水镁石纤维对固井水泥石力学性能的增强效果及机理

Reinforced mechanical properties and mechanism of well-cementing stones by brucite fiber

固井水泥石的脆裂微裂缝破坏了水泥环完整性,从水泥材料方面改善水泥石的性能一直是国内外固井界研究的一个热点。为此,实验研究了水镁石纤维对水泥石劈裂抗拉强度、抗压强度和抗折强度的影响;模拟井下环境进行了水镁石纤维水泥石的三轴应力一应变测试;使用扫描电镜观察水镁石纤维水泥石的微观形貌,进而探讨了水镁石纤维对水泥石的增强机理。结果表明:①水镁石纤维掺量适当时,水泥浆的应用性能良好;②水镁石纤维显著增强水泥石力学性能,水镁石纤维掺量为5.0%(质量分数)时,水镁石纤维水泥石的28 d劈裂抗拉强度、抗压、抗折强度较之纯水泥石分别提高32.8%、15.3%和32.2%,而其弹性模量较之空白试样水泥石降低34.5%;③水镁石纤维的亲水性良好,可在水泥石中乱向分布形成三维网络结构,通过拔出耗能作用和桥联作用控制了微裂纹的产生和发展,增强了水泥石力学性能。

Micro-fractures generated by brittle ruptures in well-cementing stones may destroy the integrity of the cement sheath, and accordingly, the enhancement of properties of well-cementing stones from the aspects of cement materials has been a hot topic for researches related to cementation technologies around the globe. This paper reviewed the impacts of brucite fibers on tensile strength, compressive strength and flexural strength of set cements. Tri-axial stress-strain tests of well-cementing stones reinforced by brucite fiber were conducted in simulated downhole environments. In addition, scanning electron microscope （SEM） was deployed to determine the micro structures of well-cementing stones reinforced by brucite fiber and further to probe the mechanisms related to such reinforcement. Test results show that： （1）application of brueite fiber with suitable proportions can generate cement slurries with satisfactory performances; （2）after curing for 28 days, the mechanical properties of well cementing stones with 5.0% （mass fraction） brucite fiber are enhanced significantly with compressive, flexible and splitting tensile strengths increased by 15.3 %, 32.2% and 32.8%, respectively, while the modulus of elasticity of well cementing stones reduces by 34.5% than pure cement; （3）with outstanding hydrophilic properties, brucite fiber may generate 3D network structures in a disordered manner in well-cementing stones. Through actions of energy consumption for removal and bridging, these structures can effectively control generation and development of micro-fractures. In this way, mechanical properties of oil well cement can be enhanced dramatically.