The U.S. Energy Information Administration (EIA) said underground natural gas storage capacity in the Lower 48 states grew 2% in 2013, due in large part to storage gains through salt domes in the Producing region and depleted wells in the West, but there was almost no growth in storage capacity in the East.

In a report issued last Friday, EIA said the two criteria it uses to assess underground gas storage -- demonstrated and design capacity -- had increased by 1.6% and 2.3%, respectively, between November 2012 and November 2013, the former measuring five-year periods that ended in those months. But the agency said it had also found "significant regional disparities" in capacity.

According to EIA, demonstrated maximum working gas volumes at salt domes in the Producing region increased 6.5% -- from 371 Bcf to 395 Bcf -- between five-year periods that ended in November 2012 and November 2013. During the same time frame, volumes increased 4.7% in non-salt storage fields in the West region (from 616 Bcf to 645 Bcf), and 1.3% in non-salt storage in the Producing region (from 1.08 Tcf to 1.09 Tcf). But EIA said volumes in the East region were unchanged, remaining at 2.2 Tcf.

Total demonstrated maximum working gas volume in the Lower 48 rose from 4.26 Tcf to 4.33 Tcf, an increase of 68 Bcf, for the five-year period that ended in November 2013.

"EIA's data on demonstrated capacity come from monthly surveys of storage operations," the agency said. "Storage peaks typically occur in October or November each year in preparation for the winter heating season; thus, November is a good month to take the measure of working gas actually injected into storage facilities. For demonstrated capacity, the reason for using a rolling period is to capture the actual peaks that likely would not occur simultaneously across all 407 active facilities."

In terms of working gas design capacity, EIA said volumes increased 10.3% in the Producing region's salt domes between November 2012 and November 2013, from 407 Bcf to 449 Bcf. During the same time frame, volumes increased 6.8% in the West (from 753 Bcf to 804 Bcf); 0.8% in the non-salt Producing region (from 1.11 Tcf to 1.12 Tcf); and 0.2% in the East (from 2.3 Tcf to 2.31 Tcf).

Working gas design capacity, as of November 2013, had increased 2.3% over the previous year, from 4.58 Tcf to 4.68 Tcf, an increase of 106 Bcf.

"Expansion projects led most of the 106 Bcf increase in design capacity for the Lower 48 states," EIA said. "Only two new fields began operations during 2013, together accounting for about half of the 50 Bcf year-over-year [y/y] increase in design capacity in the Producing region alone. Two expansion projects in the West accounted for 50 Bcf, or nearly all, of the y/y increase in design capacity in the region during 2013."

EIA said the demonstrated maximum working gas share of working gas design capacity fell between November 2012 and November 2013, from 93.2% to 92.5%.

The agency said most of the storage projects in the planning phase are salt dome projects in the Producing region and other facilities in the West.

"Completion of these storage projects in 2014 could increase design capacity by 63 Bcf, including 50 Bcf from facilities currently under construction," EIA said. "New salt facilities currently under construction in the Producing region account for 22 Bcf of the additional working gas capacity. In the West, completion of new facilities could increase design capacity by 28 Bcf. Expansion of existing facilities totaling 13 Bcf of new capacity also is planned for 2014."

EIA's Producing region includes eight states -- Alabama, Arkansas, Kansas, Louisiana, Mississippi, New Mexico, Oklahoma and Texas. The East region comprises 27 states -- all of the remaining states east of the Mississippi River, plus Iowa, Missouri and Nebraska. The remaining 13 states are in the West. EIA said working gas, which is the volume of stored gas available for use, is roughly balanced 50-50% between the East and the other two regions combined.