Subsea methane hydrate production
An offshore methane hydrate production assembly ( 1 ), having a tubing ( 41 ) extending into a subsea well ( 5 ) that extends down to a methane hydrate formation ( 7 ) below the seabed ( 3 ). A submersible pump ( 45 ) is arranged in the tubing ( 41 ). A methane conduit ( 35,35 ) extends down from a surface installation ( 49 ). A well control package ( 15 ) landed on a wellhead ( 13 ) is positioned at the upper end of the subsea well ( 5 ). Moreover, an emergency disconnection package ( 25 ) is arranged between the methane conduit ( 35,135 ) and the well control package ( 15 ). The tubing ( 41 ) is suspended from the well control package ( 15 ). Other aspects of the invention are also disclosed.
1. A method of providing a methane hydrate production string extending between a subsea methane hydrate formation and a surface installation, wherein a drilled well extends between the methane hydrate formation and the seabed, the method comprising:
a) joining tubing pipe segments into a tubing string configured for transporting liquid, and arranging a submersible pump as a part of the tubing string for pumping the liquid through the tubing string;
b) suspending the tubing string from the surface installation;
c) connecting a lower end of a landing string to an emergency disconnection package which is arranged above a well control package;
d) landing and connecting, at the surface installation, the well control package with a connector to an upper end of the tubing string, while the tubing string is suspended from the surface installation; and
e) on the landing string, lowering the tubing string from the surface installation through the open water into the well until the well control package lands on a wellhead on top of said well.
2. The method according to claim 1 , wherein the landing string used to lower the tubing string in step e), is a riser string which is maintained as a part of the methane hydrate production string when the tubing string is installed in the well.
3. The method according to claim 1 , wherein the landing string used to lower the tubing string in step e), is a landing wire.
4. The method according to claim 2 , wherein:
step c) comprises connecting the lower end of the riser string to an emergency disconnection package main bore; and
step d) comprises connecting the tubing string to a well control package annulus bore.
5. The method according to claim 1 , wherein:
step b) comprises:
i) suspending the tubing string in an installation skid at a lower deck;
step c) comprises:
ii) joining riser joints at an upper deck or preparing a landing wire;
iii) moving the installation skid out of a well center position below the upper deck;
iv) moving a stack comprising the well control package and the emergency disconnection package into the well center position below the upper deck;
v) connecting the landing string to the emergency disconnection package and suspending the stack on the landing string;
and step d) comprises:
vi) moving the installation skid back into the well center position; and
vii) landing the stack onto the installation skid.
6. The method according to claim 5 , wherein step d) comprises one of the following steps:
viii) by means of an elevation arrangement on the installation skid, engaging a lower portion of the well control package with a connector on the tubing string; and
ix) by means of a derrick winch, lowering the well control package, while suspended on the landing string, onto a connector on the tubing string.
7. The method according to claim 1 , wherein the upper end of the tubing string is not connected to a tubing hanger.
8. The method according to claim 1 , wherein the connecting the well control package with the connector to the upper end of the tubing string comprises, connecting a pup joint extending below the well control package to the connector at the upper end of the tubing.