Abstract: Jiyuan sag is a Mesozoic-Cenozoic superposed basin that has experienced multi-stage structural movement and reformation, after Early- Middle Triassic carbon basin shrinking. Upper Paleozoic (C-P) and Mesozoic (T3, J1-2) are main hydrocarbon source beds, multi-stage structures and fault-block activity lead to multi-stage hydrocarbon generation and a number of oil and gas migration and accumulation periods. Reservoirs were mainly accumulated during the secondary hydrocarbon generation from mid-Yanshanian to Himalayan. Intersected fault blocks are themain traps in the structures dominated by fault nose and fault blocks. Secondary pores or structure fracture zones developed in deep reservoirs are the key factors for hydrocarbon accumulation.Many a sets of reservoir combinations are connected through late-stage fault activities, so hydrocarbon reservoirs including faults, lithologic faults and buried hills are distributed congruently. And the distribution pattern of the reservoirs is the controlling factor for the formation and preservation of hydrocarbon reservoirs. The unique secondary hydrocarbon generation leads to the formation of abundant oil and gas resources, and the gas prospect in the sag gets broad. However, no breakthroughs have been made in the exploration of the sag in the past years.So there still exist many difficulties in finding out new geological theories and evaluating methods that are urgently needed for the recognition and understanding of multi-stage reservoir formation and preservation.

Key words: Jiyuan sag, hydrocarbon regeneration, reservoir forming factor, fault gas reservoir, hydrocarbon potential