Analysis of interfacial debonding of geopolymer annular sealing in CO2 geo-sequestration wellbore

For the geological sequestration of atmospheric CO2 to be viable, it is important that leakage of stored gas back to the atmosphere is prevented for a long period. Apart from other modes of failure, damage of the bond between interfaces can open up migratory pathways for leakages of CO2 to occur. A stress induced debonding mechanism for well bore interfaces has been studied. A numerical modelling approach was used to investigate a wellbore composite cylinder system using finite element software. Analysis was performed for the wellbore annular cement sheath, both for static pressure and temperature increase/decrease. In addition, geopolymer, a novel acid resistant cementitious binder, has been considered as an annular cement system. From analysis, it has been observed that debonding can occur at discrete locations for the wellbore pressure and/temperature increase. However, for the wellbore pressure and/temperature decrease, it was found that stress-slip failure occurs when tensile normal stresses along interfaces equal the interfacial bond strength. In addition to that, for pressure and/temperature decrease, shear stresses developed in the circumferential direction appeared insignificant in debonding failure. Thermal dilation of wellbore material can help preventing discrete debonding of wellbore interfaces in the case of wellbore pressure and temperature increase. Conversely, a wellbore temperature decrease contributes to microannular formation along interface because of the material shrinkage effect. (C) 2013 The Authors. Published by Elsevier Ltd.