东营凹陷南坡沙四上亚段滩坝储层碳酸盐胶结壳发育特征及控制因素

Development and controlling factors of the carbonate cementation in the beach-bar reservoirs in the upper part of the fourth member of the Shahejie Formation on the southern slope of the Dongying depression

关键词:  胶结壳  碳酸盐胶结  砂泥岩地层  成岩演化  东营凹陷

Key words:  cement layer  carbonate cementation  sandstone-mudstone strata  diagenetic evolution  Dongying depression

摘要:

砂-泥岩界面是砂-泥岩互层储层水-岩相互作用的活跃地带。东营凹陷南坡沙四上亚段发育了广泛的滨浅湖滩坝沉积,储层碳酸盐胶结作用强烈,常在砂-泥岩界面富集形成致密胶结壳。综合利用钻井、物性及黏土矿物资料,结合铸体薄片观察,对储层碳酸盐胶结壳的发育规律及控制因素进行了系统的研究。碳酸盐具有多期胶结的特征,砂-泥岩接触界面处胶结物含量高,多为基底式胶结。向砂体内部胶结物含量逐渐减少,砂体中部胶结物含量少且相对稳定,以孔隙式胶结为主。半干旱碱性水体环境形成的滨浅湖泥岩中的高碳酸盐含量流体、泥岩黏土矿物转化和有机质演化析出有机-无机组分、碳酸盐胶结作用发生所需的可容空间、砂-泥岩之间的物质传递能力、砂体的厚度及岩相组合控制了储层胶结壳的发育程度。胶结壳对储层质量并非简单的"破坏性成岩作用",早期碳酸盐胶结对储层的抗压实效应以及致密层构成的异常压力系统对储层后期溶蚀孔隙的发育以及油气的充注和保存提供了有利的条件。

Abstract:

The sandstone-mudstone interface is considered as the active zone of water-rock interaction in interbedded sandstone-mudstone reservoirs. The littoral-shallow lake beach-bar deposits occur on a wide range of scales in the upper part of the fourth member of the Shahejie Formation on the southern slope of the Dongying depression, in which the carbonate cementation is highly intense, and results in the formation of the tight carbonate cement layers at the sandstone-mudstone interface. The present paper deals systematically with the development and controlling factors of the carbonate cementation on the basis of well logs, cast sections, physical properties and clay minerals. The carbonates have the features of multiphase cementation. The cement contents are higher at the sandstone-mudstone interface showing the basement-type cementation, and decrease gradually toward the central parts of the sandstones, showing the porosity-type cementation. The development of the cement layers is controlled by the fluids with high carbonate contents in the littoral-shallow lake mudstones formed in the semi-arid alkaline water environments, organic and inorganic components precipitated from the transformation of clay minerals and organic matter evolution, accommodation spaces for the carbonate cementation, transmission capacity of the matter between sandstones and mudstones, sandstone thickness, and lithofacies associations. The pressure resistance effects of early carbonate cementation on the reservoirs and abnormal pressure systems formed by dense layers may provide favourable conditions for the development of later dissolution pores, and filling and preservation of hydrocarbons in the reservoirs.