Fan deltas are important reservoirs for hydrocarbon accumulation. A reliable depositional model of fan deltas is an essential guide for reservoir prediction. The Baikouquan Formation of Lower Triassic in the Mabei area, a target of hydrocarbon exploration, is characterized by the development of fan-delta systems. Although a lot of studies have been done, it is still controversial about the depositional model of fan delta. Many researchers suggest that inner-channel and inter-channel of fan-delta plain are coarse-grained deposits and muddy deposits respectively, and fan-delta front is dominated by coarse-grained deposits from channel flow. This model, however, is not consistent with a comprehensive analysis of flume experiment, modern depositional systems and a subsurface dataset from the Mabei area. Such contradiction probably means that depositional model of fan delta has to been improved. (1) Fan-delta plain is completely coarse-grained deposits without muddy deposits, while mudstones interbeded with coarse-grained deposits are actually formed at fan-toe and inter-fans during the regression of fan deltas. (2) Fan delta front is dominated by sheet-like, coarse-grained deposits from sheet flow, which is adjacent to coarse-grained deposits of fan delta plain. (3) In fan-delta plain, four types of deposits, including braided channel deposits, conglomeratic overbank deposits, subaerial outer-fan mud deposits and subaerial debris flow deposits, have been identified, and the braided channels deposits are excellent reservoirs for hydrocarbon accumulation. (4) In fan-delta front, four types of deposits, including conglomerate shoal deposits, sandy shoal deposits, subaqueous debris flow deposits, and subaqueous outer-fan mud deposits, have been identified, and the sandy shoals deposits are excellent reservoirs for hydrocarbon accumulation. Based on these different viewpoints, the understanding and prediction of the Baikouquan reservoirs could be enhanced. Additionally, the models constructed in this paper may have important implications for reservoirs prediction in other areas.
