Vertical Radar Profiling To Determine Dielectric Constant, Water Content And Porosity Values At Well Locations

Abstract

A vertical radar profiling (VRP) experiment was conducted at the Boise Hydrogeophysical Research Site to determine if direct arrivals and reflections can be recorded using the surface-toborehole survey geometry. The receiving antenna was deployed downhole to insulate it from cultural noise. The transmitting antenna was located on the surface near the wellhead and oriented radially to the well axis. Although the antenna polarizations are perpendicular, we were able to record radar direct-arrivals and reflections. Picked first-arrival traveltimes were inverted to determine layer interval velocities. The VRP-derived velocity estimates fall in the same range as velocity estimates determined from crosshole radar tomography at the site; average velocities for the unsaturated and saturated zones are 0.140 rn/ns and 0.080 m/ns, respectively. Resolution of the VRP-derived velocity estimates is significantly better than the resolution of CMP-derived velocity estimates. Dielectric constant and porosity estimates were also derived from the VRP data using a simple petrophysical model, and compared to porosity estimates derived from neutron logging. Correlation between the two porosity estimates is encouraging. While the VRP method has not been widely used in site investigations to date, the results of this study suggest that VRPs provide an accurate, high-resolution, and cost-effective means of obtaining dielectric constant, EM velocity, volumetric moisture content and porosity values at well locations.