Abstract
The viscous character of rock salt can cause problems during drilling and well construction operations, but can be favorable during well abandonment. The natural process of salt creep can reinstate the integrity of rock salt caprocks and create an additional well barrier. The method requires removing of a part of the casing set across a salt caprock formation. Differential stresses at the wellbore wall will initiate the process of creep leading to a reduction of wellbore radius and closure of an uncased wellbore section. Geomechanical numerical simulations were conducted to evaluate the creep-induced wellbore convergence in salt formations. A two-component creep constitutive material model was used, which takes into account the contributions of both the non-linear creep component, dominant under high differential stresses, and the linear creep component, dominant under low differential stresses. The calculation results expectedly show an increase in the creep strain rate with depth due to increasing temperature and differential stress. However, the creep strain rate decreases exponentially as the wellbore radius decreases. The shortest borehole closure time for a depth of 3.5 km, which is applicable to well abandonment in the K12-B CO2 Injection Project in the Netherlands, amounts to about 500 days.
