Abstract: Comprehensive studies on seismic, core, well logging, mud logging, well testing and laboratory data show that the primary reservoirs in lower Es₁(the lower first sub-member of Shahejie Formation) of the Banqiao slope in the Qikou sag are sand reservoirs developed with hyperpycnal flow. Such sediments are generally located in a semi-deep to deep lacustrine environment. The lithologic composition is characterized by gray-black mudstone with medium-fine sandstone or their interbeds. In the sandstone segment, the sequence of sedimentary grains is a series of upwardly-coarsening units (inverse grain sequence) in pairs with a series of upwardly-thinning units (positive grain sequence); intralayer eroded surfaces are developed; and various types of fluviatile bedding structures can be found, such as cross-bed bedding, parallel bedding, climbing bedding and lenticular bedding. Hyperpycnal flow sediments involves eroded water channels, channel complexes, branch channels, proximal sand bars, distal sand bars and sheet lobes, of which the channel complexes have large monolayer thickness, coarse granularity, good sorting, low shale content and good reservoir properties. According to seismic attributes, sandstone thickness and core observations, the sedimentary distribution of the hyperpycnal flow has been analyzed in lower Es₁ of the Banqiao slope in the Qikou sag. Based on the result, the targeted pre-exploration plan has delivered good results; the single-well production test is high and stable. This proves the promising exploration of lithologic reservoirs in the middle and deep hyperpycnal flow in continental rifted basins.

Key words: rifted basin, Qikou sag, hyperpycnal flow, lithologic reservoir