POLL-US natural gas stockpiles likely rose by 31 billion cubic feet last week

March 18 (Reuters) - U.S. energy firms likely added 31 billion cubic feet (bcf) of natural gas into storage last week as mild weather kept heating demand low, according to the average estimate in a Reuters poll released on Wednesday.

It is somewhat unusual for energy firms to add to stockpiles this early in March when utilities generally pull gas out of storage to meet heating demand.

The forecast for last week compares with a withdrawal of one bcf during the same week a year ago and an average decline for this time of year of 29 bcf over the past five years.

In the prior week ended March 6, utilities pulled 38 bcf of gas from storage. USOILN=ECI

If correct, the forecast for the week ended March 13 would increase stockpiles to 1.879 trillion cubic feet. That would be about 10.1% above the same week a year ago and about 2.3% over the five-year (2021-2025) average for the week.

The U.S. Energy Information Administration is scheduled to release its weekly storage report at 10:30 a.m. EDT (1430 GMT) on Thursday.

There were about 72 heating degree days (HDDs) last week, compared with a 30-year normal of 119 for the period, data from financial firm LSEG showed.

HDDs measure the number of degrees a day's average temperature is below 65 degrees Fahrenheit (18 degrees Celsius) to estimate demand to heat homes and businesses.

Reuters polled 11 analysts, whose estimates ranged from injections of 15 bcf to 50 bcf, with a median increase of 28 bcf.

Early estimates for the week ending March 20 ranged from withdrawals of 45 bcf to 74 bcf, with an average decrease of 62 bcf.

Those figures compare with an injection of 33 bcf during the same week last year and a five-year average decrease of 21 bcf.

Following is a list of poll participants. All figures are in billion cubic feet: