The Five Myths About Fracking

[Dinwar]

Are you sure that those quartz grains are not too strong. Are they not the stongest ones that remained after all the processes that broke down the parent rock and transported it until the deposition occurred ?

The issue is, what you're talking about is weathering. There are two processes involved: physical and chemical weathering. A lot of minerals are physically strong, but chemically very, very weak-- meaning that after a few millenia bouncing around in streams and lakes and whatnot they degrade into other minerals. The reason yon don't see much feldspar isn't because feldspar is physically weak, but because it becomes clay minerals by the time the sand is rounded.

 

[Libra]

The issue is, what you're talking about is weathering. There are two processes involved: physical and chemical weathering. A lot of minerals are physically strong, but chemically very, very weak-- meaning that after a few millenia bouncing around in streams and lakes and whatnot they degrade into other minerals. The reason yon don't see much feldspar isn't because feldspar is physically weak, but because it becomes clay minerals by the time the sand is rounded.

Yes, but quartz minerals provide stronger bonding than calcite and clay minerals. I understood it as such that during an UCS test (unconfined compressive strength), the propagation of fractures is dictacted by the weakest bonds, it doesn't fail through the mineral itself.

Quartz also has a higher Mohs hardness (about 7) than clay minerals (about 6 to 6.5) and there is a good correlation between UCS and hardness.

These factors lead me to think that the UCS done on a quartz sand grain would be higher than that of clay minerals.

 

[Dinwar]

Yes, but quartz minerals provide stronger bonding than calcite and clay minerals.

I'm not disputing that. All I'm saying is that chemical weathering is a major cause for the loss of feldspars and other minerals during the processes that weather sand. My comments are limited to the scope of the following quote:

Are they not the stongest ones that remained after all the processes that broke down the parent rock and transported it until the deposition occurred ?

 

[Skeptic Ginger]

You're awefully big on insults and ranting about education. Two quick questions: Have you ever installed a well? And are you aware of the fact that the petroleum industry is different from the environmental industry?

Clean the spittle off your screen and let's discuss this as adults. If you can't, that's your problem. ...

You attacked his post with insults, and you claim he's the one that isn't being an adult?

Thanks Macdoc, I'll look into the methane greenhouse gas issue a little deeper since I also thought it was a worse contributor to heating the planet.

 

[DavidS]

On the drilling technique, I would have thought that reverse circulation would be the best bet for this application ? Deep drilling, requirement to flush out drill chips etc etc.

That's an awfully big can of worms you have there... maybe we should keep the lid on. When you get into all the niggling but critically important details of borehole and drillstring hydraulics, cuttings transport, hole stabilization, well control, yada, yada, drilling fluid selection and application starts to look a like rocket science or voodoo (depending how intimately one appreciates the details). Drilling engineers are highly technical professionals; for the rest of us heathen it's best to pay what it costs to hire a good one, tell him how it needs to look when it's done, and then do it the way he says. FWIW, I cannot imagine a situation where completion intentions would strongly influence a circulation direction decision, nor have I ever heard one mentioned by my drilling engineer brothers.

On the fracturing itself, is it not highly unlikely that this is the formation of NEW fractures and much more likely that it is the existing discontinuities in the sedimentary rock that is forced open by the pressure ? Alot of these distontinuities (joints, bedding plans, stress fractures etc etc) could be discoulored (typically in shales / mudstones) indicative of waterflow and/or chemical weathering, implying some form of permeability here ? So permeability would be increased rather ?

No, it's not highly unlikely. Though I can't lay my hands on specific publications, I'm certain it's been done in the lab with beautifully homogeneous samples in representative subsurface conditions. I recall seeing actual test facilities and photos of tests at University of Tulsa and at Halliburton research center. I'm sure a search through JPT (Journal of Petroleum Technology) and SPEJ (Society of Petroleum Engineers Journal) will find several reports. Ordinary materials science considerations lead directly to initiation of brand new fractures without appeal to planes of weakness. Put enough pressure into a cylindrical steel tank and it'll crack nicely (suggestion: stand way back); the principle is the same (almost). In the case of bedding planes, they're typically "horizontal", but (at sufficient depth) the fracture proceeds vertically across them.

