Application and Analysis of the Synergy between Oil Well Cement Expanding Agents and Oil Well Cement Tougheners

Two expanding agents and two tougheners were selected to explore the synergy between oil well cement toughener and expanding agent. The expanding agents selected were a lattice expanding agent and a gas expanding agent, the tougheners selected were a fiber and a carbon nanotube (CNT). A cement slurry was treated with these agents whose synergy was investigated. Laboratory study was performed on the expansion performance, mechanical properties, pore structure and regular performance of the cement slurry, and the operating conditions of different combinations of the tougheners and expanding agents were analyzed. It was found from the study that under the condition of free expansion, the toughener and the gas expanding agent had higher synergistic expansion rate. The combination of CNTs and the expanding agents had better contraction inhibition effect at high temperature and high pressure. When CNTs were combined with the lattice expanding agent, the increase in the strength of the set cement was the greatest, the porosity of the cement matrix was the lowest and the pores were mainly micro ones. When the fiber was combined with the gas expanding agent, the crack residue strength was the highest. Combination of the expanding agents and the tougheners to some extent improved the filter loss and the settling stability of the cement slurry and retarded the thickening time of the cement slurry. Of the combination of the four agents studied, the combination of CNTs and the two expanding agents rendered the cement slurry higher yield point and stronger thixotropy. The study can be used as a reference and a guidance for the design of cement slurries used at different work conditions.