碳纤维增强油井水泥石的力学性能

油井水泥石在井下易脆裂,造成油井层间封隔失效,进而影响油井开采。为了解决这一问题,需要对水泥石进行降脆增韧。首先,考察了甲基纤维素和羧甲基纤维素对碳纤维的分散效果;然后,研究了碳纤维对油井水泥石抗压强度、抗折强度和劈裂抗拉强度的影响,并模拟井下环境测试了水泥石单轴和三轴应力-应变曲线;最后,使用扫描电子显微镜对碳纤维增强水泥石的微观形貌进行观察,探讨碳纤维对水泥石的增韧机制。结果表明:0.2wt%的羧甲基纤维素溶液可有效分散碳纤维;养护28d后,0.3wt%碳纤维增强水泥石的抗压强度、抗折强度和劈裂抗拉强度较纯水泥石的分别提高8.6%、31.5%和52.4%,三轴直接加载条件下,其弹性模量较纯水泥石的低49.5%;经过分散的碳纤维在水泥石中乱向分布,形成三维网络结构,通过桥联、剥离及拔出耗能作用增强水泥石。研究结果为解决油井水泥石易脆裂的问题提供了理论参考。

Mechanical properties of carbon fiber reinforced oil well cement composites

Oil well cement composites are apt to embrittlement crack downhole, and that will lead to the failure of interlaminar packers of oil well, then effect the exploitation of oil well. In order to solve this problem, it is necessary to reduce the brittleness and increase the toughness of oil well cement composites. Firstly, the dispersancy effectiveness of methylcellulose and carboxymethylcellulose toward carbon fibers were investigated. Then, the effects of carbon fibers on the compressive strength, flexible strength and splitting tensile strength of oil well cement composites were investigated, and the uniaxial and triaxial stress-strain curves of cement composites were measured under the simulated downhole environment. Finally, the microtopographies of carbon fiber reinforced oil well cement composites were observed by scanning electron microscope and the toughening mechanism of carbon fibers toward cement composites was discussed. The results demonstrate that 0.2wt% carboxymethylcellulose solution can disperse carbon fibers effectively. After cured for 28 d, the compressive strength, flexible strength and splitting tensile strength of 0.3wt% carbon fiber reinforced cement composites increase by 8.6%, 31.5% and 52.4%, respectively, under the condition of triaxial direct loading, the elastic modulus reduces by 49.5% comparing with the pure cement composites. The dispersed carbon fibers distribute in cement composites disorderly, form the three-dimensional network structures and toughing cement composites by the energy-dissipation effects of bridging, peel and pulling-out. The conclusions provide theoretical reference to solve the problem of brittleness of oil well cement composites.