That said, it's almost certain that the precise point of initiation is strongly influenced by stress concentration or weakness at some local heterogeneity or flaw, but once initiated the fracture provides its own stress concentration to propagate happily through homogeneous material. Consider a glass "cutter"; it just scratches the surface to invite the fracture to start where you want, after which it propagates through flawless material.

The frac job could, of course, open any fractures, joints, etc. that are already present. If none are present, the frac job can make one. If they're present and conductive enough, there's probably little for the frac job to gain. If a few are present but poorly connected and poorly conductive, the frac job can prop them open and improve their conductivity. If many are present, well connected, but poorly conductive, it gets tricky... pumping will only open them up until your fluid leaks away as fast as you can pump; you have to pump hard enough to open them up, fast enough to open them up as far as you want, starting with enough proppant-free fluid to get them open to accept your proppant before the leakoff piles up your proppant to block your pumping.

Yes, the permeability in the fracture itself is much greater than in the original rock matrix (for many purposes it's enough to consider the fracture to be infinitely permeable), and that makes the large-scale average permeability in the direction of the fracture plane a bit larger. Outside the negligible fracture volume, though, the rock matrix is no more permeable than it was (until the frac fluid gets recovered it's actually much worse locally), and the large-scale average permeability perpendicular to the plane is no greater. The benefit is that the fracture plane presents a large area for flow through tight rock to reach the fracture, through which it can flow easily to the wellbore; that's what I meant by "makes the well look wider".

Stress-wise, we are not talking about a isolated slice of rock here, laterally the induced fracture would wedge to zero and vertically upward you will find bridging and doming with increased upward stresses closing shallower discontinuities. A pocket of localised rock is thus rendered less permeable and the extraction proceeds, I would presume. Would this be grouted up / sealed afterwards ?

The details controlling fracture height are way beyond my ken, well into voodoo territory. All I can offer is a handwave to stress dissipations at physical property discontinuities (e.g. sandstones may be more brittle than overlying shales), and a generalization that pumping faster and harder helps the fracture grow taller and cross those discontinuities.

I'm sure, though, that there's generally no good way for unwanted parts of the fracture to be "grouted up / sealed afterwards"; once you break it, you bought it. A frac job that makes the fracture tall enough to connect your well to an underlying or overlying permeable zone is a Very Bad Thing, especially for a tight gas well that has enough trouble producing without handicaps.

 

[Texastwister]

I have been designing fracs for the last 20 years, hope I can add something to this debate.
A few things I noticed reading the posts

A large frac would be ~300 ft horizontally, 100 ft high. This depends on rock mechanics ofcourse, and the objective is to get as long of a frac as possible, while keeping the height in the payzone.

If height increases too much the frac becomes too narrow and wont accept the sand/proppant.

Diesel has been almost completely eliminated from frac fluids. There could be a small frac company using diesel, but I havent seen it.

Fracing has been around for 60 years and has been very common since the 70's.

During the 80's and 90's they fraced in New York state, but on shallow oil wells. Seems everyone has forgotten about that.

The chemical recipes are readily available and I personally had to send to the State of Penn each MSDS on every chemical pumped. So anyone that says they dont know whats in the fluid are not doing any research

 

[Libra]

. . . FWIW, I cannot imagine a situation where completion intentions would strongly influence a circulation direction decision, nor have I ever heard one mentioned by my drilling engineer brothers.

Thanks for you input DavidS. Agreed, let's keep the lid on it, however the RC drilling does have advantages over normal circulation like returning drill chippings through he hollow stem drill rod as opposed to the annulus between the casing and the drill hole edge.

