Study On Well Cement Structure Integrity Under Conditions Of CO₂ Injection And Storage

In the implementation of carbon capture,utilization and storage technology projects,the carbon dioxide injection and storage will damage the wellbore cement structure integrity.Radial crack,interfaces between cement and formation and/or casing,and casing and plug were identified as the preferential pathways for fluid flow.Hence,this paper studies the mechanism of wellbore cement structure failure due to crack initiation and propagation in carbon dioxide injection and storage wells based on the perspective of fracture mechanics,and analyzes the influence of operation parameters such as loading condition,geometry parameters and material properties on the structural integrity of cement.This paper constructs a simulation corrosion environment based on the field data and determines the fracture mechanical properties of cement materials before and after carbonation.Furthermore,the damage and deterioration mechanism of mechanical properties of cement after corrosion is analyzed by combining the micro-performance tests such as XRD and SEM.In this paper,a finite element model of the wellbore with cracks under the condition of carbon dioxide injection in vertical wells was established,and the fracture parameters of cement interface cracks and radial cracks were evaluated.According to the propagation criterion,the mechanical failure caused by cracks in cement structure was discriminated,and the impact of temperature and pressure conditions,cement mechanical and thermal properties on crack propagation was revealed.Taking account of the influence of the change of the deviation angle on the temperature and pressure in the flow and heat transfer process of the wellbore,taking this as the load boundary,In view of the eccentric casing,a finite element model of the wellbore with cracked cement sheath under the condition of casing eccentricity is established,and the effect of casing eccentricity on the cracking existed in wellbore is evaluated.the evaluation of the impact of various engineering factors on the crack propagation under the condition of casing eccentricity is provided.Considering the implications of carbonation on the mineral percent and mechanical parameters of cement plugs in abandoned wells during carbon dioxide storage,a finite element model of long-term corrosion cement plugs was established to calculate the stress distribution and energy release rate at the cement plug-casing interface during carbon dioxide storage,and the impact of corrosion,in-situ stress,edge pressure,etc.parameters on the bearing capacity and crack propagation of cement plugs was analyzed,and the thickness and material of cement plugs were optimized.The results of this study indicate that the variations in temperature and pressure caused by carbon dioxide injection will increase the risk of radial crack and interface crack propagation,optimizing the injection construction parameters and improving the mechanical and thermal performance parameters of cement can maintain the cement sheath integrity.the carbonation caused by carbon dioxide storage will lead to the deterioration of fracture mechanical properties of cement plug and reduce the bearing capacity of the cement structure.By optimizing the plug injection process,adding anti-corrosion materials,and optimizing the geometry and material of the cement plug,the failure risk of the cement plug interface is reduced.This research provides an evaluation of the wellbore cement structure integrity and optimises construction parameters under the condition of carbon dioxide injection and storage.