Methane Hydrates ??

Chapter 10.  Methane Hydrates – The Next Major Energy Source?

     Do you know what we will use for major energy sources (i.e., fuels) when we finally exhaust the fossil fuels that can be found and economically recovered (petroleum, coal, natural gas)?  Well, I don’t, either.  But the replacement fuel will have to be something the earth provides us that we are not exploiting at present.  Solar, hydroelectric, wind, geothermal and biomass-derived power will all be important after fossils fuels run out but those sources can only fill in the gaps in energy demand – some new major fuel source must be found.  And history suggests it will be found and probably is already known to exist.  And, no surprise, the deep oceans might be a good place to look for it.

     One candidate already identified under the oceans in significant quantities is methane hydrate deposits.   So … what are methane hydrates?  I am going to delve into a little geochemistry here, so bear with me.  I am not a geochemist so this will have to be presented in layman’s terms, which is probably better for the majority of my reading audience.  (If you actually are a geochemist and find errors in the following I’d love to hear from you – dphuey48@gmail.com).   

    Methane hydrates are a combination of methane gas and fresh water that form an intriguing little molecule called a clathrate.  Clathrates (there are other kinds besides the methane variety) are gas and water formed into a combo that is not quite a normal compound, which is to say the gas and water are not chemically bound to each other.  It is more like they are a couple living together.  This is significant when we get to the fuel source part of the story because the methane can be separated without addition of energy to break the bonds – like the couple living together can just decide to split with no divorce energy required. 

     The way clathrates get formed to produce methane hydrates under the oceans is this.  A happy methane gas molecule wanders around like an unattached bachelor.  Sometimes it is dissolved in pore fluids, sometimes existing as free gas, generally with no permanent attachments – a bachelor who has not settled down.  Then, inevitably, it meets a comely water molecule and the two of them decide to move in together.  No marriage, per se, thus no tough-to-break chemical bonds, but a very stable relationship nonetheless.  Presumably good for both of them (or so their friends all say).  And a then a funny thing happens.  Their earlier properties as individual gas and liquid molecules disappear and their new condition, the methane hydrate, becomes a solid.  You can really wear out the girl-meets-boy-and-settles-down analogy here -- it is not really one methane molecule per water molecule – there is about 1 mole of methane gas for every 5.75 moles of water in the stable solid, but you have to be a chemist to comprehend that.  



The image here shows the cartoon version of the clathrate structure.  The yellow sphere with four spikes represents the methane molecule; the surrounding blue matrix is the water.

      The new solid methane hydrate looks a lot like dry ice, but the resemblance ends at appearances.  The hydrate requires both the right pressure range and the right temperature range to continue to exist as a stable solid.  If you add heat or simply lower the surrounding pressure the methane immediately returns to gas form and the water turns back into a liquid.  That is why we don’t just find methane hydrates everywhere, even though we know the earth has a lot of both methane and H2O. 

     Methane is the most elementary of hydrocarbon molecules; one carbon atom locked to four hydrogen atoms, CH₄.  Petroleum molecules are hydrocarbons, as well, but infinitely more complex.  Methane makes a lovely fuel because it will give up a lot of energy (heat) when burned (oxidized).  Natural gas is almost 100% methane.  But methane as a free gas is hard to trap.  Hence natural gas wells tend to be difficult to locate and are often found at great depths under land and seafloor.  Those reserves of natural gas that got naturally trapped for millions of years are the ones we are tapping now and will run out of eventually.

    Methane hydrates, on the other hand, form without the geo-pressure cooker effects required to produce natural gas or petroleum deposits.  They do not require millions of years to form, like petroleum or coal, and they are stable once formed so long as they stay in a place with the correct temperature and pressure.  No impermeable seal or cap structure is required to retain them.  Such places can, in theory, exist anywhere under the shallower parts of the oceans in the near-surface sediments.  They are even known to exist under land in the permafrost regions of the Arctic and in the Antarctic ice pack.

    The potential for methane hydrates as a useable energy resource of the future is easy to picture.  Find subsea deposits of hydrates, dig them up or pump them to the surface, reduce the pressure a little (just removing them from the depths of the oceans accomplishes that) and, bingo, you get a steady flow of pure methane suitable for burning as a fuel.   A few elementary questions of importance come up immediately; the first of which must be – just how much methane hydrate is out there under the oceans?  Ah, things get a little tougher here, which is why this obvious windfall source of easy energy is not already on line.  Nobody knows how vast subsea hydrate deposits are on the global scale.  Actually, I think there is still a lot of debate about how much is to be found even on a local scale, like in the Gulf of Mexico or offshore India, for example.  And another pretty important question would be – how do we mine or produce this source of methane efficiently?  Can it be done at all?