No, it's not highly unlikely. Though I can't lay my hands on specific publications, I'm certain it's been done in the lab with beautifully homogeneous samples in representative subsurface conditions.

I am yet to come across Homogeneous Sedimentary Rocks.

Ordinary materials science considerations lead directly to initiation of brand new fractures without appeal to planes of weakness. Put enough pressure into a cylindrical steel tank and it'll crack nicely (suggestion: stand way back); the principle is the same (almost). In the case of bedding planes, they're typically "horizontal", but (at sufficient depth) the fracture proceeds vertically across them.

Might be, but Sedimentary Rock is no ordinary material and is typically a non-linear elastic material with significant anisotropy. Also note that the bedding planes were only typically deposited nearly horizintal, but a rock formation a few thousand metres deep is highly likely extensively folded and with member legs dipping and striking at acute values.

Yes, the permeability in the fracture itself is much greater than in the original rock matrix (for many purposes it's enough to consider the fracture to be infinitely permeable), and that makes the large-scale average permeability in the direction of the fracture plane a bit larger. Outside the negligible fracture volume, though, the rock matrix is no more permeable than it was (until the frac fluid gets recovered it's actually much worse locally), and the large-scale average permeability perpendicular to the plane is no greater. The benefit is that the fracture plane presents a large area for flow through tight rock to reach the fracture, through which it can flow easily to the wellbore; that's what I meant by "makes the well look wider".

That makes alot of sense, somehow it seems that not everyone looking into the whole fracking situation comprehends this.


With your knowledge and experience, could you fill me in about the typical control measures employed during such an operation ? Are there any monitoring wells surrounding the production well provided for sampling, testing and monitoring ?

Sealing the well, do they only use cementicious grout to seal, or does it get a bentonite plug isolating the strata of concern with a cementicious seal above it ?

Are there any systems installed in the cementicious seal that allows re-injection of grout for repairs ? In complex piling designs, I have included cast-in ducts, post-fitted with packers to enable a high pressure grouting opperation, for this specific reason.

 

[ThunderChunky]

They don't rise above opinion. The truth is, fracking doesn't have enough history yet for any definite answers about it.

Every single point he makes is a factual claim, with the exception of point three which is opinion. He's debunking outlandish claims that are not supported by the evidence. That doesn't mean fracking is good, it just means the loudest people that oppose it are blatantly making crap up.

 

[ectoplasm]

The chemical recipes are readily available and I personally had to send to the State of Penn each MSDS on every chemical pumped. So anyone that says they don't know whats in the fluid are not doing any research

Here is a piece from a lawyer's newsletter discussing the regulatory and legal issues behind the disclosing of frac chemicals in Canada.

 

[DeathDart]

How long will the concrete seals in oil wells last?

Often when oil wells are re-entered the previous concrete seals have started to break down in only twenty years. Horizontal fracking wells also tend to have roof collapses which can bypass the seals.

When drilling oil wells, the drillers are fastidious about keeping water out of the oil. Water can poison an oil well (plug it up). Also when drilling you can encounter highly pressurized salt water. So they put concrete or steel seals in place to isolate that strata. Natures seals have lasted for 100’s millions of years, how long will man’s last?

Roman concrete can last 1000’s of years. Portland concrete in underground situations might last 50 years.

The fracking well may not immediately contaminate the water aquifers, but as the well deteriorates it will compromise nearby strata.

Gravity abhors a vacuum underground. So the horizontal well bore will collapse. This weakness will propagate upwards over time. In a thousand years it could move as much as 100 feet toward the surface. This could move the well contents into an aquifer or into permeable rock.

All drilling disrupts the segregation of geological strata. Over time, all well bores can become unintended conduits for poisons.

 

[DavidS]

...
I am yet to come across Homogeneous Sedimentary Rocks.
...
Might be, but Sedimentary Rock is no ordinary material and is typically a non-linear elastic material with significant anisotropy. Also note that the bedding planes were only typically deposited nearly horizintal, but a rock formation a few thousand metres deep is highly likely extensively folded and with member legs dipping and striking at acute values.

