Thomas S. Ahlbrandt¹

(1) United States Geological Survey, Denver, CO

ABSTRACT: Evolution of Modern Petroleum Resource Assessment

Assessment methodology over the past few decades has become increasingly sophisticated, more data intensive, and moved from an effort of small groups of experts to teams. Methodologies for assessing undiscovered resources have evolved from fairly general, basin wide, areal and volumetric yield estimates for only oil and gas through an evolution of statistically and/or geologically based approaches that incorporate more hydrocarbon commodities as well as ancillary data. Statistical methods, such as discovery process, or fitting to an idealized distribution (parabolic fractal, linear fractal or derived equation) that fits a field population are more useful in mature petroleum provinces. In addition to statistical data, frontier provinces and frontier plays in mature provinces require not only considerable geologic, geophysical and geochemical input but analogs. Such geologically based resource assessment techniques have evolved from basin level to play level and finally to petroleum system level. In a petroleum system assessment understanding the source, seal, expulsion, migration, reservoirs, and traps of hydrocarbons requires considerably more data and greatly increases the use of computers and specialists in many fields working together as a team. A comparison of methodologies utilizing the same dataset from the Neuquen Basin and from North African basins demonstrates the variability of estimates. Integration of geoscientific elements in the estimation process is deemed critical for modern assessments. The increasing importance of so called unconventional resources, such as basin-center gas or self-sourced oil reservoirs, have become an integral part of a petroleum system analysis. Future assessments of unconventional resources are also data intensive as a cell-based methodology is developed.

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