Design And Simulation Analysis Of Downhole Oil-water Separator Based On Membrane Separation

With the development of major oilfields in China,the water cut of produced fluid in oil wells is increasing day by day,which brings a series of problems for crude oil exploitation:the production cost of oilfields is increasing,production efficiency is getting worse,formation energy attenuation is intensifying,a large number of oil wells are facing the risk of shutdown,environmental protection pressure is increasing,etc.In order to solve the production contradiction in the middle and late stages of oilfield,Canada C-FER took the lead in putting forward the Downhole Oil-Water Separation System(DOWS)in early 1991.In recent years,DOWS system has been favored by many experts and researchers at home and abroad for its advanced production concept,environmentally friendly production mode and open application market.At present,DOWS system is mainly divided into swirl type and gravity type.On the basis of literature research at home and abroad,this paper finds that the current downhole oil-water separation technology has the following shortcomings:low system stability,adaptability limitation,high application cost,low processing capacity and so on.In view of the shortcomings of the current DOWS system,combined with the principle of membrane separation and cyclone separation,a downhole oil-water separator based on membrane separation was proposed,and design calculation,flow field simulation and prototype analysis of the separator was carried out.The specific research contents are mainly embodied in the following aspects:(1)Domestic and foreign literature,patents,product research.The structure and performance parameters of the current cyclone downhole oil-water separator are fully investigated,the working principle of the cyclone separator is clarified,the design and calculation methods are summarized,the development status and separation mechanism of the membrane separation technology are investigated,and the oil-water separation membrane products at home and abroad are investigated,purchased and analyzed;(2)The overall design of downhole oil-water separator based on membrane separation.A superhydrophilic/super-thin oil film was selected as the separator membrane through the performance test.Using the classical design method of cyclone for reference,the conventional liquid-liquid cyclone separator was reformed,and the structural design calculation of separator unit and the scheme design of matching pipe string were completed;(3)Establishment of hydrodynamic model of flow field in downhole oil-water separator unit based on membrane separation.The RSM turbulence model and Mixture multiphase flow model are selected by analyzing the suitable conditions of different models.The pressure-velocity curve of the separation membrane is fitted by experiments,and the parameters of the membrane porous media are solved.The pre-processing devices of porous media model,boundary conditions and solution parameters are completed;(4)The rationality of the structure design was verified by comparing and analyzing the internal flow field of conventional cyclone and membrane-based cyclone.(5)Separator unit prototype experiment.The correctness of structure design and simulation is further verified by the prototype experiment of separator unit,and the operation parameters of downhole oil-water separator based on membrane separation are optimized.