Rapid measurements of diffusion using PFG: Developments and applications of the Difftrain pulse sequence

Abstract

Pulsed-field gradient (PFG) nuclear magnetic resonance (NMR) is one of the few experimental techniques that can determine directly mean square molecular displacements, allowing self-diffusion coefficient of liquids to be derived. PFG measurements are used commonly for diffusion, flow, and microstructure characterization. However, these conventional PFG experiments are often time consuming, requiring the gradient strength or observation time to be incremented independently. Here we discuss how the rapid Difftrain pulse sequence has proved invaluable in the study of time sensitive systems by allowing multiple observation times to be probed in a single scan. Difftrain has been applied successfully to the study of emulsions, surfactant solutions, bead packs, and permeable rock cores. We discuss various implementations of the Difftrain pulse sequence, suggest suitable phase cycles, and review the applications to date.

Contributed Review: Nuclear magnetic resonance core analysis at 0.3 T

“…5) is associated with water bound on clays. In Estaillades limestone, a distinct bimodal distribution is observed for 23 Na, corresponding to brine in the macropores and micropores. Another interesting feature in Fig.…”

“…A magnetic field of B 0 = 0.3 T is sufficiently high to allow straightforward detection of nuclei other than 1 H. In petrophysical applications, 23 Na is an obvious choice 115,116 as many reservoirs contain sodium salts in brine. Importantly, sodium NMR provides unambiguous detection of the aqueous phase.…”

“…JMitchell16@slb.com lower gyromagnetic ratios than 1 H are more readily accessed (e.g., 23 Na, 19 F, 31 P, 13 C, 2 H) for studies of molecular structure and chemical reaction monitoring. High-field NMR also offers the advantage of shorter radio frequency (rf) probe recovery times, allowing the detection of short relaxation time components in solids.…”

“…21 The inclusion of a 3D gradient set enables robust measurements of diffusion and flow through the application of orthogonal homospoil gradient pulses. 22 An intermediate field magnet is suitable for rapid diffusion measurements 23 and quantitative determination of advective displacements through the flow propagator experiment. 24,25 Therefore, intermediate field magnets allow techniques that are slow or impractical at low field to be implemented rapidly and robustly on rocks, offering an excellent compromise between quantitative interpretation and experimental versatility in the core analysis laboratory.…”

Nuclear Magnetic Resonance: Basic Principles and Liquid State Spectroscopy

“…Therefore, any new developments that significantly improve NMR sensitivity, such as the advent of cryoprobes, are of great importance to NMR spectroscopy. Other recent developments to boost sensitivity and to speed up NMR data acquisition are reviewed in references (Edgar, 2010;Mitchell and Johns, 2009). These include new approaches for dynamic nuclear polarization (DNP) transfer, the use of superconducting quantum interference device (SQUID) detection, single scan methods for 2D experiments where spins are spatially decoded, and applications of Difftrain pulse sequences for rapid diffusion measurements.…”