The Estimation to the Service Life of Casing in Salt Formation

The casing failure is serious in Zhongyuan oil field，This case happened frequently in the salt formation of the Tertiary shahejie group. And the casing deformation is the main form of failure. Research reveal that the main cause of casing failure is that the external load acting on casing due to salt formation creep under the nonhomogeneous in-situ stresses exceeding the collapsing strength of the casing. The key to avoid casing failure is the proper casing grade. The salt formation is regarded as Maxwell model, and a viscous elastic mechanical model for plane strain features is established. based on the experimental results of triaxial multilevel loadings for the salt rock creep, the creep constitutive model and creep parameters is given，Combined with geologic condition of the Tertiary salt formation in Zhongyuan Oilfield, with the analysis and calculation of the external load acted on casing due to salt formation creep under the nonhomogeneous in-situ stresses by finite element method，the variation laws of the external load are achieved. The relationship of the external load and the collapsing is close. Establish the predicting model of casing service life. Considering the affect of corrosion, estimated the casing service life in salt formation and get the exact result which can guide the casing string design in this oil field.