CO2 Leakage Risk

1. After a significantly large time, following CO2 injection, and upon increasing porosity and permeability by mineral dissolution, and with volumetric expansion of CO2 with declining pressures, how do we ensure, whether, the flow paths like fractures, faults and boreholes, within or in the vicinity of geological CO2 storage site, through which CO2 could migrate and eventually reach the surface - remain overlooked or not (at the early stage itself)?

2. How do we have a control over the suppression of CO2 Migration – following CO2 injection – in the long run - resulting from (a) Reduced mobility of CO2 under multiphase conditions; (b) Reduced porosity and permeability resulting from Mineral Precipitation; (c) Temperature drop due to Joule-Thomson Expansion; and (d) Phase transitions between liquid and gaseous CO2 [adiabatic volume expansion of CO2 upon decompression can significantly limit upward migration of CO2 by Joule-Thompson cooling, which can give rise to phases transitions, leading to the development of multi-phase system with severe CO2 flow disturbance]?

3. With CO2 tending to ascend against gravity at high volumetric rate due to its density and viscosity lower than those of brine, and since, a large compressibility of CO2 gives rise to large volume expansion during depressurization; at some point of time in the future, whether, a significant fraction of the injected CO2 could proceed back to the atmosphere, unless CO2 migration remains arrested either by self-limiting processes?

4. Whether ALL of the following parameters greatly affect CO2 migration? (a) Juxtaposition; (b) Fault core; (c) Damage zone; (d) Slip Magnitude; (e) Cementation; and (f) Stress state (shearing)

5. If pressure buildup by sufficient supply of CO2 exceeds a critical threshold for the CO2 displacement over geological time, can a low-permeability fault completely prevent CO2 leakage to the surface?

6. How could we ensure the location and depth of a target reservoir for geological CO2 storage – considering the fact that CO2 plume could advance to shallower depths along the dip of formations and eventually reach the surface?

Suresh Kumar Govindarajan, Professor [HAG]

IIT Madras 18-Dec-2024