Simulation And Optimization Of Plunger Drainage Technology

Plunger lift is an artificial lift method, which can make full use of the energy of produced gas, without injecting extra gas, to effectively stop the liquid falling back, enhance the lifting efficiency, discharge the downhole liquid and recover the production of gas wells by the stable gas-plunger-liquid slug flow, which is formed by the solid surface of the plunger in lifting tube. The method has already become the key technology of deliquification and been widely used in the gas well with low liquid rate in Sulige Gas Field. Due to the big difference of produced fluid and gas rate in the gas well at different period, the work system optimization of plunger lift is particularly important. Usually, the optimization of plunger lift only considers the well system, but ignores the effect of work system of the plunger lift on the water saturation and the cumulative gas production. Therefore, this paper will consider the reservoir and the plunger lift system as a whole system to carry on the simulation and optimization. Following works are completed.(1) Based on the principle of conservation of mass, a mathematical model is established for describing the process of plunger lift by considering the formation inflow performance as well as the expansion of the gas in wellbore, the model consists of the period of the well production and shut in. Meanwhile, a differential numerical method is applied to solve the mathematical model. The performance of plunger in well X1is below:the calculated and measured upstroke time are respectively1206s and1320s, the error is8.64%; the case pressure after shut in is4.26MPa, but the measured is4MPa, the error is6.50%. It shows the model can actually represent the variation of parameters in plunger lift process.(2) The simulation program of the process of plunger lift is written through the Visual Basic programming language, which can be used to calculate and graph the transient change of the tubing pressure, the casing pressure, the bottom hole pressure in a cycle of plunger lift, as well as the transient change of the velocity, the acceleration, the gas production rate during plunger upstroke. It provides an important technical means for optimizing the work system of plunger lift.(3) The single-well radial mechanism model is set up by Eclipse. This model is used to simulate the influence of the different work system on reservoir parameters under the same flowing period. With the operating cycle changing from3times per day to6times per day, after240days production, the water saturation value in the first grid of the zone nearby wellbore decreases from51.02%to50.15%, and the average gas production increases from3238m3/d to4292m3/d. The result shows that, during the same flowing period, the smaller the cycle is, the better the recovery will be.(4)The analysis result of Well X2in Sulige Gas Field shows that, under the cycle of4times one day with1.5hours production each time, the tubing pressure drops to output pressure but the casing pressure almost keeps at the same level after produced1hour. Then keeping producing0.5hour, the produced gas is not able to carry the produced fluid to the ground, which may lead to the accumulation of liquids at the downhole. Considering the disadvantages of current work system, the work system should be changed to the cycle of6times one day with1hour production each time, so as to achieve the purpose of reducing liquid loading and increasing gas production.