Fluids have been injected in underground reservoirs for temporary or permanent storage for more than a century. The first natural gas storage operations were undertaken in 1915 at a gas field in Canada. By the 1920s, the injection of water to increase oil recovery had been successfully demonstrated and the widespread use of injection wells to dispose of produced water began in the 1930s. The history of these operations provides insights into the types and frequency of unexpected events and failure incidents.
Overall, underground fuel storage projects have an impressive safety track record, but there is also a catalogue of failures involving financial or property loss, closure, and in a few cases, casualties or evacuations. A historic review of 228 reported events and failures worldwide by Evans (2009) showed that most failures are associated with leaking wellbores or surface facilities. In many cases, these projects are using wells that are decades-old, providing a sense of what could happen 40 or 50 years from now when carbon storage projects will be reaching the end of their injection lives.
A small but significant fraction of injection project events can be attributed to geological factors. These include, but are not limited to:
- Induced seismicity
- Injected fluids spilling out of the intended container
- Migration of injected fluids along fractures or across faults previously considered sealing
- The misidentification of a storage reservoir
- Lower-than-expected seal capacity of the caprock
- Migration of fluids away from the injector in an unanticipated direction
- Overestimation of the storage volume
- Underestimation of reservoir heterogeneity, which could increase storage volumes, as in the Sleipner project
- Pressure maintenance issues
The figure below depicts many of these geological factors and the movement of CO2 into unintended portions of the subsurface.
Reference: Evans, D.J. 2009. A review of underground fuel storage events and putting risk into perspective with other areas of the energy supply chain. Geological Society, London, Special Publications, 313, 173-216.