Study on the migration of gas kicks in undulating sections of horizontal wells

Undulations are typically encountered in horizontal wells. Gas gathers at the top of undulating sections at low liquid velocity or well shut-in conditions. Thus, a gas slug is formed if gas kicks occur because of buoyancy, which makes well control more complex and difficult. In this paper, the storage and removal processes of the gas slug are simulated by experiments and the migration of the gas slug are analyzed. The results indicate that a minimum circulation velocity is required to remove the gas slug for a certain size and shape of undulating section of horizontal well. In addition, a migration model of gas kicks in undulating sections of horizontal wells is proposed based on the theoretical analysis. The model considers the effects of density difference, degree of curvature, surface tension, viscosity, and pipe diameter on gas slug removal rate and shows a good consistence with experimental results.