Abstract: In terrestrial rift basins, faults and sand bodies are the main elements of hydrocarbon migration network. In order to explore the mechanism of hydrocarbon migration and accumulation in the Chengbei fault terrace zone of Qikou sag under the control of fault-sand configuration transportation conditions, the types of fault-sand configuration and their controlling effect on hydrocarbon migration and accumulation were analyzed through quantitative evaluation of fault and sand body conductivity. The results show that the fault-sand configuration can be divided into four types according to the main functions of faults in the process of hydrocarbon accumulation, including configuration of oil source faults and multiple sets of sand bodies superposed vertically, configurations of transport faults and sand bodies terraceped forward and backward, and configuration of adjusting faults and sand bodies in "Y" shape with a "relay-style" accumulation model formed in the space. The controlling effect of fault-sand configuration on hydrocarbon enrichment is mainly reflected in three aspects:1) Control the types of oil and gas reservoirs:The configuration of oil source faults and multiple sets of sand bodies mainly controls the formation of structural-lithologic and fault block oil-gas reservoirs, the configurations of transport faults and sand bodies in the forward or reverse direction control the formation of fault block, fault nose, and composite oil-gas reservoirs, and the configuration of regulating faults and sand bodies in "Y" shape controls the formation of fault block oil-gas reservoirs; 2) Control the hydrocarbon migration process:The configuration of oil source faults and large zone sand bodies at the fault root connects the deep hydrocarbon source, during the activity period of oil source faults, oil and gas migrate along the fault to the shallow layers, and then accumulate in the high part of fault terrace zone after a long distance migration. The terrace-by-terrace vertical or reverse configuration of transport fault and sand body provides the terrace-by-terrace vertical and lateral migration channel for hydrocarbon, and the configuration of adjusting faults and sand bodies plays a role of readjustment and distribution in the process of hydrocarbon accumulation; 3) Control the position of hydrocarbon migration and accumulation:When the probability of fault migration f is more than 50% and the ratio of sandstone thickness to total formation thickness is more than 0.50, the fault-sand configuration is considerred to be completely fluidly connected. In the middle-shallow layers, oil and gas migrate along the transport fault, and the sealing property of the transport fault controls the hydrocarbon accumulation, while in the middle-deep layers, the degree of oil and gas accumulation is positively related to the ratio of sandstone thickness to total formation thickness.

Key words: fault-sand configuration, fault transport probability, hydrocarbon accumulation, reservoir forming model, Chengbei fault terrace zone, Qikou sag