[All] offshore oil

[Louisette Lanteigne]

Here's a quick info page regarding sink holes in General. How this dynamic would work underwater is more complex I'm sure but this illustrates the kind of geological incidents that can occur.

http://plants.ifas.ufl.edu/guide/sinkholes.html

Lulu

--- On Wed, 10/6/10, keller0 at unbc.ca <keller0 at unbc.ca> wrote:

From: keller0 at unbc.ca <keller0 at unbc.ca>
Subject: Re: [All] offshore oil
To: "Susan Koswan" <dandelion at gto.net>
Cc: "'GREN2'" <all at gren.ca>
Date: Wednesday, October 6, 2010, 6:42 AM

Hey, look, I actually may have learned something in those classes I took...

There are some incidences of considerable land subsidence in the US as a
result of underground water resource depletion (there must be pictures on
the web).  If I recall correctly, it depends on the type of aquifer it is
being taken (i.e. whether the water is in spaces in between the structural
components of the rock, or actually making up/floating some of the
structural components of the rock).  In the case of overburden aquifers, I
don't think it can happen, and it doesn't happen with the majority of
bedrock types.

When it occurs in liquid form rather than as part of rock or overburden
deposit, oil is in diapirs: pocket structures that are actually floating
towards the surface of the bedrock because oil is less dense than rock. 
Because these are pockets, they can subside as they are evacuated, again
depending on the properties of the overlying rock.  I don't know much
about, it, but I imagine they backfill the pocket with water so that
collapse doesn't happen on land, but under water perhaps they just aren't
concerned with that?

Hope that helped,
Linette

> FYI, for those of you who get National Geographic make sure you check out
> the map of all the offshore oil platforms in the Gulf of Mexico off Texas
> and Louisiana. If you don't, find a copy. I can't tell you the last time I
> was so shocked. The number of platforms is absolutely mind boggling. Who
> knew.
>
>
>
> Apparently the shoreline is actually getting lower. It's obvious that it's
> a
> huge connected reservoir of oil. Is it the same with groundwater? If
> groundwater reservoirs get "used up" and are not continually recharged, is
> it possible for sinkholes to form? The ground above to collapse? Just
> wondering.
>
>
>
> Susan Koswan
>
>
>
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