Uncertainty in USGS Estimates of Undiscovered Arctic Petroleum Resources
Ronald R. Charpentier
U.S. Geological Survey, Denver, CO.
In 2008 the U.S. Geological Survey (USGS) estimated undiscovered, conventional, technically recoverable oil and gas resources north of the Arctic Circle. All estimates were given as probability distributions. Because of the high uncertainties associated with frontier areas, the distributions are of even greater than usual importance compared to point estimates such as the mean values.
Many of the 69 areas assessed in the USGS Circum-Arctic Resource Appraisal (CARA) had low levels of exploration with few or no previous discoveries, and thus are not amenable to the use of appraisal methods such as discovery process models. Analog appraisal methods were therefore employed. An analog database was constructed based on the 246 quantitative assessments of undiscovered petroleum resources in the USGS 2000 World Petroleum Assessment. The database included information on numbers and size distributions of fields (discovered and estimates of undiscovered), petroleum compositions and properties, and geologic characteristics useful in choosing appropriate analogs. The quantitative methods used in calculating estimates were similar to those used in previous USGS assessments and relied on probabilistic estimates of overall risk, and numbers and sizes of undiscovered fields.
A study was conducted of basins worldwide and the probability of existence of fields of various sizes (risk). For assessment units roughly the size assessed in CARA, the probability of existence of at least one 50-million-barrel-equivalent (MMBOE) or larger field (the minimum size estimated for CARA) was estimated at approximately 50 to 60 %. Post-assessment review of the risks used in CARA show that, of the 69 assessment units, only 25 had a 50 % or more probability of at least one field of minimum size or larger. Thus, in general, the Arctic areas were considered to have less than the average world probability for existence of large fields.
Post-assessment comparisons showed that median field sizes for both oil and gas fields were comparable to those in the analog database, which is not unexpected as median field sizes do not vary much for groups of fields larger than 50 MMBOE. The largest undiscovered oil field sizes were comparable to those in the analog database, but the largest undiscovered gas field sizes were about 50 % larger. The ranges of largest undiscovered field sizes were less than the range of the entire analog database.
AAPG Search and Discover Article #90096©2009 AAPG 3-P Arctic Conference and Exhibition, Moscow, Russia