Study On The Boundary Conditions Of Unheated Gathering And Transportation In High Water Cut Oilfield

The significant increase of water content of the oil well produced fluid can improve the fluidity of the produced fluid,which provides a good precondition for the unheated oil gathering.In order to avoid the high back pressure at wellhead,it is necessary to determine the key factors of the rise of friction,and to determine the boundary conditions for application of unheated gathering and transportation technology.The factors influencing oil pipeline friction include oil-water mixed liquid viscosity,liquid production,gas-liquid ratio and pipe diameter.Taking the surface gathering system in Banbei oilfield as the subject,the sensitivity of these factors were studied by PipePhase model.The results show that the decrease of flowing area contributes the most increase of back pressure at wellhead.And wall sticking is the fundamental reason for the decrease of circulation area.In order to study the law of wall sticking,a new experimental device and method are developed on the basis of traditional cold finger device.The new experimental device realizes the continuous renewal of the oil sample in the stirring tank by setting the circulating storage tank,which makes up for the defect that the wax molecules can`t be replenished after their deposition in the traditional cold finger device.Then the process of gelled oil sticking to wall was simulated by the stirring shear and also the law of wall sticking was studied from the 5 aspects consisting of oil temperature,temperature difference,water content,shear strength,duration of the development of wall sticking.Through the experiments of 3 kinds of waxy crude oil and 3 kinds of heavy oil,it is found that there is a turning temperature named the initial wall sticking temperature,at which the rate of wall sticking began to increase greatly during the decrease of oil temperature.And it is also found that the initial temperature is 0~4 degrees lower than gelling temperature of the 3 kinds of waxy crude oil.Due to the fact that wall sticking is not obvious at the temperature higher than the initial wall sticking temperature,it is suggested that the initial wall sticking temperature should be used as the boundary temperature.The wall sticking of oil is the result of the condensation of oil and the erosion of pipe flow.In the experiment,it is found that the thickness of the wall has a limited value when the two effects are in equilibrium.The variation of wellhead back pressure caused by the limited thickness is an important basis for judging the feasibility of unheated gathering and transportation technology.Based on the known oil fluidity,the law of wall sticking,the feasibility of unheated gathering process can be judged by PipePhase model with the boundary conditions that back pressure is no more than 1.5 MPa.Using the method above,the result shows that the unheated gathering process can be applied to Banbei oilfield.