Now we're getting into mere quibbles, I think. Homogeneity lies in the eye of the beholder, a question of both scale and degree. By "vertical" I mean the nonspecific convention of "across the bedding planes", not "closely aligned with gravity"; apologies for forgetting that such convention useful and familiar to oilfield folk is less so for real people (similarly, "bedding planes" were the surfaces on which sediments that now form the rock were deposited, not geometrically flat nor even horizontal surfaces then nor now)

That said, I can assure you that hydraulic fractures (generally, at sufficient depth 3000+') don't follow bedding planes because the rock breaks across the planes before enough pressure can be developed to break along the planes. For most reservoirs, bedding planes are more or less horizontal. To open a more-or-less horizontal fracture, all the overburden weight would have to be carried by fluid pressure in the fracture. The required pressure would be a bit more than 1 psi per foot of depth. Fracture initiation and propagation is easy enough to detect by monitoring pressure while pumping the job. Measured "frac gradients" comfortably below 1 psi/ft (commonly near 0.7 psi/ft) confirm that the hydraulically induced fractures are much more vertical than horizontal.

Ah, you work with pilings and such? Presumably at depths the oil patch would call "piddlingly shallow"? Shallower than about 2000', the overburden stress may be low enough that the tensile strength and compressibility of the rock resists fracturing until the pressure rises high enough to lift the world above. "Horizontal" fractures, quite probably along bedding plane weakness, are more likely at shallow depths.

In fact, if a deep frac job were to create a "vertical" fracture that propagated way up toward the surface, at some point it will reach the crossover point where overburden stress falls lower than tensile strength; the fracture would "roll over" and propagate more "horizontally".

somehow it seems that not everyone looking into the whole fracking situation comprehends this.

I agree there seems to be an awful lot of that. It's why I posted this high-level handwave.

With your knowledge and experience, could you fill me in about the typical control measures employed during such an operation ? Are there any monitoring wells surrounding the production well provided for sampling, testing and monitoring ?

OK, now we're getting into implementation details. I'm not the guy and this ain't the place for quantitative specifics, but with that disclaimer I can offer handwaving generalities better than the average non-oilfield-trash bear:

During the well drilling, casing, cementing, and completion operations there are many routine tests and measures to confirm whether the casing is well cemented into the hole. The hole gets measured by caliper logs to determine its volume (local rock properties may make it less round or bigger or even smaller than the bit) and look for problem areas. While drilling, mud volumes pumped in and returned out of the well are monitored to detect zones of fluid entry or loss that could be a problem later (and for warning if the mud tries to drain away or climb out to let the well burn down the rig). The volume of cement pumped is carefully measured (often counting individual pump plunger strokes) to know how far it's displaced and much of the hole it *should*. Various logging tools then measure how much of the hole it *did* cover (a simple temperature log can pinpoint TOC "Top Of Cement" from the heat it evolves while setting) and how well it fills the space between the casing and the hole (these are more complex electronic sensing tools, e.g. the CBL: Cement Bond Log). If it don't look right, now is the time to fix it or adapt later operations (and hopes for the well) to its limitations.

During pretty much any operation involving pumping into the well, especially during cementing and stimulation operations, pressures are monitored on all the tubing and casing strings and the annuli (annuluses?) between. Temperature differences will impose some slight pressure changes, but at the high rates and pressures involved in a frac job a major isolation failure will be glaringly obvious: a large pressure spike correlated across the pipes/annuli and rate changes or even by crushing the inner pipes into steel junk you'll have no end of fun and expense fishing out of the hole. (I am personally aware of one such case where the collapsed casing was recovered by "washing over" [drilling with a ring-shaped bit to recover the "fish" inside the pipe, like a core]... several joints of 5.5" casing were collapsed small enough to recover inside 4.5" washover pipe.) To ensure you *will* clean up any such mess, you didn't get a permit to drill the well until you posted a bond or other financial surety to get that done.

