Research On Design For Electrical Submersible Pump Technology Process Considering The Effect Of Gas

As one of the most commonly used artificial lifting methods in the petroletum industry at present,the electrieal submersible pump(ESP)has become an important measure to maintain a high level of production.However,its performance of boosting pressure deteriorates with the increase of gas entrainment,deviating from the expected lifting effect of the design.At present,the research on boosting characteristic of ESP under the condition of gas-liquid two-phase flow mainly focuses on the relationship between the flow patterns in impeller and the rule of two-phase characteristic curves.The derived mechanism model is more inclined to centrifugal pump design than to the basic theory of ESP lifting design.The boundary of the inlet gas volumetric fraction(GVF)for the stable operation of ESP is still unclear,which leads to the mismatch between the design method for reducing GVF and the characteristic of ESP itself and the poor application effect.To solve above problem,the technical route of combining the experimental study,the theoretical study and the engineering application were adopted in this paper.The boosting characteristic of ESP under high GVF condition was deeply studied.Specific work is as follows:(1)An experimental loop for simulating the ESP under the condition of gas-liquid two-phase flow was established with an eleven-meter high main support frame.The frame meanly consists of a twenty-five-stage Baker Hughes CRELCP40000 pump with a maximum head of about 109.3 meters.Gas-liquid circulation system and data measurement system are also included in the experimental loop.It is ready for the boosting characteristic of ESP study under the conditions of different gas rate,liquid rate,inlet pressure and rotational speed.(2)Using air and water as the experimental fluids,a total of 6 single-phase characteristic curves and 40 two-phase characteristic curves experiments were carried out.The effects of the gas rate,liquid rate,inlet pressure and rotational speed on the boosting characteristic were then analyzed.The zero pressure points and the turning points of two-phase characteristic curve were defined as open:flow boundary and abnormal boundary respectively.Therefore,the two-phase characteristic curve was divided into negative boosting period,normal boosting period and abnormal deterioration period respectively.(3)The effective working period of ESP under the condition of two-phase flow was defined.It is a closed area consisting of two kinds of boundaries,one is the liquid boundary composed of the open flow boundary and the abnormal boundary,and the other is the gas boundary represented by the limit GVF.Based on the analysis of experimental results,the mathematical model of liquid boundary was established.The comparison between model predictive data and experimental data shows good agreement with the average relative prediction errors are 0.29%and 3.88%respectively.The characteristic curves prediction model of the effective working period was established subsequently with an average relative error of 3.88%.In addition,the similarity law of two-phase flow was proposed.It can be used to predict the variation of two-phase flow characteristic curves of ESP under frequency conversion condition.(4)A mathematical model of ESP under two-phase flow was established by using the nodal system analysis method.Based on the conventional design method of ESP lifting technology and the modified model,a new design method of ESP lifting technology under high GVF conditions was proposed.In addition,the design program of ESP with high gas-liquid ratio was compiled.The downhole gas-liquid flow conditions,the parameters of centrifugal pump and the lifting effect under changing working conditions can be calculated by this program.It can provide an important key tool for lifting of ESP wells efficiently.(5)Well X in Halfaya oilfield was selected as an example well for ESP lifting design.Compared with the conventional method,the single-stage head of centrifugal pump calculated by the design method of ESP with high gas-liquid ratio presented in this paper decreases by 21.76%.Therefore,the series increases by 25 stages.The results of this paper enhance the understanding of boosting characteristic of ESP under the condition of gas-liquid two-phase flow.Furthermore,it provides important technical supports for the lifting design,judgment of operation period and adjustment of working system for the high gas-liquid ratio ESP wells.