Using Air-Cap Testing to Monitor and Measure Geothermal Well Casing Integrity

Abstract

Monitoring and managing well casing integrity is an important part of safely managing geothermal wells over their lifetime. A failure of casing integrity can lead to contamination of shallow aquifers and ultimately could even lead to an uncontrolled blowout.
Historical methods for monitoring well casing integrity involve go-devils, casing corrosion caliper logging, camera surveys and pressure-temperature-spinner (PTS) surveys. Go-devils, casing corrosion caliper logging and camera surveys can give indications of physical damage with no information on whether integrity is compromised, whilst pressure-temperature-spinner surveys can give results on well casing leaking but only if the conditions are suitable to indicate the loss of containment.
Over the last 2 years Contact Energy (Contact) has developed a new well casing integrity assessment method. This method involves applying compressed air to the well to depress the water level, pressurise up the casing and then monitoring for leakage.
Analysis of the results of these tests can categorically indicate the existence of any leak, the depths and nature of the leak and also provide indicative leak rates that can be used to guide better engineering risk assessment and decision making.