Determining pore length scales and pore surface of rock cores by internal magnetic fields modulation at 2 MHz NMR

摘要

Pore length scales and pore surface relaxivities of rock cores with different lithologies were studied on a 2 MHz Rock Core Analyzer. To determine the pore length scales of the rock cores, the high eigenmodes of spin bearing molecules satisfying the diffusion equation were detected with optimized encoding periods in the presence of internal magnetic fields B-in. The results were confirmed using a 64 MHz NMR system, which supports the feasibility of high eigenmode detection at fields as low as 2 MHz. Furthermore, this methodology was combined with relaxometry measurements to a two-dimensional experiment, which provides correlation between pore length and relaxation time. This techniques also yields information on the surface relaxivity of the rock cores. The estimated surface relaxivities were then compared to the results using an independent NMR method. (C) 2014 Elsevier Inc. All rights reserved.