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samples collected during the drilling process. Two approaches are
applied in studying the heterogeneity of rocks:
- deterministic: maps for the distribution of heterogeneity
along the horizontal and the scheme of distribution of
heterogeneity through the thickness of the productive stratum are
generated (both are based on the information obtained in the
geological-geophysical and industrial study of the non-uniformity
of the reservoir under different parameters);
- probabilistic: by applying mathematical statistics
establishing distribution law, which match actual distribution.
However, it is more useful to use this both approaches.
For reservoir engineering, the most important parameter is
permeability. Therefore, during the calculations it is necessary to
establish the distribution law, cumulative distribution function and
plot the distribution polygon.
The study of heterogeneity, in particular the
establishment of patterns of permeability change, is carried out
using the following basic statistic characteristics: mathematical
expectation, variance, coefficient of variation, and others. These
mathematic criterias enable us, although not fully, to express
quantitatively and qualitatively the characteristic of heterogeneity
change through the formation:
- the study of heterogeneity with the aim of making
geological correlation;
- discovering the influence of heterogeneity on reservoir
development and field development strategy.
For establishing statistic characteristics and comparison of
production, target graphical dependencies are plotted. They are
setting up the connection between researched parameter (in most
cases it is permeability k) and frequency of occurrence n. The
significance of change in permeability is described by the
permeability distribution polygon or, in other words permeability
spectrum.

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