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01 Jul - Oil Rigs and Drilling Platforms

RRS Ernest Shackleton Diary


Position @ 1200: 57°04'North 002°05'East. Inside 500 m zone of the Sedco 714 Semi-submersible Drilling Platform.
Conditions: Wind WxN x 23 kts; Barometer 1022.1 mb; Air Temperature 14.0° C; Sea Temperature 12.6°C; Scattered clouds but Sunny and bright.  Seas moderate with moderate swell and maximum visibility.
Map of survey sites (located on the Machar field 138nm due East of Aberdeen).


In the words of Gary Glitter... I'm back, I'm back, as a matter of fact, as a matter of fact, I'm back

Your friendly Web page editor Steve B has taken over the reigns of power once again from Mike Gloistein who has gone for some well-earned leave, and many thanks to Mike for his sterling efforts over the last 4 months.

Thank you also to those members of the public who have reported back to BAS to say how well-appreciated the web pages are every week.  It makes our job so much more pleasurable to hear that there are people out there who are actually READING this stuff.   I certainly don't !!!


This week saw RRS Ernest Shackleton visit Aberdeen for a day.  Primarily to effect a crew change of the charter personnel onboard, but also allowing other BAS crew members to change early of the main crew change due on July 12th.

From the Neptune Platform on Sunday, the ship proceeded to Aberdeen via the CATS pipeline and the Lomond Platform to the East.  Several ROV deployments were carried out at these sites before the ship finally arrived in Aberdeen on Thursday morning 28th June.  Arriving at the fairway buoy by 0720 hours, the Ernest Shackleton was alongside the Duthies Quay in the old harbour by 0800 hours.  The weather was excellent and was no bar to the bunkering and stores operations that started immediately upon arrival.  By 1500 hours, the stores and bunkers were loaded and remedial repair/upgrade work on the ship and ROV systems were well under-way.  But the port call was only brief and by 2000 hours the ship was again made ready for sea.

Ernest Shackleton departed the Aberdeen harbour at 2044 hours with a different Chief Engineer and Radio Officer (ETO comms) onboard and a whole fresh scattering of faces amongst the Charter personnel.  The next change of faces will occur in two weeks when the main crew change for BAS personnel is due to take place.

Back to work.  The ship proceeded 150nm directly East to arrive at the Lomond Platform exactly 12 hours later.  The seas were calm and the weather was sunny and warm - excellent conditions to re-commence the work alongside the Platform.  The usual DP Checks were performed according to procedures set down, that is when a fault showed up on the main DP (Dynamic Positioning) console.  Without 100% on the DP System, the ship is unable to proceed alongside the Platform and work, so it was 'all stop' whilst the ETO effected repairs.  By lunch time, those repairs had been completed and the checks confirmed we were once again at 100% performance and so were granted permission to enter alongside and deploy our ROV's.  Gripping stuff this !

Surveys of the sub-sea equipment at the Lomond Platform was completed by early Saturday morning and the weather was again kind to us.  Indeed, there were no hold-ups and at 0520 hours, the Ernest Shackleton cleared the 500 metre Zone and sailed the 1 hour to the ETAP (see map) and the Sedco 714 Semi-submersible drilling rig on top of it.  Once all the necessary checks had been completed, and the ship given permission to go inside the 500 metre Zone, the Lynx Remote Operated Vehicle went into the water to survey the anchor chains of the Rig before proceeding to work on the sub-sea structures.

Sunday lunchtime still found the ship at the ETAP and working alongside the Sedco 714.


A PRÉCIS OF OIL RIGS AND DRILLING PLATFORMS
By an Ex-Oil Rig Worker.

Before having set foot on an oil rig or platform of any description, it was amazing to think that I knew nothing about them whatsoever.  Subsequently, I discovered friends and family ashore equally had no idea of the variety of installations there are working offshore.  Basically they fall into 4 categories, or 5 if you count the ones that the Texans build on the land and have 'nodding donkeys' pulling the oil out of the ground. (you've all seen Dallas !).

The Platform is the final stage in offshore gas and oil production.  Once the surveys have been carried out and the drilling rigs have been in to estimate the potential of a field, then the Platform is built in order to facilitate the removal of the 'product' from beneath the sea bed.   The Platform is a structure which is fixed in location and looks like a monstrous lollipop with most of the weight situated high above the waterline on stilts or a tower, or 'jacket'.  see picture.  They always look 'top-heavy' and leave you wondering 'why don't they topple over' ?  They really are a fantastic piece of design and engineering.  Once the jacket is sunk into place - either metal or concrete in construction - then the 'plant' and accommodation is placed on top and there it stays for the length of it's working life.  There are Platforms in the North Sea that date back to the early 1970's, so they are not necessarily 'short term' structures.

A platform. Click to enlarge A plan section of a platform. Click to enlarge

A platform and a plan section of a platform
Click on image to enlarge


The Rig is the penultimate stage in Oil and Gas extraction.  Once seismic surveys have established the probability of product under the sea bed, it is the job of the drilling rig to explore the possibility of exploiting the find.  Unlike the Platform this is not a fixed structure, but mobile, allowing the rig to be used throughout the oil and gas fields and indeed, worldwide.  I have worked on rigs that have spent a long and productive life in the North Sea only to be towed off to a future life in the South China Seas and the Far East.  They really are that mobile. These 'floating rigs' fall loosely into two varieties.  The Semi-submersible, and the Jack-up type rigs.

