Definitions, Sources and Explanatory Notes

 Category:   Natural Gas Exploration & Reserves
 Topic:   Shale Gas Proved Reserves


Key Terms Definition
Acquisitions The volume of proved reserves gained by the purchase of an existing fields or properties, from the date of purchase or transfer.
Adjustments The quantity which preserves an exact annual reserves balance within each State or State subdivision of the following form:

Adjustments + Revision Increases - Revision Decreases - Sales + Acquisitions + Extensions + New Field Discoveries + New Reservoir Discoveries in Old Fields - Report Year Production = Published Proved Reserves at End of Report Year

These adjustments are the yearly changes in the published reserve estimates that cannot be attributed to the estimates for other reserve change categories because of the survey and statistical estimation methods employed. For example, variations as a result of changes in the operator frame, different random samples or imputations for missing or unreported reserve changes, could contribute to adjustments.
Extensions The reserves credited to a reservoir because of enlargement of its proved area. Normally the ultimate size of newly discovered fields, or newly discovered reservoirs in old fields, is determined by wells drilled in years subsequent to discovery. When such wells add to the proved area of a previously discovered reservoir, the increase in proved reserves is classified as an extension.
New Field Discoveries The volumes of proved reserves of crude oil, natural gas and/or natural gas liquids discovered in new fields during the report year.
New Reservoir Discoveries in Old Fields The volumes of proved reserves of crude oil, natural gas, and/or natural gas liquids discovered during the report year in new reservoir(s) located in old fields.
Proved Reserves Proved reserves of natural gas as of December 31 of the report year are the estimated quantities which analysis of geological and engineering data demonstrate with reasonable certainty to be recoverable in future years from known reservoirs under existing economic and operating conditions.

Reservoirs are considered proved if economic producibility is supported by actual production or conclusive formation test (drill stem or wire line), or if economic producibility is supported by core analyses and/or electric or other log interpretations.

The area of a gas reservoir considered proved includes: (1) that portion delineated by drilling and defined by gas -- oil and/or gas -- water contacts, if any; and (2) the immediately adjoining portions not yet drilled, but which can be reasonably judged as economically productive on the basis of available geological and engineering data. In the absence of information on fluid contacts, the lowest known structural occurrence of hydrocarbons is considered to be the lower proved limit of the reservoir.

Volumes of natural gas placed in underground storage are not to be considered proved reserves.

For natural gas, wet after lease seperation, an appropriate reduction in the reservoir gas volume has been made to cover the removal of the liquefiable portions of the gas in lease and/or field separation facilities and the exclusion of nonhydrocarbon gases where they occur in sufficient quantity to reder the gas unmarketable.

For dry natural gas, an appropriate reduction in the gas volume has been made to cover the removal of the liquefiable portions of the gas in lease and/or field separation facilities, and in natural gas processing plants, and the exclusion of nonhydrocarbon gases where they occur in sufficient quantity to render the gas unmarketable.

It is not necessary that production, gathering, or transportation facilities be installed or operative for a reservoir to be considered proved. It is to be assumed that compression will be initiated if and when economically justified.
Revisions Changes to prior year-end proved reserves estimates, either positive or negative, resulting from new information other than an increase in proved acreage (extension). Revisions include increases of proved reserves associated with the installation of improved recovery techniques or equipment. They also include correction of prior report year arithmetical or clerical errors and adjustments to prior year-end production volumes to the extent that these alter reported prior year reserves estimates.
Sales The volume of proved reserves deducted from an operator's total reserves when selling an existing field or property, during the calendar year.
Shale Gas Natural gas produced from organic (black) shale formations.

For definitions of related energy terms, refer to the EIA Energy Glossary.


Energy Information Administration, Office of Oil, Gas, and Coal Supply Statistics.

  Explanatory Notes

  • Miscellaneous States includes Arizona, Illinois, Indiana, Maryland, Missouri, Nebraska, Nevada, Oregon, South Dakota, and Tennessee.
  • Data is based on shale natural gas proved reserves and production volumes as reported to the EIA by more than 1,200 operators. It does not include EIA-estimated volumes for the non-surveyed operators. For this and other reasons (e.g., incorrect or incomplete respondent submissions, respondent mis-identification of shale vs. non-shale reservoirs) the actual proved reserves and production of natural gas from shales my be higher or lower. The production estimates are offered only as an observed indicator of production trends and may differ from offical EIA production volumes listed elsewhere.
  • Shale production volumes are broken out separately for 2008 and 2009 but remain embedded in gas well volumes for prior years and 2010. Similarly, coalbed volumes, first broken out as a separate production category in the 2008 NGA, are included in gas well production totals for years prior to 2007 and 2010.
  • Related data and background information are published in the U.S. Crude Oil, Natural Gas, and Natural Gas Liquids Reserves Annual Report.