Unconventional gas – A review of estimates

Mr Jamie Speirs, Imperial Centre for Energy Policy and Technology (ICEPT)

The future potential for unconventional gas production remains contentious, with questions over the size and recoverability of the physical resource being central to the debate. While interest has focused upon shale gas over the last three years, there is also considerable potential for coal bed methane (CBM) and tight gas to contribute to global gas supply. However, despite recent advances there remains considerable uncertainty over the size of recoverable resources for each type of gas, at both the regional and global level. This even applies to the United States, where the development of shale gas resources is relatively advanced. This paper summarises and critically evaluates the regional and global estimates of CBM, tight gas, and shale gas resources and compares these with current estimates of conventional gas resources.

The paper identifies a total of 56 studies providing original country-level estimates of unconventional gas resources, with 38 of these (70%) being published since the beginning of 2007. These estimates have been derived from a variety of methods and are presented in a variety of ways, which makes comparison between them very difficult. Hence the paper first explores the meaning and appropriate interpretation of the various terms and definitions that are currently employed, focussing in particular on the influential estimates provided by the United States Geological Survey (‘USGS’). It then presents the different regional and global resource estimates that have been produced, shows how these have increased over time, compares the results, highlights the variability in these results and the inadequate treatment of uncertainty and summarises the overall implications.

The paper concludes that shale gas may comprise some 30% of the global technically recoverable resource of natural gas. However, the main lesson is the wide variability and large uncertainty in current estimates, with many regions remaining entirely unexamined.