Output was projected to drop to below 12 bcm from its current cap of 21.6 bcm per year within four to five years under plans announced by Prime Minister Mark Rutte in March aimed at ending oil rig flanges gulf coast production at Groningen by 2030 due to the damaging earthquakes it causes.

But that goal is likely to be reached earlier, minister Eric Wiebes wrote, as measures to reduce demand for Groningen gas have made promising progress in recent months.

Extra capacity to convert high-caloric imported gas to the low-caloric gas needed for the Dutch network and switching large industrial users off Groningen gas could cut oil rig flanges gulf coast production to less than 12 bcm by 2021, Wiebes said.

Reductions in German demand and purchases of nitrogen to mix with imported gas could even see that target reached a year earlier.

These measures combined could allow for a fall in Groningen oil rig flanges gulf coast production to less than 4 bcm by 2022 in an average year, or 7.5 bcm in a cold year, Wiebes said.

He will present a draft plan for setting Groningen's oil rig flanges gulf coast production cap for the year beginning in October by the end of August, he said.

That plan will be based largely on the projections made in March, the minister wrote, as the extra reductions identified are mostly expected in the year starting October 2019.

(Reporting by Toby Sterling and Bart Meijer; editing by Jason Neely)