Geological Assessment Techniques

David A. White

What are the best geologic methods of assessing undiscovered petroleum potentials? For prospects, these methods are estimating probable trap-reservoir volume, if possible, with hydrocarbon fill fraction from analysis of oil and gas generated, migrated, and trapped; for plays (geologically coherent prospect groups), these methods are summing prospect assessment or evaluating future field numbers and sizes for the group; and for basins or regions, the best methods are summing play assessments. Methods such as delphi, subjective, probability, arbitrary analogy ratings, and basin volumes and yields are obsolete.

Play analysis is the key to any assessment. Play maps of the source, reservoir, and trap controls of oil and gas provide the best perspectives on prospect risking and main basin potentials. The most practical play approach, under the usual limits of time and data, is by grouped geologic field numbers and sizes. Play assessment at its best uses a prospect count and success ratio for estimating future fields, a field-size distribution tied to the largest undrilled prospect, and an evaluation of geologic risk.

Geologic play assessment has powerful advantages over purely statistical approaches. It spatially locates perceived areas of greatest success, it can provide estimates for subareas of special economic or environmental interest, and it is fully compatible with prospect summation. It applies to all exploration stages and knowledge levels, readily handles oil vs. gas, and is documentable, flexible, reproducible, and updatable.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.