Experimental study and numerical simulation on the influence of coating on liquid flow in the center tube of gas anchor

In the mid-to-late stages of gas drive production, the substantial intake of gas by the pump negatively impacts pumping efficiency. Gas anchors are employed for gas-liquid separation to enhance pump efficiency in oil fields. However, the gas separation performance of gas anchors is influenced by various factors. Their gas separation efficiency has inherent limitations. To overcome these challenges and improve pumping efficiency, innovative approaches are necessary. This study investigates the effect of coatings on liquid flow within the center tube of gas anchors using both experimental methods and numerical simulations. The results demonstrate that adding a coating to the center tube wall enhances liquid-phase flow. Mass production and water content increase progressively with the use of different coatings, in the following order: the original inner wall, nano coating, graphene epoxy coating. The minimum gas-liquid ratio corresponding to the lowest liquid production rate on the original inner wall is 250 m3/m3. The gas-liquid ratio corresponding to the lowest liquid production of the other two coatings is between 300–400 m3/m3. Concurrently, the pressure difference between the inlet and outlet of the gas anchor decreases. The pressure gradient with coating is 0.02–6.61 Pa/m lower than that of the original inner wall. Numerical simulations further reveal the fluid flow characteristics inside both the uncoated and coated center tubes. The presence of the coating reduces the intensity of fluid backflow and attenuates the pressure gradient changes. The difference in flow velocity between gas and water is between 0.003–0.004 m/s. The calculated dynamic viscosity suggests that the coating's influence on gas-liquid two-phase flow is primarily due to the complexity of flow direction induced by varying wall wettability. The dynamic viscosity of the fluid is closely tied to its flow velocity, impacting the system's frictional pressure loss. This study indicates that applying coatings to the center tube of gas anchors benefits liquid flow. It offers a new insights and guidance for enhancing pumping efficiency.