A novel thermo–salinity-responsive nanographite system, known as the MEGO system, has been developed by researchers at the China University of Petroleum and the University of Alberta, offering a promising solution for enhanced oil recovery (EOR) in deep oil reservoirs. The study, published in Engineering, details how this system overcomes challenges associated with high-temperature and high-salinity conditions that are typical in deep reservoirs.

Deep oil reservoirs, often found at depths greater than 4500 meters, are crucial for large-scale oil production. However, traditional EOR techniques, such as water flooding, face significant challenges due to the formation of high-permeability channels in these reservoirs. These channels allow injected water to flow directly to the wells without effectively displacing oil, leading to reduced sweep volumes and lower recovery rates. Existing profile-control agents often fail under extreme conditions, lacking stability and resistance to high temperatures and salinities.

The MEGO system addresses these issues by incorporating polyether amine (PEA) grafting and noncovalent interactions with disodium naphthalene sulfonate (DNS) molecules. This functionalization enhances the thermal and salinity resistance of nanographite particles, which are known for their high-temperature stability and ease of modification. The PEA grafting and DNS interactions provide steric hindrance and electrostatic repulsion, delaying particle aggregation and improving dispersibility under harsh conditions.

Experiments showed that the MEGO system forms stable particle aggregates ranging from 55.51 to 61.80 μm after ten days of aging, making it suitable for deep reservoir migration and profile control. The aggregation process is influenced by temperature and salt ions, with divalent ions (Ca²⁺ and Mg²⁺) promoting aggregation more strongly than monovalent ions (Na⁺). This is attributed to double-layer compression and bridging effects.

Core displacement experiments demonstrated the MEGO system’s superior performance in reservoirs with permeabilities between 21.6 and 103 mD. The aggregates formed within pore throats significantly increased flow resistance, expanded the sweep volume, and enhanced overall oil recovery to 56.01%. These results highlight the MEGO system’s potential for improving oil recovery in deep reservoirs.

Molecular dynamics simulations further elucidated the aggregation behavior of the MEGO system. The simulations revealed that PEA grafting and DNS interactions significantly delay aggregation by increasing interlayer spacing and reducing interlayer attraction. The simulations also showed that temperature and salt ions influence the mobility and interaction energy of the particles, with higher temperatures and salt concentrations promoting aggregation.

The MEGO system offers a new technological pathway for reservoir profile control in deep oil reservoirs. Its thermo–salinity-responsive properties and enhanced dispersibility make it a viable option for improving oil recovery in challenging reservoir conditions. Future research may focus on optimizing the system for specific reservoir environments and exploring its potential applications in other EOR techniques.

The paper “A Novel Thermo–Salinity-Responsive Nanographite System for Enhanced Oil Recovery in Deep Reservoirs,” is authored by Caili Dai, Wanlei Geng, Jiaming Li, Guang Zhao, Bin Yuan, Yang Zhao, Tayfun Babadagli. Full text of the open access paper: https://doi.org/10.1016/j.eng.2025.04.009. For more information about Engineering, visit the website at https://www.sciencedirect.com/journal/engineering.