UV Raman spectroscopy of hydrocarbon-bearing inclusions in rock salt from the Dongying sag, eastern China

Compositions of hydrocarbon-bearing inclusions in rock salt (halite) from the Shahejie Formation in the Dongying sag, Bohai Bay Basin, eastern China have been analysed by Raman spectroscopy coupled with a 244 nm UV laser source. The fluorescence effect caused by the conventional visible laser excitation of the aromatic fractions of HC-bearing inclusions can be effectively avoided. Six types of HC-bearing inclusions belonging to two generations have been identified in halite according to their hydrocarbon types and petrographic characteristics. The presence of HC-bearing inclusions in halite provides evidence of crystal fracturing and healing, plastic deformation and dynamic recrystallization of rock salt in the Dongying sag. This proves that rock salt may have repeatedly lost and then recovered its sealing capacity during two stages of oil emplacement. Water and hydrocarbons were detected by UV Raman spectroscopy in the studied samples, in both HC-bearing inclusions and aqueous inclusions. These results are important for understanding the formation conditions of these fluid inclusions and the interactions between the formation water and petroleum in reservoirs. Our results show that UV Raman spectroscopy has a potential to become a powerful tool for analyzing hydrocarbon-bearing fluid inclusions trapped in various elements of a petroleum system.