莱州湾凹陷层序地层格架及幕式油气成藏

莱州湾凹陷是渤海湾盆地典型的断陷湖盆之一,由于受构造升降、古地貌和古气候等因素的影响,其层序地层格架由低位、湖侵、高位和河流体系域组成。构造升降不仅是莱州湾凹陷油气成藏具有幕式成藏特点的直接原因,而且晚期构造活动是影响该区早期形成的油藏最终能否保存下来的关键因素。古近纪晚期济阳坳陷的区域性地壳抬升,使莱州湾凹陷走滑构造带的主断层上升盘东营组顶部沉积盖层遭受剥蚀,使早期运聚形成的油藏中的部分原油被生物降解,新近纪充注的油气因上覆地层加厚而得以成藏。从而可以预测,该凹陷周缘走滑构造带的主断层下降盘和中央隆起构造带是其最有利的油气聚集区带。

Sequence Stratigraphy Model and Episodic Generation and Accumulation of Oil-gas Reservoirs in Laizhouwan Sag,Bohai Gulf Basin

Laizhouwan sag is one of the typical rift lacustrine basins in the Bohai Gulf Basin. Due to tectonic movement, palaeotopography and palaeoclimate, the sequence stratigraphy models of Laizhouwan sag are composed of lowstand, transgressive, highstand and fluvialsystem tracts. Tectonic movement is the direct cause of episodic hydrocarbon accumulation of Laizhouwan sag and the neotectonicmovement or late-stage tectonization determines whether the hydrocarbon reservoirs formed at early stage can preserve well or not in thesag. The partial crude oil of reservoirs that formed by being migrated and accumulated at early Paleogene is biodegraded due to the topsedimentary cover of Dongying Formation, which is the upthrow side of the main faults in strike-slip structural belt, Laizhouwan sag, isexposed to denudation caused by the tectonic uplift of Jiyang Depression in Late Paleogene. As a result, the oil and gas were poured inNeogene is preserved and formed reservoirs. Therefore, it is predicted that the downthrow side of main fault in the strike-slip structuralbelt and the central uplift zone are most favourable for oil and gas accumulation.