济阳坳陷滨海地区沙河街组隐伏剥蚀圈闭识别与描述

摘要

The seismic reflection characteristics of buried denudation trap in Shahejie Formation in coastal area of Jiyang depression are parallel,blank or overlapping reflection,causing the difficulty to accurately describe the erosion pinch-out.Research shows that the trap characteristics in the study area are summarized as thin bed,small slope and high impedance of surrounding rock.The two reasons causing the difficulty of trap description are:poor seismic resolution that causes parallel reflection,and blank reflection because of the thin strata and interference of high velocity surrounding rock.A method to identify and describe the buried denudation traps is established with geophysics techniques constrained by geological conditions.Buried denudation traps are identified based on the structural evolution and logging data.The pinch-out line is described with frequency attribute and increased frequency information,then the relationship of erosion pinch-out with dip angle of stratigraphic and unconformity and the stratigraphic thickness is calculated,and the accurate position of erosion pinch-out is finally determined.The proposed technique is used for Chengdao,Gudao,Changdi,Zhuangxi and Xinbei oilfields with good exploration results.The method can provide reference for identification of stratigraphic traps and description of the erosion pinch-out.%济阳坳陷滨海地区沙河街组隐伏剥蚀圈闭的地震反射特征为平行反射、空白反射甚至超覆反射等地震假象,故剥蚀尖灭点难以准确落实.研究表明研究区该类圈闭具有地层薄、夹角缓、高阻抗围岩等3个特点,难以识别的主要原因有2个:一是地震资料分辨率低,形成了平行反射;二是地层厚度薄,受高速围岩的相干作用,形成了空白反射.提出了地质条件约束下运用地球物理技术有效识别和描述隐伏圈闭的方法,即依据构造演化特征和测井及录井资料识别隐伏剥蚀圈闭,利用频率属性和提频资料描述尖灭线,并计算出剥蚀尖灭点与地层和不整合面夹角、地层厚度的关系,最终精确落实剥蚀尖灭点位置.本文提出的隐伏剥蚀圈闭识别与描述技术已成功应用于滨海地区的埕岛、孤岛、长堤、桩西、新北等油田,都取得了良好的勘探效果,对其他地区类似地层圈闭识别和剥蚀尖灭线精确落实具有借鉴意义.