(click here to download MS Word version)

Just after the Lencois Maranhenses National Park, we land on a small airstrip close to a town. "Paulino Neves," advises your companion "temporary waystation for the Northern Miners, I'm going on to Fortaleza". You say your goodbyes.

It's 10.45 am. and hot already, but it's only a short hop to the helicopter and you have no time for hesitation. The pilot is a cheerful young man. "Hi, I'm Oliviera Paes". You introduce yourself.

"It's about 100 kms to the Northern Miners, they're on the move all the time and we've just started using this airstrip for access."
We fly off into the sun and you are grateful for the overhead shade and your polaroid sunglasses.

Your pilot is well educated and it soon becomes clear that he knows quite a bit about the miners and considers himself one of the team.

How do they locate the Methane hydrate? You want to know. Is it similar to oil?

"No, hydrate occurs in 'patches' rather than reservoirs. Large patches can be detected with remote instruments, but we want all of it! Hydrate is fairly widely distributed on the Brazilian continental shelf at depths over 400 metres. Our miners work a strip between 370 and 620 metres. We don't find much at 370 metres, but what is there is very unstable so the shallow miner tries to get it all. There is more in water deeper than 600 metres, but it's locked up safely and we just note its location for future use."

He points. "We're approaching the miners now, you can just see them beyond that ship, almost dead ahead"Yes, you can see a semi-submersible, with its familiar support columns & drilling derrick and to the left a few smaller objects, a bit like lighthouses with large heads!
Are these really high-pressure miners?

"Yes, those at the left are the daughter hydrate miners", he points to three towers spread out in a wide arc at right angles to the coast, "each one works at a different depth, obviously the closest to us is the shallowest. To the right is the Mother Miner, which is a bit bigger and the service semi-sub is the Father Miner, which follows behind and looks after the pipelines and wellheads. They are moving from right to left, as we look at them"

Under the water, beneath one of the miners is the outline of a huge hexagonal base. Why is that one different?

"It's not different - just working closer to the surface than the others, consequently you can see the subsea structure more clearly. The miners sit on the bottom most of the time, which means they have variable amounts of water cover. N3, for example, is obviously near her depth limit." Sure enough, the further tower does look shorter than the others. "Between the three of them, they cover 150m of water depth, which on this stretch of coast represents a 3km wide track."

The chopper heads for the central object, which looks to be a small living quarters perched on a tapering concrete pillar. The pilot has been on the radio… "Right, we're going in to Northern 2, she's due to move this morning so the OIM says you may as well go along for the ride."

On the helideck, it is windy and you are grasped firmly by a substantial figure wrapped in an orange jacket. Once inside, the quiet hits you after the noise of the chopper. Leading the way downstairs, the man introduces himself.

"Hello, I'm Carlos Braga, the master of Miner N2, officially Northern Methane Miner Bravo, come in and have a coffee while I introduce you to the crew." He pours a strong brew while introducing the other four people in the room. "Driller, assistant Driller, Mud & Shots, Survey. Our mechanic and roustabout are downstairs. The cook is in the galley". You nod politely, trying to get your bearings.

"What do you know about the HP Miners?" he asks.

Just the little I picked up on the way from LP Central.

He points to a diagram on the wall. "OK, let's look at the big picture!"

Overview Elevation – Daughter Miners

"This is an elevational view of three of the five daughter miners, operating over their full range of depth. The left one is just breaking into the hydrate patch, the middle one in full production and the right one cleaning up prior to transit. It shows the way the caisson is telescoped down to stimulate the right circulation. Each miner is like an iceberg… 90% is under the sea… all that shows is the 75 metre high tower which supports the topsides where we are at the moment."

75m. is almost 30 stories high, that's presumably so that you can operate in a range of water depths?

"Yes, I see that you have been doing your homework… when we're at maximum depth (515 metres for us), only 20 metres of the tower is showing… whereas when we are at minimum, 70 metres is above sea level."

OK, so in that case only 5 metres of the tower is below water, with the hexagonal base almost showing.

