# Feasibility Assessment of Acid Gas Injection in an Iranian Offshore Aquifer
## 3 Geomechanical Study  
When CO\({}_{2}\) is injected and stored in an underground geological structure, pore pressure buildup is inevitable. This change in pore pressure redistributes stress and induces a poroelastic response in both caprock and target formation. In some cases, this can lead to geomechanical hazards, such as leakage of the injected CO\({}_{2}\), uplift of the surface, and induced seismic activity. These issues are significant environmental concerns during CCS projects. It is also important to consider the integrity of the well, as the injected CO\({}_{2}\) could potentially leak through any well component intended to serve as the expected flow path. Uncontrolled release of the injected fluid can shorten well life and increase the risk of CO\({}_{2}\) leaks. Therefore, establishing an optimal CCS design that takes into account geomechanical hazards is critical to ensure environmentally safe implementation of the design and to gain public acceptance. A comprehensive geomechanical study has been conducted in the field using both 3D MEM (Mechanical Earth Modeling) calibrating with 1D MEM approaches, incorporating all available data. For 1D MEM construction, information such as formation tops, drilling and completion reports, location maps, graphic well logs, final geological reports, compressional and shear slowness data, open hole logs (including measurements such as gamma ray, density, neutron porosity, and resistivity), static formation pressure data from  
Figure 6: Empirical correlation for permeability vs. porosity using the literature—blue for carbonate, red for Dolomite. MDT/XPT (Modular Formation Dynamics Tester/Express Pressure Tool) tools, especially in the reservoir section, caliper logs, and core data. Afterward, the vertical stress was calculated based on the weight of overburden layers. In addition, a poroelastic horizontal strain model was used to estimate horizontal stresses' magnitudes in an anisotropic medium. In addition, the maximum horizontal stress direction was detected using full waveform acoustic data and a formation micro imager (FMI) log through the wellbore path. After finding the properties by using a proper failure criterion, mud weight boundaries can be determined, in which a safe mud weight window would be between breakout and loss limits [13; 17; 18; 19; 20; 21]. A 3D Seismic Cube is utilized to obtain volumetric data of subsurface properties, unveiling structural and stratigraphic details about the Earth's subsurface. The pre-stack inversion technique is applied to estimate properties like acoustic impedance (AI) and density from seismic data, with calibration and validation using core data and conventional well logs from two wells. Vertical Seismic Profile (VSP) data validate the density and AI values near the wells. Subsequently, constructed 1D MEMs for each well serve as references for 3D MEM construction. Integration of 3D seismic cube data, pre-stack inversion results, and 1D MEMs results in a preliminary 3D MEM, refined iteratively to match observed seismic data. The final 3D MEM visually represents the subsurface, aiding in structural feature identification and drilling target assessment, while considering uncertainties to gauge model reliability [13; 17; 18; 19; 20; 21]. The geomechanical model was employed to estimate pore and fracture pressures in the Surmeh formation (Figure 7). Drilling data were used to estimate the pore pressure specifically in this formation. Drilling data indicate that the lower portion of the Surmeh formation exhibits higher permeability, as evidenced by the mud loss data. However, the porosity in this area is very low, suggesting a higher degree of fracturing. Using the Geomechanical Earth Modeling (GEM) approach, the estimated pore pressure in the Surmeh formation is 3800 psi, while the estimated fracture pressure is 6100 psi. Seismic thickness mapping revealed that the integrity of the Hith formation caprock varies at the desired location for injection well drilling (Figure 8).