Effects of Constant Pressure Boundary on Multiphase Flow Behavior in Horizontal Wells

Abstract

Abstract Multiphase flow behavior in a wellbore is inherently coupled with a reservoir, which is controlled by pressure boundaries. Most of the previous experimental studies in the laboratory have been performed at constant liquid and gas mass flow rates boundary conditions. This study experimentally compares the gas-liquid flow behaviors between constant pressure and constant mass flow rates boundary conditions in a toe-down horizontal well and investigates the effect of constant pressure boundary on the system stability. The experiments were conducted in a large-scale experimental facility to study the flow behavior in a toe-down horizontal well. They were performed at two different permeabilities for a constant pressure boundary (CPB) condition. Results were compared against experiments with constant mass boundary (CMB) conditions from different aspects, including outflow performance relationship (OPR), liquid holdup, and dynamic analysis. The experimental study on system stability was analyzed for three different operating conditions, namely, constant flow rate, constant gas liquid ratio (GLR), and constant liquid permeability. Similar tests were also studied using a numerical simulator. The results show that the time-averaged OPR and liquid holdup from constant mass and constant pressure boundary conditions match well. However, the amplitude of pressure and flow rate fluctuations are different, which causes the instabilities on the left side of the minimum of the OPR for high gas permeability reservoir at CPB conditions, where production persists for the CMB. The amplitude of pressure and gas rate fluctuation depends on reservoir permeability. It is found that the multiphase flow behavior in the wellbore for a constant mass boundary is closer to that for low permeability reservoirs, which commonly occur in shale plays. The total liquid inventory decreases as superficial gas velocity increases, and the fluctuations in superficial gas velocity have no evident impact on its behavior. Both experiments and numerical simulations show that system instability also depends on reservoir permeability. Stable production still exists on the left of the minimum OPR if the permeability is sufficiently low.