* Planned maintenance may tighten supply
* Poor demand offsets impact of reduced supply
* LNG terminal output drops
LONDON, May 14 (Reuters) - British prompt gas prices sank on Monday due to ample supply and below-average demand but upcoming maintenance outages and cooling temperatures may drive gains later in the week.
Gas for Tuesday delivery dropped 1.35 pence to 58.50 pence per therm at 09:30 GMT chiefly due to an oversupplied pipeline network, with demand about 19 percent below seasonal norms.
Lower demand offset drops in liquefied natural gas (LNG) terminal output, which led a reduction in overall UK imports, and also cushioned the impact of reduced production from North Sea fields.
Maintenance at Norway’s Ormen Lange gas processing plant saw depressed flows via the Langeled pipeline - Britain’s main sub-sea import route - at 18 million cubic metres/day.
Ormen Lange is scheduled to remain out of action until Wednesday.
The mid-range Aldbrough storage facility began scheduled maintenance with immediate effect until May 27. This could tighten supply-demand fundamentals by reducing the UK’s capacity to withdraw gas held in storage, analysts from Point Carbon said.
“As Aldbrough is scheduled to be in maintenance, flexibility is somewhat limited,” the analysts said.
The UK’s biggest underground storage facility Rough was unavailable for injections and withdrawals for most of last week due to a technical problem, but resumed operations on Friday.
Total storage withdrawals are currently nominated at 11 mcm/day.
Britain’s Theddlethorpe receiving terminal is due for maintenance this weekend, removing a further supply source from the UK gas market.
Within-day gas fell nearly one penny to 58.60 pence.
The month-ahead contract dropped 0.8 pence to 55.67 pence.
Benchmark winter 2012 gas sank to their lowest point since January after failing to find support at the 68 pence per therm mark.
The contract’s 50 exponential daily moving average (DMA) value fell below its 100 exponential DMA on Monday and looks set to cross its 200 exponential DMA - key support levels - hinting at further downside.
The contract has been in a clear downtrend since late March.
Baseload power for 24-hour delivery traded on Monday at 46.85 pounds per megawatt hour.