Analysis of the Rate of and Reasons for Injection Well Mechanical Integrity Test Failure

Abstract

An operator of a Class II injection well (Le., used in conjunction with oil and gas production) is required to perform a mechanical integrity test (MIT) at least once every five years. We studied the rates of and reasons for failure of over 10,000 scheduled MITs, for a variety of completion types, in the States of Louisiana, Michigan, Nebraska, and Pennsylvania, over two 5-year MIT cycles. The failure rate for State/cycle combinations ranged from 3 percent to about 12 percent for scheduled MITs. However, we found that the actual rate of well failure was at least 50 percent greater, considering the rate of reported well failures in service and evidence of operators pretesting and repairing wells prior to the scheduled MIT. We found that the primary reason for MIT failure was casing failure (45 percent to 85 percent of State failures), compared to tubing, packer, or wellhead failures. Over 26 percent of wells with casing failures were plugged within 60 days of the test, which suggests problems of a more serious nature. For about 22 percent of the wells with casing failures, the failure involved the only layer of protection, and it allowed waste to be injected outside the wellbore.

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“…Other studies have not supported the API low failure rates. For example, Browning and Smith ( 39 ) find an average 10% failure rate for mechanical integrity tests of oil and gas injection wells. Presumably, the actual leakage rate is much lower.…”