Characteristics of Neogene Tan-Lu Faults and Its Role in Controlling Young Traps: An Extreme Case of the Eastern Offshore Bohai Bay Basin, Eastern China

Qiang Kun-sheng, Lü Xiu-xiang, Zhou Xinhuai, Xu Changgui, Lan Xiaodong

The Tan-Lu fault zone, which was initially recognized from an aeromagnetic anomaly in 1957, is the most important structure in eastern China. The zone originates in central China, cuts across the entirety of eastern China and finally extends into Russia, striking NNE-SSW along a length of about 3000 km. The fault a length of about 400 km, and a width of about 20km-45 km in the Bohai sea area. So that, The Tan-Lu fault is an important factor controlling hydrocarbon accumulation in the eastern offshore Bohai Bay Basin. Most researchers have concentrated on the characteristics of Paleogene fault, but the characteristics of fault in Neogene, such as spatio-temporal distribution, fault level, activity phase and dynamic model, and its controlling effect upon young traps is little studied in the study area.

By using high-resolution 3D seismic reflection datasets, structural mapping, balanced cross-section analysis with borehole data of the study area, we determine the typical characteristics of fault and impact of the Neogene continual strike-slip movement and its derived movement to types, position of young traps and their relationship with both faults and fractures.

Analysis of the characteristics of Neogene active faults shows that two major tectonic stages with different stress systems contribute to development of extensive faults, strike-slip faults and a little reverse faults during the Neogene. In the plane, the fault is mainly NE, NW-trend. In the section, the fault shows obvious hierarchical differences. In Miocene, the extension movement predominates and only a few faults develop. While in Pliocene the en echelon normal fault is most developed. The seismic data shows the flower and floral-like structure, and oblique-slip phenomenon also has been seen near the boundary faults of depression and uplift. Balanced cross-section analysis shows that in Miocene tectonic activity is weak, but from the Pliocene to quaternary strike-slip activity intensifies. The NNE-trending main faults and its associated en echelon tensional faults control the development of faulted anticline, complex fault blocks and nose-fault traps. Faulted anticline traps formed by transtension are the most common. In the transition part of the fault, transpression stress forms transpressional faulted anticlinal traps. The recent important breakthrough of hydrocarbon exploration has demonstrated that the faults continued in the Pliocene strike-slip activities lead to the formation of plenty of complex fault block traps, the rapid accumulation of hydrocarbon and the effective improvement of the reservoir properties. The Pliocene shallow strata (610m-1499m, 2001ft-4918ft) will be the favorable exploration areas.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013