Wellbore integrity is a critical component of long-term carbon storage. Depleted reservoirs that are potential CO₂ storage sites, typically contain several wells. Due to years of operations and abandonment, these wells can have cracks in the cement, cement-casing interface, and/or cement-formation interface. During CO₂ injection, changes in temperature may result in stress variations that can further damage the well, threatening its integrity. The temperature difference between the cold injected CO₂ and warm reservoir, and different thermal properties for the wellbore casing, cement, and the lithology, will stress the near wellbore environment, potentially extending pre-existing defects creating leakage pathways from the storage reservoir to the overlying strata. We have conducted a systematic numerical study to explore the role of CO₂ injection temperature, downhole effective in-situ horizontal stress, and the thermo-mechanical properties by coupling a linear elastic stress model with heat conduction. We consider conditions in non-perforated casing above the injection zone where conductive heating is dominant. The injection temperatures considered covers current industrial practice as well as sub-zero temperatures. The latter represents direct injection following ship transport, without pre-heating.

In this study, we consider the connection between damage risk and the temperature difference between the injected CO₂ and the formation and downhole effective in-situ horizontal stress. The study found that the negative impacts of thermal stress in the wellbore environment are mitigated by the presence of effective in-situ horizontal stresses. Stresses normal to the well have the potential to reduce the tensile stress and stress intensity factor. In the absence of sufficient effective in-situ horizontal stress, thermal stress may cause the fracture to propagate due to high stress concentration near the fracture edges. In general, formations with large effective in-situ horizontal stress can prevent leakage paths from growing even when large temperature difference exists between the formation and the injected CO₂. Our simulations suggest that CO₂ can be injected at sub-zero temperatures, suitable for ship transport, when the downhole effective in-situ horizontal stress is greater than 10 or 12 MPa, depending on the location of the pre-existing cracks. For onshore transportation, injection of liquid CO₂ results in minimal damage, provided there is ample in-situ horizontal stress.

井筒完整性是长期碳储存的关键组成部分。枯竭的油藏可能是潜在的CO ₂储存地点，通常包含数口井。由于多年的运营和废弃，这些井在水泥，水泥套管界面和/或水泥地层界面中可能会出现裂缝。在注入CO _2的过程中，温度的变化可能会导致应力变化，从而进一步损坏孔，从而威胁其完整性。冷注入CO ₂之间的温差井筒，水泥和岩性的不同热学性质以及热储层，将对附近的井筒环境造成压力，潜在地扩展先前存在的缺陷，从而形成从储层到上覆地层的渗漏通道。我们已经进行了系统的数值研究，以通过将线性弹性应力模型与热传导耦合来研究CO ₂注入温度，井下有效原位水平应力以及热力学性质的作用。我们考虑注入区域上方非穿孔套管中的传导加热占主导的条件。所考虑的注射温度涵盖了当前的工业实践以及低于零的温度。后者表示船舶运输后的直接喷射，没有预热。

在这项研究中，我们考虑了损坏风险与注入的CO ₂之间的温差之间的联系地层和井下有效的原位水平应力。研究发现，有效的原位水平应力可以减轻井眼环境中热应力的负面影响。垂直于井的应力可能会降低拉伸应力和应力强度因子。在没有足够有效的原位水平应力的情况下，由于裂缝边缘附近的高应力集中，热应力可能会导致裂缝扩展。通常，即使在地层与注入的CO ₂之间存在较大的温差时，有效的原位水平应力大的地层也可以防止泄漏路径的增长。我们的模拟表明，CO ₂当井下有效原地水平应力大于10或12 MPa时，可根据预先存在的裂缝的位置，在低于零的温度下注入，适用于船舶运输。对于陆上运输，只要有足够的原位水平应力，注入液态CO _2所造成的损害就很小。