Hydrates : Dissociation or dissolution...?

Hydrates have been on the table for discussion for quite some time, there have been many conjectures about methane, venting of the seafloor, giant methane bubbles, etc, etc. I would like to take a stab at describing some possibilities that might explain some of the things we have all been seeing on the ROV feeds.

Especially the " white things " everyone sees " swimming " around on the live feeds and can't decide whether they are hydrate chunks, gas bubbles ,crustaceans , marine snow, silt, floating bacterial mats, oil ,...or alien fire bugs,lol.

 I'll give you a hint....

It's 7 out of 8 things I just mentioned.

And most interesting,...free floating hydrate chunks exhibit what is called " wiggling "

There is a big difference between the acts of dissolution and dissociation in hydrates.

 " Dissociation is due to inherent instability (similar to melting of ice) with or without water (although presence of warm water may increase the dissociation rate). Dissociation of methane hydrate into gas and water is similar to ice melting and is controlled by heat transfer. Hence dissolution is relatively slow and dissociation is rapid. "

 " Dissolution is due to instability in the presence of seawater (similar to dissolution of NaCl in water) and is controlled by mass transfer. "


 Hydrates  form where they can and when they can. If rock or mud is already saturated than hydrates will not form, the gas will vent upwards through the seafloor because it has to, although there are such things as gas traps, they are not know to be the size of Rhode Island..it would be almost physically impossible unless there were a massive upturned cup structure ( a fold ) in the bedrock consisting of very non-porous rock, and it would have to be massive, and it would have had to have had a massive "washout " to excavate the cavity for the gas to collect in , in the first place....highly unlikely.

Originally, I had become curious about hydrates and the characteristics of the gas I was seeing on the live feeds.

In particular, I noticed bubbles of gas that were leaking from a certain pressure-fit connection between the original BOP stack and the additional " 3-ram capping stack  ". The feeds were showing the buildup of hydrates on the structure, but was most puzzling to me was the way the bubbles were rising up hitting the hydrates....and then careening straight off at a 90 degree angle....this didn't make much sense to me....you would think that a bubble would rise up, hit the hydrates, bounce off and continue upward, right ?

You would expect to see it go from a vertical trajectory to the bounce and a gradual arc as it resumed a vertical trajectory. I made the above crude diagram to demonstrate what I am talking about, where A: would be what I would expect to see, and B: what I did see. I really wish I could have gotten video captures, it was when the feeds were of higher quality.....I searched for some vids to show what I saw, but I have not found any.

Odd behavior for a bubble,I thought , so I asked a friend, this is what he said.


"Presumably the hydrate formers pickup water quickly and become more hydrophilic, they would bounce off of presumed hydrophobic oil. It may be worth looking at the surfaces of some of these things and see how they can segregate under various forces. Hydrophilic/phobic drives many things- for example protein folding that makes enzymes works can be driven by this. Pressure gradients through various size pores of course select on size, and I wouldn't ignore electrochemical issues too. A field will orient polar molecules, induce dipoles and get net-neutrals to migrate. Electrophoretic separation if you will. Interesting, but a couple of lidar hits on the different blobs would be a lot more informative. "

..lol...so basically this is a small but violent transfer of mass that sends the bubble on a horizontal trajectory.
The warmer gas escapes from a higher pressure to a lower pressure, rises up, hits the much colder hydrates where it instantly becomes much lower in temperature, in turn lowering the temperature of the water it contacts, resulting in the rapid growth of the typical crystalline structure of a hydrate ( there are 7 I believe ) and trapping a small amount of gas When the temperature differentials of the gas bubble and the hydrate and the ambient temperature converge, the reaction can longer take place, but is also halted in a very fast and (micro) violent way,ie: a sudden stop, which provides the opposite force to send the bubble careening off.

( The following is quoted from a linked paper below )

" If the bonds in the crystal are weak and hence easy to break, then interface reaction rate would be high, and dissolution would be controlled by mass transfer. If the bonds are strong and hence difficult to break, then interface reaction rate would be low and dissolution would be controlled by the interface reaction rate. "

 Then there is Snell's law, which I may be applying incorrectly to prove a point, although I have read it can also be used to describe what I am talking about, ipse dixit.

