Development of Charcoal-Based Nanofluids for Enhanced Oil Recovery

Abstract

Amid global efforts to combat climate change and transition to renewable energy sources, the importance of oil and gas for meeting current energy demands remains undeniable. As initiatives like the Paris Agreement aim to limit global warming, cost-effective and sustainable methods for oil recovery become increasingly crucial. This study delves into the development of charcoal-based nanofluids for enhanced oil recovery (EOR) flooding. Oil recovery is carried out in stages; The first is the primary stage via natural pressure depletion, which generally drives about 20% of the original oil in place (OOIP) to the oil well. Next is the secondary stage also known as water flooding, at this stage, an incremental recovery of ̴ 30% of OOIP can be achieved from a high-quality reservoir. To further recover the remaining 60-70% OOIP, the tertiary stage also known as the EOR (enhanced oil recovery), is applied, which can recover an additional 10-30% of OOIP at the best case scenario. The fluid flooding of EOR needs to overcome the flow path formed during water flooding and effectively spread to a large volume of the complicated structured reservoir driving out the oil in a mixture of brine and gas. Nanofluids of various metal oxides such as SiO2 and TiO2, Al2O3 and Fe2O3 have been examined for their performance in enhanced oil recovery and have demonstrated an oil recovery capacity of 8-16% of the original oil in place (OOIP) after water flooding for SiO2, Al2O3 and TiO2. Charcoals derived from abundant and agricultural wastes rice husk (RHC), wheat straw char (WSC) as well as active carbon (AC) as a reference sample were selected for this study. The study covers the preparation and characterisation of their aqueous nanofluids for size/size distribution of nanoparticles, nanoparticle surface chemistry and interaction with each other, and more importantly, their enhancement on the viscosity of the aqueous charcoal-based nanofluids. The charcoal nanofluids were prepared by wet milling in water. Size analysis detected the nanoparticle size approximately at 154 nm for RHC, 96 nm for WSC and 210 nm for AC at pH 7.0. These sizes varied with the pH values of the nanofluids according to their surface chemistry. The viscosity of the charcoal-based nanofluids was systematically studied for the effect of charcoal concentration (0.5 - 2.5 wt%) and pH values (pH 2.0-pH 11.0). The viscosity enhancement was observed from the three types of charcoal-based nanofluids in the concentration and pH ranges studied. The enhancement was evaluated by the Dispersion Factor (DF), which is proposed in this study based on Chen et al. (2007) equation to comprehensively evaluate the effect of nanoparticle dispersion in a fluid on its viscosity. The higher the dispersion factor, the stronger the interaction of the nanoparticles to the dispersion liquid, and the higher the viscosity enhancement. The DF values of RHC and WSC nanofluids were slightly higher than those of the nanofluids of TiO2 and SiO2 with 5-10 times smaller particle sizes in the literature. More impressively the viscosity enhancement of AC nanoparticles is comparable to that of carbon nanotubes at concentrations below 0.6 vol.% and surpasses carbon nanotubes when the concentration is higher than 0.6 vol.%. The viscosity study shows the potential of the charcoal-based nanofluids to enhance their oil displacement efficiency in EOR. The EOR flooding tests of the charcoal-based nanofluids were conducted on sand-packed cores to mimic sandstone-dominated oil reservoirs. A sectional flooding method is applied, i.e., the nanofluids equivalent to 20% of the pore volume were injected into the packed cores after water flooding saw a levelled oil recovery rate. Water flooding was restored after the nanofluid injection. The effect of nanoparticle concentrations and pH levels of the nanofluids were examined on the enhanced oil recovery. The results showed that 1) a higher nanofluid concentration recovered more original oil in place in the range of 15.4% - 19.3% of OOIP for AC pH 6.0 1 wt% and 2 wt% respectively; 2) the pH value of the nanofluids had a sensible effect on their EOR performance. At a pH that the nanofluids showed a higher viscosity, the oil recovery rate is higher. 3) Most impressively the active carbon nanofluid at pH 2.0 demonstrated a manipulatable flow pattern by pH value in the side of the packed core and eventually yielded a notable further 34.1% of original oil-in-place at a concentration of 2 wt%. Overall, the findings underscore the promising potential of charcoal-based nanofluids as effective EOR flooding fluids. Their abundant renewable nature, as a by-product of biofuel productions and low-cost position them as attractive alternatives of viscosity enhancement agents for advancing EOR technologies and, meanwhile, storing the carbon-rich nanoparticles in the oil reservoir after utilisation.