Abstract: Subtle hydrocarbon reservoirs in Nanpu Sag are mainly divided into updip pinch out reservoirs, lenticular reservoirs, fault-lithologic reservoirs, and unconformability of lap screened reservoirs. Their distribution is determined by the types of the slope break belts, such as fault, flexure, sedimentary, and erosional slope break belts. Geologically, the subtle oil-gas reservoirs are mainly controlled by faults, of which major syn-sedimentary basement faults dominate the formation of various slope break belts that determine the formation and distribution of subtle traps, while oil source faults play an important role in transporting oil and gas from hydrocarbon source rocks to subtle traps. Therefore, the reservoir-forming of subtle reservoirs can be divided into three stages: firstly, faults control slope break belts; secondly, the slope break belts control subtle traps; thirdly, oil source faults transport oil and gas to form reservoirs.

Key words: subtle oil-gas reservoir, genetic type, slope break belt, Nanpu Sag