Six-Component Tensor of the Surface Electromagnetic Field Produced by a Borehole Source Recorded by Innovative Capacitive Sensors

Summary Saudi Aramco and GroundMetrics, Inc. collaborated to conduct the first measurements of the surface electric field produced by a borehole-to-surface electromagnetic (BSEM) source in the direction tangential to the well and in the vertical direction above the Earth’s surface. The full six-component tensor of the electric and magnetic fields produced by a borehole source inside an oil reservoir was measured at the surface, kilometers away from the transmitted wellbore. Specifically the horizontal E-field was measured by a new type of high impedance E-field sensor (eQube) [Hibbs, 2012] that can be emplaced in seconds and is essentially immune to the quality of its electrical contact to the ground. This ease of use greatly facilitates large area surface surveys. The vertical E-field was measured by a new type of electric field sensor that has microvolt per meter sensitivity and has not been previously applied in a geophysical survey. In addition, all three components of the magnetic field were acquired. We believe this is the first time all six components of the electromagnetic (EM) field have been measured in a geophysical survey at signal frequencies below 1 kHz, and certainly at signal frequencies below 10 Hz. In fact, signal frequencies as low as 0.1 Hz were acquired in all six channels. The use of the new high impedance sensing technology greatly eases the challenges of deploying large arrays of E-field sensors. This project has shown that these innovative capacitive sensors can measure BSEM signals at considerable range.