Investigating the flow behaviour of CO2 and N2 in porous medium using core flooding experiment

Abstract

Several researchers employed N 2 to augment CH 4 recovery efficiency and CO 2 sequestration during the Enhanced Gas Recovery (EGR) process in consolidated rocks. To our knowledge, there has been limited data backing the reason why CO 2 experienced a more extended breakthrough during the EGR process in the presence of N 2 gas. This study investigated CO 2 and N 2 behaviour during the core flooding experiment by CO 2 injection in Bentheimer core plug. N 2 was used as the continuous phase during the core flooding process, while CO 2 was the dispersed phase. The experiment was designed with varying injection rates at 30 and 40 °C temperature points. The experimental findings showed that the dispersion and diffusion coefficient, CO 2 storage, concentration profile and breakthroughs were highly influenced by temperature change, especially at lower injection rates. However, at high injections, those properties are less sensitive to change in temperature, with most of the curves overlapping in the concentration profile. The highest and most negligible dispersion and diffusion coefficients were recorded at the highest and lowest injection rates respectively. These results agree with those reported by several researchers for sandstone rocks. Thus, higher temperatures have a more substantial effect on dispersion and diffusion coefficient, which eventually led to higher mixing between CO 2 and N 2 . The breakthrough time decreases with an increase in reservoir temperature, confirming the diffusion and dispersion coefficients are temperature dependent. The experiment at 30 °C recorded an extended breakthrough time over that at 40 °C. The maximum breakthrough time at 0.52 PV was recorded at 30 °C at the lowest injection rate. The concentration profile highlighted the trend between the displacing and displaced gas during the core flooding experiment. From the range of injections and temperatures tested, the CO 2 PV stored decreases as the rate of injection increases from 0.4 to 1.2 ml/min. However, the CO 2 stored was more promising at higher rates, corresponding with high differential pressure, due to flow resistance within the tortuous flow channels in the porous medium. • The maximum breakthrough of 0.52 PV was recorded at 30 °C at the lowest injection velocity. • The CO 2 stored was more promising at higher rates, corresponding with high differential pressure. • For 30 and 40 °C of temperature, α = 0.00222, and 0.002265 m. • Both N 2 and CO 2 experienced similar phase change behaviour at higher interstitial velocity.