Subsurface fracture characterisation using full polarimetric borehole radar data analysis with numerical simulation validation
Khamis Mansour 1 2 4 Motoyuki Sato 31 Graduate School of Environmental Studies, Tohoku University, 41 Kawauchi, Sendai, 980-8576, Japan.
2 National Research Institute of Astronomy and Geophysics, 11722 Helwan, Cairo, Egypt.
3 Center for Northeast Asian Studies, Tohoku University, 41 Kawauchi, Sendai, 980-8576, Japan.
4 Corresponding author. Email: khamis@cneas.tohoku.ac.jp
Exploration Geophysics 43(2) 125-135 https://doi.org/10.1071/EG11040
Submitted: 8 August 2011 Accepted: 6 March 2012 Published: 24 April 2012
Abstract
We report on the utilisation of a full polarimetric subsurface borehole radar measuring system for efficient characterisation of subsurface fractures. This system can measure the full polarisation (HH, HV, VV and VH) of electromagnetic waves for one borehole, and thus enables us to obtain more information about subsurface fractures compared to that obtained from conventional borehole radar systems, which usually use only single polarisation. Polarimetric datasets have been acquired at several sites, particularly at Mirror Lake, USA, which is a well known site for testing subsurface fractures. Nine fracture sets were observed in one borehole, FSE-1, in the Mirror Lake site. These were divided into four category fracture sets depending on polarimetric analysis of alpha, entropy and anisotropy decomposition analysis of scattering behaviour from fractures at frequency 30 MHz. We found that the characterised four fractures sets have the highest hydraulic permeable zones at depths of 24.75 m, and 47.80 m. The lowest hydraulic permeable zones were found to be at 28.50 m, 36.15 m and 44.80 m. These results show a good consistency with the hydraulic fractures permeability tracer test that was done by USGS. To validate these conclusions we implemented numerical simulation for a synthesised fractures property using the Finite Difference Time Domain (FDTD) method. Here, we used a plane wave as an electromagnetic source with frequency ranging from 1 MHz to 200 MHz, and monitored the electromagnetic scattering for various fractures. We found that distributions of alpha, entropy and anisotropy polarimetric parameters differ with the fracture roughness property which validates the polarimetric analysis of the measured data.
Key words: fracture characterisation, fractal fracture, FDTD, polarimetric analysis, polarimetric borehole radar.
References
Brown, S., 1995, Simple mathematical model of a rough fracture: Journal of Geophysical Research, 100, 5941–5952| Simple mathematical model of a rough fracture:Crossref | GoogleScholarGoogle Scholar |
Brown, S., and Scholz, C. H., 1985, Broad bandwidth study of the topography of natural rock surfaces: Journal of Geophysical Research, 90, 575–582
| Broad bandwidth study of the topography of natural rock surfaces:Crossref | GoogleScholarGoogle Scholar |
Cloude, S. R., and Pottier, E., 1997, An entropy based classification scheme for land applications of polarimetric SAR: IEEE Transactions on Geoscience and Remote Sensing, 35, 68–78
| An entropy based classification scheme for land applications of polarimetric SAR:Crossref | GoogleScholarGoogle Scholar |
Lee, J.-S., and Pottier, E., 2009, Polarimetric radar imaging: from basics to applications: CRC Press, Taylor and Francis.
Kranzz, R. L., Frankel, A. D., Engelder, T., and Scholz, C. H., 1979, The permeability of whole and jointed Barre granite: International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, 16, 225–234
| The permeability of whole and jointed Barre granite:Crossref | GoogleScholarGoogle Scholar |
Lane, J. W., Jr, and Haeni, F. P., 1998, Use of a multi-offset borehole-radar reflection method in fractured crystalline bedrock at Mirror Lake, Grafton County, New Hampshire: Proc. Symp. Appl. Geophys. Eng. and Environ. Problems, 359–368.
Sato, M., Takeshita, M., Miwa, T., and Lane, J. W., Jr., 1999, Polarimetric borehole radar measurement at the Mirror Lake test site: Proc. SPIE, vol. 3752, 104–112.
Mandelbrot, B. B., 1982, The fractal geometry of nature: W. H. Freeman.
Mansour, K., and Sato, M., 2010, FDTD simulation of electromagnetic wave scattering from a rough surface synthesized by fractal theory: Proceedings of the Formation Evaluation Symposium of Japan, E1–E7.
Paillet, F. L., Hess, A. E., Cheng, C. H., and Hardin, E., 1987, Characterization of fracture permeability with high-resolution vertical flow measurements during borehole pumping: Ground Water, 25, 28–40
| Characterization of fracture permeability with high-resolution vertical flow measurements during borehole pumping:Crossref | GoogleScholarGoogle Scholar |
Peitgen, H.-O., and Saupe, D., 1988, The science of fractal images: Springer-Verlag.
Power, W. L., Tullis, T. E., Brown, S. R., Boitnott, G. N., and Scholz, C. H., 1987, Roughness of natural fault surfaces: Geophysical Research Letters, 14, 29–32
| Roughness of natural fault surfaces:Crossref | GoogleScholarGoogle Scholar |
Sato, M., and Takeshita, T., 2000, Estimation of subsurface fracture roughness by polarimetric borehole radar: IEICE Transactions on Electronics, 83, 1881–1888
Yee, K. S., 1966, Numerical solution of initial boundary value problems involving Maxwell’s equations in isotropic media: IEEE Transactions on Antennas and Propagation, 14, 302–307
| Numerical solution of initial boundary value problems involving Maxwell’s equations in isotropic media:Crossref | GoogleScholarGoogle Scholar |
Zhao, J.-G., and Sato, M., 2006, Radar polarimetry analysis applied to single-hole fully polarimetric borehole radar: IEEE Transactions on Geoscience and Remote Sensing, 44, 3547–3554
| Radar polarimetry analysis applied to single-hole fully polarimetric borehole radar:Crossref | GoogleScholarGoogle Scholar |