摘要
为了准确了解多级压裂过程中水泥环的应力变化规律,基于分步有限元的思想,构建了考虑页岩各向异性的套管-水泥环-地层组合体有限元瞬态分析模型,模拟多级压裂过程中水泥环的应力变化特征。新的模型考虑了注液温度、套管内压、地应力、孔隙压力、水泥环以及地层性质等因素对水泥环受力状态的影响。研究结果表明:高压注液过程中,采用传统模型会低估井下水泥环周向应力的变化程度;大排量压裂施工过程中,井筒内温度震荡变化,注液温降导致水泥环应力发生剧烈变化;储层改造后的地应力以及孔隙压力变化对水泥环周向应力均有较大影响;水泥环周向应力随着地层各向异性程度的增加而有所增加;调节施工内压并适当降低水泥环刚度可明显降低水泥环发生拉伸破坏的概率。研究成果可为页岩气开发提供理论指导。
To give a precise insight into the stress of cement sheath during multistage fracturing, based on the step- by-step finite element method, a finite element transient analysis model of casing-cement sheath-formation con-sidering shale anisotropy has been established to simulate the stress variation of cement sheath in multistage fractu-ring. The new model integrated the effects of injection fluid temperature, casing inner pressure ？ in-situ stress, pore pressure, cement sheath and formation properties on the cement sheath. The results show that the traditional model underestimates the variation intensity of the circumferential stress of the cement sheath under high pressure fluid in-jection process. During the operation of large displacement fracturing, the temperature fluctuates in the wellbore. The temperature decrease of the injection fluid leads to intense change of cement sheath stress. Both the formation stress after stimulation and the pore pressure has great effect on the circumferential stress of cement sheath. The cement sheath stress increases with the increase of the formation anisotropy. The adjustment of operation inner pressure and appropriate reduction of cement sheath stiffness can significantly reduce the probability of tensile failure of cement sheath .The research results could provide theoretical guidance for shale gas development.
出处
《石油机械》
2017年第8期45-49,共5页
China Petroleum Machinery
基金
国家自然科学基金重点项目"控压钻井测控理论及关键问题研究"(51334003)
中国石油科技创新基金研究项目"面向页岩气体积压裂的分簇射孔技术研究"(2012D-5006-0303)
中国石油西南油气田公司页岩气开发事业部科研项目"威远长宁页岩气水平井固井质量对井筒完整性的影响研究"(XNS21JS2014-04)
关键词
页岩
体积压裂
分步有限元
套管
水泥环
数值模拟
shale
volume fracturing
step- by-step finite element
casing
cement sheath
numerical simulation
