Drag reducers have become a common method for reducing resistance and increasing transportation efficiency in pipeline transportation of waxy crude oil. The prominent heat transfer weakening effect of drag reducers may impact the deposition of waxy oil. This study uses cold finger experiments to clarify wax deposition characteristics and mechanisms in drag-reduced waxy oil. The wax deposition mass and components are examined under different temperatures, stirring rates, drag reducer dosages, and types. The results show that a low dosage of drag reducer at high stirring rates can simultaneously reduce the total wax deposition and the overall wax content in high waxy oil. 5 mg/kg drag reducer can reduce total wax deposition by up to 15.66% and overall wax content by 7.26%. A systematic investigation reveals that adding drag reducers changes the carbon number distribution in the wax deposition layer. This change is similar to the effect of increasing wall temperature. The heat insulation and transfer weakening effects of drag-reducing fluids are likely the main mechanisms inhibiting the increase in wax deposition mass and wax content. The heat insulation effect reduces the temperature gradient near the pipe wall, while the transfer weakening effect decreases radial heat transfer. However, under low stirring rates and high dosages, the deposition mass of the drag-reduced waxy oil system increases, with the adhesive effect of polymer-type drag reducers becoming more pronounced. These findings provide a foundation for optimizing drag reducer usage in waxy crude oil pipelines, potentially leading to significant energy savings and improved operational efficiency.
Yi-Hai Yang,Li-Na Zhang,Zheng-Nan Sun,Ming-Xing Bai,Guo-Lin Jing,Yang Liu,Xiao-Yan Liu
Modified ethylene-vinyl acetate copolymer (EVAM) and amino-functionalized nano-silica (NSiO 2 ) particles were employed as the base materials for the synthesis of the nanocomposite pour point depressant designated as EVAM-g-NSiO 2 . This synthesis involved a chemical grafting process within a solution system, followed by a structural characterization. Moreover, combining macro-rheological performance with microscopic structure observation, the influence of the nanocomposite pour point depressant on the rheological properties of the model waxy oil system was investigated. The results indicate that when the mass ratio of NSiO 2 to EVAM is 1:100, the prepared EVAM-g-NSiO 2 nanocomposite pour point depressant exhibits excellent pour point reduction and viscosity reduction properties. Moreover, the nanocomposite pour point depressant obtained through a chemical grafting reaction demonstrates structural stability (the bonding between the polymer and nanoparticles is stable). The pour points of model waxy oils doped with 500 mg/kg ethylene-vinyl acetate copolymer (EVA), EVAM, and EVAM/SiO 2 were reduced from 34°C to 23, 20, and 21°C, respectively. After adding the same dosage of EVAM-g-NSiO 2 nanocomposite pour point depressant, the pour point of the model wax oil decreased to 12 °C and the viscosity at 32 °C decreased from 2399 to 2396.9 mPa·s, achieving an impressive viscosity reduction rate of 99.9%. Its performance surpassed that of EVA, EVAM, and EVAM/SiO 2 . The EVAM-g-NSiO 2 dispersed in the oil phase acts as the crystallization nucleus for wax crystals, resulting in a dense structure of wax crystals. The compact wax crystal blocks are difficult to overlap with each other, preventing the formation of a three-dimensional network structure, thereby improving the low-temperature flowability of the model waxy oil.
Wax deposition and hydrate formation are two unwelcome problems that can threaten the safety of pipeline transportation in the oil and gas industry. The existing prevention methods mainly aim at the flow blockage resulting from single solid phase, but rarely take into account multi-solid-phase systems, such as hydrate-wax, hydrate-sand, etc. Recently, it has been proposed that adding pour point depressants (PPDs) can not only improve the rheological property of waxy oil but also have potential to inhibit hydrate formation. In this study, a series of PPD polymethylsilsesquioxane (PMSQ) microspheres were synthesized by a two-step sol–gel method. First, the effect of PMSQ microspheres on wax deposition in waxy mineral oil was tested by differential scanning calorimetry (DSC). Then, the influence of PMSQ microspheres on the cyclopentane (CP) hydrate formation in waxy oil–water systems at the atmospheric pressure and temperature of −3 °C was investigated by using a self-assembly high-pressure reactor. The experimental results showed that the addition of PMSQ microspheres could reduce the wax appearance temperature (WAT) of waxy oil and prolong the nucleation time of the CP hydrate. Powder X-ray diffraction and laser confocal micro-Raman data indicated that the presence of PMSQ did not affect the sII crystal structure of the CP hydrates. A possible inhibition mechanism of PMSQ microspheres by the steric hindrance effect was proposed.
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