Campaigners calls for ban on acid stimulation of onshore oil and gas wells – DRILL OR DROP?

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Markwells Wood oil site in the South Downs National Park where the use of acid was proposed. Photo: DrillOrDrop

Friends of the Earth has called for a ban on the use of acid to stimulate the flow of oil and gas in onshore wells.

In a report called The Acid Test, published this week, it said many of the risks linked to acid stimulation were similar to those for fracking, including contamination of groundwater, soil and air, industrialisation of rural areas, noise, increased traffic and earth tremors.

It said current regulations were not strong enough to deal with these risks and there were gaps in knowledge about the chemicals used. Acid stimulation would also contribute to climate change, it said.

As well as ban, Friends of the Earth called for:

  • An assessment of the health and environmental impacts of acid well stimulations in England
  • Identification of chemicals of concern used in all onshore well stimulation operations
  • Government publication of data on the number and type of acid stimulations in England
  • A requirement for exploration companies to state explicitly in planning applications whether they want to use acid and for what purpose.

Oil and gas companies say they have routinely used acid for decades. But it is not always clear whether this was to clean scale or other deposits from the well, known as acid wash, or to stimulate the flow of hydrocarbons in rock formations.

Acid stimulation is likely at several new oil exploration sites in the Weald basin in southern England, some in protected areas.

Brenda Pollack, south east campaigner for Friends of the Earth, said:

“Residents are right to be worried about the increasing use of acid well stimulation to produce oil and gas in this area. There are a lot of unknowns about the quantities and type of chemicals being used and where they end up.

“It’s clear that we should be reducing fossil fuel use, yet the government is encouraging the industry. Plans to fast track shale gas operations could have implications in the Weald basin which is a known shale oil area.”

What is acid stimulation?

In acid stimulation, companies inject a fluid containing acid and other chemicals into the rock formation. The chemical concentrations are usually 6-18%, higher than the 0.5% concentration used in hydraulic fracturing.

In acid fracturing, one form of acid stimulation, the fluid is injected at pressures high enough to fracture the rocks, as with hydraulic fracturing.

Hydrochloric acid is usually used where the rocks are limestone and hydrofluoric acid in sandstone formations. But sometimes combinations of acids are used.

Key issues

Climate change

Friends of the Earth said:

“[Acid stimulation] is being proposed and is potentially already being used in England to increase fossil fuel production. But, to avoid the worst impacts of climate change, we need to reduce fossil fuel use fast. Increasing fossil fuel production is not compatible with the climate change goals the UK has signed-up to.”


The regulations covering fracking are unlikely to deal with acid stimulation, Friends of the Earth said.

Legislation on hydraulic fracturing applies only where individual fracture treatments use 1,000m3 of water or 10,000m3 in total.

Acid fracking tends to use smaller volumes of fluid, though at higher chemical concentrations. This means there is no automatic requirement to carry out baseline monitoring of methane in groundwater nor monitor methane levels in the air, Friends of the Earth said. There is also no legislation banning surface development of sites using acid stimulation in protected areas like National Parks.

Friends of the Earth said:

“Regulations are not strong enough to cover the risks associated with acid stimulation. No proper environmental risk assessment study appears to have been performed.”

Gaps in knowledge

Friends of the Earth said:

“There are a lot of unknowns about acid stimulation. Whilst we know that many of the chemicals used in the processes can be hazardous, there have been very few studies on the risks and impacts.

“There are significant gaps in knowledge about the chemicals used in the treatments, including overall volumes used, and their toxicity and persistence in the environment, meaning that there are clear risks that residents are right to be concerned about.”

The first toxicological study purely dedicated to acidising was published in the U.S. in 2017. But Friends of the Earth said in England the Environment Agency had not carried out any studies of its own.

“It appears that the Environment Agency has not historically given permits for acid well stimulation operations and is unable to provide data on where acidising has taken place.”

Friends of the Earth added:

“As far as we are aware, there have been no studies to look at the quantities and profiles of chemicals used in acidising operations in England. This means there is a lack of analysis of how much has been used in the past to determine levels of current and future risk.

“Given the number of applications coming forward this must be addressed. The government needs to ensure that adequate reporting is carried out by the industry and that relevant cumulative data on chemical use is publicly available.”

Environmental impacts

Friends of the Earth said:

“acid stimulation could involve hundreds of new oil wells, some in our most precious areas of countryside.

“It is important that there is more clarity when [planning] applications are made so that the public and local decision makers know exactly what type of treatment a developer wants to carry out.”

Industry reaction

Ken Cronin, chief executive of the industry organisation, UK Onshore Oil and Gas, said in response to the Friends of the Earth report:

“The use of acid is a standard water services and oilfield practice for many developments and is clearly outlined in the Environment Agency’s Q&A documentation. Indeed, as Friends of the Earth themselves note, this is a technique that has been widely used since the 1950s.

“Acidisation, both in the water industry and our own, is a regulated practice that allows us to effectively ‘clean’ or improve recovery from a well. It dissolves fine particles and scale, allowing a better flow of what we’re trying to extract. As with household kettles, which need to be treated for limescale build-up, the use of this process merely increases the efficiency of our practices.

“An environmental permit is only issued for this technique if the Environment Agency are satisfied that the proposed activities meet the requirements of all the relevant legislation. Friends of Earth would have you believe that ‘acid’ automatically means a hazard to human health, but according to this report, they would ban us from using formic acid – something commonly found in both bees and nettles.

“According to the OGA, the UK’s oil import dependency is forecast to increase from 30% today to almost 70% by 2035, and the prediction for gas is equally bleak. Under the Committee on Climate Change limits on oil consumption, the use of 46 million tonnes equivalent in 2040 satisfies the Climate Change Act. With oil the biggest sole source of UK energy, instead of proposing ill-informed bans Friends of the Earth should ask themselves why they want us to become a country beholden on others for our basic needs.”

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