循环载荷作用下水泥环完整性试验研究
Experimental Study on the Integrity of Cement Sheath Under Cyclic Loading
陈硕 1王琳琳1
作者信息
摘要
在页岩气井多级压裂过程中,从地下很难直接获取水泥环温度和应变等用于评估其完整性的信息.为此,结合光纤光栅传感技术和全尺寸物理模拟试验装置,通过试验获得了水泥环在候凝阶段和完井阶段的温度和应变变化规律,分析了压力和温度循环载荷对水泥环完整性的影响.研究结果表明:在候凝阶段,水泥环峰值温度比养护温度高 1.9℃,水泥环周向应变为拉应变,最大值为403.7×10-6 m/m;在完井阶段,在40 和50 MPa内压循环载荷作用下,水泥环产生塑性应变并不断累积,当累积塑性应变达到临界值 87.1×10-6 m/m时,界面微环隙会导致环空气体泄漏;在温度循环载荷作用下,水泥环产生周向压应变,该收缩会在第一界面产生周向和径向拉应力,导致出现微环隙的风险增加.研究结论可为多级压裂现场施工提供理论参考.
Abstract
In the multistage fracturing process of shale gas wells,the information such as cement sheath tem-perature and strain used for evaluating the integrity of cement sheath is difficult to be directly obtained from the wellbore.Therefore,combined with the fiber Bragg grating sensing technology and full-scale physical simulation test device,tests were conducted to obtain the temperature and strain changes of cement sheath during the WOC(waiting on cement)and completion stages,and the influence of cyclic loads of pressure and temperature on the integrity of the cement sheath was analyzed.The study results show that during the WOC stage,the peak tempera-ture of the cement sheath is 1.9℃higher than the curing temperature,and the circumferential strain of the cement sheath is tensile strain,with a maximum value of 403.7×10-6 m/m;during the completion stage,under cyclic loading of 40 MPa and 50 MPa internal pressures,the cement sheath undergoes continuously accumulated plastic strain;when the accumulated plastic strain reaches the critical value of 87.1×10-6 m/m,the interfacial micro-an-nulus leads to annular gas leakage;under cyclic loading of temperature,the cement sheath undergoes circumferen-tial compressive strain,which increases the risk for occurrence of micro annulus.The study conclusions provide theoretical reference for field construction of multistage fracturing.
关键词
水泥环完整性/循环载荷/光纤光栅/微环隙/循环次数/多级压裂Key words
integrity of cement sheath/cyclic load/fiber Bragg grating/micro annulus/cycle index/mul-tistage fracturing引用本文复制引用
出版年
2024
NETL
NSTL
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