"Yes, you've seen it, of course. The hexagon at 330 metres across is the main part of the rig and is called the Gas Storage Head or GSH for short. It is made up of 90 independent hexagonal cells, each of which stores gas at the pressure at which it was captured… for example, if we are at normal operating water level of -250 metres then the gas harvested will be at about 25 bar and stored in the relevant cells. "

So, a huge honeycomb… concrete, by any chance?

He grins. "Right again, and although the concrete structure weighs 5½ million tons and contains some 80 thousand tons of gas, its overall density is only 0.87, so it provides flotation for the rest of the rig."

So, the structure is partially floating and partially resting on the bottom?

"Yes, basically we float from one station to another, but ballast down to the bottom before beginning production. We normally put about 1% of our weight onto the seabed but even so that's 75 thousand tons. However it's essential for two reasons; firstly it anchors us in place while we are drilling and mining, but more importantly it ensures we can't be sunk by gas blowouts; these are an extreme hazard for any floating vessel!"

Are you saying there's no danger of this rig sinking?

"I'm saying we are just about immune from gas bubbles. Even the air we breathe can be switched to bottles at the first sign of gas. Of course, we get several minutes warning standing in 500m of water; our instruments on the bottom are on constant alert. There have been two instances of big gas bubbles over the last 35 miner-years, and either would have sunk a semi-sub according to calculations made at the time. Of course, we have improved our operational procedures since then, but with hydrate, you never know!"

It's a wise man who respects his enemy - you feel a bit more comfortable. How about other hazards?

"Well, like any major industry, we have our minor accidents, but overall our safety record is good and we pay a lot of attention to it! My father was a coal miner, and I can assure you this is a hundred times safer than that industry!"

OK, so what's under the Gas Storage Head, the GSH?

"Well, immediately underneath there's a 50 metre dia. shaft, in our case it's 170 metres high, but our sisters vary from 120 to 220 (and the next generation will extend to 320)… and at the bottom there is a flared region we call the skirt. This is divided into upper and lower by a horizontal diaphragm; the lower skirt is the mining zone and the upper skirt is separation. The skirt is 250m in diameter with a stiffening ring around the outside weighing 96 thousand tons. It forms a kind of keel as well as spreading the dead load widely."

So how is the mining actually done?

"Well, let's take it in sequence…
First the sniffer robots scout ahead for a couple of kilometres or so, finding the hydrate and the methane emissions. They mark the hotspots with acoustic beacons so that we can just float into a pre-planned position. The mining team has three robot probes which scout ahead looking for patches just in front of the workface. Initially we used to follow the seismic indications, but recently we have found it worthwhile to sniff the whole area on a grid basis. The probes test for dissolved methane in the seawater… this approach is particularly useful in shallow water where the hydrate may already have disappeared, but the underlying gas pocket is still active. Then there is another test called dipole measurement which we use to gauge larger deposits. Altogether we know exactly where we will be going for the next couple of months, and roughly for the next six.
Then we ballast down and cut the skirt ring into the seabed with a bit of fancy gyrating motion", he smiles - obviously a speciality of his! " then it's drilling and sampling until we are right through the hydrate and into the gas source… a hydrate bed is always created by an underlying methane reservoir. Having hit solid ground, we cement in some casing and fit a down-hole valve before starting gas production."

OK! Standard drilling technology! You know that bit.

"Every bed of hydrate comes from a source of methane generated within the earth; it's only when it hits the surface of the seabed and reacts with the water that hydrate is formed. Often the hydrate plugs the gas pocket, which can thus be under quite high pressure. That's one reason why we employ experienced drillers - they know all about gas pockets! So normally there is a reservoir underneath, but not always, because it could have blown out in historical times, for example when the sea level was lower."

What pressure is the gas?

"Normally it's about 60 bar, but it can be considerably more if it's deep; the rate at which the field depressurises soon tells you how much is down there. The normal rule is 'small and shallow or big and deep'. Either is OK with us; small pockets rapidly depressurise and deep fields have enough overburden to enable us to strip the hydrate without fear of a massive blowout. 'Big and shallow' are the only problems, and they are rare."

