Plunger lift system simulation and process design
|School||Southwest Petroleum Institute|
|Course||Oil and Gas Field Development Project|
|Keywords||plunger lift efficiency liquid fallback afterflow design|
Plunger lift is an intermittent gas-lift method which using the plunger or piston as a solid interface between the expanding gas and the liquid slug helps prevent gas breaking through the slug and decreases liquid fallback. Gas stored in the tubing-casing annulus provides the energy required to lift the liquid slug and plunger. If the energy is not enough to lift the liquid slug and plunger, some high-pressure gas must be injected into well bore, which is named as plunger gas lift. The plunger and the liquid slug move upward driven by the gas expansion. With the liquid slug is produced to the surface, the producing pressure differential and the producing period increases. Plunger lift can take full advantage of reservoir energy to remove the accumulated liquids from the well bore and improve production, and major advantages over other artificial lift methods for lifting liquid are the relatively small investment and reasonable operating costs. It is used to produce high gas-liquid ratio oil wells or for unloading liquid in gas wells.For effectively designing and operating plunger lift system and grasping the changes of the plunger dynamics and tubing and casing pressure, the dynamics of the upstroke and after flow and buildup stage is simulated. The main work is as follows:(1) Based on the energy conservation equation, a model is presented, which can value the lift efficiency of plunger lift and intermittent gas lift and involves the friction and fallback loss. Using the model, a case is analyzed to compare the lift efficiency between them.(2) The mathematics model about liquid loss is established by using of the continuity and Navier-Stokes equations, which assumes that the fluid between plunger and tube travel along the beeline and axial symmetry.(3) There are three stages for each plunger lift cycle: upstroke, after flow and buildup. Considering the gas expansion behind the plunger and the transient behavior of the gas above the slug, the dynamic characteristic is analyzed by mass and momentum conservation equation and the dynamics model of plunger movement is made. The relationship among tubing, casing and bottle hole pressure is analyzed by use of mass conservation equation which assume a GLR had liquid accumulation only in the tubing during buildup.(4) After validating the feasibility of the plunger lift system model, combined the plunger lift data of literature, the main factors that affect plunger lift operation areanalyzed, which provide academic base for optimizing the plunger lift operation.(5) Maximizing production is the key to optimizing techniques parameters. The casing head pressure and afterflow time are studied to optimizing plunger lift operation.This validation is made with the basic data of Wei37 well. By employing the calculation program of self-organized, a cycle of plunger lift is simulated. The changes are simulated, such as tubing pressure, casing pressure, bottlehole pressure and gas production rate, length of liquid slug in the tube and acceleration, velocity and plunger position. Redesign some parameters of the well by the model.