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The trip to Mother is rapid and noisy. You note the daughter miners with new appreciation. One of them is loading from a supply vessel, hauling containers straight from the ship up into the stores level.
Attached to Mother is a smaller semi-submersible… “Power plant” shouts the pilot in response to your pointed finger.
The helipad on the mother miner is bigger and even features a kind of hangar to one side. The figure who meets you looks familiar in the orange suit, but proves to be a standby pilot who takes you to speak to the OIM.
Marco Pinheiro is flamboyant in a pirate-style outfit… he seems to be dealing with several things concurrently… you give him the envelope and wait. Some minutes later it is with a start that you realise he is now talking to you. “Welcome to Northern Mother… if you look at the diagram on the wall, you will see the layout of our operation.. I will explain:”
There are some familiar features, and some obvious differences from the daughters; you have no time to ask.
“Our function is:
- 1. Control Centre and Permanent Living Quarters for the daughter miners
- 2. To compress the LP (low pressure) and HP gas to pipeline pressure. We export 140 million cubic metres of gas per day, and that will eventually rise to 240 million.
- 3. To pulverise and clean the MHS. We export 720 thousand tons per day, and that will rise to 1.3 million.
- 4. Production of hydrogen for our power systems and those of the daughters.
- 5. Buffer tank for the production - we store 100,000 tons of High Pressure gas, 1,200 tons of Hydrogen plus about a million tons of MHS (Methane Hydrate Slush) and up to 2,000 tons of CO2 and 500 tons of minerals.
- 6. To send the Gassy water in batches to Central for processing
- 7. To collect minerals and reinject into the MHS stream.
"The base of the MM (shaft and skirt) is split vertically - the forward tank receives slush from the miners, making it a production buffer, while the rear tank pumps slush out to Central and is an export buffer. Between them is the Milling core, which pulverises the incoming (golfball-sized) chunks to granulated sugar."
You look at the scale on the drawing; it’s vast! Why do you need to store so much MHS
"Well, the daughters produce in batches so we even out the flow to Central. Also we need settling time; while the slush is in these two holding tanks (a day and a half on average), the alluvium settles out, is processed and returned to the seabed and more gas is released which then joins the overhead gas buffer."
How are you connected to the Daughter miners?
"Fluids flow via a bundle of pipes which form a U-shaped subsea umbilical connection. This allows the daughters to move independently up to a certain limit. Every 650m or so, the mother relocates following the daughters' progress. We're preparing for a move now; perhaps you would like to go and have a look?"
You follow Marco down to the lower deck. He points at some massive vertical cannons whose base is connected to pipes..
"These are pig-traps for the export lines: 42" Gas, 36" MHS. We send stoppling pigs down the lines before moving; the pigs seal off the area where the new sections of pipeline will be inserted. We propel the pigs down the pipe with a slug of seawater; when the insert is finished, the process is reversed."
But the lines go straight down into the water!
"Yes, but once underwater they execute a slow curve, bottoming out on the seabed beneath where the Father miner is stationed at the moment." He points at the semi-sub some distance away “You will observe the flotation buoys which mark the track of the pipeline… we normally operate with 5 buoys floating; if the line is too tight, you see more buoys and vice versa”
Why are you breaking the lines just there?
"It's where we always extend the lines, just over a kilometre from here, there's a permanent break-point there; it’s a safety factor, keeping operations well away from us."
So where are the insert lengths of line?
"They are fabricated on Father in 650m lengths and laid on the subsea sled ready for placement. One end has a flange ready for connection to the forward line (the other end of this one, which has a permanent flange on it)" He pats one of the monstrous pipes… "and the other end of the insert is welded directly to the permanent pipeline going to Central by subsea robotic machines."
So you must cut the old flange off the rear section before you weld on the new insert!
"That's right. We use a machine called a 'cold cutter' which removes the flange and bevels the pipe ready for welding at the same time. The entire operation takes five hours, extending both lines in parallel. Its entirely automatic, although closely monitored, of course"
How about instrumentation and control?
"There are two fibre optic cables spooled on the sled; it's just a matter of undoing a connector, unrolling 650m and remaking the connection - nothing to it! Every 50km we need a new reel, but that's all easy stuff."
How does data get through when the lines are broken?
"You can break a ring at any point without severing the connection… information can always travel the other way round the loop."
And what’s on the ‘Power Plant’ semi?
