Abstract
In case of altering PVT-properties change of the aggregate state of oil is one of the main issues in the oil processing. When oil lifts to the surface the most advantageous energy state of high weight components becomes the state in which a part of the molecules becomes solid. Phase behavior diagrams could actually be plotted using typical compositional simulator. But even if one knows the phase behavior, he still won't be able to understand the WAX deposition in the tubing or pipeline and will not forecast this process performance.
As some authors mentioned, the resins and asphaltenes concentration in the oil affects the WAX deposition velocity. Due to the high complexity of a crystallization mechanism the high weight molecules are not taken into consideration in a phase behavior simulator. Thus for the opportunity of qualitative characterization of the oil tendency to the aggregation the oil from different reservoirs has been compared.
Due to the temperature gradient between rock (permafrost) and oil the probability of WAX deposition in the tubing appears. Deposition growing model presupposes different diffusion assumptions. Equilibrium model and film mass transfer model (as well as solidification and separation) have been applied. Using these models the WAX growing velocity and tubing drift diameter have been forecasted.
Due to the harsh north environment there is a serious risk of oil solidification in the surface pipeline in a case of pump stopping. Based on the laboratory measurements, with the help of stepwise approximation the oil viscosity dependence on temperature has been derived. By solving heat transfer equation (between oil in the pipeline and environment) and using nodal analysis the maximum safety time in a case of accident in the pipeline has been determined.
