Effect of Magnetic Nanoparticles on Strength Development and Microstructural Properties of Cement Slurry

Abstract

Abstract The typical solution in the cement industry to respond to the application challenges is the use chemical additives to adapt cement characteristics to the scenario. However, this approach may weaken cement integrity especially in long term. The use of physical properties to obtain similar performance may be a new frontier as cement can be kept without changes and the new additives are inert to the mixture. A proof of concept study was carried out on using magnetic nanoparticles (MNP) and an oscillating magnetic field source to replace chemical additives in the objective of reducing Waiting on Cement (WOC) time during cementing operations in oil and gas wells. A rigorous process was executed to select the most promising particles and several experiments testing different cement slurries designs were executed to confirm the feasibility of this patented technology. Magnetite nanoparticles were blended in 15.9 ppg class G Portland cement slurries in amounts of 0.25% and 0.50% by weight of cement (BWOC). The slurries were cured in atmospheric conditions up to seven days and characterized to determine the influence of the nanoparticles on early age compressive strength development and microstructural properties. Compressive strength development was tested both by destructive testing and by ultrasonic cement analyzer (UCA). Microstructural properties were determined by isothermal calorimetry, scanning electron microscopy, X-ray diffraction and thermogravimetric analysis. Destructive testing of samples cured at atmospheric conditions up to 168 hours showed that the use of magnetic nanoparticles did not affect the compressive strength of cement. UCA experiments, carried out in temperatures similar to those obtainable by magnetically induced heating, confirmed the potential of the technology to accelerate strength development. Isothermal calorimetry results showed that the presence of MNP did not interfere with the normal hydration reaction of cement, fact that was confirmed by the thermogravimetric analyses, where the amount of hydration products was found to be similar for all samples. Scanning electron microscopy imaging showed MNP agglomerations in the pores of cement slurry, which might compromise their heating potential. X-ray diffraction showed the formation of ettringite in all samples. It was concluded that the presence of MNP in the cement slurry was not found to be detrimental to the mechanical and microstructural properties, which open a new frontier to the use of free-additive cement slurries, a cheaper solution built with components where the degradation along the life is well understood, in the opposition to the chemical additives, which degrade faster than cement by itself especially in long term such as well abandonment and carbon storage applications (CCS).