“It’s an Oxycell plant using our low-pressure gas as feedstock and producing hydrogen, electricity and compressed CO2. It’s a ‘hot’ process so we keep it at arms length for safety purposes.”
What happens to the CO2?
“It’s piped to Central in batches down the CNG line, separated by ball pigs”. He looks at his watch. "We've still got an hour before the move takes place; just time for a look downstairs."
You make your way to the lift
"There are six levels in the topsides:- Helideck, Offices, 3 PLQ (Permanent Living Quarters) decks, air intakes & stores, but we are going down"
The lift stops automatically at 'Lobby' and you have to get out to log in with the storeman who keeps a constant record of who is 'downstairs'. Another lift takes you further down, without tilting this time, and stops at 'Maintenance'. You emerge onto a vast suspended walkway which surrounds an open well of about 30m diameter. From above, huge air conditioning ducts descend and belch air in all directions. Despite their affect, it's hot!
"So this is the top level of the machinery hall, located at the base of the tower, which goes up another 60m from here, as you can see. We're already about 30m below the sea surface, and out of the worst of the wave zone, so at this level the tower is 90m diameter. Alternatively you can think of the Hall as a separate structure built around the 30m diameter foundations of the tower. The void in the centre provides maintenance space and access; if you look down, the 'floor' six stories below us, is actually the top of the Gas Head."
It's an impressive view, similar to that from a balcony on a tall building. You can see behind you an open area with a number of machines in various stages of disassembly and a pair of men working over them, but opposite, in a number of recesses, are a number of large humming boxes.
What are the boxes?
"Oh, the maintenance area doesn't occupy the whole of this level. What you can see on the other side is the top half of some Fuel Cell stacks, we'll see those better downstairs. We overhaul most of our own stuff here, with the help of the Vendor's reps, of course. It tends to be easier than trying to wrestle big machines out through the top of the tower. It is possible, of course."
And what are those machines hanging in frames outside the handrail?
"Those two are spare MHS pumps, already overhauled and ready to drop in next maintenance period. The other unit is a spare grinder shaft. Shutdowns have to be kept to a minimum so there are lots of spares available… and we don't have the space and weight limitations that plague most offshore installations!"
You can certainly see that; there is an impressive amount of space available. We descend one level via the stairs; it's 12m (40 feet) down. All around are a series of deep 'garages' with coloured boxes inside. The hum is furious here!
"This is the main PEM (Proton Exchange Membrane) Cell level, producing Electricity from Hydrogen. The cells are stacked because they are linked in series to boost the voltage. Hydrogen enters from the rear, air from the front and exhaust is ducted away from above."
Why are the cells in each 'garage' painted a different colour?
"With a number of similar enclosures like these, it is easy to become disorientated. Although all the cells are labelled, of course, the colour helps as well. Each enclosure has a fire door at the front and can be isolated and flooded with inert gas within 30 seconds. Hydrogen makes a nasty fire!"
I'm not sure I would want to work all day in the purple enclosure!
On a different subject, why so many huge ducts?
"Half these ducts are delivering fresh air from the filter house on topsides, and the other half are removing depleted air and water vapour. Makes it quite breezy altogether. It's quieter downstairs"
We descend another flight, only 6 metres (20 feet) this time.
"Inverters and motors here. The inverters are the magic boxes that turn Direct Current from the PEM cells into Alternating; they feed directly into the motors, providing the regulation at the same time. As you can see, the motors are mounted vertically, the pumps and compressors are on the floor below"
Why not use DC direct into the motors?
"AC motors can be totally enclosed and spark free; much safer. With modern electronics, the speed control is easy as well"
The motors are enormous, how do you get them out for repair?
"Yes, each of those monsters weighs over 50 tons, but we can jack them up and skid them out on skates along those rails, there, in a couple of hours. The 100t overhead crane picks them up and drops them straight into maintenance, no problem!"
What is the enclosed room for?
"Aha, that's the Main Switchgear room; pressurised to prevent gas entering. Distributes power from here to the rest of the Rig. Normally unmanned."
We descend to 'Floor Level'.
"And here are the gas compressors, 18 of them, and behind, against the outside wall, the intercoolers… direct seawater cooled, of course. The main distribution pipework is in the headspace of the GSH underneath us, so it is all relatively uncluttered. Again the pipes can be disconnected from the sides so that the machine will skid forward if it needs to come out for maintenance."
