Experimental Investigation to Quantify Gas Hydrate Formation during Shutdown in the Wellbore Near the Wellhead: Impact of Thermodynamic Inhibitors

In most cases, concerns about gas hydrates in hydrocarbon production are often associated with shut-in and restart of the production system associated with the fluids in the wellhead and the main flowline. The exposure of the wellhead to cold temperatures during shutdown can cause severe hydrate formation even with stagnant fluid in the wellbore. Similar conditions may exist at the top of the gas line in flowlines for hydrate formation when gas is saturated with water. This study investigated the hydrate deposition kinetics and morphology at 10 MPa (ca. 1400 psi), with the goal of preventing severe solid hydrate formation from the vapor or supercritical phase near the wellhead or a vertical conduit exposed to cold conditions such as road overpass or river crossing during shutdown and providing operating guidelines for hydrate management by understanding the impact of volatile (methanol) and non-volatile (monethylene glycol, MEG) thermodynamic hydrate inhibitors (THIs). These results may also apply to top of line hydrate and its inhibition. It was verified that non-volatile THI is ineffective in preventing hydrate deposition near the wellhead, showing growth behavior of hydrate formation in the presence of MEG similar to that with lower pressure without inhibitors. However, volatile THI prevents hydrate deposition in a cold wellhead even though the experimental condition provides sufficient convection and water condensation. In the warm wellhead, volatile THI does not prevent hydrate formation, but it delays the growth of hydrate deposits. In the presence of volatile THI, the dissociation and reformation of hydrate deposits on the vertical wall are observed. This study provides a quantifiable method for hydrate growth in real-time and insight into better management strategies for THI usage to mitigate hydrate blockage risk near the wellhead.

Automated summary

In this study, the deposition kinetics and morphology of methane hydrates were investigated at 10 MPa. It was found that non-volatile thermodynamic hydrate inhibitors (THIs) were ineffective in preventing hydrate formation near the wellhead, while volatile THIs could prevent hydrate deposition even under cold conditions. However, volatile THIs only delayed the growth of hydrate deposits in warm wellheads. The study provides insight into better management strategies for THI usage to mitigate hydrate blockage risk near the wellhead.