Vertical fracture detection by exploiting the polarization properties of ground penetrating radar signal

George Tsoflias, Formerly The University of Texas at Austin, Department of Geological Sciences and Institute for Geophysics, Austin, Texas 78759; presently The University of Kansas, Lawrence, Kansas 66045, Jean-Paul Van Gestel, Formerly The University of Texas at Austin, Department of Geological Sciences and Institute for Geophysics, Austin, Texas, 78759; presently BP, Houston, Texas 77079, Paul L. Stoffa, The University of Texas at Austin, Department of Geological Sciences and Institute for Geophysics, Austin, Texas 78759, Don D. Blankenship, The University of Texas at Austin, Institute for Geophysics, Austin, Texas 78759, Mrinal K. Sen Institute for Geophysics, The University of Texas at Austin, 4412 Spicewood Springs Road, Bldg. 600, Austin, TX 78759-8500, USA.

Vertically oriented thin fractures are not always detected by conventional single-polarization reflection profiling ground-penetrating radar (GPR) techniques. We study the polarization properties of EM wavefields and suggest multipolarization acquisition surveying to detect the location and azimuth of vertically oriented fractures. We employ analytical solutions, 3D finite difference time-domain modeling, and field measurements of multipolarization GPR data to investigate EM wave transmission through fractured geologic formations. For surface-based multipolarization GPR measurements across vertical fractures, we observe a phase lead when the incident electric-field component is oriented perpendicular to the plane of the fracture. This observation is consistent for nonmagnetic geologic environments and allows the determination of vertical fracture location and azimuth based on the presence of a phase difference and a phase lead relationship between varying polarization GPR data.

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