Both known and unmapped plugged and abandoned wells are potential leakage pathways for CO₂ from geologic carbon sequestration (GCS) sites. Although many abandoned wells have cement bridge plugs installed to prevent leakage, the seal between the cement and the inner casing wall is subject to failure. In this study, we carried out detailed T2Well simulations of cases of sudden non-Darcy flow of CO₂ and brine leakage up the gap between a cement plug and the inner steel casing wall that becomes a fully connected flow path during the post-injection period. The goal of our study was two-fold: (1) to understand the dynamics, rates, and the characteristic temporal signals associated with the onset of leakage through various gap-aperture sizes, and (2) to suggest potential monitoring strategies based on the findings. Simulation results show that the leakage of CO₂ and brine upward is transient with interesting phase interference behavior. Time-dependent oscillatory flows with varying pressure, temperature, and flow rates of CO₂ and brine show strong dependence on gap aperture. Phase-change and decompression lead to very low temperatures at the top of the well for gap apertures larger than 4 mm suggesting that remote thermal monitoring at the ground surface may be an effective way of monitoring even if well locations are not known a priori. Pressure in the well is also indicative of CO₂ leakage. The temporal patterns of changing temperature and pressure may be useful diagnostic signals for leakage detection. Finally, these transient leakage signals may provide information on the cause of leakage and/or characteristics of the flow path that could inform effective remediation design and execution approaches.

已知和未映射的堵塞井和废弃井都是从地质碳固存（GCS）站点泄漏CO _2的潜在途径。尽管许多废弃的井都安装了水泥桥塞以防止泄漏，但水泥与内套管壁之间的密封会失效。在这项研究中，我们对CO ₂突然非达西流动的情况进行了详细的T2Well模拟盐水泄漏沿水泥塞和钢制套管内壁之间的缝隙泄漏，在注入后阶段，该缝隙成为一条完全连通的流路。我们的研究目标有两个：（1）了解通过各​​种间隙孔径大小与泄漏的发生相关的动力学，速率和特征性时间信号；（2）根据检测结果建议潜在的监测策略发现。仿真结果表明，CO ₂和盐水的向上泄漏是瞬时的，具有令人感兴趣的相位干扰行为。随时间变化的振荡流，其压力，温度和CO _2的流量均发生变化盐水显示出对间隙孔径的强烈依赖性。相变和减压导致间隙孔大于4 mm的井顶部温度非常低，这表明即使事先不知道井的位置，对地面进行远程热监测也可能是一种有效的监测方法。井中的压力也表示CO ₂泄漏。温度和压力变化的时间模式可能是用于泄漏检测的有用诊断信号。最后，这些瞬态泄漏信号可以提供有关泄漏原因和/或流路特性的信息，这些信息可以指导有效的补救设计和执行方法。