Investigation of the Wellbore Wall Deformation due to Creep Behavior in Rock Salt

In this study, the deformation of wellbore wall due to creep behavior in the salt rock was investigated during drilling and production operations in one of the oil fields of Iran. The deformation of the wellbore wall was numerically investigated during the drilling operation without the use of the casing and considering the different mud weight. The results showed that increasing the mud weight reduced the deformation and convergence of the wellbore wall. Excessive mud weight will lead to divergent deformations which can cause tensile fractures on the wellbore wall, resulting in the lost circulation and instability of the wellbore. In order to investigate the effect of the casing on wellbore wall deformation, the analyses were performed in two states; running the casing in the wellbore without the cementing operation and running the casing in the wellbore with the injection of cement behind it. By considering the cement behind the casing, the maximum stress applied to the wellbore wall was reduced. By reducing the stress on the wellbore wall, the deformation rate is reduced and as a consequence, the stability of wellbore is significantly increased against casing collapse.