Other Operational LL with Wellesley

Schweinsteiger (6204/11-3) – Top hole

What happened:

Hit shallow gas at 331m, only 24m below 36″ conductor shoe. Killed with 1.50 SG kill mud. Drilled ahead 1 stand with 1.25 SG “pump and dump” mud/3000 lpm, no gas. Displaced back to seawater and reduced flow, began to flow at 1500 lpm, unable to regain control dynamically with seawater at 3000 lpm, killed well with 1.25 SG, stable.
Drilled ahead 9 7/8″ pilot hole with seawater and sweeps, dynamically flowchecking with ROV (rotary off) on connections, then controlling well with 25-27 m3 1.25 SG “mud cap” displaced into drill string / conductor annulus above gas zone before connections.
Drilled to TD (631m), displaced to 1.50 SG kill mud, POOH. Opened hole to 17 1/2″ to 630m, displaced to 1.35 SG kill mud, POOH.
Ran and set 13 3/8″ casing as per programme but filled with 1.25 SG mud to avoid gas zone ever seeing less than 1.25 SG. Washing down not required. Retrieved running tool, ran stab-in sub to just above landing collar, displaced to string to fresh 1.25 SG mud, stabbed in, displaced annulus from 1.35 SG to 1.25 SG, pumped 1.26 SG spacer then 100% + excess Expandacem 1.53 SG unretarded slurry with full returns.

What was planned:

No shallow gas expected in top hole.

What was learned:

Learned ?? There are no procedures nor manuals in the world that tell you how to do this stuff. Focus of all Well Control manuals and “Standard Procedures” for shallow gas is how to keep personnel and the rig as safe as possible, move rig off location, drop string etc…..but nothing on “what to do next”.
The lesson is that with a sensible, pragmatic team approach, both onshore and offshore between client and drilling contractor, supported by good service support, then problems like this may have a solution. The use of the 1.25 SG mud cap and ROV for flowchecking allowed the section to be successfully drilled.

What actions are required:

To solve this required mud – and lots of it (350 m3 used ??). There was no time to build cheap weighted mud from scratch, so planned KCl mud volumes planned for the next section had to be used.
In future, investigate ahead of spud what possibilities there might be to build large volumes of cheap CMC weighted mud 1.25 SG, shoreside in the nearest accessible mud plant (Fløro ??) if required.
Is a viscous weighted 1.25 SG brine an option ?? Could then use the rig’s brine column tanks to store.