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Shale Drilling question

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2006/12/10 19:49
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Does anyone know what the spec is for the concrete used to ''line'' the gas well as it passes through an aquifer ? Just curious as I think it usually is about 1'' thick. what would be the PSI, 3000,4000, or 5000...? Or is it more like a ''grout''/hydraulic cement. My obvious question is how does it not crack??

Posted on: 2013/7/24 20:39


Re: Shale Drilling question

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2011/7/24 7:01
From SWPA
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First, it's cement, not concrete. There is no aggregate used in the cement. (no sand or gravel) Particle size in oilfield cement is very important and not just any cement can be used due to the changing conditions down hole. There is a whole industry based on just this one aspect of well drilling. The cement is there to effectively seal the wells annulus between the casing and the borehole wall and between the various casings. As you can imagine, every well cementing company has its own additives that make it set slower, faster, more or less strength, pumpability, gas blocking ability, elasticity and on and on and on....

As far as cracking, there are some instruments that can be run to check the cements bond but those are only run on single strings of casing just after the cement is pumped if there is a reason to doubt the cement job. Well casings have been cemented in this area for about the last 50+ years, before that the casings were "gelled" with bentonite and water.

Below is a pretty good definition of cement as it pertains to drilling. Hope this helps.

Cement:
The material used to permanently seal annular spaces between casing and borehole walls. Cement is also used to seal formations to prevent loss of drilling fluid and for operations ranging from setting kick-off plugs to plug and abandonment. The most common type by far is API Oilwell Cement, known informally as Portland cement. Generally speaking, oilfield cement is thinner and exhibits far less strength than cement or concrete used for construction due to the requirement that it be highly pumpable in relatively narrow annulus over long distances. Various additives are used to control density, setting time, strength and flow properties. Additionally, special additives are often used to reduce the occurrence of annular gas flow. The cement slurry, commonly formed by mixing Portland cement, water and assorted dry and liquid additives, is pumped into place and allowed to solidify (typically for 12 to 24 hours) before additional drilling activity can resume. The cement usually must reach a strength of 5000 psi [34,474 KPa] before drilling or perforating. More advanced oilfield cements achieve higher set-cement compressive strengths by blending a variety of particle types and sizes with less water than conventional mixtures of Portland cement, water and chemical additives.


Posted on: 2013/7/25 5:27


Re: Shale Drilling question

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2006/9/13 10:18
From LV
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I happen to believe that's the weak link. Cement cracks, whether it's old or new.

Posted on: 2013/8/1 17:32
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Re: Shale Drilling question

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2013/5/28 12:09
From Lilly, PA
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The steel casing used is probably a weaker link than the cement. Cement can be formulated with addatives to prevent cracking and add strength and protect it from acidic groundwater. Steel has a tendancy to corrode rapidly depending upon the chemistry of the rock/water in contact with it. That is why I use PVC or HDPE as well casing when possible. Most steel cased wells I have put in have failed within a few years.

Posted on: 2013/8/3 21:38
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Re: Shale Drilling question

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2009/4/1 21:52
From Johnstown, PA
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YEAH!!! it's prioritory though , what they used to call a TRADE SECRET they don't have to reveal what is in it.

Posted on: 2013/8/4 9:55


Re: Shale Drilling question

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2007/10/17 10:49
From florida
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You'd think that they would use kevlar or someother high strength material. Guess the cost is to high. GG

Posted on: 2013/8/4 11:56
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Re: Shale Drilling question

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I work as a construction manager and what I see at work raised the question for me, cement cracks. It doesn't crack all the time but it does and why would you use a product like that when going through an aquifer ? I've seen some pretty strong cement used but I guess the 1" thick part of it leaves me wondering...

Posted on: 2013/8/4 16:05


Re: Shale Drilling question

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2011/7/24 7:01
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The steel casing will not corrode or rust unless there is oxygen present. The outer "conductor" string of pipe is the only string that generally would see that situation. That is why the casing is cemented, to stop that from happening. And, it is only 40' deep. Coal seams that have been mined may also show very acidic waters due to the amount of oxygen in the water and IF NOT CEMENTED, may also corrode.
The issues are many with using PVC or HDPE, one of which is that it is not strong enough to handle the hydraulic pressures at depth and the forces of trying to run 11000' of it.

