Abstract
Anthropogenic CO2 emissions are a major driver of climate change, highlighting the urgent need for effective mitigation strategies. Carbon Capture, Utilization, and Storage (CCUS) offers a promising approach, particularly through CO2-enhanced gas recovery (EGR) in shale reservoirs, which enables simultaneous hydrocarbon production and CO2 sequestration. This study employs a numerical simulation model to compare two injection strategies: CO2 flooding and huff-and-puff (H&P). The results indicate that, without accounting for key mechanisms such as adsorption and molecular diffusion, CO2 H&P provides minimal improvement in methane recovery. When adsorption is included, methane recovery increases by 9%, with 14% of the injected CO2 stored over 40 years. Incorporating diffusion enhances recovery by 19%, although with limited storage potential. In contrast, CO2 flooding improves methane production by 26% and retains up to 94% of the injected CO2. Higher storage efficiency is observed in reservoirs with high porosity and low permeability, particularly in nano-scale pore systems. Overall, CO2 H&P may be a viable EGR option when adsorption and diffusion are considered, while CO2 flooding demonstrates greater effectiveness for both enhanced gas recovery and long-term CO2 storage in shale formations.