An Experimental Study of the Dynamic Mass Transfer Process During Carbonated Water Injection

Abstract

Carbonated water injection (CWI) is a modified CO2 flooding method for enhanced oil recovery, which takes the both advantages of CO2 flooding and water injection and have attracted much attention recently. The objective of this study is to mimic the dynamic mass transfer process of carbonated water to "live" crude oil through a series of well-designed multi-contact tests. In each test, carbonated water (CW) was brought into contact with live crude oil in a high-temperature and high-pressure PVT cell. Pressure changes during the test were observed and recorded. After equilibrium, all of the transferred carbonated water was taken out of the cell and the swelled oil was proceed to the next contact. The volume of water and liberated gas were measured. The oil swelling factor was also measured, which would verify the existence of moving interface between carbonated water and live crude oil. A total of 12 contact tests were performed. It was observed that the pressure rapidly builds up immediately after the contact of carbonated water and live crude oil in the closed system. For the first contact, equilibrium pressure increased by 6.46MPa and for the last contact equilibrium pressure increased by 2.16Mpa. This result indicates a strong mutual interaction of carbonated water with live crude oil and be beneficial to maintain reservoir pressure. Due to large amount of CO2 transferred from carbonated water to the live crude oil, the swelling effect was quite obvious and a total swelling factor of 1.26 was obtained at the end of the experiments. The volume changes of carbonated water and live crude oil could be good evidence of the existence of moving interfaces during the dynamic mass transfer process. The other enhanced oil recovery mechanism by CWI such as viscosity reduction was also found in the tests. The experimental results clearly indicate that the pressure buildup during the diffusion process originated from the CO2 dissolution from carbonated water and swelling of the oil phase. The partition coefficient is relevant to CO2 solubility in water and live crude oil. The tests vividly replicated the dynamic interactions between live crude oil in a closed system and the flowing carbonated water, in which the oil would be contacted by fresh carbonated water.