(728b) Quantifying the Severity of Hydrate Blockage in Systems with Under-Dosed Thermodynamic Inhibitors

Traditionally, the risk of hydrate blockage in gas and oil long subsea tiebacks has been managed through the use of thermodynamic hydrate inhibitors (THIs), which interact with water molecules and prevent them from forming the hydrogen-bonded cage network. Developments in deepwater offshore locations or near the end of field life require large dosages of thermodynamic hydrate inhibitor (THI) with increase in formation water breakthrough to fully protect the system against gas hydrate formation. Operationally, the required dosage of THI may not be achievable due to financial or injection capacity limitations, increasing the potential for hydrate formation during operation. To date, only limited experimental evidence has been collected to assess the severity of hydrate formed in under-dosed conditions. In this study, a high-pressure sapphire autoclave cell was used to deliver the first systematic and quantitative characterization of hydrate blockage risk during under-inhibited operations. Hydrate growth rate and particle transportability were measured for systems containing ultra-high purity methane, crude oil, deionized water and industrial -grade monoethylene glycol. Hydrate formation was detected by a sharp decrease in pressure and the rate of hydrate growth calculated from system pressure drop with time. The severity of hydrate formation was quantified by measuring the torque required to maintain constant mixing speed. Images of the sapphire cell were captured using a high-definition mode camera, which were used to characterize the presence of hydrate deposition on the cell wall. The results demonstrate that the highest obtained growth rate corresponded to a system with low MEG dosage (10 wt%). An increase in MEG above this threshold monotonically decreased the hydrate growth rate and suppressed the torque response during hydrate formation. Under higher MEG dosages, the formation of hydrate may not rapidly initiate a blockage scenario, but the observation of a thin hydrate film on the sapphire wall suggests that under-inhibited operations may be best-suited for transient shut-in/restart scenarios.