GEOL 482.3 OUTLINE ELECTRICAL METHODS GEOL 482.3 email: jim.merriam@usask.ca ELECTRICAL METHODS IN GEOPHYSICAL PROSPECTING COURSE DESCRIPTION This course reviews the background theory for the electromagnetic exploration techniques, including the mechanisms of conduction and polarization in earth materials. Each of the major exploration techniques resistivity, induced polarization, vlf, time domain em, frequency domain em (slingram etc) and magnetotellurics, are then covered in turn, with emphasis on survey design, data analysis and interpretation. Labs are required every week with at least one on each of the above techniques. 1
MARKING SCHEME Mid Term Exam 30% Labs 20% Final Exam 50% All LABS must be complete within one week, and results will be discussed at the next weeks lab meeting. Late labs will be docked marks. REFERENCES Reynolds An Introduction to Applied and Environmental Geophysics van Blaricom Practical Geophysics II for the exploration geologist Grunt and Sweat Interpretation Theory in Applied Geophysics Ward Geotechnical and Environmental Geophysics Nabighian Electromagnetic Methods in Applied Geophysics Keller and Frischnecht Electrical Methods in Geophysical Prospecting 2
I have put some supporting material on PAWS 482notes.pdf SomeLoopLoop.pdf RCcircuits.pdf Channeling.pdf tdem.pdf Induction Pictures and notes for some of the common loop loop instruments These notes on RC circuits are background for a rock equivalent circuit Channeling effects in DC and low frequency. Resolution of electrical modes in time domain em data. This will help with lab 9. Lopp loop induction. 482notes.pdf MejuCaseStudies.pdf slee.pdf An EM case studies paper by Max Meju. longitudianl and transverse resistivity. Helpful for lab 1 SUMMARY WEEK 1) Overview of Electrical techniques in geophysics. What the various techniques are used for, and the level of activity of each in the exploration industry. WEEK 2) Electrical properties of rock: conductivity, (emphasizing the importance of water), magnetic permeability and dielectric constant, polarization effects. WEEK 3) The wave equation, and limiting solutions to the generalized wave equation; the dielectric limit and the pure wave equation, the inductive limit and the diffusion equation, 3
and the quasi-static limit (Laplace). WEEK 4) Plane wave solutions to the wave equation, plane waves in an insulator, and in a conductor. The concept of the skin depth. The loss tangent. The wave impedance, and Cagniard resistivity. WEEK 5) Boundary conditions, reflection, refraction, charge build-up on a boundary. WEEK 6) Time domain induction, propagation of a pulse in a conducting medium, dispersion, the penetration depth. WEEK 7) Resistivity. The current pattern produced in homogeneous ground by a single current source, and a source and sink. The depth of investigation, the K factor, the paradox of anisotropy, array strengths and weaknesses, modeling. WEEK 8) Induced Polarization (IP). The Cole-Cole description of frequency domain IP. Time domain vs frequency domain, pseudo sections, polarity conventions, operational considerations. WEEK 9) Background to induction techniques, in-phase, out-of-phase, response parameter, induction number, near zone, intermediate zone, far zone. Decay times in time domain. Strengths and weaknesses of time domain vs frequency domain. Frequency domain methods, slingram vs tilt angle. WEEK 10) Time domain loop systems, em47, em37, Sirotem. Currents and fields in early, intermediate and late times. Late time apparent resistivities. Identifying late-time behaviour. Sounding and profiling. WEEK 11) The Very Low Frequency (VLF) technique. Sensitivity to target strike and source azimuth. Apparent resistivities, tilt angles, polarization ellipse. TM and TE mode responses. WEEK 12) Magnetotellurics MT, AMT, CSAMT. Identifying 1D, 2D and 3D responses. Estimating the impedance tensor. Rotation of the impedance tensor. Tipper, skew and ellipticity. TM and TE mode responses. The static shift. Induction vectors. 4
WEEK 13) Ground Penetrating Radar. Principals, the importance of water and air in pores. Electrical techniques in the petroleum industry. LABS LAB 1 Borehole conductivity, longitudinal conductance, and transverse resistance. LAB 2 Pseudo-sections of IP and resistivity. LAB 3 Resistivity modeling. Survey design, equivalence and suppression. LAB 4 Forward modeling and inversion of selected resistivity profiles. LAB 5 Time domain IP. Interpretation of Cole-Cole models. LAB 6 VLF responses. Tilt angle, IP, Q, field strength, polarization ellipses and yaw. LAB 7 Maxmin. Interpretation of In-Phase and Quad. LAB 8 Time domain em sounding. LAB 9 Time domain EM in loop profiling. Separation of target response from host response. Identification of channeling, induction, and magnetic responses. LAB 10 Magnetotellurics I. Identification of plane wave micropulsations. Simple calculation of a real impedance tensor and tipper and their rotation. Identification of TE and TM polarization and strike. LAB 11 Magnetotellurics II. Calculation of complex impedance tensor, rotation of the impedance tensor, SKEW, ELLIPTICITY. Calculation of apparent resistivities. or Audio Frequency Magnetotellurics. Identifying Spherics. Limitations of source azimuth. Construction and manipulation of impedance tensor. 5
