title: Bootstrap calibration and uncertainty estimation of downhole NMR hydraulic conductivity estimates in an unconsolidated aquifer.
abstract: Characterization of hydraulic conductivity (K) in aquifers is critical for evaluation, management, and remediation of groundwater resources. While estimates of K have been traditionally obtained using hydraulic tests over discrete intervals in wells, geophysical measurements are emerging as an alternative way to estimate this parameter. Nuclear magnetic resonance (NMR) logging, a technology once largely applied to characterization of deep consolidated rock petroleum reservoirs, is beginning to see use in near-surface unconsolidated aquifers. Using a well-known rock physics relationship-the Schlumberger Doll Research (SDR) equation--K and porosity can be estimated from NMR water content and relaxation time. Calibration of SDR parameters is necessary for this transformation because NMR relaxation properties are, in part, a function of magnetic mineralization and pore space geometry, which are locally variable quantities. Here, we present a statistically based method for calibrating SDR parameters that establishes a range for the estimated parameters and simultaneously estimates the uncertainty of the resulting K values. We used co-located logging NMR and direct K measurements in an unconsolidated fluvial aquifer in Lawrence, Kansas, USA to demonstrate that K can be estimated using logging NMR to a similar level of uncertainty as with traditional direct hydraulic measurements in unconsolidated sediments under field conditions. Results of this study provide a benchmark for future calibrations of NMR to obtain K in unconsolidated sediments and suggest a method for evaluating uncertainty in both K and SDR parameter values.
authors: Currently at the Department of Geology and Geophysics, University of Wyoming, 1000 E. University Ave., Laramie, WY.
authors: A D
authors: AD
authors: Parsekian
authors: K
authors: K
authors: Dlubac
authors: E
authors: E
authors: Grunewald
authors: J J
authors: JJ
authors: Butler
authors: R
authors: R
authors: Knight
authors: D O
authors: DO
authors: Walsh
mesh_terms: D002138:Calibration; D019015:Geologic Sediments; D060587:Groundwater; D057446:Hydrodynamics; D007615:Kansas; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D016062:Porosity; D035501:Uncertainty