EFFECT OF STRATIGRAPHIC HETEROGENEITY ON UPWARD MIGRATION OF CO2 IN SATURATED POROUS MEDIA: LABORATORY EXPERIMENT AND NUMERICAL SIMULATION

GCS (Geologic Carbon Sequestration) is considered as primary technique for reducing the greenhouse gas emission, particularly carbon dioxide. Many countries are developing their techniques for capture, storage, transportation as well as MMV (Measuring, Monitoring and Verification). In the view of MMV, early detection of CO₂ leakage is one of the main considerations. Before constructing the shallow subsurface monitoring system using sensors near the GCS site or the buried pipeline, it is important to choose monitoring point where leaked CO₂ might be passed. Naturally, subsurface media might have stratigraphic heterogeneity such as layer or lense, and it has potential to affect the upward migration of CO₂.

To identify CO₂ leakage potential according to different stratigraphic heterogeneity, 2-D laboratory experiment was conducted using glass beads and transparent acrylic tank for visualization. The experiment conditions of embedded layer had seven different grain size ranges and each condition had slightly different physical properties such as capillary pressure and permeability. In homogeneous condition with which the layer has same grain size with background, the upward movement of CO₂ occurred all the way to the top surface. As difference of grain size between background and layer increases, upward migration through the layer gradually disappeared. The coarser layer had relatively lower capillary pressure and higher permeability compared to neighboring regions and it became a preferential flow path of CO₂. Whereas, the finer layer which had higher capillary pressure and lower permeability than background region acted as a barrier preventing CO₂ rising. Numerical simulation using TOUGH2 was performed to generalize the previous experiment results and to apply more detailed conditions. The simulation results showed that not only the CO₂ saturation but also the position where the CO₂plume accumulated were affected by the layer conditions.

These results suggest that the geological stratigraphic heterogeneities should be considered when selecting monitoring point to achieve the successful detection of CO₂leakage.

Acknowledgement: Financial support was provided by the "R&D Project on Environmental Management of Geologic CO2 Storage" from the KEITI (Project Number: 2014001810003)