Single-Phase Wax Deposition Experiments

Abstract

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.

Online estimation of wax deposition thickness in single-phase sub-sea pipelines based on acoustic chemometrics: A feasibility study

“…Hoffmann and Amundsen [15] in their earlier investigations conducted experiments to verify the reproducibility of wax deposition in this experimental rig. From their investigations, they concluded that the wax deposition in the single-phase investigations were reproducible.…”

“…1). For detailed description of the experimental facility interested readers are referred to Hoffmann and Amundsen [15]. In this feasibility study only a brief description of the experimental facility is presented.…”

“…In this feasibility study, two of the methods were combined in view of obtaining a more accurate wax deposition profile. By measuring the increase in pressure drop, the wax deposition build-up can be determined [15] from Haaland's friction factor correlation [18]. …”

“…The feasibility study is a piggy back on the single-phase experimental investigations conducted and reported by Hoffmann and Amundsen [15]. The main objective for the experiments conducted in Hoffmann and Amundsen was to obtain experimental data to validate the basic assumptions of a model since field data from production pipelines are difficult to obtain.…”

“…In this feasibility study both principal component analyses (PCA) and partial least square regression (PLS-R) were applied to signals from the acoustic sensor to investigate the potential application of this technique for online estimation of the wax deposition thickness in a single-phase sub-sea oil pipeline. The reference measurements adopted in this study were based on pressure drop measurements and measured final wax deposition thickness by weight which was reported in [15]. The calibrated PLS-R model was validated with a fully independent data set.…”