Hydrocarbon accumulation is closely related with regional tectonic setting and basin formation and evolution.It's pointed out that four stages of critical tectonic transformation occurred in Jiulongjiang Sag through the analysis of two-dimensional multichannel seismic data and regional geological data.As a result

four unconformities formed during the Taiping

Oujiang

Puli and Hai'anshan movements.Controlled by different geodynamic backgrounds and tectonic stress fields at different stages

three styles of extensional structures

namely the stepwise

horst-graben and sliding fault terrace

and two styles of inverted structures

namely fault-restricted and flexural fold structures

are developed in the sag.Through the analysis of tectonic stress backgrounds and hydrocarbon accumulation conditions at different stages

it is believed that the Taiping and Oujiang movements laid the foundation for the formation of traps in the Jiulongjiang Sag

and was a major factor for the development of extensional structural traps;while the uplifting caused by the compressive force from the late Oujiang movement prompted the formation of inverted structures

providing favorable trap conditions for hydrocarbon accumulation.