Effect of modified sepiolite and carbon fiber composite on performance of oil-well cement and mechanism analysis

Sepiolite fiber (HPS), as a cheap and environmentally friendly mineral fiber material, has good application value in toughening filler of oil well cement stone and is the best substitute for toxic asbestos material. However, due to the defects of conventional industrial HPS such as low purity, poor dispersion, it will produce great incompatibility with cement slurry, which will adversely affect its performance. In this paper, conventional industrial HPS was treated with activation modification. The changes of surface groups of sepiolite before and after modification and the actual dispersion effect in aqueous solution were studied by FTIR and dispersion state of aqueous solution. In addition, the effects of modified sepiolite fibers (H-HPS) and carbon fibers (C-Fibers) on oil well cement were also investigated. The mechanism of the micro-morphology of the toughened cement paste was analyzed. The results show that the dispersion and suspension of H-HPS in aqueous solution have been greatly improved. The rheological test results of cement paste also support the improvement. At the same time, the optimum mixing ratio of the two materials was screened out by synergistic study with C-Fibers. It was found that the composite fiber cement slurry system synthesized the advantages of the two kinds of fiber materials, and the toughening effect was obviously better than that of the modified cement paste with a single admixture. From the analysis of SEM, it can be seen that HPS in the composite fiber cement slurry system fills in micro-voids on the one hand, and forms a uniformly dispersed network structure on the other hand, The C-Fibers in the system can effectively dissipate the tensile energy of the fracture interface of cement paste by interacting with hydration products, thus reducing the filtration of cement paste and improving the bulk toughness of cement paste.