A method to probe the pore-throat structure of tight reservoirs based on low-field NMR: Insights from a cylindrical pore model

Abstract

Abstract This research proposes a new method of estimating pore-throat size distribution that converted based on nuclear magnetic resonance (NMR) T2 spectra, so as to more accurately explore the pore-throat structures of tight reservoirs. In this work, one of the most potential shale formations, Yanchang shales in the Ordos basin, NW China, was targeted. Take Chang 2 Member as an example, the experimental parameters were comprehensively analyzed, including petrological property analysis, NMR, and constant-rate mercury injection porosimetry (MIP). This research compared the pore-throat size distributions which are converted from NMR T2 spectra using a conventional method, an empirical formula method, and the new method. The research found that the results obtained through the linear relationship of the conventional method showed low accuracy, and the fitting coefficients vary from 0.5339 to 0.8238. Although the empirical method lacks physical significance and mathematical derivation, the fitting coefficients are from 0.8565 to 0.9886, which is referable. The new method brought in the physical significance of formula derivation and took into account the distribution characteristics of experimental data, resulting in higher fitting coefficients of 0.9928–0.9999. Based on the fitting results, the new method is more reasonable and feasible, which can be used for conversion of pore-throat size distribution through NMR T2 spectrum to obtain the NMR pore-throat structure.