Calling all chemists and fluid dynamics people - Hydraulic Fracturing

[lewelma]

Older DS is doing a paper on the chemistry of fracking. He needs to explain *how* the chemicals work to solve specific problems. This paper is for a national chemistry standard, but he chose the topic (so made it challenging because that is who he is!).  It is not a research standard, so I can hand him sources. He is looking into how citric acid prevents precipitation of metal oxides, the purpose of the buffers, how acids dissolve minerals, and how polyacrylamide reduces friction.  So the first 3 are easy, but the last one is super hard to figure out.

 

The question: how specifically does polyacrylamide reduce friction?

 

The best paper I have found, although at way too high a level, is "Applications of water-soluble polymers in turbulent drag reduction"  It is a review paper published in Processes.  There is so much in there that I don't have the background for (let alone ds), that we kind of need a dummies version, which I am hoping you guys can provide.

 

The paper is discussing:

 

1) anomalous performance of fluid particles during rapid deformation. "in this scenario, vortex stretching arises near the wall, and extensive elongation of polymeric molecules may take place, causing large elongational forces in the direction of the streamlines...." 

 

2) Molecular stretching of the polymers.  possibly polymeric chain extension

 

3) extended laminar flow

 

4) bead spring model. This section referred to molecular dissipation, stochastic velocity field, connector potential, dumbbell probability density, hookean potential, turbulent strength, probability density, and infinite second moment.  All in 2 sentences.  Summarizing with : "that is to say, the polymer molecule expands in the turbulent flow."  (They should have said that first!)

 

DS clearly doesn't have to write a PhD thesis on fluid dynamics for a high school standard.  But he does want to understand how they make slickwater using friction reducers specifically polyacrylamide.  And how specifically the additional of these large molecules reduces friction of water in the pipes/downwell.

 

Also he has to explain *how* the reactions affect the chemicals leading to by-products and then how those are treated.  As far as I can tell, high temperatures (in the bottom of the well) break down polyacrylamide into acrylamide which is toxic to humans and comes up in the backwater.  So it needs to be treated somehow.  But I can't find the chemical equation for any treatment. 

 

This stuff is SUPER cool.  And I am really enjoying learning about it.  But it is also pretty complicated for this biologist.  I never in a million years thought homeschooling would lead me to studying fluid dynamics.  :-)

 

Thanks for any help, explanations, and resources that any of you lovely people can provide us.

 

Ruth in NZ

 

Edited February 25, 2018 by lewelma

[JanetC]

This is probably too obvious, but has he tried emailing the corresponding author of the paper?

[lewelma]

No, we are WAAAY too low a level to want to bother a professor in Polymer Science and Engineering.  Just need the basics.   :001_smile:

[Dicentra]

Hi Ruth!

 

I can do a bit of reading on the chemistry of the polymer stuff and possibly help you out with that but the physics of fluid flow is beyond my pay grade. :D  Maybe Regentrude can help with that part.  Give me a little while (I'm prepping chem classes for my college courses for next week right now) and I'll see if I can come up with something. :)

[lewelma]

Cool, thanks!  He has to explain the chemistry, not the physics.   :001_smile:

[JanetC]

No, we are WAAAY too low a level to want to bother a professor in Polymer Science and Engineering. Just need the basics. :001_smile:

Well my kid has been emailing questions to planetary scientists since middle school. They don't all answer, but it truly doesn't hurt to ask!

 

1. Introduce yourself and give a quick snapshot of your background (so the answer isn't too high or too low). Make sure to mention that you found their paper and tried to read it, they prefer helping those who try to help themselves first.

2. Ask a specific question - what resource do you recommend to better understand how polyacrylimide reduces friction in fracking applications?

3. Thank the professor their time

4. Keep it under a screenful

[Blossom'sGirl]

I don't have the answers, but when New York State was considering it, we attended a local meeting which offered differing viewpoints about it.  One of the speakers was a professor from Cornell who presented/explained it very well including  the chemicals and why and how much are used.  Maybe you could find something searching there.  I don't remember his name.

[Dicentra]

Older DS is doing a paper on the chemistry of fracking. He needs to explain *how* the chemicals work to solve specific problems. This paper is for a national chemistry standard, but he chose the topic (so made it challenging because that is who he is!).  It is not a research standard, so I can hand him sources. He is looking into how citric acid prevents precipitation of metal oxides, the purpose of the buffers, how acids dissolve minerals, and how polyacrylamide reduces friction.  So the first 3 are easy, but the last one is super hard to figure out.

 

The question: how specifically does polyacrylamide reduce friction?

 

The best paper I have found, although at way too high a level, is "Applications of water-soluble polymers in turbulent drag reduction"  It is a review paper published in Processes.  There is so much in there that I don't have the background for (let alone ds), that we kind of need a dummies version, which I am hoping you guys can provide.

 

The paper is discussing:

 

1) anomalous performance of fluid particles during rapid deformation. "in this scenario, vortex stretching arises near the wall, and extensive elongation of polymeric molecules may take place, causing large elongational forces in the direction of the streamlines...." 

 

2) Molecular stretching of the polymers.  possibly polymeric chain extension

 

3) extended laminar flow

 

4) bead spring model. This section referred to molecular dissipation, stochastic velocity field, connector potential, dumbbell probability density, hookean potential, turbulent strength, probability density, and infinite second moment.  All in 2 sentences.  Summarizing with : "that is to say, the polymer molecule expands in the turbulent flow."  (They should have said that first!)

 

DS clearly doesn't have to write a PhD thesis on fluid dynamics for a high school standard.  But he does want to understand how they make slickwater using friction reducers specifically polyacrylamide.  And how specifically the additional of these large molecules reduces friction of water in the pipes/downwell.

 

Also he has to explain *how* the reactions affect the chemicals leading to by-products and then how those are treated.  As far as I can tell, high temperatures (in the bottom of the well) break down polyacrylamide into acrylamide which is toxic to humans and comes up in the backwater.  So it needs to be treated somehow.  But I can't find the chemical equation for any treatment. 

 

This stuff is SUPER cool.  And I am really enjoying learning about it.  But it is also pretty complicated for this biologist.  I never in a million years thought homeschooling would lead me to studying fluid dynamics.  :-)

 

Thanks for any help, explanations, and resources that any of you lovely people can provide us.

 

Ruth in NZ

 

With the understanding that I am IN NO WAY a chemical engineer, never mind an expert on fluid dynamics :), here's my take-away in simple terms (and it might be too simple for what your ds needs):

 

The mechanism of drag reduction by polyacrylamide (PAM) is not completely understood.  From a chemical (as opposed to a physics/engineering standpoint), I'd say it would be due to the long chain length and lack of branching on the PAM polymer.  Drag reduction inside a pipe is a delicate balance between having the fluid flow fast enough but not too fast.  It seems as though dilute PAM solutions are able to reduce the friction between fluid and the walls of the pipes because the solutions are viscoelastic - that is, they have properties of both an elastic material and a viscous one (like combining a rubber band with honey :) ).  This viscoelasticity could be in part due to the long, unbranched chains of the polymer and the fact that the molecules are cross-linked. Imagine a large number of long pieces of string bundled together.  Each individual string will have some elasticity and one string piece moving past another will also account for some elasticity but the strings also tangle somewhat (which would be the like the cross-linking which occurs between PAM molecules) which allows the whole bundle to be molded and shaped into whatever shape is needed and the bundle will stay in that shape - hence, elastic and viscous properties.  That's how I imagine the long chain polymer molecules would behave. :) The lack of branching on the polymer chains and the cross-linking would mean that the balance between the chains being able to move past one another vs. tangling/cross-linking with one another (like my string bundle analogy) puts PAM solutions in the "sweet spot" for allowing the fluid in the pipe to flow quickly but not too quickly.  I think the chemical reasons that PAM was chosen (instead of another long chain polymer) along with allowing the fluid in the pipe to hit the flow "sweet spot" is that it's infinitely soluble in water, it is already readily available in a variety of forms because it's already used in so many other industries, and it's possible to make high viscosity aqueous solutions of it with low concentrations - therefore, it's cheap to use. :)

 

This pamphlet was quite good at explaining things in less technical terms:

https://www.snf.us/wp-content/uploads/2014/08/EOR-Oil-30-Years-of-EOR1.pdf

Particularly - take a look at p.10-top of 13 for some overviews of some processes by which the polymers could break down.

