MAGNETITE-SILICA NANOPARTICLES WITH A CORE-SHELL STRUCTURE FOR INHIBITING THE FORMATION DAMAGE CAUSED BY THE PRECIPITATION/DEPOSITION OF ASPHALTENE

摘要

Asphaltene precipitation/deposition is one of the most difficult type of formation damage to overcome. Recently, nanoparticles have become a cost-effective alternative for the inhibition/mitigation of formation damage caused by asphaltene [1-3]. The main objective of this study is to develop magnetite-silica nanoparticles with a core-shell structure for inhibiting the formation damage caused by asphaltenes. This type of nanoparticle has a high adsorptive capacity, and due to the magnetic properties of the core, it can be recovered during the production step and subsequently regenerated and reused. Nanoparticles with a core-shell structure were synthesized through the combined sol-gel and co-precipitation methods. They were characterized through X-ray diffraction, field emission scanning electron microscopy, dynamic light scattering, N_2 physisorption at -196°C, Fourier transform infrared spectroscopy and the Curie temperature. The performance of core-shell nanoparticles were evaluated through batch-mode adsorption experiments using UV-vis spectrophotometry. The asphaltene adsorption isotherms were modeled with the solid-liquid equilibrium model. In addition, the kinetics of asphaltene aggregation/fragmentation in the absence and presence of nanoparticles were determined through dynamic light scattering measurements. Nanoparticles with a core-shell structure were obtained with a mean particle size of 52 nm and a surface area of 121 m~2/g. The mean particle size of the magnetite core was estimated to be 40 nm, with a surface area of 66 m~2/g. Silica nanoparticles with a mean particle size of 54 nm were also used for comparison. It was observed that the core-shell nanoparticles were prone to adsorb asphaltene and successfully reduce its aggregation, which would result in the inhibition of their precipitation and subsequent deposition. It was observed that core-shell nanoparticles adsorbed up to 400 and 410 mg/g of asphaltene more than the magnetite core and silica nanoparticles, respectively, confirming the synergistic effect of the core-shell nanoparticles. The core-shell nanoparticles influenced the reduction of the asphaltene mean aggregate size, and lower values were obtained compared with those of silica nanoparticles and the magnetite core. Displacement tests were carried out to determine the effect of the selected nanoparticles in inhibiting the precipitation of asphaltenes under reservoir conditions. The oil relative permeability followed the order: after nanoparticles system > blank system > base system. The oil recovery for the base system was 68% and that after treatment with nanofluid was approximately 79%. These results show that nanoparticles can inhibit damage associated with asphaltene precipitation/deposition. Nanoparticles can be recovered after the adsorption process and regenerated. The regeneration can be performed through asphaltene gasification, thus promoting the production of synthetic gas that could be further used for oil upgrading processes. Hence, asphaltenes absorbed on the nanoparticles were submitted to catalytic steam gasification using a thermogravimetric analyzer. It was verified that the nanoparticles that have a core-shell structure can produce lighter and more valuable gaseous products from asphaltene for the oil and gas industry at lower temperatures than in the absence of nanoparticles. These results indicate that the nanoparticles with a core-shell structure have the significant potential to be developed as a cost-effective treatment for asphaltene-related problems.