The UK’s newest oilfield has begun producing water, the operator has confirmed.

Egdon Resources reported that the Wressle site, in North Lincolnshire, had produced “limited volumes of water” during July 2023.

Produced or formation water can be an expensive problem for oil companies. The water must be treated or reinjected because it is often salty and can be radioactive.

Company statements about Wressle, which began formal production in July 2022, have previously noted that the well had a zero water cut, the proportion of water in the total volume of liquid produced from the field.

Egdon Resources said the water cut, averaged 3.72% in July 2023.

Most UK onshore oil wells produce some water.

The water cut in May 2023, the most recent available official data, ranged from 96% at Wytch Farm in Dorset to 1% at Farleys Wood in Nottinghamshire. The water cut often increases as an oilfield ages.

In May 2023, Wressle was one of only three onshore fields which did not produce water along with oil. (The others were Humbly Grove in Hampshire and Kimmeridge in Dorset).

Wressle is the second biggest UK onshore oil producer, after Wytch Farm. In May 2023, it produced 3,837m3, representing 5.95% of UK onshore oil.

Egdon Resources said: “The start of water production is significantly later than originally anticipated”.

The company said this was evidence that the expected recoverable volumes of oil from the Ashover Grit formation would be higher than estimates made in 2016.

It said the start of water production was being incorporated into reservoir modelling and would be reflected in a new competent person’s report on the field being prepared.