Effects of progressive dolomitization on reservoir evolution: A case from the Permian–Triassic gas reservoirs of the Persian Gulf, offshore Iran

Abstract

Dolostones are among the most important reservoir units within the Permian–Triassic Dalan and Kangan formations throughout the central Persian Gulf. In this study, petrographic and geochemical (carbonate carbon and oxygen isotopes) analyses led to the identification of several dolomitization phases from sabkha and hypersaline to burial diagenetic realms. An integration of the estimated temperatures of dolomites and their textural properties results in the differentiation of three thermal domains of dolomitization including low (LTD; < 30 °C), moderate (MDT; 30–50 °C), and high (HDT; > 50 °C) temperature dolomites. They are respectively associated with primary/fabric retentive and early micro-fabric destructive, late micro-fabric destructive, and fabric destructive (recrystallization) and saddle dolomites. Combination of petrographic, geochemical, and petrophysical results (core porosity and permeability, and pore-throat size distribution) shows a good correlation between the higher estimated temperatures of dolomites and progressive destruction of the primary depositional textures, larger crystal sizes, and higher porosity and permeability values. In general, the late micro-fabric destructive, wholly fabric destructive, and recrystallized dolomites led to the improvement of flow capacity in the studied intervals via increasing pore-throat size, decreasing tortuosity, and enlarging the crystal size.