CO2 microbubbles - A potential fluid for enhanced oil recovery: Bulk and porous media studies

Microbubble size analysis revealed that most of the initial microbubbles located within a diameter range of 100-120 µm. After PVT tests, fewer amounts of large microbubbles (due to the coalescence of small bubbles) existed compared to that of preserved samples under low pressure condition. This result demonstrates good capability of CO2 microbubbles to maintain their stability under the high pressure and temperature conditions. Compression/decompression of microbubbles revealed that microbubbles can survive up to at least a pressure of 2000 psi, demonstrating its potential for subterranean applications. However, above 50 °C (122 °F), the stability of microbubbles was decreased after compression/decompression up to 2000 psi. Higher temperatures decrease viscosity and elastic/viscous moduli of microbubbles and this study showed that temperature above 50 °C can be critical for rheological properties and the P-V relation of CO2 microbubbles. Furthermore, PVT studies showed that the lower compression/decompression rate drastically affects the stability of CO2 microbubbles and the higher temperature enhances this effect. Finally, the flow resistance characteristic of microbubbles as well as their favorable injectivity indicated the potential of this fluid to enhance heavy oil recovery, particularly in heterogeneous reservoirs with low sweep efficiency.