A Mini Pilot-Scale Flow Loop Experimental Study of Turbulent Flow Wax Deposition by Using a Natural Gas Condensate

Abstract

Wax deposition is one of the important flow assurance problems in oil and gas production for both offshore and onshore fields. In this study, we experimentally investigated the turbulent flow wax deposition phenomena under single-phase turbulent flow conditions. The experiments were conducted in a mini pilot-scale flow loop by using Garden Banks condensate from the Gulf of Mexico. Condensate velocities of 1.89, 2.83, 3.78, and 4.72 m/s and testing durations of 2.67 h (2 h, 40 m), 8 h, 16 h, and 24 h were used for the deposition test. The initial value of the Reynolds number, wall shear stress, and heat-transfer coefficient corresponding to these four flow velocities were in the ranges of 7300–19 000, 12–60 Pa, and 1200–2900 W/(m2 K), respectively. Deposit thickness data based on the mass and pressure drop measurements were obtained. The deposit composition was analyzed by using high-temperature gas chromatography (HTGC). The results revealed that more than 45% of the total wax mass flux (from the bulk oil to the deposit interface) contributed to the aging of the deposit. Solubility and heat- and mass-transfer analogy methods were used to calculate the theoretical lower and upper limits of the total wax mass flux, respectively. A new method to calculate the ratio of aging wax mass flux to the total wax mass flux directly from experimental data was developed. A new concept on the superficial wax crystal aspect ratio was introduced. It was found that the superficial wax crystal aspect ratio has an abnormally decreasing trend, with respect to the deposit wax fraction. The experimental wax mass flux was found to be significantly less than the minimum theoretical limit. These findings of the abnormal trend in the superficial wax crystal aspect ratio and the experimental incoming wax mass flux are the indication of another factor, in addition to the conventional diffusion–deposition, which impacts the deposition behavior. The deposit composition and thickness data from this study also increased the available paraffin deposition data, which was very limited but required for a reliable deposition model development.

Fundamental Study of Wax Deposition in Crude Oil Flows in a Pipeline via Interface-Resolved Numerical Simulations

“…In order to validate the numerical model, we consider the wax deposition data of Singh et al 22 . The authors conducted wax deposition experiments using a Garden Banks condensate as operating uid, circulated in turbulent ow conditions in a D = 16.5 mm internal diameter pipe.…”

“…63 No data are available for the remaining properties of the deposit, which are set equal to those of the crude oil, except for the viscosity µ d that will be subject of a parametric analysis. Singh et al 22 reported that the deposit critical carbon number (CCN) of the operating uid was ∼ 30 and considered the total fraction of alkanes with carbon number above 30 (n-C30+ fraction) as the wax fraction of the uid. Accordingly, in the numerical model we assume that the non-wax pseudo component with the crude oil ow rateṁ c because the more ecient heat convection at the wall leads to a higher wall temperature gradient.…”

“…From a numerical perspective, it is impractical to track the concentration of each single component as the flow evolves within a pipe. Experimental evidence suggests that high molecular weight paraffin waxes are the major constituents of solid deposits from crude oils ,, because of their lower solubility in the liquid phase as the pipe wall temperature drops due to the cold environment. At early stages, only a few percent of precipitated wax content in the deposit is sufficient to gel the fluid, with liquid oil entrapped in a matrix of wax crystals .…”

“…Signicantly dierent trends have been reported for cold ow conditions (T c < T W AT ) by Bidmus and Mehrotra 19 , with the deposit rate increasing as the mixture temperature approached WAT and a negligible impact of the mixture ow rate. Wax deposition from South Pelto crude oil and Garden Banks condensate were studied in a ow loop apparatus by Panacharoensawad and Sarica 21 and Singh et al 22 . These studies revealed much slower deposition processes compared to the data from Mehrotra and co-workers, with the deposit thickness still increasing even after 48 hours, due to considerably smaller wax content (< 1 %) in the crude oils.…”

A review of heat‐transfer mechanism for solid deposition from “waxy” or paraffinic mixtures

“…[18,72] 4.4 | A model for deposit aging: shear deformation of a cubical cage A number of studies have reported that, with time and under shear stress, the incipient gel-like structure undergoes compositional changes through a process called deposit aging. [33,50,54,[75][76][77][78]93,[129][130][131][132][133] During deposit aging, the concentration of lighter paraffins in the deposit decreases with time and that of the heavier paraffins increases. Experimental results have shown that a harder deposit, with a lower fraction of the entrapped oil, is formed under higher shear rates.…”