As to monitoring where the actual fracture goes if the well doesn't break, there's not much you can do (that I can talk about... maybe somebody with more confidence in his ethical position and knowledge of microseismic techology will chip in). Detailed logs of rates and pressures are recorded during the frac job, from which analyses beyond my expertise can glean much information about the fracture geometry, well integrity, and who to blame if something went wrong.

Monitoring wells aren't generally employed to monitor hydraulic fracture stimulations; there's simply no reason to believe they can reveal anything that won't be far more obvious otherwise. Again, stimulation operations aren't particularly relevant to more subtle communication issues through the wellbore. Redundant "surface" casing strings, cement, and annulus monitoring pretty much serve the function of monitoring wells, especially since the wellbore itself is by far the most vulnerable path from the completion to the surface.

Sealing the well, do they only use cementicious grout to seal, or does it get a bentonite plug isolating the strata of concern with a cementicious seal above it ?

Oilwell cements aren't your grandpa's Portland cement (well, that is sometimes used for shallow "conductor" and "surface" pipes). There are numerous special formulations for the unique range of conditions and operations involved in getting it mixed, pumped, and set in a well. That's a study of its own; it's what made HOWCO rich (Halliburton Oil Well Cementing Operators) and why they had the big pumps and blenders that proved to be useful for stimulation operations.

I'm out of my league here, but the purpose of oilwell cement isn't primarily structural (except for surface conductor pipes), but to seal the annulus outside the casing. I'm sure there are structural benefits, but I think establishing the hydraulic seal you need pretty much guarantees all the structural support you could want.

REALLY old wells have used other stuff to seal casings and plug holes (I've worked with pre-WWI wells with casings seated into lead wool and pre-WWII wells plugged with wood [better than you might think, and a royal bitch to get through if you want to re-enter the well]), but cement is the modern gold standard (with various mechanical plugs and additives that may provide sealing benefits). Crosslinked polymers, plastics, and various oilfield snakeoils du juor are sometimes used in specialized cases, but "never" without cement.

Are there any systems installed in the cementicious seal that allows re-injection of grout for repairs ? In complex piling designs, I have included cast-in ducts, post-fitted with packers to enable a high pressure grouting opperation, for this specific reason.

Systems for re-cementing are "never" installed a priori; cementing is tricky enough without putting tools in your way that you expect never to need and could fail on their own... or spoil a cement job that would've been perfect if the recementing tool hadn't been in the way.

The typical remediation for isolation failure or casing leak or inadequate primary cementing is a "squeeze job": The casing near (and/or above and/or below) the point of failure is perforated (much like for the production zone) and cement is pumped in forcibly, usually to the point that it packs tightly in the annulus and against the borehole and sets firmly as pressure squeezes out excess water. That can be tricky; if you don't pump hard enough you won't push cement or pack it firmly enough where it needs to go, if you pump too hard you can make a new fracture that can leak around the tip where it's too narrow to push cement particles, or the pressure you apply can get around behind some outer casing and make it collapse. Sometimes it's better to cut out the casing entirely, run a new string and do the primary cementing operation againr from scratch. Or if the well can't pay back that effort and expense, take your ball and go home:

The ultimate fallback remediation is to plug and abandon the well: pull as much stuff as you can out of the hole and pack it with cement and mechanical plugs, to standards defined by numerous regulatory authorities as well as sensible self-interest. The plugging bond you established before drilling pays for that if you go bankrupt or die or disappear before then.

Assuming you don't vanish from the earth somehow, your liability for the borehole never goes away. If a well you thought you plugged decades ago starts leaking, you'll have to come back to deal with it and clean up the mess. Even if you sold it off to somebody else, you'll be on the hook to get it done if he doesn't. If you're not an idiot, you'll do your damnedest to get it right the first time or screen prospective buyers for idiocy.

