Overview

EIA estimates that the demonstrated peak working gas capacity for U.S. underground working natural gas storage for the Lower 48 states rose by 3 percent, or 136 billion cubic feet (Bcf), between April 2011 and April 2012. It then totaled 4,239 Bcf. Most of the increase came in the form of more use of traditional storage in the West (56 Bcf) and salt cavern storage in the Producing region (58 Bcf). Salt cavern storage allows rapid injection and withdrawal to respond to market conditions and other short-term events. Demonstrated peak working natural gas in the East rose by only 14 Bcf (less than 1 percent), but this small increase coincided with the rapid growth of production from the Marcellus Shale.

Estimates of Natural Gas Storage Capacity, as of April 2011 and April 2012 (Billion cubic feet, unless otherwise noted)
	Demonstrated Peak Working Gas Capacity1		Working Gas Design Capacity2		Demonstrated Peak Working Gas Capacity as Percent of Working Gas Design Capacity
Region	Apr-11	Apr-12	Apr-11	Apr-12	Apr-11	Apr-12
East	2,205	2,219	2,288	2,298	96%	97%
West	558	604	694	742	80%	81%
Producing	1,340	1,417	1,406	1,458	95%	97%
Salt	298	356	305	365	98%	98%
Nonsalt	1,042	1,060	1,101	1,093	95%	97%
Lower 48	4,103	4,239	4,388	4,498	94%	94%
Totals may not equal sum of components because of independent rounding. Note: 1) 'Demonstrated Peak Working Gas Capacity' is the sum of the highest storage inventory level of working gas observed in each facility over the prior 5-year period as reported by the operator on the Form EIA- 191M, "Monthly Underground Gas Storage Report." The timing for peaks for different facilities need not coincide. 2) 'Working Gas Design Capacity' is an estimate of a natural gas facility's working gas capacity, as reported by the operator on the Form EIA-191A "Annual Underground Gas Storage Report," and represents the sum of the result across all fields. It is a measure based on the physical characteristics of the reservoir, installed equipment, and operating procedures particular to the site that is often certified by Federal or State regulators. Information for all facilities, including inactive fields is available at: http://www.eia.gov/cfapps/ngqs/ngqs.cfm?f_report=RP7. R - Revised Information about storage regions is available at "Storage Basics." Sources: Form EIA-191M, "Monthly Natural Gas Underground Storage Report" and Form EIA-191A, "Annual Natural Gas Underground Storage Report."

Working gas design capacity increased 110 Bcf in the lower-48 States from April 2011 through April 2012. The largest increases occurred in the Producing region, where working gas design capacity increased 52 Bcf, or nearly 4 percent since 2011. Capacity additions in the West region posted relatively larger year-on-year increases, rising nearly 7 percent, or 48 Bcf.

Increases in working gas design capacity since April 2011 resulted from the completion of four new storage facilities in addition to approximately 50 expansion projects. Four new storage facilities accounted for nearly 38 Bcf of the year-on-year increase in working gas design capacity, and the remaining 72-Bcf increase in design capacity resulted from other storage expansion projects. In the West region, working gas design capacities of 2 new facilities totaled nearly 23 Bcf, and other net increases in working gas design capacity totaled about 26 Bcf. Expansions in the Producing region included the completion of two new salt dome facilities with working gas design capacity of nearly 15 Bcf, in addition to net working gas design capacity additions at existing salt dome facilities totaling about 45 Bcf. Non-salt dome facilities in the Producing region posted a net decrease of nearly 8 Bcf as a result of reductions in capacity and other adjustments, since April 2011.

Demonstrated peak working gas capacity relative to design capacity has increased in each of the regions since April 2011. This pattern of growth occurred because growth in capacity utilization outstripped growth in capacity. In fact, this dynamic resulted in the 2012 demonstrated peak capacity in the Producing region exceeding the working gas design capacity reported last year at this time, as a significant amount of the newly available storage capacity has already found considerable usage.

Demonstrated peak working natural gas capacity as a percentage of working gas design capacity is lower in the West region than the East and Producing regions for several reasons. The West region has several still-active fields whose primary role is not seasonal storage. These include fields used for pipeline load balancing and fields that are being drawn down to be taken out of service. Also, some fields in the West region have large design capacities, but have infrastructure constraints such as limited pipeline and compression capacity that limit actual storage utilization and peak capacity.

The status of several previously inactive natural gas storage fields changed since April 2011, with differing impacts on working gas design capacity. The Pecan Station storage field, in Texas, resumed operations in 2012, contributing about 1 Bcf to the year-on-year increase in working gas design capacity, since being categorized as an inactive storage field in April 2011. Two other previously inactive storage facilities were removed from the Natural Gas Annual Respondent Query System for 2012, because they are no longer being operated as natural gas storage facilities. The remaining base and native gas volumes in Brown's Creek and Lake Facilities, in West Virgina, are being withdrawn and reported as natural gas production. The removal of these fields from the query system does not affect working gas design capacity or peak storage estimates in 2011 or 2012.