ABSTRACT: Determination of Rank in Source Rocks by High Resolution NMR Spectroscopy
DICKINSON, WARREN, Victoria University, Welling, New Zealand, R. H. NEWMAN, Chemistry Division, DSIR, Petone, New Zealand, and J. D. COLLEN, Victoria University, Wellington, New Zealand
Nuclear Magnetic Resonance (NMR) spectroscopy provides a nondestructive technique for measuring the chemical properties of organic matter. When first used to study maturation in source rocks over 10 years ago, 13C-NMR could only measure the aromatic and aliphatic structural groups in kerogen. Now, with further refinement of technique we can measure oxygen-substituted phenolic groups on aromatic rings, as well as carboxylic groups and secondary alcohols.
We have examined over 150 coal and shale samples of various ranks from mines, outcrops, and wells in New Zealand and North America. All parameters measured by vitrinite reflectance, Rock-Eval, and NMR show a high degree of correlation to increasing rank. However, between serial plies or samples known to have the same rank, all of these parameters except oxygen-substitution, as determined by NMR, show a certain degree scatter. Much of this scatter is due to variation in the chemical composition and hydrogen content of the vitrinite. Our findings suggest the oxygen-substitution parameter is invariant to chemical variations in type III kerogens of the same rank. This parameter, which measures the loss of oxygen from aromatic carbon, is a site-specific reaction dependent on temperature. T us, it is free from the many variables that plague other maturation indices and prevent accurate determination of rank.
Although NMR equipment is expensive, the chemical information obtained from small samples of potential source rocks make it a valuable tool for petroleum geochemistry. However, to become widely used, NMR methods and hardware must become standardized.
AAPG Search and Discovery Article #91015©1992 AAPG International Conference, Sydney, N.S.W., Australia, August 2-5, 1992 (2009)