Excerpt:
As a forceful reminder of the potential harm, the well beneath BP's Deepwater Horizon rig was being sealed with cement for temporary abandonment when it blew April 20, leading to one of the worst environmental disasters in the nation's history. BP alone has abandoned about 600 wells in the Gulf, according to government data.
There's ample reason for worry about all permanently and temporarily abandoned wells -- history shows that at least on land, they often leak. Wells are sealed underwater much as they are on land. And wells on land and in water face similar risk of failure. Plus, records reviewed by the AP show that some offshore wells have failed.
Experts say such wells can repressurize, much like a dormant volcano can awaken. And years of exposure to sea water and underground pressure can cause cementing and piping to corrode and weaken.
"You can have changing geological conditions where a well could be repressurized," said Andy Radford, a petroleum engineer for the American Petroleum Institute trade group.
Whether a well is permanently or temporarily abandoned, improperly applied or aging cement can crack or shrink, independent petroleum engineers say. "It ages, just like it does on buildings and highways," said Roger Anderson, a Columbia University petroleum geophysicist who has conducted research on commercial wells.
Despite the likelihood of leaks large and small, though, abandoned wells are typically not inspected by industry or government.
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