Multi-scale experimental study of carbonated water injection: An effective process for mobilization and recovery of trapped oil

• Gas exsolution during carbonated water injection (CWI) is studied.
• Experiments are performed at macro and micro scales using X-ray CT imaging.
• Oil recovery factor increases significantly due to gas exsolution during CWI.
• CWI has applications in both environmental engineering and petroleum engineering.
• CWI offers a possibility for CO2 sequestration in petroleum oil reservoirs.

Steady flow of a disconnected gas phase (bubbles) is realized in porous media during carbonated water injection (CWI) under conditions that promote continuous exsolution of the dissolved gas. Using microfluidic pore networks etched on glass as well as a miniature core-flooding setup integrated with micro computed tomography (CT) imaging apparatus, we demonstrate capillary interactions of the flowing gas bubbles with a previously trapped oil phase (three-phase ganglion dynamics), which lead to mobilization of oil ganglia and remarkably high oil recovery. When three-phase ganglion dynamics are induced by carbonated water injection in low-permeability Berea sandstone core samples containing waterflood residual oil, more than 34% and 40% of the original oil in place additional recoveries are achieved in macro- and micro-scale flow tests, respectively, while a significant amount of CO2 is permanently sequestered in the pore space as capillary-trapped and dissolved gas. It is observed that when oil globules come into contact with CO2, they form thick spreading layers between brine and gas and are carried by moving gas clusters. The oil layers stay stable until the gas clusters leave the medium. Individual oil and gas blobs captured during micro-CT imaging are statistically analyzed to further examine underlying pore-level displacement physics of the process.