Fabrication of CO2-Saturated Nanofluids with Optimized Interfacial Properties for Carbon Capture, Utilization, and Storage
Authors: Liu Jiang , Wu Hua , Xu Xingguang , Wang Bo , Wu Yunkun , Gu Jun 
Published: January 2025

Summary
In the pursuit of carbon neutrality and mitigation of carbon dioxide (CO2) emissions, researchers have been exploring various approaches to integrate carbon capture, utilization, and storage (CCUS) with enhanced oil recovery (EOR) techniques. CO2 injection has been identified as a promising method to reduce crude oil viscosity and enhance its mobility within the reservoir. However, the high mobility of CO2 can lead to gas fingering, causing channeling and reducing the sweep efficiency. While CO2 foam has been considered to improve conformance during CO2 flooding, its longevity is negatively affected by harsh reservoir conditions. Polymers, which could be used as CO2 foam stabilizers, are limited by high injection pressures and CO2-induced viscosity reduction, hindering their widespread industrial application. Nanofluids, which are colloidal suspensions of nanoparticles in a base fluid, have emerged as a potential solution for various petroleum industry applications, including wettability alteration, interfacial tension (IFT) reduction, and sweep efficiency improvement. Functionalized nanoparticles can enhance oil recovery by intensifying interactions with oil, particularly through CO2 adsorption, which promises to be a more desirable solution for CO2-EOR. Inspired by drug delivery in nanomedicine, this study proposes a novel approach where CO2 is loaded onto the amine groups of nanoparticles for controlled and slow release in target zones, aiming to mitigate CO2 channeling and maximize CO2 utilization, thereby enhancing the CO2-EOR performance. Amine-functionalized nanoparticles were prepared by 3-aminopropyltriethoxysilane (KH550), grafted and polyethylenimine (PEI)-coated to load CO2 within their structure, and the interfacial characteristics between crude oil and the nanofluid were extensively examined. It was revealed that amine-functionalized nanoparticles exhibited a decent CO2 adsorption capacity of 3.3 mmol/g. Following the absorption of CO2 at 25°C by the nanofluid, the ζ-potential of the CO2-saturated nanofluid increased to +38.21 mV, which significantly enhanced the nanofluid stability. The CO2-saturated nanofluid considerably reduced the IFT between crude oil and the nanofluid from 34.78 mN/m to 7.82 mN/m at 80°C, 12 MPa. After 36 hours of soaking at 80°C, the contact angle on the oil-wet sandstone surface decreased from 121.39° to 57.95°. Furthermore, it was revealed that a distinct phase rich in heteroatoms appeared at the nanofluid-crude oil interface. Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometry (MS) demonstrated that the microdispersed phase was predominantly composed of acidic heteroatom compounds, mainly in the form of CxHyOz and CxHyOzSn, highlighting the potential of amine-modified nanoparticles to alter interfacial properties. These compounds played a crucial role in the formation and stabilization of emulsions, as well as in the optimization of oil-water interfacial properties. Ultimately, in the coreflooding experiments, the injection of nanofluid recovered an additional 15.33% of the crude oil following waterflooding.