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Abstract 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.
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Received: 14 April 2010
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2010, Vol. 29 
