Arthur H. Saller
Meteoric diagenesis during subaerial exposure was important to the development and retention of porosity in many carbonate reservoirs. Concepts associated with sequence stratigraphy have made subaerial exposure and related unconformities more predictable. Tools for predicting subaerial exposure include seismic stratigraphy (identification of erosional truncation, onlapping strata, "lowstand" deposits), eustatic sea-level curves, variations in cycle thickness (Fischer plots), stable isotopes, and computer modelling of basins. These tools for predicting subaerial exposure and unconformities have been successful in many cases, but not in others.
Porosity associated with subaerial exposure is difficult to predict in frontier basins. Substantial reservoir porosity is present below some unconformities in some locations, but not others. Factors important to development and preservation of porosity associated with subaerial exposure include: (1) mineralogy, (2) facies, (3) duration of exposure, (4) burial history, and (5) dolomitization.
2. Porosity is commonly facies-selective in carbonates, even where porosity is associated with subaerial exposure. Grainstones subjected to subaerial exposure may have high porosity, but wackestones below the same unconformity surface have little porosity.
AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994