Internal casing corrosion in the upper gas-filled portion of the tubing-casing annulus is a costly and widespread problem in the West Texas-New Mexico area. Severity of the problem is illustrated by experiences in the Wasson Field where an estimated $1,400,000 was spent in casing repairs during the first fifteen years after development of the field and other large losses occurred which could not be estimated. This problem also has been detected in at least six other large fields in the area.
It is believed that corrosion results from the condensation of moisture on the casing interior and subsequent absorption of acid gases. All findings to date substantiate this theory.
Corrosion of this type is being controlled by packing off and filling the tubing-casing annulus with a noncorrosive fiuid, thereby excluding the corrosive gases and protecting the casing from future failures. Application of this protective measure costs about $1200 per well as compared to the $3000 to $40,000 expenditure for repair operations in the event of a casing failure. Other promising protective measures, which would be more easily applied and less costly if effective, are currently being tested.