Wavefronts from a point source in the context of Snell's law.

...so that's my attempt to explain that , it is slightly ipse dixit .



..... Let's look at some things.

First , a video a good friend sent me of a venting of gas from the seafloor.





The only things that makes me question the origin of the gas in that video above are: the characteristics of what I observed in that release, compared to all of the other videos on natural methane seeps, those of which are from footage pre-Horizon. Normal natural releases of methane are released as bubbles in a fairly steady stream.


I specifically remember before they put on the " 3 ram capping-stack, that they expected to see some gas venting in the surrounding area. I also remember Ken Wells saying this gas was from a biogenic source. That video is not biogenic gas production. That is a rather large bubble of gas rising up through the mudline, breaking the surface, and being forced into a vortice by ambient pressure. I observed the same event several times when the cap was initially applied.

When the cap was installed, I saw several of these gas vortices, sans sediment, that lasted for around 45 seconds each, from the POV( point of view ) which was at least 10' off the seafloor, probably more like 20+', they were inches from the camera . The ROV operator noticed them too, he panned the camera to look at it. An undulating silver snake dancing in the depths, it was beautiful really, and I was too stunned to capture the vid...dang.

If these vortices were propwash, they would not be monitoring them , let alone from the same spot. I don't think a vortice created from an ROV thruster could generate enough power to suck gases out of the mudline against ambient water pressure,jmnsho. Gas vents from the seafloor either when the mud and rock cannot absorb anymore gas, or there is a clear/semi-clear path that has already been established, ie: a vent or chimney.

I do believe that it's possible different gases would travel differently due to their characteristics, some gas would be less prone to creep through rock pores, some would be more prone.

.......The hydrate stability zone only extends to around 1000' down.
.......Hydrates normally form in the mudline/stability zone because of contact with liquid (seawater)and temperature/pressure ( P/T )but also dependent on inhibitors to formation like salt and methanol.

....So back to the difference between dissolution and dissociation.

One is happening because hydrates are subjected to heat outside the gradients to keep them stable. Here is a video of hydrates being dissociated from heat, the gas comes up providing lift to the fluids by way of what's known as " gas lift ", basically, the gas expands as it rises, almost dragging the fluids with it, although it is not the prime mover. But observe how the CO2 behaves when clinging to this ROV....




Next is a vid of somebody parking an ROV on a bed of methane hydrates on the seafloor.

** Note : When the video text commentary says that sediment can get stuck to the Plexiglas bubble and the camera will auto focus on it....this could explain many many " sightings " of weird things people have seen.....something I suspected, but it's comical really if you think about it. It's like getting scared while looking through a telescope when a fly lands on the outer lens...lollol.

Also note around 2:20 in the video , the exposed chunks of hydrate. Notice how it's not doing anything basically because its nice and cold., but also because on a molecular level, the rate of slow release of methane from hydrates is partially dictated by the amount of methane already found in the surrounding water saturated by slow rates of dissolution.




 ...so what i really find curious is tha fact that hydrate chunks we see on the live feeds are appearing to wiggle and swim...this means they are not decaying by dissolution, but by dissociation, which provides thrust force in the form of lost mass. I am wondering if this is from preventative methanol applications remaining in the surrounding are( seawater) or from....raising of the ambient temperature of the seawater , because it would only take a raise of a few degrees to produce rapid dissociation.


Originally for me , the confusion was because the terms of biogenic, methogenic, & chemosynthetic have been used rather loosely in a fair amount of the literature I have come across.( That's about 8-10 hours a day , 7 days a week reading and studying many of these topics ) Than there was petrogenic and thermogenic gas as well. Phew..


" Preliminary Evaluation of In-Place Gas Hydrate Resources: Gulf of Mexico Outer Continental Shelf "

" The rationale is that, if there is sufficient methane flux to vent methane to the seafloor surface (in gas and/or solid phases), the available pore volume must be fully saturated, and, if biogenic gas is not available to completely saturate the section, thermogenic gas is available to do so. "

" Hydrocarbon Systems Analysis of the Northern Gulf of Mexico: Delineation of Hydrocarbon Migration Pathways Using Seeps and Seismic Imaging. "

 

 ....so after all that reading, here's some more.