 

[Dinwar]

I am yet to come across Homogeneous Sedimentary Rocks.

I think this is a matter of scale. Dolomitic limestone such as that found in much of Northwest Ohio is pretty damn homogenous; it's only when you get to extremely small scales that any heterogeneity becomes apparent. Salt can also be homogenous, due to the migration of the material post-deposition. I'm not getting into the sedimentary/metamorphic debate.

Also note that the bedding planes were only typically deposited nearly horizintal,

One issue I can see is that they don't frequently STAY nearly horizontal. A lot of the rocks near the Appalachian Mountains have been extensively deformed.

In fact, if a deep frac job were to create a "vertical" fracture that propagated way up toward the surface, at some point it will reach the crossover point where overburden stress falls lower than tensile strength; the fracture would "roll over" and propagate more "horizontally".

You know, from an academic standpoint it would be interesting to see where that point is. I remember in college seeing talks about magma moving up vertical fissures, than along horizontal bedding planes. The talk I'm thinking of was about using magnetic minerals to determine fluid flow (magnetic minerals tend to be long and skinny, or at least in this magma they were), but I've seen that type of structure numerous times. I've little doubt the work has already been done, but this concept is applicable well outside the oil field.

 

[CapelDodger]

... apologies for forgetting that such convention useful and familiar to oilfield folk is less so for real people ...

We're picking it up.

... pumping the job ...

Very colourful .

In fact, if a deep frac job were to create a "vertical" fracture that propagated way up toward the surface, at some point it will reach the crossover point where overburden stress falls lower than tensile strength; the fracture would "roll over" and propagate more "horizontally".

The principle of laminar armour. Don't ask me why that comes to mind; it's just that kind of mind.

I agree there seems to be an awful lot of that. It's why I posted this high-level handwave.

I, for one, thank you for it. It's way better than looking ths stuff up.

My own experience of the oil industry is at the suit-wearing end, the land of accountants, lawyers, MBA's and other corporate junk, where "oilies" are figures of fun. The origin of that sucking sound which somehow explains why you ain't rich (except in vocabulary and experience) but they are. I particularly miss the trophy secretaries; nothing beats eye-candy for getting you through a tedious day. You well-head guys may have to take my word for that, I guess.

... (a simple temperature log can pinpoint TOC "Top Of Cement" from the heat it evolves while setting) ...

Gems like that are what I thank you for .

 

[CapelDodger]

Every single point he makes is a factual claim, with the exception of point three which is opinion.

Factual claims don't always rise above opinion. His claim that no aquifers in the US have been polluted is not supportable by evidence. Nobody knows yet. His claims about methane release are disputed; his opinion of the available evidence is unsurprisingly industry-friendly in all cases. The water-use problem is indisputable in some places. Does anybody claim that fracking uses hundreds of chemicals, or is that just a "they say" strawman? DavidS might have a ball-park figure. Point five involves damaging earthquakes; damage is, at the margin, a matter of opinion, and the earthquakes in Lancashire have, in my opinion, been very damaging for frackers' prospects in England's green-and-pleasant.

He's debunking outlandish claims that are not supported by the evidence.

He's not actually debunking anything, he's just stringing words together and creating an impression.

That doesn't mean fracking is good, it just means the loudest people that oppose it are blatantly making crap up.

Are these actually the loudest people, or are they the ones selected by the likes of Ridley as being representative? Are they perhaps loud on Fox News but not in the normal world? Opinions naturally differ on the answers.

It seems to me that the loudest voice is the one expressing caution. Nobody doubts the fracking industry, they flat-out don't believe a word they say. Can you blame them?

 

[CapelDodger]

You know, from an academic standpoint it would be interesting to see where that point is. I remember in college seeing talks about magma moving up vertical fissures, than along horizontal bedding planes. The talk I'm thinking of was about using magnetic minerals to determine fluid flow (magnetic minerals tend to be long and skinny, or at least in this magma they were), but I've seen that type of structure numerous times. I've little doubt the work has already been done, but this concept is applicable well outside the oil field.