Where does the gas go?

"Field gas, as we call it, goes straight to the Mother Miner at full pressure.. any stray gas from bubbles or dissociating hydrate is caught by the skirt and rises to the GSH. While drilling is going on, our instruments are busy analysing the hydrate under the skirt and planning the shots. We can't start mining until we are happy that the gas field is stable; that normally takes about 18 hours."

That's pretty fast!

"True, but when you're operating a machine which costs as much as this, time really is money! Besides, the reason we're here is to reclaim the hydrate before rising ocean temperatures release it into the atmosphere. It is actually a race against time. Originally it was envisaged that we would be able to work one kilometre per week, but we're finding so much gas these days that progress is only about 700m, although production quotas are up 50% on original targets. At that rate I could be out of work in about 120 years time," he grins, "if we stick to Brazil only, of course"

You mentioned shooting

"Yes that's exactly what it is! We use bullets to break up the hydrate mass, they're fired from the shooting sheath which is lowered from centre of the skirt, like a sleeve around the production casing. The bullets are fired radially to impact the hydrate at about 1 metre square centres. Initially some are fired downwards, of course, to create a sort of pit within which the hydrate nuggets can be collected."

I thought that bullets didn't travel underwater?

"These certainly do! They're specially shaped to form a gas pocket and travel within it… you need to ask Eduardo if you want the details. Once they penetrate the hydrate a couple of metres, they mushroom and the released energy causes a gas flash which rips the matrix open - it looks amazing on slow-motion video!"

How much of the hydrate flashes into gas at this point?

"Oh, less than 1%! It generally just breaks up into lumps between 1mm and 1 metre across and floats around - its density is theoretically 0.91, but the bigger bits normally have mineral inclusions and are about neutral buoyancy. Our mining progress is limited by the rate at which we can clear up the shattered hydrate. Seawater enters here, through valves near the base of the skirt, is circulated through the mining zone, up the 25m diameter caisson tube via the pumps and spinner – these break up the large hydrate blocks and impart a swirling motion to the mixture which then rises into the separation chamber. Here the heavier elements (mud and stones) are thrown to the outside while lighter stuff (gas and hydrate) stay near the axis. The gas diffuses up the shaft through the porous diaphragm at the top of the skirt, and the hydrate is harvested through the skimmer tube along with approximately the same volume of water. From the skimmer, the hydrate slush, as we call it, is pumped through an umbilical to the Mother Miner. Look at this diagram of the skirt circulation”

What happens to the mud and stones?

“Having been thrown outwards by the cyclone, they follow the curve of the skirt and fall into the settling area. From there they are sorted by vibrating screens. Useful minerals are collected while the rest is ejected through ports in the lower skirt and find their way back to the seabed.”

What useful minerals are we talking here?

“Manganese nodules occur within the hydrate and also harbour copper, nickel and cobalt. We try to shoot the hydrate ‘clean’ ie without getting surrounding rock in it. Then we can be fairly sure that most of the mineral inclusions are useful. They are batched back to Mother via the hydrate transfer line”

So you don't vaporise the hydrate at this point?

"We don't vaporise the hydrate at all! It goes all the way to the mainland as a slush; a much more compact medium than a gas. On arrival at the Mother Miner, it is crushed to 50mm nuggets and put into a settlement tank to separate more mud and minerals, but otherwise it is not treated at all until the onshore terminal."

Amazing! And how much can you mine at one sitting?

"Well, we're limited by the 250m diameter of the skirt, of course, but we can shoot up to a few metres of that. Normally, however, the hydrate is getting very patchy at that distance from the source, unless the gas has come up through a crack, in which case we work our way along it progressively. From a reasonable bed, we would expect to recover ¾ million cubic metres of hydrate and say 120 Million scm of gas. There are often small patches we can't get to, so we note their position and leave, after all our job is to get the majority of the stuff fast."

