Case Study 7 Gulf of Mexico Plug Removal in Gas Export Line

1 Case Study 7 Gulf of Mexico Plug Removal in Gas Export Line 

Ahydrate blockage in the export line from Shell s Bullwinkle platform in the Green Canyon Block 65 to the Boxe platform was reported in DeepStar Report A208-1 (Mentor Subsea, 1996, p. 52). The 12 in., 39,000 ft line was not insulated. The seawater temperature was 50°F at the base of the platform in 1,400 ft of water. Gas gravity was 0.7 and the flow rate was 140 MMscf/d at an inlet pressure of 800 psi. 

Gas hydrates formed during a restart after the platform was shut down due to a hurricane. During the shut-in period the gas dehydrator partially filled with water. After production restarted, since the dehydrator was not cleaned properly, it was not dehydrating gas as designed and wet gas entered the export line, causing 

To remove the blockage, the line was depressured on both sides of the plug. Then methanol was circulated into the line to accelerate the hydrate dissociation rate. After complete removal of the hydrates, the dehydrator was cleaned, inspected and restarted properly. The entire remedial operation required 36 h to complete. The major cost was the lost production time. 

---