Investigation of Thermal Effects on Gas-Oil Stratified Flow Wax Deposition

Abstract

Abstract Two-phase flow wax deposition is a flow-pattern-dependent phenomenon. The thickness and hardness of the deposit vary along the pipe circumference. In this work, two-phase gas-oil stratified flow wax deposition experiments at various liquid and gas flow rates have been conducted systematically using Garden Banks condensate and natural gas in a 2-inch I.D. multiphase flow loop under the pressure of 350 psi. Both deposit mass and wax content increased as superficial gas and liquid velocities increased. The local deposits were observed to be thinner but harder at the sides compared to the bottom of the pipe. Meanwhile, the cross-sectional deposits were crescent-shaped with an increasing local wax mass flux along the circumferential direction. The local multiphase hydrodynamic and heat transfer characteristics are known to play an essential role in the wax deposition process, and the temperature gradient is critical for establishing the concentration gradient. Thus, it is paramount to have a proper understanding of the local momentum and heat transfer to predict wax deposition in multiphase flow accurately. Therefore, numerical simulations with an SST (Shear Stress Transport) k∼ω turbulent model was implemented to understand local heat transfer in two-phase gas-oil stratified flow. After each simulation, the ANSYS CFD-Post was used to export, visualize, and analyze the simulated results. A total of 19 locations were selected for circumferential sampling to analyze the local heat transfer in the model. Detailed information on liquid volume fraction, shear stress, and temperature were analyzed. It has been observed that the local shear stress, temperature gradient, and inner wall temperature decrease with increasing θ. The thickness of the thermal boundary layer increases as θ increases due to reduced Nuθ. The comparison between the localized Nuθ and Nu from unified heat transfer model has revealed that variation in Nuθ is critical in the circumferential heat transfer calculation and wax deposition modeling.