How Well Do We Know the Size of the U.S. Natural Gas Resource Base?

Abstract

Summary Published estimates of the U.S. potential gas resource base vary considerably in magnitude. However, one finds a general agreement that a large, accessible natural gas resource base exists that both backs up the current inventory of proved gas reserves and is available to make a larger contribution to the nation's energy supply. From a comparison of six such estimates by four industry and government organizations, this paper attempts to facilitate understanding of the differences in their (1) perceptions of the resource base, (2) data sources, and (3) analytical approaches. These differences lead directly to the differences in reported results. The apparent magnitudes of these differences diminish, however, on examination of the assumptions made by the organizations (particularly concerning the role of technology) and how they have defined the categories of assessed gas resources. Introduction The continuing decline in U.S. oil E&P activities has been partially offset by a generally brighter picture for natural gas. Projections by gas industry research organizations and trade associations indicate that gas consumption (predominantly supplied by Lower 48 drilling) will increase into the early part of the next century by more than 20%, from the current 20 Tcf to in excess of 25 Tcf/yr by 2010. This paper presents a comparison of six sets of estimates of the magnitude of the U.S. natural gas resource base, which were published between 1989 and 1995. The comparison examines potential gas resources and does not consider gas already classified as proved reserves. This paper intends to provide an unbiased look at the reported results and the methods used by each organization; consequently, no attempt has been made to select the "most accurate" or "correct" gas resource estimate. Estimation of any natural resource is a time-dynamic process. Because the process involves estimating the location and magnitude of an inherently unknown quantity, the accuracy of estimates may be considered limited by (1) our perception and understanding of the origin and occurrence of the resource, (2) the quality and distribution of available data from which to project our estimates, and (3) the tools that we use to facilitate the estimates. The effects and relative importance of these limitations change with time, particularly as our knowledge of the resource improves. In the case of natural gas resources, the types of resource assessed also change with time. The estimates compared in this report were published by the organizations listed in Table 1. Additionally, Enron Corp. has reported a single value (1,103 Tcf, net of reserves) for the total U.S. Appendix A summarizes the methods used by each organization and source documents. The comparisons presented here are subdivided into analyses of (1) the total potential gas resource base that is considered technically recoverable, (2) potential gas resources attributed to the lower 48 states and to Alaska, and (3) estimates of "conventional" and "unconventional" gas for the lower 48 states and for Alaska. A discussion also is included on the amount of gas considered economically recoverable for given wellhead prices according to two of the organizations.