Control of Asphaltene Damage by In Situ Preparation of α-Fe₂O₃ Nanoparticles in Reservoir Model Oils: Miscible Displacement in Low-Perm Carbonates at Typical Reservoir Pressure and Temperature

Asphaltene deposition in near-wellbore tight carbonate formations has detrimental influences on the well productivity index and, thus, causes a loss in oil production. Nanoparticles exhibit remarkable capacities for the adsorption and control of asphaltene aggregation. In this work, the in situ synthesis of iron oxide nanoparticles in a model oil was studied to evaluate the effects of the thus-prepared nanoparticles on the control of asphaltene damage in tight carbonate core plugs. Novel dynamic interfacial tension and interfacial elasticity measurements were employed to optimize the model oil composition and prepare stable emulsions of iron salt aqueous solutions in the model oil. Following the exposure of the emulsions to a typical reservoir temperature and pressure, α-Fe2O3 nanoparticles were synthesized in the model oil. Two carbonate core plugs, with almost the same flow zone index, were saturated with either the emulsions or the model oil, soaked for 14 h, and shut at 120 °C for 5 h. Then, n-hexane as the asphaltene precipitant was injected at a very low flow rate for miscible displacement and monitoring of asphaltene damage under typical reservoir conditions. Cyclohexane was then injected at several flow rates, during which the hydrocarbon effective permeability was monitored. The results of XRD, FESEM, FTIR, and TGA analyses of the in situ prepared nanoparticles indicate a crystalline structure, a mean particle size of 65 nm, and 1.43 g/g uptake of heavy hydrocarbons. During the n-hexane injection, asphaltene damage leads to 62 and 88% permeability impairment in the absence and presence of nanoparticles, respectively. At high injection flow rates of cyclohexane, nanoparticles are effective in permeability restoration, leading to 63% removal of the damage, which is considerably higher than the 22% damage removal in the absence of nanoparticles. However, at the low flow rates of cyclohexane, the in situ synthesis procedure exhibits a higher permeability impairment compared to that observed in the absence of nanoparticles. Trapping of aqueous droplets in pore throats by the Jamin effect and deposition of the asphaltene/nanoparticles at almost stagnant conditions may result in a higher permeability impairment at low fluid velocities in porous media.