Layer Stripping in Magnetotellurics (MT) for Enhancement of Resistivity Change Effect in Reservoir: Equivalence Analysis
Keywords:alternative MT modeling, anomaly enhancement, MT impedance, resistivity monitoring, time lapse
AbstractMagnetotellurics (MT) can be applied to monitor resistivity change at depth that is for example due to fluid injection in enhanced oil recovery or CO2 storage. The observed MT data changes at the surface may be insignificant, but the effect can be enhanced using the layer stripping method, i.e. calculating MT data changes that would be observed at depth based on data from the surface. Two well-known formulas for MT 1D forward modeling were reformulated to allow for calculation of the impedance at depth based on the impedance at the surface. We applied the layer stripping technique to synthetic data associated with models that were representative of a likely CO2 storage site. We also used an equivalent model and the Monte Carlo approach to estimate the sensitivity of the method to cope with the uncertainty of the host model and the input data. The layer stripping calculation has the greatest uncertainty at short periods, where the real and imaginary parts of the complex impedance tend to be equal, i.e. an homogeneous medium response. The layer stripping technique should be used with great caution based on a relatively precise 1D host model.
Zhang, P. & Chouteau, M., The Use of Magnetotellurics for Mineral Exploration: an Experiment in the Chibougamau Region of Quebec, Can. J. Earth Sci., 29(4), pp. 621-635, 1992.
Farquharson, C.G. & Craven, J.A., Three-Dimensional Inversion of Magnetotelluric Data for Mineral Exploration: An Example from the Mcarthur River Uranium Deposit, Saskatchewan, Canada, J. Appl. Geophys., 68(4), pp. 450-458, 2009.
Pellerin, L., Johnston, J.M. & Hohmann, G.W., A Numerical Evaluation of Electromagnetic Methods in Geothermal Exploration, Geophysics, 61(1), pp. 121-130, 1997.
Munoz, G., Exploring for Geothermal Resources with Electro-Magnetic Methods, Surv. Geophys., 35(1), pp. 101-122, 2014.
Mitsuhata, Y., Matsuo, K. & Minegishi M., Magnetotelluric Survey for Exploration of a Volcanic-Rock Reservoir in the Yurihara Oil and Gas Field, Japan, Geophys. Prospect., 47(2), pp.195-218, 1999.
Connell, D. & Key K., A Numerical Comparison of Time and Frequency-Domain Marine Electromagnetic Methods for Hydrocarbon Exploration in Shallow Water, Geophys. Prospect., 61(1), pp. 187-199, 2013.
Ogaya, X., Ledo, J., Queralt, P., Jones, A.G. & Marcuello, A., A Layer Stripping Approach for Monitoring Resistivity Variations Using Surface Magnetotelluric Responses, J. Appl. Geophys., 132, pp. 100-115, 2016.
Rees, N., Carter, S., Heinson, G. & Krieger, L., Monitoring Shale Gas Resources in the Cooper Basin Using Magnetotellurics, Geophysics, 81(6), pp. E423-E432, 2016.
Pedersen, J. & Hermance, J.F., Least Squares Inversion of One-Dimensional Magnetotelluric Data: An Assessment of Procedures Employed by Brown University, Surv. Geophys., 8(2), pp. 187-231, 1986.
Grandis, H., an Alternative Algorithm for One-Dimensional Magneto-telluric Response Calculation. Comp. Geosci. 25, pp. 119-125, 1999.
Tsuji, T. & Gundih CCS project team, Reservoir Characterization for Site Selection in the Gundih CCS Project, Indonesia, Energy Procedia, 63, pp. 6335-6343, 2014.
Zhdanov, M.S. & Keller, G.V., the Geoelectrical Methods in Geophysical Exploration, Elsevier, 1994.
Zhdanov, M.S., Geophysical Electromagnetic Theory and Methods, 2nd ed., Elsevier, 2017.
Simpson, F., Bahr, K., Practical Magnetotellurics, Cambridge, 2005.
Ward S.H. & Hohmann, G.W., Electromagnetic Theory for Geophysical Applications, Electromagnetic Methods in Applied Geophysics, Nabighian, M.N., ed., Society of Exploration Geophysicists, pp. 131-311, 1988.
Warsa & Grandis, H., Sensitivity Study of 3-D modeling for Multi-D Inversion of surface NMR, AIP Conference Proceedings, 1454, pp. 130-133, 2011.
Irawan, D., Grandis, H. & Sumintadireja, P., Quasi-2D Resistivity Model From Inversion of Vertical Electrical Sounding (VES) Data Using Guided Random Search Algorithm, J. Math. Fund. Sci., 47(3), pp. 269-280, 2015.
Srigutomo, W., Warsa, Sule, M.R., Trimadona, Prasetyo, D., Saito, A., Nakayama, K., Hato, M. Prasetyo, A. & Widarto, D.S., Time-Domain Electromagnetic (TDEM) Baseline Survey for CCS in Gundih Area, Central Java, Indonesia. Proceedings 12th SEGJ International Symposium, Tokyo, Japan, 2015.
Prasetyo, D., Non-Linear Inversion Modeling of Transient Electro-magnetic (TEM) Data for Hydrocarbon Reservoir Characterization (in Indonesian with English abstract), Master Thesis, Geophysical Engineering Program, Institut Teknologi Bandung, Bandung, Indonesia, 2017.