Crossing Conjugate Normal Faults and Hydrocarbon Accumulation in the Offshore Bohai Bay Basin, Eastern China

Yu, Yixin; Zhou, Xinhuai; Xu, Changgui

Conjugate normal faults are two sets of steeply dipping normal faults having parallel strikes but opposite dips, which are commonly developed in regions of extensional setting. Intersecting and crossing conjugate normal faults can produce the characteristic of simple and complex X-pattern faults system in cross-section. Although many researches on conjugate normal faults have been completed, there are some controversy on their formation processes and mechanisms. The high-quality 3-D seismic data in the offshore Bohai Bay Basin which is a Cenozoic rift basin with a rhombus-shape and one of the largest oil production basins in eastern China, clearly show numerous simple and complex conjugate normal faults, which offers good examples for analyzing conjugate normal faults. According to their properties, the conjugate normal faults in the study area could be divided into two types which involves the incipient and inherited conjugate normal faults. The incipient conjugate normal faults with samll scales and simple X-pattern in cross-sections are limited to the vicinity of the Tan-Lu strike-slipping fault, and develop in the Neogene and Quaternary. The inherited conjugate normal faults have larger scales, and also occur in wider area. In cross-sections, the inherited conjugate normal faults have complex X-pattern and formed linked faults system. The strara faulted by the inherited conjugate normal faults involve the pre-rift basement, syn-rift Paleogene and post-rift Neogene. In addition, the two types of conjugate faults have different formation mechanisms. The incipient conjugate normal faults were related with the dextral strike-slipping movement of the Tan-Lu fault, and formed during the simultaneous slip on the crossing faults. However, the development of the inherited conjugate normal faults were resulted from the preferentially reactivation of the pre-existing basement faults. The unique conjugate assemblage of the X-pattern normal faults offer abundant traps for hydrocarbon accumulation, which involve faulted block traps, faulted anticline traps and buried hill traps. The faults are also favorable migration pathways along which oil and gas could migrate from deep source rock into shallow reservoirs.

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