" Kinetics of convective crystal dissolution and melting, with applications to methane hydrate dissolution and dissociation in seawater "

 "  Large quantities of methane hydrate are present in marine sediment. When methane hydrate is exposed or released to seawater, it dissolves in seawater or dissociates into methane gas and water. There was some confusion in the literature about the kinetics of these processes. It is critical to realize that dissolution and dissociation are two different processes. Dissolution is due to instability in the presence of seawater (similar to dissolution of NaCl in water) and is controlled by mass transfer. Dissociation is due to inherent instability (similar to melting of ice) with or without water (although presence of warm water may increase the dissociation rate). Dissociation of methane hydrate into gas and water is similar to ice melting and is controlled by heat transfer.

Hence dissolution is relatively slow and dissociation is rapid. "

Now, when I originally posted what my friend had told me, in terms of what was possibly causing the bubbles I was seeing to travel vertically, somebody at the Oil drum ( great site Btw ) asked me this .

"  Isaac - perhaps you could venture into this new topic of magnetics and how such a factor would influence the stability of the formations with forced introduction of reactive polar opposites. Very, very interesting - even if only in a speculative manner. Thanx. "

http://www.theoildrum.com/node/6849#comments_top
I remembered a paper I read....

Perhaps you already read it in my " capture and tame " proposal I sent to BP, I'm sure they got a laugh.

From the Japanese Journal of Applied Physics

" Promotion of Methane Hydrate Dissociation by Underwater Ultrasonic Wave "

" The methane hydrate that exists in the abyssal floor is receiving attention as a nonconventional type of natural gas resource. An efficient dissociation technology is necessary and indispensable to achieve a steady supply of methane from methane hydrate because it does not easily dissociate in a stable environment of high pressure and low temperature. We consider that underwater ultrasonic wave irradiation may be a method of promoting the dissociation of methane hydrate on the basis of the facilitator effect. We carried out a preliminary examination using dry ice at various pressures, water temperatures, and input electric power. Methane hydrate was similarly examined. As a result, it was clarified that the dissociation time was shorted by the ultrasonic wave, and the wave was effective when the water temperature was low at the time of dissociation. "
 ...hhhmmmm...'thinks'...

Het is tijd om enkele beste knoeiboel te roken die ik ooit heb gezien.

Es ist Zeit, etwas von dem besten Durcheinander zu rauchen, das ich überhaupt gesehen habe.
Lol....so that got me starting thinking about sonar, because they are using sonar to image the seafloor,.... and doing it constantly.

そして心からの感謝への Hikaru Miura、Makoto Takata、Daisuke但馬およびKenichirou Tsuyuki

あなたの研究をするために私がたばこを吸われた挽肉料理疑うが。
Sonar operation is affected by variations in sound speed, particularly in the vertical plane. Sound travels more slowly in fresh water than in sea water, though the difference is small. The speed is determined by the water's bulk modulus and mass density. The bulk modulus is affected by temperature, dissolved impurities (usually salinity), and pressure. The density effect is small. The speed of sound (in feet per second) is approximately:

4388 + (11.25 × temperature (in °F)) + (0.0182 × depth (in feet)) + salinity (in parts-per-thousand ).

 

...ok...I'll take a stab at that for fun....sadly I took a test the other day and my math abilities are around 7th grade according to modern educational standards....lol...but then I read this from a writeup by the physicist Richard Feynman of his experiences on a school textbook review board.

 

http://www.textbookleague.org/103feyn.htm

 

4388 +

(11.25*3ºC)  = 33.75

(0.0182*5k') = 0.03014284

(salinity in ppt) = 34.9 ( average at that depth )

= 4456.08014284...that's feet-per-second, or the speed that sound would travel at this depth, pressure and salinity.

This empirically derived approximation equation is reasonably accurate for normal temperatures, concentrations of salinity and the range of most ocean depths. Ocean temperature varies with depth, but at between 30 and 100 meters there is often a marked change, called the thermocline, dividing the warmer surface water from the cold, still waters that make up the rest of the ocean. This can frustrate sonar, because a sound originating on one side of the thermocline tends to be bent, or refracted, through the thermocline. The thermocline may be present in shallower coastal waters. However, wave action will often mix the water column and eliminate the thermocline. Water pressure also affects sound propagation: higher pressure increases the sound speed, which causes the sound waves to refract away from the area of higher sound speed. The mathematical model of refraction is called Snell's law.

