Mitigation of Paraffinic Wax Deposition and the Effect of Brine
- Taniya Kar (Reservoir Engineering Research Institute) | Abbas Firoozabadi (Reservoir Engineering Research Institute)
- Document ID
- Society of Petroleum Engineers
- SPE Annual Technical Conference and Exhibition, 30 September - 2 October, Calgary, Alberta, Canada
- Publication Date
- Document Type
- Conference Paper
- 2019. Society of Petroleum Engineers
- wax, crystal modifier, dispersant, wettability, deposition
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- 173 since 2007
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Wax deposition in wells from shale oil production is a major challenge. Crystal modifiers and dispersants may mitigate wax deposition via steric hindrance and wettability alteration, respectively. Interaction of reservoir brine coproduced with oil and the chemicals may increase mitigation efficiency. This study investigates quantitative effect of brine on inhibitor performance, at three different flow rates, representing different field conditions.
Two dispersants and two crystal modifiers at low concentrations (500-1000 ppm) are selected among eight chemicals after screening. In our work, pressure drop in flowlines is a measure of mitigation efficiency. Three light crude oils are investigated; they are from shale formations which have high wax content. Brine effect on chemical performance is investigated from high flow rate to low rates. To select chemicals and provide a guide for flow experiments, we include optical microscopy with polarized light, rheology, and particle size measurements as part of the study.
Crystal modifiers are observed to delay pressure build up from deposition significantly compared to dispersants. For dispersants, the effect of brine is found to improve efficiency. At the intermediate flow rate, brine is found to increase efficiency of two dispersants, AO4 and PARA, by 70% and 21%, respectively, in terms of total fluid transported before blockage. For crystal modifiers, there is practically no increase in flow throughput by brine. Dispersant and brine have a synergistic effect, leading to decrease in adsorption of wax crystals on the surface of pipeline. Crystal modifiers do not have an appreciable effect on surface wettability in the presence of brine and no significant improvement is observed in inhibitor efficiency. The observation is the same for all four crystal modifiers in the screening tests at three different flow rates in the flow experiments. The eight chemicals used in this work were provided from different companies. The basis of their selection was on reduction of viscosity in vials from the addition of small amount of chemicals. We find that viscosity reduction alone is not a measure of effectiveness of chemicals. All the chemicals supplied by various companies reduce viscosity of the shale oil sample at the conditions of wax formation. However, deposition in dynamic flow tests do not relate to bulk viscosity reduction.
Our investigation includes a comprehensive set of particle size and flow measurements of low dosage crystal modifiers and dispersants in wax mitigation over a range of flow rates. There is a significant synergistic action of dispersants and brine. Chemical inhibitor performance is a strong function of flow rate and metal surface.
|File Size||1 MB||Number of Pages||13|