胜坨地区沙四上亚段近岸水下扇相砂砾岩体成岩矿物类型及分布特征

Types and Distribution of Diagenetic Alterations in the Nearshore Subaqueous Fan of the Upper Es_4 in Shengtuo Area of Dongying Depression

成岩矿物的类型及分布影响着砂砾岩体油藏的储层预测。根据岩心观察、薄片岩石学分析、物性和碳氧同位素测试等多种技术方法,对东营凹陷北部陡坡带胜坨地区沙四上亚段近岸水下扇砂砾岩体的不同相带、不同成岩期的成岩产物及分布特征进行了研究。研究表明,近岸水下扇相砂砾岩体的成岩产物类型多样,早成岩期主要包括机械渗滤的黏土、方解石和白云石胶结,中成岩期主要包括铁方解石和铁白云石胶结、伊利石等黏土胶结、石英次生加大等。近岸水下扇相砂砾岩体的成岩产物与沉积相带的对应关系较好,早期的机械渗滤黏土在扇根沟道和沟道间砂砾岩中丰富,方解石和白云石胶结在扇根和扇端非常发育;铁方解石和铁白云石胶结、石英次生加大等在扇中沟道砂砾岩中更发育。早期成岩产物的分布以及中成岩期的后续影响对储层储集质量的改变有重要意义,扇中沟道砂砾岩溶蚀作用发育、储集性能好,广泛发育的扇根和扇端早期成岩方解石胶结层可作为砂岩油气储层的潜在封堵层。

Based on observation of core and thin section,combined with petro-physical property,isotopes,and other experimental analyses,types and distribution of diagenetic alterations in different depositional facies and different diagenetic stages were studied from the nearshore subaqueous fans of the Upper Es4 sandstones in Shengtuo area of Dongying Depression.Diagenetic alterations which were encountered in the nearshore subaqueous fans are diverse.Eogenetic diagenetic alterations include mechanically infiltrated clays,calcite and dolomite cementation.Mesogenetic alterations include ferruginous calcite and ferruginous dolomite cementation,diagenetic clay mineral cementation,quartz overgrowths,and so on.Relationship between diagenetic alterations and facies in the nearshore subaqueous fans are very clear.Eogenetic mechanically infiltrated clays are abundant in sandy conglomerate of channels and interchannels of inner fans.Eogenetic calcite and dolomite cementation are extensive in inner and outer fans.Ferruginous calcite and ferruginous dolomite cementation,and quartz overgrowths are most abundant in mid-fan sandbodies than that in inner and outer fans sandbodies.Dissolution is most clear and reservoir property is best in midfan channel sandbodies.Extensive calcite cements may act as potential sealing layers for the reservoir compartments of underlying sandstones.Integration of diagenesis with depositional facies of nearshore subaqueous fans is beneficial to predict the distribution of diagenetic alterations,and thus on prediction of favorable reservoirs.