Development of Rapid Scanning Surface-NMR for Wide Area Hydrogeologic Mapping

Abstract

Surface nuclear magnetic resonance (Surface-NMR) measurements hold the valuable capability to directly image groundwater and to characterize aquifer flow and storage properties. Historically, implementations of surface-NMR have been limited by long stacking times and slow survey deployment, restricting applications primarily to 1D soundings and short 2D profiles. Through advancements in acquisition schemes, hardware, and deployment platforms, we demonstrate the ability to deploy surface-NMR as an efficient wide-area mapping technique. To increase measurement efficiency, we have developed acquisition schemes to improve the inherently low signal-to-noise-ratio of Earth’s field NMR. Adiabatic pulse sequences are used to increase the detected NMR signal amplitude and to reduce requirements to scan over a wide range of pulse moments. Newly developed wireless noise-reference coil stations are used to cancel environmental noise without increasing the size or footprint of the signal-detection array. Smaller footprint wired signal-detection arrays are transported efficiently using mobile platforms, including towed coil mats and elevated coil forms. The detection array can be moved along a profile line and left in a static position for short time intervals to acquire measurements before being moved to the next position. These newly developed rapid scanning NMR technologies are demonstrated at a collection of sites in the Western United States.