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Numerical Investigation on Gas Accumulation and Gas Migration in the Wavy Horizontal Sections of Horizontal Gas Wells

Wavy horizontal sections are typically encountered in horizontal gas wells, which will result in gas accumulation on top of the wavy horizontal sections. This gas accumulation can be a problem and may trigger gas kick or blowout accident while tripping and pulling this gas into the vertical section. In this paper, a numerical model for gas accumulation and gas migration in the wavy horizontal sections of the horizontal gas well is developed; meanwhile, the gas accumulation and gas migration process is numerically investigated. The results show that the gas exhausting time in the wavy horizontal section increases with the increase of the wellbore curvature and the critical drilling fluid flow velocity for gas exhausting increases with the increase of the wellbore curvature. When the drilling fluid flow velocity is higher than the critical drilling fluid flow velocity for gas exhausting, no gas accumulation will occur. With all other parameter values set constant, the number of the wavy horizontal sections has a great effect on the gas-liquid flow pattern while it has little effect on the efficiency of the gas exhausting. This work provides drilling engineers with a practical tool for designing the drilling fluid flow velocity to avoid gas kick or blowout accident in horizontal gas well drilling.