Optimization of Carbon Sequestration and Carbon Displacement in Fractured Horizontal Wells in Low Permeability Reservoirs

The increasing use of fossil fuels has raised concerns about rising greenhouse gas emissions. Carbon capture, utilization, and storage (CCUS) is one of the most important technologies for achieving net zero carbon emissions. In oil reservoirs, fully understanding their geological characteristics, fluid characteristics, and pressure distribution and injecting CO2 in a reasonable scheme, some remaining oil can be recovered to improve oil recovery and even obtain certain economic benefits. In this paper, we investigate the effect of CCUS implementation in low-permeability reservoirs from both technical and economic aspects. First, based on the parameters of a low-permeability reservoir, a numerical simulation model of a reservoir with gas injection in a multi-stage fractured horizontal well at the top of the reservoir and oil recovery in a multi-stage fractured horizontal well at the bottom is established. Next, four cases of continuous CO2 injection, intermittent CO2 injection, CO2 injection after water flooding, and water alternating gas drive (WAG) are designed to evaluate their effects on CO2 storage and enhanced oil recovery. Finally, an economic evaluation model is developed to evaluate these four cases. The results show that fractured horizontal wells can improve the injection capacity, increase the swept volume of injected gas, cause CO2 to fully contact the crude oil, greatly increase the contact area between the wellbore and crude oil, and greatly improve oil recovery. The WAG injection-production method can effectively inhibit gas channeling, reduce the production gas-oil ratio, improve oil recovery, and, at the same time, bury more CO2 into the reservoir. Its economic benefit evaluation is also the best among the four cases. In addition, the remaining oil distribution and CO2 buried distribution under different injection-production schemes are also analyzed. This study provides a scientific basis for the operation scheme design of CCUS in low-permeability reservoirs.