A Low-Disturbance Workflow for Determining NMR T2 Cutoffs in Mechanically Sensitive Core Samples

Abstract

Centrifugation is widely used to determine the NMR T2 cutoff of core samples, but it may alter pore structures and is particularly unsuitable for mechanically sensitive cores. This study proposes a low-disturbance workflow combining staged gas displacement with deuterium oxide (D2O) displacement, in which physical displacement replaces centrifugal drainage. The residual proton-bearing-water response is treated as a bound-water reference for determining the T2 cutoff. The method was tested on one weakly consolidated core (R1500) and two conventional cores (R7 and R30) and compared with centrifugation using NMR T2 spectra and magnetic resonance imaging. The workflow yielded T2 cutoff values of 32.45 ms, 5.66 ms, and 24.25 ms for R7, R30, and R1500, respectively. In contrast, R1500 failed during the first centrifugation step, whereas R7 and R30 fractured at high rotational speeds; MRI also revealed outlet-end residual-water accumulation. The displacement-derived T2 cutoff was subsequently used to partition bound and movable fluid volumes for permeability evaluation using the Timur-Coates model. The staged gas/D2O workflow provides a low-disturbance alternative to centrifugation for the three tested cores; the present validation covers two conventional cores and one weakly consolidated core.