Abstract
Cement provides zonal isolation and mechanical support, and its integrity is critical to the safety and efficiency of the CO2 injection process for geologic carbon storage. This work focuses on interfacial debonding at wellbore interfaces and radial cracking in cement during CO2 injection. It adopts the definition of the energy release rate (ERR) to characterize the propagation of cracks. Based on the finite element method, the proposed model estimates the ERRs of both types of cracks with practical wellbore configurations and injection parameters. Further parametric studies reveal the effects of cement’s mechanical and thermal properties and the crack geometry on crack propagation. Simulation results show that the ERRs of interfacial and radial cracks would surpass 100 J/m2 with typical cement properties. The cement’s thermal expansion coefficient is the most influential factor on the ERR, followed by its Young’s modulus, Poisson’s ratio, and thermal conductivity. The initial sizes and positions of the cracks are also important parameters for controlling crack propagation. Moreover, non-uniform in situ stresses would accelerate crack propagation at the interfaces. These findings are valuable and could help to optimize cement sheath design in order to ensure the long-term integrity of wells for geological carbon storage.
Highlights
Carbon capture and storage (CCS) is one of the potential climate change mitigation strategies for reducing carbon dioxide (CO2 ) emissions in the atmosphere [1,2]
This study aims to reveal the impacts of cement’s mechanical and thermal properties, initial crack sizes and positions, as well as in situ stresses on interfacial debonding and radial cracking in wellbore components
The current study suggests the use of soft cement to reduce the energy release rate (ERR) at the cement-formation interface and to reduce radial cracking
Summary
Carbon capture and storage (CCS) is one of the potential climate change mitigation strategies for reducing carbon dioxide (CO2 ) emissions in the atmosphere [1,2]. Geologic CO2 storage—the injection of CO2 into underground formations without economic exploitation, such as deep saline aquifers or depleted oil and gas reservoirs, both on-shore and off-shore—contributes largely to this goal. Secure geological storage of CO2 is supposed to limit leakage rates to 0.01% per year [4]. Oil and gas wells are the primary channels for injection of CO2 into the subsurface, but are potential pathways for CO2 to escape from the reservoir. Long-term well integrity is necessary to inhibit fluid leakage and is essential to CO2 storage security [5,6]
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