Mitigating paraffin wax deposition by dispersants and crystal modifiers in flow testing

Abstract

Functional molecules such as dispersants and crystal modifiers can be effective in mitigating wax deposition from crude oils and gas condensates. Both chemicals reduce the average wax particle size to sub-micron and change the crystal morphology. Water has a further significant effect on size reduction in dispersants. This work focuses on the effectiveness of these two additives in flow condition in a stainless-steel capillary tube. Unlike conventional flow loop systems, a simple open flow system is used to ensure constant wax content to avoid large fluid volume handling. Capillary tubes of 1- and 2-ft long are used to investigate effectiveness of dispersants and crystal modifiers in the laminar flow regime for a light shale oil with saturate content of 80 wt%. The effect of flow rate, concentration of the chemical additives (dispersant, crystal modifier), tube length, and brine on wax deposition are studied. An optimum concentration of chemical additives is found in flow tests, above which the effectiveness of additive decreases. Without aqueous phase, the crystal modifier is more effective than the dispersant. However, with 4% volume brine (of 5 wt% NaCl), the dispersant becomes more effective than the crystal modifier. Both additives are more effective at a higher flow rate; the influence of flow rate is more pronounced in the crystal modifier system than the dispersant. Wettability alteration to hydrophilic state is induced by adsorption of the dispersant backbone chains onto the stainless-steel (and wax molecules). Our results reveal that water improves dispersant effectiveness even in small amounts. A major observation in this work is pronounced pressure fluctuations in dispersants which relate to adhesion.