Pore size distribution obtained from multi-frequency NMR relaxometry and a semi-permeable membrane: comparison and analysis
M.Y. Shumskayte1, K.V. Dolzhenko2, T.A. Yanushenko1, N.A. Golikov1, D.A. Markushin2, A.D. Zakharov2
1Trofimuk Institute of petroleum geology and geophysics SB RAS, Novosibirsk, Russia
2Fianumlab LLC, Moscow, Russia
Keywords: Spin-spin relaxation time, frequency characteristics, pore size distribution, terrigenous rocks, nuclear magnetic resonance
Abstract
The influence of the operating frequency of the laboratory NMR relaxometry method (2, 12, and 22 MHz) on the accuracy of determining the pore size distribution in terrigenous rocks ranging in size from medium-grained sandstone to silt-argillite is demonstrated. Measurements at 12 and 22 MHz are found to enable the detection of pore throats with small radii, which are characterized by a shift in the spin-spin relaxation time spectra toward shorter times. The high-frequency measurement data are in good agreement with the results of the semipermeable membrane method. A frequency of 2 MHz is shown to systematically overestimate the proportion of large pores, especially in low-permeability samples, which constitute half of the studied collection. The obtained results emphasize the importance of choosing the operating frequency for analyzing rock porosity and permeability using NMR relaxometry, which is particularly important for the application of such data in digitalization and hydrodynamic modeling.
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