Effect of Salinity on Mechanical Behaviour of Well Cement: Application to Carbon Capture and Storage Wells

Integrity of injection wells play a vital role in the success of carbon capturing storages (CCS) and oil/gas extraction projects. Well cement plays a vital role in ensuring well integrity and the loss of well integrity may be caused due to the down-hole curing conditions. The salinity in the storage reservoirs varies from 0-30% NaCl depending on the geological location, and hence a typical well cement is exposed to a range of salinity levels. Therefore, aim of this research was to analyze the mechanical behaviour of cement cured in saline water. Testings such as uniaxial compressive strength (UCS) test, X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) were conducted or well cement cured in different NaCl brine concentrations (0-30%) with various curing periods (7-45 days). Based on the experimental outcome, it was observed that the strength and the Young modulus of OPC based well cement decreases with salinity levels and with ageing in time. Moreover, SEM test results showed that the NaCl penetration and deposition into the samples is high at higher salinity levels and longer ageing periods. On the whole, OPC based well cement experiences cement degradation in saline aquifers and hence this should be considered in the design of these wells.