Stability analysis of a granite-based geopolymer sealant for CO2 geosequestration: In-situ permeability and mechanical behavior while exposed to brine

Abstract

When considering the use of geopolymers (GPs), as potential alternatives for Portland cement, high durability during exposure to brine at encountered downhole is a key requirement. This study delves into the response of a granite-based GP system designed especially for CO2-geosequestration upon exposure to brines with different concentrations of NaCl. Exposure was carried out by imposed flow in a triaxial apparatus, at 90 °C and 13.8 MPa confining pressure. Mechanical properties were tested in the same apparatus once exposure was completed. A suite of micro-scale analytical techniques was then used to assess the GP's microstructure, mineralogical composition, and chemical bonding. The obtained results revealed increasing compressive strength with increasing brine salinity, suggesting greater resistance to deformation and potential cracking. Concurrently, decreasing Poisson's ratios and increasing Young's moduli could lead to an elevated risk of mechanical failure under strain. In addition, following a 3-week injection period, permeability of NaCl-flooded samples decreased by 20%–35% from initial values. Analysis of the effluents showed fluctuations in the pH and ion content with time, mainly attributed to complex chemical interactions including cation exchange, silicate dissolution and hydrolysis, precipitation of alkali-enriched gels, and mineral alterations. Micro-scale analyses revealed that the improved durability is linked with the formation of new minerals, especially zeolites in the presence of NaCl or portlandite when deionized water was introduced. In conclusion, this study presents new data on the durability of a rock-based GP system when exposed to brine and elevated pressure and temperature, offering insights for optimization to downhole environments.