Total Organic Carbon Determination by 13C CP/MAS Solid-State NMR in Unconventional Oil/Gas Source Rocks: A Case Study from the Neuquen and Cuyo Basins in Argentina

One of the key parameters in assessing the production potential of unconventional oil and gas reservoirs is the quantification of organic matter, which is generally determined by pyrolysis. Laboratory nuclear magnetic resonance (NMR) is widely used in the oil industry; being a nondestructive method, it enables the possibility to perform several analyses on the same sample, which is desirable due to the heterogeneity of these types of geological formations. C-13 spectra provide much information, from speciation to maturity determination. The main drawback of this technique is the inherently low signal obtained for these nuclei, rendering extremely long experimental times. A solution is using cross-polarization schemes that transfer the high polarization of nearby H-1 nuclei to C-13 ones, with the penalty that quantification is a priori not feasible. In this work, we analyze the cross-polarization evolution and conclude that quantifying the total organic content (TOC) is possible for a wide range of organic matter content and maturities for rock samples corresponding to the Neuquen and Cuyo basins in Argentina.