Abstract: A Protocol for the Evaluation and (Semi-)Quantification of Secondary Migration Efficiency

David S. Muller

The concept of secondary migration efficiency is simple. It is, however, often under-analyzed, misunderstood, or misrepresented in our assessments of exploration opportunities.

The fundamental equation for determining migration efficiency is:

Migration Efficiency=(original change-migration loss)/original change

Secondary migration efficiency is trap specific. It is not synonymous with trapping efficiency, seal capacity, trap capacity, or exploration efficiency. Migration efficiency refers to that percentage of the "charge" leaving the source facies within a trap's fetch area that reaches that trap. The geometry of the fetch area for a given trap may vary through time.

The evaluation of migration efficiency begins with an estimate of the amount of oil expulsed from the source facies within the fetch area of the trap under consideration. Charge potential is a function of the "absolute potential" for hydrocarbon generation from the source interval(s) of interest, the kinetics of the source strata, their thermal and burial history, and the expulsion (primary migration) efficiency. These factors determine the "realized potential," and yield resulting from generation within and expulsion from the source strata (primary migration). Realized Potential = (Transformation Ratio) × (Absolute Potential) × (Expulsion Efficiency).

Potential types of migration loss should subsequently be evaluated. Four

principal categories of potential secondary migration loss are proposed. The migration loss categories are: (a) loss to the atmosphere; (b) loss to subsidiary traps en route; (c) loss as residual saturation within the void system of the migration pathway, and (d) destruction due to microbial or hydro-washing activity.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994