Using Quaternary Reefs and Platforms as a Comparative Tool*
William F. Precht1 and Paul M. (Mitch) Harris2
Search and Discovery Article #50082 (2008)
Posted June 3, 2008
*Adapted from oral presentation at AAPG Annual Convention, Calgary, Alberta, June 16-19, 2005
1PBS&J, Miami, FL
2ChevronTexaco Energy Technology Company, San Ramon, CA ([email protected])
Exposures of Quaternary reefal limestones provide an excellent opportunity to evaluate carbonate platform history relative to high-frequency sea-level change. Detailed comparative studies of these reef systems from localities worldwide reveal a distinct and similar relationship between relative sea level history, sedimentary sequences, internal facies mosaics, and subsequent overprinting by fabric specific diagenetic alteration.
Reef complexes generally consist of discrete depositional stages (cycles or parasequences) that can be correlated within and between complexes. The complex stacking patterns observed between the individual cycles and systems tracts put facies with very different petrophysical properties in both temporal and spatial contact. Understanding the spatial context of facies within the sequences is essential to predicting porosity and permeability distributions across ancient carbonate platforms. Further analysis indicates that the diagenetic potential of the various facies and their position relative to sequence boundaries also control the heterogeneous reservoir properties observed throughout these reef complexes.
The exploitation history of many hydrocarbon bearing reef complexes of various ages from around the world underscores the significance of discerning reservoir continuity relative to individual cycles of deposition. Because of the ability to unravel relative sea level history in Quaternary reefs, their use as a counterpart for comparative studies makes them an invaluable tool for developing sound models for reefs through time and space.
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