The Observation of Residual Oil Evolution During Waterflooding Using NMR D–T ₂ Maps

Abstract

By supplementing standard relaxation time measurements with diffusion information, nuclear magnetic resonance (NMR) D–T ₂ mapping provides a powerful tool for characterizing fluids in a core. In this study, a D–T ₂ mapping technique was designed and applied to investigate waterflooding behavior and pore-level residual oil distributions. NMR measurements were conducted at different stages of the waterflooding process, and corresponding D–T ₂ maps were acquired. The oil and water signals were easily separated using a diffusion coefficient cut-off of 3 × 10⁻⁶ cm²/s. The oil saturation values measured via the NMR method were highly consistent with the volumetric method results. The pore-level residual oil distributions could be calculated by analyzing the oil T ₂ spectra during waterflooding. The injected water was found to preferentially displace oil in large and medium-sized pores having relatively low capillary pressures. The final residual oil saturation measured via the NMR method was 18.9 %, with 15.7 % occurring in medium-sized pores (10 ms < T ₂ < 100 ms).