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The AAPG/Datapages Combined Publications Database

GCAGS Transactions

Abstract


Gulf Coast Association of Geological Societies Transactions
Vol. 48 (1998), Pages 275-288

Oil Exploration Analysis of Recent Carbonate Facies

Hugh J. Mitchell-Tapping

ABSTRACT

Recent carbonate sediments have been and are being studied by numerous researchers, but most of these studies have been directed towards gathering information on carbonate sedimentation processes, early diagenesis, sediment types and ecology. This study takes a different approach and looks at methods of analysis to develop carbonate sedimentation models that will aid subsurface exploration for ancient carbonate reservoirs and seismic stratigraphic interpretation. The subsurface exploration for stratigraphic carbonate traps is very difficult due to the complexity of diagenesis and distribution. By correctly interpreting the facies patterns and the relationship of one facies to another, the exploration success ratio can be improved. Sedimentary and ecological processes that form the rocks are considered more important than clastic-carbonate ratios or crystallinity of the end products. Therefore, the objective of this study was to investigate sediments from areas where the environmental factors control deposition and production. Analysis was performed on more than one hundred modern carbonate sediments from eight different environments to determine the mineralogy and trace element content, chemical composition, pore and grain size distribution, constituent composition, and hydrocarbon content. The analytical results showed that mineralogical composition indicated that aragonite is the most abundant mineral in all environments except island beaches, where calcite is the dominant form of carbonate. The mineralogy of adjacent environments is frequently quite different and this aspect could be used to define the boundaries of modern carbonate facies. The K, Mn, and Ba are either absent or have very low values in the clay-free carbonate bank environment. The amount of Zn, Sr, and Cu is relatively uniform in all environments, but the slight variations in the amount of copper from one environment appears to be significant and is related to the magnesium skeletal component in the sediment. The sands vary from very coarse to fine grained and have sorting values that ranged from very well to poorly sorted. Wide ranges exist in skewness and kurtosis with a considerable amount of internal variation and overlap within each environment. Large differences in the percentage composition of the constituents are found between one environment and another, and are sensitive to minor variations in the physical parameters of each area. As expected, the organic carbon and hydrocarbon content show high values in the interior shelf and near margin areas, lower values along the periphery of the shelf, with the low energy muddier sediments have the highest organic content.


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