渤海湾盆地渤中凹陷西南洼古近系东营组超压分布特征及成因

Distribution and origin of overpressure in the Paleogene Dongying Formation in the southwestern sub-sag， Bozhong Sag， Bohai Bay Basin

杨小艺 刘成林 王飞龙 李国雄 冯德浩 杨韬政 何志斌 苏加佳

Xiaoyi YANG Chenglin LIU Feilong WANG Guoxiong LI Dehao FENG Taozheng YANG Zhibin HE Jiajia SU

渤海湾盆地渤中凹陷西南洼古近系东营组超压广泛发育，但压力分布特征、超压形成机理及其对油气成藏的影响尚未完全明确。基于实测地层压力和测井资料，对渤中凹陷西南洼地区东营组现今地层压力进行研究，分析现今地层压力空间分布特征，并通过测井曲线综合分析法及声波速度-密度交会图法分析超压成因类型，根据盆地模拟技术恢复成藏时期古压力演化，研究地层古压力对油气成藏的影响。研究结果表明：①东营组纵向上发育一套完整的超压系统，平面上超压围绕生烃洼陷分布，越靠近凹陷中心超压越大。②超压由浅层欠压实主导型转化为深层欠压实-生烃膨胀复合型。③东营组三段和东营组二段下亚段烃源岩层内发育的超压不仅为油气运移提供充足动力，同时向下形成超压流体封盖，阻止油气向上逸散。最后提出古潜山是渤中凹陷西南洼下一步深层和超深层油气勘探的有利目标。

Overpressure is extensively distributed in the Paleogene Dongying Formation in the southwestern sub-sag of the Bozhong Sag， Bohai Bay Basin. However， there is a lack of a clear understanding of the pressure distribution， the formation mechanisms of overpressure， and the effects of overpressure on hydrocarbon accumulation in this formation. In this study， we explore the present-day pressure in the formation and its spatial distribution using measured formation pressure and logs. Based on a comprehensive analysis of log curves and the cross plots of sonic velocity vs. density， we analyze the genetic types of overpressure in the formation. Furthermore， through basin modeling， we reconstruct the paleopressure evolution during hydrocarbon accumulation to assess the effects of the formation paleopressure on hydrocarbon accumulation. Key findings are as follows： （1） The Dongying Formation exhibits a complete overpressure system vertically. Horizontally， the overpressure is distributed around hydrocarbon-generating sub-sags， intensifying closer to the sag center； （2） The genetic type of overpressure shifts from predominant undercompaction in shallow strata to a combination of undercompaction and hydrocarbon generation-induced expansion in deep layers； （3） The overpressure within the source rocks of the Dongying Formation， including the 3 member and the lower sub-member of the 2 member， offers a sufficient dynamic for hydrocarbon migration. Furthermore， it forms seals for the underlying overpressured fluids， preventing the upward escape of hydrocarbons. It is proposed that ancient buried hills represent favorable targets for future deep and ultra-deep hydrocarbon exploration in the southeastern sub-sag of the Bozhong Sag.

10.11743/ogg20240107