Software and modeling development for wax deposition phenomenon



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Wax deposition is an inevitable phenomenon in subsea pipelines where surrounding temperature is well below the Wax Appearance Temperature (WAT). Formation of waxy deposit is extremely problematic because it can result in reduction of cross-sectional area of pipe, potential blockage of production stream, elevated pressure-drop, increased risk of production shutdowns, etc. Therefore, it is crucial to have a reliable model to predict various characteristic of wax deposition for optimum treatment planning. In this study, we have developed two software which account for important aspects of wax deposition. Through our first software (SP-Wax), thermodynamic properties of waxy solutions are predicted and validated by extensive experimental data. In our second software (SP-Depo), we developed a new wax deposition model to predict deposit’s thickness, solid wax fraction and carbon number distribution under single-phase turbulent flow. Within both software, core calculation is coded in C++ and the OpenMp parallel programming technique is incorporated to improve the performance. Also, a C# Windows Forms user interface is created for maximum reusability for technical and non-technical users.
SP-Wax is our first software to predict different SLE thermodynamic characteristics of the paraffinic solutions. In SP-Wax, solid solubility, precipitation curve, Wax Appearance Temperature (WAT), equilibrium constant, relative concentration gradient, liquid and solid phase compositions are predicted as a function of temperature. SP-Wax predictions are validated by experimental data of five binary and seven multicomponent systems. Using SP-Wax, the aging concept in wax deposition phenomenon is verified thermodynamically and a new CCN determination method was introduced. Through further investigation, it is also shown that SP-Wax thermodynamic software can be used as a quick tool to predict the deposit’s solid phase carbon number distribution in pipes. For our second software (SP-Depo), a new thermodynamically-coupled wax deposition model was developed and verified by data from 12 flow-loop experiments. Through our new model, deposit’s thickness, solid wax fraction and Carbon Number Distribution (CND) are predicted. Moreover, the effect of shear stress on solid phase average carbon number (ACN) was elucidated using SP-Depo predictions and experimental ACN data. SP-Depo software is coded in an object-oriented format (containing more than 40 classes and 350 methods) and incorporates the SP-Wax thermodynamic model for the solid phase composition prediction. In SP-Depo, Levenberg-Marquardt optimization tool is coded to tune the model using the fitting parameters.



Petroleum engineering, Wax deposition, Software development, Thermodynamics, Transport phenomena