Pore-Scale Imaging to Quantify the Evolution and Reduction in Trapped CO <sub>2</sub> due to Ostwald Ripening
Rukuan Chai, Sajjad Foroughi, Sepideh Goodarzi, Anindityo Patmonoaji, Foo Yoong Yow, Branko Bijeljic, Martin J. Blunt
Abstract
High Resolution Image Download MS PowerPoint Slide Geological carbon storage is a key strategy for mitigating climate change, but the long-term stability of trapped CO 2 remains uncertain. Transport of dissolved CO 2 in the aqueous phase can cause the rearrangement of capillary-trapped CO 2 in the pore space, which is called Ostwald ripening. Using high-resolution three-dimensional X-ray imaging, we visualized the in situ evolution of CO 2 ganglia in reservoir sandstone during storage and quantified its impact on trapped CO 2 saturation. Pore-scale imaging showed the concurrent shrinkage and growth of CO 2 ganglia, reduced morphological complexity, and enhanced connectivity, resulting from Ostwald ripening. Ganglia exhibited a size-dependent response: small ganglia dissolved and disappeared, intermediate ones shrank or grew, and large ganglia stabilized with occasional fragmentation. After waiting for 58 h with no flow, originally residual CO 2 reconnected, and subsequent brine injection led to a decrease in saturation from 22.8% to 15.6%, consistent with previous estimates based on pore-scale modeling. This work suggests that measurements that ignore the effect of Ostwald ripening overestimate the residual saturation by a factor of approximately a third.