The Hydrocarbon Migration and Accumulation Model of Shallow Layers in Sub-Sag, Slope and Salient of Continental Rift Basin: A Case Study of Huanghekou Sag in Bohai Bay Basin

Chen, Lei; Tian, Lixin; Zhou, Xinhuai; Niu, Chengmin; Zeng, Xuan

Huanghekou sag which is a dustpan shape sag in Cenozoic is a hydrocarbon-rich area in Bohai Bay basin, with many large-scale extensional faults that provide a good pathway for the vertical migration of hydrocarbon. Up to now, over 600 million cubic meters of oil equivalent have been found here, while shallow layers is the main and mature exploration layers, the ratio of reserve is mostly 70%.

In order to keep a sustainable exploration in shallow layers, three different hydrocarbon migration and accumulation models are generalized: meshwork-carpet model in sub-sag, transfer station model in slope and notching model in salient. The meshwork-carpet model is made up of three-layered structure: the lower section is meshwork layers of oil source passages, which consist of many faults cutting in source rocks and providing hydrocarbon for shallow layers; the middle section is storage layers, and it is glutenite of fluvial facies, with good connectivity, wide distribution and large thickness, which accumulates hydrocarbon from deep source rocks through faults; the upper section is meshwork layers of hydrocarbon accumulation, including the faults cutting in storage layers and shallow sandbodies, through which hydrocarbon migrates and accumulates. In the transfer station model, the subsea fan sandbodies deposited in the downthrow block of the large-scale extensional faults play an important role, and they could absorb most of the hydrocarbon produced in the hydrocarbon rocks, because of the large contact plane with the hydrocarbon source rocks; the episodic activities of the faults lead to the migration of hydrocarbon from sandbodies to shallow layers along the faults, which forms the reservoir. In the notching model, hydrocarbon migrates from the high potential area in slope to the low potential area in salient along faults, unconformity interfaces and sandbodies spatially, forming the stepped passage system; therefore, the shallow layers in salient is the final destination of accumulation.

In recent years, many shallow fields have been found from sub-sag to salient with reserve of 150 million cubic meters under the guidance of the three models, which are also a great help to the exploration in the similar continental rift basin.

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