Research On Lifting Method Of Electric Submersible Pump For Low-yield Well In Offshore Oilfield

Offshore oil fields are characterized by high single well productivity and deep burial depth,and electric submersible pumps are often used for lifting.However,for some low production wells,the average production is about 20m~3/d.The electric submersible pump lifting will cause the motor temperature to be too high due to the low liquid volume,and the pump burning accident will occur,which will greatly affect the normal production of low production wells.According to the geological characteristics and actual production situation of WS oilfield in the west of South China Sea,this paper analyzes the reservoir seepage law,establishes the productivity prediction model of low production wells,and analyzes the productivity;Through theoretical research and field investigation,this paper analyzes the causes of accidents easily occurred in the lifting of electric submersible pump in low production wells,puts forward the method of backflow,fluid replenishment and cooling,and studies the lifting supporting technology of offshore low production wells.The results show that:(1)Conventional displacement electric submersible pump is used to lift low production wells.Due to the low liquid supply capacity of the formation,it is easy to cause insufficient dynamic liquid level and less liquid entering the pump,and insufficient heat dissipation capacity for the submersible motor,resulting in high winding enameled wire temperature in the submersible motor and pump burning accident.(2)The working states of electric submersible pump well are analyzed as normal working state and low production working state respectively.Through finite element simulation,the temperature field distribution and service life of the electric submersible pump under two working conditions are analyzed.It is found that the lifting fluid of the electric submersible pump is mostly liquid under normal working conditions,which can effectively carry heat.The temperature of the submersible motor is within the safe temperature range,and the service life is long;Under low production conditions,the lifting fluid is mostly gas,which can not effectively carry heat.The submersible motor has high temperature and short service life.The above results are verified by experiments.Finally,the empirical formula is used to determine that the service life of the electric submersible pump is reduced to about 0.21 times of the original under low production.(3)In order to solve the problem of short service life of electric submersible pump in low production wells,a new type of reflux fluid make-up cooling device is designed,which can adjust the return flow according to the flow to reduce the impact on pump efficiency,and the application effect of the device is analyzed.It is found that the device can improve the submergence under low production state,change the low production working state into normal working state,and effectively reduce the temperature of submersible motor,with an average decrease of 122.87℃;At the same time,the influence of different flow rate and fluid temperature is analyzed.It is found that the degree of influence is small and within the safe temperature range;Finally,the relevant working parameters of the device are optimized,and the optimal size of the reflux channel is determined to be between 3-4cm.(4)According to the actual situation of a block in an offshore oilfield,based on the design results of the backflow and fluid make-up device,the downhole backflow production system is designed,the lift,pump type,submersible motor power stage,pump depth and supporting devices are determined,and the electric submersible pump lifting scheme for low production wells is formed.