Carbon dioxide capture and geological storage (CCS) is a climate change mitigation measure that seeks to reduce the greenhouse gases emitted to the atmosphere by injecting carbon dioxide in a supercritical state (scCO2) into deep reservoirs. The injection wells are a source of weakness in the "rock-cement-casing" system. Cement fills the annular space between the casing and the rock borehole. Once the scCO2 is stored, the rock-casing-cement system must ensure that the scCO2 does not migrate through the different possible paths. These paths can be the seal rock containing the reservoir, the cement-rock interface, the cement itself, and the cement-casing interface. This work focuses on studying cement as a possible migration pathway for scCO2. It will mainly focus on lightweight cement pastes, which will be achieved by replacing cement with hollow glass microspheres (HGMS). The stability of wells cemented with lightweight cement pastes under CCS injection wells conditions is studied. Cement pastes were subjected to carbon dioxide geological storage conditions for 60 days. The evolution of the cement pastes' physical and mechanical properties was measured before and after this procedure. By analyzing the data obtained from the laboratory tests, the presence of HGMS influence the performance of cement pastes subjected to CCS conditions. HGMS provide the cement matrix with a high amount of unconnected porosity, which lightens it without affecting its mechanical properties. Nevertheless, under CCS conditions, this porous structure could modify the carbonation mechanisms and the advancement of carbonation in the cement sheath.

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