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Abstract: Models for Previous HitPredictingNext Hit Subaerial Exposure and Previous HitPorosityNext Hit in Carbonates

Arthur H. Saller

Meteoric diagenesis during subaerial exposure was important to the development and retention of Previous HitporosityNext Hit in many carbonate reservoirs. Concepts associated with sequence stratigraphy have made subaerial exposure and related unconformities more predictable. Tools for Previous HitpredictingNext Hit 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 Previous HitpredictingNext Hit subaerial exposure and unconformities have been successful in many cases, but not in others.

Previous HitPorosityNext Hit associated with subaerial exposure is difficult to predict in frontier basins. Substantial Previous HitreservoirNext Hit Previous HitporosityNext Hit is present below some unconformities in some locations, but not others. Factors important to development and preservation of Previous HitporosityNext Hit associated with subaerial exposure include: (1) mineralogy, (2) facies, (3) duration of exposure, (4) burial history, and (5) dolomitization.

1. In some locations, sediments with abundant depositional aragonite developed and retained Previous HitporosityNext Hit, whereas calcitic sediments did not.

2. Previous HitPorosityNext Hit is commonly facies-selective in carbonates, even where Previous HitporosityNext Hit is associated with subaerial exposure. Grainstones subjected to subaerial exposure may have high Previous HitporosityNext Hit, but wackestones below the same unconformity surface have little Previous HitporosityNext Hit.

3. Previous HitPorosityNext Hit may decrease with length of subaerial exposure. Long exposure often decreases matrix Previous HitporosityNext Hit, but enhances permeability.

4. Deep burial may obliterate Previous HitporosityNext Hit unless the rock has a rigid internal fabric that resists compaction or a buoyant subsurface fluid to retard compaction.

5. Dolomitization helps preserve Previous HitporosityNext Hit by decreasing burial-related compaction. The challenge is to predict which factors will be critical, and where Previous HitreservoirNext Hit-grade Previous HitporosityTop will be present.

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