedielectric response of brine-saturated rocks. Physical Review B34 (8): 5145-5153. doi: 10.1103/PhysRevB.34.5145.
Thevanayagam, S. 1997. Dielectric dispersion of porous mediaas a fractal phenomenon. J. of Applied Physics 82 (5):2538-2547. doi: 10.1063/1.366065.
Toumelin, E. and Torres-Verdín, C. 2007. 2D pore-scale simulation ofwide-band electromagnetic dispersion of saturated rocks. Geophysics72 (3): F97-F110. doi: 10.1190/1.2561301.
Toumelin, E., Torres-Verdín, C., Chen, S., and Fisher, D.M. 2003.Reconciling NMR Measurements and Numerical Simulations: Assessment ofTemperature and Diffusive Coupling Effects on Two-Phase Carbonate Samples.Petrophysics 44 (2): 91-107.
Toumelin, E., Torres-Verdín, C., Sun, B., and Dunn, K.-J. 2006. Limits of 2D NMR InterpretationTechniques To Quantify Pore Size, Wettability, and Fluid Type: A NumericalSensitivity Study. SPEJ 11 (3): 354-363. SPE-90539-PA doi:10.2118/90539-PA
Zhang, G.Q., Hirasaki, G.J., and House, W.V. 2003. Internal field gradientsin porous media. Petrophysics 44 (6): 422-434.