Shale-Gas Assessment: Comparison of Gas-In-Place Versus Performance-Based Approaches H. Stueck, 1,4 D. Houseknecht, 2 D. Franke, 1 D. Gautier, 3 A. Bahr, 1 and S. Ladage 1 Received 7 April 2015; accepted 20 August 2015 The recent interest in exploration for shale gas increases the demand for a reliable, com- patible resource assessment. Many different assessment methods are used, commonly depending on types and quantity of data available, which may lead to significantly divergent results for the same shale-gas play. This study compares results obtained using performance- based and gas-in-place methodologies to assess a well-developed and active shale-gas play (Woodford Shale, Arkoma Basin, USA) and two untested, hypothetical shale-gas plays (Shublik and Brookian, Alaska North Slope, USA). Results show that the two assessment methods produce comparable results when assessment units are identically defined and similar geological constraints are used as input parameters. Inherent uncertainties are associated with both assessment methods, and these are related to aspects of shale-gas production that are not well understood. The performance-based method relies on decline trend analysis to generate distributions of estimated ultimate recovery (EUR), and uncer- tainty increases in cases of short production history. The gas-in-place method requires the application of a recovery factor to estimate technically recoverable resources, and both absolute values of recovery factors and their spatial variability are poorly documented, and therefore a source of uncertainty. KEY WORDS: Shale gas, Shale-gas assessment, Gas-in-place, Performance-based assessment, Recov- ery factor, Alaska North Slope, Woodford Shale. INTRODUCTION The recent shale-gas boom in the United States (USA) has generated significant international interest in evaluating the potential for this uncon- ventional energy resource, starting in many coun- tries with an assessment of shale-gas resources. Different assessment techniques commonly are used depending on the data available. Largely because of the availability of well-production data in the USA, the U.S. Geological Survey (USGS) applies an assessment method that uses large sets of well-per- formance data. In other countries, where few shale- gas production data are available, different assess- ment methods, such as a volumetric approach (TNO 2009; Kuuskraa et al. 2011; EIA 2013), have been developed and applied. In general, different assessment methods may lead to strikingly different results. For example, the U.S. Energy Information Administration (EIA) estimate of PolandÕs Lublin Basin shale-gas resource was reduced from 44 trillion cubic feet (TCF; 1246 billion cubic meters, BCM) in 2011 to 9 TCF (255 BCM) in 2013 (EIA 2013). This significant reduction resulted mainly from the rigorous application of geological screening criteria, along with better understanding of structural complexity, and the resulting reduction of the prospective area by 80%. 1 Federal Institute for Geosciences and Natural Resources, 30655, Hanover, Germany. 2 U.S. Geological Survey, Reston, VA 20192, USA. 3 U.S. Geological Survey, Menlo Park, CA 94025, USA. 4 To whom correspondence should be addressed; e-mail: heidrun.stueck@bgr.de Ó 2015 International Association for Mathematical Geosciences Natural Resources Research (Ó 2015) DOI: 10.1007/s11053-015-9283-y