Abstract:

Recent exploration within the second member of Funing Formation（hereinafter referred to as Fu-2 member）in Gaoyou Sag of Subei Basin has marked a significant advancement in the understanding of shale oil potential, highlighting its role in enhancing future reserves and production. This study focuses on Well-X1, utilizing a comprehensive suite of analytical techniques, including imaging logging, core examinations, and micro thin section analysis, to investigate the fracture characteristics across different scales. Additionally, statistical analysis of fracture parameters and isotopic studies of stable carbon and oxygen in fracture fillings provide insights into the formation stages of the fracture. The research delves into the dynamic evolution of fractures and their influence on the accumulation of shale oil and gas. Key findings indicate that structural fractures, predominantly brittle shear and tensile shear fractures, are prevalent and characterized by substantial length and excellent transverse connectivity. Non-structural fractures, including bedding fractures and calcite veins, exhibit some areas of abnormal development. These natural fractures have undergone modifications during later stages, with incompletely filled fractures, pore spaces from dissolved fracture fillers, overpressure bedding fractures, and micro fractures identified as particularly favorable reservoir spaces for shale oil. The results of this study not only shed light on the complex fracture dynamics within the shale but also provide a robust theoretical foundation for evaluating deep shale oil prospects in Gaoyou Sag.

Key words: Gaoyou Sag, Fu-2 member, shale, characteristics of fractures, formation stage