Abstract

The role of stylolites in the diagenetic evolution and resulting reservoir quality of an Upper Jurassic carbonate sour-gas reservoir, in Abu Dhabi, United Arab Emirates, was examined using petrographic, isotopic, fluid-inclusion microthermometric, and Raman spectroscopic analyses. Better reservoir quality in the crest than in the flank of the studied anticline is attributed to more common stylolites and particularly the higher amplitude of those in the flank. The preservation of reservoir quality in the crest is attributed to gas emplacement, which is considered to slow diagenesis, including limestone dissolution. Incipient stylolitization occurred during the initial burial stage (i.e., from deposition but before obduction of the Oman ophiolites) before gas emplacement across the anticline, and continued in the flanks of the anticline during a second burial stage (after obduction to current burial depths), but stopped or slowed in the crest. The presence of saddle dolomite, calcite, fluorite, and sphalerite cements, and of gas in fluid inclusions along stylolites, indicates that these have acted as conduits for fluid flow. Low δ18OVPDB values, high homogenization temperatures, and high salinity of fluid inclusions in these cements suggest that the fluids circulating along the stylolites were both hot and saline. Contrasting stylolite evolution between the crest and flanks of anticlinal structures in gas fields has significantly controlled the distribution of reservoir quality. Linking the history of stylolite formation and associated diagenesis to the tectonic evolution of carbonate successions improves the models constraining the impact of diagenesis on evolution of reservoir quality in foreland basins.

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