Research on casing deformation mechanism and prevention technology in salt rock creep formation

Aiming at casing damage in the salt rock, the creep characteristics of the salt rock in the southeastern China are investigated by triaxial creep test. Based on the experimental results, an unsteady creep model which can describe the creep and steady stage of the salt rock is set up combined with the Kelvin model and the Heard model by the deviation stress. The unsteady creep model was used to calculate the radial displacement of the wellbore based on ABAQUS platform. The results show that the higher casing pressure can effectively reduce the creep displacement of the rock, and the higher horizontal principal stress and the overburden pressure can increase the formation deviation stress, thus increasing the creep displacement of the salt rock. The maximum displacement of the casing caused by the formation is 25 mm by a string simulation device. The elastic modulus of the cement is effectively reduced by adding hollow ceramic particles to the cement, so that the strain energy added to the wellbore system by the formation radial creep can be fully absorbed by this cement sheath. Combined with the numerical simulations and the cement tests with the addition of hollow ceramic particles, a casing deformation prevention method is finally established in this paper.