渤海东部馆陶组岩性特征及成藏规律

LITHOLOGY OF GUANTAO FORMATION IN THE EASTERN BOHAI SEA AND ITS BEARING ON OIL AND GAS ACCUMULATION

馆陶组作为渤海东部新近系重要的勘探层系,垂向上岩性组合变化明显,岩性特征的精细研究具有重要成藏意义。利用丰富的钻井、古生物、岩心等资料,并且依据层序地层、古生物组合、岩电等特征认为,馆陶组垂向呈现粗—细—粗的沉积特征,相应划分为馆陶组上、中、下3段;馆陶组不同层段的沉积期存在水浅—水深—水浅旋回过程,相应也存在辫状河三角洲—曲流河三角洲—浅水三角洲的相变,并在垂向上形成3套储盖组合;馆陶组下段储盖组合较差,骨架砂岩具有一定的横向输导能力;结合运移断层与馆陶组储层的配置关系,建立馆陶组上、中、下3套储盖组合的成藏模式,并利用断层活动性、区域盖层厚度、砂岩相对含量等创建分流判别参数C定量标定新近系优势成藏层段,当C>0.4时,馆陶组中、上段为主要成藏层段;当C<0.4时,馆陶组上段及明化镇组下段为主要含油层系。

Detailed lithological study has been made for the Guantao Formation,the main target layer for oil exploration in the eastern Bohai Sea.Based on the paleontological and cores data from drilling wells,combined with sequence stratigraphic analysis and various well log data,the Guantao Formation is divided vertically into three members consisting respectively of coarse,fine and coarse clastic deposits,indicating a cycle of water regression,transgression and regression.A braided river delta,a meandering river delta,and a shallow water delta occur in a vertical succession and form three reservoir-seal assemblages.The sand body of the lower member consists of high content of sand and thus good for lateral hydrocarbon migration.Specific oil and gas accumulation models for the three members are established by combination of migration faults and reservoirs.Advantageous accumulation assemblage is quantitatively predicted with the newly invented Index C which is established on fault activity,regional seal rock thickness,relative sand percentage of the Guantao and Minghuazheng Formations.The upper and middle members of the Guantao Formation will be the main target layers if the Index C is bigger than 0.4,while the upper member of the Guantao Formation and the Minghuazhen Formation will be the main target layers if the Index C is smaller than 0.4.