Evolution of sulfur speciation in bitumen through hydrous pyrolysis induced thermal maturation of Jordanian Ghareb Formation oil shale

摘要

Previous studies on the distribution of bulk sulfur species in bitumen before and after artificial thermal maturation using various pyrolysis methods have indicated that the quantities of reactive (sulfide, sulfoxide) and thermally stable (thiophene) sulfur moietiesChange followingConsistent trends under increasing thermal stress. These trends show that sulfur distributionsChange during maturation in ways that are similar to those ofCarbon, mostClearly illustrated by the increase in aromatic sulfur (thiophenic) as a function of thermal maturity. In this study, we have examined the sulfur moiety distributions of retained bitumen from a set of pre-and post-pyrolysis rock samples in an organic sulfur-rich,Calcareous oil shale from the UpperCretaceous Ghareb Formation. SamplesCollected from outcrop in Jordan were subjected to hydrous pyrolysis (HP). Sulfur speciation in extracted bitumens was examined using K-edge X-ray absorption near-edge structure (XANES) spectroscopy. The most substantialChanges in sulfur distribution occurred at temperatures up to the point of maximum bitumen generation (similar to 300 degrees C) as determined fromComparison of the total organicCarbonContent for samples before and after extraction. Organic sulfide in bitumen decreased with increasing temperature at relatively low thermal stress (200-300 degrees C) and was not detected in extracts from rocks subjected to HP at temperatures above around 300 degrees C. SulfoxideContent increased between 200 and 280 degrees C, but decreased at higher temperatures. TheConcentration of thiophenic sulfur increased up to 300 degrees C, and remained essentially stable under increasing thermal stress (mg-S/ g-bitumen basis). The ratio of stable-to-reactive+ stable sulfur moieties ([thiophene/(sulfide + sulfoxide+ thiophene)], T/SST) followed a sigmoidal trend with HP temperature, increasing slightly up to 240 degrees C, followed by a substantial increase between 240 and 320 degrees C, and approaching aConstant value (similar to 0.95) at temperatures above 320 degrees C. This sulfur moiety ratio appears to provideComplementary thermal maturity information to geochemical parameters derived from other analyses of extracted source rocks.