Heat, supply forecast caps gas price gains

LONDON (Reuters) - British prompt gas prices rose on Friday morning because of an undersupplied network, but gains were capped by the expected onset of warmer weather and key fields returning to operation next week after maintenance work.

The UK gas network was undersupplied by 20 million cubic meters per day (mcm/day), or 12 percent of total supply, as Norway reduced flows and the Netherlands cut exports via the BBL pipeline to Bacton, England. Centrica's South Morecambe gas field in the Irish Sea also halted output.

Send-out from the Isle of Grain liquefied natural gas (LNG) import terminal fell to zero from nearly 30 mcm/day on Friday morning, further reducing supplies of gas to the UK.

However, demand for gas in Britain was 23 percent below seasonal norms at 185 mcm/day.

Gas for Monday delivery traded 0.2 pence higher at 54.25 pence a therm, while same-day gas rose by more than half a penny to 54.8 pence, chiefly because of the supply-demand imbalance.

The string of supply losses comes on top of the North Sea's summer maintenance programme, which has seen some offshore production platforms and beach terminals idled for repairs, though some are scheduled to return to service soon.

Flows into the Teesside PX terminal ceased at the start of the month, cutting 7 mcm/day of supply, but are expected back on Wednesday. Furthermore, a capacity cap imposed on LNG terminal output from the Milford Haven port in Wales is lifted on Sunday, potentially boosting supplies to the system.

"The prompt has been moderated by a pick up in temperatures, with August set to be warmer than average, and South Hook and Teesside both boosting supplies," one trader said.

But BP's Unity riser platform starts maintenance in August, resulting in a potential loss of 15 mcm/day. At the same time, Bacton Total will see a 10 mcm/day reduction in flows.

The benchmark front-season gas price rose, gaining 0.2 pence day on day to 63.2 pence, reflecting strengthening oil prices and a bullish prompt.

In Britain's electricity market, spot prices fell despite further lost nuclear output after EDF Energy took offline its 610-megawatt (MW) Heysham 1-1 reactor, adding to the 1,200 MW of output that was idled on Thursday.

Gas-fired generation rose five percentage points to 38.6 percent, grabbing share from coal and nuclear.

(Reporting by Oleg Vukmanovic; Editing by David Goodman)