Mud Systems
•Many different mud systems can and have been used in deep water applications. –They range from systems as simple as seawater-base lignosulfonatemuds to environmentally approved high-performance synthetic muds.Gas Hydrates
•Gas hydrates are an “ice-like”mixture of gas and water. At atmospheric pressure, freshwater freezes at 32°F (0°C).
–At high pressures, gas hydrates will form at moderate temperatures —even as high as room temperature.
–Gas hydrates occur naturally in arctic permafrost and deepwater seabed deposits, usually at depths greater than 800 ft.
•One cubic foot of gas hydrates can contain 170 ft3 of natural gas.
–Naturally occurring gas hydrates can pose a well-control problem when drilled, but gas hydrate formation in the drilling fluid is a more significant well-control problem in deep water situations.
•Gas hydrates can form in low-salinity drilling muds under pressure/temperature conditions as mild as 480 psi and 45°F (7.2°C), conditions which are common when controlling kicks in deep water.
•During well-control situations, hydrates can plug risers, BOP lines and choke-and-kill lines, interfering with effective well control.
•Reported cases of gas hydrates are few, the risk of losing the ability to operate BOP equipment adequately is always present.
–For this reason, all deepwater mud systems must be formulated to suppress the formation of gas hydrates.
•Increasing the salinity of water-base muds is the common method used to suppress hydrates.
–The standard deepwater water-base mud system uses 20% by weight salt to inhibit gas hydrates.
–Increasing the salinity of a water-base mud system will reduce the temperature at which gas hydrates can form at a given pressure.
–The amount of salt required depends on both hydrostatic and shut-in pressures and the seafloor temperature
–At higher pressures and colder temperatures, a combination of salt and either glycerol or water-soluble glycol is recommended for greater inhibition.
•Diesel oil, mineral oil and synthetic systems all provide excellent hydrate suppression.
–This inhibition is a result of the limited amount of water contained in them and the fact that the water phase generally has a high concentration (>25% wt) of calcium chloride.
–Dissolved gasses can reduce suppresion
–At high pressures, gas hydrates will form at moderate temperatures —even as high as room temperature.
–Gas hydrates occur naturally in arctic permafrost and deepwater seabed deposits, usually at depths greater than 800 ft.
•One cubic foot of gas hydrates can contain 170 ft3 of natural gas.
–Naturally occurring gas hydrates can pose a well-control problem when drilled, but gas hydrate formation in the drilling fluid is a more significant well-control problem in deep water situations.
•Gas hydrates can form in low-salinity drilling muds under pressure/temperature conditions as mild as 480 psi and 45°F (7.2°C), conditions which are common when controlling kicks in deep water.•During well-control situations, hydrates can plug risers, BOP lines and choke-and-kill lines, interfering with effective well control.
•Reported cases of gas hydrates are few, the risk of losing the ability to operate BOP equipment adequately is always present.
–For this reason, all deepwater mud systems must be formulated to suppress the formation of gas hydrates.
•Increasing the salinity of water-base muds is the common method used to suppress hydrates.
–The standard deepwater water-base mud system uses 20% by weight salt to inhibit gas hydrates.
–Increasing the salinity of a water-base mud system will reduce the temperature at which gas hydrates can form at a given pressure.
–The amount of salt required depends on both hydrostatic and shut-in pressures and the seafloor temperature
–At higher pressures and colder temperatures, a combination of salt and either glycerol or water-soluble glycol is recommended for greater inhibition.
•Diesel oil, mineral oil and synthetic systems all provide excellent hydrate suppression.
–This inhibition is a result of the limited amount of water contained in them and the fact that the water phase generally has a high concentration (>25% wt) of calcium chloride.
–Dissolved gasses can reduce suppresion