南堡凹陷东营组低阻油层控制因素

Control factors of low-resistivity oil reservoir in Dongying Formation of Nanpu Sag

受沉积、成岩和构造等作用的综合影响,南堡凹陷东营组地层中发育了常规测井识别难度较大的低阻油层。文中利用岩心分析化验资料进行岩石物理分析,明确了南堡凹陷东营组低阻油层成因。结果表明:微观上受蒙皂石、伊/蒙混层等阳离子交换能力强的黏土矿物体积分数增加的影响;宏观上受辫状河三角洲沉积背景控制,在粒度细、分选差、泥质体积分数高的水下分流河道分叉处、末端、侧翼或河道叠置处及河口坝微相砂体中易发育低阻油层。地层现今处于中成岩演化期,黏土矿物类型以伊/蒙混层、高岭石、绿泥石和伊利石为主,压实作用中等—强,储层孔隙结构复杂。东营组和明化镇组沉积时期的火山运动导致圈闭中油气发生再次运移,含油饱和度降低,也易形成低阻油层。

The Dongying Formation in Nanpu Sag is influenced by sedimentation,diagenesis and structure,and forms low resistivity reservoirs which is difficult to be identified by conventional logging.Based on petrophysical analysis with laboratory core data,the genesis of low resistivity oil reservoirs in Dongying Formation of Nanpu Sag is determined.Microscopically,the most fundamental influencing factors are the increase of the volume content of clay minerals with strong cation exchange ability such as hydrophilic montmorillonite and imolecite.Macroscopically,it is affected by the sedimentary characteristics of braided river deltas.The low resistivity oil layers tend to develop at the bifurcation of underwater distributary channels,terminal river,flanks and estuary dams with fine grain size,poor separation and high shale content.The formation is at the middle diagenetic stage at present,and the clay mineral types is dominated by imonade montmorillonite,kaolinite,chlorite and illite.Compaction is moderate to strong.In the middle diagenetic period,these clay minerals were enriched and filled in the pores,which not only increased the complexity of pore structure,but also reduced the resistance of the reservoir.The strong volcanic movement occurred in Dongying Formation and Minghuazhen Formation led to the secondary migration of oil and gas and the formation of secondary oil reservoir,and the oil saturation decreased,forming the low resistivity oil layer.