(114d) Formation of Hydrate Plug in Water-Decane-Natural Gas Systems with Varying Watercut and Inhibitor Concentrations
AIChE Spring Meeting and Global Congress on Process Safety
Tuesday, April 28, 2015 - 11:15am to 11:35am
The risk of hydrate blockage in subsea oil and gas pipelines represents a critical operational and safety hazard. To date, many studies have focused on predicting hydrate growth and plug formation in oil-continuous systems at low watercut. This study used a high-pressure autoclave to investigate hydrate growth rate and resistance-to-flow at watercuts of 20 to 100% in decane. The results suggest that the high watercuts generated late in the field life do not represent the greatest plugging risk. Instead, moderate watercuts of 40-60% show the largest increase in resistance-to-flow (motor torque), with deposition and sloughing-type behavior apparent in the signal. The motor torque increases associated with this high-risk region were effectively suppressed with the addition of both 10 and 30 wt% MEG in the aqueous phase, where 42 wt% MEG was required for complete inhibition in the systems studied. In the 10 wt% MEG cases, the relative torque increased smoothly from 1 to 2 or 2.5 N·cm at both watercuts. These mild torque increases were fully suppressed through the addition of 0.5 wt% PVCap in the oil phase. No torque increases were detected for the 5 vol% hydrate formed in the 30 wt% MEG trials. Together, these data suggest that mild under-inhibition (within 25% of the required quantity) could lower the risk of hydrate blockage sufficiently to warrant flow loop or even field-scale trials.