Tests of the first shale well at Cuadrilla’s site in northwest England show a rich reservoir of high quality and recoverable gas, the British firm said on Feb. 6, adding that rules that have constrained its testing work should be eased.

Cuadrilla is using a technique called hydraulic fracturing that involves injecting water and chemicals at high pressure to break up rock and extract gas. The practice, known as fracking, can cause tremors and environmentalists oppose the development.

The company repeatedly stopped operations last year at its Preston New Road site in Lancashire because of minor seismic events. British regulations demand that work be suspended if seismic activity of magnitude 0.5 or more is detected.

Cuadrilla said it could only partially test the horizontal shale well because of the operating limits. It said it fully fractured 2 out of 41 stages along the horizontal well and less than 14% of sand was injected.

“Nonetheless the natural gas still flowed back from the shale at a peak rate of over 200,000 standard cubic feet (scf) per day and a stable rate of some 100,000 scf/day,” Francis Egan, CEO, said.

Scaling up the results suggested a flow range of between 3 million to 8 million scf/day for a 2.5 km (1.6 miles) section once all stages were hydraulically fractured, Cuadrilla said.

“We have also confirmed that the Bowland shale formation fractures in a way that, from U.S. experience, is typical of an excellent shale gas reservoir,” Egan said.

Fracking techniques were pioneered in the U.S., which has turned from an importer of gas to a net exporter.

Cuadrilla said more production data was needed to refine the preliminary results and this could only be done if seismicity limits are lifted to allow more effective fracturing.

The firm has asked the regulator to review rules on seismic activity to allow more thorough testing of exploration wells.

Depending on the outcome, Cuadrilla plans to complete fracking its first well at Preston New Road, start a second and carry out flow testing of both later this year.

Rival Ineos, which has the largest shale gas license acreage in Britain, has called on the government to change seismicity regulations. Experts have also said the limit for tremors could be safely raised at fracking sites.

Environmentalists have campaigned against fracking, saying extracting more fossil fuel is at odds with Britain’s commitment to reduce greenhouse gas emissions. They have also raised concerns about potential groundwater contamination.

Greenpeace UK said the government should not waste time on fracking and support clean energy infrastructure instead.

Britain’s government has said it wants to cut reliance on imports of gas, which heats about 80% of British homes. It has proposed measures to speed up planning applications to support the development of the U.K. shale gas industry.

The British Geological Survey estimates shale gas resources in north England could reach 1,300 trillion cubic feet, 10% of which could meet Britain’s demand for about 40 years.

Cuadrilla is 47.4% owned by Australia’s AJ Lucas and 45.2% owned by a fund managed by Riverstone.