进积型三角洲交汇区沉积模式--以东营凹陷沙三中亚段为例

作为碎屑岩储层发育的最主要沉积相类型之一，进积型三角洲在油气勘探领域具有举足轻重的地位；加强对进积型三角洲沉积模式的研究，对于油气储层预测具有重要现实意义。渤海湾盆地东营凹陷古近纪湖盆内发育的东营三角洲和永安三角洲在沙河街组三段中亚段沉积期发生了交汇，而有关两个三角洲的交汇方式、沉积特征及交汇区储层的预测尚未引起足够的重视。以岩芯观测、录井和地震资料为基础，分析了东营凹陷古近系沙三段中亚段三角洲交汇区沉积特征，探讨了沉积期次、交汇过程，建立了三角洲交汇区沉积模式。研究表明，东营凹陷沙河街组三段中亚段主要发育湖泊、进积型三角洲沉积；储集砂体主要形成于三角洲前缘水下分流河道，河口坝微相次之，浊积岩主要分布于深湖区。认为此前界定的东营三角洲的分布范围可能被夸大，而永安三角洲的沉积规模可能被低估。东营凹陷古近系沙三中亚段可划分为9个期次，其作用过程可分为局部交汇阶段和完全交汇阶段。三角洲水下交汇区是水流汇聚和沉积物卸载的有利场所，叠置砂体可成为有利的油气储层，因而具有重要的油气勘探价值。

Depositional Model of Prograding Delta Confluences: A case from Es3m Members in the Paleogene Dongying Sag

As one of the most important sedimentary facies for development of clastic rocks, prograding deltas are critical to petroleum exploration. Hence, it has important significances to reservoir prediction to strengthen researches on depositional model of prograding delta confluences area. Confluences of Dongying delta and Yong'an delta took place in the middle depositional stages of the third section in the Paleogene Shahejie Formation (Es₃m) in Dongying Lake, Bohai Bay Basin. However, it has not received adequate attentions to issues of confluences patterns, and reservoir predication about the two delta systems. Based on core observations, loggings and seismic data, this presentation analyzed sedimentary characteristics of confluences deltas of Es₃m in Dongying sag, discussed sedimentary stages and confluences process, and constructed a depositional model for prograding confluences deltas, for sake of providing reference for further exploration deployment and geological research. Results show that lake and prograding delta deposits were well developed and reservoir sandbodies were mainly deposited in underwater distributary channels, mouth bar secondary and scattered turbidites in the Es₃m in Dongying Sag. It is considered that sedimentary scope of Dongying delta were possibly over estimated and extent of Yong'an Delta were probably underestimated. Depositions of the Es₃m in Dongying Sag can be divided into 9 stages and their processes are differentiated to part-confluence and full-confluence stages. Subaqueous deltas confluences are suitable place for water flow convergence and loading of sediments. Superimposed sandbodies are favorable reservoirs with crucial significances for petroleum explorations in delta confluences area.