Feasibility of a Borehole VHF Radar Technique for Fracture Mapping

Abstract

Experiments were conducted to establish the feasibility of a downholes high frequency electromagnetic technique for location of fractures in the vicinity of boreholes. An existing flame cut slot in granite was filled with salt water to simulate a brine filled fracture. A transmitter consisting of a phased dual dipole array arranged to provide a directional signal toward the fracture. A receiver operated at 30 to 300 MHz was also located in the same borehole. The radar returns from the simulated fracture were detectable in boreholes located at distances o up to 12 meters from the fracture. These results indicate for the first time the feasibility of a downhole VHF radar of use in a single borehole for detection of fractures located away from the borehole.