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Q: Closed Oil Wells ( Answered 5 out of 5 stars,   3 Comments )
Subject: Closed Oil Wells
Category: Science
Asked by: rootbeer-ga
List Price: $20.00
Posted: 28 Oct 2005 13:22 PDT
Expires: 27 Nov 2005 12:22 PST
Question ID: 586143
After an oil well has completely run dry, do they just cap the well or
do they fill the hole? If they fill, what material is used ?  If you
do a good job I?ll throw in a $10 tip.

Request for Question Clarification by pafalafa-ga on 28 Oct 2005 19:24 PDT

I'm not sure why one of the commenters below remarked that wells
aren't filled in.  Perhaps that's the practice in some places in the
world, but in the US, an abandoned oil well is generally filled in
with cement.  In fact, most oil well states have a set of regulations
requiring plugging of wells as they are taken out of service.

On occasion, a specialized metal plugging device called (for some odd
reason) a bridge plug may also be used to permanently close off a
section of a well.

What sort of information are you looking for to make for a full answer
to your question?


Clarification of Question by rootbeer-ga on 30 Oct 2005 19:43 PST
The statements you made are exactly the kind of information that I'm
looking for.  All I need is for you to give me some links to sources to
support what you're saying.  Thanks!
Subject: Re: Closed Oil Wells
Answered By: pafalafa-ga on 30 Oct 2005 20:10 PST
Rated:5 out of 5 stars

Thanks for getting back to me on this. 

Here are a few links to sites that provide a quick overview of how oil
wells are regulated, and what happens to wells at the end of their
useful lives:

California Department of Conservation 


...In the plugging process, a portable rig is placed over the well.
Cement and special drilling mud are alternately pumped deep into the
well casing through tubing. When the cement hardens, it stops oil, gas
and water from entering the well and migrating to the surface. The mud
acts as a secondary barrier.
Alaska Oil and Gas Conservation Commission


(a) Plugging of the uncased portion of a wellbore must be performed in
a manner that ensures that all hydrocarbons and freshwater are
confined to their respective indigenous strata and are prevented from
migrating into other strata or to the surface. The minimum
requirements for plugging the uncased portion of a wellbore are as

(1) by the displacement method, a cement plug must be placed

(A) from 100 feet below the base to 100 feet above the top of all
hydrocarbon-bearing strata;

(B) from the well's total depth to 100 feet above the top of all
hydrocarbon-bearing strata...

(2) by the displacement method, a cement plug must be placed from 100
feet below the base to 50 feet above the base of each abnormally
geo-pressured stratum and from 50 feet below the top to 100 feet above
the top of each abnormally geo-pressured stratum...

(3) by the displacement method, a cement plug must be placed from 150
feet below the base to 50 feet above the base of the deepest
freshwater stratum...

[the description continues, but I didn't want to overwhelm you with
the whole thing!]

As I mentioned, specialty bridge plugs are sometimes used -- a
mechanical device, usually used in conjunction with cement, that helps
to seal an abandoned well.

Here's an example, again from Alaska, of a regulation requiring a bridge plug:

E) if the perforations are isolated from open hole below, a mechanical
bridge plug set no more than 50 feet above the top of the perforated
interval, and either a minimum of 75 feet of cement placed on top of
the plug by the displacement method or a minimum of 25 feet of cement
placed on top of the plug with a dump bailer...

and here's what some of the suckers look like:

I trust that's the information you needed.

However, please don't rate this answer until you're fully satisfied
with the information you've received.  If there's anything else I can
do for you, just post a Request for Clarification to let me know, and
I'm at your service.



search strategy--

Google searches on:  

abandoned oil well regulations cement  

abandoned oil well regulations "bridge plug"

and a Google Images search on [ "bridge plug" ]
rootbeer-ga rated this answer:5 out of 5 stars and gave an additional tip of: $10.00
Fantastic!  This was exactly what I was looking for.  I didn't have
nearly as much luck as you did finding information, but it sounds like
you had some background knowledge on the topic already.  How long did
it take you to put together the answer?  Thanks!

Subject: Re: Closed Oil Wells
From: qed100-ga on 28 Oct 2005 13:30 PDT
Wihtout knowing more authoritatively, I'd wager that an oil company
just caps the well. This would make the well easily accessible if, at
some time in the future, some innovative method allows the reserves to
be extracted profitably.
Subject: Re: Closed Oil Wells
From: markvmd-ga on 28 Oct 2005 17:48 PDT
Adding to qed100-ga's comment-- oil is mixed in with rock in sort of a
matrix, like a sponge. The well doesn't need to be filled in. I will
leave it to an actual Answerer to explain the details.
Subject: Re: Closed Oil Wells
From: pafalafa-ga on 31 Oct 2005 13:51 PST

Thanks so much...the stars, tip and kind words are much appreciated.

As for answering the question, you're right -- I did have some
background on the topic, which made the research much easier than it
would have been otherwise.  I estimate it took about an hour to
research your question and write up the results.

Hope to see you back here one day soon.


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