韧性材料对页岩气压裂井水泥环界面完整性影响  

Influence of Tough Materials on Cement Sheath Interface Integrity for Shale Gas Fracturing Wells

作　　者：郭雪利 沈吉云 武刚 靳建洲 纪宏飞 徐明 刘慧婷 黄昭 GUO Xue-li;SHEN Ji-yun;WU Gang;JIN Jian-zhou;JI Hong-fei;XU Ming;LIU Hui-ting;HUANG Zhao(CNPC Engineering Technology R&D Company Limited,Beijing 102206,China;PetroChina Dagang Oilfield Branch,Tianjin 300457,China)

机构地区：[1]中国石油集团工程技术研究院有限公司,北京102206 [2]中国石油大港油田分公司,天津300457

出　　处：《表面技术》2022年第12期232-242,共11页Surface Technology

基　　金：中国石油天然气集团有限公司科学研究与技术开发项目(2021DJ4403,2020F-49,2021DJ5203);中国石油集团工程技术研究院有限公司科学研究与技术开发课题(CPET 2022-04S)。

摘　　要：目的提高页岩气井多级压裂过程中水泥环界面完整性。方法针对4种在页岩气井中使用的水泥浆体系,基于水泥环完整性评价装置,开展在循环压力条件下水泥环界面完整性实验。采用高精度流量计、扫描电镜和核磁共振等监测手段,定量检测环空气窜速率,探索水泥环在加载前后的微观结构变化。根据实验装置基础参数,采用有限元方法模拟循环加载过程水泥环界面的损伤演化情况。结果常规水泥浆、18%(均为质量分数)胶乳剂水泥浆、36%胶乳剂水泥浆、18%胶乳剂加1%增韧剂水泥浆,其环空气窜速率分别为722、300~677、20~45、10~25 mL/min。经循环载荷作用后,常规水泥浆在水泥环本体出现明显径向裂缝和界面微环隙,且水泥浆水化产物较疏松;36%胶乳剂水泥浆仅在水泥环界面产生较小的微环隙,水化产物在界面处较致密,水泥石孔径较小。在循环载荷作用下,水泥环界面孔隙显著增加,界面处产生塑性应变并不断增加。结论胶乳剂和韧性剂材料可有效填充水泥颗粒之间的间隙,降低水泥石孔径尺寸。胶乳剂通过改善水泥环的微观形态结构,避免在本体产生裂缝,提高了界面密封性能。增韧剂对水泥颗粒产生较强的粘结作用,与胶乳剂的配合使用进一步增强了水泥环界面的密封效果,两者共同作用可显著提升水泥环空密封能力。在循环载荷作用下,水泥环界面易形成微环隙,为环空气体提供了窜流通道,造成环空带压。现场采用添加18%胶乳剂加1%增韧剂的韧性水泥浆体系开展固井施工,水泥石力学性能能够满足水泥石强度大于30 MPa和弹性模量小于7 GPa的性能要求。同时,使用韧性水泥浆的井段固井质量也较好,后续压裂施工过程也未见环空带压问题。通过合理优选韧性水泥浆添加剂含量,能够为环空提供良好的密封效果,提升水泥环的密封完整性。To improve the cement sheath integrity during multi-fracturing for shale gas wells,four kinds of cement slurry systems were tested to evaluate cement interface integrity based on the cement sheath integrity device under the condition of cycle load.High-precision flowmeter was used to quantitatively detect the annulus gas flowing rate to evaluate the annulus sealing ability.Electron microscope scanning and nuclear magnetic resonance were adopted to measure the micro-structural changes of the cement sheath.The plastic finite element model of wellbore was established to simulate the damage of cement sheath interface during the cycle load.The results show that the annular gas flow rates of conventional cement slurry,18wt.%latex,36wt.%latex,and 18wt.%latex+1wt.%toughening were respectively 722 mL/min,300-677 mL/min,20-45 mL/min,10-25 mL/min,indicating that the addition of latex can greatly reduce the gas flow rate in the annular interface and enhance the interface sealing ability.At the same time,the toughener can enhance the effect of the latex and improve the sealing integrity of cement sheath interface.After cyclic load,there were radial crack and microscopic crack at the cement interface for the conventional cement slurry,with the maximum width of 17μm and length of 32 mm for radial crack.For the cement slurry with 36wt.%latex,there was only small micro annulus at the cement sheath interface.The hydration product was denser for the cement slurry with 36wt.%latex.Under cycle load,the pore size of the cement sheath body did not change much,but the pore size at the interface increases significantly.The finite element results show that plastic deformation occurred at the cement sheath interface under cyclic loading.With the increase of the number of cycles,the plastic strain increases continuously,and micro-annulus is easily formed.It could be concluded that the latex and ductile materials can effectively fill the gaps between the cement particles and reduce the pore size of the cement matrix.When the tough cement sl

关 键 词：页岩气压裂 水泥环界面 韧性水泥浆 密封完整性 微环隙 有限元 

分 类 号：TG174[金属学及工艺—金属表面处理]