Abstract:

The analyses of the mode of structural evolution in Qikou sag showed that，graben faulting of Paleogene generate complex half graben-like framework on NW-SE orientation and complex duplex fault graben on N-S orientation in Qikou sag. The tectonic framework of the convex, concave and concave-uplift alternately formed in Qikou sag，which created favorability for the formation of the lithologic reservoir. The high-quality source rocks developed in the sedimentary center were material foundation of the development of the lithologic oil reservoirs. Synsedimentary fault and its configuration decided the characters of gullies controlling sources，transform zones controlling fans and faulted slopes controlling sands，and that the middle of subaqueous fan，delta front and infralittoral subaqueous fan were the most favorable hydrocarbon accumulation zones. The development of the faults make the deep oil-gas accumulation more favorable，which provided effective reservoir space for the development of the lithologic oil reservoir. Tectonic activity and sedimentary evolution formed the optimal configuration relationships of the source-reservoir-cap，which created favorable conditions for the formation of multi-types lithologic oil reservoirs. According to the lithologic oil reservoir types，spatial distribution characteristics and oil accumulation characters in Tanan sag，four kinds of lithologic oil reservoir forming modes are summarized，including the fault terrace-steep slope-break belt，fault terrace-gentle slope-break belt，cliff-steep slope-break belt and inner basin slope, break belt reservoir forming mode of Qikou sag, combining the geological structure characters. In Qikou sag, 4 types of oil-gas accumulation modes are formed：accumulation of shelving, accumulation of actic region, accumulation of fault flight of stairs, accumulation of break in slope of Qikou sag.

Key words: Qikou sag, structural evolution, oil-gas accumulation mode