Analysis of wax deposition phase change law and main influencing factors in oil-water mixed transportation pipeline under unsteady working conditions

With the middle and late stage of oilfield exploitation, the water content is rising, and at the same time, the wax deposition in the mixed pipeline causes the effective circulation area of the pipeline to decrease, the energy loss to increase, and even the pipeline is blocked in serious cases. In this paper, the effects of oil temperature, velocity and water content on the phase change behavior of oil-water two-phase wax precipitation are comprehensively considered, and a three-dimensional theoretical model of wax precipitation process in the pipeline is established to simulate the flow and heat transfer process from the wellhead to the metering room, and the change of wax deposition amount and the distribution of deposition layer in the pipeline are creatively studied from the perspective of time and space. The initial area of wax precipitation, the fluctuating area of wax deposit distribution and the stable thickening area of wax deposit distribution are put forward. By using multivariate nonlinear regression method, the model of main influencing factors in each region is established, and the influence mechanism between wax deposition thickness and liquid content in the pipe and fluid temperature, velocity and water content in each season is quantitatively characterized. The results show that in the initial area of wax precipitation, the phase transition phenomenon of oil wax precipitation near the wall is the most intense, but no obvious deposition layer will be formed in a short time. In the fluctuation area of wax deposition distribution, there is a continuous water phase near the wall, which distorts and reduces the diffusion path of dissolved wax, resulting in sheet-like accumulation of deposition layer. The oil-water flow state in the thickening area with stable distribution of wax deposition is smooth stratified flow, and the thickness of deposition layer reaches a stable value. At the same time, the annular flow pattern appears in the elbow and vertical pipeline, and the precipitated wax crystals are suspended in the oil to form solid and liquid phases, and no obvious wax deposition layer is formed near the wall.