Influence of turbostratic carbon nanostructures on electrical conductivity in shales

• Shales (~0.6 to > 4.5 %Re) were examined by HRTEM
• Turbostratic carbon nanostructures were found in all samples and verified by EELS
• Organic rich shales ( > 3.6 %R) exhibit anomalously high electrical conductivity
• Electrical conductivity correlates with the frequency of turbostratic carbon

Shales spanning a range of thermal maturity (~ 0.6 to > 4.5%Re) were examined by high resolution transmission electron microscopy (HRTEM) in order to characterize the occurrence of turbostratic carbon nanostructures. Such structures, termed Basic Structural Units (BSU), were found in both demineralized and whole-rock samples. Highly aromatic turbostratic nanostructures found in a pre-oil window shale were verified by electron energy loss spectroscopy (EELS). Turbostratic nanostructures increase in abundance with increasing thermal maturity with their greatest frequency occurring in high maturity (> 3.6%R), natural and artificially matured organic rich shales that exhibit anomalously high electrical conductivity in well logs. We hypothesize that these turbostratic carbon nanostructures initially form upon oil generation, increase in frequency with increasing thermal maturation, and eventually become numerous enough to establish mutual contact, either directly or through graphene-like sheets, so that the shale becomes conductive on a macroscopic scale.