Can you explain exactly what the USGS assessed in its 2011 oil and natural gas resource assessment for the Marcellus Shale?
During 2010 and early 2011, the USGS examined the Devonian Marcellus Shale in the Appalachian Basin of the eastern United States using the National Oil and Gas Assessment (NOGA) methodology for continuous resources (see for articles explaining this methodology). In order to have comparable results, we have used the same USGS methodology for assessing continuous petroleum resources since 2003.
The relevant publications that provide background information on the methodology we used in the Marcellus assessment are as follows:
U.S. Geological Survey Assessment Concepts for Continuous Petroleum Accumulations (chapter 13 of Petroleum Systems and Geologic Assessment of Oil and Gas in the Southwestern Wyoming Province, Wyoming, Colorado, and Utah, U.S. Geological Survey Digital Data Series DDS–69–D)
U.S. Geological Survey Input-Data Form and Operational Procedure for the Assessment of Continuous Petroleum Accumulations, 2002 (chapter 18 of Petroleum Systems and Geologic Assessment of Oil and Gas in the Southwestern Wyoming Province, Wyoming, Colorado, and Utah, U.S. Geological Survey Digital Data Series DDS–69–D)
Analytic Resource Assessment Method for Continuous Petroleum Accumulations—The ACCESS Assessment Method (chapter 22 of Petroleum Systems and Geologic Assessment of Oil and Gas in the Southwestern Wyoming Province, Wyoming, Colorado, and Utah, U.S. Geological Survey Digital Data Series DDS–69–D)
Klett, T.R., and Charpentier, R.R., 2003, FORSPAN Model Users Guide: USGS Open File Report 03-354, 37 p.
Application of the USGS resource assessment methodology results in a statistically based estimation of technically recoverable, undiscovered resource volumes for the unit studied. The assessment model provides a means to estimate quantities of undiscovered oil, gas, and natural gas liquids (petroleum) in accumulations that have the potential to be added to reserves. For purposes of this model, undiscovered petroleum is that which is postulated from geologic knowledge and theory to exist outside of known accumulations, and which resides in accumulations having sizes equal to or exceeding a stated minimum volume. Undiscovered petroleum volumes include initial accumulation sizes as they are perceived at the time of discovery, as well as any reserves anticipated to be added as these discoveries are developed and produced.
The assessment model does not attempt to predict volumes of petroleum that will actually be discovered in a given future time span. To do so would require full knowledge of future petroleum economics and exploration technologies, and the extent of exploration effort that will be conducted in the area being assessed. Rather, the assessment model is used to estimate volumes of petroleum having potential, from a geologic standpoint, to be discovered over some undefined span of time.
Thus, we conduct assessments on undiscovered, but technically recoverable resources - that is, technically recoverable with today's technology and industry practice (we assume no future technological developments).
The Devonian Marcellus shale as examined during our assessment is that volume of rock that has been shown by geological study to be a relatively continuous volume of strata of the same age and having generally the same rock properties that extends from New York to Tennessee and Ohio to Virginia and Maryland. The extent of the Marcellus as included in the assessment is shown on Figure 1 of USGS Fact Sheet 2011-3092 The assessment did not include any other shale units such as the Ordovician Utica shale or the other Devonian shales which are gas productive (Ohio, Huron, Chattanooga). The Marcellus assessment area is divided into three assessment units, which encompass three geographic areas of similar rock properties, all of which make up the Marcellus shale. These three units are described in the Middle Devonian Marcellus Shale 2011.
The USGS used publically available information from over 4300 wells as of March 17, 2011, producing from Marcellus reservoirs in West Virginia, Pennsylvania, and New York.