Dolomitization is one major control on the reservoir quality of Arab -Asab carbonates. Overall, the dolomites have higher porosities and permeabilities than the limestones. Petrography and stable isotopic analysis reveal the presence of two types of replacive dolomite with different reservoir properties.

Type-I dolomite is finely crystalline, planar, and facies-controlled, occurring almost exclusively in sabkha, tidal flat and lagoonal sediments. Type-I dolomite occurs paragenetically early, and is interpreted as having precipitated from evaporitic brines generated within sabkhas and lagoons. δ¹⁸O values for Type-I dolomite are consistent with precipitation from a fluid with δ¹⁸O up to +4‰ SMOW (Jurassic seawater –1.2‰ SMOW) at temperatures between about 35º and 100ºC.

Neomorphism of early-formed dolomite could have occurred in a meteoric or mixed marine-meteoric fluid δ¹⁸O < -1.2‰ SMOW. Type-II dolomite is coarsely crystalline, non-planar, not facies-controlled, but aerially restricted. “Ghost” textures indicate that Type-II dolomite post-dates significant compaction, is paragenetically late, and precipitated from evolved brines at high temperature. δ¹⁸O values for Type-II dolomite are consistent with precipitation from a fluid with δ¹⁸O as high as +3.8‰ SMOW, at temperatures up to 140ºC (maximum burial temperature). Type-II dolomite is intimately associated with late-stage anhydrite. It is proposed that late-stage dolomitization and anhydritization were linked.

The permeability and total porosity of Arab-Asab dolomites are largely independent of primary (limestone) texture. In both dolomite types, permeability tends to increase with increasing porosity but, for a given porosity, Type-II dolomites tend to have the higher permeability.