The Environment Agency is seeking public comments on its expected approval of a wide range of new operations at the Horse Hill oil site in Surrey.
The site operator, Horse Hill Developments Limited (HHDL), has applied to vary the site’s environmental permit, to allow water reinjection and more drilling, testing, well treatments and oil production.
A public consultation began today on the draft permit and runs until 31 March 2022.
The Environment Agency described the application as a “substantial variation” to the environmental permit. But it said it was minded to allow the changes. It said today:
“The Environment Agency are satisfied that the scope of the works proposed by the applicant and the resulting changes to the environmental permit will not give rise to pollution of groundwater or surface water receptors.
“Unless we receive information that leads us to alter the conditions in the draft permit, or to reject the application altogether, we will issue the permit in its current form.”
This is the third consultation on the proposed permit changes at Horse Hill. The first, in 2019, received nearly 500 responses. A second consultation in 2021 had 180 comments.
If approved, the permit changes would allow:
- Drilling of four boreholes and repurposing of two boreholes for water reinjection
- 90-day extended well tests, including flaring, for the additional wells
- Production from additional wells
- Reinjection of produced and clean treated surface water to support hydrocarbon production
- Burning up to 10 tonnes of waste gas per day during production
- Well treatments, including acid wash and use of solvents
- Disposal of uncontaminated surface water from the well pad into a nearby stream during testing and production
- Injectivity tests on two wells earmarked for water reinjection
The decision document, which explains why the EA proposes to allow the changes, revealed disparities between HHDL’s permit and planning applications.
Surrey County Council granted planning permission in September 2019 to allow changes which included drilling four new hydrocarbon wells and one water reinjection well.
Today’s draft permit notice said HHDL planned two reinjection wells: a repurposed existing well (HH-2z) and one of the additional four new wells.
The council said this could indicate “a material change to the planning permission” and HHDL should ensure it contacts the planning authority.
The EA said:
“It is the responsibility of the operator to hold all necessary permissions to undertake the described activity.”
The EA said it needed to set conditions that must be met before HHDL could carry out some operations. The company must:
- Notify the EA before it begins water reinjection
- Confirm whether any changes to boreholes are needed for reinjection
- Confirm whether there have been any changes to integrity of the HH-2z borehole
- Provide at least three months of groundwater and surface water monitoring to establish a baseline and determine any changes from site operations
The EA has also said there should be limits on:
- Disposal of waste gas from extended well testing and production
- Reinjection of produced water
- Emissions of nitrogen oxides, carbon monoxide and total volatile organic compounds
There should also be monthly monitoring of the feed gas to the flare, the EA said.
The UK Health Security Agency in its comments on the permit changes noted the levels of nitrogen dioxide and benzene may breach air quality standards at the site boundary during drilling.
The EA said it agreed with HHDL’s air quality modelling:
“Environmental standards for human health and critical levels or loads for ecological receptors are unlikely to be breached.”
Under the permit, gas produced along with any oil would be burned in a flare during well testing and production.
The EA agreed with HHDL’s conclusion that this was the best available technique for disposing of gas, which is regarded as a waste product. Flaring was the only “technically and commercially viable solution for disposal of gas”, HHDL said.
The site is expected to use two flares: one suitable for low flow volumes and one for up to 250,000 standard cubic feet of gas per day. HHDL will have to inform the EA if it uses the higher flow rate flare.
The company has also committed to revise its gas management plan if the wells generated enough gas to change the assessment on flaring.
Charlwood Parish Council, in an earlier response to the EA, said gas flaring should not be considered best available technique because of the expected volume and the additional effects of nearby Gatwick Airport.
The campaign group, Weald Action Group, said the gas management plan should include estimates of gas associated with oil production from the four new wells. It also said there was no justification for not using the gas to generate electricity for the site. Changes in government guidance soon may mean that flares may no longer be considered best available techniques, the group added.
The area around Horse Hill experienced a swarm of earthquakes between 1 April 2018 and 27 February 2019. The strongest, on 27 February 2019, measured 3.1ML and prompted more than 1,600 reports to the British Geological Survey (BGS). A report for the Oil & Gas Authority concluded that the earthquakes were not likely to have been caused by hydrocarbon operations.
Despite this, the EA received comments that changes at Horse Hill could lead to more earthquakes.
Charlwood Parish Council said precautionary measures should be applied following the earlier swarm.
The campaign group, Markwells Wood Watch, said the site’s geo-hazards assessment should have been updated to reflect the new operations, particularly reinjection.
HHDL wants to carry out treatments on the existing and new wells to improve their performance. These comprise:
- Hydrochloric and acetic acids at concentrations up to 15% to remove damage to the wellbore
- Xylene solvent treatment to remove paraffin precipitates to improve flow in production wells
- Hot oil recirculation to remove waxy precipitates in production tubing and casing
- Potassium chloride and ORCA B and CS-SAF-2 to remove filter cake that could build up in the near well bore area
The EA said well treatments would not to extend beyond 10cm of the wellbore and they met the “requirements of published guidance”.
Markwells Wood Watch said the application lacked a sufficient risk assessment for proposed well stimulation. Weald Action Group said pressures and quantities of acid should be recorded and reported to the EA.
The permit would allow HHDL to reinject produced and surface water into the Portland sandstone formation to a maximum depth of 762m.
The injection rate must be no more than 2.6 litres/second and no more than 80m3 in a day (eight or 12 hours).
The EA said gauges would be installed to ensure water reinjection did not exceed 90% of formation fracture pressure. Wellhead and annuli pressures to be monitored and logged hourly.
Markwells Wood Watch asked the EA for details of how much produced water would be reinjected and at what pressures.
The permit also allows HHDL to discharge clean surface water to Spencer’s Gill brook during well testing and production and when site was not operating
The permit would not allow discharge to the gill during drilling and any well workovers, the EA said. During these operations surface water will be collected by tanker and taken to a waste facility.
The EA said it was:
“satisfied that the controls … provide sufficient levels of protection to protect Spencer’s Gill and other receiving water bodies at distance from the site.”
But Weald Action Group said surface water should be sent to a treatment plant, rather than discharged into Spencer’s Gill.
Broadford Bridge Action Group Pollution Watch (BBAGPW), a campaign group based near a site run by a sister company, said there were risks to groundwater from pollution incidents or emissions.
HHDL proposes to install groundwater monitoring wells next to the wellpad to identify any deterioration in quality. But BBAGPW was concerned about the level of monitoring of surface collected water.
Charlwood Parish Council said all the site’s carbon emissions should be considered. These should include transport to and from the site for its lifespan, as well as emissions from processing and burning the produced oil and gas.
Concerns have been raised about the durability of the impermeable line under the Horse Hill site.
BBAGPW said the liner would not last for Horse Hill’s lifetime. The EA said the integrity of the liner would be tested every three years and remedial action would be taken if needed.
Salfords and Sidlow Parish Council raised concerns about whether the EA had sufficient resources to monitor and enforce regulations.
The regulator responded:
“The Environment Agency undertake regular compliance checks at permitted facilities to ensure that conditions and limits within the permit are complied with.”
Broadford Bridge Action Group Pollution Watch said the permit variation application form had been filled in incorrectly and the geological and hydrogeological reports were inconsistent with information given by shareholding companies. The group also said there was not enough detail about formation thicknesses, dip, faulting and stresses to support the risk assessment.