oa Impact of CO2 Injection on Stability of Perforation Tunnels

The injection of CO2 in the geological storage layers is associated with cooling effects imposed to the downhole formations around the wellbore. Subsequently, the magnitude of the stresses around the boreholes where the CO2 passes, i.e. wellbore and perforation tunnels, are affected. This may induce failures around the boreholes which may impact the integrity of the injection wells during the CO2 injection. In this study, a workflow is presented to analyse the stability of the perforation tunnels in CO2 injectors. The analyses were carried out under different reservoir pressure, bottom hole pressures and temperatures. The tendency of shear and tensile failures were modelled using numerical and analytical approaches. The results are demonstrated for a case study from southeast Asia. The results shows that in general injecting CO2 does not induce excessive compressional and shear stresses to collapse the perforation wall. However, the perforations may collapse during flow backs when the injection is stopped. Also, the CO2 injection cooling effect may exacerbate the potential tensile failures in the perforation tunnels. The results were also used to optimise the perforation density and phasing from the stability point of view.