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1 Statoil, Stavanger, Norway, and Department of Geology, United Arab Emirates University, P.O. Box 17551, Al Ain, United Arab Emirates; sne{at}uaeu.ac.ae
2 Rosenstiel School of Marine and Atmospheric Sciences, University of Miami, 4600 Rickenbacher Cswy., Miami, Florida 33149; geberli{at}rsmas.miami.edu
3 Research Institute of Petroleum Industry, National Iranian Oil Company, P.O. Box 1863, Tehran, Iran
4 Research Institute of Petroleum Industry, National Iranian Oil Company, P.O. Box 1863, Tehran, Iran
Steve has a Ph.D. from the University of California at Los Angeles (1978). He has worked at Shell Development Company's Bellaire Research Center (1981–1985) and Statoil (1985–2005) and has recently begun teaching at the United Arab Emirates University.Gregor Eberli received his Ph.D.s from the Swiss Institute of Technology (ETH), Zürich, Switzerland, in 1985 and the University of Miami in 1991. With his colleagues at the Comparative Sedimentologic Laboratory, he conducts research in sedimentology, stratigraphy, geochemistry, and petrophysics of modern and ancient carbonates. In several projects, he investigated the influence of sea level changes on sedimentary architecture. He was an AAPG Distinguished Lecturer in 1996–1997 and a Joint Oceanographic Institutions/U.S. Science Advisory Committee Distinguished Lecturer in 1998–1999.
Keramati holds an M. Tech. degree and a Ph.D. in petroleum geology from Roorkee University, India (1990). He joined the Research Institute of Petroleum Industry in 1990 as a petroleum geologist and has led several research projects in petroleum exploration and reservoir studies. His area of interest is reservoir geology and characterization. He is currently the head of the Institute of Reservoir Studies at the Research Institute of Petroleum Industry.
Ali holds an M.Sc. degree in sedimentology (1994) from Azad University of Tehran and is a Ph.D. candidate in the Department of Geology at Shahid Beheshti University. He is a senior research scientist at the Research Institute of Petroleum Industry, working on carbonate reservoir characterization research. His major interests include carbonate sequence stratigraphy, depositional systems, and diagenesis.
Porosity and permeability data from five carbonate platform successions of different settings, ages, and burial depths are examined to identify overall similarities and differences in the reservoir quality of interlayered limestones and dolostones. Each succession consists mainly of limestone and dolostone, with subordinate proportions of intermediate, partly dolomitized compositions. In the three deeply buried platforms, the key features are that limestones have much lower average porosity than associated dolostones, and that limestones and dolostones show little difference in average permeability-for-given-porosity. In contrast, the shallowly buried platforms show little difference in average porosity between limestones and dolostones and also display higher average permeability-for-given-porosity in dolostones than limestones.
These data suggest the following general guidelines for depositional and diagenetic controls on reservoir architecture in carbonates consisting of interlayered limestone and dolostone.
(1) Reservoir compartmentalization by the formation of tight limestone barriers is largely a burial diagenetic process involving calcite cementation locally produced by chemical compaction. (2) Both the pattern of early dolomitization and the distribution of clay minerals (because they influence the localization of chemical compaction) are key factors that determine the distribution of tight limestone barriers separating flow units. Thus, the pattern of eventual burial compartmentalization follows a template that is hardwired into the stratigraphic architecture by depositional mineralogy and early diagenesis. (3) After burial (2–3 km; 1.2–1.8 mi), dolostones should not be expected to have higher permeability-for-given- porosity than associated limestones.
These rules assume dolomitization to occur early relative to chemical compaction, which will commonly be the case because of combined hydrologic and mass-balance constraints. Dolomitization and concentration of clay appear linked to cycle and sequence architecture in the present examples and thus may have a useful degree of predictability, at least in terms of statistical parameters, such as net/gross and probability of flow-unit thickness distribution.
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