An oil well in Purbeck has been legally pumping methane into the atmosphere for nearly 60 years.

The Environment Agency has confirmed the Perenco-operated Kimmeridge well, installed in 1961 and thought to be the oldest still in use in the UK, "has a permitted release point for methane" and released 284 tonnes of the gas in 2017.

The agency says the gas volume is an estimate based on a gas to oil ratio as the quantity released is not measured on site.

Methane is thought to be 34 times more potent as a greenhouse gas than carbon dioxide over a 100 year period.

A spokesman said: "The site operators have tried a number of different technologies to reduce the volume of methane escaping (cold venting) into the atmosphere, including using the gas to generate electricity, but none have proved cost-effective.

"This is partly due to the remote geographical location of the well."

The release was revealed by Dorset environmental campaigner Stuart Lane, based on a tip-off from an industry insider.

He said: "The regulatory system appears to be permitting gross levels of pollution that are at odds with legally binding climate change commitments including the 2008 Climate Change Act.

"It is clear the mitigation options have been investigated but the most obvious and simplest approach in my opinion would be to close any well that is not designed to avoid methane emissions.

"This one small well exposes wider concerns. A regulatory system that has approved massive levels of pollution. An industry that is apparently prepared to operate to the minimum standards that regulations impose, however low."

The agency said that Perenco, which operates the neighbouring Wytch Farm oil field, will need a new licence for the Kimmeridge well as part of a review of old permits.

In response to Mr Lane's Freedom of Information request it said "many" conventional oil wells were "venting associated gasses" into the atmosphere, and it was now placing more stringent conditions on permits.

"Existing sites will be issued with new permits with an improvement condition which requires them to submit a written gas management improvement plan and obtain the Environment Agency’s written approval for it.

"The plan must contain detailed consideration of all available options for the beneficial utilisation of all of the available gas from their activities.

"Where such utilisation is not feasible, the plan must consider in detail all available options, both combustion and non-combustion based, for the disposal or abatement/mitigation of waste gas so as to minimise its environmental impacts as far as available techniques allow."

A spokesman for Perenco said: "Although the Kimmeridge well is not currently producing, when production recommences we will ensure we continue to operate in line with the regulator’s permit conditions, and ensure that any gas emissions are minimised through regular maintenance and inspection.

"Although no decisions have yet been made, we have also been reviewing a number of ways to invest in the well site at Kimmeridge in order to further reduce gas emissions, such as gas compression or temporary storage at the site."

A small town's carbon footprint

The climate impact of the well over its lifetime is equivalent to the annual impact of a town, Stuart Lane claims.

Based on the Environment Agency’s data, Mr Lane has carried out his own calculation of the amount of gas released between the well’s installation in 1961 and 2003, over which time some three million barrels, or 420,000 tonnes, of oil were extracted.

From this production he has estimated a release of 37,521 tonnes of methane, based on the agency's oil to gas ratio.

This, he says, is the equivalent of 1,125,637 tonnes of carbon dioxide based on the 'global warming potential' of the two chemicals as used in international treaties.

“To give some sense of perspective, estimates of the carbon footprint for a UK citizen are about 10 tonnes per year,” he said.

“Based on these figures, the Kimmeridge well has produced at least as much carbon dioxide equivalent by the venting of methane to match the pollution from 112,500 people’s carbon emissions for an entire year.

“The population of Poole, the closest large town to the well, is about 150,000 people.”

Mr Lane also says that national regulator the Oil and Gas Authority uses a different ratio for oil and gas estimates which assumes a higher gas output than the Environment Agency.