Numerical investigation of the effect of riser spacing on gas explosion from semi-submersible platform

Riser is one of the most essential components of a semi-submersible platform for deep-water natural gas exploration and development. A group of risers with specific spacing are configured between the platform drilling and accommodation modules. Once natural gas explosion occurs, the riser spacing could significantly affect the flame propagation and the subsequent maximum overpressures on the accommodation module. This study numerically investigates the effect of riser spacing on natural gas explosion from a semi-submersible platform. A 3D numerical model of gas explosion from a semi-submersible platform considering different riser spacings is conducted by using XiFOAM solver, and its accuracy was verified through previous experimental studies. 4 types of dimensionless riser spacings and 2 ignition points are numerically configured. The results demonstrate that smallest propagation speeds through the riser area and overpressure peaks on accommodation front wall are generated given the riser spacing equivalent to the riser diameter since the obstructed effect of this smallest spacing is larger than the acceleration effect by the induced between-riser vorticity field. Given the riser spacing 2 times of diameter, the vorticity field with larger intensity contributes to the flame front propagation, inducing the largest overpressure peaks. By further increasing the riser spacing, both the positive effect on flame propagation by the between-riser vorticity field and the overpressure peaks are on the accommodation front wall are reduced. This work provides theoretical support to design the riser layout to mitigate gas explosion on semisubmersible platform.