Maximizing CO2 Sequestration and Utilization Using Viscoelastic Surfactants Alternating Gas: Optimizing Efficiency and Environmental Impact

Abstract Greenhouse gases, particularly CO2, are driving significant environmental challenges, necessitating urgent measures to mitigate their impact. CO2 Enhanced Oil Recovery (EOR) presents a viable strategy for contributing to net-zero emissions by capturing and injecting CO2 underground to boost oil recovery, while promoting sustainable energy production. Despite its promise, the high mobility of CO2 poses risks such as viscous fingering, which limits recovery efficiency. Our study addresses this challenge by integrating viscoelastic surfactants (VES) into the CO2 injection process to maximize recovery and CO2 storage. The dual functionality of VES plays a critical role: CO2 reduces heavy oil viscosity, while VES increases the viscosity of the displacing phase and reduces interfacial tension (IFT), improving capillary action and enhancing both oil recovery and CO2 trapping. A calibrated simulation model was employed, using data from a core flooding experiments conducted at 90°C and 1500 psi combined with micro-CT imaging, to optimize recovery and CO2 sequestration. The model was history-matched to experimental data to define the critical capillary number for desaturation and to refine the curvature of the relative permeability curves across various flooding schemes. Several scenarios were tested, examining the influence of injection rates, slug sizes, and the sequence of CO2 and VES injections. Results from these simulations confirmed the effectiveness of VES in controlling CO2 mobility. When VES is injected before CO2, it diverts gas flow into smaller pores, increasing capillary trapping and minimizing gas breakthrough. This leads to improved oil recovery and enhanced CO2 storage, with CO2 dissolution in brine and mineral trapping contributing to long-term sequestration. The optimal injection sequence achieved a recovery factor of 59%, surpassing the recovery of other tested sequences. Additionally, the best-performing scenario resulted in a CO2 storage volume of 4,071 cc under standard conditions (SC). These findings demonstrate that incorporating VES into the CO2 EOR process significantly improves both recovery efficiency and CO2 trapping. By optimizing the injection sequence and ensuring that critical capillary numbers for desaturation are exceeded, this approach not only maximizes oil recovery but also provides a viable solution for large-scale CO2 storage in depleted reservoirs. The application of VES combined with CO2 offers a promising pathway to more sustainable oil production while contributing to global carbon sequestration efforts. This method enables more efficient use of potential storage reservoirs, advancing efforts toward environmental sustainability and helping to mitigate the effects of greenhouse gas emissions.