Methodology for Assessing Oil and Gas Potential in Extreme Frontiers
Ronald R. Charpentier
U.S. Geological Survey, Denver, CO
The recent U.S. Geological Survey (USGS) assessment of undiscovered oil and gas potential of the circum-Arctic required development of new methodologies appropriate to frontier areas. Many of the areas assessed are extreme from the standpoint of scarcity of geologic information, immaturity of exploration, and harsh development environments. More traditional assessment methodologies that rely on extrapolation of development history or well-understood petroleum system concepts are not appropriate.
The USGS circum-Arctic assessment was done at a scale of one or a small number of assessment units per basin, thus at a more aggregated scale than in many previous assessments. Because of the high technologic and economic constraints in these harsh environments, only relatively large accumulations were assessed. A minimum accumulation size of 50 million barrels of oil equivalent recoverable (MMBOE) was used in order to include small satellite accumulations that might be part of a development plan.
The estimation of probability of occurrence of large fields in assessment units of this scale was based on a study of exploration results worldwide. The study showed that probability of occurrence depends on geology, accumulation size, and size of area assessed. The base probability of occurrence for at least one accumulation of 50 MMBOE or larger in assessment units of this scale is approximately 50 percent.
For assessing numbers and sizes of accumulations in the circum-Arctic, the recently published USGS analog database was critical in that it related accumulation densities per 1,000 square kilometers and accumulation size distributions to geologic factors such as basin tectonic style and expected trap types. The analog database also provided realistic ranges of uncertainty for sets of analogs based on these geologic factors.
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