巴西桑托斯盆地盐下碳酸盐岩油藏硅化作用成因及其对储层的影响

Silicification geneses and their effects on pre-salt carbonate reservoir in M Oilfield,Brazil Santos Basin

巴西桑托斯盆地M油田盐下巨厚湖相碳酸盐岩储层发育硅化作用,目前尚未有相关研究探讨其成因机制。为此,综合利用岩心、薄片、流体包裹体测试和X射线荧光分析等资料,对M油田不同硅化作用特征开展成因探讨,并在此基础上分析其对储层的影响。研究结果表明:硅化作用在M油田较为普遍,超过一半样品受硅化作用影响,但仅有17%的样品属于中-强硅化作用。硅化作用成因类型包括3种,分别为沉积型、早期成岩型和热液型。沉积型和早期成岩型硅化作用对储层物性影响有限。综合证据显示,强热液硅化层段与侵入岩空间分布关系密切;同时其主要氧化物含量介于侵入岩和碳酸盐岩围岩之间,呈二者混染特征,且流体包裹体均一温度较高(87~193℃),证明热液硅化作用为岩浆期后热液所致。岩浆期后热液倾向于沿碳酸盐岩地层内部的断层、裂缝、不整合面等构造薄弱带以及与这些薄弱带相连通的高基质孔隙带流动,使储层发生强烈硅化作用。当硅质含量大于10%,对储层物性产生较大影响。

The reservoir in the huge thick pre-salt lacustrine carbonate of M Oilfield in Brazil Santos Basin is silicified,and there are no relevant researches to clarify its geneses.Based on the data of core,thin section,fluid inclusion and X-ray fluo⁃rescence,the various silicification geneses in M Oilfield are discussed and their effects on reservoir are analyzed.The re⁃sults show that the silicification in M Oilfield is common;more than half of samples in reservoirs are affected by the silicifi⁃cation,but only 17%of them are moderately and strongly silicified;the silicification can be divided into three categories:the sedimentation,early diagenesis and late hydrothermal fluid.Among them,the precipitation and early diagenesis silicifi⁃cation have limited effects on reservoir physical properties.The comprehensive evidences show that the strongly hydrother⁃mal silicified intervals are closely related to the spatial distribution of intrusive rocks.Meanwhile,the main oxide contents of strongly silicified intervals are between those of the intrusive rocks and the surrounding carbonate rocks,showing a mix⁃ing characteristics of the two.Furthermore,the homogenization temperatures of the primary quartz fluid inclusions are high in the range of 87-193℃.These comprehensive evidences indicate the hydrothermal fluids resulting in silicification were originated from magmatic activity.Post-magmatic hydrothermal solution tended to move along the weak structure zones,in⁃cluding faults,fractures and the high-porosity matrix pores connecting with fractures,which leaded to strong silicification in reservoirs.When the silica content is more than 10%,reservoir physical properties are dramatically affected.