Effect of Crystal Modifiers and Dispersants on Paraffin-Wax Particles in Petroleum Fluids

Abstract

Summary Petroleum fluids from shale light-oil and gas/condensate reservoirs generally have a high content of normal paraffins. Paraffin-wax deposition is among the challenges in shale gas and oil production and in offshore flow assurance. Low-dosage chemical additives can be effective in paraffin-wax mitigation because of their high efficiency and economics. These additives are divided into broad categories of crystal modifiers and dispersants with vastly different molecular structures and mechanisms in wax-crystal-particle stabilization and wetting. This investigation focuses on the understanding of the differences in the aggregate size and morphology of chemical additives, and it centers on (1) wax-particle sedimentation from diluted petroleum fluids in vial tests, (2) wax-crystal-particle-size distributions and morphology by dynamic light scattering (DLS) and polarized-light microscopy, and (3) the wetting state from the effect of water. In two of the three petroleum-fluid samples used in this work, there is no visible precipitation at the bottom of the vials at temperatures below the wax-appearance temperature (WAT). The microscopic image of fluids along the length of the tube shows that the wax-particle size and intensity increase from top to bottom. To observe precipitation, we dilute the crude with a hydrocarbon such as n-heptane. The sedimentation of wax is then observed. The petroleum fluids used in this work have very low asphaltene content, and there is no complication from asphaltene precipitation. Our study shows that a small amount of crystal modifier and dispersant can reduce crystal-particle size to the submicron scale, and change the crystal morphology. We investigate the differences in the mechanisms of dispersants and crystal modifiers in bulk. Water, which is often coproduced with petroleum fluids, can increase the effectiveness of dispersants significantly by altering the wetting state of the wax-particle surface. Such enhancement is not found in crystal modifiers. Both additives affect the rheology of petroleum fluids.

Improving the Efficiency of Oil and Gas Wells Complicated by the Formation of Asphalt–Resin–Paraffin Deposits

“…The main methods for preventing (preventive measures) the formation of ARPDs include: (1) the use of protective coatings (coating of pipes with epoxy resins, finely crushed glass, Bakelite varnish, resins, the use of glass-reinforced plastic rods); (2) physical methods (vibrational, ultrasonic methods, exposure to magnetic, electric, and electromagnetic fields); (3) chemical methods (the use of wetting agents, modifiers, depressors, and dispersants) [34][35][36]. Modifiers and dispersants with completely different molecular structures and mechanisms of action can be effective in the fight against asphalt-resin-paraffin deposits due to their high efficiency and cost-effectiveness [37]. However, the use of modifiers requires protecting them from the cold to prevent freezing.…”

Effect of nano pour point depressant on the flow properties of the waxy crude oil from Changqing Oilfield

“…n-alkanes with higher molecular sizes would converse into the wax at higher temperatures if no wax inhibitor is injected into the production liquids. The formation of wax would reduce the production rate, and also lead to the blockage of the pipelines [5][6][7]. The traditional methods to mitigate the risk of pipeline blockage caused by the wax deposition including the injection of chemical additives into the flowlines of the extracted hydrocarbons [1,8].…”

“…in the molecule of modifier do not cocrystallize with the original paraffin waxes in the crude oil. The non-wax-like segments provide steric hindrance on the wax surface that retard the growth and aggregation of the crystals [7]. There are many publishes claiming that the size of the wax crystals can be significantly reduced by the polyaminoamide additives [2,12].…”

Effect of a rapeseed oil derived pour point depressant on the flow properties of the waxy oil from Changqing Oilfield

“…Wax dispersants are usually inter-surface active agents containing wax-philic groups and water-philic groups. Therefore, the wax dispersants can be adsorbed onto the wax surface and deposition surfaces, altering the wettability of these surfaces to water-wet conditions, and preventing further aggregation and buildup of these wax crystals [7][8][9]. There are many factors affecting the performance of the chemical inhibitors, for example, the type of the hydrocarbon fluid, properties of the wall surfaces, and the crude oil-chemical interactions.…”