Ann: West Erregulla Update, page-53

Pressure testing of the wellhead seals was unsuccessful and upon investigation it was found that the slip and seal assembly for the 13-3/8” casing connection had failed.With the slip and seal assembly not suitable for reuse, a new assembly will be required and is currently due to arrive in approximately one week.

There are essentially two styles of land wellheads.....'conventional' where you have to install one spool at a time (after each casing run) and install the BOPs on top. So the 17 1/2" was drilled, the 13 3/8" was run and cemented......then they have to run the slip and seal assembly which is either run through the rotary table or the crews go into the cellar, nipple down the BOPs, raise same and install the slip and seal, set the slips, pressure test same, rough cut the casing, layout the cut off, final cut on casing at correct height to all the next spool to be installed followed by lowering the BOPs and nippling them up ......then go drilling after some more pressure tests.......the other style of wellhead is a 'multi bowl' type, where it is installed (In this case on the 20" casing string) and it is machined in such a way on the inside with a shoulder to match a 13 3/8" mandrel hanger which is run on the last joint of casing and lands out on the shoulder. Do the cement job and then nipple down the BOPS and install a multi bowl intermediate spool, N/U BOPs, pressure test etc....and drill the next section, run 9 5/8" casing, land out with a 9 5/8" mandrel hanger without ever having to remove the BOPS again.....this includes the 5 1/2" casing after the 8 1/2" hole is drilled....

The conventional systems are cheaper but when the economics are run with the operating daily spread rate and times taken for each option, it closes the gap considerably.

So, after an 'after action review' on this seal failure, documenting the lessons learnt, hopefully there will not be any recurrence of this type on the balance of this well and future wells.