The formation and architecture of Penglai granite intrusion reservoir along the Tanlu strike-slip fault: Implications for basement exploration in the offshore Bohai Bay Basin, North China

Abstract

The hydrocarbon in the basinal basement mostly occurs in the topmost of buried hills along the unconformity, while we present a special play in architecture with the oil-bearing in the lower geomorphic position at the Penglai buried hill. Based on the cores, thin sections, whole rock X-ray, physical property, well logging, and seismic data, we investigated the characteristics of the reservoirs of the Penglai oilfield and discussed the controlling of strike-slip activity, weathering, and lithology on the reservoir in this paper. The results show that the Penglai buried hill reservoirs were mainly distributed in the fractured and weathered granites. The quality of the reservoir is related to mechanics and weathering dissolution behavior among different rocks. The strong dextral strike-slip activity of the Tanlu strike-slip fault zone during the Paleogene resulted in the strong uplift of the Penglai buried hill and also provided the stress condition for tectonic fractures to develop. The dissolution of atmospheric water along the tectonic fractures further improved the reservoir’s physical properties during the nearly 30Ma exposure interval. Compared to granite rocks, mica quartz schist, with higher content of the femic mineral and lower content of feldspar, presents lower brittleness and less soluble minerals. Therefore, the relatively stronger of weathering resistance of mica quartz schist resulted in a higher ring-landform in buried hill geomorphology which surrounds the granite intrusion, controlling the special oil play in architecture with hydrocarbon accumulated in the lower-seated granite reservoir underlying the unconformity.