Overview on Underground Storage of Natural Gas
Authors: Katz Donald L. , Tek M. Rasin 
Published: December 2007

Summary
Underground storage of natural gas is a mature industry vital to a gas delivery system. It developed as a subdiscipline of gas technology with certain additions. This overview treats containment of gas without migration, monitoring, inventory verification, retention of well deliverability, practice and advantages of delta pressure, aquifer behavior, and compressed air storage.

Introduction
Underground storage is the process which effectively balances a variable demand market with a nearly constant supply of energy provided by the pipeline system. Storage reservoirs are the warehouses to give a ready supply of gas that can serve a market with high peak demands in cold weather. The natural gas simply is injected into-underground storage reservoirs when market demand falls below the supply available from the pipeline. It is withdrawn from the storage environment to supplement the steady supply from the pipeline when the demand exceeds the supply. Through the years, underground storage has become a mature industry.For northern climates, storage gas represents about 20% of the annual sales - on a cold day, storage gas may reach 50 to 70% of gas sold. With a superb record of providing continuous fuel service to residences, hospitals, and commercial buildings, underground gas storage has been a vital part of natural gas distribution systems.
Historically, underground storage (which was practiced first in 1915) experienced a remarkable growth starting in 1950, resulting in nearly 7.5 Tcf (212 × 10 m) of storage in more than 399 pools in 26 states by 1979. Some gas storage literature covering developments over the years are listed in Refs. 1 through 12.

Current Status
The underground storage committee of the American Gas Assn. (AGA) compiles annual statistics for the industry. Fig. 1 shows the growth of the total quantity of gas in storage reservoirs and the quantity of working gas withdrawn in a given year. Table 1 gives AGA statistics on the reservoirs, facilities, and magnitude of certain parameters. Fig. 2 is the AGA map showing the location of storage projects. Although the annual volumes of gas distributed currently are not increasing and may even decrease in some areas as a result of conservation, the change toward a larger fraction of the gas going to spaceheating has a tendency to increase the need for storage.When the expensive synthesis gas from coal and pipeline-accessible gas from Alaska and Mexico arrive in the market, storage will become increasingly important. In the case of synthetic natural gas (SNG), storage will permit matching a variable supply to the variable demand of the markets.A brief history of the technical developments during the past 40 years is given next. Early field design procedures were adapted from natural gas production technology. A series of studies conducted during the 1950's resulted in (1) practices for more efficient use of the storage reservoir, (2) assurance that injected gas remained in the reservoir, and (3) ways to handle new problems as they arose. Some of our more recent activities are described in the following sections.
Development of Underground Storage Historical records show that gas storage began by allowing depleted gas reservoirs produced in the winter to be recharged in summer by pipeline gas. As the intercontinental pipeline systems spread rapidly in the postwar period, reservoirs were selected and refurbished for full use as underground storage reservoirs.
JPT
P. 943^