In 1980, the National Petroleum Council (NPC)1 / published the most authoritative and comprehensive estimates to date of the technical and economic potential of tight sands gas.
While the NPC study remains the landmark effort on this subject, its estimates for recoverable natural gas are considered by many to be optimistic. The Gas Research Institute (GRI) and the Department of Energy (DOE) jointly commissioned construction of the Tight Gas Analysis System (TGAS) as a vehicle to perform systematic sensitivity analyses of the NPC study, to serve as a repository for future additions to the data base and analytical understandings of the technology, and to estimate the benefits of specified R&D advances. This paper describes TGAS briefly, demonstrates its reconciliation with published NPC results, and reports sensitivity analyses of:
Improved fracture effectiveness with and without closer well spacing;
Producing from gas-bearing lenses encountered by the wellbore versus lenses lying remote from the wellbore; and
Altering the NPC's assumptions about the relationship between reservoir permeability and thickness.
The reconciliation and sensitivity studies confirm the analytical integrity of the NPC study but also point out that the NPC's results contain significant uncertainties.