Aggregation Methodology for the Circum Arctic Petroleum Assessment
In May 2008 a team of U.S. Geological Survey scientists completed an appraisal of possible future additions to world oil and gas reserves from new fields discoveries in the Circum-Arctic. In this appraisal, 48 assessment units (AU’s) were identified as having at least a 10-percent chance of one or more significant oil or gas accumulations. The AU’s are mappable units of rock with common geologic traits. The distribution of resources within AU’s was determined by simulation from geologic inputs including expert opinion. The AU’s were aggregated to higher levels including the province level, total volume by resource categories, off-shore volume and off-shore volume by country. In some previous assessment, plays or AU’s were considered independent or totally dependent. This aggregation methodology incorporated perceived dependencies by asking assessors to specify pairwise correlations between AU’s for charge, rocks and timing. The specified correlations of high, medium or low were converted to numerical values. In addition, a lower level of correlation was specified to account for general geologic similarities among provinces and that induced by using a common assessment team. Elements of the three matrices were averaged and the resultant matrix checked for consistency. A biasing constant was added as necessary to ensure a correlation structure. An analysis was conducted to determine sensitivity of results to the specified values of correlations. The 48 AU simulation files were sampled from the bias adjusted correlation matrix (ACM) so that the correlation structure in the aggregation results reflected the ACM to within sampling error. Because the size distributions of oil and gas fields are highly skewed, sampling to achieve aggregation was based upon ranks of field sizes. The variables sampled were oil in oil fields and gas in gas fields. A review of results by members of the assessment team indicated that the aggregation achieved an appropriate level of dependency.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009