Types of Active Sonar

Different types of active sonars operate at different frequencies, according to their purpose.
High Frequency: High frequency sonar (>10 kHz) is primarily used for determining water depth (fathometers), hunting mines, and guiding torpedoes. At higher frequencies, the sound energy is greatly attenuated (weakened due to scattering and absorption) as it travels through the water. This results in shorter ranges, typically less than five nautical miles.

Mid Frequency: Mid frequency sonar, which includes the AN/SQS-53 system, has been in use since World War II, and is the primary tool for identifying and prosecuting submarines. Mid frequency sonar (1 kHz - 10 kHz) suffers moderate attenuation and has typical ranges of 1-10 nautical miles.

Low Frequency: Low frequency sonar (< 1 kHz) produces sound that suffers less attenuation as it travels through the water, providing greater range than other sonars. Achieving ranges up to 100 nautical miles, low frequency sonars are primarily used for long-range search and surveillance of submarines. Surveillance Towed Array Sensor System Low Frequency Active (SURTASS LFA) is the U.S. Navy's low-frequency sonar system.

 

http://www.solcomhouse.com/SONAR.htm

 

 

 ....so I am going to assume, safely, that for close-range sonar operations, they are using active sonar, high-frequency to look for gas seeps after shutting in the well., it would pointless to use anything else, although infrared has been in the back of my mind for quite some time now, because it would work quite well to look for seeps of any kind......unless the ambient temperature of the seawater has been raised....then the higher temp fluids would not show up as easily, granted they would not be very hot at all, they would loose most of their heat migrating up though the mud and surrounding seafloor, unless they were being propelled at a great velocity and high volume, which would indicate a rather large leak, I think we can rule that out, it would be visible from space.

...>10khz ....

Sonar works as follows:

• A machine sends out sound waves ("ultrasound," or ultrasonic sound)
• The sound bounces off the seafloor; the reflected sound waves are detected by the machine
• The distance between the machine and the reflecting surface can be calculated from the time the sound takes to travel to the seafloor and back
• By making measurements in different places, the contours of the seafloor can be plotted. As a general rule, the closer you can get the instrument to the seafloor, the greater the resolution of the contour map.

 ....so's I ask myself/s,...what kind of equipment would they be using to look for hydrates....and would they be looking for hydrates, ...which they wouldn't if the surrounding seafloor/mudline was slowly heating up, if it were, the methane released would be diffused in bubble form so small you wouldn't see them anyway.....you only see large bubbles when methane is either from a thermogenic release ...ie...with heat.


so anyway...Ultrasound attenuation spectroscopy is what is used. Here's a handy project from the D.O.E.


" Characterization of Natural Hydrate Bearing Sediments and Hydrate Dissociation Kinetics "

...remember, processes like extra-corporeal shock wave lithotripsy.?..the process used for kidney stones...

 

From Wikipedia :

" The successive shock wave pressure pulses result in direct shearing forces, as well as cavitation bubbles surrounding the stone "

So then with ultrasonic sonar and suspended gas being present there is what's known as "  inertial cavitation "

From Wikipedia :

" Inertial cavitation can also occur in the presence of an acoustic field. Microscopic gas bubbles that are generally present in a liquid will be forced to oscillate due to an applied acoustic field. If the acoustic intensity is sufficiently high, the bubbles will first grow in size and then rapidly collapse.

Controlled cavitation can be used to enhance chemical reactions or propagate certain unexpected reactions because free radicals are generated in the process due to disassociation of vapors trapped in the cavitating bubbles. "

http://en.wikipedia.org/wiki/Cavitation
...so in conclusion to this particularly flatulent post,: :

I think that many of the things we see on the ROV cams can easily be explained with modern scientific knowledge. Hydrate chunks will " swim " as they lose gas, etc.

But one thing I know after all this conjecture for sure....and that's that normal established gas and oil seeps always have other established marine life where they are found.

Always.

If you have any questions just leave a comment if you can't get ahold of me in the chatbox

Thanks for reading my blog, Isaac