Centrica estimates point to low British gas stocks next winter

(Adds comment, prices, background)

By Nina Chestney

LONDON, Aug 4 (Reuters) - Britain could go into next winter with very low levels of gas stocks, according to estimates by Centrica Storage Limited (CSL (Other OTC: CMXHF - news) ) for withdrawals from its Rough gas storage site, published on Thursday.

Centrica (LSE: CNA.L - news) , which owns British Gas, one of Britain's largest energy suppliers, imposed restrictions in March last year on how much gas could be stored at Rough as a safety precaution after identifying potential issues with well integrity.

Following the investigations, Centrica shut down the facility for injections and withdrawals of gas in June this year and then said the outage would be extended until March or April next year.

However, it also said it hoped to be able to re-open at least four wells for withdrawal only by Nov. 1, 2016.

Based on four wells returning to service this winter, the site could have a maximum withdrawal rate of around 5 million standard cubic metres per day, CSL estimates showed.

This translates into 231 days to withdraw existing stock. If 20 wells were available for withdrawal, it would take 45 days to withdraw the existing stock.

Thomson Reuters (Dusseldorf: TOC.DU - news) gas analyst Cecile Langevin said from October 2015 to April this year (last winter's gas season), there was an average 13 mcm/d of net withdrawals from Rough, which accounts for 70 percent of the UK's storage capacity.

However, last winter was quite mild.

In the colder winter of 2012-13, an average 18 mcm/d was withdrawn from Rough, she added.

"Actual withdrawal rates achieved will be influenced by a number of factors including the characteristics of any wells actually returned to service, the ambient conditions, well performance and the pressure of gas on the National Transmission System in the vicinity of Easington," CSL said.

The number of wells that can return to service are still subject to CSL's investigation, the operator added.

Centrica's Easington gas terminal on the North Sea coast in Yorkshire, northern England, processes gas before it is sent into the UK's system to transport gas all over the country.

Britain's gas storage sites are currently around 48 percent full, data from Gas Infrastructure Europe shows.

"This is bullish for UK gas prices. The winter gas price could reach as high as 100 pence per therm if we have a very cold snap and liquefied natural gas or other sources do not come to our rescue," a trader said.

"It (Other OTC: ITGL - news) is not right that we go into winter with such low levels of storage," he added.

The winter 2016 gas contract was trading at 42.80 pence per therm at 1513 GMT, up 0.35 pence from the previous settlement.

Centrica document: http://www.centrica-sl.co.uk/sites/default/files/csl_withdrawal_curve_scenarios_040816.pdf

(additional reporting by Susanna Twidale; Editing by Alexandra Hudson and Susan Fenton)