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NMR measurement of oil shale magnetic relaxation at high magnetic field

Joseph D. Seymour·Kathryn E. Washburn·Catherine M. Kirkland·Sarah J. Vogt·Justin E. Birdwell·Sarah L. Codd
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Abstract

Nuclear magnetic resonance (NMR) at low field is used extensively to provide porosity and pore-size distributions in reservoir rocks. For unconventional resources, due to low porosity and permeability of the samples, much of the signal exists at very short T 2 relaxation times. In addition, the organic content of many shales will also produce signal at short relaxation times. Despite recent improvements in low-field technology, limitations still exist that make it difficult to account for all hydrogen-rich constituents in very tight rocks, such as shales. The short pulses and dead times along with stronger gradients available when using high-field NMR equipment provides a more complete measurement of hydrogen-bearing phases due to the ability to probe shorter T 2 relaxation times (<10 -5 sec) than can be examined using low-field equipment. Access to these shorter T 2 times allows for confirmation of partially resolved peaks observed in low-field NMR data that have been attributed to solid organic phases in oil shales. High-field (300 MHz or 7 T) NMR measurements of spin-spin T 2 and spin-lattice T 1 magnetic relaxation of raw and artificially matured oil shales have potential to provide data complementary to low field (2 MHz or 0.05T) measurements. Measurements of high-field T 2 and T 1 -T 2 correlations are presented. These data can be interpreted in terms of organic matter phases and mineral-bound water known to be present in the shale samples, as confirmed by Fourier transform infrared spectroscopy, and show distributions of hydrogen-bearing phases present in the shales that are similar to those observed in low field measurements.

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Joseph D. Seymour, Kathryn E. Washburn, Catherine M. Kirkland, Sarah J. Vogt, Justin E. Birdwell, Sarah L. Codd. 2013. NMR measurement of oil shale magnetic relaxation at high magnetic field. https://pubs.usgs.gov/publication/70074054

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