     Answering the how-much-is-there and how-can-we-exploit-it questions is, initially, the role of ocean research.  So we have come full circle in this story and are back to deep ocean research drilling for science.   Methane hydrates in oceanic sediments has been one of the focuses of the Deep Sea Drilling Project and Ocean Drilling Program since the early 1970s. First, hydrate deposits had to be located.  If fact, a reliable means of locating them had to be developed.  Then they had to be drilled for sampling in order to get specimens into the hands of the scientists in the labs so their properties could be understood.

     So, first things first, how to find them?  This turns out not only to be easy, but problematic in how often they turn up unexpectedly.  If you drill and take samples of ocean sediments just about anywhere on or near continental shelves there is a pretty good chance methane hydrates will find you.  The gas hydrate stability zone (deep in the water and sediment column to have the correct pressure but not so deep that the geothermal gradient has made subterranean temperatures too hot) exists in many sediment regimes about 200-500m below the seafloor.  In some areas hydrates outcrop in solid form on the seafloor itself.  This condition is quite rare – stories exist of trawl nets coming to the surface with fizzing and foaming white chunks of “ice” that could NOT be ordinary frozen water.



Solid methane hydrate
disassociating with methane
gas ignited in room conditions

     Most solid methane hydrates exist under the seafloor intermingled with sediments in one of three apparently natural forms:  tiny granules like grains of sand or gravel, bigger chunks the size of walnuts or eggs, and in at least in one known example, in a virtual “ore body” with a lens of solid pure hydrate meters thick.  Whatever the form, when they are sampled subsea then brought back to the surface where pressures are lower and temperatures higher they immediately begin to disassociate – the methane escapes as a gas leaving the water behind as a puddle.  The picture at left shows such a lump on a lab table with the escaping methane burning nicely like a candle.  This sort of appearance of methane hydrates occurs commonly in ocean coring operations, even when no hydrates are expected at the target drill site.



Example seismic profile of
seafloor - no BSR evident here
(but there may be methane
hydrates anyway)

    When hydrates are expected at a location never before cored it is because there is a hint of their presence from prior seismic profiling of the target drill site.  The example seismic record here does not indicate the presence of solid hydrates because there is no tell-tale BSR (bottom simulating reflector).  If there were a BSR you would see a dark, relatively continuous line (reflector) several hundred meters below the seafloor that cut across all of the other layered reflectors as if they were not there.  And it would mirror the shape of the seafloor (the bottom) exactly.  This type of reflector is thought to exist in sediments with significant hydrate deposits because it represents the transition from solid stuff (the hydrate layer) to the gas phase methane trapped in the slightly warmer zone below.  This hard-to-miss seismic indication is not only good for finding hydrate deposits but suggestive of trapped gaseous methane that could be recovered as well.  But not so fast – it doesn’t always work that way.  In fact, in my experience participating in ocean drilling operations such reflectors in the seismic profile failed to predict the existence of solid hydrates just about as often as it succeeded.  And it went both ways – we found hydrates where no BSR was seen, and we found no hydrates where resounding BSRs appeared on the seismic record.

     This was demonstrated spectacularly on a DSDP cruise I worked offshore on the Pacific side of Central America in 1982.  Part of our mission was to find and sample solid methane hydrates and we had chosen certain sites with unmistakable BSRs.  To capture the elusive hydrates we brought along our first generation Pressure Core Barrel (PCB).
  

Pressure Core Sampler in
place at bottom of drillstring

A drawing of a later version, the PCS, is shown here.  Those specialized core barrels are designed to lock in place just above the core bit and accept a short, solid core in a cylindrical pressure chamber while coring proceeds downhole.  Then, before being retrieved, a valve is closed on the bottom end trapping the sample in a sealed pressure vessel.  The core barrel is then pulled rapidly to the surface where the temperature increases but the downhole pressure is contained.  As soon as it gets on the deck the PCB is immersed in an ice bath to bring it back to the insitu temperature where the sample was collected.  In all of our pressure sampling attempts at the designated hydrate sites on that voyage we never got a single confirmed trace of hydrates.

