Combined Effect of Temperature and Salinity on the Triaxial Mechanical Behaviour of Geopolymers: An Experimental and Numerical Study

Well cement plays a major role in providing the required wellbore integrity of carbon capture and storage projects. Geopolymers have gained recent attention as a low-cost and environmentally friendly substitute to ordinary Portland cement (OPC) based well cement to overcome the wellbore integrity issues related to OPC. Therefore, fly ash based geopolymer was used as well cement in the present research. As a typical well cement is exposed to a variety of temperatures, salinities and confinements under down-hole conditions, this research focused on the combined effect of temperature and salinity on the triaxial mechanical behaviour of geopolymers. The research work comprised: (1) experimental work where a series of uniaxial compressive strength (UCS) tests were performed on geopolymer samples cured at different temperature and salinity combinations; and (2) numerical work where a model was devised using COMSOL software and the model was validated based on the laboratory scale uniaxial stress-strain behaviour. The model was then extended to predict the triaxial mechanical behaviour of geopolymer under varying confinements. Results revealed that the resulting failure strength of geopolymers increases with increasing salinity, confinement and temperatures up to 60 C. A maximum average failure strength of 66.4 MPa was obtained for the possible worst combination (temperature of 80ºC, salinity of 30% NaCl and confinement of 25 MPa) which satisfies the strength requirement for a typical well cement. On the whole, the combined effect of temperature and salinity acts favourably for geopolymers and they can be successfully used as well cement.