The capacity of underground natural gas storage facilities increased by about 2% from November 2011 to November 2012, the Energy Information Administration (EIA) said in a new report. The increase was seen in both demonstrated maximum and design capacities.

Demonstrated maximum working gas volume represents an operational measure of underground storage capacity, whereas the design capacity reflects an engineering measure of capacity. Demonstrated maximum working gas volume increased 77 Bcf from the level of the 2006-2011 period to the 2007-2012 period. Working gas design capacity increased 91 Bcf, to 4,575 Bcf between 2011 and 2012, according to the report.

Based on projects currently under construction, EIA estimated that another 71 Bcf of planned design storage capacity may be added to the grid in the Lower 48 in 2013. This includes 34 Bcf of salt dome capacity in the Producing region and another 37 Bcf in the West region, with no capacity expected to come online in the East region this year. “This lack of growth in natural gas storage capacity may be partly explained by readily available volumes of Marcellus Shale gas,” EIA said.

The maximum demonstrated working gas volume is a measure of full storage. Filling storage becomes more difficult and expensive as storage volume nears its maximum and pressures inside storage facilities increase, which is why the demonstrated maximum capacity is generally less than the design capacity, averaging 93% over the past two five-year comparison periods, and why any given week’s storage inventory is generally less than the demonstrated maximum, EIA said.

The maximum demonstrated volume provides guidance to operators and market analysts on the economics of filling the system. Last October, for example, when working gas in storage reached a record high of 3,930 Bcf, a simple calculation using the then-current maximum demonstrated volume (4,188 Bcf) showed storage to be 94% full, EIA said.

Storage capacity rose in most regions between November 2011 and November 2012, reflecting a mix of aquifer, depleted field and salt dome storage.

In the East region, design capacity was virtually unchanged at 2,300 Bcf, but the demonstrated maximum working gas volume for November 2011 fell by about 8 Bcf in the East region because the demonstrated maximum working gas volumes declined for some storage fields since the previous (December 2006-November 2011) comparison period.

In the Producing region, design capacity of facilities accounted for the biggest increase in net capacity of 56 Bcf. Increases took place mostly at existing facilities, with the largest expansions occurring at salt dome facilities in Mississippi and Louisiana. The demonstrated maximum working gas capacity for salt dome and non-salt dome facilities rose 32 Bcf and 25 Bcf, respectively, in the Producing region.

Three new facilities came online during the period in the West region.

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