渤海湾盆地大港探区加里东期不整合面特征再认识

A new perspective on the features of the Caledonian unconformity in Dagang exploration area,Bohai Bay Basin

应用“地层尺度”方法,通过在区域地层框架下的岩性组合和电测曲线特征,将大港探区奥陶系峰峰组划分为若干小层,并在全区开展小层对比,研究不同小层经加里东运动改造后在奥陶系顶部不整合面的出露情况,以期还原加里东运动后的古地貌形态。研究结果表明,大港探区加里东期不整合面是小层(十~几十米)级别的低角度不整合,加里东运动改造后地势总体呈北高南低、东高西低的地貌形态,峰峰组小层出露具有由低向高逐渐变老的特点;该低角度不整合的存在改变了以往的认识,还原了加里东运动对奥陶系地层的影响,同时在峰峰组小层框架下,揭示了受第5小层控制,上、下碳酸盐储层在纵向上具有不同的发育规律,其上发育岩溶喀斯特及团块状白云岩储层,其下发育层状白云岩储层,在黄骅坳陷中南部地区连续分布,具备较好的储集性能。上覆煤系地层沉积覆盖后与下伏奥陶系储层形成多类型的源-储配置关系,具有捕获后期生成油气的条件。

To restore the post-Caledonian paleogeomorphy of the Dagang exploration area,an innovative“scaled stratigraphy”method,in which a regional substratum division coupled with the substratum correlation based on lithological composition and electric logs is conducted,is used to investigate the substratum outcrops of the Ordovician Fengfeng Formation in the area.The result shows that the Caledonian unconformity is of low-angle substrata of ten to dozens of meters thick and its paleo-geomorphology shows an overall northward and eastward rising,and that the outcropped substrata have a tendency of aging upward.This low-angle feature altered the conventional understanding of the Caledonian unconformity in the area and highlighted the influence of Caledonian movement on the Ordovician strata.This study also reveals that,within the Fengfeng Formation,the Substratum V controls the vertical distribution of carbonate reservoirs,which are considered quality reservoirs as they are sandwiched between karst with lumpy dolomite at the top and layered dolomite at the bottom,and continuously occur in central and southern Huanghua Depression.The Ordovician Fengfeng Formation bounded by the Caledonian unconformity as a whole,together with overlying coal seam sedimentation and underlying Ordovician reservoirs,forms a good source rock-reservoir combination for later generated oil or gas.