Impact of Thermal Stresses on Wellbore Integrity during CO2 Injection

Thermal stresses caused by injection of cold CO2 into warmer storage reservoirs could create leakage pathways out of the storage reservoir. Although few studies have been conducted to investigate the well bore integrity subjected to thermal cycling during CO2injection, a systematic investigation on thermally induced expansion and contraction affecting the debonding and cracking of the well barrier materials has not yet been performed. In this work, we have analyzed the thermo-mechanical characteristics of the well barrier materials undergoing repeated thermal cycling using a multiscale, multiphysics platform named GEOS. More specifically, we model the modes of failure during thermal cycling to assess the temperature range for minimal impact on well integrity. A finite element solver was used for the geomechanics and a finite volume solver was used for the thermal diffusion. Results of the initiation and propagation of fractures due to temperature variations in the cement sheath are presented. Preliminary results suggest that radial fracture develops as the cement is heated while debonding occurs in the casing-cement and cement-rock interfaces during the cooling period. The effects of different confinement conditions based on in-situ stresses were also analyzed. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under the Contract DE-AC52-07NA27344. This work has been produced with support from the BIGCCS Centre, performed under the Norwegian research program Centres for Environment-friendly Energy Research (FME) and the KPN project "Ensuring well integrity during CO2 injection". The authors acknowledge the following partners for their contributions: Gassco, Shell, Statoil, TOTAL, GDF SUEZ and the Research Council of Norway (193816/S60 and 23389).