Analysis of the Subsidence History in Nanpu Sag

Nanpu Sag is a small scale fault basin in Bohai bay, and great breakthrough has been made in recent years in oil and gas exploration. Comparatively speaking, the understanding about the basin structure and subsidence evolution is poor. The research of subsidence history is very importance for the research of oil and gas and forecast the favorable structural belts. With back stripping method, tectonic subsidence rate of Nanpu Sag has been restored, and the phases of tectonic activity have been divided. Controlled by tectogenesis, the tectonic subsidence of Nanpu Sag can be divided into three phases, including rifting phase, depression phase, and post rift accelerated subsidence phase. Paleogene is charactered by episodic subsidence. Es₃⁴⁺⁵ is phase I rifting episode, Es₃³-Es₂ is phase Ⅱ rifting episode, Es₁ is phase Ⅲ rifting episode, Ed₃-Ed₁ is phase Ⅳ rifting episode. Back stripping method is an effective method for geohistory restoration, providing theoretical basis for the research of subsidence history.