Influence of Short Polypropylene Fibers on the Toughness of High Performance Cement Slurries

In oil wells, one of the goals of the cement sheath is the hydraulic seal. Generally, cement pastes, which are adopted in cementing operations, exhibit brittle fracture when subjected to tensile stresses. This behavior can compromise the hydraulic seal promoted through the sheath. One way to mitigate this problem is the use of slurries with more deformability. In this context, this work aims the determination of the toughness of high performance cement slurries reinforced by different volume fractions (0.50% and 0.75%) of short polypropylene fibers (6mm long). The influence of fiber addition in the rheological behavior, free fluid, density, stability and unconfined compression of the slurries was also determined. The obtained results indicated an increase in the yield strength and a reduction in the spreading of the reference mix with the increase of the fiber volume fraction. The free fluid, density and stability behavior of the reinforced slurries were similar to that of the control mix. An expressive change in the fracture behavior of the brittle matrix was observed in both mechanical tests carried out. Under uniaxial compression loads, although the ascending branch of the stress-strain curve did not show expressive differences with the fiber reinforcement (only minor modifications in the peak load), the descending branches were significantly modified with the reinforced mixes presenting a smooth post-cracking behavior. The greatest benefit provided by the fibers was observed, however, in the bending tests. Both, the maximum post-cracking strength and bending toughness, were significantly augmented with the increase of the fiber volume fraction.Copyright © 2014 by ASME