[OpendTect_Users] MPSI_Plugin

[Renaud Meunier]

Dear E. Falebita,

> I tried to compute the deterministic Inversion from my 3D Impedance Model
> without success. The Screen showed something like this, "On Deterministic
> Inversion: Problem with the inversion, reflectivity 1.16676 out of range."
>
> My question is: what is responsible for this? What are the many options
> that would make reflectivity to be out of range.

The reason is the wavelet scalar that is not accurate (i.e. the scaling
between the seismic amplitudes and the wavelet’s ones). If you haven’t set
it in your inversion settings, MPSI computes a default value at the well
location. This default value is reported in the OD log file. Now it is
only a first guess, so might not be always the best scalar to use. In
order to find the good one you will have to do some scalar tests (at a
given set of in-lines or cross-lines). The way to do that is by setting
the well constraints to a very low value (i.e. <= 0.1) as you want as
minimal model contribution as possible and manually edit the scalar
starting from the default and progressively increasing or decreasing it. A
last thing you need to be aware of is that the default scaling computation
is not done using the well logs but the initial model values at the well
location (something we need to change in the future) so you will need to
use a broadband model (or as high as the max seismic frequency) to do the
default scalar computation (the synthetic used in the computation to
compare with the seismic trace is done from the model reflectivity
convolved with the wavelet, so a too hash model filtering will give too
low reflectivity response).

> Also, what is the minimum number of wells that can be used for inversion.

You can use any number however they need to be within your survey range.

Best regards,

Renaud.

-- 
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


> Please
> I tried to compute the deterministic Inversion from my 3D Impedance Model
> without success. The Screen showed something like this, "On Deterministic
> Inversion: Problem with the inversion, reflectivity 1.16676 out of range."
>
> My question is: what is responsible for this? What are the many options
> that would make reflectivity to be out of range.
>
> Also, what is the minimum number of wells that can be used for inversion.
>
> Thanks
>
> --
> D. E. Falebita
> Department of Geology,
> Obafemi Awolowo University, Ile-Ife,
> NIGERIA
>
>
>
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