Hydrocarbon liquid consists of a range of components with different physico-chemistry characterization. Sometimes there are heavy component with crude oil such as asphaltene, naphthenic and paraffinic wax components and etc. Deposition of wax in both onshore and offshore pipelines presents a costly problem in the production and transportation of oil. There are several parameters contributing to wax deposition in multiphase crude oil flow, e.g. pressure drop, flow rate, pipe internal body surface roughness, surface energy of the pipe, liquid wetting of pipe wall as well as temperature difference between fluid and surroundings [1,2]. Application of internal coating of subsea pipelines can reduce wax deposition. The aim of the present work is to experimentally study the wax deposition in Malaysian waxy crude oil, where the data set studied was gathered from several experiments. Most of the methods can be used to remove the paraffinic wax deposition after it occurs. However, insulation systems yielded in better performance as it was found to help in the prevention of heat loss and solid deposition during flow conditionsThis study utilized flow loop apparatus. This paper compared the wax deposition behaviour with temperature, roughness and flow rate within the tested pipes [Polyvinyl Chloride (PVC), Ethylene - TetraFluoroEthylene (ETFE), and steel as a reference material]. Moreover, the prevention of temperature loss from liquid to surrounding and corrosion control significantly affects pressure drop across the pipeline [3]. The conducted experiments concluded that ETFE had a better effect on the paraffin wax deposition control. Moreover, ETFE as a novel polymer based coating material was economically feasible to be utilized in the oil and gas downstream and upstream systems exposed to wax deposition.
The deposition of wax on the inner surface of subsea pipelines is a prevalent problem during the production and transportation of waxy crude oil. It can reduce effective diameter and restrict fluid flow through the pipeline. In this study, we evaluated the effect of Steel pipe, Polyvinyl Chloride (PVC) pipe and Ethylene-Tetra-Fluoro-Ethylene (ETFE) – coated – pipe on wax deposition at different temperatures and flow rates. A flow loop facility was designed to investigate the effect of different pipe surfaces on wax deposition or inhibition. Increasing temperature differential between crude oil and pipe wall, generally increased the aggregates in the three pipes. However, the amount of deposited wax gradually reduces as deposition thickness increases due to increasing trapped oil within the wax aggregates. Thus, the volume of the trapped oil increases with temperature differential. Conversely, as flow rate increases, the deposition thickness reduces, indicating less trapping of the oil as the concentration of the deposited wax increases. The least amount of deposition was observed for the ETFE – coated – pipe and a higher wax deposition reduction efficiency (70 % in average) obtained compared to steel pipe and PVC pipes. The ETFE – coated – pipe reduces wax deposition by modifying the wetting properties of the inner walls of the pipe and reducing the free surface energy of the pipe wall. ETFE has low thermal conductivity which prevents heat loss thereby making it more effective in reducing wax deposition.
The thermodynamic description of wax deposition is a relatively new approach to solving the problem of wax precipitation, which the oil and gas industry has been struggling with for a long time. Many models exist in the literature to predict the thermodynamic conditions under which the first paraffin crystal is formed. The first task in all models is to determine the stability of the hydrocarbon mixture in order to define the possibility of wax precipitation. The stability of a mixture is determined by the thermodynamic behavior of the phases of a multicomponent mixture, namely, the presence of all existing phases in equilibrium. To this end, a new stability algorithm with Gibbs energy minimization to determine the wax precipitation in hydrocarbon mixtures has been developed. The algorithm is based on multi-solid thermodynamic model with EOS concepts. The main criterion for stability is the existing of the mixture at its global minimum. Proposed stability analysis predicts whether a given mixture will be split into multiple phases or will exist as the single phase at a given temperature and pressure conditions. The model was proven with 6 samples from fields X and Y showing the instability of original petroleum mixtures that agree with the real behavior of the oil in in-situ conditions. The results of the new stability algorithm are comparable with the results of the models presented previously. The main advantage of the method is its simplicity and reliability.
Wax deposition on inner surfaces of pipelines is a costly problem for the petroleum industry. This flow assurance problem is of particular interest during the production and transportation of waxy oils in cold environments. An understanding of known mechanisms and available thermodynamic models will be useful for the management and planning of mitigation strategies for wax deposition. This paper presents a critical review of wax prediction models used for estimation of wax deposition based on chemical hydrocarbon compositions and thermobaric condition. The comparative analysis is applied to highlight the effective mechanisms guiding the wax deposition, and how this knowledge can be used to model and provide solutions to reducing wax deposition issues. One group of thermodynamic models assume that the precipitated wax is a solid solution. These models are divided into two categories: ideal (Erickson and Pedersen models) and non-ideal solutions (Won and Coutinho models). In the other group of models, the wax phase consists of many solid phases (Lira-Galeana model). The authors summarized the limitations of the models, evaluated, and identified ways to represent the overview of existing thermodynamical models for predicting wax precipitation. Within the strong demand from industry, the results of this manuscript can aid to aspire engineers and researcher.
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