The use of acid in oil and gas wells is dividing opinion across the country, particularly in southern England and parts of the East Midlands.
Operating companies have argued it is a routine technique designed to clean wellbores. Campaigners have argued that it could be fracking under the radar with similar risks.
The Environment Agency recently published a set of frequently asked questions and answers (FAQs) about the use of hydrochloric and hydrofluoric acids at oil and gas exploration and production sites.
The FAQs give details of how the Environment Agency will interpret techniques including acid wash, matrix acidisation, acid squeeze and fracture acidising.
DrillOrDrop asked groups researching and campaigning about acidisation in southern England to review the FAQs. This post looks at the key points and the groups’ responses.
Some of the comments are from the Weald Action Group, which has produced its own leaflet (link to pdf here). The group described the Environment Agency’s FAQs as “a start in the right direction” but “too vague to give confidence that this operation can be properly regulated”.
The Environment Agency’s FAQs describe a range of techniques using acids.
Acid wash The Environment Agency defines this as a technique to clean the well following drilling or after use. It is not considered to be a well stimulation method. The FAQs suggest acid wash usually uses hydrochloric acid (HCl) at a concentration of about 7%.
Matrix acidisation According to the FAQs, this technique involves injecting or squeezing dilute acid into the geological formation at a pressure below that needed to fracture rocks. The acid enlarges natural pores, fractures and fissures, increasing the productivity of the well. The Enviornment Agency said it considers this to be a form of stimulation.
Acid fracturing or fracture acidisation This is defined in the FAQs as pumping dilute acid into the formation at pressures that will fracture as well as dissolve rocks. This is also regarded as a form of stimulation.
Acid squeeze The FAQs say this technique dissolves rock and may open new fractures. It is used for areas close to the well to make it more productive.
Weald Action Group said:
“We are pleased to see some distinction between routine maintenance and stimulation.
“Setting the bar at 7% hydrochloric acid for acid wash is again a good start but how will this be regulated?
“The Environment Agency assumes industry usually uses 7% and that acid wash is not considered a stimulation of the formation. Yet at Markwells Wood, a UKOG site in West Sussex, the company consistently claimed it was going to wash with 15% hydrochloric acid.
“How will the Environment Agency be able to distinguish between a matrix acidisation and an acid frack?
“Matrix acidisation and acid fracking carry similar risks as hydraulic fracturing but there are even more unknowns with acidisation because of the lack of historical permitting and monitoring. “Acidisation also uses a higher percentage of chemicals than hydraulic fracturing and there may be a greater cumulative impact because a well can be repeatedly acidized within its lifetime.”
The FAQs say hydrochloric acid is used to dissolve carbonate rocks, such as limestone (calcium carbonate) and dolomite (calcium magnesium carbonate), or calcite cement.
Hydrofluoric acid is less commonly used and is required to dissolve quartz or silica in rocks, such as sandstone or clay.
The FAQs say other chemicals may be added to protect the integrity of the well and refer to:
- Inhibitors to prevent acid damaging the steel casing
- Sequestering agents to prevent the formation or gels or precipitation of naturally-occurring iron compounds.
Weald Action Group responded:
“Acidising tight reserves is complex and typically many kinds of chemicals are used along with the acid, not just two”.
The group asked:
“What about cationic surfactants to inhibit sludge, mutual solvents, friction reducers, acid fluid loss additives, diverting agents, clay stabiliser, calcium sulphate inhibitors, scale inhibitor, ph adjusting agent, clean-up additives and biocides?
“In recent applications at Broadford Bridge, Lidsey and Wressle, there was a list of about 20 chemicals, many of them extremely toxic.”
The FAQs explain that hydrochloric acid reacts with calcium carbonate rock to form calcium chloride salt and water plus carbon dioxide gas. Acid that has reacted with rocks is referred to as “spent acid”. The FAQs say:
“It is expected that the amount of acid used will be calculated to balance with the amount of rock that needs to be treated, so that the acid will have been used up in the chemical reaction. If the fluid coming to the surface is still acidic, it is neutralised with soda ash.
