塔里木盆地东河1油藏东河砂岩隔夹层形成的主控因素及流体来源

Major controlling factors for the formation of inter-layer of Donghe sandstone of Donghe1reservoir in Tarim Basin and its fluid source

通过大量的岩心、薄片观察,依据填隙物的种类和含量,将东河1油藏东河砂岩隔夹层分为钙质隔夹层、(含)泥钙质隔夹层和泥质隔夹层3类,以钙质隔夹层和(含)泥钙质隔夹层为主,泥质隔夹层相对不发育。隔夹层的形成主要受控于早成岩期的碳酸盐胶结作用。碳酸盐胶结物类型包括方解石、菱铁矿、铁方解石和铁白云石。根据岩相学和阴极发光特征的不同,识别出4期碳酸盐胶结物,各期碳酸盐胶结物成因和流体来源存在一定差异。第Ⅰ期胶结物为连晶或粗大片状的无铁无镁方解石,Fe、Mn元素含量很低,形成于未埋藏或浅埋藏与海水沟通的开放、氧化环境,钙质来源于海水;第Ⅱ、Ⅲ期胶结物沉淀于点-线接触的颗粒间,Mn元素含量显著上升,形成于半封闭—封闭的成岩环境,钙质流体来源于第Ⅰ期胶结物或同沉积期的碳酸盐颗粒的溶解;第Ⅳ期胶结物为铁方解石、铁白云石,具交代石英、长石矿物的特点,Fe元素含量远高于Mn元素含量,形成于相对深埋的还原环境,其形成与长石的溶解有关。

Through massive cores and thin sections observation,and according to the types and content of interstitial materials,inter-layers of Donghe sandstone in Donghe1 reservoir were classified into three categories：calcareous inter-layer,mud-calcareous inter-layer and mud inter-layer.Calcareous inter-layer,mud calcareous inter-layer are predominant while mud-calcareous inter-layers are less developed.The formation of inter-layers is primarily controlled by carbonate cementation in the early diagenetic stage.Carbonate cements include calcite,siderite,ferrocalcite and ferrodolomite.Four phases of carbonate cements with different causes and fluid sources were identified according to the different petrographical and cathode luminescence characteristics.The first-phase cements is inter-growth or coarse flaky,iron and magnesium free calcite with low content of Fe and Mn,formed under non buried or shallow buried open oxidizing environment which is connected with seawater.Calcium originates from seawater.The second-and third-phase cements are precipitated between point-line contacted particles.Mn content is increased significantly,formed under semi closed or closed diagenetic environment.Calcium fluid is sourced from the firsvphase cements or syn-sedimentary dissolution of carbonate particles.The fourth phase cements were ferro-calcite and ferro-dolomite with replacing quartz and feldspar features.The content of Fe was much higher than that of Mn.It formed under relatively deep buried reducing environment,with relevance to the dissolution of feldspar.