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A FIELD STUDY OF NUCLEAR MAGNETIC RESONANCE LOGGING TO QUANTIFY PETROLEUM CONTAMINATION IN SUBSURFACE SEDIMENTS
Fay, E.L., R.J. Knight, and E.D. Grunewald.
Geophysics 82(4):EN81-EN92(2017)

In a field study conducted in Pine Ridge, South Dakota, nuclear magnetic resonance (NMR) logging measurements were used to investigate an area of hydrocarbon contamination from leaking underground storage tanks. NMR logging measurements are directly sensitive to hydrogen-bearing fluids in the sediments surrounding a well and can be used to estimate in situ fluid volumes. The relaxation time T2 and diffusion coefficient D of the fluids were used to differentiate between signal from water and signal from contaminant, enabling the estimation of the hydrocarbon volume. Based on NMR measurements collected in two PVC-cased monitoring wells, D and T2 measurements were used together to detect a contaminant smear zone at both wells. Although the contrast in D between the fluids was found to be inadequate for fluid typing, the T2 contrast between the contaminant and water in silt enabled estimation of contaminant volumes. Using this technique, the vertical extent of the smear zone was estimated to be more than 3 m with up to 5 vol% contaminant in the sediments at one well and up to 9.5 vol% at the other well. Under appropriate circumstances, NMR logging can be used to detect and quantify contamination in situ; however, sediment and contaminant properties at many sites might result in insufficient contrast between T2 and D.



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