Better controls during well drilling and cementing operation are critical to ensure safety during construction and the entire service life of the wells. For a successful cementing operation determine the setting of cement in place length of cement supporting the casing and performance of the cement after hardening. At present there are no technologies available to monitor the cementing operations without using buried sensors that could weaken the cement sheath.
In this study, smart cement with 0.38 water-to-cement ratio was modified with Iron nanoparticles (NanoFe) to have better sensing properties, so that its behavior can be monitored at various stages of construction and during the service life of wells. A series of experiments evaluated the smart cement behavior with and without NanoFe in order to identify the most reliable sensing properties that can also be relatively easily monitored. Tests were performed on the smart cement from the time of mixing to hardened state behavior. During the initial setting the electrical resistivity changed with time based on the amount of NanoFe used to modify smart oil well cement. A new quantification concept has been developed to characterize cement curing based on electrical resistivity changes in the first 24 hours of curing. When cement was modified with 0.1 percent of conductive filer (CF), the piezoresistive behavior of the hardened smart cement was substantially improved without affecting the rheological and setting properties of the cement. For the smart cement the resistivity change at peak stress was about 2000 times higher than the change in the compressive strain after 28 days of curing.
The shear thinning behavior of the smart cement slurries with and without NanoFe at two different temperatures (25°C and 85°C) have been quantified using the new hyperbolic model and compared with another constitutive model with three material parameters, Vocadlo model. The results showed that the hyperbolic model predicated the shear thinning relationship between the shear stress and shear strain rate of the NanoFe modified smart cement slurries very well. Also the hyperbolic model has a maximum shear stress limit were as the other model did not have a limit on the maximum shear stress. Based on the hyperbolic model the maximum shear stresses produced by the 0 percent, 0.5 percent, and 1 percent of NanoFe at temperature of 25°C were 175 Pa, 224 Pa, and 298 Pa, respectively. The maximum shear stresses produced by the 0 percent, 0.5 percent, and 1 percent of NanoFe at temperature of 85°C were 349 Pa, 377 Pa and 465 Pa respectively. Additional of 1 percent NanoFe reduced the initial resistivity of the smart cement by 16 percent. In a 24-hour period the maximum change in the electrical resistivity (RI24hr) for the smart cement without NanoFe was 333 percent. The RI24hr for the smart cement with NanoFe increased with the amount of NanoFe. Addition of 1 percent NanoFe increased the compressive strength of the smart cement by 26 percent and 42 percent after 1 day and 28 days of curing respectively. The test results showed that NanoFe decreased the electrical resistivity of the smart cement slurries with and without NanoFe. For the smart cement modified with NanoFe, the resistivity change at peak stress was over 2800 times higher than the change in the compressive strain. A linear correlation was obtained between the RI24hr and the compressive strength of the modified smart cement based on the curing time.