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

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.