枯竭油气田中废弃井密封性研究

利用X粉晶衍射技术进行板新803井中泥岩盖层成分测试,通过室内常规力学与蠕变实验,分析泥岩的力学性质与蠕变变形特征。利用FLAC3D软件对钻孔周边围岩进行数值模拟计算,分析不同时间时泥岩的蠕变变形,研究泥岩层段缩径变化规律,在此基础上分析废弃井的密封性。通过以上研究获得如下主要结论:(1)泥岩中含有较多的伊利石、高岭石与绿蒙混层等黏土矿物,易产生井壁垮塌;(2)泥岩在长期围压作用下,将会产生较大的蠕变变形,在有钻井液作用时,变形更明显;(3)钻具周围泥岩通过蠕变变形向环空内挤压,经过30 a产生的变形会使井壁与落鱼之间的环空由下而上充填满;在考虑泥岩遇水后产生的掉块与扩径作用时,35 a后环空也将被充填满,原有泥岩盖层被密封,从而产生较好的密封效果。

STUDY OF SEALING PROPERTIES OF ABANDONED WELLS IN EXHAUSTED OIL AND GAS RESERVOIRS

Components and contents of clay minerals in mudstone in cap rock in Banxin well #803 are tested firstly. Then some mechanical tests including uniaxial and triaxial compression，creep tests are performed to obtain the strength parameters and deformation features of mudstone. Thirdly，FLAC3D is used to simulate the rock deformation around the well and analyze the creep deformations at different times. Based on the calculation，shrinkage law of wellbore and sealing features of cap rock are studied. The results show as follows：(1) Several clay minerals such as kaolinite，illinite and mixed layered illite/smectite are the main contents of mudstone which made the mudstone around the well easier to collapse；(2) Creep deformation of mudstone is significant under long-term confining pressure conditions and the deformation rates increase with the role of drilling fluids；(3) Mudstone around well logs would creep and extrude into annulus space slowly. After 30 years，the annulus space between rocks and casing fish would be filled without considering the expansion and collapse roles. When considering the expansion and collapse roles，after 35 years，the annulus space would be filled by the fragment and the creep deformation which made the layer sealed at present.