Determination of Hydrocarbon Charging History by Diagenetic Sequence and Fluid Inclusions: A Case Study of the Kongquehe Area in the Tarim Basin

Abstract

Petrographic analysis of hydrocarbon inclusions in reservoirs is the basis and prerequisite for study of hydrocarbon charge history using fluid inclusion analysis. Samples from Silurian reservoirs in the Kongquehe area were studied with microscopy, cathode luminescence and scanning electron microscopy, and the paragenetic sequence of diagenetic events was established. Aqueous and oil inclusions were found in four different occurrences, i.e., ① in healed cracks in detrital quartz grains, ② in quartz overgrowths that were formed relatively early in diagenesis, ③ in healed cracks crosscutting quartz overgrowths and detrital quartz, and ④ in paragenetically late calcite cements. Solid bitumens were found in intergranular pores and in late fractures, whereas gas inclusions occur in healed cracks crosscutting quartz overgrowths and detrital quartz. The homogenization temperatures of aqueous (Thaq) and oil incluisons (Tho) within individual fluid inclusion assemblages are very consistent, suggesting that the microthermometric data are reliable. The Thaq values are generally larger than Tho, indicating the oil charging events took place at significant depths. The results suggest that there were at least two episodes of hydrocarbon charging in the Kongquehe area: the early hydrocarbon charging occurred in late Caledonian, dominated by oil, and the late hydrocarbon charging occurred in the Yanshan‐Himalayan, first by oil and then gases. In addition, two episodes of hydrocarbon reservoir adjustment and destruction occurred in the Hercynian and Himalayan, respectively, forming solid bitumen.