Most estimates of the resource endowment (original gas in place) reported for world unconventional gas start with Rogner’s 1997 "top-down" study. That global estimate is most likely quite conservative, since the oil and gas industry has discovered enormous volumes of shale gas around the world since the 1990’s. The data from these new reservoirs add substantially to our understanding of the unconventional resource base. Furthermore, the uncertainty of Rogner’s assessment was not quantified. Thus, a new assessment of original unconventional gas in place worldwide with considering the uncertainty is needed.
The objective of this project was to estimate the probabilistic distributions of original volumes of gas trapped in coalbed, tight sand and shale reservoirs, worldwide. To accomplish this objective, we reviewed published assessments of coal, conventional and unconventional resources and established the quantitative relationship between unconventional gas (coalbed methane, tight sands gas, and shale gas) and the conventional hydrocarbon (coal, conventional gas and oil) resource endowments for North America. Then, we used this relationship to extrapolate original unconventional gas in place, worldwide. Our assessment of the world resource endowment established an unconventional OGIP of 83,400 Tcf (P90)-184,200 Tcf (P10), which is 2.6-5.7 times greater than Rogner’s estimate of 32,600 Tcf.
Our regional assessments of unconventional OGIP should help industry better target its efforts to rapidly accelerate the development of unconventional gas resources worldwide. The methodology used to assess the distribution of each type of unconventional OGIP may be used to estimate unconventional gas resources at the country or basin level, knowing the coal in place and technically recoverable resources of conventional hydrocarbons.