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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 71 (1987)

Issue: 11. (November)

First Page: 1440

Last Page: 1441

Title: Carbonate Facies and Reservoir Heterogeneity--The Value of Modern Analogs: ABSTRACT

Author(s): Paul M. Harris

Article Type: Meeting abstract

Abstract:

Secondary and enhanced Previous HitprocessingNext Hit of hydrocarbon fields requires a critical understanding of reservoir heterogeneity by both geologists and engineers. Carbonates have more varied facies and diagenetic patterns than their siliciclastic counterparts, thus offering a greater challenge to reservoir evaluation. This challenge is illustrated by American Petroleum Institute data showing average primary plus secondary recovery efficiencies of carbonate reservoirs of only 32% original oil in place. Studies of modern analogs are valuable because they constrain interpretations and lend predictability to unraveling facies patterns in reservoirs. These patterns help to understand the lateral continuity of

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stratification, variation within layers, heterogeneity, and performance of reservoir examples.

An appreciation of facies variability and depositional processes for carbonates can come from examination of modern environments of deposition. Common patterns in structural, textural, and diagenetic trends can be summarized from several modern settings for reefs and mounds, sand shoals, and lagoons and tidal flats. The lessons learned from detailed studies of modern examples center on several important points: (1) the trend and continuity of facies belts vary, but the patterns are orderly when the setting is understood; (2) typically, carbonate deposits form in localized ovoid or elongate thicks, not in widespread sheets; (3) the depositional systems contain complex, highly variable facies patterns in map view; (4) a predictable sequence of sediments, although not fully developed thr ughout the depositional environment, typifies the setting; (5) the stratigraphy as revealed by sediment coring is highly variable, recording a short-lived, but exceedingly complex geologic history; and (6) early diagenesis related to evolving depositional environments can significantly alter the porosity and permeability of the sediments.

Carbonate depositional systems, as shown by modern examples, are complex from the scale of a producing field right down to that of a pore throat. This fact, coupled with frequent Previous HitcontrolNext Hit by facies over subsequent diagenesis, imparts the great heterogeneity to carbonate reservoirs. Log response and reservoir Previous HitqualityNext Hit are directly related to facies and diagenesis, with varying grain size a major Previous HitcontrolTop over permeability amounts in porous intervals. Permeability affects recovery efficiency and thereby links the depositional facies through sediment texture to reservoir performance.

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