Establishing confidence on containment of injected CO₂ is a critical element to CCS project development and a requirement for determining CO₂ Storage Resources under the SPE Storage Resources Management System (SRMS). Demonstrating containment warrants careful consideration of geological factors – including evidence of laterally extensive and competent seal(s) – and also the integrity of any wellbores intersecting the seal(s). Site screening should seek to avoid (or minimise) significant geological risks and any new wells should be designed with CO₂ service and long-term containment at the forefront of consideration. Consequently, legacy wells become the most significant risk to be managed. The increasing focus on repurposing of depleted hydrocarbon reservoirs for CCS is further amplifying attention to this challenge, with a need to address greater numbers of legacy wells potentially nearing end-of-life or designed without consideration for prolonged CO₂ exposure. Failed exploration wells in potential aquifer stores where past abandonment is driven by reducing costs are another category of risky legacy wells. Some are left largely un-cased, or with plugs set at shallow depths likely without focus on isolating the target storage reservoir, and without consideration of future pressure increase. Either of these characteristics limits the maximum storage pressure and therefore the prospective CO₂ volumes that can be stored.

This session will address the key risks presented by legacy well design and status. It will explore identification and assessment of unique risks posed by prolonged CO2 exposure and downhole pressures higher than initially designed for, along with methods to address, mitigate or tolerate these risks to ensure long-term containment of CO2.