Cold venting and acid squeeze have been approved at Rathlin Energy’s oil and gas site at West Newton in East Yorkshire.
The Environment Agency (EA) confirmed last week it had accepted variations to the site’s environmental permit.
The changes relate to plans to test the flow of oil and gas in the second well at the site, known as WNA-2. Testing operations are due to start soon and are expected to run for four to eight weeks, 24 hours per day.
The EA said there may be “a number” of extended well tests but it did not set a limit on how many.
Rathlin applied in December 2018 to vary the permit originally issued in 2015. The changes involve:
- Acid wash and squeeze
- Cold venting of gas during nitrogen lift
- Incineration of gas in a specific flare during well cleaning and tests
- Loading, handling or storage of crude oil on site
Use of acid
Rathlin Energy proposes to use a 15% solution of hydrochloric acid in acid washes and squeezes.
The Environment Agency said the acid wash would clean the well after drilling to return the natural porosity and permeability of the damaged formation.
On acid squeeze, EA guidance said acid is squeezed into the rock formation, dissolving the rock. It is an industry term used where the permeability of the rocks is low and where the operator intends the acid to not travel farm from the well into the geological formation, the EA said.
“This [acid squeeze] may enhance or create new flow paths to enable the well to be more productive.”
There is no limit in the revised permit for West Newton on the number of acid washes or squeezes, the volume of acid solution that can be used in the well, the distance that the acid can travel into the formation or the pressure used. The new permit nor the decision documentclarify whether the EA considers an acid squeeze to be well stimulation.
The decision document does say that the acid wash and squeeze may be “undertaken a number of times” and that each squeeze would use up to 15m3 of acid solution.
The EA described the operations as a “common method” to treat onshore oil and gas wells. It said:
“we are satisfied that the proposed activities will not pose a risk to groundwater”.
Under the new permit changes, the EA has allowed Rathlin Energy to cold vent gas during the nitrogen lift. Cuadrilla is also seeking a permit variation to allow cold venting at its site at Preston New Road in Lancashire.
Nitrogen is introduced into the wellbore to displace fluids and aid the initial flow of petroleum. The EA’s decision document for West Newton said the use of nitrogen may result in cold venting of gas for “a short period of time”. The vented gas would include climate-changing methane and other gases from the well. Previously, the EA has permitted cold venting only in emergencies.
Companies argue that cold venting cannot be avoided because the use of nitrogen makes the gas mixture incombustible in a flare. At West Newton, the EA said the mixture of methane and oxygen would ignite in the flare as nitrogen levels fell.
The EA said it was satisfied that the nitrogen lifting was “appropriate” and “justified”. It said there were additional controls on smell generated from the use of nitrogen in an updated odour management plan for the site, the EA said.
The failure of the flare to ignite gas during testing the first West Newton well in September 2014 led to complaints about smell 50m from the site. On that occasion, a breach of the permit was recorded against the site. (DrillOrDrop report)
The new permit does not put a limit on the duration or number of times cold venting can happen at West Newton. There is also no limit on the volume of methane or other substances that can be emitted during cold venting.
Rathlin Energy had proposed to use either a PW Well Test Shrouded Ground Flare or the Aeron CEB 1200 flare for the extended well tests, depending on which were available. The EA has accepted this for the gas extended well test.
For the well clean-up and oil extended well test it said the higher efficiency low emission burner CEB 1200 and/or CEB 4500 should be used. If these flares were not available, the operator would have to demonstrate this were the case. The alternative shrouded flare may be used if the EA accepted the justification, the decision document said.
Updated 13/8/2019 to correct issues raised in comment by Hewes62