Fracking. What could be better?
Posted on 02/24/2014 4:58:18 AM PST by thackney
:: did your Dad put a large hunk of lead in your family water well? ::
Sounds like he also “pulverized” that hunk of lead.
Being a highly technical engineer-type, I’ve always wondered what the actual pressures are in fracking for gas?
We had a dry well fracked successfully, but that only took a small 3,000 lbs/psi.
Add jobs, improve the economy, and become an energy self-sufficient nation?
Or continue to be beholden to those who want us dead?
Hmmm.....
I like to tell the anti-fracking crowd to do an internet search for towns named "burning springs".
” Dad put a large hunk of lead in your family water well?”
Nope, it was made out of cast iron. We have always been into reloading and making our own bullets for target practice, so using lead as a weight would been out of the question.
I didn’t know about using nitro, but I did know that my grandfather used the dynamite technique long before I was born.
Dynamite is based on nitroglycerin.
Can someone explain the validity of laws on 'low flush' toilets again...
Don’t know, but a column of merely static liquid over a mile high would express one helluva pressure at the bottom.
You got that right!
BUT, as the mass of rock is many times more than the mass of water, at any given depth, the pressure on the rock should be the same multiple of rock to water.......
I.e., wouldn’t the rock pressure a mile deep be greater than the water pressure in the ocean a mile deep?
Yes, but only if the rock were a liquid. As it is a solid, the pressure is probably nil at any given point, being distributed over a huge volume.
Have to ask my structural engineer son......I’m electrical......
For those who want to see a 6 minute video showing how horizontal drilling and fracking is done, Northern Gas and Oil has done a great one.
It includes a visual piece on how fresh water aquifers are protected from contamination.
http://www.northernoil.com/drilling-video
Knowledge is power, keep the link and pass it on.
In the absence of tectonic forces, Pressure to maintain an open vertical fracture the rock, (PR/(1-PR))X(Sig V - Pres) + Pres
where PR = poissons ratio of material = lateral strain/longitudinal strain under longitudinal applied stress. about 0.15 to 0.25 for hard sedimentary sandstone reservoir rock, higher for limestone and shale.
Sig V = vertical stress, aka overburden. basically pressure exerted by overlying rock. 1.1 to 1.15 psi/ft
Pres = Pressure in the reservoir pore space, normal is 0.43 to 0.45 psi/ft, water gradient
it gets more complicated for laminated rocks, grains laid out more like plywood than bound spheres in a sandstone or silt matrix. one must apply variability of horizontal properties (parallel to bedding) and vertical properties (perpendicular to bedding). you can get close on the low side with general isotropic equation above.
induced fractures are almost always vertical, as the horizontal stresses in the earth are almost always less than overburden. Vertical growth stops when layers with stress higher than is within the fracture is encountered. you can build pressure in the fractures exceeding frac pressure which induces greater width. generally extending fracture length is the easier path than creating large widths. widths are on the order of 0.05 to 0.25 inch.
breakdown pressure, necessary to get a fracture started is higher than fracture pressure. usually by a factor of 1.1 to 1.4
so without spending a million or ten acquiring data, usually around 0.55 to 0.80 psi/ft (vertical feet depth)plus all the friction getting the fluid down there. 5000 psi in shallow basins is common (8000’ or less) 10,000 in deeper basins and 12,000+ psi in deep basis with high reservoir pressure. Fracs have been done over 20,000 psi at surface, but rare. the 3000 psi job mentioned was probably on what’s nicknamed a post hole, under 3000’ deep.
Haha, me too, but I also took strengths of materials and fluids. But that was back...way back! You raise good points. I guess the liquid needs to be forced into the cracks to further fracture the rock. The solids prolly don’t harbor any gas anyway, so who cares. It’s in those pesky cracks.
Wow! Thank you. The math surprisingly simple, but I get the drift.
News to me: fractures are mostly vertical , I thought they were mostly horizontal. And the pressures -even at 20k lbs./psi - are far below what I thought were required.
Isn’t fracking done in granite too? What is the PR for granite?
Granite PR is probably around 0.2. not tolerating a lot of bend before it snaps.
there have been be instances of frac’ing granite, but not like in the simple planar fracturing sense. What would be the use? It’s very low porosity and can’t store much or any reservoir fluids. There are rare hydrocarbon deposits seeped out of sedimentary source rocks above or alongside granite. In order to store hydrocarbons, or water in geothermal heat operation, the granite must have a naturally fractured secondary porosity and permeability system in place. Granite formation frac jobs are really just injection to sweep reservoir damage from drilling out away from the wellbore. There may occur induced fracture components in the process, but likely not the main objective.
Though I did teach science once upon a life, what I don’t know about geology would fill half the universe.
But I do know enough to understand what you are saying - it only makes sense. I know nothing of the geology of where oil and gas are, except for hearing the word “sands” a few times.
Thanks again!
Fracking. What could be better?
Bfl
bkmk
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