M.E. Henry¹, R.R. Charpentier¹

(1) US Geological Survey, Denver, CO

ABSTRACT: Comparison of Recent Natural Gas Estimates for the Western Canada Sedimentary Basin

Recent estimates for undiscovered gas resources of the Western Canada Sedimentary Basin vary by more than an order of magnitude. The Canadian Gas Potential Committee (CGPC) in 1997 estimated 122 trillion cubic feet of gas (TCFG) ("marketable potential"). The Canadian National Energy Board in 1999 estimated 176 TCFG ("undiscovered resources"). The U.S. Geological Survey (USGS), as part of its 2000 World Petroleum Assessment, estimated 15.6 TCFG ("undiscovered recoverable").

For the Mannville Group and related Lower Cretaceous undiscovered conventional gas reservoirs, the CGPC estimated 26.1 TCFG and the USGS estimated 4.6 TCFG. The CGPC considered pools as small as 0.016 billion cubic feet of gas (BCFG), whereas the USGS used a minimum estimated pool size of 3 BCFG. The amount of resource estimated by the CPGC in pools 3 BCFG or larger was somewhat more than 5.7 TCFG.

For the Devonian Leduc plays, the CGPC estimated 8.3 TCFG and the USGS estimated 3.2 TCFG, but in this case the CGPC estimated little resource (less than 1.6 TCFG) in pools smaller than 3 BCFG. The CGPC estimated that the largest undiscovered pool would be 4.2 TCFG (in place) and the USGS estimated the expected largest undiscovered pool size for these plays would be about 0.3 TCFG (recoverable). The largest discovered pool in these mature plays is 1.8 TCFG (in place).

Use of estimates of undiscovered resources in modeling future availability can be misleading if one only considers the "bottom line" of total resource. Such details as pool-size distribution are critical to potential deliverability of Canadian gas to the United States.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado