# Feasibility Assessment of Acid Gas Injection in an Iranian Offshore Aquifer
## 2 Case Study  
The proposed concept involves injecting the sour gas into the reservoir with the produced gas, which has a high H\({}_{2}\)S content of around 40,000 ppm. To make the gas suitable for commercial use, a sweetening process is necessary to remove unwanted components. However, the gas containing H\({}_{2}\)S, CO\({}_{2}\), and CH\({}_{4}\), which is not economically viable, must be disposed of properly. The disposal process ensures proper handling of gases that are not economically feasible for commercial use, while maintaining safety and environmental standards. Safety and environmental considerations for AGI encompass gas composition, adherence to safety standards, injection well integrity, environmental protection measures for emissions reduction and containment, compliance with varying regional regulations, continuous monitoring and reporting, closure planning, and public engagement when necessary. Specific references and standards can differ by region and may involve organizations such as the Environmental Protection Agency (EPA) (Washington, DC, USA), the International Organization for Standardization (ISO) (Geneva, Switzerland), and national/regional authorities. The study area selected for this research is located in the Persian Gulf, approximately 100 km from the Iranian shoreline and 120 km from the city of Bushehr. The geological features of this region include basal forces and salt diapirism, which have contributed to the formation of an asymmetrical dome structure with an east-west (E-W) trend [13] (see Figure 2). Figure 3 represents the stratigraphic column of the field. The Surmeh formation, as shown in Figure 3, was selected as a candidate for studying the feasibility of AGI. The upper part of the formation is primarily composed of dolomite, whereas the lower part consists mainly of carbonate rocks. The Surmeh formation has a total thickness of approximately 800 m, with both the upper and lower sections measuring around 400 m each. Based on the available log data (Figure 4), the porosity in the upper part of the formation is relatively higher (approximately 6%) and less permeable than the lower part (2.5%), where mud losses have been recorded due to the higher permeability. Figure 3: Upper Jurassic stratigraphy of the Surmeh reservoir and its equivalent in the southern part of the Persian Gulf [14]. Figure 2: Injection site location near Bushehr, Iran (red arrow). The conventional approach for determining the permeability coefficient has involved fitting data using the particle size gradient and soil porosity. Nevertheless, assessing soil porosity, obtaining samples at specific depths, and preserving the initial pressure during field sampling and laboratory testing present considerable challenges [15]. We present a graphical representation of porosity versus permeability, categorized into different groups based on varying degrees of dolomitization (replacive and cement types) within the carbonate rocks of the Arab Formation (depicted in Figure 5). The porosity-permeability relation for the Arab formation (Surmeh) [11] reveals that dolomitization exerts diverse influences on reservoir quality, resulting in considerable variations in both porosity and permeability. Additionally, this plot illustrates a notable positive correlation between porosity and permeability across the entire dataset. As previously mentioned, due to the lack of available permeability data, empirical correlation was used to incorporate permeability into the simulator for both carbonate and dolomite formations (Figure 6). Figure 4: Schematic representation of Surmeh formation in two wells (FA_02 and FA_03 of the injection field). Figure 5: Porosity–permeability relation for the Arab formation (Surmeh) [16]. Based on this correlation, the average permeability for the upper part of the Surmeh formation was estimated to be approximately 0.1 mD. The Arab formation in the Iranian zone corresponds to the Surmeh formation.