浅析北京通州地区雾迷山组热储微观特征

Discussion on Microscopic Features of Geothermal Reservoirs from Wumishan Formation in Tongzhou of Beijing

为解析通州地区蓟县系雾迷山组热储层的微观结构,本文通过显微镜观测、乂射线衍射测试和扫描电镜分析,对研究区内的白云岩岩石学特征、矿物成分特征和空隙结构进行表征。结果表明,研究区内的蓟县系雾迷山组以粉晶白云岩为主,粒径集中在0.01~0.085mm,大小相对均一,分选较好,多为自形一半自形晶体,白云石的菱形晶体结构明显,同时燧石条带较为发育,可见粒径不均的隐晶质细小颗粒;其次为他形镶嵌结构的泥晶白云岩,粒径多小于0.005mm;此外还有少量粒径为0.1~0.25mm的细晶白云岩,主要为自形一半自形晶体结构。白云岩中主要矿物为白云石,含量约为72.8%~98.9%,其次为石英和长石,其中的黏土矿物含量较低,对白云岩的孔隙度和渗透率的影响有限。蓟县系雾迷山组白云岩的微观空隙结构以次生孔隙为主,孔径较大,多是由于后期的热流体溶蚀白云石的结果,原生孔隙的孔径相对较小,可能主要是在成岩阶段形成。

In order to analyze the microscopic characteristics of geothermal reservoirs from Wumishan Formation in Tongzhou of Beijing,the article researches the characteristics of the petrology,mineral composition and pore structure of dolostones by microscope observation,X-ray diffraction and scanning electron microscope analysis.The result indicates that dolostones of Wumishan Formation are mainly composed of crystal powder dolomite,which grain sizes are from 0.01mm to 0.085mm,meanwhile the dolomite grains are mainly composed of idioplasmic-hypidiomorphic texture with the developed obvious rhombic structure and chert bands;sometimes aphanitic fine particles can be seen.The micrites with the grain sizes less than 0.005mm,are characterized by the allotriomorphic mosaic texture.Fine-grained dolostones with the idioplasmic-hypidiomorphic texture can be found in the Wumishan Formation,which grain sizes are from 0.1mm to 0.25mm.Dolostones of Wumishan Formation are mainly composed of dolomites(72.8%-98.9%),secondly quartz and feldspar.Just a few clay minerals could appear in the dolostone,having limited influence on the porosity and permeability of the dolostone.Microscopic vacuity structure in dolostone of Wumishan Formation,Jixian System is dominated by secondary pores with the bigger sizes,which is resulted from the dolomite being corroded by later thermal fluid;however,the primary pores have the smaller sizes,probably forming in the diagenesis stage.