Hydrate Plug Remediation in Deepwater Well Testing: A Quick Method to Assess the Plugging Position and Severity

摘要

Gas hydrates can form during deepwater well testing, resulting in serious flow assurance problems. Once plugs form, remediation operations must be carried out to remove the plugs. We developed a method to quickly locate the plugging position and assess the severity of hydrate plugs. The proposed method was developed based on hydrate thermodynamics, kinetics, and hydrate particle transport & deposition dynamics. The application procedure was established. Flowrate, pressure and temperature data in well testing was collected and used as input data for hydrate plugging development analysis, from which the plugging location and severity could be quickly assessed. The plugging position and severity under various water depth, gas production rate and inhibitor concentration conditions were obtained. It indicates that hydrates generate and attach to the tubing wall and form a growing hydrate layer, which narrows the effective flow area of the tubing. As the hydrate layer becomes thicker, the plugging becomes more severe and bring a greater interference to well testing operations. A significant choking effect is encountered when the hydrate layer thickness increases to a critical value, resulting in distinct pressure drop increase in the testing tubing. It indicates the occurrence of conduit blockage. The plugging position is found at the site where the maximum subcooling is encountered, rather than where the lowest ambient temperature presents. For a typical deepwater gas well, the plugging position is at 150 m below the sea surface. The effects of gas production rate, inhibitor concentration and water depth on plugging position are studied. It is found that the plugging position becomes deeper as the water depth increases and/or the production rate decreases. More severe plugging can be encountered when the gas production rate is lower, the water is deeper, and/or the inhibitor concentration is lower. The proposed method can help operators locate the plugging position and assess the severity of hydrate plugs in a shorter time compared to traditional methods. This study provides key instructions and helps reduce uncertainties involved in removal work. Therefore the operational risk and duration can be significantly cut down.