Rheological Properties of Piezoresistive Smart Cement Slurry Modified With Iron-Oxide Nanoparticles for Oil-Well Applications

Abstract In this study, rheological properties and piezoresistivity of the oil-well smart cement slurry modified with iron-oxide nanoparticles (NanoFe2O3) at a water-to-cement ratio of 0.38 were investigated. Series of experiments were performed immediately after mixing to evaluate the piezoresistivity of the smart cement slurry with 0.1 % of conductive filler (CF) and up to 1 % NanoFe2O3 to identify the most reliable sensing property that can be relatively easily monitored. To evaluate the piezoresistive behavior the applied pressure was varied up to 5.5 MPa for the smart cement slurries with and without NanoFe2O3 in the high-pressure–high-temperature cylinder where a two-probe method was used with the impedance spectroscopy (IS) to measure the resistivity of the slurry. The shear-thinning behavior of the smart cement slurries, with and without NanoFe2O3, have been quantified using the new hyperbolic rheological model and compared with the Vocadlo model with three material parameters. The results showed that the hyperbolic rheological model predicated the shear-thinning relationship between the shear-stress and shear-strain rate of the smart cement slurries very well. Based on the hyperbolic rheological model the maximum shear stresses produced by the smart cement slurries modified with 0 %, 0.1 %, 0.5 %, and 1 % were 183 Pa, 199 Pa, 232 Pa, and 300 Pa, respectively. The resistivity of the basic cement slurry did not change with pressure. The electrical resistivity of the smart cement slurries with and without NanoFe2O3 decreased with increasing the pressure. The smart cement without and with 1 % NanoFe2O3 additive changed its resistivity by 14 % and 24 %, respectively, when the pressure was increased to 5.5 MPa. A piezoresistivity (stress-resistivity) model was developed to predict the observed piezoresistive behavior of the smart cement slurry and can be used to predict the pressure on the smart cement.