The deep hydrocarbon accumulation process in the Tuoputai area, Tarim Basin: Constraints from calcite U-Pb and crude oil Re-Os dating

Abstract

The deep Ordovician reservoirs within the Tuoputai area, Tarim Basin, exhibit a complex geological setting involving multi-stage hydrocarbon generation and charging. Traditional methods for reconstructing the hydrocarbon accumulation process, such as fluid inclusion analysis combined with basin modeling, are often unreliable due to controversial burial and thermal history. Recent advances in in-situ calcite U-Pb dating and crude oil Re-Os dating have provided precise chronological constraints on hydrocarbon charging and generation. In this study, we synergistically combined traditional fluid inclusion analysis with advanced in-situ calcite U-Pb dating and crude oil Re-Os dating, focusing on crude oil samples and calcite fabrics hosting oil inclusion, to quantitatively constrain the timing of oil charging and generation and then reconstruct the hydrocarbon accumulation process. Integration of fluid inclusion data with basin modeling revealed three distinct charging episodes: Late Caledonian, Late Hercynian, and Himalayan orogeny. Calcite U-Pb dating constrained the timing of the initial two charging events at approximately 433.0 Ma and ca. 278.9 Ma, respectively. Re-Os dating of northern heavy oils and southern medium/light oils provided absolute chronological constraints for two generation events during the Late Hercynian (270 ± 20 Ma) and Late Caledonian (459 ± 81 Ma) orogeny, respectively. Isotope dating data provided crucial absolute age constraints for accurately restoring the complex hydrocarbon accumulation process. The method has great potential for application in the study of the accumulation process in similar complex basins worldwide.