help me to calculate Shale volume

[cherif1660]

salam alikum
i am new in the domain of logging interpretaion , i want people who can calculate shale volume with several formulas , how do you use it in your interpretation?
please help me, god bless you
your brother Nadjib.

[oanabar]

SHALE VOLUME CORRECTION:
Porosity data should be corrected for shale content in the zone of interest. Porosity values are optimistic when shale is present.
Depending on the value of Rmf/Rw, either the natural gamma data or SP data is used to determine shale volume.
Not all rocks are perfect insulators when dry. Many ores,
such as galena and chalcopyrite, have high conductivities
and conduct electrical current even when totally dry. Obviously,
the resistivity and water s&ration equations,
which assume that the saturating fluid is the only electrically
conductive medium, do not apply when the rock
matrix is also conductive. Fortunately, in most oil provinces
a significant quantity of conductive mineral in a
potential reservoir rock is rare, but when the rock does
contain a conductive mineral, the log interpretation must
consider that conductivity.
Clays and shales, however, are not rare, and they do
contribute to formation conductivity. Shale exhibits conductivity
because of the electrolyte that it contains and
because of an ion-exchange process whereby ions move
under the influence of the impressed electric field between
exchange sites on the surface of the clay particles. The
effect of the shaliiess on shaly sand conductivity is often
disproportionately large relative to the quantity of shale.
The actual effect depends on the amount, type, and
dishibution of the shale and on the natare and relative
amount of the formation water.
Evaluation of shaly formations, usually shaly sands,
is somewhat complex. All logging measurements are influenced
by the shale, and corrections for shale content
are required.
Through the years, investigators have proposed various
interpretation models for shaly sands. In some cases, the
model is based upon the shale existing in a particular
geometry within the shaly sand; for example, the shale
may exist in the form of thin laminae between layers of
clean sand, or as grains or nodules in the sand matrix
structure, or may be dispersed throughout the pore system
of the sand in the form of accumulations adhering to or
coating the sand grains. Other shaly sand models are based
upon some. speciiic characteristic of the shale, such
as its cation exchange capacity or surface area.
Regardless of the basic assumption, most shaly sand
interpretation models employ a weighted-average techaique
to evaluate the relative contributions of the sand and
shale phases to the overall shaly sand response.

[Shakespear]

There is a simple answer but it does not always apply to every situation :-(

Use several equations for calculating shale content (word clay is also used here) ,Vshale, and use the minimum Vshale calculated.

However the local lithology and the tools you use influence Vshale values you will get.

For example, Gamma Ray Tool is popular as a basic Vshale indicator. However you will not be able to use it if there are radioactive sands in the zones of interest.

You take the value of GR in the nearest 100% shale, take the GR value where YOU thing you see 100 % sand. Using the simple ratio equation you calculate what fraction of sand-shale you have in the zone you are analyzing. Notice this is very SUBJECTIVE (you need to make a decision as to what is SHALE and what is CLEAN SAND, which may be off by say 10%) leading to potential errors. This is where experience comes !!!!

In Limestone/Dolomite environments GR maybe useless. Or if you have a mixture Limestone/Sandstone, GR is not good. What to do? You use X-plots and here you need to do a little reading and use a spreadsheet or a computer program :-)

The following book may help you out.

[link Point to another website Only the registered members can access]
Another POTENTIAL problem to remember is that the logging tools may not be calibrated correctly !!!! Then you calculation are completely suspect or useless. Here we need to look into Quality Control of the logs. You look at the log readings in same lithology zones in different wells and see if the log reading are similar. This is just one way of doing this. There are other things to look at.

Hope that helps

PS: Try not to make this too complicated. Read about it, try it out and then talk to a geologist or a log analyst for help. If possible that is.

[cherif1660]

thank you my friend Shakespear for this explanation, but the link of your book doesn't work , you can give me another liknk for this book, i will be very happy, and thank you a lot for your help and i want to thank too Oanabar.
see you next reply
best regards
NADJIB.

[Shakespear]

Cherif

The link is good, here you can see the whole thing versus how it shows up in the message

rs649.rapidshare.com/files/247477838/e0750677112.pdf

Give it a try, but for me it works.

I found the book here

avaxhome.ws/ebooks/engeneering_technology/petrophysics__second_edition__theory_and_practice_ of_measuring_reservoir_rock_an.html

[paolomaldini]

please share the link again..... I need all the considerations to obtain a good data of vshale.

[paolomaldini]

please share this paper:


The Correct Shale-Volume Characterization Increases Hydrocarbon Reserves: Case Study of Cretaceous Formation, Lake of Maracaibo, Venezuela
Paper Number136811-MS

thanks

[samuelektro]

thanks