People are invited to comment on proposals by Angus Energy to dispose of waste water into a borehole at its Brockham oil site in Surrey.
The company is seeking changes to its environmental permit that would allow it to inject what’s known as formation or produced water that comes to the surface along with oil.
The consultation, by the Environment Agency (EA), began today (23 March 2021) and runs for six weeks until Tuesday 4 May 2021.
In 2018, the EA refused a previous request for water injection because it said Angus had failed to provide required information or to assess adequately the risks to groundwater.
In the current application, Angus said there was a negligible risk to groundwater. It also said there was no need for groundwater monitoring because it had robust procedures and tests confirmed the integrity of the injection well.
The company said the permit change was needed to support oil production at Brockham by increasing reservoir pressure. If approved, it would also eliminate the cost of transporting and disposing of the water, which is very salty. In October 2020, Angus said it would abandon Brockham if reinjection was refused again.
There is currently no activity at the site. It made local news headlines in 2017 when Angus drilled a side-track well. Surrey County Council said this did not have planning permission. Angus Energy disagreed but later applied and was granted retrospective consent. Angus said it proposed to use this side-track, BRX4-z, to produce oil from the Kimmeridge formation.
“Water from the Weald Basin”
The application said there would not be enough produced water from Brockham alone to increase the pressure in the formation and restart production at the site.
It said produced water from the Portland and Kimmeridge formations at Brockham would be mixed with water “from another source(s)”, the company said. It said water would be brought from the company’s other south-east site at Lidsey in West Sussex and from “compatible producing fields” in the Weald Basin.
It would be injected into the Portland Sand formation at a depth of 700-750m below ground level. Injection would be through the BRX3 well, drilled in 2007.
A hydrogeological risk assessment included with the application said the maximum volume of injected water would be 24 m3 or 150 barrels in any 24-hour period or up to 8,395 m3 a year.
The risk assessment said reservoir pressure at Brockham had fallen to about 500 pounds per square inch (psi), thought to be less than 50% of the original pressure. It said:
“At current reservoir pressure production is only viable for a very limited period of time.”
Water injection would restore reservoir pressure to 65-80% of original pressure and allow production of around 300,000 barrels of oil, the document said.
On the threat to ground water, it said:
“there is a negligible risk of the migration of injected water to shallower aquifers and that these aquifers are in any case unlikely to contain potable [fresh usable] water.”
It said freshwater in the aquifer would be protected from contamination by:
- Local geological structures
- Physical barriers in the well
- Reservoir pressure which meant water would flow to, not from, the injection reservoir
The risk assessment said reinterpretation of seismic data showed there was no connection or pathways between the oil reservoir and shallower strata.
Potential aquifers in the Ashdown Beds and Tunbridge Wells sands were sandwiched between impermeable claystones, which formed an effective barrier, it said.
A recent test on the wellbore showed there was more than 126m of good to excellent cement bond, it added.
DrillOrDrop will report on responses to the application.