(65c) Modeling Wax Deposition with Advanced Heat and Transfer Algorithms

Wax deposition has been a significant flow assurance challenge in the past decades. As this phenomenon occurs due to the radial heat loss of the petroleum fluids towards the surrounding environment, the knowledge of the transport phenomena in the radial direction is essential to the modeling of wax deposition. However, for the past decade, the industry mostly relies on flow simulators with a 1-D (axial direction) discretization to determine bulk flow properties, because of its less stringent requirement on computational intensity.^1–3 However, it is shown in this study that with this 1-D discretization it is not sufficient to accurately determine the heat transfer characteristics near the wall, which is especially important for wax deposition prediction. In addition, mass balance on the precipitated wax crystals in the bulk oil are usually not considered in these models, which makes it not possible to correctly model wax deposition after the mixing and heating of waxy fluids. A axis-symmetric 2-D model, known as the Michigan Wax Predictor (MWP), has been developed recently with radial discretization to capture the details in the transport phenomena in the boundary layer of the flow.^4,5By comparison with extensive wax deposition experiments carried out at different operating conditions, it is revealed that the MWP achieves much superior performance than most of the conventional 1-D wax models with still reasonable computational intensity. Furthermore, its 2-D discretization allows the use of a kinetic precipitation model, which keeps track of the amount of precipitated solids to better model wax deposition downstream of process equipment where further cooling occurs.

References:

1. Erickson DD, Niesen VG, Brown TS. Thermodynamic Measurement and Prediction of Paraffin Precipitation in Crude Oil. In: SPE Annual Technical Conference and Exhibition. Houston, Texas, USA; 1993

2. Matzain A, Apte MS, Zhang H-Q, et al. Multiphase flow wax deposition modeling. In: ETCE 2001: Petroleum Production Technology Symposium. Houston, Texas, USA; 2001.

3. Hernandez OC, Hensley H, Sarica C, Brill JP, Volk M, Delle-case E. Improvements in Single-Phase Paraffin Deposition Modeling. In: SPE Annual Technical Conference and Exhibition. Denver, Colorado, USA. 2003

4. Lee HS. Computational and Rheological Study of Wax Deposition and Gelation in Subsea Pipelines. Ph.D. Thesis. University of Michigan. 2008.

5. Huang Z. Application of the Fundamentals of Heat and Mass Transfer to the Invesitgation of Wax Deposition in Subsea Pipelines. AIChE J. 2011;138:2955-2964