Cobalt coated optical fiber in distributed optical fiber sensing for effective tracking and monitoring of magnetic nanoparticles in the reservoir

Enhanced and Improved Oil Recovery (EOR/IOR) projects critically depend on effective tracking and monitoring of fluid mobility in the reservoir for optimal operation. Traditional fluid tracking methods often struggle with low spatial resolution and fail to accurately monitor low-contrast fluids in complex reservoirs, leading to gaps in understanding fluid movement. This paper introduces an innovative subsurface monitoring approach for EOR/IOR that leverages magnetic nanoparticles (MNPs) combined with a cobalt-coated fiber optic (CoF) sensing system installed along the borehole. The CoF system is optimized for high magnetic sensitivity (10^-5 T) and sub-meter spatial resolution, enabling precise detection of MNP movements within the reservoir. Our research includes a sensitivity analysis that identifies the ideal magnetic permeability (μ between 10 and 100) for effective MNP injection and laboratory-scale experiments in a sand column setup to validate magnetic modeling. The CoF sensors demonstrated a 30 % improvement in magnetic field sensitivity compared to nickel-coated fibers, while effectively distinguishing between magnetic field changes and minor temperature variations, with a tolerance threshold of ± 2°C. The results show that CoF sensors can reliably track MNPs, map fluid flow along the borehole, and provide continuous, real-time data on fluid dynamics. Additionally, the study addresses the impact of temperature fluctuations on sensor performance and proposes mitigation strategies. These findings suggest that this novel approach significantly enhances the accuracy and reliability of EOR/IOR monitoring, leading to improved reservoir management, operational efficiency, and oil recovery.