The Role of Wellbore Cement in Energy Transition: CO₂ Storage and Emissions

Sustainable development demands a fundamental transformation in energy generation, requiring innovations in subsurface management and geomaterial manufacturing. Cement plays a crucial role in facilitating this transition on two fronts. Firstly, as carbon dioxide (CO₂) storage emerges as a promising strategy for mitigating emissions from large-scale industrial operations, its effective implementation relies not only on identifying suitable reservoirs with proven storage capacities but also on the performance of wellbore cement in providing long-term mechanical and hydraulic sealing. Secondly, the production of cement demands an environmentally conscious alternative to traditional Portland cement (PC) capable of both curbing CO₂ emissions during the calcination process and bolstering the resilience of wellbore casing under pressure. Our research adopts a dual-pronged approach. We investigate the chemical interactions between supercritical CO₂ and cement, analyzing their effects on cement porosity, permeability, strength, and failure mechanisms. Concurrently, we explore the properties of a low-carbon cement formulation derived from a volcanic blend composition. This formulation aims to reduce reliance on limestone as a primary resource, thus cutting emissions and minimizing reactivity with CO₂. Our findings reveal that exposure to CO₂ triggers well-documented carbonation reactions in Portland-based cement, commonly used in older and legacy wells. These reactions lead to calcite mineralization within the cement pore space, resulting in decreased porosity, reduced permeability, and increased strength. While these outcomes show promise for effectively sealing stored CO₂ and furthering sustainability goals, it is crucial to note that increased strength does not necessarily correlate with improved toughness. Our findings underscore that calcite mineralization exacerbates cement brittleness and damage, evident from crack propagation detected through acoustic emissions (AEs) monitoring. Over time, crack development worsens fluid flow and heightens the susceptibility of calcite to dissolution in the presence of acidic fluids generated by continuous CO₂ injection. Conversely, the volcanic-based formulation yielded lightweight cement samples with density ranging from 1100 kg/m³ to 1300 kg/m³ and a remarkable CO₂ reduction of up to 85%. The microstructure resulting from the volcanic blend composition enables ductile mechanical behavior, with peak strength and permeability ranging between 30MPa to 46MPa and 680μD to 30μD, respectively, thus appearing promising when cement is exposed to CO₂.