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40 comments on Completing and Perforating a Well

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drillo on September 20, 2009 - 3:09pm Permalink | Subthread | Comments top

Heading 0ut, thanks for this (as always) excellent post, which comes quite in time:
I would be glad to find some information about a process not mentioned here, which is the backfilling and sealing of the annular space surrounding the well as well as the sealing of entire abandoned wells.

The background is a technical discussion about the long-term performance of Carbon capture and storage (CCS). One potential leakage path is through abandoned wells within the storage area, whose backfilling isn't tight enough to retain the carbon dioxide from moving to the surface.

I know about an incident where this happened with an underground natural gas storage: According to the responsible company (the responsible government agency had misteriously "lost" their documents) the gas leaked through the wells, which obviously had an unsuitable backfilling, so that within a year the gas was noticed at the surface.
This gas storage project was in the early 60s and the company was still in the "learning by error" mode with (one of?) its first projects, so maybe suitable backfilling was used in all later wells, but there are no evidences to be sure.

I have read that according to the 

IEA Greenhouse Gas R&D Programme (2007): 
»Summary Report (No 2007/6 July 2007) 
of 3rd Well  Bore  Integrity  Workshop.«  
Meeting  held March 12–13, 2007 in Santa Fe, New Mexico, U. S. A.

for example the state of Alberta has a regulation demanding that all existing backfilled wells have to be re-opened and backfilled again with suitable material. According to an expert the cost of doing this would probably make most CCS projects unfeasible.

My questions:
I suppose that the backfilling of an abandoned oil or gas well is only designed to prevent the mixture (saline and fresh) groundwater from different aquifers and (when indicated) the rise of remaining gas or oil under low pressure.
I don't expect that it was designed to retain (gaseous or hypercritical) carbon dioxide under high pressure nor to withstand aggressive carbon acid.
I expect this even less from the backfilling of unsuccessful dry wells.

Does anyone have information on the CCS-suitability of the typical backfilling of oil or gas wells?

Thank you very much!

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Heading Out on September 20, 2009 - 3:46pm Permalink | Subthread | Parent | Comments top

If I understand you correctly you are talking about the cement that is injected between the casing and the rock wall, and which I described in an earlier part of the series .

Abandoning a well comes under a different set of rules, and I'm not close to getting to that as a topic, sorry.

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drillo on September 20, 2009 - 4:22pm Permalink | Subthread | Parent | Comments top

Yes, I mean the cement that is injected between the casing and the rock wall as well as the well sealing of an abandoned well.

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Gail the Actuary on September 20, 2009 - 4:15pm Permalink | Subthread | Parent | Comments top

We read about the concern that natural gas get into water supplies after fracking. It would seem like CCS with its constant high pressure and its issue with acid formation would be worse.

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joule on September 20, 2009 - 5:09pm Permalink | Subthread | Parent | Comments top

Gail -

I tend to agree.

From the admittedly small amount of geology and hydrogeology that I do know, I think the widespread application of CCS is a very dubious proposition, particularly when viewed over the long term (say up to 100 years). Unless one has ideal conditions and a near perfect uniform formation, that high-pressure CO2 is going to sooner or later find a path of least resistance and wind up back in the atmosphere.

CCS strikes me as wheel-spinning at its worst, and I strongly suspect that the coal people know it's really going to go nowhere but just want to throw it out as a red herring to make people believe that coal is going to be 'OK'. I doubt that it's ever going to happen except for a few highly publicized demo projects.

Not to mention the fact that it takes one hell of a lot of energy to separate CO2 from all that stack gas and to then force it way down underground. CSS is hardly an elegant solution, and is in fact an exceedingly ham-fisted one. We can do better.

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Gail the Actuary on September 20, 2009 - 5:36pm Permalink | Subthread | Parent | Comments top

I know I went to a conference at Georgia Tech a couple of years ago. Several people talked about CCS, and they were uniformly not optimistic about its ability to perform as planned long term.

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Cold Camel on September 21, 2009 - 2:25am Permalink | Subthread | Parent | Comments top

The problem is not only that CCS is a dead end but that we debate ineffective solutions to nonexistent problems. Climate fears disappear if you factor in Peak Oil and the resultant economic crash. Production proves reserves. Declining production is reality.

Significantly increased poverty will lead to significant suffering and early death for billions over the next 50 years. That's a real problem with no profitable quasi-solution for the presently entrenched, so they ignore it. Just as they will ignore solutions for the rest of us. So it doesn't really matter if a solution exists, you'll never hear about it in the media unless there is potential profit.