“We require details of the treatment to be included in a waste management plan, which is submitted with the environmental permit application documents.”
Weald Action Group said the description of waste products was “inadequate”:
“There is no consideration of the unpredictable nature of by-products. We’d like to see a requirement for on-site testing of waste water and for logging and monitoring of this.”
“We need to demand that the companies are bonded or pay financial guarantees for transport of waste water considered hazardous, just as with fracking.”
No Fracking in Balcombe, which campaigned against Cuadrilla’s oil exploration site in the village, said:
“Companies, for example Cuadrilla in Balcombe, call their waste water euphemistically ‘salty water’, yet it is likely to contain heavy metals brought up from underground, radioactive materials, and quantities of salt up to five times the typical level in sea water.
“It is likely to be difficult and expensive to treat, and once treated it is likely to be dumped on land or (diluted until the contaminants fall below legal limits) into the sea. Returning acidising fluids are by no means always neutralised. Workers have to take great care, especially when using the very highly corrosive hydrofluoric acid. American unions are campaigning to have hydrofluoric acid banned on oil and gas sites.”
The FAQs say the Environment Agency would not permit a proposed activity if it posed an unacceptable risk to the environment.
“We will only issue an environmental permit if we are satisfied the proposed activities meet the requirements of all the relevant legislation”.
Weald Action Group responded:
“What is the relevant legislation around acidisation?
“There are still so many unknowns about acidisation. We are not being adequately protected. Loopholes still exist that make life very easy for industry.”
The FAQs say that as part of its assessment of risk, the Environment Agency looks at the acid and other chemicals, the proposed activity, the geology, the well and the treatment of waste. It applies a standard Source-Pathway-Receptor conceptual model to assess risk, considering how the acid could reach the groundwater.
Weald Action Group said:
“There are no peer reviewed studies available regarding the dissolution and mobilization of naturally-occurring heavy metals and other pollutants from the oil-bearing formation, specifically with regard to acidisation.
“There is no analysis of the chemicals being injected and the fate and effect of well stimulation fluids in the subsurface.
“How then can the EA make proper assessments using the Source-Pathway-Receptor model?”
Brockham Oil Watch, which has been following Angus Energy’s operation at Brockham in Surrey, pointed to stricter regulation in the US. The environmental conservation committee of Florida’s senate unanimously approved a bill recently to ban fracking of all kinds, including acid fracking and matrix acidising. In 2013, California’s state legislators required permits for all well stimulation treatments, including the use of acid. The regulations also require the notification of neighbours, public disclosure of all chemicals and groundwater and air quality monitoring.
Conventional or unconventional?
The Environment Agency says the FAQs apply only to the use of acidisation at what it calls conventional oil and gas exploration and production sites.
No Fracking in Balcombe said:
“This document discusses forms of stimulation, including acid fracking, which would clearly be used in unconventional situations. The Environment Agency is either naïve or keen to maintain the political fiction that limestone and sandstone are always conventional sources of hydrocarbons.
“Who do they think they are fooling? The use of acid is proposed at a number of sites in southern England that are described as conventional by operators when speaking to the general public, but unconventional when they address current and prospective shareholders.”
Weald Action Group said until target formations in the Weald and areas such as north Lincolnshire were defined as unconventional, regulation would be “inherently flawed”.
Brockham Oil Watch has questioned Angus Energy’s description of its operations at Brockham as conventional:
“We have asked the Environment Agency to clarify how they define conventional versus unconventional sites, where Brockham would fall, and how the approach is different for unconventional sites.
“Based on the proposed completion programme of work for BRX4Z that Angus presented to, and received approval for from the Oil and Gas Authority, the proposed perforation interval is a c190 m zone that includes multiple layers of micrite and shale.
“Where shale rock is the source of hydrocarbons, the Planning Practice Guidance on mineral extraction defines them as unconventional.
“This matters because unconventional reservoirs will likely require stimulation to enable commercially viable flow.”
