Experimental and Numerical Simulation Analysis of Factors Affecting CO₂ Geological Storage and Enhanced Oil Recovery in Extra-Low Permeability

Carbon neutrality has become the long-term development strategy of many countries worldwide, and the widespread implementation of CCUS (carbon capture, utilization, and storage) is critical for achieving this goal. Ultralow permeability reservoirs have good storage and shielding properties, making them ideal for CO2 geological storage. CO2 into these reservoirs has the dual purpose of improving crude oil recovery and protecting the environment. However, the physical properties of ultralow permeability reservoirs are poor. Furthermore, the distribution of fractures is often complex. The mechanism and influencing factors of the CO2 storage are still unclear. Here, the CO2 storage in ultralow permeability reservoirs is analyzed through core displacement experiments and numerical simulation. The main influencing factors of cumulative oil production and CO2 storage capacity were calculated through gray correlation theory, including CO2 injection rate, permeability, porosity, the solubility of CO2 in water, and the bottom hole flow pressure of production wells. The research results show that the geological storage of CO2 in ultralow permeability reservoirs mainly consists of structural trapping and dissolution into the residual fluids; in the short term, mineralization is relatively small and can be ignored. Within the 15 years predicted by numerical simulation, the injected CO2 into the Y28-102 well group in the Huang3 district was structurally trapped, with a total capacity of 6.59 x 10(4)t. The burial ratio was 63.4%, of which structural burial accounted for 82%, oil dissolution accounted for 9%, water dissolution accounted for 8%, and mineral burial accounted for approximately 1%. The research results reference CO2 flooding and geological storage in ultralow permeability reservoirs.