Alon Amrani, Ph.D.
Professor at the Institute of Earth Sciences
Hebrew University of Jerusalem
Predicting and measuring the extent of thermochemical sulfate reduction (TSR) and thermal cracking of organic sulfur (TCA) are important elements in risk assessment that seek to understand hydrocarbon quality and H2S concentration in petroleum reservoirs. Compound specific S isotope analysis (CSSIA) of organic S compounds (OSC) using a GC coupled to multi-collector inductively-coupled plasma mass spectrometry (GC-MC-ICPMS) have been shown to be very useful for such studies (Amrani et al., 2012 , Rosenberg et al., 2017, Amrani et al., 2019). This new and highly sensitive approach enables us to evaluate the occurrence and extent of TSR and TCA and identify reaction pathways in several key petroleum basins from around the world. These basins include the Smackover Formation (USA), Tarim Basin (China), the Big Horn (USA), Alberta Basin (Canada) and the Middle East. Results from these studies have shown that the d34S values of specific OSC groups such as sulfides, benzothiophenes (BTs), dibenzothiophenes (DBTs), and thiadiamondoids (TDs) varied significantly (up to 50‰) and have unique patterns according to their thermal stability (Gvirtzmann et al., 2015). Experiments and Ab Intio calculations at different temperatures, pH, ionic strength, hydrocarbon compositions and isotopic exchange in recent years revealed further important insights about TSR and TCA mechanisms. In recent years this approach was also applied to natural gas, even without the presence of liquid petroleum, thus expanding our ability to trace the sources of H2S, and provide new and possibly improved proxies for such process (Kutuzov 2021).