纳米SiO_2溶胶缓解油井水泥高温强度衰退的作用机理  

Working mechanism of nano-SiO_2 sol to alleviate the strength decline of oil well cement under high temperature

作　　者：王成文[1,2] 陈新[2,3] 周伟 王永洪[4] 薛毓铖[2] 罗发强 Wang Chengwen;Chen Xin;Zhou Wei;Wang Yonghong;Xue Yucheng;Luo Faqiang(Key Laboratory of Unconventional Oil & Gas Development//China University of Petroleum , Qingdao, Shandong 266580, China;School of Petroleum Engineering, China University of Petroleum , Qingdao, Shandong 266580, China;Department of Civil and Environmental Engineering, University of Alberta, Edmonton, Alberta T6G 2W2, Canada;Research Institute of Petroleum Engineering, Sinopec Northwest, Urumqi, Xinjiang 830011, China)

机构地区：[1]非常规油气开发教育部重点实验室.中国石油大学(华东) [2]中国石油大学(华东)石油工程学院 [3]加拿大阿尔伯塔大学土木与环境工程学院 [4]中国石化西北油田分公司工程技术研究院

出　　处：《天然气工业》2019年第3期72-79,共8页Natural Gas Industry

基　　金：国家自然科学联合基金重点项目"超深井安全高效井筒工作液构建及调控方法基础研究"(编号:U1762212);国家自然科学基金项目"CCS咸水层封存中二氧化碳-硫酸盐-镁盐协同作用下油井水泥石的腐蚀机理"(编号:51704325);山东省自然科学基金项目"高温高密度水泥浆恒稳调控方法及其作用机理研究"(编号:ZR2017MEE056);长江学者和创新团队发展计划(编号:IRT_14R58)

摘　　要：油井水泥石强度衰退是高温固井所面临的主要难题之一,而添加纳米SiO_2能否缓解水泥石的高温强度衰退以及其作用机理是什么,还有待于验证和确认。为此,通过室内试验,基于X射线衍射仪、扫描电子显微镜和能谱仪分析水泥石的矿物组成、微观结构和水化产物的元素,测定了高温条件下(150℃/35 MPa)纳米SiO_2溶胶对G级油井水泥石抗压强度的影响及变化规律,据此研究纳米SiO_2溶胶在高温下对水泥水化产物的作用机理。研究结果表明:①纳米SiO_2溶胶可以提高G级油井水泥浆的稠度系数,对水泥浆的流变性会产生不利的影响;②在高温养护初期,纳米SiO_2溶胶会降低水泥石的抗压强度,但加入纳米SiO_2溶胶的水泥石的抗压强度不会随着养护时间的增加而产生明显的变化;③加入少量纳米SiO_2溶胶的G级油井水泥中的纳米SiO_2颗粒吸附在水泥矿物表面阻碍水化反应,能够缓解水泥水化产物的高温脱水变质,纳米SiO_2颗粒还可以提高水泥微观结构的致密性;④加入大量纳米SiO_2溶胶的G级油井水泥中的纳米SiO_2与氢氧化钙发生火山灰反应生成一种新型的、结构松散的薄片蜂窝状CSH产物,难以提供较高的抗压强度。结论认为,纳米SiO_2可以作为水泥添加剂以缓解油井水泥高温强度衰退,该研究成果为高温固井水泥浆体系的设计提供了一条新的思路。Strength decline of oil well set cement is one of the major challenges during well cementing under high temperature. Therefore, it is necessary to verify and confirm whether nano-SiO2 can mitigate this problem and its working mechanism. In this paper, the mineral composition and microstructure of set cement and the elements of its hydration product were experimentally analyzed by using a X-ray diffractometer, a scanning electron microscope and an energy spectrometer. Then, the effect of nano-SiO2 sol on the compressive strength of Class G oil well set cement and its change laws under high temperature (150 ℃/35 MPa) were investigated. Based on this, the working mechanism of nano-SiO2 sol on the hydration product of cement under high temperature was studied. And the following research results were obtained. First, nano-SiO2 sol can increase the consistency coefficient of Grade G oil well slurry and has an adverse impact on the rheological property of slurry. Second, nano-SiO2 sol can decrease the compressive strength of set cement in the early stage of high temperature curing, but the compressive strength of the set cement with nano-SiO2 sol will not change obviously as the curing goes. Third, if a small amount of nano-SiO2 sol is added into Grade G oil well cement, nano-SiO2 particles are adsorbed to the surface of cement minerals to hinder the hydration reaction, so it can mitigate the evaporation metamorphism of the hydration product of cement under high temperature. Besides, nano-SiO2 particles can improve the micro-structural compactness of the cement. Fourth, if a large amount of nano-SiO2 sol is added into Grade G oil well cement, pozzolanic reaction happens between nano-SiO2 and calcium hydroxide, generating a new type of structurally loose honeycomb calcium silicate hydrate (CSH) product, which cannot provide higher compressive strength. In conclusion, nano-SiO2, as cement additive, can mitigate the strength retrogression of oil well cement under high temperature. These research results provide a new ide

关 键 词：纳米SiO2溶胶 高温 G级油井水泥 水泥石 抗压强度 缓解强度衰退 水化产物 微观结构 

分 类 号：TE256.6[石油与天然气工程—油气井工程]