Structural Evolution and Deformation Mechanism of Maichen Sag in Beibu Gulf Basin,South China Sea

In light of offshore seismic and well data,from key controlling factor——tectonic stress field and its changes V. S geological time,structural style,fault system and structural evolution and structural deformation mechanism of Maichen Sag in Beibu Gulf Basin were re-analyzed through structural geometry and structural kinematics method. Study showed that Maichen Sag experienced two periods of crucial changes of tectonic stress field: One was,since Early Oligocene,regional tectonic stress field changed from NW-SE trend extension of early rift stage to nearly S-N trend extension clockwise,and made structural deformation of Maichen Sag change from simple orthogonal extension to oblique extension. Another,the end of Oligocene,Maichen Sag evolved from rift-depression to depression.On regional tectonic stress field change,the Cenozoic of Maichen Sag was divided into early rift,middle rift-depression transition and late depression. Stratigraphic sections of different structural evolution stages displayed difference and regularity of structural style and fault system,and controlled pool-forming factors and their match as well. Oligocene Weizhou formation during middle rift-depression stage was thought of as the most favorable for hydrocarbon migration and accumulation.