De minimis: what is it and why does it matter?
The FAQs say a permit for groundwater activity is not needed if the volume of substance used is too small to risk deterioration of the groundwater. It calls this activity de minimis.
The FAQs say an operation would be considered de minimis if:
- The volumes of acid in an acid wash were very small
- The acid would come into contact with a very small area of rock in the target formation
- The acid would react to form an inert salt solution, water and carbon dioxide
- The activity was not intended to inject acid a significant distance into the formation
- There would be no significant residual acid fluid remaining in the target formation
The FAQs give as an example:
“The groundwater may contain naturally high concentrations of hydrocarbons and salts, making any impact from the discharge on the groundwater insignificant or trivial. The fluid is introduced under a controlled pressure so as not to create new fractures in the rock and so that it only penetrates the minimum required distance into the formation.”
Brockham Oil Watch said:
“We are concerned that much of the document is focused on the issue of how to define and deal with a de minimis activity, for which, in effect, regulation is not required.
The FAQs make no attempt to quantify what a de minimis activity is and so it is open to interpretation and potential avoidance of regulation by the oil companies.
“We have also asked the Environment Agency what volume of acid per unit of formation (based on its specific geological characteristics) will be the threshold between acid wash and acid stimulation for the two wells that Angus Energy say they will acid wash: BR-X2Y and BR-X4.”
Weald Action Group asks:
“We’d like to have further information on how the Environment Agency reaches the conclusion that a procedure is ‘environmentally trivial’. Will the 7% HCl be regulated?”
The group said some companies were claiming that their operations fell under routine well maintenance and were therefore de minimis when, in fact, they may be intending to stimulate the formation.
“Will the EA enforce these rules? And if the industry is non-compliant how long will this take to enforce?’’
No Fracking in Balcombe said:
“The Environment Agency’s grasp of acidisation is weak and waffly.
“The Environment Agency has learnt about acidisation and developed its stance on the hoof over the last couple of years, much, we would contend, in response to opinion, queries and FOIs from the public.
“On the positive side, it’s good to see the Environment Agency admit that an acid wash typically uses no more than a 7% acid solution, and that matrix acidising and an acid frack are forms of stimulation. It is good that the Environment Agency is beginning to see acidising as a process worthy of its attention.
“But this document selects its vocabulary with care, emphasising ‘cleaning out the well’, comparing acidising an oil or gas well to descaling a domestic kettle, comparing it spuriously to the use of acidisation in the water industry. ‘Only a small volume of dilute acid is required’. The Environment Agency’s vocabulary is de minimis.
“The Environment Agency writes of its commitment to protecting public and environment, and of its regulatory powers and potential sanctions. Guardian angels? After six years dealing with the Environment Agency, we see them as fallen, toothless angels, locked in a government and industry embrace, dwindling in number, and reduced to ticking boxes.”
Weald Action Group concluded:
“It is clear that this is a nascent regulatory regime based on very little knowledge about the impacts of acidisation on our environment and human health.
“We would like to see a moratorium on the practice until there is sufficient research on all aspects of acidisation.
“We deserve strong, meaningful, protective legislation that puts the health of our communities and environment first.”
“The concern is that in UK regulation the use of acid still falls under the wrong category of conventional production. We know that the target geology in the Weald is complex and oil does not flow naturally. We know that it is low permeability and large quantities of chemicals and/or acid fracking is are needed to release the oil. Acid maintenance procedures are passed off as routine and standard and bypass important regulatory scrutiny.
“Data gaps exist in all aspects of acidisation, including acid washing. There are significant uncertainties about the kinds of adverse health outcomes that may be associated with chemicals used in acidising and the effectiveness of some of the mitigation measures in reducing or preventing environmental impacts which could adversely affect public health.
“There is no evidence that this process can be conducted without risk to the environment and human health. We would expect the Environment Agency to have revised guidance and very distinct regulation for all aspects of acidisation. What is the guidance on acidising in unconventional formations?”