Underground gases and pressure changes make steel casings prone to corrosion

By Sam Phipps

The Idle Iron NTL issued to operators in October 2010 has not so much changed the procedure for dealing with non-producing wells in the Gulf of Mexico as it has clarified definitions and concentrated minds.

If wells have not produced oil or gas for five years or if there are no plans for future output, they are classed as “no longer useful for operations”. In that case the Bureau of Safety and Environmental Enforcement (BSEE) will order operators to permanently or temporarily abandon them.

If a well poses a hazard to safety or the environment, it must be permanently abandoned.

However, it is important to note that the thousands of wells abandoned at some point over the last few decades will not suddenly be subject to greater scrutiny or monitoring.

Leaky evidence

There were 24,486 known permanently abandoned wells as of October 2011, of which 3,593 “temporarily” abandoned, according to the Bureau of Ocean Energy, Management and Reinforcement (BOEMRE). The latter category includes some dating back to the 1950s.

The BSEE said it was wrong to assume that any of these were necessarily leaking and refused to estimate the scale of any such defects.

But companies such as Wellcem, based in Norway but active around the world, would disagree, and have developed specific products to tackle the problem.

The problem with current well-plugging procedures is that the cement poured into the metal casings of the well is designed for surface applications, and is prone to shrinkage. Meanwhile, pressure changes from underlying aquifers or fluid injections to stimulate nearby wells can result in wells flowing again, making the steel casings prone to corrosion.

Alf Jan Wik, sales and marketing director of Wellcem, says leakage is widespread from abandoned wells in addition to those still producing hyrdrocarbons, as the cement used to plug them is prone to cracking after an indeterminate time.

Its Thermaset innovation has 60 times the tensile strength of concrete but much higher compressive strength and ductility. It can be applied in a temperature range between 20C and 135C and setting can be controlled “100%” according to the specific conditions, Wik says.

“Many of these leaks are high volume and we have spent about US$30m trying to get the right kind of setting properties.”

Idle Iron guidance

Eileen Angelico of BSEE emphasised that the Idle Iron NTL was in the works long before the Deepwater Horizon disaster of April 2010.

“It was not a reaction to that, it was a reaction to Hurricane Katrina, Gustav, Ivan, Ike, when it was documented that it’s much more costly to decommission wells that are below a toppled platform or in a mudslide area than it is to decommission them when you are supposed to,” she said.

“We clarified the definition of ‘no future utility’ for a well, which would then put it into a category where it was required by legislation to be temporarily or permanently plugged and abandoned.”

The authorities checked their records of all wells and platforms that had been in non-producing status for more than five years and asked operators either to show a plan for how they were going to plug and abandon wells or else outline future utility.

Operators could start work abandonment at the same time as submitting a plan.

A total of 156 letters went out to operators and BSEE received 97 Idle Iron plans in response.

These covered 3,092 idle wells (96%) out of 3,233 total idle wells; 1,056 expired wells (85%) out of 1,246 total expired wells. Of the 97 plans, 37 requested future use and have been sent to BSEE’s production and development section for review.

No pending regulation

Angelico of BSEE said it was vital to apply correct terminology in this area, particularly the difference between abandoned and “orphan” wells (those that could not be traced to any operator). “We have no orphan wells in federal waters,” she said.

“Wells that are properly abandoned would no longer be in the Idle Iron initiative. Idle Iron applies to non-producing wells that are on an active lease – we are asking operators to put a schedule on them. An abandoned well is OK, it’s not left unattended; it has proper plugs in it and cement.”

Existing regulations cover how many plugs must be applied and where cement must be placed. No further regulations on this process were pending, she confirmed.

Notwithstanding the question of more legislation, Ian Smith, global business unit manager, well abandonment and rigless intervention, at Weatherford said operators realised that “doing it right first time” could prevent additional costs in future.

“It can be many times more expensive to rectify a problem in a previously abandoned well, not to mention in terms of restoring reputation,” he said.

“I would imagine there would be more focus on reservoir isolation and more effective barrier standards to ensure no potential reservoir-to-wellbore and reservoir-to-annulus communication.”

He expected more stringent verification processes to be required in the longer term to show no potential leak paths.

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Image courtesy of WellCem