This paper presents an analysis of the dynamic pressures imposed on the marine riser and diverter line during the gas removal from a riser-diverter system. The occurrence of formation gas in the riser may lead to a drilling accident known as "riser blowout" that can cause the collapse of the riser pipe in addition to the inherent risk of fire.

This analysis makes use of a numerical simulator, detailed in this study, that models the pressure and flow rate behavior in the riser-diverter system. The simulator is based on the numerical solution of a system of flow equations for a two-phase mixture moving upward in the riser-drill pipe annulus. The model accounts for the acceleration of the drilling fluid flowing ahead the two-phase mixture and the sonic flow at the diverter line exit.

In this paper, the approach of circulating a fluid through the lower portion of the marine riser to displace the gas up and inside the riser and diverter system is extensively investigated. Through a sensitivity analysis, the effects of pertinent parameters – especially the circulation rate – on the pressures generated inside the riser-diverter system during the gas removal process are discussed. Non-circulation situations are also studied.

You can access this article if you purchase or spend a download.