[BITList] Fwd: Centaur identified with video footage

[John Feltham]

But wait, there's more....

Begin forwarded message:



Hi John,
 
Excellent description of those Riser Tensioners  - thanks.
I believe they also act to reduce the roll of the ship as well as her rise and fall.
Here is some more,  and if I've made any mistakes I would appreciated correcting by Hugh or Frank.
I've been away from this game for over 10 years and the technology advances at a remarkable pace.
 
Once the initial hole has been made  it is enlarged in the early stages,  and the hole then looks like an inverted telescope with the widest at the top.  The initial section are lined with drill pipe which is cemented in position,  and on the top of that,  at the sea bed,  the Blowout Preventer is installed.  With exploration rigs (those floating platforms),  a large diameter pipe - the 'riser'  is connected between the blowout preventer and the rig.  Through this passes the drill string.
 
The drill pipe is hollow and chemical mud is pumped down throught this  to the drill head.  It cools and drives the older drill bits,  flushes the bit clear of debris,  and returns to the drill ship/rig/platform outside the drill string and up inside the riser, to the drill platform  where it is inspected by the mud engineer (highly qualified) to confirm what it is drilling through.  It is then sieved and returns to the mud tank for further use.  Eventually when too saturated with gasses,  it is returned ashore for refining as it's expensive,   often oil based, stuff.
The pressure of the mud can also be used to counter pockets of high pressure encountered by the drill.  Blowouts are awful - the whole string is blown out of the well,  often followed by explosions and fire at the drill floor.
 
Further parts of the well might be lined with pipe,  but only those where the drill string passes through a soft strata (sand, etc.)
 
 
In answer to Hugh's final comment - the drill string is withdrawn.
 
Big job:  some strings are over a mile,  with those from platforms (the fixed structures) extending up to 5 miles.  As platforms often have 20+ wells,  and the drill bits can now drill horizontally as well as vertically  using gyro stabilized and video controlled drill bits (!!!),  the subsea bed  well distribution can look like spagetti junction beneath one of those bigger production platforms.
 
The trick,  for the Installation Manager of an exploration rig,  is to decide when to ride out the storm,  and when to draw back the drill string.  The latter can put days onto an exploration,  and that costs big bucks.
 
So the local met man really does put his job on the line.
 
Looks like quite a few ex BI men also went into the offshore arena.  It can be a wild,  exciting,  dangerous,  and ultimately very satisfactory work place.  Working 1 on 1 off is also an attraction.
 
The South China Seas are rough areas to work.  Most of my work with the drilling side of offshore ops in the North Sea.  Initially (1982) we were dedicated to Magnus,  B.P.s major UK platform - and the most northern platform in the North Sea,  close to the Faroes.  It was built with an airgap of 100 feet - the space between the sea surface and the underside of the platform - to allow for the predicted once every 100 year,  100 foot wave.  There were two in the first year which shook everyone and broke the back of our ship (converted 15,000 ton product tanker).  The king beam went,  and the maindeck split open between some badly constructed modified hatch openings,  but being 25 years old and built like an outside toilet,  she was o.k.
 
As she was needed on site and only went into port once every 5 years (surveys etc.) we were asked to strap her together.  A load of 1 mtr square, 2" plate was sent out,  with two opposite ends champhered (is that the correct spelling:  cut at 45° for welding).
Each plate was individually welded to the main deck, abutting each other with the champhered ends together, in four rows fore-and-aft,  two pair on the port side and 2 on the stbd side of the maindeck,  and each time we had a calm day,  the cut edges of the plates were filled with weld (we had many offshore grade welders on board as part of our flotel/disaster/workshop role).    In the end we had 4 massive straps holding her together.  The break in the kingbeam was in the old pumproom just abaft amidships and I scaffolded down from the under maindeck and constructed a platform so that the beam could be strapped and welded together.
Took about 3 weeks and we had a remarkable weather wind of calm seas.
 
When we finished at Magnus,  we worked in the winters in the Atlantic to the west of the Shetlands,   on the edge of the Continenal Shelf.  Kinda lonely out there,  and Big swells!
During the summers we would go piping acrtoss the North Sea,  in the Med,  etc., or get involved in survey and other odd jobs.  My last job was piping off Sable Island,  Canada.
 
Some photos somewhere,  if your ex-BI guys can stomache the occassional (Shshsh converted tanker )
Chris



ooroo

Bad typists of the word, untie.




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