渤海湾盆地歧口凹陷地层压力结构特征

深化含油气沉积盆地的压力结构研究，厘清异常压力的空间展布，对划分含油气系统、评价有利输导体系与明确勘探甜点区带具有重要的理论和实践意义。为深化渤海湾盆地富油凹陷的油气二次勘探，本文以歧口凹陷为研究对象，对其压力结构进行重点刻画。在实测地层压力的校正下，综合单井、连井和二维地震地层压力结构分析，厘清了歧口凹陷的压力结构特征，识别出4类纵向压力结构：①单超压带结构；②双超压带结构；③多超压带结构；④静水压力结构。纵向上，歧口地区存在3类纵向压力系统样式——单超压系统、双超压系统、静水常压系统。双超压系统是歧口凹陷的主要压力系统样式，广泛发育于主凹和各大次凹；从凹陷中心向盆地边缘，双超压系统逐渐向单超压系统、静水常压系统过渡。单超压系统主要分布于盆地边缘的斜坡和潜山区，如歧北高斜坡、羊三木-扣村潜山等。静水常压系统则主要分布在离深凹区更远的沈青庄潜山和埕北斜坡区域。上部超压系统和下部超压系统的顶板分别位于东营组和沙三段内部，侧向上受盆地边缘和深大断裂控制。上部超压系统的形成主要受欠压实作用控制，以歧口主凹为中心呈环带分布；而下部超压系统的形成主要受生烃作用控制，以主凹和几大次凹为中心分布。未来，下部超压系统中保存的天然气将成为歧口地区超深层天然气勘探的重点对象。

Characteristics of Formation-Pressure-Structure of Qikou Sag,Bohai Bay Basin

It is of great theoretical and practical significance for the classification of petroleum-bearing systems, the evaluation of favourable petroleum migration pathways, and the clarification of sweet spot for exploration to deepen the study of formation-pressure-structure in oil-bearing sedimentary basins and to clarify the spatial distribution of abnormal pressures. In order to carry out the secondary exploration of the oil-rich sags in Bohai Bay basin, we took Qikou sag as the research object and focused on its formation pressure structure. By calibrating the measured formation pressure, the single well formation-pressure-pattern analysis, the well-correlation profile analysis, and the 2-D seismic profile analysis were integrated to clarify the formation-pressure-pattern of Qikou sag. Four vertical formation-pressure-patterns were identified:the pattern with a single overpressure zone, the pattern with double overpressure zones, the pattern with multiple overpressure zones,and the hydrostatic formation pressure pattern. Vertically, there are three types of pressure systems in Qikou sag:single-overpressure-system, double-overpressure-system, and hydrostatic system. The double-overpressure-system is the main type of overpressure system in Qikou sag, which is widely developed in the main sag and the sub-sags. In the direction from the main sag to the edge of the basin, the double-overpressure-system gradually transits into the single-overpressure-system and the hydrostatic system. The single-overpressure-system is mainly distributed in the slope areas and the buried hills, such as Qibei high slope and Yangsanmu-Koucun buried hill. The hydrostatic system is mainly distributed in the Shenqingzhuang and Chengbei slope areas, farther away from the main sag. The seals of the upper and lower overpressure systems are located in Dongying Formation and Es₃ Formation, respectively. Laterally, the overpressure systems are controlled by the basin edges and deep faults. The formation of the upper overpressure system is mainly controlled by undercompaction, and is distributed in a ring around the main sag; while the formation of the lower overpressure system is mainly controlled by hydrocarbon generation, and is centered on the main sag and sub-sags. In the future, the main target of ultra deep gas exploration in Qikou area will be the natural gas stored in the lower overpressure system.