塔里木盆地肖尔布拉克组溶蚀型白云岩储层发育特征

Features of dissolved dolostone reservoirs in the Xiaoerbulak Formation,Tarim Basin

塔里木盆地肖尔布拉克组为一套深灰色粉晶、细晶白云岩,且发育有不同类型及不同程度的溶蚀孔隙。尤其在肖尔布拉克组顶部附近,顺层发育良好的溶蚀孔,具有较好的储集能力。基于野外观察和显微镜下观测,并结合电子探针和扫描电镜研究分析,发现该区白云岩的溶蚀作用具有多类型,多期次和溶蚀流体多样化的特点。该组的溶蚀作用可以划分为顺层溶蚀、白云岩充填再溶蚀、粒间溶蚀及表生溶蚀等4种类型。顺层溶蚀主要沿层理发育,溶蚀孔直径大小为几毫米,大多溶孔内壁有白云石充填。充填白云石较基质白云石更富含Fe,Mn,Na和Ba等元素,显示其与深部热流体的密切关系。充填白云石亦有发生再溶蚀现象,乃至发生再次沉淀,对已有孔隙进行改造。溶蚀沉淀物富含S,Si,Sr等元素,指示流体成分比较复杂,来源也具有多样性。另外,局部可见颗粒白云岩发生溶蚀,有些地方具有表生溶蚀作用的特点,对白云岩储集空间的发育有一定贡献。

The Xiaoerbulak Formation consists mainly of dark gray silt- and fine-sized crystalline dolostones with dissolution porosity of different types and values.Highly-developed bedding-parallel dissolution pores within the top of the Formation may have high storage capacity.Based on field and microscopic observations as well as EPMA and SEM analysis,the authors suggest that dolostone dissolution in the area features in multi-period developments and diversified dissolution fluids.The dolostone dissolutions can be classified into four types：beddingparallel dissolution,dolostone pore-filling re-dissolution,inter-grain dissolution and hypergene dissolution.Bedding -parallel dissolution occurs mainly along the bedding.The diameters of dissolution pores are about a few millimeters and most of the pores are lined with dolomite.Compared with matrix dolomite,the pore-filling dolomite is richer in such elements as Fe,Mn,Na and Ba,indicating its close relationship with deep thermal fluid. Some pore-filling dolomite may re-dissolve and re-precipitate-a process that could alter the existing pores.The precipitates are rich in S,Si,Sr and other elements,indicating a dissolution fluid with complicated compositions and diversified sources.In addition,dissolution of grain dolostone also occurs and shows the characteristics of hypergene dissolution in some places,which may contribute to the development of reservoir space.