Study on Gas-Liquid Two-Phase Flow Law in Shale Gas Horizontal Wellbore

The gas-liquid two-phase flow is a production feature throughout the entire lifecycle of shale gas horizontal wells. Deepening the understanding of two-phase flow laws in wellbore is an important foundation for conducting dynamic analysis of shale gas well production and optimizing the design of horizontal well parameters. Based on the well types, inclinations, and production conditions of shale gas wells in southern Sichuan, a large-scale physical model experiment method considering the inflow of gas and liquid along the horizontal wellbore was established by using principle of similarity. And then, the gas-liquid two-phase flow in horizontal wellbores under different well types, inclinations, and gas-liquid production conditions was simulated. The research results show that there are significant differences in the two-phase flow laws and liquid-carrying capacity among different well types. For upward-inclined wells, due to the combined action of gravity and gas flow, the liquid inside the wellbore automatically flows towards the inclined section, exhibiting the strongest liquid-carrying production capacity. For horizontal wells, under the influence of gravity differentiation, the liquid phase inside the horizontal wellbore mainly exhibits stratified flow, and with the increase of gas flow rate, the liquid flow pattern transitions to wavy flow and agitated flow, resulting in a lower liquid-carrying production capacity. For downward-inclined wells, as the direction of gas phase acting on the liquid phase is opposite to the direction of gravity acting on the liquid phase, when the flow velocity of gas phase is low, the liquid phase automatically flows towards the toe under the influence of gravity, leading to liquid accumulation in the lower section of the well, and causing a larger pressure drop gradient and additional backpressure on the formation compared to upward-inclined and horizontal wells under the same gas and liquid flow conditions, which significantly affects gas well productivity and reduces gas well EUR. The research results can serve as a basis for optimizing gas well production allocation and drainage gas production processes.