LAB 13 Ground penetrating radar. Velocities. Descriminating between reflections, multiples and sideswipes. Identification of the water table. f-k filtering with VISTA. 6
REFERENCES Basokur, A.O., T.M. Rasmussen, C.Kaya, Y. Altun and K. Aktas. 1997 Comparison of induced polarization and controlled source audio-magnetotellurics methods for massive chalcopyrite exploration in a volcanic area. Geophys, 62 No. 4 1087-1096. Beamish, D. 2000. Quantitative 2D VLF data interpretation. Jour Applied Geophys. 45, 33-47. Beamish D., and R.J. Peart, 1998. Electrokinetic Geophysics - A Review, Terra Nova 10, 48-55. Benson, A.K., K.L. Payne, and M.A. Stubben, 1997. Mapping groundwater contamination using DC resistivity and VLF geophysical methods - A case study. geophys 62,No 1 80-86. B: orner, F.D., J.R. Schopper and A.R. Weller, 1996 Evaluation of fluid and storage properties in the soil and ground water zone from induced polarization measurements. Geophysical Prospecting. 44, 583-681. B: orner, F.D., M. Grunhe, J.H. Sch: one, 1993. Contamination indications derived from electrical properties in the low freqiuency range. Geophysical Prospecting, 41, 83-98 Campbell, J.E., 1990. Dielectric properties and the influence of conductivity in soils at 1 to 50 megahertz. Am. J. Soil Sci. 54, 332-341. Das, U.C., 1995. Apparent resistivity curves in controlled-source Electromagnetic sounding directly reflecting true resistivities in a layered earth, Geophysics 60, No 1 53-60. Eaton, P.A. and G.W. Hohmann, 1989. A rapid inversion technique for transient electromagnetic soundings, Phys. Earth Planet. Int. 563, 383-404. Frangos, W. 1998. Electrical detection of leaks in lined waste disposal ponds. Geophys. 7
63 No. 6, 1737-1744. Guerin R., A Tabbagh, and P. Andrieux, 1994. Field and/or resistivity mapping in MT-VLF and implications for data processing. Geophysics, 59, No. 11, 1695-1712. Karous, M. and S.E. Hjelt, 1983. Linear filtering of VLF dip angle measurements. Geophysical Prospecting, 31, 782-794. Ktarakci, H.K. N. Harthill, and M.W. Blohm, 1997. Time domain electromagnetice survey for gold. Geophys 62,No 5 1409-1418. Lane, J.W., F.P. Haeni, and W.M. Watson, 1995, Using a square array direct current resistivity method to detect fractures in crystaline bedrock in New Hampshire: Ground Water, 33, no 3, 476-485. Levchenko, A.V. and O.A.Shushakov, 1998. Inversion of surface NMR data Geophys. 63, No. 2, 75-85. Lilley, F.E.M., 1998 Magnetotelluric tensor decomposition: Part II, Examples of a basic procedure, Geophysics, 63, No. 6 1898-1907. Meju, M.A. 1998. A simple method of transient electromagnetic data analysis Geophys. 63 No. 2, 405-410. Nesbitt, B.E. 1993. Electrical resistivities of crustal fluids. Jour. Geophys. Res. 43,123-136. Pellerin, L., and G. Hohmann, 1995. A parametric study of the vertical electric source, Geophysics 60, No 1 43-52. Qian W. and D.E. Boerner, 1994. Electromagnetic response of a discretely grounded circuit - An integral equation solution Geophysics, 59, No 11 1680-1694. Qian W. and D.E. Boerner, 1995. Electromagnetic modelling of buried line conductors using an integral equation. Geophysical J. Int. 121, 203-214. 8
Sasaki Y., 1994 3-D resistivity inversion using the finite element method. Geophysics, 59, NO 12, 1839-1848. Siegel, H.O. H,. Vanhalla and N.S. Sheard, 1997. Some case histories of source discrimination using time domain spectral IP. Geophys. 62, No. 5 1394-1408. Smith, R.S., R.N. Edwards and G. Buselli, 1994. An automatic technique for presentation of coincident-loop, impulse-response, transient, electromagnetic data, Geophysics 59, No 10, 1542-1550. Taylor, R.W. and A.H. Fleming, 1988. Characterizing jointed systems by azimuthal resistivity surveys, Ground Water, 26, no. 4, 464. Wannamaker, P.E., J.M. Johnstone, J.A.Stodt, and J. R. Booker, 1998. Anatomy of the southern cordilleran hingelineline, Utah and Nevada, from deep electric resistivity profiling. Geophys. 62 No. 4, 1069-1086. Weller, A. and F.D. B: orner, 1996. Measurements of spectral induced polarization for environmental purposes. Environmental Geology, 27,329-334. Weller, A., M. Seicher and A. Kampke. 1996. IP modelling using complex electrical conductivities. Geophysical Journal Int. 127, 387-398. White, P.A. Measurement of ground water parameters using salt water injection and surface resistivity. Ground Water, 26, no. 2 179-186. Yuval, D.W. Oldenburg, 1997. Computation of Cole-Cole parameters from IP data. Geophys, 62,No 2. 436-448. 9