The Structural Styles and Strike-slip Movement of Tan Lu Fault Zone in Late Pleistocene and The Formation of Oil Traps in Bohai Bay Area

Gong, Zaisheng¹, Sitian Li² (1) China National Offshore Oil Corporation, Beijing, China (2) China University of Geosciences, Beijing, China

In the 1990's, seven important oil fields, including the giant oil field PL19-3 have been found in Bohai Bay area and located in or near the Tan Lu fault zone---the largest strike-slip fault zone in eastern China. Based upon the 3D seismic data analysis, the detailed structural images of the oil bearing areas in Tan Lu fault zone have been revealed. During the rifting phase in Paleogene, the evolution of Tan Lu fault zone was controlled by right-lateral tenso-shear tectonic regime and a series of NNE and EW trending depressions and uplifts were formed, which were the primary controlling factors on the depositional processes and framework. After a relative quiescent post-rifting stage in Neocene, the evolution of Tan Lu turned into right-lateral compresso-shear regime in late Quaternary. 3D seismic images shows that lots of close NE trending faults in en echelon style distributed in Tan Lu zone in many districts, and the anticline traps with flower structures, including the traps PL19-3 and PL25-6, were developed in the same processes. Dating ages of carbon isotope and uranium series analysis revealed that the unconformity on the top of the anticline trap PL19-3 were formed in late Pleistocene which indicate the oil migration and accumulation processes have been developed in a very short geological period.