Efficent hydrogeologic characterization with a new direct push magnetic resonance system

Abstract

A new system of instrumentation and tooling is presented that enables magnetic resonance characterization of hydrogeologic properties using direct push profiling. Magnetic resonance measurements deliver direct determination of saturated porosity, as well as estimation of pore size distributions and hydraulic conductivity. Compared to conventional borehole magnetic resonance logging in open or PVC-cased wells, use of direct push equipment and tooling is highly efficient, minimally invasive, and does not produce any drilling waste material. The new magnetic resonance system is designed for use with 2.25” outer-diameter Geoprobe rods, which are more commonly stocked and can be advanced to greater depths that larger diameter rods. The newly miniaturized magnetic resonance sensor package has an outer diameter of 1.4” and is deployed through the hollow 1.5” diameter of the rods. The sensor is deployed through the bottom of the rods and data is acquired as the rods are retracted. Two sensor variants have been developed with vertical resolutions ranging from less than 10 cm to 25 cm, and an echo spacing less than 500 μs. Experimental field data were acquired with repeated runs to compare the two sensors and assess variance. Direct push hydraulic profiling tool (HPT) measurements were also acquired at coincident locations for comparison. The field results show excellent repeatability and high correlation between the magnetic resonance, HPT data, and known hydrogeology. Apparent advantages of direct push magnetic resonance data include the ability to quantify porosity, bound/mobile fluid fractions, and sensitivity to hydraulic conductivity variations ranging over several orders of magnitude. This technology opens new opportunities for the use of magnetic resonance in environmental remediation, geotechnical, and water resource applications.