辽东湾地区东营组湖底扇地震响应机理分析及储层描述

Seismic response mechanism analysis and reservoir description for sublacustrine fan of Dongying Formation in Liaodong Bay

辽东湾地区锦州A构造带勘探程度相对较低,该构造带发育两类湖底扇沉积体,储层预测难度较大。地震反射特征分析表明:A区湖底扇规模小,连续性差,扇体外形呈楔形,沉积环境为大套低速泥岩,扇体内为厚层砂岩;B区湖底扇规模较大,连续性好,扇体外形呈丘状,上覆围岩为泥岩与低速泥岩互层,扇体内为砂泥岩互层,并且内幕存在亚相。湖底扇响应机理分析表明:含气砂岩顶对应强波谷反射,气砂水砂界面对应强波峰反射,常规砂岩与低速泥岩界面对应弱波峰反射,常规泥岩与低速泥岩界面对应强波峰反射;由于III类AVO效应和薄层的干涉效应,含气扇体顶部反射振幅明显增强,扇顶对应一个强波谷的反射特征,在剖面上出现明显的"亮点";湖底扇主体部位主要富砂,使得地震剖面频率变低,能量和连续性都变差,湖底扇边缘部位主要富泥,地震反射特征与富砂型相反。在此基础上,通过地震多属性分析技术对研究区湖底扇的宏观平面分布特征进行了准确预测,利用波形聚类属性清楚地识别了湖底扇的内幕相带发育区,对该区东营组湖底扇岩性油气藏勘探具有指导意义。

Jinzhou A structure zone with relatively low level of exploration in Liaodong Bay develops two types of sublacustrine fan and reservoir prediction is difficult. Seismic reflection characteristics analysis shows that sub-lacustrine fan in A area is small in size, poor continuity, and tapered shape, the sedimentary environment is low- velocity shale and its lithology is thick sandstone. Sublacustrine fan in B area is large in size, good continuity and mound shape, the overburden rocks are shale and low-velocity shale layers, its lithology is shale and sand layers, and exists subfacies. Response mechanism analysis shows that the top of gas-bearing sand starts with a strong trough reflection, interface between gas-bearing sand and water-bearing sand corresponds to a strong peak reflec-tion, interface between the sand and low-velocity shale corresponds to a weak peak, and the interface between the shale and low-velocity shale corresponds to a strong peak. Due to Class III AVO anomaly and interference effect, the trough reflection amplitude of gas-bearing sand top obviously enhances, so the bright point appears on seismic profile. The main part of the fan is sand-rich, but the margin is shale-rich. Sandstone makes the seismic section lower in frequency and poorer in continuity, but the shale is the opposite. On this basis, with multi-attributes a-nalysis, lateral distribution of sublacustrine fan can be well depicted. And cluster analysis attributes can clearly predict inter fan belt, which has a significance to guide exploration of this type lithologic reservoir.