多级压裂一界面破坏试验及数值模拟研究

Experimental Investigation and Numerical Simulation of the Casing-Cement Sheath Interface Debonding During Multi-Stage Fracturing

现有多级压裂套管-水泥环破坏研究方式有限,无法准确反映其界面实际破坏情况。为此,结合试验与数值模拟方法,通过研制的胶结参数测试装置,获得界面胶结参数并将其赋予套管-水泥环界面中的Cohesive单元,以此开展在不同套管内压下套管-水泥环界面(一界面)破坏数值模拟研究。研究结果表明:建立的套管-水泥环-地层有限元模型可使一界面破坏数值模拟最大程度贴近实际界面物理破坏情形;在增压阶段,套管内压值越高,水泥环塑性变形程度越大;水泥环塑性变形程度及一界面微环隙宽度在周向上均不一致,在水泥环塑性变形程度越大的区域一界面微环隙越宽。所得结论可为油田压裂施工参数设计提供理论参考。

The existing research methods are inadequate to accurately characterize the actual casing-cement sheath failure.By combining numerical simulation with laboratory experiment,a test device was developed to measure the casing-cement sheath interface bond parameters,which were then assigned to the Cohesive element of the casing-cement sheath interface,so as to study the interface debonding during multi-stage fracturing under different internal casing pressures through numerical simulation.The results show that the built finite-element model of casing-cement sheath-formation delivers numerical simulation of the casing-cement sheath interface debonding with maximal consistency with the practice.During the casing pressurization,higher casing pressure results in larger plastic deformation of the cement sheath;the cement sheath plastic deformation and the microannulus at the casing-cement sheath interface are varied along the wellbore circumference;larger plastic deformation of the cement sheath is associated with a wider microannulus of the casing-cement sheath interface.The research findings provide references for the design of fracturing treatment parameters.