Viscosity and fracture toughness of fiber-reinforced cement slurries at elevated temperatures

Cement slurries are used for the construction of oil wells as deep as 30,000 ft (9,000 m). The severe performance requirements of such materials have prompted the search for appropriate fiber reinforcement to improve their tensile strength, impact resistance, and fracture toughness, without decreasing their pumpability. This paper reports on an experimental test program to investigate, among others, the fracture toughness and pumpability of fiber-reinforced cement slurries at the elevated temperatures encountered in deep oil wells, i.e. as high as 400 degreesF. The most promising type of fiber that appears to satisfy best the performance requirements is basalt fiber. Preliminary test results indicate no obvious improvement of the material's fracture toughness (measured according to ASTM C1018) at the two temperatures investigated. Studies are still ongoing to explain this unexpected finding. It could be caused by the fact that the basalt fibers are chopped into too little fragments during mixing or by the absence of aggregate. Also, the difficulty of performing such experiments may have contributed to it. The flow and pumpability properties were comparable with those of the standard cement slurries, and all the viscosity coefficients decreased as temperatures increased.