Detecting Sorbed Hydrocarbons in a Porous Medium Using Proton Nuclear Magnetic Resonance

• Published in: Environmental science & technology Vol. 34; no. 2; pp. 332 - 337
• Main Authors: Daughney, Christopher J, Bryar, Traci R, Knight, Rosemary J
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 15.01.2000
• Subjects: Analysis methods; Applied sciences; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Environmental impact; ENVIRONMENTAL SCIENCES; Exact sciences and technology; HYDROCARBONS; MONITORING; Natural resources; NMR; NUCLEAR MAGNETIC RESONANCE; OIL SPILLS; PETROLEUM; Pollution; Pollution, environment geology; POROUS MATERIALS; Protons; REMEDIAL ACTION; Soil and sediments pollution; SOILS; Sorption; Laboratory study; Hydrocarbon; Investigation method; Hydrogen; Crude oil; Porous medium; Soil interaction; NMR spectrometry; Soil pollution; Relaxation time
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es990637m

An ability to detect residual (sorbed) concentrations of hydrocarbons in a porous medium using nonintrusive geophysical methods is of interest in the remediation of hydrocarbon-contaminated sites. Proton NMR is an noninvasive analytical technique that can be applied to characterize several rock properties in the lab and the field. In this study, we perform a series of laboratory experiments to quantify the effect of sorbed crude oil on the NMR relaxation time (T 1) of water-saturated silica gels, both in the presence and absence of iron oxyhydroxide. The experimental data indicate that in the absence of paramagnetic iron impurities, T 1 remains constant in the presence of sorbed hydrocarbons. T 1 increases with increasing hydrocarbon concentration only if the silica surface is coated with a paramagnetic substance such as iron oxyhydroxide. These results suggest that increases in T 1 previously observed for water in natural materials coated with oil are caused by the shielding of paramagnetic surface sites by the sorbed hydrocarbons. The major implication of this study is that proton NMR is a potential means of detecting sorbed or residual hydrocarbons in natural environments.