Construction and use of an analog database containing number and sizes of oil and gas accumulations

A database was constructed that contains information on discovered and undiscovered oil and gas accumulations to be used as analogs for the assessment of frontier areas of the world. In addition, the database can be used to investigate patterns of oil and gas occurrence. This analog database was used for the recent U.S. Geological Survey (USGS) circum-Arctic oil and gas assessment. Because many of the areas being assessed were frontier areas with no or few discoveries, discovery-process models were not applicable and some type of analog methodology was required. The database includes geologic information such as basin type, structural styles, trapping mechanisms, source rock characteristics, reservoir rock characteristics, properties of oil and gas fluids, and the number and size distributions of discovered and undiscovered accumulations for each of the areas assessed for the USGS World Petroleum Assessment 2000. These areas were divided into assessment units (AUs), of which 246 AUs outside the United States were assessed. These AUs include approximately 95 percent of the discovered oil and gas resources outside the United States. Numbers and sizes of discovered fields from the IHS Energy (1996 and 2006) database were aggregated for each AU. For the Western Canada Sedimentary Basin AUs, pool sizes from the NRG Associates Canadian database were used instead of field sizes. Although sizes and other information for individual discovered accumulations could not be released because these data are proprietary, aggregate data could be made publically available. Therefore, counts of discovered and undiscovered accumulations per size class (as of end of 1995) are provided for each AU. The standard USGS accumulation-size classes were used (that is, size classes of 1 to 2 million barrels equivalent (MMBOE), 2 to 4 MMBOE, and so on). Counts of undiscovered accumulations per size class were based on the mean estimates from the USGS World Petroleum Assessment 2000. Quantitative measures summarizing the size distributions were calculated. Some measures (density of accumulations per 1,000 square kilometers, median and maximum accumulation sizes) are dependent on choice of minimum accumulation size considered. For ease of use, these were pre-calculated for minimum accumulation sizes of 5 and 50 MMBOE, but such measures can be approximated for any other minimum. Measures pertaining to the accumulation distribution can then be related to geologic characteristics. The circum-Arctic assessment process indicates that number and sizes of accumulations are best assessed when compared to groups of analogs with similar tectonic styles and trapping mechanisms.