Evaluation of enhanced oil recovery potential using gas/water flooding in a tight oil reservoir

In this study, experimental research was implemented to optimize production performance using flooding processes. Firstly, the phase behaviors of live oil–gas (N₂, natural gas, and CO₂) systems were studied in a pressure-volume-temperature cell to measure the properties of the gas-saturated live oil (including gas-oil ratio, oil-swelling factor, density, and viscosity). Secondly, water flooding and gas flooding were carried out in long-core plugs to study the mechanisms and production performance of water/gas flooding. The experimental results of the phase behaviors indicate that, among the three gases, CO₂ is the best choice to boost the properties of live oil, evidenced by high mole fraction in the saturated oil (58.65 mol.%), high oil-swelling factor (1.4482), and high viscosity reduction ratio (90.6%). N₂ showed the lowest property performance in the gas injection process when the phase behavior experiment was carried out. The production performance of water/gas flooding applied in the long-core plugs showed the following: (1) With water injection, earlier breakthrough occurred, and water flooding showed an oil recovery factor as high as 25.50%. (2) Compared with water flooding, the three gas-flooding processes achieved higher oil recovery factors. (3) With the best performance shown in the pressure-volume-temperature test, CO₂ flooding could enhance oil recovery factor significantly; an oil recovery factor as high as 56.15% was obtained in the optimized flooding experiment with an injection rate of 0.10 cm³/min. CO₂ storage potential was also investigated with CO₂ flooding applied in a tight oil reservoir under reservoir conditions. At the end of the laboratory-scale test, a CO₂ storage ratio of 56.92% was observed.