Abstract:

Different oil resources and hydrocarbons accumulation model were identified in the lower Kongdian Formation and upper Shahejie Formation in the south slope of Niuzhuang sag, Bohai Bay.Oil and source rocks correlation showed that oils of Kongdian Formation were derived from deep Ek₂ and Es₄ members, which have much higher maturity than that of the oils from upper Shahejie Formation. While the oils of the Shahejie Formation and the overlapped formation were sourced from the middle and upper Es₄ member within normal oil window. Several faults with hundreds fault throw developed in the southern Niuzhaung sag make it possible that the Es₄ source rocks met the Ek₁ reservoir resulting in hydrocarbons from the Es₄ accumulated in Ek₁ strata, which caused the formation of the mixed oils of the Kongdian Formation. It was observed that the oils of the Kongdian, Shahejie formations etc were controlled by main faulted tectonic belts. The oils were distributed in the three tectonic belts including Wangjiagang-Dingjiawozi, Bamianhe and Shicun. The oils migrate through faults, uncomformbilities and sand reservoir etc along upper tilted south slope of the Niuzhuang sag. There are at least two primary hydrocarbons migration pathways having a controlling on oil migration of the area.It was proved that the geological background of Dingjiawozi tectonic belt is suitable to form oil pools of lower Kongdian, while Bamianhe faulted belt is much more suitable to form upper oil pools of Shahejie Formation.The Tertiary hydrocarbon accumulation models of the south slope of the Niuzhuang sag are actually controlled by several factors including oil resource, migration system, traps and the distribution of sand reservoir etc. It is significant for extensive oil exploration to recognize the hydrocarbons accumulation models and their primary controlling factors of different formations of the area.

Key words: Shahejie Formation, Kongdian Formation, oil migration, hydrocarbon accumulation model, Niuzhuang sag, Shandong