Kinetics of Waxy Gel Formation from Batch Experiments

Abstract

In spite of its importance, wax deposition is still not fully understood, and a reliable physical description of wax deposition is still to be agreed upon. Up to now, the focus in wax studies has been mainly on the radial transport of waxes to the cold wall through molecular diffusion, but other mechanisms that have been cited (and so far neglected) may count on the kinetics of deposit formation. An analysis of the experimental evidence is presented here, leading to the conclusion that an important role may be played by the axial convective transport and the oil gelation on the cold surface (i.e., by the bulk liquid-to-gel change driven by the temperature change). Gelation is faster than molecular diffusion and may lead to the formation of a loose solid network that is slowly filled by diffusion (by aging) in a successive step. An experimental apparatus has been employed to measure the gelation kinetics both on a model mixture and on a stock tank oil. Obtained data have been modeled by employing a classic solution of the conductive heat transfer problem. The qualitative agreement obtained indicates that the physics involved in gelation have been well identified.

Deposition apparatus to study the effects of polymers and asphaltenes upon wax deposition

“…While flow loop deposition studies date back several decades (Jessen and Howell, 1958;Cole and Jessen, 1960;Hunt, 1962;Jessen and Mendell, 1970;Mendell and Jessen, 1972;Weingarten and Euchner, 1988) more recent work has focused on the fundamental understanding to the deposition process, as well as the ability to accurately model deposition behavior (Burger et al, 1981;Brown et al, 1993;Creek et al, 1999;Singh et al, 2000;Apte et al, 2001;Singh et al, 2001a,b;Matzain et al, 2002;Paso and Fogler, 2003;Venkatesan and Fogler, 2004;Parthasarathi and Mehrotra, 2005;Merino-Garcia et al, 2007). A survey of such studies shows that four key factors determine the rate and nature of the deposit formed: the flow rate (Weingarten and Euchner, 1988;Creek et al, 1999;Singh et al, 2000), the temperature field, (Cole and Jessen, 1960;Burger et al, 1981;Creek et al, 1999;Singh et al, 2000) the composition of the oil Singh et al, 2001b), and the nature of the surface (Cole and Jessen, 1960;Parks, 1960;Jorda, 1966;Kok and Saracoglu, 2000;Zhang et al, 2002).…”

Effect of pour point on wax deposition under static cooling conditions

“…The influencing factors of wax deposition include crude oil composition, transportation temperature, temperature difference between oil and pipe wall, flow velocity, flow pattern, material of pipe, deposition time, and so on. Consequently, scholars have researched the problem of wax deposition for a long time; however, the mechanism of wax deposition is still not recognized thoroughly . The concept of ‘aging’ is a good supplement to the traditional wax deposition mechanism .…”

A Survey on Mathematical Modelling of Deposition in Waxy Crude Oils

“…Basically, WCOs are characterized by a specific temperature, which is of extreme importance for scientists and engineers handling with these fluids. When the oil is being extracted from reservoir, the temperature may drop below a certain value (the so called Cloud Point or Wax Appearance Temperature, WAT), at which waxes start to solidify and may deposit on the pipe walls (see for example [25]). The most striking consequence can be seen when a WCO is pumped e.g.…”

“…On the physical mechanisms involved in wax deposition, apart from one of the first works on this subject [5], a good and critical review can be found in [4] and in [25].…”