Tailored Cement Solution for CCUS Wells: Case Study from the Adriatic Sea

A case study is presented for the first application in Italy of an innovative technology designed to address key carbon capture, use, and storage (CCUS) well challenges, specifically barrier integrity maintenance and long-term containment of stored CO2 assurance. The approach adopted in this case followed a six-step process: 1) select a suitable cement system through research and development, 2) mold and cure the sealant under anticipated wellbore conditions, 3) expose the sealant to supercritical CO2 at planned conditions, 4) measure the cement's permeability and mechanical properties before and after exposure, with comparison to reference samples, 5) execute a finite element analysis (FEA) at critical wellbore locations to evaluate the potential for cracking, debonding, or plastic failure, and 6) identify operational activities that could damage the cement sheath and propose mitigation strategies. An immersion-type exposure test was conducted using wet supercritical CO2 (scCO2). The introduction a small quantity of water—beyond the solubility limit of CO2—into an autoclave occurred first, followed by injection of CO2 gas. The system was then pressurized to 90 bar and heated to 60°C (bottomhole static temperature BHST) to reach supercritical conditions. Samples were suspended to help prevent contact with excess water at the bottom. The exposure lasted 28 days. To simulate long-term conditions, additional samples were subjected to scCO2 with a 34-bar axial differential pressure across 80 mm at 80°C for six months. Post-exposure inspection and testing followed. FEA results identified mechanical sheath failure and debonding prevention as critical factors to minimize CO2 exposure and potential flow paths. Cement design with favorable resilience and elasticity emerged as key factors for risk mitigation. Several significant challenges were successfully addressed during the delivery of a tailored, CO2-resistant cement system. Challenges included control of equivalent circulating density (ECD) in depleted gas reservoirs with narrow margins between pore pressure and fracture gradient, along with accommodation of tight restrictions in wellbore geometry. Successful execution of the cement operation occurred, with top of cement confirmed as planned. A cement bond log verified acceptable cement quality. This innovative cement system provides reliable long-term zonal isolation in CO2-rich environments, with well integrity maintained throughout the well's life cycle. The technology represents a favorable step in effective well integrity solutions and supports global CO2 emission reduction efforts. Results confirm that Portland cement-based systems can achieve adequate resistance to CO2 exposure through proper engineering.