摘要
为准确量化循环载荷对井筒水泥环密封性的影响,基于页岩气井多级压裂过程中套管内压多次升高和降低的实际情况,开展了高温三轴循环载荷作用下水泥石岩心应力-应变试验,建立了套管-水泥环-地层组合体数值模型,基于Mohr-Coulomb准则和损伤理论,计算了多级压裂过程中循环载荷作用下水泥环内边界处等效塑性应变量。分析结果表明:循环载荷作用下水泥石累积塑性应变显著,初始塑性应变量最大,后续呈线性增加;多级压裂过程中,水泥环、套管胶结面处易出现累积塑性应变,初始塑性应变量最大,后续呈线性增加,与试验结果具有较好的对应性;降低水泥石弹性模量,增大泊松比、黏聚力和内摩擦角有利于降低累积塑性应变量,保护水泥环密封的完整性。研究结果可为页岩气井压裂过程中水泥环密封完整性设计和控制提供参考。
In order to accurately quantify the influence of cyclic loading on the cementing performance of cement sheath,core stress-strain test of set cement under the action of high-temperature triaxial cyclic loading is carried out based on the actual situation that the internal casing pressure goes up and down many times in the process of multi-stage fracturing in shale gas wells.The numerical model of casing-cement sheath-formation combination is established.And the equivalent plastic strain magnitude at the inner boundary of cement sheath under the action of cyclic loading in the process of multi-stage fracturing is calculated according to Mohr-Coulomb criterion and damage theory.The results show that the accumulated plastic strain on the set cement is significant and the initial plastic strain magnitude is the greatest and then increases linearly.In the process of multi-stage fracturing,accumulated plastic strain is likely to occur at the cementing interface of cement sheath and casing and the initial plastic strain magnitude is the greatest and then increases linearly,which is better accordant with the test results.It is favorable to reduce the accumulated plastic strain magnitude and ensure the sealing integrity of cement sheath by decreasing Young’s modulus and increasing Poisson’s ratio,cohesive stress and internal frictional angle of the set cement.
作者
席岩
王海涛
李军
王江涛
吴宏明
Xi Yan;Wang Haitao;Li Jun;Wang Jiangtao;Wu Hongming(Beijing University of Technology;CNPC Beijing Richfit Information Technology Co.,Ltd.;China University of Petroleum(Beijing)at Karamay;China University of Petroleum(Beijing);No.3 Drilling Company,CNPC Daqing Oilfield Drilling Engineering Company)
出处
《石油机械》
北大核心
2021年第2期88-93,共6页
China Petroleum Machinery
基金
国家自然科学基金联合基金重点项目“页岩气水平井井筒完整性失效机理与控制方法”(U1762211)
北京市博士后工作经费资助项目“页岩气水平井套管剪切变形演变机理及控制方法研究”(Q6004014202003)。
关键词
页岩气井
循环载荷
胶结失效
等效塑性应变
损伤理论
shale gas well
cyclic loading
cementing failure
equivalent plastic strain
damage theory
