Abstract: Horizontal well technology has been widely used as the main development technology in shale gas exploitation. Horizontal section of shale gas well has ultra-long, complex and changeable well trajectory. At the beginning of production, daily gas production and water production of gas well are large, and then daily gas production and water production rapidly decrease. Affected by many factors such as complex well trajectory, low gas production and low pressure, some gas wells have accumulated liquid in horizontal section. In order to solve the above problems, based on CFD simulation technology, this paper establishes borehole geometry model of typical horizontal section of wells, simulates and calculates gas-water two-phase flow characteristics and influence rules of upset structure in horizontal section under different operating conditions using Eulerian-Eulerian coupling Multi-Fluid VOF mixing method. The results show that with the increase of fluid flow rate, the liquid holdup curve of full borehole in horizontal section of upset structure fluctuates to varying degrees, and the concave point under borehole, At the uphill section of outlet, liquid phase is easy to fall back and causes accumulated liquid. The liquid accumulation height at the downhole of the well bore slowly decreases with the increase of gas flow rate, which can carry the liquid out of the well bore when the gas flow rate reaches 2.2 m/s. When the gas well is in low production period and the gas flow rate reaches the maximum 1.1 m/s, the liquid layer height is also more than half of the size of borehole inner diameter, and $h/D$ is about 0.55.

Key words: shale gas well, horizontal section, undulating feature, CFD, liquid holdup