What about gas remaining in the reservoir?

"Yes, good point! We cap the well on leaving, and if it's still got plenty of capacity, the Father Miner will connect it to a subsea manifold later. Otherwise, it has a pressure monitor attached so it can be connected if it recharges itself in due course. About 10% of the wells we abandoned a couple of years ago have come online now… normally they would not be commercially interesting, but when it's methane that we can keep out of the atmosphere, that's something different!"

"If you've no more questions, and have finished your coffee, there's just time for a trip downstairs before we begin the Float."

Your mind is full of half-formed queries, but it's definitely time for a change of scene. A couple of the other crew members have also departed.

Going down in the lift starts off as a conventional experience. The button for each floor has a label, which illuminates as you pass by. Carlos notes your gaze and comments:
"We're leaving 'Control Room', upstairs is 'Helideck'. Next floor down is 'Electrical' and under that 'Hydraulics'… then 'Stores' - that's it for the topsides."
Suddenly, the lift begins to tilt; it's an unnerving experience.
"Just entered the tower; it tapers, of course, and we have to follow the outside wall to keep away from drilling operations - soon be there"
You pass 'Racking' then sure enough, just as you were getting used to the tilt, you're level again and the lift stops - 'Drillfloor. Hard hats and boots only' says the notice. Just as well you put on full safety gear before coming down! You notice that 'Mud Tanks' and 'Wellheads' are the last two stops on the lift.

As you step out into the harsh lights, it is difficult to restrain a gasp; so much space!

"Yes," agrees your guide, "it's actually a conventional fully automated drilling rig, but the effect of removing the derrick, or rather using the tower itself as the structure, is quite dramatic.. The tower is 25 metres diameter at this point, so even a 10 metre drillfloor is dwarfed" His finger points out some familiar features; mousehole, iron roughneck, rotary table, drillers cabin… hello, there's somebody at the controls! "Yes, Santos likes to keep his hand in, although I don't think he has turned off the automatics yet!" Mud tanks are under the drillfloor all around the walls. Wellheads are the next level down, actually in a chamber in the top of the core cell.

The elevators are lifting 24" casing at the moment, it goes up and up, almost out of sight.

"Yes, that's another advantage, we have height for sixers in this rig rather than just triples, cuts down on trip times significantly." He means that the drillpipe is in 6 x 30ft lengths, that's almost 55 metre pieces! Yet there are still joints at familiar intervals.

"You're right, we still have to bring the stuff in as 30 footers, don't forget we're actually underwater here, so no V-door, everything has to be slung in through the sky hatch." He points up but you can see nothing. The roughneck trundles out to break the joint and the length of casing swings across to the tiny setback area - of course, long lengths, shallow wells equals small setback area for storing the pipe. "We can stack it all here, drillpipe and casing, nine lengths get you to the seabed, and we rarely drill below 3000 ft."

Where is the production liner?

"Don't use it; we produce straight up the 24" casing. That's one of the ways we reduce depressurisation time. OK, it means we don't get maximum productivity from the field, but that's not the game here. Did you notice another strange thing about the casing?" You hesitate.. "It's smooth on the outside for easy passage through the gaslocks. The collars are on the inside. Of course, it can still be broken at any joint with the right tool."

On the drillfloor the last piece of casing has been racked and the drillstring is going in again with a strange device on the end..
"That's a subsea well cap - we don't expect to have to produce from this well again, but just in case there is a pressure detector which can be periodically interrogated by the Father Miner. If the pressure gets too high, all he has to do is replace the cap with a wellhead and connect up to the nearest manifold."
He looks at his watch. "However, it's also our cue that I should be on the bridge"

Upstairs in daylight again, it seems like a different world. The 'bridge' proves to be a console in one corner of the control room, and Carlos, once again the master checks out the surrounding sea and speaks into a mike. "Daughter N2 preparing to Float-off, we're relocating 430 metres on 046, all stations report please."
"This is Mother, we have you on green, N2, 12-hour forecast good, proceed at your own pace"
"Cain here, strain taken on 180, green board"
"Able reporting, strain taken on 150, all green board"
"Those are the two tugs." mutters Carlos "there's a strong Northern drift in these waters, and we need them to keep us near enough on station. Our own thrusters only do the fine tuning"
"Engines ready", comes another voice. You didn't realise we had any engines!
"Drilling secure".. that was Santos.
"Topsides secure - all crew present" from Eduardo.

