Common Terms
The following terms typically apply to all types of storage:
Balancing
A hub transaction in which a storage operator injects or withdraws a volume of gas so that a customer’s supply of gas at a pipeline delivery point is in balance with the customer's requirement to deliver gas at that point. The customer then receives or delivers the same volume of gas at a later time. Balancing volumes are typically expressed in MMBtu or dth.
Bcf
A billion cubic feet. It is the unit most commonly used to express the capacity of a natural gas storage facility in the United States.
Capacity (or Total Capacity)
The maximum volume of gas that can be stored in an underground storage facility. Capacity is expressed in some multiple of a cubic foot of natural gas, most commonly Mcf, MMcf, or Bcf. Total Capacity includes both Base Gas and Working Gas as described below.
Base Gas (or Cushion Gas)
The volume of gas that must remain in the reservoir to maintain adequate pressure to support deliverability in any type of reservoir and to preserve the integrity of the working capacity in salt caverns and aquifers.
Working Gas
Is equal to the Total Capacity minus the Base Gas. Working Gas is the volume of gas in the reservoir above the Base Gas requirements at any given time. Working Gas is the gas available to the market.
Cycling
Refers to the storage facility's ability to complete the injection and withdrawal of Working Gas. Traditionally reservoir storage has been designed to complete one cycle in each year, typically injecting gas when seasonal demand is low and withdrawing gas when demand is high. Recent trends, especially the increasing use of natural gas for power generation, have created the market for storage facilities capable of completing multiple cycles per year. Depending on the service level a customer selects, the Central Valley facility will be designed to be capable of cycling as many as 3.5 times per year.
Decatherm (dth)
A measure of the heat content of natural gas. A decatherm equals ten therms. Since a therm is equivalent to 100,000 British Thermal Units, a decatherm is equivalent to one MMBtu.
Deliverability
The capability of the storage facility to withdraw Working Gas from the reservoir for delivery into pipelines to serve the marketplace. Various terms that refer to deliverability are: delivery rate, withdrawal rate, or withdrawal capacity. Deliverability is typically expressed as a flow rate in units of millions of cubic feet per day (MMcf/d), millions of British thermal units per day (MMBtu/d) or dekatherms per day (dth/d). Conversely, the rate at which the facility can inject Working Gas into storage is referred to as the Injection Rate.
Hub Services
Refers to a number of services that might be provided by a storage facility. These services usually include Balancing, Loans, Parks and Title Transfers.
Injection Rate
The capability of the storage facility to receive gas into the reservoir from pipelines. It is also commonly expressed either in MMcf/d, MMBtu/d or dth/d.
Loan
Refers to a hub transaction in which a storage facility operator delivers gas from storage to a customer at the pipeline receipt point and the customer later injects the same amount of gas into the storage facility from the pipeline delivery point. Loan volumes are typically expressed in MMBtu or dth.
Mcf
Thousands of cubic feet. Depending on the exact heat content of natural gas, one Mcf is approximately equal to one MMBtu.
MMBtu
One million British Thermal Units. MMBtus express the heat content of natural gas.
MMcf
Millions of cubic feet.
Park
Refers to a hub transaction in which a customer injects gas into storage from a the pipeline delivery point and the storage facility operator later delivers the same amount of gas to the customer from the storage facility at the pipeline receipt point. Park volumes are typically expressed in MMBtu or dth.
Title Transfer
A hub transaction in which a change in the ownership of gas stored at the facility is recorded by the storage facility operator.
