Analysis Method For Dynamic Performance Of Gas Lift Valve

Gas lift valve (GLV) is the key component to send natural gas into well in the oil production. Its opening depends on the injection pressure and the production pressure. Under certain injection and production pressure, the stem position depends on the interaction between the flow in the chamber and the sliding rod in the valve. As efficiency and cost of the oil production is closely relevant to flux of the valve, it is an important issue to obtain the dynamic performance of GLV in the design and technology of gas lift.The coupling between the flow of gas and the displacement of valve stem is represented by the force of fluid flow acted on the stem, and the moving boundary conditions of flow field formed by the stem. The coupling analysis of the gas flow and motion of the valve stem is realized by FLUENT software and the development of its UDF (User Defined Function). Objective of the research is to establish a feasible and reliable procedure to calculate the flux and stem displacement under any injection pressure and production pressure. Then the effect of inner configuration and pressure drop between inlet and outlet can be simulated.A numerical simulation of fluid field is done by FLUENT software. Based on the method for unsteady fluid flow analysis, the simulation obtained a steady state solution after the transient process. An algorithm of fractional step on alternative analysis on solid and fluid domains is adopted to simulate the process for the stem to achieve its balanced position. Based on the pressure field obtained by simulation, it is proved that the stem displacement obtained by numerical simulation is more reliable than the result of empirical formulas.Two kinds of gas-lift performance test, Constant Production Pressure Test and Constant Injection Pressure Test, have been simulated. The operating mode in actual testing specifications is modified to fit the requirement of computation. It is proved that there is subsonic flow in the valve chest, and Laval nozzle effect is the cause of flux blockage in the gas lift valve. The simulation on steady model is made to solve in the fluid domain, too. A group of the comparison and validation is made. This research has demonstrated its value in the engineering application.