Carlos points to the coloured graphic of miner N2.
"Right, we're ready to go.. we've finished evacuation of the methane-saturated water from skirt to Mother, so we'll raise gas pressure in the shaft to lower water level and increase buoyancy. We always make sure that before float-off, there are at least 10 cells of High Pressure (42 bar) gas and 6 cells of LP (14 bar) gas. Our IWL (Internal Water Level) at flotation is about -310 metres; gas pressure 31 bar and we can adjust that by opening valves to either the HP or LP cells… bit of a juggling act, actually, because theoretically there is no stable state until you hit the surface, but the computer manages it fine… not that this thing is going to bob around like a cork at 5 million tons anyway"

You are not quite sure if these assurances are for your benefit, or just thoughts spoken aloud, but you don't like to interrupt.

"OK, IWL at -290, time to close the skirt vents." He watches as the green indicator lights go red, one at a time. "Now, as the IWL drops it will pressurise the skirt and force water out under the rim, breaking our stuction on the seabed and clearing the mining debris." He points at a scale.. "Buoyancy coming up to -4, that's only four thousand tons negative... time to switch IWL to automatic.' An amber light turns green.

"Deballasting now", once more into the mike, and a few prods of the finger at the console… "Clearance" and a few more prods.

"Cain 70%" comes from the speaker, "Able 25%" The graphic shows the strain on the lines as slightly different figures, but near enough.
"Watch the GPS" says Carlos, pointing to yet another indicator in a blue surround. Sure enough, the depth figures are reducing.
It's difficult to believe that we're moving, there's no sensation whatsoever, yet according to the GPS, we've moved 28 metres at 032 degrees and risen to within 10 metres of sealevel.
"Able, up five" says Carlos
"Able 30%" comes the reply after a moment.
123 metres at 039 degrees says the GPS. Zero metres below sea level.

"Able, up three" says Carlos
"Able 33%" comes the reply.

"Have a look outside" says Carlos. "downwards" he adds, when he sees you staring at the horizon! Yes, the outline of the hexagonal Gas Storage Head is quite clear now, and it's like looking down on a football pitch from the grandstand… well several football pitches, actually.

275 metres at 044 degrees says the GPS; 350 at 045; 400 at 046

"Able, down three" says Carlos. "Cain up five"
"Able 30%" comes the reply. "Cain 75%"

"Now we use the Acoustic Target Tracker" says Carlos "it shows distance to target". The ATT is in white area with the same layout as the GPS. 22 metres at 048 degrees.

"ATT engaged" into the mike.

"Thrusters 33%" comes a response. 13 metres at 047 degrees says the ATT

"Ballasting down" into the mike. "Watch the depth" to me. Ah yes, there's a depth readout on the ATT of 43.8 metres. "Water under the keel", says Carlos. 43.7 metres, 43.5, 43.4 that's what you would call controlled descent… "we're pumping in ballast water at thousands of gallons per minute, right now" says Carlos. There's still no sensation and no sound either except for the aircon fans. Santos is making a cup of coffee, Ed is doing paperwork, the others are at various stations around the control room.

"Thrusters 35%" from the speaker. 9.2 metres at 046 degrees 43.0m down says the ATT

"Seabed pictures coming up" says Carlos. A rather small screen shows an indeterminate picture, predominantly green. "that's what is under the skirt now; it's actually composite sonar in false colours" he prods; contour lines spring up and you can make out a low hill. "Fauna shows red, flora blue"… but it's all green. "that's usual; too dark for plant life. The fish rely on scraps falling from above, so they're not affected by us. The only thing we've ever found on the bottom here is hydrate worms; horrible looking things, but the scouts move them out of the target zone so I'm afraid your looking at a bare hydrate mound".