The Jack-up Rig is exactly that.  A structure with 3 or 4 long legs which can be lowered and once firmly established on the sea bed, further 'jacking' can lift the drilling/accommodation structure high above the water level and away from the forces of the sea.  When you see the apparent flimsiness of the legs - some tubular structures and other solid metal - it leaves you wondering how they can bear the weight ?  Once jacked up in position, these rigs are very stable platforms from which to drill deep into the earth's crust.  So stable infact, that I have seen pool tables installed on these type of rigs.

The main limitation of the Jack-up is that is it restricted to the shallow waters where the length of leg can reach the bottom.

A jack-up rig. Click to enlarge A plan section of a jack-up rig. Click to enlarge

A jack-up rig and a plan section of a jack-up rig
Click on image to enlarge


The Semi-submersible Rig alternatively is an ingenious vessel which is more akin to a ship than an oilrig.  The usual arrangement is for a low profile drilling platform and accommodation to be mounted upon two or more 'torpedoes' which form the hull of the vessel. Just like some strange catamaran.  When in transit, the torpedoes are 'pumped out' which allows them to float on the surface and the rig can be towed into position.  Some semi-subs even have their own propulsion systems and can make headway on their own !  But once on location, the torpedoes are flooded and the additional weight makes the rig 'sink' way down like an iceberg with the majority of the structure below the waterline.  This gives stability against tides and weather, but unlike the jack-up it has no 'fixed' connection to the seabed to keep it in position.  So this is effected by an array of anchors on chains that emanate from the rig in all directions.  As can be seen, this leaves an arrangement similar to that of a grotesque water-spider just below the surface.  The anchor chains are kept on tension and this effectively keeps the rig stationary despite the best efforts of wind and weather.  There have been occasions when anchor chains have parted but with 8 or more chains taking the strain, there is plenty of allowance for the odd loss.

The main advantage of the Semi-sub is that it can work in deeper waters and only the length of anchor chain limits the depth of water in which it can operate.

A semi-submersible rig. Click to enlarge A plan section of a semi-submersible rig. Click to enlarge

A semi-submersible rig and a plan section of a semi-submersible rig
Click on image to enlarge


The other type of rig is actually a Drilling Ship.  The Drill ship is a purpose built (or converted) seagoing vessel which has been adapted particularly for drilling operations.  This uses thrusters and propulsion units in order to maintain position over the drilling site and therefore is not restricted to depth of seabed limitations.  It is also very transportable and has arenas of operation throughout the world.  This is what the Ernest Shackleton - Drill ship might look like !!!

How the Ernest Shackleton might look as a drilling ship. Click to enlarge Click on image to enlarge photograph.


 
Author - Ex-North Sea Rig Pig


And Finally ...

In keeping with our Antarctic flavour, the following was kindly plagiarized from the pages of the Polar Ship Management's 'Polar News'.

'Polar Bird Shooting film on Greenland'.

Of all the special tasks undertaken by our ships over the years, Polar Bird's last charter is one of the more exotic ones :-
When this is being read, the ship is enroute for Greenland to operate as hotel - and baseship for a major film-project.  The ship is chartered to a British film company which is producing a major film about the great British Polar hero, Sir Ernest Shackleton, and his incredible voyage with the ship 'Endurance' to the Antarctic from 1914 to 1916.  Our company is not entirely a stranger to this story ... We willingly admit that the special connection that our company has to these names makes it especially interesting to be allowed also to participate in producing the film about Ernest Shackleton.

Not only was the original 'Endurance' built in Norway as 'Polaris', but today's modern HMS Endurance is also known as our ex-'Polar Circle', whilst ex-'Polar Queen'today sails for the British Authorities under the name of RRS Ernest Shackleton.

'Polar Bird' completed an especially long Antarctic season for Australia in Hobart on March 31st,  where after she immediately sailed in ballast for Europe.  After a quick stop in Cape Town for bunkering, she arrived London around 10th May where she mobilized for the film task.

'Polar Bird' has had many different cargoes onboard these years, but we bet you that she has never before had onboard a containerized make-up room !  Onboard will also be copies of the lifeboats that Shackleton and his crew used for their rescue after the 'Endurance' was crushed by the ice.  Enroute for Greenland 'Polar Bird' will stop at Reykjavik to take onboard as many as 99 actors and film crew, so that the ship will be packed throughout the task.  In addition there will be a large number of sledge dogs onboard, having their important roles to play.  We assume that it will be crowded in the cinemas and in front of the televisions as well, with Ernest Shackleton being played by no other than Kenneth Branagh, one of Britain's great actors, known from major film and stage events such as 'Hamlet' and 'Henry V'.  If we are lucky, the 'Polar Bird' will perhaps herself become a film star - a documentary will be produced on the making of the film, which will be shown on the BBC and various other channels around the world.   There will also be a special edition on the film and it's making in the Sunday Times.

The Web Page gratefully acknowledges the contribution of the Polar News.


Forthcoming events: Working in the Central North Sea in Scottish waters.

Contributors this week: Grateful thanks to Polar News for the article on filming in Greenland.

North Sea Diary 08 will be written on 8 July 2001 and should be published on Monday 09 July 2001.

SteveB


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