Natural Gas

Overview

Natural gas working storage capacity increased by about 2 percent in the Lower 48 states between November 2011 and November 2012. The U.S. Energy Information Administration (EIA) has two measures of working gas storage capacity, and both increased by similar amounts:

• Demonstrated maximum volume increased 1.8 percent to 4,265 billion cubic feet (Bcf)
• Design capacity increased 2.0 percent to 4,575 Bcf

Maximum demonstrated working gas volume is an operational measure of the highest level of working gas reported at each storage facility at any time over the previous five years, according to EIA's monthly survey of storage operators. Working gas is the volume of natural gas in an underground natural gas facility available to be withdrawn, not including base gas.

The maximum demonstrated working gas volume is a practical measure of full storage. Filling storage, which requires compressors to inject the gas into the storage facility, becomes more difficult and expensive as storage volume nears its maximum and pressures inside the facility increase. That's why the demonstrated maximum is generally less than the design capacity, averaging 93% over the past two measurement periods (see Table 1), and why any given week's storage inventory is generally less than the demonstrated maximum. 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.

Working gas in natural gas storage fields in the Lower 48 states typically reach their peak levels during October to November each year. As a result, underground storage data for November 2012 in EIA's Natural Gas Monthly can be used to update EIA's estimate of demonstrated maximum working gas volume for 2012, calculating the total field-level maximum levels over the 60-month period ending in November 2012.

Table 1. Estimates of Underground Natural Gas Storage Capacity, as of November 2011 and November 2012 (billion cubic feet, unless otherwise noted)
	Demonstrated Maximum Working Gas Volume1		Working Gas Design Capacity2		Demonstrated Maximum Working Gas as Share of Working Gas Design Capacity
Region	(Dec 2006 - Nov 2011)	(Dec 2007 - Nov 2012)	Nov 2011	Nov 2012	Nov 2011	Nov 2012
East	2,210 R	2,202	2,300	2,300	96%	96%
Producing	1,391 R	1,448	1,466	1,522	95%	95%
Salt	339 R	371	344	407	98%	91%
Nonsalt	1,052	1,077	1,122	1,114	94%	97%
West	587	616	717	753	82%	82%
Lower 48	4,188	4,265	4,484	4,575	93%	93%
(1) Demonstrated maximum working gas volume is the sum of the highest storage inventory levels of working gas observed in each facility over the previous 5-year period as reported by the operator on the Form EIA- 191, Monthly Underground Gas Storage Report. The timing of the peaks for different facilities need not coincide. Estimates of demonstrated maximum working gas volume for November 2011 include a downward revision of 10 Bcf in the East region, because working gas volumes for storage fields that ceased operations within the previous 5-year reporting period (December 2006 -November 2011) were excluded from the estimate. Demonstrated maximum working gas volumes in the Producing region were revised downward by 7.5 Bcf, based on other methodological revisions. (2) Working Gas Design Capacity is an estimate of a natural gas facility's physical working gas capacity as reported by the operator on the Form EIA-191 Monthly Underground Gas Storage Report, and represents the sum of the results 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. R=Revised Data Note: Information for all facilities, including inactive fields is available in the Natural Gas Annual Respondent Query System. Totals may not equal sum of components because of independent rounding. Information about storage regions is available at Storage Basics. Sources: Form EIA-191, Monthly Natural Gas Underground Storage Report and predecessor surveys.

Between November 2011 and November 2012, increases in the comparative 5-year periods of demonstrated maximum working gas volume occurred in areas that, for the last year of each period, also had the largest increases in design capacity. In the Producing salt and West regions, demonstrated maximum working gas volume at facilities with increased design capacity rose 29 Bcf and 25 Bcf, respectively (Table 2). In contrast, fields without significant increases in design capacity posted gains of only 3 Bcf and 4 Bcf in the Producing salt and West regions, respectively. The Producing nonsalt region posted larger gains in demonstrated maximum working gas volume levels from greater usage of existing storage facilities than from expansions to design capacity.

Working gas design capacity is an engineering measure of the estimated maximum volume of working gas that physically can be stored in an underground facility given its design specifications, physical characteristics, compression equipment, temperature, and pressure. Growth in this measure between November 2011 and November 2012 was led by salt capacity additions in the Producing region, one of three regions used by EIA for reporting on gas storage, as well as growth in the West region (Table 1). New facilities completed in 2012 included the Ryckman Creek, East Cheyenne, and Princeton Field projects in the West region, and the Stratton Ridge salt dome in the Producing region. Design capacity for nonsalt storage facilities in the Producing region declined 8 Bcf during 2012 because of a downward adjustment in reported working gas capacity at the Clear Lake storage field following a change in ownership in 2012.

According to EIA's compilation of planned storage projects, another 71 Bcf of design capacity could be added in 2013 from projects that are reported to be currently under construction. This rough estimate includes 34 Bcf in the Producing salt and 37 Bcf in the West region. EIA has seen no reports of capacity that would be added in the East in 2013. This may be partly explained by readily available volumes of Marcellus Shale gas.

Table 2. Changes in Demonstrated Maximum Working Gas Volume Categorized by Design Capacity Expansion and Contraction Activity, November 2011 to November 2012 (billion cubic feet)
Changes in Demonstrated Maximum Working Gas Volumes at:	East	West	Producing	Salt	Nonsalt	Lower 48
Facilities with Increased Design Capacity	2	25	40	29	10	67
Facilities with Unchanged Design Capacity	-9	4	18	3	15	13
Facilities with Decreased Design Capacity	-1	0	-1	-1	0	-2
Net Change in Demonstrated Peak Capacity	-8	29	56	32	25	77
Note: Totals may not equal sum of components because of independent rounding. Sources: Form EIA-191, Monthly Natural Gas Underground Storage Report and predecessor surveys.