"Able here. Can we come round now?" Carlos checks a reading "Yes, sorry João, come round to 170, please".

3.2 metres at 085 degrees 21.7m down
How come we went down so much more slowly than coming up, you want to know.
"Well, coming up we can use gas buoyancy assistance, after all the surface is a fairly soft target. Going down however, we keep gas buoyancy strictly controlled and just use the ballast tanks; effectively we have to pump enough water to counteract the extra tower displacement. Even at this rate of descent, the bottom can be a fairly hard landing."

"Able on 170" a quick glance "Make it 168, please Able and drop down 2 more.
"Able 28%" comes the reply. "coming round to 168"

"Just balancing the tugs up, taking the load off our thrusters." says Carlos.

As if to prove the point: "Thrusters 15%" from the speaker. "Thrusters 8%"

3.9 metres at 225 degrees 8.8m down on the ATT.
"Overshot a little bit, but she'll soon stabilise. Now we need skirt penetration" Another graphic reveals itself; a circle with numbers every 15 degrees. "the ATT just gives the depth to the beacon; as it's located near the top of the hydrate mound, the skirt will make contact some metres lower, here, for example we've still got 17 metres under the rim, and here on the West side, only 9.6 metres"

How come we can't see the beacon on the screen?

"Because it's only virtual! we don't want to land on a real beacon, it would be pretty hard to recover!" then seeing your puzzlement "The probes put a real beacon in place, then put 3 satellites on prominent points at some distance around. After they have sonar triangulated between themselves, the real beacon can be removed, and the satellites remember the location. They are now communicating with our skirt instruments and the computer is working it all out, but as far as us humans are concerned, we're just chasing a beacon… the fact that it is no longer there is irrelevant"

1.1 metres at 229 degrees 1.8m down says the ATT

"Initiating program Touchdown22" to the mike. "wrote it myself" he says to me with a grin.

0.2 metres at 277 degrees -0.8m down says the ATT -0.1 metres says the West skirt penetration

"Just getting bedded in a bit, we'll start to gyrate soon". You can hardly imagine this monster 'gyrating'!

"Thrusters 80%" from the speaker. Yes, perhaps the window frame is moving relative to the Mother Miner.
"Ten degrees, back and forth" says Carlos "but that's 23 metres movement at skirt radius, and the base is serrated and studded with pig iron"
You can't hear anything, but a vibration is transmitted via your legs.
"Something hard down there"

-4.8 metres says the West skirt penetration; +3.6 in the South-East.
Gas bubbles in luminous yellow disappear from the top of the green screen. The vibration intensifies, now rattling the furniture.
"Thrusters 90%" Buoyancy -10, 'thousands of tons' says the scale.

"One more twist and that's it" says Carlos. All the penetration figures are negative by now
0.3 metres at 007 degrees -11.8m down says the ATT

"Touchdown" into the mike.
"Mother here, looks good to us N2"

"You've done it again, Carlos", says Ed, "I had only calculated 11.6 metres" He waves his hydrate field calculations. "Yes. But we've wandered off target a bit. 88 minutes transit time; that's not too bad" "Won't hold it against you!"

There is a general air of relief in the control room now that the transit is complete, and a late lunch materialises from the galley.

"We'll just ballast down, then we'll release the tugs. Perhaps you'd like a coffee and then go downstairs with Ed - he's got a little job to do. Your chopper to Mother is at 1530, I'll just confirm it" Carlos is back to being a guide again.

Back on the drillfloor, the string is just descending with a special tool on the end, one more 'sixer' follows, but soon it is ascending again with a much fatter piece of pipe. Santos is definitely driving this time!

