| Pig lift that uses a U-shaped double completion string in the well bore (one for injection, the other for production)is a new efficient method .By launching the ball into the injected gas, it can form the steady slug flow and prevent liquid to fall back because of the solid interface between gas and liquid phases. Thus, it can improve the instability of gas lift, and reduce the slippage between gas and liquid phases thereby, increase lifting efficiency. It can be the alternative method for the upper continuous gas lift and enhance the ultimate recovery. It has more important scientific significance and great application future especially for low pressure and low penetrability gas&oil reservoir.The main study contents are made in the aspects of basal theory and application of new Pig Lift are as follows:1. A mathematics model that can value the lift and energy loss efficiency is presented and using this model, the main factors that affect the lift efficiency are analyzed deeply.2. The mathematics modelis established, which can calculate the pressure down when there is slippage between gas and liquid. By employing software Winsurf ,the three dimension figure is drawn, which reflects the relation among slippage loss , liquid production and total gas production. Factors that affect the slippage pressure loss are compared and analyzed synthetically. It can supply academic base for work such as selecting suitable well and admeasuring reasonable gas volume when pig lift is applied on the spot.3. A deep study of the mechanism of gas-liquid-ball three-phase flow is made. Considering the separate process of gas and liquid, the dynamic numerical simulation theory and method in gas-liquid-ball three-phase flow of Pig Lift system is advanced. Sensitive analysis of the frequency that we cast lift ball is made, which is significant for optimizing the technical design of pig lift when it is applied in field.4. The process of piglift's unloading is divided into three stages: gas injection release and two-phase flow phase. For each stage, a corresponding transient mathematics model is established. The model accounts for factors such as liquid transfer between formation annulus and tube, the transient characteristics of flow pattern change and the acceleration term.5.Combined the solution of conservation equation group with complex difference scheme and employed character line to solve boundary conditions, the numerical scheme for two-phase transient flow non-linear partial differential equations is presented.6.Employed Visual Basic language in Windows, the above theory and method are formed by software. It can provide the technical method for the applications of new Pig Lift in field.The validation is made with the basic data of Si47 well(typical low pressure and low production gas well) in ShuNan gas field. By employing the calculation program of self-organized, the process of pig lift's unloading and lifting are simulated. The physical parameters which affect the flow process are analyzed. The change of well head pressure, gas injection rate and liquid level in tubes etc vs time during the process of unloading is also simulated by the software. Of course, the release tube pressure is calculated. In addition, this paper also presents a complete design project for construction in gas&oil field for the first time, which includes draining and production flgure, plane construction simplified figure, injection and production flow chart for well head and the step of construction, request and something that must take care, the main material and equipment etc. |
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