Ethanol plasma-induced polymerization of carbon fiber surface for improving mechanical properties of carbon fiber-reinforced lightweight oil well cement

Carbon fiber (CF) pretreated with oxygen plasma and modified with ethanol plasma was employed to improve the mechanical properties of lightweight oil well cement (LOWC). Surface properties of the modified CF and mechanical properties and structures of the CF-reinforced LOWC (CFRLOWC) were investigated using contact angle tests, Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM) and mechanical-property tests. The modified CF surface showed a higher roughness than the raw CF. Further, the oxygen content was increased, and oxygen-containing functional groups were successfully grafted on the CF surface, which led to an improved wetting behavior. The flexural and tensile strengths of the ethanol plasma polymerization modified CFRLOWC significantly increased by 27.25% and 70.56% with respect to the raw CF reinforced sample. The triaxial stress-strain curve showed higher strain capacity. Further, the pressure loading and seal tests revealed improved bearing capacity and isolation ability. The critical value of the pressure under gas channeling increased from 44.8 MPa to 71.5 MPa. The ethanol plasma polymerization modified CF significantly improved the interfacial adhesion between CF and cement matrix, indicating it can improve the bearing capacity and integrity of CFRLOWC sheaths in oil and gas wells.