(85f) Effects of the Presence of Water in Cold Restart of Waxy Oils
- Conference: AIChE Annual Meeting
- Year: 2018
- Proceeding: 2018 AIChE Annual Meeting
- Group: Upstream Engineering and Flow Assurance Forum
- Time: Monday, October 29, 2018 - 9:35am-9:52am
A model oil consisting of 7% wax and about 0.5 wt% of an appropriate surfactant was used in experiments with water. Maximum amount of water in emulsions was 40%. A reproducible rigorous mixing protocol was developed to create emulsions stable over the course of the experiments. Comprehensive rheological measurements were performed on water-free and emulsified samples using cone and plate geometry. The WAT and gel point were measured using the oscillation method with a slow cooling rate. We used creep methods to measure the static yield stress for gels at 5 °C formed under hot/cold flows. Yield stress measured for emulsion gels is largely lower than that for water-free gels. We studied the effects of roughness of the cone and plate surface and found that higher yield stress was observed using the roughened geometry.
Restart studies were conducted in a bench-scale, 0.4-inch diameter, 4-foot long flow loop. The distinguishing feature of the flow loop was a conditioning loop consisting of a scraped heat exchanger to prepare the cold slurry for restart experiments. Water-free cold flow experiments were first performed to establish a baseline. The measured restart pressures for cold flow restarts at 5 °C when shutdown temperatures were 5-10 Â°C below the WAT were approximately three times lower than when âhotâ restart (cooling from above the WAT to the designated temperature) were used. The restart pressures decreased as progressively lower temperatures were used at shutdown. Restart with emulsions showed that even lower restart pressures were needed for both cold and hot restart. The flow loop experiments results agreed with the rheological measurements that emulsion gel is weakened comparing with the water-free waxy gel. The dependence of lower pressure for progressively colder restarts observed for water-free systems was minimal to non-existent and consistently lower restart pressures were observed. Observations of gelled emulsions under the microscope at different temperatures confirmed the disorganized structure of the gel with water present. We believe this morphology of the gel was primarily the cause of the lower restart pressures observed for emulsified waxy oils.