Changes sought to Horse Hill environmental permit

People are being invited to comment on changes to the environmental permit for the Horse Hill oil site in Surrey.

Horse Hill oil site in Surrey in April 2020. Photo: Used with the owner’s consent

A consultation by the Environment Agency opens on 22 March 2021 and runs until 21 April 2021.

The site operator, Horse Hill Developments Ltd (HHDL), is seeking consent to:

  • Flare up to 10 tonnes per day of waste gas from the wells
  • Drill up to four new boreholes
  • Carry out well treatments
  • Test the oil flow in the new wells, each for 90 days
  • Use at least one of the boreholes as a waste water reinjection well
  • Carry out an injectivity test on the existing HH-2z well

The company already has planning permission to drill and test the new wells.


The non-technical summary, which accompanies the application, said flaring should continue until incineration of gas was no longer considered a best available technique.

Data from the Oil & Gas Authority shows that Horse Hill flared nearly 150 tonnes of waste gas from March-November 2020 (the most recent figures available).

In 2018, HHDL told residents living near Horse Hill that  gas would not be flared during oil production.

It said then:

“The solution gas separated from the oil will be used to generate electricity to power the site and go into the national grid.”

DrillOrDrop asked HHDL’s parent company, UK Oil & Gas, whether the plan to generate electricity for the grid had been dropped.

The company said:

“Current gas production levels are very low. It is intended to continue to use a flare at Horse Hill until more production wells are drilled, increasing gas production.

“A future gas to grid scheme will be considered in conjunction with future drilling at Horse Hill.”

Last year, the government’s climate change advisor, the Climate Change Committee, said flaring and venting should be permitted from 2025 only for safety reasons on both onshore and offshore fields.


HHDL’s application also sought to dispose of produced or formation water in a reinjection well. This would eliminate the cost of treating the water, produced alongside oil and gas, at a specialist disposal centre. A reinjection well could also be used to improve oil flows.

HHDL said:

“The proposed activities include the reinjection of produced water into a geological formation from which hydrocarbons will be produced in order to provide production support. A groundwater activity permit is being applied for to facilitate the proposed reinjection activity.”

Horse Hill produced more than 1,100 tonnes of formation water between March and November 2020, with more than 200 tonnes each month in June-August.

Well treatments

HHDL is seeking permission for the following well treatments to improve oil flows:

  • Acid wash using either hydrochloric acid (up to 15%), acetic acid (up to 15%), ORCA B and CS-SAF-2
  • Xylene solvent to remove wax and asphaltic materials
  • Hot oil treatment to remove build-up of wax precipitates within the production tubing and casing

The application said:

“Such treatments are applied to the formation at low pressures and pump rates determined by an injectivity test. This is described as “an engineering test which will apply increased pressure to the oil-bearing reservoir formation until it reaches a point at which injectivity starts to occur”.

UK Oil & Gas confirmed that pressure used in the injectivity test would be “well below” that required to fracture rocks.

  • At the time of writing, there were more than 430 responses to the public consultation.

Updated with responses from UK Oil & Gas (5/3/2021) and correction to closing date (17/3/2021)

3 replies »

  1. Interesting one about the electricity generation. I think Wressle are going ahead with that. Wonder why HH hasn’t? Must be a logical reason, as increasing income would seem to be the way to go if there wasn’t a reason for not doing so. Perhaps it has something to do with timing of the other wells and thus volume to manage, which, presumably, would then dictate size of the unit required? Bit like not ordering the car until you know if the wife is having twins, or not?

  2. The amount of gas being produced, Associated Gas Production Volume (ksm3) 9.54 for November, is only enough to supply a small house for for just over 2 days.

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