Oil and Gas Resources of the United States: The 1995 National Assessment
*The U.S. Geological Survey has been conducting oil and gas assessments     for many years. The first one I know of was conducted in 1909 by David T.     Day. Other assessments will be conducted in the future. The scope of this     National Assessment is expanded to include unconventional resources that might     be produced from a well; gas from tight sands, heavy oils, coalbed gas, and     so on. Mineable hydrocarbon resources are not included. Also, the USGS will     examine reserve growth and its impact on our estimates.*- Dr. Donald Gautier,        U.S. Geological Survey   
  **The American public needs to know the extent of the Nation's oil and gas resources at any given time.**
Knowledge of oil and gas resources is needed for strategic planning, formulating economic and energy policies, evaluating lands in the purview of the Federal government, and developing sound environmental policies.  The U.S. Geological Survey (USGS), in collaboration with the Minerals Management Service (MMS), is the only independent body able to conduct such a study.  The USGS National Assessment is a dispassionate and scientifically-based analysis that is unencumbered by vested interest in the outcome.
**USGS scientists are developing hypotheses rather than conducting inventories of oil and gas resources, as the basis for preparing the National Assessment .**
The end result will be an estimate of the quantity of oil and gas yet to be discovered and recovered and of the past and future growth  in hydrocarbon reserves.  The Energy Information Administration however, conducts inventories of oil and gas reserves based on information supplied by industry interests.  The USGS approach to developing hypotheses about oil and gas resources is much like its approach to developing hypotheses about the nature of the Earth's interior or the far side of the Moon; best estimates are made with data and information available.  As new data and information become available, better estimates can be made.
**The USGS works with many Federal and State agencies and industry sources to gather relevant information.**
The USGS maintains primary responsibility for the assessment of all onshore lands (including Federal, State, private, and Trust lands) and all State offshore waters.  The MMS maintains primary responsibility for Federal offshore waters.  The USGS and MMS cooperate in those areas of responsibility that are geographically close, however the two agencies employ different techniques to develop their hypotheses largely because of differences in the types of information available.  For example, MMS has access to industry-confidential geophysical data used to develop prospects and relies heavily on this source of information to prepare its assessment.  The USGS relies primarily on geological interpretations of rock structure, organic geochemistry, and field and reservoir data in preparing its assessment.
**Play analysis is the basis for the National Assessment.**
The USGS used "play" analysis in the 1989 National Assessment, and since then MMS has adopted this method.  A play is a set of discovered or undiscovered oil and gas accumulations or prospects that are geologically related.  A play is defined by the geological properties (such as trapping style, type of reservoir, nature of the seal) that are responsible for the accumulations or prospects.  The beauty of play analysis is that it ties the statistics of oil and gas exploration and development to geologic expertise.
**The USGS is attempting through sophisticated models   to estimate the amount of hydrocarbons that will be available to humans from   unconventional resources over the next few decades.**
The USGS now includes unconventional (not generally economically recoverable using existing technology) oil and gas resources in its National Assessment and investigates complex properties of unconventional hydrocarbon reservoirs.  For example, USGS scientists know there is abundant gas in coal and in tight (low-permeability) reservoirs.  Scientists not only quantify the amount of resource in place, but more importantly, they estimate the amount of resource in place that will become available for human activity over a reasonable period of time.  A recent USGS study indicates that about 5,000 trillion cubic feet of gas is locked up in tight sands of the Green River Basin, yet only a fraction of it will ever be recovered for human activity.  By comparison, the total proved reserves of gas in the entire United States are approximately 200 trillion cubic feet.
**USGS studies indicate that much of the unconventional hydro-carbon resources is found on Federal lands.**
USGS studies focus on two issues_what portion of an unconventional hydrocarbon resource is recoverable, and how much of that resource is located on Federal lands.  In the lower 48 States, the amount of unconventional resources far outweighs the undiscovered conventional resources, whether on Federal lands or not.  Vast unconventional resources can probably also be found in Alaska, including tight sands, coalbed gas, hydrates, and heavy oils.  Although a large proportion of these Alaskan resources may be technically recoverable, the economics of their recovery put these resources out of reach.  Even most conventional gas accumulations in Alaska are not currently economically recoverable.  
**Results of recent USGS studies indicate that the phenomenon of reserve growth is much more important than previously believed.**
Over the past 15 years, USGS scientists have modeled reserve growth to arrive at some important conclusions.  For example, oil fields brought on line in the early part of this century continue to produce beyond original expectations.  This is partly an artifact of reporting of reserves and partly an enhanced understanding of reservoir heterogeneity and technological innovation.  Growth of fields affects a national assessment in two ways.  First, the reserve growth expected for existing fields may exceed all the undiscovered conventional resources in the United States today.  Second, this reserve growth enlarges the estimated undiscovered conventional recoverable oil and gas resources.  This growth must be accounted for or the National Assessment will be too low.
**Knowledge of unconventional hydrocarbon resources and reserve growth improves the ability to provide a rational basis for formulating energy and environmental policies.**
The USGS reports clear estimates of available oil and gas resources.  The National Assessment will describe the sources of oil and gas, where they are, what technology may be needed to recover them and at what price, and at what rate they can be withdrawn.  This more comprehensive view of the National Assessment will provide a new understanding of U.S. oil and gas resources.  Preliminary work suggests that the oil and gas resource base will increase, and that the relative amounts of oil and gas will change in favor of gas. 
For More Information:
Dr. Donald Gautier  Email: gautier@usgs.gov
March 1993