Fluorescence lifetimes of crude oils and oil inclusions: A preliminary study in the Western Pearl River Mouth Basin, South China Sea

Abstract

Abstract The fluorescence lifetimes were measured for crude oils and oil inclusions in the Western Pearl River Mouth Basin, South China Sea. The results show that the fluorescence lifetimes are long for crude oils in the WC-A sag, short for those in the WC-B sag and moderate for those in the Qionghai and Shenhu uplifts. Two types of oil inclusions were identified in the reservoirs. The fluorescence lifetimes of type I oil inclusions are longer than those of the crude oils in the same reservoir; however, the fluorescence lifetimes of type II oil inclusions are slightly shorter than those of the crude oils in the same reservoir. The fluorescence lifetimes of crude oils have negative correlations with oil density, viscosity, sulfur content, and polar component content, including aromatics, resins and asphaltenes; however, they have a positive correlation with the saturates content of the crude oils. According to these correlations, the physical properties and gross chemical compositions of the two types of inclusion oils were inferred. The characteristics of the type I inclusion oils differ from those of the type II inclusion oils and reservoir crude oils, indicating that two oil charge events occurred in the reservoirs. The reservoirs in this area are inferred to have been first charged by high maturity oils sourced from the Wenchang Formation mudstones deeply buried in the WC-A sag, and then the reservoirs were charged by low maturity to high maturity oils sourced from the Enping Formation mudstones in the WC-A sag and partially mature oils sourced from the Wenchang Formation mudstones in the WC-B sag.