摘要：The high temperature and high pressure in ultra-deep wells pose great challenges to the cement sealing integrity in southern margin of Junggar basin.Therefore,a numerical model of casing-cement-formation was set up by characterizing elastoplastic constitutive relationship of cement with concrete plastic damage model in this paper.Then the Mohr-Coulomb criterion was used to evaluate the failure of cement,and the influence of the cement elastic modulus,Poisson's ratio,and cement sheath thickness on the failure coefficient was analyzed.The numerical results show that the cement integrity of Well Gao-tan-1 scores good during development.The cement slurry after solidification should have a lower elastic modulus and a higher Poisson's ratio,which is conducive to the cement integrity.When designing the well structure,the thickness of the cement sheath should always be kept above 11mm to ensure the wellbore sealing integrity.As the decreasing amplitude of failure coefficient gradually decreases with an increasing thickness,the upper limit of thickness was recommended as 38mm with the consideration of drilling costs.This research can be used to analyze the failure mechanism of the cement sheath in HTHP wells and provide technical support for the wellbore integrity of deep/ultra-deep wells in the southern margin of the Junggar basin.
