Print this pageThe Importance of Quantitative Stratigraphic Modeling to Basin Modeling
MATTHEWS, MARTIN D., and MICHAEL J. ZEITLIN
Basin models are typically employed early in the exploration process, when
stratigraphy is loosely constrained by seismic 
interpretation
and wells rarely
penetrate into, or below, the source rock. These models are usually forced to
simulate stratigraphy at the formation level. Rock properties, however, are
commonly estimated at, or below, bed level and must be grossed up to the
formation level. This process is critical, and usually controls the model's flow
properties. Permeability may vary by 10 orders of magnitude within a formation.
Quantitative stratigraphic models are an excellent method of estimating
formation properties, because they predict internal geometric relationships
between depositional events. The translation of this information into
appropriate formation-scale properties is, however, difficult. Non-quantitative
techniques such as empiricism and analogues, border on self-fulfilling
prophesies. Quantitative techniques such as weighted averages are more
objective. Internal geometric relationships of the depositional events are
accounted for by the averaging technique (arithmetic, harmonic, or geometric). A
more elegant technique is the use of a power law [bulk property = (<sigma>X[i] *
P[i]{w}){1/w}, where X is the percentage of each rock type (i), P is the value
of a property of each rock type, and w is a geometric dependent variable between
plus and minus
one].
Quantitative stratigraphic models represent an excellent technique to estimate the most likely end member rock types present, their percentages, internal geometries, and relationships.