    With that apparent failure weighing on our morale we moved the vessel to some other sites nearby, without BSRs, where we intended normal coring operations for other, non-hydrate sampling.  And, sure enough, that is when the most famous chunk of drilled hydrate in history came up totally unexpectedly in a standard, non-pressured core barrel.  It was perfect piece of solid methane hydrate about a meter and a half long and about the normal 5-6 cm diameter.   The scientists on duty in the core receiving lab went berserk.  Not only was this completely unanticipated (there was no BSR at this site!) but they had none of their sampling and preservation equipment on hand.  And, of course, the hydrate “log” was merrily fizzing away and disassociating right before their eyes.  In the end a few residual chunks got thrown in pressure containers for later examination, but most of the huge sample was only captured on film and in our collective memories.

     So I am not a big believer in seismic profiling as a way of positively identifying methane hydrate beds beneath the seafloor.  I hear over drinks now and then that in certain areas (like the Gulf of Mexico) seismic procedures have been developed that identify hydrates with a better batting average but I have not seen the data so remain skeptical.  Finding methane hydrate beds scattered all over the oceans is an important endeavor but it appears the only way to positively know where hydrates accumulate in volume and what properties the deposits exhibit can only be achieved with drilling.  (Actually much the same can be said about prospecting for oil.)

     Finding and exploiting gas hydrate deposits can certainly become a major economic endeavor.  Indications of hydrates have appeared on almost every expanse of the continental shelves. 

See the map.  Estimates of how much there might be are educated guesswork (because you can only know by drill sampling) but the amount is believed to be huge.  Early over-enthusiastic estimates of total world amounts at the time of the earliest discoveries in the 1960s have been decreased by later researchers by about a magnitude per decade.  Even at that most current estimates place the total amount at 2 to 10 times the amount of normal natural gas believed to exist – which differs a little from the legend on the 2005 map, but still a substantial amount for an energy-starved world of the future.

     Scientists, engineers and strategic planners in the nation of Japan have committed themselves to exploiting hydrate deposits off their coastlines in hopes of enabling an energy industry of the future within their own borders.   (The internationally recognized Exclusive Economic Zone extends offshore 200 miles for all nations with sea coasts.)  In recent years they have successfully extracted methane from hydrate deposits under the Arctic permafrost in Alaska (by two different methods in small demonstration experiment) as well as from one offshore pilot rig in the Pacific about 30 miles offshore central Japan.  They are now in the process of determining how much gas they believe can be extracted from offshore deposits and at what operational cost.  I expect methane hydrates will ultimately prove to be cost-effective as an energy-producing fuel source.  That will then leave the question of drilling hundreds of potential sites to do reservoir evaluation to determine how much is down there.

     The problem with pressure core samplers.  Determination of hydrate extent and properties requires sampling and recovery of solid material.  But when the sampler (core barrel) is retrieved the sample is literally locked inside.  You can’t open the sampler without depressurizing the sample causing rapid disassociation before it can be examined in lab conditions.  The answer is a laboratory pressure transfer chamber to accept the samples from the core barrel where they can then be examined under proper stabile temperature and pressure conditions keeping them solid until the researcher wishes to let them disassociate into gas and liquid water.  This step was the hurdle of the future when I stepped away from the problem.  I believe industry and/or the Japanese government is working on this stage of the problem but much of that detail is proprietary – more indication that the economic potential for gas hydrates is very real.

     There is more to the lore of methane hydrates for those interested, including how they often form and clog natural gas pipelines, their role in the Deepwater Horizon blowout control efforts, and their theoretical role in global warming.

General methane hydrate information can be found at:

http://en.wikipedia.org/wiki/Methane_clathrate

http://geology.com/articles/methane-hydrates/

Anecdote:  “Microscopes, Scales, Clocks, etc, on a Ship”

     The anecdote for this chapter is about equipment instead of people.  It is really just a little collection of interesting tidbits on the subtleties of setting up an efficient geo-science research lab on a ship at sea.  If you imagine the tasks required to create a high level set of laboratories on a large ship you can visualize some of the essentials fairly easily.  You need space (always tough on a cramped ship), in this day and age you will need a good computer network, plenty of clean electricity, instruments of all kinds normally found in any university research lab, doorway access big enough, and so on.  But when you try it you discover that many of the seemingly straightforward issues become tricky, new problems when they have to be solved anew.  Clean electrical power, for example, sounds like a no-brainer.  The ship (JOIDES Resolution in this case) has diesel engines that permanently power electric generators.  This electricity powers everything on the ship, from the main screws to the lights in the staterooms and all the normal electrical power for the labs.  But shipboard power is notoriously “dirty” – the nice 60 cycle waveform is full of spikes and irregularities picked up from other power cables running all over the vessel.  So in the end clean lab power had to be provided by a dedicated generator set that charged a huge battery bank, which then settled out the irregularities and provided suitable power for sensitive lab instruments.  That is just a mundane and mostly predictable example of ship-specific lab instrument problems.  Here are few more that took some of us by surprise or had us scratching our heads for a solution. 