 

I don't think there is one single chemical reaction that your ds could state as being responsible for the breakdown of the PAM into acrylamide.  Acrylamide molecules are simply the monomers from which polyacrylamide (PAM) is made.  Polymer chemistry is a different beast from "normal" chemistry. :)  The breakdown of a polymer isn't a chemical reaction in terms of what most people imagine - molecules breaking apart into individual atoms and then those atoms rearranging to form new molecules.  Polymer chemistry is more like imagining beads strung together with each bead being a monomer made up of a number of different atoms (here's the structure of acrylamide, for example) - the string of beads could be separated into single beads, into shorter bead chains, the bead chains could be cross-linked to one another, or new beads of a different "colour" could be interjected into the pattern but we don't usually smash the beads themselves apart. :)  I think the article above gives a good description of some of the ways PAM could break down.

 

In terms of treating the wastewater, again - I don't think there is one single chemical reaction that I could give.  The wastewater from fracking is a complex mixture with many different components, both inorganic and organic, that need to be dealt with.  I think there's more a push recently to recycle the produced water (wastewater) back into the system and reuse it:

https://www.scientificamerican.com/article/analysis-fracking-waters-dirty-secret/

Acrylamide itself decomposes in the presence of acids, bases, oxidizing agents, iron, and iron salts so some of those might be used to break it down.  It decomposes non-thermally to form ammonia, and thermal decomposition produces carbon monoxide, carbon dioxide, and oxides of nitrogen.  Again - I can't really say if any or all of those decomposition methods are used because the produced water is such a complex mixture.  Thermal treatment might be the best for decomposing the acrylamide, say, but be disastrous for another compound involved.

 

This is from the executive summary of the first article listed below:

"Hydraulic fracturing wastewater is managed using several options, including: disposal in UIC (underground injection control) wells (also called disposal wells or deep disposal wells); through evaporation ponds; treatment at CWTs (centralized waste treatment facilities) followed by reuse or by discharge to either surface waters, or POTWs (publicly owned treatment works); reuse with minimal or no treatment; and land application or road spreading."

 

Some other articles I found that you might find helpful:

https://cfpub.epa.gov/ncea/hfstudy/recordisplay.cfm?deid=244651

http://www.mdpi.com/2073-4360/7/7/1279/htm

https://ac.els-cdn.com/S1876619612000034/1-s2.0-S1876619612000034-main.pdf?_tid=spdf-6c239112-5d1b-494b-abe1-1bf9950c89c3&acdnat=1519610991_e794ddf13de23bc29499b6f3489135fd

 

I don't know if that made things better or worse. :)  Certainly much of the discussion of fluid dynamics is well beyond me.  I think the specifics of wastewater treatment don't seem to be given in any details partly because they could differ so much from well site to well site depending on what else ends up in the wastewater and because it might be possible that some of the treatment processes might be proprietary.  But I'm only guessing. :)

 

Interesting stuff and it's very cool that your ds is digging into it! :)

[lewelma]

Thank you so much! I can't wait to read your references -- they look really good!  I'll get ds to read over your explanation before he starts reading the articles.  I think that he can put in the required equations (and calculations like Ka) for the other chemicals like the acids, buffers, carbonates, rust etc, and then just explain the drag reduction in words. This is going to be a very interesting paper to write, and challenging I think. 

 

Thanks so much for your help!

 

 

[Dicentra]

Thank you so much! I can't wait to read your references -- they look really good!  I'll get ds to read over your explanation before he starts reading the articles.  I think that he can put in the required equations (and calculations like Ka) for the other chemicals like the acids, buffers, carbonates, rust etc, and then just explain the drag reduction in words. This is going to be a very interesting paper to write, and challenging I think. 

 

Thanks so much for your help!

 

You're welcome, although I don't know that I was that much help. :)  And I apologize if I explained things that you already knew (polymer chemistry, etc.).  Polymers weren't really my specialization in my O Chem degree but I did take a few upper level courses.

 

Hoping that the references I linked are more helpful than I was! :)