裸眼临时弃置井水泥塞-地层界面剥离数值模拟

Numerical Simulation on Cement Plug/Formation Interface Debonding of Open Hole Temporary Abandoned Wells

地层流体沿水泥塞-地层界面运移并泄漏至地面会影响裸眼临时弃置井井筒密封完整性。为此,建立基于Cohesive单元方法的水泥塞-地层系统三维有限元模型,模拟水泥塞-地层界面裂缝的萌生及扩展过程,并与现有微环隙计算模型进行对比以验证模型的可靠性。定量分析了水泥塞-地层界面剥离过程中裂缝发展形态、裂缝扩展压力和裂缝剥离高度的变化,并对水泥塞力学参数、界面胶结强度及水平地应力差进行了敏感性研究。研究结果表明:较大的界面胶结强度和较高的水泥塞弹性模量有益于增大水泥塞-地层界面裂缝扩展压力,降低裂缝剥离高度,减小界面剥离失效的风险;在非均匀水平地应力条件下,地应力差越大,界面越容易剥离;水泥塞泊松比对裂缝扩展压力及剥离高度影响较小。研究结果为预测水泥塞-地层界面剥离导致的裸眼临时弃置井井筒密封完整性失效提供了有效方法。

The migration and leakage of formation fluid to the ground along the cement plug/formation interface imposed adversely influences on wellbore seal integrity of open hole temporary abandoned wells.Based on the Cohesive zone method,a three-dimensional finite element model of cement plug/formation system was developed to simulate the fracture initiation and propagation process of the cement plug/formation interface,and was compared and verified by microannulus calculation model.The fracture development form,fracture propagation pressure and fracture debonding height in the process of cement plug/formation interface debonding was quantitatively analyzed,and the sensitivity of the mechanical parameters of cement plugs,the interfacial bonding strength,and the horizontal in-situ stress difference are also studied.The results showed that higher interface cementation strength and cement plug elastic modulus were beneficial to increase fracture propagation pressure,decrease fracture debonding height,and reduce the debonding failure risk of cement plug/formation interface.When the horizontal in-situ stress was non-uniform,larger in-situ stress difference results in easier interface debonding.Cement plug Poisson’s ratio has little effect on the fracture propagation pressure and fracture debonding height.The research results provide an effective method for predicting the failure of the sealing integrity of the open hole temporary abandoned well caused by the cement plug-formation interface debonding.