Transport and Retention of Pickering Nanoemulsions in Fractured Reservoirs

Deliverable of nanoparticles via the surface of nanodroplets and deliverable of non-aqueous phase fluid via nanodroplets in geologic porous media provides enormous potential in various applications, such as subsurface energy recovery, environmental remediation, and CO2 sequestration. Accumulation and retention of these nanodroplets pose both opportunities and challenges to different applications. Effluent analysis through breakthrough curves has been extensively used to investigate the retention behavior of these nano-colloidal dispersions. However, limited data and quantitative analysis are available for in-situ flow behavior in porous media. This work is aimed to address this knowledge gap.

Magnetic iron oxide nanoparticles were firstly functionalized to improve their hydrophilicity and hence were able to stabilize the nano-oil-droplets in the continuous water phase. Enhanced characterization of nanoemulsion stability was performed and was identified quantitatively through nuclear magnetic resonance (NMR) and X-ray computed tomography (CT). In-situ transport of the nanoemulsions in water-saturated sandpack was quantified spatiotemporally through X-ray CT. Effluents were collected and analyzed to further examine the nanoemulsion transport and retention in porous media. Experimental results reveal that accumulation and retention of the nanodroplets in porous media are stimulated by ionic strength, nanodroplet size distribution, and nanoparticle wettability. Three transport modes in porous media (flow through with minimal retention, migration of accumulated nanodroplets, and retention of accumulated nanodroplets) can be achieved through carefully designing the nanoemulsion system.

These findings demonstrate the stability and transportability of the Pickering stabilized nanodroplets, hence demonstrating nanodroplets as vehicles for delivering nanoparticles and non-aqueous phase fluid in porous media. This sheds light on the fundamental understanding of the nano-colloidal dispersions transport in porous media and provides implications for subsurface reactive transport, CO2 sequestration, and subsurface energy recovery.