CO2 Underground Storage and Wellbore Integrity

Capturing and storing carbon dioxide (CO2) underground for thousands of years is one way to reduce atmospheric greenhouse gases, often associated with global warming. CO2 injection candidates may be new wells, or old wells that are active, closed or abandoned. In all cases, it is critical to ensure that the long-term integrity of the storage wells is kept ; in others words wellbore integrity is one of the key performance criteria in the geological storage of CO2. Underground gas storage operations and CO2 sequestration in aquifers relay on both proper wellbore construction and sealing function of the cap rock. The potential leakage paths are the migration CO2 along the wellbore due to poor cementation and flow through the cap rock. The permeability and integrity of the cement will determine how effective it is in preventing leakage. The integrity of the cap rock is assured by an adequate fracture gradient and by sufficient cement around the casing across the cap rock and without a micro-annulus. The paper describes geochemical alteration of hydrated Portland cement due to supercritical CO2 injection and new cement with better CO2 resistance.