From http://en.wikipedia.org/wiki/Chobham_armour

'Because the ceramic is so brittle the entrance channel of a shaped charge jet is not smooth — as it would be when penetrating a metal — but ragged, causing extreme asymmetric pressures which disturb the geometry of the jet, on which its penetrative capabilities are critically dependent as its mass is relatively low. This initiates a vicious circle as the disturbed jet causes still greater irregularities in the ceramic, until in the end it is defeated. The newer composites, though tougher, optimise this effect as tiles made with them have a layered internal structure conducive to it, causing "crack deflection" '

Nothing gets work funded quite like being defence-related, but there's an obvious downside in accessibility. Some of it might have leaked into the public domain, though.

 

[DavidS]

I remember in college seeing talks about magma moving up vertical fissures, than along horizontal bedding planes.

Yeah, I kinda did give short shrift to the possibility of a hydraulic fracture intersecting a pre-existing conduit upward. Consider, though, that the hydrocarbon accumulation itself is good evidence there isn't any such geological feature near the reservoir; the hydrocarbons would have leaked away before we got there. An inadequately plugged old abandoned wellbore, on the other hand... but that brings us back to the issue of wellbore integrity rather than risks peculiar to hydraulic fracture stimulations.

 

[DavidS]

I particularly miss the trophy secretaries; nothing beats eye-candy for getting you through a tedious day.

I sense a priorities mismatch here. Eye-candy gals are certainly a joy to behold, but there are thousands of those just running around wild. Trophy secretaries/administrative assistants are worth their weight in gold, however heavy or homely (especially a good drilling secretary back in the day when she'd have to take dozens of daily drilling reports over the phone and assemble dozens of copies typed up in cryptic codes in time for the 0800 staff meeting. Pop quiz: MIRU HOWCO NUBOP). I can be perfectly content for my boss to regret the day I joined his staff, but he and I and everybody else I can try to whip better treat our gals Friday like queens; if they ain't happy, ain't nobody gonna be happy.

You well-head guys may have to take my word for that, I guess

I don't mean to mislead anybody about my wellhead proximity. While my youth covered broader ground, my role for a long time has been reservoir engineering -- what my iron-mongering brothers call "the land of Nod" (if a RE dies at his desk... how do you tell?). We're not so directly involved with anything that looks like actual work, though we work closely with those who do to decide what work needs doing, is worth doing, or how it's working out. My father (oilfield foreman) used to say you get rich in the oil business not by being smart, but by not being stupid. In a very real sense, reservoir engineering is about stupidity control.

Move In (arrive on location) and Rig Up (set up equipment for) Halliburton Oil Well Cementing Operators. Nipple Up (assemble, attach, connect to wellhead) BlowOut Preventer.

 

[DavidS]

Often when oil wells are re-entered the previous concrete seals have started to break down in only twenty years. Horizontal fracking wells also tend to have roof collapses which can bypass the seals.

When drilling oil wells, the drillers are fastidious about keeping water out of the oil. Water can poison an oil well (plug it up). Also when drilling you can encounter highly pressurized salt water. So they put concrete or steel seals in place to isolate that strata. Natures seals have lasted for 100’s millions of years, how long will man’s last?

Roman concrete can last 1000’s of years. Portland concrete in underground situations might last 50 years.

The fracking well may not immediately contaminate the water aquifers, but as the well deteriorates it will compromise nearby strata.

Gravity abhors a vacuum underground. So the horizontal well bore will collapse. This weakness will propagate upwards over time. In a thousand years it could move as much as 100 feet toward the surface. This could move the well contents into an aquifer or into permeable rock.

All drilling disrupts the segregation of geological strata. Over time, all well bores can become unintended conduits for poisons.

