INFLUENCE OF DEPYRITIZATION ON NMR RELAXATION PARAMETERS OF ALEKSINACOIL-SHALE KEROGEN

Parallel proton and cross-polarization/magic-angle spinning (CP/MAS) n uclear magnetic resonance (NMR) relaxation measurements are reported o n Aleksinac oil shale kerogen concentrate and pyrite-free kerogen conc entrate. Possible relaxation mechanisms considered include proton-prot on and C-13-proton interactions. The influence of depyritization on re laxation parameters is estimated. Depyritization prolongs the T-1H rel axation time constant by about five times. However, depyritization has no significant influence on relaxation in the rotating frame (<5%). T he probable explanation is that there is a certain motion of structura l units with spectral density in the kHz region, which averages dipola r interactions between protons and pyrite. The repetition delay is fou nd to be 150 ms for kerogen concentrate and 1-2 s for depyritized kero gen concentrate. The favourable value of contact time is identical for both samples, i.e., 1 ms. At the same time there are no significant c hanges observed in the CP/ MAS spectra of Aleksinac oil shale kerogen due to depyritization treatment, except for a small band (approximate to 60 ppm) assigned to alcoholic groups which appeared as a result of the partial reduction of carbonyl groups. Use of the pyrite-containing Bg sample in solid-state NMR investigations is found to be more favou rable because of its shorter T-1H relaxation time and, consequently, s horter (by a factor of about five) experimental time. (C) 1998 Elsevie r Science Ltd. All rights reserved.