Heave-tolerant lab scales.  Any laboratory needs a scale or two to weigh small samples accurately.  On land this is easy – use a classic old triple-beam balance or a modern digital scale.  But a ship heaves and this reflects weight changes on a scale the same way jumping up and down on your bathroom scales would do.  So the question was – how to create a laboratory scale on the ship that either ignored or compensated for non-stop, and irregular ship heave motions.  At first our proposed approach was overkill – a common occurrence when faced with a new problem.  We considered what it would take to put a triple-beam or digital scale on a miniature heave compensator.  This would entail creating a little moveable platform driven by a servo-motor system sensing and responding to actual ship heave.  The idea was to create a mount for the scale that would cancel out heave motions - stay steady relative to the earth while the ship heaved up and down around it.  Easier said than done.  Never mind that the lab tech would put working with a scale that from his perspective never stopped moving.  Nothing of the kind could be bought off the shelf and we never got around to trying to invent our own.  The reason we were fortunate enough to jump right to the correct solution was that when we considered what we would use as a sensor to detect ship heave we realized we had the answer right in front of us.  You detect heave (or any other varying motion) with an accelerometer.  Think about it long enough and you realize a scale to weigh things IS an accelerometer.  It measures the acceleration of gravity on any object and reports that result as weight.  So if we used a digital scale in the lab to measure a sample while the ship, sample and scale were heaving, the result would not simply be weight of the sample but weight of the sample constantly changing due to heave effects.  The nice thing about a digital scale is that it is very fast-response and can be programmed to take multiple measurements.  So all we had to do was program the little scale to take, say, a thousand measurements of the unknown weight over the course of a few minutes.  And then you average the results to get the correct weight of the sample.  Can it really be that simple?  Sure.  The errors in the real weight caused by heave acceleration all must average out to zero over time.  If not, after some time interval, the sample would either be on its way to the moon or to the center of the earth.  If it was still where you left it a few minutes later the heave-induced errors must have averaged out to nothing.  Neat and simple.



Two months at sea calls

for a lot of coffee



Scanning Electron Microscope.  Oh, we MUST have an SEM, said the scientific advisors when we began to set up the labs on the JOIDES Resolution – never mind that no ship at sea had ever installed and used one before.  So our lab technician experts found a suitable SEM on the market (it had the desired compact size, magnification power, and other features) and installed it in its own special little room in the laboratory stack on the ship.  It got clean power and very careful attention during installation and testing.  It worked great during tests in the shipyard.  Once at sea it turned to be just about useless.  Everybody overlooked or under-appreciated how much a working ship vibrates when it is full of motors and pumps, cranes and dollies, banging steel doors and waves hitting the bow.  A living ship never stops moving, either in the macro or micro sense.  And an SEM capable of 20,000x magnification can really capture all that tiny scale motion – except it captures it as blur in the imaging.  It is not a matter of increasing shutter speed to freeze the images – SEMs don’t work that way.  We eventually gave up after every vibration isolation trick available was applied with no improvement.  Blurry SEM images are no use at all and the best un-blurred images that could be produced were at magnifications no better than ordinary optical microscopes could achieve.

The Laboratory Clocks.  This tidbit is not technical, it is just cute.  When we began outfitting the new labs and offices on the ship (JOIDES Resolution) the list of necessities included lots of ordinary things like chairs, desks, filing cabinets – and wall clocks.  The most cost effective source of such items was the Texas A&M University supply system (A&M is the host institution for IODP and all the money goes through their purchasing system).  On the list of available office supplies were simple wall clocks.  So dozens of clocks were ordered to allow installation in every new lab and office space on the ship.  When they arrived we found out that each clock had as a background behind the dials the state seal of Texas, complete with the iconic Lone Star and the words, “State of Texas” boldly displayed on the face.  Now this seems just right if the clock is mounted on a wall in a state university office or classroom.  But on an international research vessel halfway around the world it looks a bit odd.  Not a problem.  It turned out that the clocks had plastic covers that hinged up to allow cleaning or setting the hands.  It also allowed access to the black “State of Texas” lettering on the nice white cardboard backgrounds.  Within the first month at sea everyone working in those labs and office spaces had discovered that white-out and a black pencil gave them full editing powers over the clock legend.  Before long a visitor could wander through the labs and notice clocks declaring, State of Confusion, State of Ecstasy, State of Anxiety, State of Paranoia, State of Delusion, State of Euphoria.  No end to those possibilities, really.