The Impact of Paleoclimate on Dolomite Reservoir Development in the Zagros and Persian Gulf Regions

Dolomite reservoirs flourished during arid climatic periods in the Middle East, primarily in the Permo- Triassic, Upper Jurassic, and Oligo-Miocene formations. These dolomitized reservoirs are frequently linked to evaporites, exhibit isotopically enriched signatures, and tend to occur predominantly in the more restricted regions of carbonate platforms. These observations strongly support their origin through sabkha and evaporative reflux processes. Consequently, dolomite formation and distribution are primarily influenced by early diagenetic processes and climatic conditions during arid periods. Dolomitization has exerted a significant influence on reservoir properties within the studied carbonate
platforms. Porosity distribution and variation are jointly controlled by several factors, including dolomite content, texture, crystal size, anhydrite abundance, dolomite cementation, and the extent of burial compaction. While dolomite textures can vary from fabric-preserving to fabric-destroying, the overall reservoir properties exhibit an ascending pattern from intertidal to shoal facies. This trend is primarily determined by the proximity to the source of dolomitizing brines. The downward percolation of brines, coupled with decreasing dolomitizing potential, leads to an increase in dolomite crystal size within depositional cycles as one moves further away from the anhydrite facies. Proximal areas, characterized by fine-grained intertidal and lagoonal facies, are more susceptible to anhydrite cementation and overdolomitization, resulting in significant porosity reduction. Conversely, in more distal regions, reservoir quality substantially improves, particularly in areas dominated by sucrosic dolomite or grain-rich facies. While this trend may be altered by compaction during burial, it
underscores the crucial role of dolomitization in preserving porosity, especially in deeply buried carbonate reservoirs