[HSC07-P06] CO2 migration characteristics of microbubble and conventional sequestration in Berea sandstone revealed by X-ray CT imaging
キーワード：CO2 migration, Microbubble sequestration, Conventional sequestration, X-ray CT imaging
CO2 geological sequestration is an effective technique to mitigate the increase of global CO2 emission and warming effect. To improve CO2 storage capacity in porous sediments, we applied a new technology, of which a particular filter is utilized to generate supercritical CO2 (SC) microbubble, for the SC injection. A Berea sandstone sample was used for the tests: the microbubble injection (MBI) and conventional injection (CI). By X-ray CT imaging, we find that the MBI can enhance the SC migration and sweep efficiency, and finally result in a higher SC saturation. To quantify the difference in SC saturation variation for MBI and CI, we classify the porous space (as imaged volume) into three subsets (low-porosity: ΦL≦19%; medium-porosity: 19%<ΦM≦22%; and high-porosity: 22%<ΦH). We identify that there are different SC migration patterns (P1: rapid and high-massed SC flow occupied large-sized porosity sites with an apparent migration trace; P2: slow and low-massed SC flow diffused into small-sized porosity sites; and P3: a mixed migration pattern of P1 and P2) dominated by the porosity distribution and sediment layers. The main differences in the flow characteristics of MBI and CI for the three groups of porosity sites are outlined as follows.
(1)-ΦH: At the beginning, the MBI formed a step-increased SC saturation gradient in the ΦH sites along the axial direction. Subsequently, several times of SC saturation accumulation occurred before the injected SC reached 0.15 PV. In contrast, in the CI, there was a continuous SC flow migrated in the high-porosity sites from the inlet side to the outlet side before the injected SC reached 0.1 PV. After the SC flow transported to the left part (with a distance >150 mm from inlet side), the SC sweep efficiency became weakened. When the injected SC was greater than 0.08 PV, the increase of SC saturation propagated simultaneously from the central position towards inlet and outlet sides.
(2)-ΦM: In the ΦM sites, before the injected SC smaller than 0.9 PV, the P1 model controlled the flow migration for MBI. Then the P3 model dominated the SC flow migration. In the CI, similar SC flow transport features also occurred, however, with a lower SC sweep efficiency, and the P3 model commenced until the injected SC approximated 0.15 PV.
(3)-ΦL: In the ΦL sites, both the MBI and CI produced only the P1-type SC transport pattern. But the MBI had an earlier trigger time and higher SC saturation than CI.
These analyses demonstrate that the SC flow in the MBI can permeate into more porous space and build a higher CO2 saturation than CI. The MBI has the potential to provide a more efficient and lower cost choice for the CO2 geological storage.
(1)-ΦH: At the beginning, the MBI formed a step-increased SC saturation gradient in the ΦH sites along the axial direction. Subsequently, several times of SC saturation accumulation occurred before the injected SC reached 0.15 PV. In contrast, in the CI, there was a continuous SC flow migrated in the high-porosity sites from the inlet side to the outlet side before the injected SC reached 0.1 PV. After the SC flow transported to the left part (with a distance >150 mm from inlet side), the SC sweep efficiency became weakened. When the injected SC was greater than 0.08 PV, the increase of SC saturation propagated simultaneously from the central position towards inlet and outlet sides.
(2)-ΦM: In the ΦM sites, before the injected SC smaller than 0.9 PV, the P1 model controlled the flow migration for MBI. Then the P3 model dominated the SC flow migration. In the CI, similar SC flow transport features also occurred, however, with a lower SC sweep efficiency, and the P3 model commenced until the injected SC approximated 0.15 PV.
(3)-ΦL: In the ΦL sites, both the MBI and CI produced only the P1-type SC transport pattern. But the MBI had an earlier trigger time and higher SC saturation than CI.
These analyses demonstrate that the SC flow in the MBI can permeate into more porous space and build a higher CO2 saturation than CI. The MBI has the potential to provide a more efficient and lower cost choice for the CO2 geological storage.