Single-Phase Wax Deposition Experiments

The behavior of waxy crude oils in subsea production lines has been successfully investigated in a 2 in. deposition flow loop. A North Sea waxy gas condensate was used to investigate wax deposition in turbulent single-phase flow under different temperature and flow conditions. A reliable and accurate procedure for determination of wax thickness and wax roughness from pressure drop, weight, and laser measurements has been developed. The laser technique is a new and promising method to measure the spatial distribution of wax thickness, which was not captured by the traditional pressure drop and weighing methods. These experiments have led to an increased understanding of the mechanisms of wax deposition, which is needed to develop more-accurate models based on physical effects. These models are then the basis for a more accurate prediction of the rate of wax deposition in production lines. The main finding is that molecular diffusion is indeed the central mechanism that steers wax deposition but that an accurate quantitative description also needs to take the wax composition of the deposit and the effects of shear stress into account. However, for higher oil temperatures it was found that the wax deposit’s structure changes from the well-known smooth homogeneous type to a new irregular, patchy type. This deposit cannot be described by the traditional diffusion models. In addition, the experiments were used to confirm that the laboratory-scale measurement techniques that are typically used to determine wax appearance temperature do result in a temperature that coincides with the temperature where wax starts to deposit under realistic flow conditions.