Nanosilica-treated shape memory polymer fibers to strengthen wellbore cement.

To attain cement sheath integrity, a tight and ductile microstructure for the cement matrix is desirable. Despite improvements achieved in cement design by employing fiber additives, limitations such as low compressive strength and formation of weak regions may result in fracture initiation points in the cement matrix. In this work we grafted silica nanoparticles on the surface of expandable polymer fibers through a sol-gel process to improve the bonding with the cement matrix and inhibit the formation of weak points in the cement sheath. Considering water-phobic nature of some of these polymeric surfaces, hydrophilic coating of fibers may improve their adhesions to the water-based cement, significantly. The mechanical performance of the samples made of treated fibers are characterized by means of compressive strength, flexural strength, and cyclic loading. Cement samples with nanosilica-treated fibers demonstrated superior results in all mechanical tests in comparison to samples made from untreated fibers. Even at low concentrations, such as 2% by weight, higher flexural strength is observed in the cement with the treated fibers. We also noticed that the flexural strength increases proportionally to the fiber concentration. Therefore, the concentration of additives may be tailored to deter crack propagation in accordance with the other requirements of the cementing operation. The expansive capabilities and rheological properties of the cement are maintained after the surface treatment. The results also demonstrate that the damage to the cement during cyclic loading is reduced when the cement is reinforced with treated fibers that can be interpreted as improved resiliency which is critical in the wells undergone frequent pressure fluctuations during hydraulic fracturing treatments. • Cement resiliency and tensile strength play important role in its integrity. • Fibers of shape memory polymers can be used to improve ductility of cement. • To improve bonding of polymer fibers to the cement matrix, a cost-effective nano-additive is proposed. • Nanosilica coatings improve cement tensile and compressional strengths. [ABSTRACT FROM AUTHOR]