While I disagree with almost every one of these assertions, I'll leave a point by point enumeration of what's wrong to others.

What's right here is redirecting the focus away from poorly supported assertions of risks peculiar to hydraulic fracture stimulation and toward concerns about wellbore integrity.

While I don't agree that all wellbores will become conduits for fluids from deep zones to contaminate shallow zones, I do agree that improperly sealed wellbores can do so.

I suggest that hydraulic fracture stimulation operations don't greatly exascerbate that risk.

I assert (but won't further argue) that I am an adequately competent expert in the field to to authoritatively assert that a hydraulically fractured well completion can extract more hydrocarbons from larger regions of a tight gas reservoir than could be extracted by an unfractured completion.

For now, consider those as premises:

1) A wellbore may pose a risk for of "surface" (groundwater, lemmings, etc.) contamination by subsurface fluids.

2) Hydraulic fracture stimulation does not much increase the wellbore's contamination risk.

3) Hydraulic fracture stimulation allows a hydrocarbon resource to be extracted by fewer wellbores.

4) The value of a well, and thereby the cost and effort justifiable for its construction, increases with the amount of hydrocarbon that well can extract.

5) The hydrocarbon resource will be extracted.

Tell me again why we shouldn't stimulate the bejeebus out of as few wells as we can get away with, to limit the total environmental risk across all the wellbores and maximize the resources we can afford to apply to each to mitigate those risks?

 

[Libra]

I think this is a matter of scale. Dolomitic limestone such as that found in much of Northwest Ohio is pretty damn homogenous; it's only when you get to extremely small scales that any heterogeneity becomes apparent. Salt can also be homogenous, due to the migration of the material post-deposition. I'm not getting into the sedimentary/metamorphic debate.

As a Geotechnical Engineer I have to see the term homogeneity not only as uniform composition, but also as uniform character in terms of engineering properties of the rock. The nature of the sedimentary processes forming these sedimentary rocks, leads to non-homogeneity in the rock-mass. A specific deposit from one event might be near-homogenous in terms of composition, but will still highly likely be structurally anisotropic.

One issue I can see is that they don't frequently STAY nearly horizontal. A lot of the rocks near the Appalachian Mountains have been extensively deformed.

Agreed, that's why I mentioned that despite having been deposited near-horizontal, these rocks are highly likely to be extensively folded and with member legs dipping and striking at acute values.

You know, from an academic standpoint it would be interesting to see where that point is. I remember in college seeing talks about magma moving up vertical fissures, than along horizontal bedding planes. The talk I'm thinking of was about using magnetic minerals to determine fluid flow (magnetic minerals tend to be long and skinny, or at least in this magma they were), but I've seen that type of structure numerous times. I've little doubt the work has already been done, but this concept is applicable well outside the oil field.

Indeed it would. It is the post deformed semi-vertical discontinuities of the sedimentary rocks that I thought might be a potential plane of weakness targeted by the fracking operations.

 

[CapelDodger]

Yeah, I kinda did give short shrift to the possibility of a hydraulic fracture intersecting a pre-existing conduit upward. Consider, though, that the hydrocarbon accumulation itself is good evidence there isn't any such geological feature near the reservoir; the hydrocarbons would have leaked away before we got there.

A very telling point.

Trophy secretaries/administrative assistants are worth their weight in gold, however heavy or homely

Trophy secretaries are only there to look good. The first thing I'd do at any new location is find out who really mattered and could get things done - most often a woman in a "secretarial" role. Management often had no idea how things actually worked even in their own departments, let alone at the workface.

... but that brings us back to the issue of wellbore integrity rather than risks peculiar to hydraulic fracture stimulations.

Indeed it does. The danger is that an executive culture in which points are scored for cutting costs while responsibility is clouded by sub-contracting (and sub-sub-contracting) is unlikely to get such things right. As an example, the guy in charge of BP's Gulf drilling when that unfortunate incident occurred built his reputation on getting things done cheap.