As gas production from conventional gas reservoirs in the United States decreases, the industry is turning more to the exploration and development of unconventional gas resources (UGR), especially shale gas reservoirs. This trend is expanding quickly worldwide. Unlike in many mature North American basins, where resources and reserves are well characterized, the volume of unconventional gas resources is generally unknown in most basins outside North America (frontier basins). Therefore, a comprehensive investigation and evaluation of North American unconventional gas resources is significant not only for identifying and understanding the quantitative distributions of recoverable UGR in North American basins, but also for estimating the volume of UGR in frontier basins. Our investigation of North American unconventional gas resources is based on the resource triangle concept, which implies that all natural resources, including oil and gas, are distributed lognormally in nature. Martin et al. (2010) described a methodology to estimate values of total recoverable resources (TRR) for unconventional gas reservoirs. In their work, the authors combined estimates of production, reserves, reserves growth, and undiscovered resources from a variety of sources into a logical distribution. They used data from 8 basins in North America to demonstrate their results. We have expanded the work of Martin et al. (2010) to include data from a total of 25 basins in North America. The results show that the overall ratio of TRR in unconventional gas reservoirs to those in conventional oil and gas reservoirs in the 25 basins is approximately 4 to 1. This means that for every Tcfe of oil and gas produced from conventional reservoirs, one could expect another 4 Tcfe to be technically recoverable from unconventional gas reservoirs in the same basin. This observation can help companies assess the potential of unconventional gas resources development in North American basins and in frontier basins worldwide.

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