Page 79 - MSc_thesis_R A Kil

6. First investigations of the recently discovered giant Perla field, which is the largest gas discovery in
Venezuela to date, associates the lithology of the reservoir with foramol (ENI and Repsol, personal
communication). This study might be very useful in the understanding of the reservoir architecture.
This identification of potential analogues to Favignana is an example of the possible applications
of this type of studies. It is by no means meant to be comprehensive. Further research might
introduce more potential reservoirs with similar depositional background, and therefore use the
Favignana dataset to improve the understanding of the reservoir facies internal architecture and the
optimisation of the development of a field. For example, during the burial process some facies behave
differently compared to others. This differential diagenesis and compaction might compartmentalise
the complex to a larger extent than is observed in field outcrops.

7.6 Modelling algorithms

The multi-point statistics modelling method used in the facies model and described in section 6.1 is not
the only available algorithm to model a property in a grid. The Petrel software package offers a wide
range of methods, providing different results (Schlumberger, 2009). This section briefly discusses the
most used algorithms and their influence — either in positive or negative sense — on the final model.

7.6.1 Object modelling

When the shape of the facies bodies that have to be modelled is very well known, such as channels, splays,
bars or scours, object modelling is the best algorithm to use. Often this method is used in combination
with other types of modelling. As described in section 6.1 this approach also has been used for the facies
model of the Favignana calcarenite. After the ’background’ is made, object modelling replaces parts of
the that model, imitating an erosion process.

7.6.2 Sequential indicator simulation

In case very little is known about the shapes of sedimentary bodies, sequential indicator simulation (SIS)
provides input possibilities for other data trends. Input can be upscaled well log data, variograms, trends
and a random seed number. The downside of the algorithm is that if the nugget-style variograms do not
match the spatial well data, very noisy results will be produced. Petrel uses the algorithm provided by
the Geostatistical Software LIBrary (GSLIB).
The resulting facies model can be found in appendix D, figure D.7. It is clearly visible that such a model
is not geologically meaningful. Conceptual geological thoughts can not be incorporated in the model,
and although the probability maps can be used, a scattered and unrealistic distribution of reservoir

60