[OpendTect_Users] MPSI Plugin

[Renaud Meunier]

Dear Mister Falebita,

As I am in charge of the client support of the MPSI plug-in I will try to
answer your questions the best than I can.

> •	how do I measure the uncertainty from the realizations?

The MPSI plug-in allows you to compute a set of equiprobable impedance
cubes (as a seismic inversion process is not unique). You can then analyse
the results using MPSI post-processing utilities. The standard deviation
cube for example will give you the departure from the mean at a given
sample position. If you consider the mean as being the most probable value
then it becomes a measure of uncertainty. Now a most meaningful
computation is to compute some probability cubes. In order to do that you
need to define impedance thresholds (see point below). These thresholds
are a sort of mapping between a Reservoir Property (let’s say Oil bearing
sand) and the impedance you have computed. The output of the probability
becomes your chance of success at a given location and therefore your
uncertainty in predicting the outcome. For example in the project you’ve
just run the sand threshold is any impedance > 8150 (m/s*g/cc) and running
the probcube utility with such a threshold gives you the probability of
having sand (value close to 1) and shale (value close to 0). It is to be
noticed as well that the Connectivity utility gives you the probability of
having sand (or any other rock type) connected to each other. The Net to
Gross utility allows you to compute P10, 
 P50, 
 P90 of Net to Gross maps
(Net being Oil bearing sand in the tutorial).

> •	how do I relate these realizations to uncertainty in water for example?

In order to do that you need to cross-plot your reservoir properties (GR,
VCLAY, Water Saturation, Porosity
) against impedance at the well
locations. You can do that in OpendTect of any other package Excel for
example.

I hope this helps.

Kinds regards,

Renaud.

> Hello everyone,
> I have gone through the tutorial of the MPSI plugin. From the Stochastic
> Impedance realizations, I have the following questions;
> •	how do I measure the uncertainty from the realizations
> •	how do I relate these realizations to uncertainty in water saturation
> for example?
>
> Thanks
> D. E. Falebita
> Department of Geology
> Obafemi Awolowo University, Ile-Ife, NIGERIA
>
>
>
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-- 
Renaud Meunier
Geoscientist
Earthworks Environment and Resources Ltd Prestex House, Edison Road
Salisbury, Wiltshire. SP2 7NU

Direct Line: 01722 343999
Fax: 01722 343991
www.sorviodvnvm.co.uk