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ROCKMAN on September 21, 2009 - 8:36am Permalink | Subthread | Parent | Comments top

joule -- I'll tend to agree with you as far as the unlikely success of CSS. Just my knee-jerk reaction but gas injection is a very expensive proposition and it's difficult for me to imagine the public willing to pay the toll. But you probably are already familiar with my low expectation of our fellow citizens to pay the price to spare the environment.

OTOH, as long as standard protocols are observed there little likelihood "that high-pressure CO2 is going to sooner or later find a path of least resistance and wind up back in the atmosphere" IMO. As long as the injection pressures don't exceed the earth's overburden pressure they won't leak THROUGH THE ROCKS. There can be some unique geologic scenarios where it might happen but they would be rare but can be anticipated and avoided. But as others have pointed out the CO2 could easily leak out of abandoned wells with bad cement jobs/corroded casing. A likely problem in the bad old days 30 years ago. But even if that happens any wells in the area of CSS would most likely be monitored for such leaks. I once even saw an old wellhead blown into the air when we frac'ed a nearby well which should not have been affecting offsets. Sh*t happens as we say in the oil patch. But when it happens you put a rig on the offending well and spend some $'s fix the problem. Lose some CO2 back to the atmosphere for sure but no one dies. But, as I pointed out above, this is purely an academic discussion for me. Given the choice of burning more coal/pumping more CO2 into the ever warming climate or abandoning any effort to maintain BAU you know my expectations.

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drillo on September 22, 2009 - 7:34am Permalink | Subthread | Parent | Comments top

But when it happens you put a rig on the offending well and spend some $'s fix the problem.

This may be okay if the amount of CO2 is so big that the leakage can be detected (e.g. by pressure measurements, carbonic acid in the groundwater or even higher CO2 levels in the atmosphere. But you have to be aware that the underground "tanks" needed to take up the emissions of even only one power plants are *huge* (a three-digit number of tonnes CO2). So if there are only small leaks where the gas seeps out slowly over decades it won't be possible to notice this by pressure measurements and I doubt that these can be detected by other methods. So these seepages may evade without being noticed.
Although you may easily find the tiny hole of a flat bike tire it may be impossible to notice such a spot on a Zeppeline.

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Heading Out on September 22, 2009 - 5:26pm Permalink | Subthread | Parent | Comments top

I rather suspect that the initial wells that are used for re-injection (bear in mind that it is something that folk are now doing) are going to be instrumented to a very high degree, and monitored in detail. It is the ones that are put in after it becomes a conventional tool that need to be of more concern, but (recognizing the caveats that reality will always bite you in painful places) with enough ingoing knowledge, there should be less reason to worry - about that part of the process anyway!

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ROCKMAN on September 24, 2009 - 9:13am Permalink | Subthread | Parent | Comments top

drillo -- I would think they would use direct detection to monitor wells. A hand held CO2 detector should ID leakage. Any volume they can't detect won't be relevent. But, as always, rules don't work if they aren't enforced. The biggest potential threat IMO would be casing leaks into shallow water reservoirs. But other then a corrosion problem with some water wells I still don't think it would add to be a big problem. But back to my earlier point: I just don't think folks will pay the cost of compressing the CO2 to levels needed for injection. I've seen cost figures for other gas injection programs and I suspect most folks don't realize how much horsepower it takes to bring those pressures up. Before I would spend much time debating leakage problems I would like to see the proponents offer total cycle injection costs. Just a guess on my part but I doubt the consumers will accept the price. Such ideas tend to look good in general discussions but hit the wall when the bottom line costs are offered.

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drillo on September 20, 2009 - 4:20pm Permalink | Subthread | Parent | Comments top

Update

Now I found an insightful document mentioning the experiences in Alberta:

http://www.co2captureandstorage.info/docs/wbifinalreport.pdf

I picked out a few highlights:

In Texas, there are 1-1.5 million wells and in Alberta there are 350,000 wells with 195,000 wells penetrating the Viking Formation alone and 15,000 new wells being added each year.
...
It can be difficult to get a perfect annular cement seal, as the cement bonding is often dependent on the rock type. Knowledge about cement is often anecdotal and based on indirect observations, and can therefore be difficult to capture. It is not known how good early cement jobs were, nor the long-term behaviour of these early cements. 3% of wells in Alberta leak gas (but may leak through connections, rather than cement). It was pointed out that injections of slurries, which exceed fracture pressure, fail ~10% of the time, resulting in leakage to surface or aquifers.
...
… It was recognised that current practice is not adequate to ensure long-term wellbore integrity, with no experience for long-term i.e. on the timescale of decades. Standard testing methods are needed ...We must make the public aware that perfection will not be achievable.
...
… There remains considerable uncertainty around remediating previously drilled and abandoned wells.

So my interim conclusion is that leakage from old wells IS an issue for the feasibility of CCS.

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40 comments on Completing and Perforating a Well

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