Along with the trend that unconventional gas resources are significant in meeting the great energy demand, it is intuitively needed to know their quantified volume, especially for the frontier basins where little exploration of unconventional resources has been undertaken. Following by our work in standardized investigation and quantified evaluation of recoverable resources in 25 mature North American basins, this paper further employs two methods to evaluate TRR (Technically Recoverable Resources) for unconventional gas in frontier basins: Source Rock method (SR) and Conventional TRR Input method (CTRRI).
The source rock method derives from the fact that source rock potential is the mechanism for generating hydrocarbons. Thus, using the relationships between TRR and source rock factors, the SR can adequately capture TRR from the indirect source rock evaluation. Combined with the ratio of unconventional and conventional hydrocarbons from our prior investigations, the method can further deduce conventional resources and unconventional resource volumes. Different from SR that provides an independent measure of TRR, conventional TRR input method requires known recoverable conventional resources for frontier basin. To calculate frontier basin TRR volume, the frontier basins recoverable conventional volume is divided by the fraction of conventional resources in the similar reference basin from basin analog system investigation (BASIN). It is noted that all the quantifications are regulated by the unified definition from petroleum resource investigation summary and evaluation (PRISE). Although the two methods estimate TRR for frontier basins in different conditions, the initial tests on three basins show that estimates by CTRRI are in accordance with those by SR. The results validate the resource triangle concept with distributions of different resource types (i.e., conventional oil, conventional gas, coalbed methane, shale gas, and tight gas sand), and can be further evaluated by more complete estimation of North American basin resources and international unconventional gas resources.