Conventional Gas Lift And The Ball Plugs, Single-tube Gas-lift Unloading Process Transient Numerical Simulation

Gas lift is one of the most widely used artificial lift methods in the world. At present, gas-lift designs are based on steady state flow, which normally can't obtain the same satisfying production performance as single-point gas injection, stable production and high efficiency. In fact, all gas-lift wells are put into production through a transient process of unloading. It is inaccurate to use steady state equations to approximate the inherently transient unloading process. Often, Continuous gas lift come forth the unstable and slipping loss serious phenomena. Pig lift launches the ball into the production tubing, in which form one length of gas column, one length of liquid column, and the ball acts as the gas-liquid solid interface. Thereby attain to be stable and to decrease slipping loss. In addition, it can lower backpressure of bottom hole, so improves recovery ratio. In order to design continuous gas lift and single tubing pig lift system, and accurately forecast unloading time and kickoff pressure, etc, the study simulates fully single-string pig-lift unloading process. The main study contents completed are as follows:1 The paper describes completely the unloading process of continuous gas lift and single-string pig lift, which are divided separately into single phase unstable flow, gas-liquid two phase transient flow, and gas injection with annular and production tubing, blowing, gas-liquid transient flow phase.2 Based on the theory of mass and momentum conservation, the study develops the governing equation of transient two phase flow, as well as continuous equation and motion equation, gas lift valve and the change of pipe diameter are considered. Based on the conservation of mass in annual, develops continuous equation and dynamic mathematical model to compute downstream pressure of surface gas injection valve. This study establishes a comprehensive mechanistic model for unloading process of continuous gas lift and single-string pig lift based on the conservation equation of mass, and momentum as well as closer relations.3 Mathematical model of two-phase unstable flow is a set of nonlinear-partial differential equations. This study establishes the numeric algorithm to solve nonlinear-partial differential equation group. The space derivative is made discrete with backward Euler differencing, and time derivative with centered space and backward differencing, then Newton Lafeison method is applied to solve the system of difference equation.4 Employed Visual Basic language in Windows, the above theory and method areformed by simulator, the software can simulate the unloading process of continuous gas lift and single-string pig lift. It may provide theory gists to design handling equipment and gas-lift stability analysis, and offer guiding opinions for field practice of single string pig lift. The simulator can be applied in guiding continuous gas-lift and single-string pig-lift design.The validation is made with the basic data of Long32 well in ShuNan Gas Field. By employing the calculation program of self-organized, the unloading process of continuous gas lift and single string pig lift are simulated. The physical parameters which affect the unloading process are analyzed, such as pressure, backflow ratio. The change of wellhead pressure, gas injection rate, liquid level in tubes etc vs time during the process of unloading is also simulated by the simulator. The study completes the contrastive analysis of Long32 continuous gas lift and single string pig lift unloading process.