Research On Wellhead Heating Technology Of Oil Well Based On Phase Change Thermal Storage

The storage and release of heat by paraffin phase change material,which is not only helpful for peak load shifting in electricity,but also can realize the comprehensive utilization of oilfield heat and achieve the purpose of the energy saving and emission reduction,,reducing cost to increase benefit,this paper aims at the problem of the oilfield wellhead heating,designs and builds a phase change heat storage test-bed to carry out a series of laboratory experiments.Firstly,in view of the disadvantages of pure electric heating at the wellhead of oilfield,the feasibility of its combination with phase change heat storage device is analyzed by considering the huge difference of peak and valley electricity price.The theoretical analysis showed that phase change heat storage device and electric heating used in combination,which can effectively solve the defects of pure electric heating,save the cost and improve the safety.Secondly,a phase change heat storage test-bed was designed and built to study the influence of different heat source temperature,flow rate and heat exchanger structure on heat storage efficiency and internal temperature distribution of phase change materials.The experimental results showed that the temperature of heat source is the most important factor affecting the heat storage efficiency,followed by the heat transfer area and the flow rate of heat source fluid.The heat flow rate of 0.27m~3/h was about 15 min faster than that of 0.15 m~3/h.The temperature of the heat storage device was higher in the upper than in the lower part,and the upper part melted about 30 min faster than the lower part.The heat transfer efficiency can be effectively improved by the homogenization design of the phase change heat storage device and the addition of circular fins to improve the heat transfer area.Finally,in order to solve the problem of low heat storage efficiency of pure paraffin,composite phase change materials of paraffin with expanded graphite,carbon fiber,copper foam and graphene were prepared respectively,and their related physical properties were comprehensive tested in turn.X-ray diffraction(XRD)indicated that the composite process of paraffin with four materials is a purely physical process without a new substance produced.Thermal conductivity measurement showed that:the thermal conductivity increased to 1.492w/(m·K)after the combination of pure paraffin with expanded graphite,2.923w/(m·K)after the combination with copper foam,0.599w/(m·K)after the combination with graphene,and 0.385w/(m·K)after the combination with carbon fiber.Scanning electron microscopy(SEM)analysis showed that the paraffin was fixed in the homogeneous pores of the copper foam,while the expanded graphite formed an inhomogeneous carbon matrix in the paraffin.Differential scanning calorimeter(DSC)demonstrated that the melting point of the composite phase change material increased slightly compared with paraffin,and the latent heat decreased from206 k J/kg to 134 k J/kg after the composite with the copper foam,and decreased from 206k J/kg to 185 k J/kg after the composite with the expanded graphite.The curve of temperature versus time showed that 80-mesh expanded graphite has the best effect on the improvement of heat transfer.The complete melting time of paraffin was shortened to330 s from 710 s,and the complete freezing time of paraffin was shortened to 7000 s from11300 s.The research results of this paper can lay a necessary foundation for the design of a new device for wellhead heating and the selection of phase change heat storage materials.