Abstract: Sedimentary facies study was combined with seismic data interpretation and tectonic correlation to analyze the features of faults development in the Mafang area of Ordos Basin,so as to gain a deep insight into the characteristics and accumulation pattern of oil reservoirs in the 8^th member of the Yangchang Formation.The research shows that the reservoirs were developed in delta-plain distributary channel sands with high-porosity and high-permeability and distributed on the slope belts along the two flanks of the Tianhuan sag.Oil reservoirs were mainly distributed in the east flank.In contrast,fewer reservoirs occur in the west flank.However,the northwest-southeast striking normal fault developed in the central Mafang area readjusted and destroyed the reservoirs in the foot wall.The accumulation pattern of the reservoirs can be summarized as the high-porosity and high-permeability sand bodies in the distributary channels were the reservoirs,litho-logical traps bounded by mudstone provided accumulation space for oil;later faulting activities connected and adjusted the previously-formed reservoirs and faulted anticline formed by opposite normal faults was important structural locations for oil and gas to accumulate.

Key words: fault, oil accumulation pattern, resesrvoiring model, Yangchang Formation, Mafang area, Ordos Basin