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

Abstract

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.