How many are working? It seems very quiet.
"The main pipeline boosters aren't running, of course, as we're preparing for the Move, but the Gas compressors are working full tilt - there are 8 of those, plus 2 spare. The daughters don’t stop working just because we are moving! Of course, quietness is also linked to efficiency… this lot has an overall energy efficiency of 68%, from chemical energy in the hydrogen through to pressure energy in the CNG. That's pretty good!"
You have to agree. And what is that in the middle of the hall floor?
"The railed-off area is the top of the gaslock used for withdrawal of the MHS export pumps and the Milling hub. These items normally operate in the MHS tanks 150 metres below us now, powered by 'totally immersed' electric motors. The big cables going through those transits are the 660 volt power supply."
A siren sounds and your guide ushers you towards the lift.
"Everybody has to be topsides during a move, so time to go upstairs!"
Thankfully there is a lift from the Compression floor. We check out with the storeman and make our way up to the Control Room.
The move involves the same pair of tugs who assisted with the relocation of Sister N2, and is equally smooth, comprising a total displacement of 635.4 metres.
"We just choose the next suitable location within our depth limit", explains the OIM, "we can normally find a firm base between 630 and 670 metres, and like the daughters we only need to put 10,000 tons or so pressure on the seabed."
How often do you have to move?
"We move every Friday! The Southern miners move on Tuesdays. We try to keep it a regular pattern so everybody is ready for it. HP Central, for example, has to be ready for the Gas flow to slow down"
Doesn't it stop completely when the lines are cut?
"No, the pipeline has quite a storage capacity, especially as it grows longer. Also, there is a powerful secondary effect as the pressure drops from its normal operating pressure of 80 bar; the partially depleted gas pockets which the Father has connected into the pipeline start to produce again. Of late, the pressure has never dropped below 60 bar even during a 12-hour outage."
During a move, the father miner follows your progress while paying out the pipeline inserts behind. How does he match your progress?
"Well, in theory that's all controlled by computers tied into strain gauges on the lines and the GPS system. However, it's normal practice to keep an eye on the flotation buoys you saw earlier; they are designed to rise if the pipeline is getting taught and sink if it sags. This 'belt and braces', computer-and-manual approach has never let us down yet."
The tannoy interrupts and the OIM excuses himself to return to his desk and ‘supervise’ the transit. Another sensationless half hour follows, the only indication being that everybody is at their stations watching various screens and instruments. Once Mother is static again, business returns to normal. The OIM returns looking more piratical than ever. He guides you to the mess for a coffee before departure. It seems pretty busy there.
How many crew are based on mother?
"Offshore we work 24 hours per day, which means basically we carry 2 crews. Directly there are:
| Mother's home crew is 12, times two shifts | 24 |
| Daughters' crews are based on mother, but only one here at any time. | 21 |
| Add temporary overnighters eg pilots, suppliers | 4 |
| Total on board as of today: | 49 |
How does that compare with the total workforce?
"Of course, everybody works 14 days on and 14 days off - so you can just about double that number if you want to compute the payroll." He pauses. "Then Father has his own crew of 54, with another 48 on leave at any time, plus 8 on tugs with 8 off, so total Northern Miners offshore workforce is about 270"
Another thought.. “Plus, of course, the support team back at base, say a dozen more, but they "
So you actually run a fair-sized hotel here?
“We have 60 rooms and a 4-man sickbay; quite modest for an offshore installation… don’t forget, many of the team are just here during transit so don’t need accommodation unless on weather hold. Currently we are rarely full because there is provision for another two daughters in a few years time as production ramps up” He looks at his watch.. “but your chopper will be here soon”.
You thank your host and take your leave of the 'Northern Family' and within an hour are flying in a 50-seater double rotor helicopter over a series of inlets to land in an industrial complex. You thought you were going to HP Central. "That's right" confirms your neighbour, "we're here!"
You are greeted by Rosita Gomez, personnel officer, who laughs at your surprise. "The original intention was to have a platform, but with the development of the new harbour complex here, it became more economic to build a landbase. It is still called 'HP Central' though"
You are allocated a room in the BHD hostel. Supper is rapidly assimilated, and although it is only 7pm, sleep is eroding your consciousness. Luckily there are no appointments that evening!
Roger Clark
STEP 2000