# Optimization of Offshore Saline Aquifer CO2 Storage in Smeaheia Using Surrogate Reservoir Models
## 3 Methodology
### Case Study Description and Its Numerical Model  
In Smeaheia, the Viking Group is the storage target, which consists of three shallow marine formations: Krossfjord, Fensfjord, and Sognefjord. Moreover, the flooding that occurred across the entire basin resulted in the deposition of mudstones in the Draupne formation, which served as the main caprock. The Troll Field wells prove the efficacy of the main caprock, which extends over the entire fault block. The storage complex is equipped with supplementary seal units made of limestone and shales from the upper groups. Tertiary and Quaternary sediments can also be regarded as having the ability to effectively seal. The gross seal spans approximately 750 m in width and 1200 m in length across the studied region. The primary seal is weakened in both the eastern and western  
Figure 3: The workflow implemented in this study. directions, parallel to the thinning of the storage from west to east. The Smeaheia storage site is located within the Troll Kystnauer fault block, specifically in the football of the Vette fault (VF) to the north and west, and in the hanging wall of the Oygarden Fault Complex (\(\mathcal{O}\)FC) to the east [50]. Smeaheia CO\({}_{2}\) storage is composed of Alpha, Beta, and Gamma prospects. As shown in Figure 4, the GN1101 seismic survey covers a large portion of Alpha and Beta (green zones), making them more dependable for examination. However, the Gamma zone, despite its enormous storage potential because of its expansion, is not as extensively surveyed. Smeaheia possesses a 3D numerical model with closed boundaries developed by Statoil [49]. This available 3D model consists of 1.5105 \(\times\) 10\({}^{6}\) active 3D cells with a 200 \(\times\) 200 m lateral resolution and 100 layers with a 1.6 m average thickness. The model exhibits significant heterogeneity, with porosity ranging from 0.13 to 0.17 and permeability ranging from 0.18 to 7103 mD. This study has preserved static properties like permeability and porosity in addition to the PVT model. A black oil fluid model is utilized to simulate the injection of CO\({}_{2}\) into a saline aquifer, with CO\({}_{2}\) density of 1.87 kg/m\({}^{3}\) and water density of 1026.03 kg/m\({}^{3}\) at surface condition (the model uses \"oil\" with brine characteristics instead of water). At a depth of 800 m, the reservoir's initial pressure is 81 bar. Additionally, rock compressibility is 4 \(\times\) 10\({}^{-5}\) bar\({}^{-1}\) at a pressure of 10 bar. The Eclipse data file of the model was regenerated in the SLB Petrel 2017.4 software [65] for further analysis, and ECLIPSE100 [66] was used as the numerical solver. The 3D numerical fluid flow model includes four virtual water production wells in the south and one in the north. These wells are used to induce depletion in the Smeaheia aquifer and Troll East field due to gas production from the Troll field. This depletion is facilitated by the hydraulic communication between the aquifer and the field. The wells commenced production in 1999 and will continue until 2060. At that point, three wells, namely WP1, WP2, and WP5, will be closed. Additionally, in 2122, WP3 and WP4 will also be closed. In addition, pore volume multipliers are present in both the southern and northern regions of the model. These multipliers are used to compensate for the undiscovered reservoir area and to align the pressure decline inside the aquifer. The simulation data file was first executed by the numerical simulator without taking into account pore volume multipliers. Figure 4: Smeaheia’s prospects location with respect to GN 101 survey [49; 64]. From January 2022, CO\({}_{2}\) was continuously injected over a period of 25 years at a rate of 5.872 \(\times\) 10\({}^{6}\) sm\({}^{3}\)/day through a well named Alpha-N. The movement of the CO\({}_{2}\) after injection was closely observed until the year 2300.