DOLOMITIZATION AND ANHYDRITE PRECIPITATION IN PERMO-TRIASSIC CARBONATES
AT THE SOUTH PARS GASFIELD, OFFSHORE
H. Rahimpour-Bonab+*, B. Esrafili-Dizaji*, and V. Tavakoli*
* Department of Geology,
+ Author for correspondence, email: firstname.lastname@example.org
Dolomitization and related anhydrite cementation can complicate the characterization
of carbonate reservoirs. Both processes have affected the Permo-Triassic Upper Dalan – Kangan
carbonates, the main reservoir at the South Pars gasfield, offshore
As emphasized in previous studies and confirmed here, dolomitization and anhydrite cementation, together with original facies type, are the major factors controlling reservoir quality in the Dalan –Kangan carbonates at South Pars. When associated with minor anhydrite cementation, replacive dolomitization has enhanced reservoir quality by increasing permeability. However, porosity in fabric-retentive dolomite was apparently inherited from the precursor rock and therefore reflects the original depositional environment.
Low-temperature dolomitization is commonly fabric-selective and partially fabric-retentive. Whole rock stable isotope thermometry indicates that fabric-destructive dolomites in the reservoir rocks formed at temperatures above 22ºC, whereas fabric-retentive dolomites and associated anhydrites formed in surface and near-surface conditions. Fabric-destructive dolomite or dolomite neomorphism post-date fabric-retentive dolomite and continued to form in deep burial conditions (~1400m). These observations may explain why fabric-retentive dolomite and anhydrite fabrics are traversed by stylolites.
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