## 2 Geology of the Ulleung Basin and Simulation Approach
### Validation of the Geomechanical Model  
A number of geomechanical simulation studies have been conducted for UBGH2-6 site [12; 18; 25; 31; 32] (Table 2). These studies used a different simulator, such as TOUGH+HY DRATE with FLAC2D or FLAC3D. The observation point, production time and depressurization rate were also different among studies. Our simulation results were compared with other results for general comparative purpose. One-month production simulations were conducted with various bottomhole pressure conditions, for example, 3, 6, 9 and 12 MPa. Moreover, the observation point was set at the top of HBS, and the depressurization rate was not considered. For comparison with previous studies, the simulation results of this study are represented in Table 3 and Figure 8. The amount of vertical displacements in all cases rapidly increased and converged to a certain level (Figure 8). As the bottomhole pressure decreased, the final amount of vertical displacement increased. The final vertical displacement was between \(-0.47\) and \(-2.30\) m, depending on the bottomhole pressure (Table 3). The results of [PERSON] [31], [PERSON] et al. [12] and [PERSON] [32] could not be compared with this study because of the different bottomhole-pressure conditions. From the results of [PERSON] [31], we see that the vertical displacement was between \(-0.36\) and \(-0.67\) m; the results of [PERSON] et al. [12] showed \(-0.4\) m as a the vertical displacement. For the results of [PERSON] [32], the range of vertical displacement was between \(-0.78\) and \(-0.85\) m. In this study, our simulation results were compared with the results of [PERSON] et al. [25] and [PERSON] et al. [18]. The results  
Figure 6: Relative permeability curve [33]. Figure 7: Permeability model [34]. over 14 days of production time were similar to those of [PERSON] et al. [25] and [PERSON] et al. [18]. The vertical displacement value was between \(-0.36\) and \(-2.06\) m in this study, compared to between \(-0.8\) and \(-1.6\) m and between \(-0.63\) and \(-1.20\) m in [PERSON] et al. and [PERSON] et al., respectively. In particular, the value of this study was \(-0.85\) m, and that of [PERSON]'s study was between \(-0.85\) and \(-0.89\) m in the case of bottomhole pressure having 9 MPa. Therefore, we confirmed that our reservoir model and CMG reservoir simulator can appropriately predict geomechanical response. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Previous Research** & **Bottomhole** & **Depressurization** & **Production Time** & **Observation Point** & **Vertical Displacement (m)** \\ \hline \multirow{3}{*}{[PERSON] (2013)} & 4 & 0.27 & \multirow{3}{*}{31} & \multirow{3}{*}{Top of HBS} & \(-0.67\) \\ \cline{2-5}  & 7 & 0.23 & & & \(-0.48\) \\ \cline{2-5}  & 10 & 0.19 & & & \(-0.36\) \\ \hline [PERSON] et al. (2014) & 5 & - & 14 & Sea floor & \(-0.4\) \\ \hline \multirow{3}{*}{[PERSON] et al. (2014)} & 3 & & & & \(-1.6\) \\ \cline{2-5}  & 5 & & & & \(-1.47\) \\ \cline{2-5}  & 9 & & & & \(-1.1\) \\ \cline{2-5}  & 12 & & & & \(-0.8\) \\ \hline \multirow{3}{*}{[PERSON] (2015)} & 3 & - & 30 & Sea floor & \(-0.85\) \\ \cline{2-5}  & 7 & & & & \(-0.78\) \\ \hline \multirow{3}{*}{[PERSON] et al. (2019)} & 6 & 0.5 & & & \(-1.20\) \\ \cline{2-5}  & & 0.3 & & & \(-0.85\) \\ \cline{2-5}  & 9 & 0.5 & 14 & Top of HBS & \(-0.87\) \\ \cline{2-5}  & & 0.7 & & & \(-0.89\) \\ \cline{2-5}  & 12 & 0.5 & & & \(-0.63\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Vertical displacements in previous researches.