Experimental and Modeling Studies of Wax Deposition in Crude Oil Carrying Pipelines

Sandeep Todi and Milind D. Deo

Department of Chemical Engineering, University of Utah

Diffusion of ‘dissolved wax’, particle transport of ‘precipitated wax’ and sloughing of deposited mass are the main mechanisms involved in wax deposition in  crude oil carrying pipelines operating below the Wax Appearance Point (WAP).  It is known that diffusion of dissolved wax plays a key role in the deposition process. The involvement of particle transport has long been questioned since most attempted experimental studies at 'zero heat flux’ have shown no measurable deposition. This study investigated the phenomenon of particle migration in the complex non-Newtonian rheology of a crude oil in pipe flow. Transparent model oil was constituted that mimicked the low temperature rheology of a crude oil. Solubility studies were done based on an FTIR method. HTGC-SimDis carbon number characterization and density measurements were also performed. Laser Light Scattering (LLS) by flow particles was used to view a diametrical plane along the test-section axis. Particle Image Velocimetry (PIV) was used to obtain radial velocity profiles. Particles showed an annular aggregation close to the pipe center. They were also seen diffused out on either side of this annular location. In a very interesting result, deposition was observed under all conditions of heat flux (positive, negative or zero) as long as the wall temperature was above the WAP. Sloughing was seen to play a  dominant role in the overall deposition process. A new theory of particle transport was proposed based on the experimental observations. This theory was also incorporated into a new deposition model and the results compared with existing models.