Risk Assessment Method and Field Application for Casing Collapse Failure During Packer Unsetting in Deep Oil Wells
When the packer is unsetted,the rapid sinking of the annulus fluid column will produce obvious suc-tion pressure,which will lead to collapse accident of the production casing.Based on the calculation method of casing effective external pressure in the specification,the calculation method for the casing effective external pres-sure during packer unsetting was established considering the annulus fluid column sinking velocity and annulus suction pressure induced.The influence law of packer unsetting on casing effective support internal pressure and casing collapse failure risk was studied.The results showed that:When the packer is unsealed,the greater the depth of the tubing fluid,the greater the annulus gap between the outer diameter of the packer rubber cylinder and the inner diameter of the casing,the greater the annulus suction pressure,the lower the equivalent pressure density within the casing support,and the greater the casing failure risk.In order to reduce the risk of casing collapse fail-ure,it is recommended to improve the deformation recovery ability of the rubber cylinder after the packer is unset-ted.At the same time,the tubing should be filled with fluid as much as possible before the packer is unsetted.The research results provide important support to ensure the safe production of deep high temperature and high pressure oil wells.
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