FINITE-DIFFERENCE MODELING OF BOREHOLE GROUND PENETRATING RADAR DATA

Abstract

In the fall of 1996, borehole ground penetrating radar (BGPR) data were acquired as part of a comprehensive characterization of a clastic reservoir analog in the Ferron Sandstone in east central Utah. BGPR data were collected in and between three 15-m-deep holes as well as surface profiles that connect each pair of holes.Two-dimensional finite-difference modeling of the data provides estimates of the distributions of velocity and attenuation, and the geometry of the reflectors. Depth control on the interfaces in the model is provided by the core logs from the three holes. Average estimated relative dielectric permittivity generally increases with depth from ~4 to ~17 in the sandy units, and is larger (as high as ~30) in the clays. The corresponding estimated electrical conductivities are from 10-8 S/m for the most sandy layers to 10-2 S/m for the most clay-rich layers.Comparing the velocities for vertical and horizontal electric field propagations shows a 20-25% anisotropy in the upper 6-7 m; vertical propagation (with horizontal polarization) is faster than horizontal propagation (with vertical polarization). This anisotropy is interpreted as being caused by the pervasive vertically oriented conjugate fractures that are visible at the site. At greater depths, the anisotropy is not seen, which we interpret as smaller fracture widths below the depths affected by surface weathering.