The fracture debonding failure of cement plug/casing interface caused by the migration of underground fluid with pressure accumulation imposed serious challenges to wellbore integrity of abandoned wells. This paper presents an investigation with a view of quantifying the relationships between the fracture debonding height and the migration time of underground fluid. A new 3D numerical model of cement plug/casing/cement sheath/formation system based on the cohesive zone method, which was validated by microannulus experiment, was developed to simulate the fracture debonding process. And then the relationships between fracture debonding height and propagation pressure was studied. Additionally, the influence of horizontal in-situ stress, cement plug mechanical parameters, and interface properties on the fracture debonding height and development geometry were also analyzed. The results of research indicated that the minimum horizontal in-situ stress played a decisive role in controlling the fracture propagation of cement/casing interface. Debonding fracture propagated along the whole circumference of the interface with the same height for the case that the horizontal in-situ stress was uniform, while propagated along a certain circumference angle of the interface with the maximum height in the direction of maximum horizontal principal stress for the case that the horizontal in-situ stress was non-uniform. The results of numerical analysis showed that lower elastic modulus and Poisson's ratio of cement plug, higher cement plug permeability, and larger critical normal strength and critical shear strength were beneficial to decrease the fracture debonding height and reduce the risk of debonding failure of the cement plug/casing interface. Finally, some effective measures to maintain the sealing integrity of abandoned wells were proposed.

由地下流体的运移和压力积累引起的水泥塞/套管界面的断裂脱胶失败对废弃井的井眼完整性提出了严峻挑战。本文提出了一项研究，以量化裂缝脱粘高度与地下流体运移时间之间的关系。建立了基于粘性区方法的水泥塞/套管/水泥护套/地层系统的新型3D数值模型，并通过微环实验进行了验证，以模拟裂缝的剥离过程。然后研究了断裂剥离高度与传播压力之间的关系。此外，水平原位应力，水泥塞力学参数的影响，并分析了界面特性对裂缝剥离高度和发育几何形状的影响。研究结果表明，最小水平原位应力在控制水泥/套管界面的裂缝扩展中起着决定性的作用。对于水平原位应力均匀的情况，脱胶裂缝沿界面的整个圆周以相同的高度传播，而对于最大水平主应力方向，沿界面的一定的圆周角以最大的高度传播。水平原位应力不均匀的情况。数值分析结果表明，水泥塞的弹性模量和泊松比较低，水泥塞的渗透性较高，更大的临界法向强度和临界抗剪强度有利于减小裂缝的脱胶高度，降低水泥塞/套管界面脱胶失败的风险。最后，提出了一些有效的措施来保持废弃井的密封完整性。