"This is what we have all been waiting for; it's the shooting sheath. When extended it's 180m long but telescoped it's 95 metres and fits neatly in the gaslock."
The first 50m. disappears up into the gloom above, and the iron roughneck reappears looking much bigger with two new sets of jaws. With the lower pair it clasps the sheath and twists to split a joint, then the upper section lifts a metre or so revealing an inner pipe. This the roughneck grabs and neatly separates with the upper pair of jaws, and the top half of the Shooting Sheath swings away to the setback area.
Down comes the tool again, this time lifting out the lower core of the Shooting Sheath. Up and across to a special maintenance area at the edge of the drillfloor. The roughneck holds the lower outer sheath until that too is stacked

"Want to have a look at the Shooting Head?"

A few strides take us to the sheath, and Ed bends down, squinting at the lower core which is hanging half a metre clear of the floor. "Just checking on possible misfires; all these instruments can't beat the human eye"

OK. So how does the shooting head work?

"Well, this is the hub of the mining system. The cartridges can be selectively fired from the control room… not all at once, of course, we trigger them in patterns to break off huge chunks of the hydrate, rather like a line of charges in a blasting operation. It's a bit of an art, I can tell you.
As you can see, the tip segment is composed of downward pointing bullets, for excavating the initial pit, and only a few of them have been used. These horizontal segments above, however, are empty" he is pointing at a 1½ m diameter cylinder riddled with 9mm holes, whereas the tip reminds you of an exotic fruit, bristling with bullets, each with a long pin projecting from the centre.

"Just stand back a moment". Ed presses a combination on a shielded touchpad.
As if by magic, the circular section of floor under the shooting head lifts on a hydraulic ram, touches the head briefly to the accompaniment of a loud click, then drops taking the segments with it. The tip segment, about 1 metre long, separates and disappears through the floor.
"Can't hang about, got to be fully recharged within a couple of hours". The charging machine repeats its trick with the next segment, and soon the upper part of the head is at eye level… it's full of bullets, and there are thousands of them! "There are normally 30 metres of cartridge segments loaded comprising just over 1¼ million bullets, potentially shifting 2½ million m3 of hydrate".

Amazing! Why so many cartridges?

"We aim to put a bullet in at least every metre, otherwise the hydrate is not broken up sufficiently. When you are working at a radius of say 100 metres, that's over 600 bullets around the perimeter, repeated every vertical metre of the workface, so say 15 thousand bullets per shot.
There are 360 cartridges in a round, so at each level we would fire one complete round plus fill-ins from other rounds - the computer has it all worked out!"

What triggers the right shot pattern?

The bullets are fired by impact pins on the inner sheath, just like a rifle. A selector robot located in the inner annulus primes the pins in the required pattern, and a trigger charge sets of just those primed cartridges and no others. The selector can set up a complex shot pattern in five minutes or so."

How long does the shooting take?

"If we're in good hydrate, we can shoot every half an hour; however if it's patchy we take longer to plan the shoot - no point in just breaking up bits of seabed! Of course, this all hinges around the original survey, the more information you have, the easier it is to plan the shoot. Normally shooting takes a day or so, but it could be a week! The limitation on how rapidly we shoot is actually how fast we can clear up the shattered hydrate; can't shoot with lumps of hydrate floating about in the water!

How do you know when it's clear?

"The false colour sonar shows it quite clearly, and the computer can even superimpose the planned shot pattern onto the field, so you can see the likely outcome before firing"

By now the head is noticeably shorter, and it looks as though the rest of the segments are full. Ed resets the robot, which now starts coming up with new segments from the floor below and adding them to the sheath..

"I've got to hang on here while the robot rebuilds the shooting head, I'll walk you to the lift and trust you not to get lost." He shakes your hand.

Carlos is just dismissing the tugs as you arrive upstairs. "77 thousand tons of base load should keep us nicely in position", he says. "Chopper's just about to leave Mother, and I would appreciate you giving this envelope to Marco Pinheiro, he's the OIM and I presume you'll be seeing him soon enough." "Nice meeting you; don't forget us when you're next using your gas cooker"

You certainly won't!

Roger  Clark
STEP 2000