Fundamental physical properties of CO2 microbubbles in CO2-EOR effects of foam stabilizers, surfactants, and gas–liquid ratios

Abstract

Due to the favorable physical properties of microbubbles, injecting CO${}_2$ microbubbles into formations is a novel and economical method to enhance the injectivity of traditional CO${}_2$ injection methods. However, this approach demands higher stability of the bubbles. This study investigates the effects of commonly used foam stabilizer XG and foaming agent SDS, as well as the gas–liquid ratio, on the physical properties of microbubbles, including their quantity, diameter distribution, and stability, using microscopic image observation and potential measurement. Experiments were conducted using a microbubble generator to observe the physical properties of CO${}_2$ microbubbles under different additive ratios. The results indicate that with an increase in the concentration of stabilizer XG, the diameter of the microbubbles initially increases and then decreases, showing varying trends across different diameter distributions. The study found that different rupture modes of the microbubbles are the reason for this trend. At the same mass fraction, SDS is a more effective foaming agent than Span20, increasing the number of microbubbles in the base liquid containing 0.1% wt XG to ten times the original amount, compared to 1.4 times with Span20. Additionally, the addition of XG polymer increased the potential of the CO${}_2$ microbubble system from $-$11.6 mV to over $-$40 mV. However, after adding SDS to the XG solution, the potential decreased from $-$51 mV to below -40 mV, indicating that the synergistic interaction of XG polymer and SDS on the microbubble surface weakens their ability to enhance system stability. This study also explores the effects of the gas–water ratio and the reasons for the observed increase and then decrease in the number of microbubbles and the initial decrease followed by an increase in bubble size with the increase in gas–liquid volume ratio. The results of this study indicate that a stabilizer-to-foaming agent ratio of 0.1% XG + 0.01% SDS not only increases the number of microbubbles but also provides better stability.