title: Real-time oil-saturation monitoring in rock cores with low-field NMR.
abstract: Nuclear magnetic resonance (NMR) provides a powerful suite of tools for studying oil in reservoir core plugs at the laboratory scale. Low-field magnets are preferred for well-log calibration and to minimize magnetic-susceptibility-induced internal gradients in the porous medium. We demonstrate that careful data processing, combined with prior knowledge of the sample properties, enables real-time acquisition and interpretation of saturation state (relative amount of oil and water in the pores of a rock). Robust discrimination of oil and brine is achieved with diffusion weighting. We use this real-time analysis to monitor the forced displacement of oil from porous materials (sintered glass beads and sandstones) and to generate capillary desaturation curves. The real-time output enables in situ modification of the flood protocol and accurate control of the saturation state prior to the acquisition of standard NMR core analysis data, such as diffusion-relaxation correlations. Although applications to oil recovery and core analysis are demonstrated, the implementation highlights the general practicality of low-field NMR as an inline sensor for real-time industrial process control.
authors.affiliation: Schlumberger Gould Research, High Cross, Madingley Road, Cambridge CB3 0EL, UK. Electronic address: jmitchell16@slb.com.
authors.forename: J
authors.initials: J
authors.lastname: Mitchell
authors.affiliation: Schlumberger Gould Research, High Cross, Madingley Road, Cambridge CB3 0EL, UK.
authors.forename: A M
authors.initials: AM
authors.lastname: Howe
authors.affiliation: Schlumberger Gould Research, High Cross, Madingley Road, Cambridge CB3 0EL, UK.
authors.forename: A
authors.initials: A
authors.lastname: Clarke
keywords: Core analysis; Diffusion; Low field NMR; Oil recovery; Oil/brine discrimination