Not only cement, but seals, valves and gaskets can deteriorate over time. A 2000 report by C-FER Technologies to the Dept. of Interior identified several different points where well leaks can occur, as this image (p. 26) reveals. To date, no regulations prescribe a maximum time wells may remain inactive before being permanently abandoned. [13]
“The most common failure mechanisms (corrosion, deterioration, and malfunction) cause mainly small leaks [up to 49 barrels, or 2,058 gallons]. Corrosion is historically known to cause 85% to 90% of small leaks.”
Depending on various factors, C-FER concludes that “Shut-In” wells reach an environmental risk threshhold in six months, TA wells in about 10-12 years, and PA wells in 25 years. Some of these abandoned wells are 63 years old.