Comparison of mechanical behaviour of geopolymer and OPC-based well cement cured in saline water

Well cement plays a vital role in maintaining wellbore integrity in a carbon capture and storage project. To date, ordinary Portland cement (OPC)-based well cement has been used and there are contrasting research findings on its suitability as well cement. This research aims to use geopolymer as well cement, and major aim of this work is to analyse the mechanical behaviour of both geopolymer and OPC subjected to various down-hole conditions including different salinity (0–30% NaCl) and confinements (0–15 MPa). This research comprises experimental and numerical works. Under the experimental work, series of unconfined compressive strength (UCS) test were conducted for geopolymer and OPC samples cured in saline water with 0–30% NaCl salinity for a period of 45 days. COMSOL multiphysics software was used for the numerical study, and first, laboratory scale uniaxial stress–strain behaviour of both geopolymer and OPC was validated numerically. The model was then extended to study the triaxial mechanical behaviour under different salinity (0–30% NaCl) and confining pressures (0–15 MPa) conditions. Based on the results, it was noticed that UCS of geopolymer increases with salinity due to the high resistance against alkali leaching in saline water compared to fresh water. The UCS of OPC increases with salinity up to 10% NaCl, and then it reduces with any further increase in salinity. The UCS of geopolymer is 6% to 66% higher than that of OPC depending on the salinity conditions and geopolymer possesses higher UCS than OPC for any given salinity condition. COMSOL multiphysics numerical software predicted the stress–strain behaviour of geopolymer and OPC accurately up to yield point. Failure strength of geopolymer in saline water is 3% to 61% higher than that of OPC for a given confining pressure. Findings of this research indicate that geopolymer can be a good alternative for OPC based well cement under deep down-hole conditions.