With North Sea offshore oil decommissioning gaining pace, does evidence of leaking abandoned wells suggest catastrophe lurking just around the corner?

Until recently the term “abandoned well”, whether temporarily or permanently abandoned, couldn’t have been more accurate. Once an offshore oil well was plugged, the book was considered closed on the oil-producing asset in question.

But a report by the Associated Press on a possible 3,500 leaking wells that have been temporarily abandoned in the Gulf of Mexico – some for more than 40 years – has blown the lid off plugging and abandonment (P&A) procedures.

“There are more leaking wells than people know about, mainly because it is something that companies do not want to advertise,” says David Weaver, former managing director of BP Northern Europe Gas, Power and Renewables, and now chief executive of clean-tech company Ultra Green.

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.

“[Underground] there are a lot of gases that speed the ageing process of cement,” says Alf Jan Wik, a senior vice-president at WellCem, a Norwegian P&A specialist.

“75% to 80% of wells are leaking worldwide … When you consider that over 10,000 wells have been drilled on the UK continental shelf alone, the cost potential of leaking wells is phenomenal,” he says.

Ticking time bomb?

Studies carried out on workers involved in the Exxon Valdez clean-up revealed serious health impacts where spilled crude oil is inhaled or handled, and where dispersants used in clean-ups have entered the food chain. Flaring of spilled oil releases heavy metals and other toxins into the atmosphere.

With North Sea decommissioning due to ramp up over the next 18 months and about 470 platforms to be decommissioned over the next 30 years, well P&A and leak mitigation should be a priority for both UK operators and regulators, given the environmental and financial stakes.

But according to Weaver, when it comes to regulation and mitigation strategies for dealing with leaking wells, “governments and oil majors prefer to keep their heads in the sand”.

Per Lund, senior vice-president for business development at Norse Cutting and Abandonment, says: “No regulation exists to ensure that a well has been properly plugged over time.

“Operators must inspect structures left in the sea regularly, but there is no such legislation or practice for abandoned wells. We know of cases where wells are leaking, so this will most certainly be a problem in future.”

In the US, operators are supposed to report oil sheens that might indicate a leak, while the UK carries out routine aerial surveillance for marine pollution. But Weaver points out that, contrary to common belief, oil and water do mix, particularly where the leakage is under water.

Referring to the recent BP-Macondo well blow-out, Weaver says: “There is growing evidence that there is more oil chemistry contamination in the water below the surface than anyone has yet owned up to.”

This raises the question: when a well is plugged, who inspects the job? According to Weaver, it is the oil companies themselves. “Governments often rely on the oil majors to do the inspections, because they are the only ones with the engineering expertise and the equipment needed to carry out the inspection.”

In most jurisdictions liability for environmental pollution is often uncapped, which in itself is a big incentive for operators to ensure they are doing things properly.

However, Toby Hewitt, consultant at international law firm Herbert Smith, notes that unless rules are explicitly built into a country’s petroleum regulations, “once a petroleum licence on a well has expired, the position on where residual liability lies becomes less clear”.

While some form of international regulation is required, many argue that the sheer number of countries and companies involved renders this nigh-on impossible.

But Weaver contends: “There are only a handful of companies – the oil majors – who are capable of drilling wells, so international regulation would not be as difficult as people make out.”