Diagenetic processes controlling reservoir quality .Controlling factors of diagenesis are important for understanding the evolution of sediments through time.

1. Diagenetic processes controlling reservoir quality Controlling factors of diagenesis are important for understanding the evolution of sediments through time. The diagenetic processes strongly affected the quality of reservoirs. Petrographic studies of thin sections in this formation show that diagenetic processes have occurred in three environments including marine, atmospheric, and burial. Early processes happened in the marine environment, where there was water circulation between the marine environment and loose sediments. The most important diagenetic processes affecting the sedimentary facies of the Shurijeh Formation include marine cementation, bioturbation, early dolomitization, and anhydrite cement and nodules. 1. 1. Bioturbation Bioturbation is the disruption of sediments by the activity of animals and plants that modifies sediment physical properties. To understand the sedimentary environment of this process, one must examine the environment in which these organisms may be present. The presence and activity of these organisms depend on various factors such as sedimentation rate, the presence of nutrients and oxygen in the sedimentary environment. Therefore, whenever the sedimentation rate is lower and the nutrients and oxygen are higher, the amount of bioturbation in the sediments is greater [14]. The bioturbation process in the Shurijeh Formation is mainly observed in mud facies, fine grains, and dominant mud (Quartz-wack) (Figure 10). Bioturbation can have a positive or negative effect on reservoir properties, especially reservoir permeability [15]. What effect did this process have on this formation? Is it discussed further? 1. 2. Cementation Cementation is one of the most important diagenetic processes and is formed when the fluids inside the porous rocks are supersaturated. Cement composition and appearance features are two essential components in deducing the origin and reconstruction of the diagenetic history. [16]. The most common diagenetic process in the Shurijeh Formation is cementation. The different types of cements identified in the thin section studies include silica, calcite, hematite, dolomite, and anhydrite cements, which are discussed below. 1. 2. 1. Silica cement The silica cement in this formation was deposited in the early stages of burial. This cement has less expansion and frequency compared to carbonate cements. Figure 11 shows the quartz overgrowth cement. This cement is deposited in water-containing parts because silica is soluble in water but not soluble in oil [17]. Therefore, it can be concluded that the absence of this type of cement in sandstones can indicate the absence of a silica source or early migration of hydrocarbons into the formation [18, 19]. 1. 2. 2. Calcite cement Calcite cement was formed during the early diagenesis and burial as mosaic and poikilotopic crystals (figure 12. A). The sandstones of the Shurijeh Formation have been affected by calcite cementation, before deep burial and compaction, so in some parts, intergranular contact surfaces have been prevented. Cathodoluminescence studies on calcite cements do not show any zonation in the cements, but the yellowish-orange luminescence indicates that these cements were formed during periods of the relative stability of iron and manganese in pore fluids [12]. Calcite cement in the Shurijeh Formation sandstones was mainly controlled by the relative density of carbon dioxide and hydrogen ions in surface waters. The origin of this carbon dioxide was probably the oxidation of remaining organic matters in river sediments and local plants that existed in an arid to a semi-arid environment [12].