Development of an Electromagnetically Compatible Imaging Fluid for Borehole Ground-Penetrating Radar in Mineral Geophysical Exploration

Source abstract

Borehole Ground-penetrating radar (GPR) is a promising technique for high-resolution geophysical imaging; however, water present in the borehole significantly affects electromagnetic (EM) waves, reducing imaging depth and resolution. Displacing borehole water with an EM-compatible imaging fluid improves borehole GPR performance. The fluid is developed and optimized through comprehensive compositional, electromagnetic, rheological, and numerical investigations. The fluid consisted of canola oil as the base fluid, stearic acid as the suspension stabilizer, and barite as the weighting agent. Barite sources and particle sizes, preparation procedures, and fluid properties were evaluated. Finite-difference time-domain (FDTD) simulations in gprMax compared air-, water-, and EM-fluid-filled boreholes using a 500 MHz source and reflections from a quartz vein and a perfect electric conductor (PEC) cylinder. The results demonstrated that a high-purity and micro-sized barite powder improved suspension stability and electromagnetic compatibility, while the oven-assisted preparation method produced the most stable formulations. Rheological analysis showed that the Herschel–Bulkley and Robertson–Stiff models provided the best agreement with experimental data. In the simulations, the water-filled borehole reduced quartz-vein and PEC-cylinder reflection amplitudes to 12% and 13% of their respective air-filled values, whereas the imaging-fluid-filled borehole produced amplitudes of 108% and 107%, respectively. Laboratory experiments demonstrated that the imaging fluid preserved electromagnetic wave propagation characteristics and improved target detectability compared with water-filled boreholes. These results support further evaluation of the imaging fluid for improving target detectability in borehole GPR investigations.