Natural Science Forum / Earth Science / Mineralogy / August 2005

What petroleum company uses cat scan on a regular basis to determine
porosity ,
permeability or anything else??
Computer axial tomodensitometry (cat scans)  may give some qualitative
information on density.
But not very much on porosity and none on permeability.

At the Saudi Aramco R&D Center we used the CAT scanner to choose cores
for permeability tests. ( I'm sure other oil companies do this, as the
techniques were developed elsewhere.)  What is mainly looked at is the
density of the core which is related to the porosity, and the porosity
is actually visible on the computer processed "core slice" data and can
be quantified.  With this imaging of cores, appropriate cores with
typical porosities can be selected for testing, and ones that have
undesirable porosity varations or large nonporous inclusions can be
rejected.  Permeability can also be evaluated at this stage by the
extent of invasion of drilling mud into the core which is easily
imaged, especially with weighted mud.  With preserved cores the fluids
can be looked at in situ in the core and inhomogenies in fluid
distributions can be observed.

Then the selected cores have fluids flowed through them.  Since the
fluids have different densities (oil, saline water, etc.), they are
easily imaged and permeability of the rock to the fluids can be
evaluated.  Fluid flow fronts and bypassing of fluids are easily
visible.

Of course, porosity and permeability is usually routinely measured by
well logging and core testing by other means.  But CAT scans are used
in special cases to determine core properties for  further evaluation
of the formation and its response to fluid flow.

Our first CAT scanner was obtained from a hospital during the early
days of the development of this technique for core analysis.  Now,
there are companies that will sell a complete CAT scanning package for
looking at cores, but at a much higher price.

George

Funny that a NASA JPL web page "www.astrobio.net" does not work.
Their hammer will (hopefully) have quite more exquisite separation and
discrimination powers, than what is needed for permeability
measurements.

I tried the link above and this time it worked.  Basically, it works
similarly to what I have described, but using neutrons instead of
X-rays, and of course the detector cannot be rotated around the source
(or vice versa) but must rely on the "reflected" gamma ray signal
instead of the transmitted original signal.  Both rely on a massive
amount of data processing.  The CAT scan has a high degree of
separation and discrimination powers, which of course only deals with
the density differences of the scanned region.  I'm not too sure what
the actual capabilities of their instrument will be (I believe that a
rough surface with holes under it may cause insurmountable problems
unlike for the CAT scanner), it will be interesting to view their
proposed images of the meteorite.  Also, I have my doubts about their
claims to be able to image (any) bacteria, it sounds like only those
that have deposited an iron (or other heavy element) sheath about them
would be imaged.  

George