Nuclear Magnetic Resonance Imaging of Fluid Displacements in Porous Media

Abstract

Measurement of the in-situ fluid saturation distributions is essential and important in laboratory coreflooding experiments in order to correctly evaluate the fluid displacement mechanisms and processes. Nuclear magnetic resonance (NMR) imaging has unique advantages for the direct measurement and visualization of insitu fluid distributions. There have' been some development of NMR imaging techniques to observe the distributions of fluids in porous media. However, most of these studies provide only qualitative measurements. Some of the quantitative methods proposed in the literature have certain limitations in practical laboratory corefloods. The objective of this research was to develop practical, quantitative NMR imaging techniques and processing procedures for the direct measurement and mapping of in-situ fluid saturation (or concentration) distributions in laboratory coreflooding experiments. v In this study, two practical and quantitative NMR imaging techniques: T1- weighted, inversion single-spin-echo NMR technique and Carr-Purcell-MeiboomGill (CPMG) multiple-spin-echo NMR technique have been successfully implemented. The inversion spin-echo technique distinguishes the water signal from the oil signal via the difference in longitudinal relaxation times T1 of oil and water, and consequently eliminates the NMR signal of oil. The CPMG technique distinguishes the water signal from the oil signal by simultaneously measuring the transverse relaxation times T2 of oil and water components. Practical and quantitative image processmg procedures have been successfully developed for the spin-echo and the CPMG NMR techniques. Through these procedures, the measured NMR signal intensities were converted into in-situ fluid saturation (or concentration) profiles and saturation (or concentration) images. Immiscible and miscible displacement experiments were conducted to validate the quantitative NMR techniques and the image processing procedures developed in this study. The results show that the spin-echo and the CPMG NMR techniques and their image processing procedures can accurately measure and map the in-situ fluid saturations in porous media in laboratory core flooding experiments. The results of this study will find applications in a variety of industrial processes that involve fluid flow and mass transport in porous media, such as improved oil and gas recovery and contaminants migration and remediation.