July 16, 2015

EIA now reporting monthly base gas levels in underground natural gas storage

---

With the release of the most recent Natural Gas Monthly, EIA began publishing base gas levels in natural gas storage facilities through the natural gas query system. Base gas plays an important role in underground natural gas storage, serving to maintain cavern or reservoir pressure and keeping natural gas storage facilities operational.

Because of the geologic properties of storage facilities, a certain level of pressure is required to maintain reservoir integrity and to withdraw gas for commercial use. This pressure is maintained by keeping a certain quantity of gas in the reservoir, known as base gas. Base gas is not typically withdrawn for commercial sale, because without it, storage fields can lose integrity, and in the most extreme circumstances they can even collapse.

Base gas requirements vary by field type, with salt facilities generally requiring less than depleted reservoirs or aquifers. In the Lower 48 states, only 30% of total storage capacity in salt facilities is base gas, whereas in nonsalt reservoirs, an average of 50% of capacity is base gas.

Salt facilities also offer more flexibility compared with depleted reservoirs. Because operators of salt facilities can sometimes temporarily remove base gas from the cavern, base gas volumes may not always match base gas capacity. For instance, as of May, base gas volumes in salt facilities equaled only 84% of base gas capacity. There may be several reasons for the difference between base gas levels and base gas capacity in storage fields, including:

• The cavern contains brine or liquids that can be pumped in and out, which displace natural gas volumes and reduce the need for base gas
• A recent facility engineering study has led to a new estimate of base gas in storage
• Base gas has been temporarily transferred out of storage to perform field testing or to meet customer demands
• A company prefers operating a field with a different volume of base gas for engineering reasons
• Base capacity metrics don't change until operations, accounting, and regulatory groups make a decision to officially change them

In addition to the recent addition of monthly storage data to the query system, EIA is planning to make other data collection and publication changes to enhance visibility into storage markets. Historically, EIA has divided the country into three storage regions: East, West, and Producing. EIA will divide the country into five storage reporting regions later in 2015, and they will be reflected in weekly, monthly, and annual storage reports.

Principal contributor: Michael Kopalek