A big problem here in PA is the lack of any well construction standards for water wells. Most that I ran into are lucky to have 1 20' joint (length) of PVC and it is NOT cemented. This allows migration from surface to aquifer of pollutants or gas to migrate between water wells and other aquifers.


Pic of casing and cement

It's hard to explain how much actual protection there is between the gas and ANY uphole aquifers, etc. This picture shows 4 strings of pipe, (sometimes in SWPA there are 5 strings due to coal mines) all have cement between each string from bottom to surface.

Corrosion is not an issue with proper well construction.

Posted on: 2013/8/5 5:31


Re: Shale Drilling question

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2010/6/23 21:57
From Butler County
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The pad I was on here in Butler County last week ran 5 strings of pipe to take care of the old mines.


Posted on: 2013/8/5 8:52


Re: Shale Drilling question

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2013/5/28 12:09
From Lilly, PA
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I agree that PVC and HDPE are not feasible on gas wells. I install wells for monitoring mine pool elevations or pumping wells for treatment. Steel doesnt last long in that environment.

Mine water is not acidic due to oxygen. The majority of abandoned coal mines that are completely flooded are anerobic environments. The acidity comes from water dissolving the various minerals found in the roof and floor of the mine, in particular the underclay and if the roof rock is a black shale.

I agree that if a well (gas, water, or any other) is constructed properly there should be no communication between the bedrock zone that is targeted and any aquifer above the targeted zone.

Also, the cement used for drilling is designed to flow into any bedrock fractures, further sealing the cased aquifer from communication with other aquifers/surface water.

Posted on: 2013/8/5 23:16
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Re: Shale Drilling question

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2008/1/31 17:19
From Pretty much everywhere at some point, Thorndale today.
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Quote:
Steel has a tendancy to corrode rapidly depending upon the chemistry of the rock/water in contact with it.


Yeah, and this is a 100% solvable problem with a different type of steel. We make lots of alloys that are designed for such environments, and will not corrode or crack in even the most severe environments. Of course, they are expensive. Often 10x what carbon steel costs, as they generally have very high concentrations of Ni and/or Co. Some of them don't have any Fe at all. Also, it doesn't matter how corrosion resistant the alloy is if it's dirty as heck, as dirt just pits out of it. Thus, not only do you need the more corrosion resistant alloy, you need much more advanced (and expensive) melting equipment as well.

And in theory, only needed for the outer casing, as Gudgeon says. So that's all they use them for, and it's cheaper stuff in the middle.

Of course, not all wells are made "properly". And also, not all cases of upward migration are due to failed casings. Poorly mapped legacy wells, poorly constructed water wells, etc.

Posted on: 2013/8/8 9:53


Re: Shale Drilling question

Joined:
2013/5/28 12:09
From Lilly, PA
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pcray...I am certainly not going to argue with you regarding the properties of metal alloys.

One could write books on all the reasons wells of various sorts fail (someone probably has).

Posted on: 2013/8/8 20:16
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Re: Shale Drilling question

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2006/9/10 21:53
From Greensburg, PA
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my guess and it is just that...is that when failure occurs it is more often operator error than faulty practices. this stuff isn't new. they've been fracking out west for decades. but screw ups come in all sizes.

Posted on: 2013/8/14 11:56


Re: Shale Drilling question

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2009/4/1 21:52
From Johnstown, PA
Posts: 4469
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Tom.......when i did some checking awhile back the thing that was on the report most often was "Casing Failure" but5 discussion arose about that being the easiest thing to blame it on ........i think Gudge said that but don't hold my foot to the fire..........heh.

Posted on: 2013/8/14 13:30


Re: Shale Drilling question

Joined:
2009/4/1 21:52
From Johnstown, PA
Posts: 4469
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A Good friend of mine who used to work for a local water well drilling co , Sperry out of Somerset area , said they use fracking in the water well drilling process and have for years. Any of you know about this? Apparently it's done to allow deposits of iron and limestone to settle.

Posted on: 2013/8/15 8:08



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