## 5 Conclusions  
Addressing the issue of possible formation of carbon dioxide (CO\({}_{2}\)) hydrates during CO\({}_{2}\) injection into subsea water zones for carbon storage, CO\({}_{2}\) injection into sandstone cores was investigated under dynamic conditions where a flow rate of 40 mL/min was maintained in a 2-inch diameter core to create a Darcy velocity of 0.0333 cm/s. The temperature varied from 0 \({}^{\circ}\)C to 5 \({}^{\circ}\)C. Analyses of experimental results allow for drawing the following conclusions:  
* The pressures required for forming CO\({}_{2}\) hydrates in dynamic conditions are much higher than those in static conditions. The reason is attributed to the disrupting effect of shear rate on the growth of hydrate crystals and the eroding effect of fluid  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Temperature** & \begin{tabular}{c} **Minimum Required Pressure for Hydrate** \\ **Formation Under Static Condition** \\ **(\({}^{\circ}\)C)** \\ \end{tabular} & \begin{tabular}{c} **Observed Hydrate-Forming Pressure Under** \\ **Formation Under Static Condition** \\ **(psi)** \\ \end{tabular} & \
\begin{tabular}{c} **Observatic Condition** \\ **(psi)** \\ \end{tabular} &
\begin{tabular}{c} **Pressure Ratio** \\ **(psi)** \\ \end{tabular} \\ \hline
0 & 145 & 365 & 2.50 \\
1 & 180 & 395 & 2.20 \\
2 & 220 & 450 & 2.05 \\
3 & 275 & 540 & 1.96 \\
4 & 315 & 595 & 1.89 \\
5 & 350 & 650 & 1.87 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Comparison between hydrate-forming pressure under static and dynamic conditions.  
Figure 8: Hindrance in gas hydrate formation (Top: Hindrance in growth of hydrate crystal; Bottom: Breakdown of hydrate film).  
flow on the development of hydrate films. Both hydrate-forming processes are well documented in the literature [13; 15; 16].
* As temperature decreases from 0 \({}^{\circ}\)C to 5 \({}^{\circ}\)C, the pressure required for forming hydrates under dynamic conditions decreases 2.50 to 1.87 times higher than that in static conditions. The reason why the pressure ratio decreases with temperature is not clear. It may be the fact that increased temperature promotes the internal energy of the hydrate-forming gas (CO\({}_{2}\) in this study) molecules in static conditions so that higher pressure is required for the water molecules to capture the gas molecules and trap them in water molecule cages. The mechanism needs more in-depth investigations.
* CO\({}_{2}\) injections into subsea water zones can be carried out smoothly as long as the injection pressure is controlled below the pressure required for forming hydrates in dynamic conditions. The required pressure at Darcy velocities other than 0.0333 cm/s should be investigated in the future.  
Conceptualization, B.G.; Methodology, M.T.I.; Validation, M.N.M.; Formal analysis, M.T.I.; Investigation, M.N.M.; Resources, B.G.; Data curation, M.T.I.; Writing--review & editing, M.N.M.; Supervision, B.G.; Funding acquisition, B.G. All authors have read and agreed to the published version of the manuscript.  
The authors are grateful to BIRD for funding the project \"Safe, sustainable, and resilient development of offshore reservoirs and natural gas upgrading through innovative science and technology: Gulf of Mexico--Mediterranean,\" through grant No. EC-19 Fossil Energy.  
Not applicable.  
The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.  
The authors declare no conflict of interest.