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.