# Dynamic Response of Drill Floor Considering Propagation of Blast Pressure Subsequent to Blowout
## 3 Blowout Explosion Analysis
### Dispersion and Gas Cloud after Blowout  
Gas cloud forms above or below the drill floor after blowout before ignition, and the corresponding sets of gas filling ratio and volume of flammable range are listed in Tables 2 and 3. The blowout scenarios are described in Tables 4 and 5. In this study, fifteen ignition points are included in the scenario for each gas cloud volume with the shape of cube. The ignition points are located at the center (1 point) and each corner (8 points) of gas cloud cube. On the center of each cube face, six ignition points are also positioned. Ignition is assigned at the designated point and propagates to the end of the gas volume. Figure 5a,b show the gas cloud with a concentration higher than 20% of Lower Flammable Limit(LFL) when gas is released from the center of the main well's rotary table on the drill floor at \begin{table}
\begin{tabular}{c c c} \hline \hline
**Ignition Points** & **Filling Ratio** & **Cloud Volumes** \\ \hline
1. Center of gas cloud (1 point) & 1. 50\% & 8450 m\({}^{3}\) \\
2. Corner of gas cloud (8 points) & 2. 40\% & 6760 m\({}^{3}\) \\
3. Center on surface of gas cloud & 3. 30\% & 5070 m\({}^{3}\) \\ (6 points) & 4. 20\% & 3382 m\({}^{3}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Blowout and explosion scenarios above the drill floor. Figure 4: Blowout location (**a**) on the drill floor and (**b**) under the drill floor. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**No** & \begin{tabular}{c} **Filling** \\ **Ratio (\%)** \\ \end{tabular} & \
\begin{tabular}{c} **Gas Cloud Dimension (m)** \\ **X** \\ \end{tabular} &
\begin{tabular}{c} **Volume (m\({}^{3}\))** \\ **Y** \\ \end{tabular} \\ \hline
1 & 50 & 26 & 20 & 16.25 & 8450 \\
2 & 40 & 26 & 20 & 13 & 6760 \\
3 & 30 & 26 & 20 & 9.75 & 5070 \\
4 & 20 & 26 & 13.34 & 9.75 & 3382 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Gas filling ratio and gas volume above the drill floor. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**No** & \begin{tabular}{c} **Filling** \\ **Ratio (\%)** \\ \end{tabular} & \
\begin{tabular}{c} **Gas Cloud Dimension (m)** \\ **X** \\ \end{tabular} &
\begin{tabular}{c} **Volume (m\({}^{3}\))** \\ **Y** \\ \end{tabular} \\ \hline
1 & 30 & 30 & 22.4 & 11.2 & 7553 \\
2 & 20 & 30 & 22.4 & 7.5 & 5022 \\
3 & 10 & 23.8 & 17.8 & 5.94 & 2516 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Gas filling ratio and gas volume below the drill floor. Figure 4: Blowout location (**a**) on the drill floor and (**b**) under the drill floor. full flow rate (150 kg/s), with 5.4 m/s wind blowing from the forward and aft directions, respectively. The simulation results imply that the released flammable gas is well vented without exposing the topside outside the derrick to the concerned level of concentration (>20% of LFL). Figure 6 shows the gas cloud with concentration higher than 20% of LFL when gas is released from the center of the telescopic joint where the inner barrel enters the outer barrel. The elevation of the leak point is assumed to be at the middle of the stroke, i.e., approximately 16.3 m below the drill floor level. The release is modelled to be upward as the inner barrel is above the outer barrel of the telescopic joint. The gas is released at full flow rate (150 kg/s), and 5.4 m/s wind blows from the forward direction. The simulation results imply that the released flammable gas is well vented without exposing the topside outside the derrick to the concerned level of concentration (>20% of LFL). According to the simulation result, the aft part of the drillship is engulfed by a gas cloud with concentration higher than 20% LFL. Explosion simulations were carried out, and snap shots for explosion over and under the drill floor are shown in Figure 7.  
Figure 5: Iso-surface with 20% LFLlower flammable limit (=0.682%) when gas is released on the drill floor with full flowrate and 5.4 m/s wind blows from (**a**) the forward (**b**) and aft directions.