State-of-the-Art of Monitoring Methods to evaluate Storage Site Performance

 
1. INTRODUCTION
 
2. MONITORING TECHNIQUES
 
3. MONITORING CONCEPTS – STATUS QUO
 
4. SETTING UP A SITE-SPECIFIC MONITORING PLAN
 
5. CONCLUSIONS AND RECOMMENDATIONS
 
6. REFERENCES
 
 
2.1 CO2 plume migration in the storage reservoir
 
2.2 Surface uplift
 
2.3 Induced seismicity and mechanical reaction of overburden
 
2.4 Faults
 
2.5 Abandoned wells
 
2.6 Overlying and adjacent aquifers
 
2.7 Freshwater aquifers
 
2.8 Near surface eco-compartments
 
 
» 2.5.1 Significance of abandoned wells in CO2 leakage
 
2.5.2 Possible pathways and common causes for CO2 leakage in an aband...
 
2.5.3 Current well abandonment practices
 
2.5.4 Applicable monitoring techniques
 
 

2.5.1 Significance of abandoned wells in CO2 leakage

Abandoned wells which penetrate the CO2 storage sites or which are in the close vicinity to those can provide pathways for CO2 to leave the storage environment and reach overlying aquifers or to the surface.

Especially if the CO2 storage is implemented in depleted natural gas and oil fields, there may be many abandoned wells within the radius influenced by the injected fluid. All of the temporarily and permanently abandoned wells located in the influence area have to be evaluated before the CO2 injection is commenced and their integrity has to be monitored over long time frames during the injection and storage operations and post-closure periods, to ensure that these wells will not be providing a pathway for the injected CO2 to leave the storage complex and migrate to upper formations or to the atmosphere (Syed, 2011).

The well abandonment procedures applied in the oil and gas industry are based on oil field practices and requirements, without any consideration of the integrity of the abandoned wells under CO2 storage applications. Although the reactivity of pure CO2 is generally considered to be low, once contacted with brine, it forms H2CO3, a weak acid. This causes the pH of the brine to decrease and makes the brine more corrosive. Therefore, the presence of CO2, particularly the presence of water acidified by CO2, may deteriorate the well cement and cause corrosion. Unless measures are taken for ensuring the long term integrity of the abandoned wells in the presence of CO2, the existing abandoned wells may be potential conduits for the leakage of CO2.