Pig delivery and transport system for subsea wells

In a transport system for the transport of a hydrocarbon product from a plurality of subsea wells to a product receiving facility, said system comprising,

• a looped line having opposed ends connected to a product receiving facility and constructed and arranged to receive a traveling pig therein movable along said line between said opposed ends;
• said looped line having a high pressure product line section extending from said subsea wells to the production facility for product transport, a low pressure non-product line section extending from the product receiving facility, and an intermediate connecting line section between said product line section and said non-product line section;
• and
• a pair of shut-off valves mounted adjacent said opposed ends of said connecting line section and movable between open and closed positions to define upstream and downstream shut-off valves, said valves permitting a pig to move therethrough from said low pressure non-product line section to said high pressure product line section.

A method for transporting a pig from one end of a looped line to the other end thereof with the ends connected to a host facility for subsea wells, the looped line having a low pressure non-product line section adjacent said one end, a high pressure product line section adjacent said other end thereof extending between the subsea wells and the host facility, and a connecting line section between said low pressure non-product line section and said high pressure product line section, said method comprising the following steps,

• positioning a closure member adjacent each end of said connecting line section, each of said closure members being selectively movable between open and closed positions, with one closure member positioned adjacent said low pressure non-product line section to define an upstream closure member and the other closure member positioned adjacent said high pressure product line section to define a downstream closure member;
• placing a vent line and a boost line in fluid communication with said connecting line adjacent said downstream and upstream closure members;
• placing a selectively operable vent line closure member in said vent line and a selectively operable boost line closure member in said boost line;
• inserting a pig in said low pressure non-product line section for movement along said non-product line section;
• opening said upstream connecting line closure member, closing said downstream connecting line closure member, opening said vent line closure member, and closing said boost line closure member, and then moving said pig from said low pressure non-product line section into said connecting line section through said upstream closure member in the open position thereof;
• and
• closing said upstream connecting line closure member, opening said downstream connecting line closure member after said pig is received within said connecting line section, and then closing said vent line closure member, opening said boost line closure member for transferring said pig from said connecting line section into said high pressure product line section through said open downstream closure member for movement of said pig through said high pressure product line section to a position at which well fluids force said pig to said host facility.