UK GAS-Prices rise as field output declines ahead of maintenance

LONDON, July 31 (Reuters) - British wholesale gas prices rose on Wednesday morning as UK gas fields started to ease output ahead of maintenance outages starting from tomorrow.

* Day-ahead gas jumped by nearly 10% to 29.50 pence per therm at 0751 GMT.

* Gas for immediate delivery was up 6% at 28.00 p/therm.

* "Heavy summer maintenance is starting - some fields are going down (in output)," a gas trader said.

* UK Continental Shelf fields are expected to ramp down ahead of a number of outages scheduled from Aug. 1.

* Maintenance outages will impact entrants into the Forties and CATS pipeline form tomorrow, including various fields into the St. Fergus terminal and the Cygnus field.

* Refinitiv analysts forecast flows of 47 mcm/day from tomorrow, rising to 67 mcm/day by Aug. 10 and 95 mcm/day by mid-August.

* "There is a small probability that fields will remain offline longer than scheduled. This would likely be for commercial reasons due to low prompt prices," said gas analyst Oliver Sanderson.

* Norwegian gas field Troll has also reduced production for commercial reasons.

* Despite this, the system is oversupplied by around 14 million cubic metres (mcm), with demand forecast at 124 mcm and flows at 138 mcm/day, National Grid data shows.

* This is because gas-for-power demand is reduced due to strong wind output.

* Peak wind generation is forecast at 6.8 gigawatts (GW) but will fall to 4.8 GW on Thursday, Elexon data shows.

* The August contract was up 1.00 pence at 29.50 p/therm.

* Dutch August gas at the TTF hub was 0.30 euro higher at 10.35 euros per megawatt hour.

* The benchmark EU carbon price was up 0.37 euro at 28.27 euros a tonne. (Reporting by Nina Chestney)