Abstract: As a landmark product of oblique extension, a fault concentrated zone is the main place for the formation and accumulation of fault block reservoirs. The hydrocarbon enrichment difference in fault concentrated zones with different strike directions in the Qikou Sag was analyzed by statistical analysis of geometric characteristics and structural combination styles of fault concentrated zones in this sag, combined with the formation and evolution law of fault zones. The results show that there are mainly three kinds of fault zones in the Qikou sag: NEE-trending, EW-trending and NNE-trending. Hereinto, the NNE-trending fault zones were formed at the earliest time, the vertical transport ability of the faults are the weakest, and hydrocarbons are enriched in the deep layers; the NEE-trending fault zones were formed later, and the faults have the strongest destructive effect on cap rocks, and hydrocarbons are distributed in both deep and shallow layers; the EW-trending fault zones were formed at the latest, and the vertical transport ability of the faults is between the former and the latter. The research results can provide theoretical support for oil and gas exploration in the Qikou Sag and similar multi-stage rift basins with concentrated fault zones.

Key words: fault concentrated zone, oblique extension, secondary fault, multi-stage rift, vertical sealing property of fault, Qikou Sag