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 T2 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 T2 relaxation times (<10-5
sec) than can be examined using low-field equipment. Access
to these shorter T2 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 T2 and spin-lattice T1 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 T2 and T1-T2 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.
Additional Publication Details
NMR measurement of oil shale magnetic relaxation at high magnetic field