Summary
This paper discusses a new method for predicting continuous logs of
effective permeability to oil in sandstone and carbonate formations from
well-logging data. This important problem in formation evaluation has remained
previously unsolved because the conventional approach used to predict reservoir
properties from well-log data relies on simple empirical equations and
idealized models of reservoir rocks. The use of such equations and models to
predict a complex reservoir property (e.g., effective permeability) can result
in an inaccurate representation of the formation.
This paper shows that accurate values of effective permeability to oil can
be predicted using model-independent mapping functions constructed from
Gaussian radial basis functions (RBFs), which can be derived from a laboratory
database of measurements on partially saturated core samples. The mapping
functions replace the empirical equations used in the conventional approach and
are model-independent representations of the database measurements. Once the
mapping functions are constructed from the database, there are no adjustable
parameters.
In this study, mapping functions for sandstones and carbonates were derived
from a worldwide database of laboratory measurements made on 79 sandstone and
25 carbonate core samples. The laboratory measurements available on each sample
included irreducible water saturation, effective permeability to oil, porosity,
and nuclear-magnetic-resonance (NMR) T2 distributions. The
mapping functions can be used to predict effective permeability to oil of
reservoirs at irreducible water saturation from input measurements of porosity,
T2 distribution, irreducible water saturation, and knowledge
of rock lithology (e.g., sandstone or carbonate).
The methodology for deriving the mapping functions is explained in detail.
The mapping functions are applied to the database itself to show the accuracy
of the effective-permeability predictions on core samples. The method is also
applied to log data from both sandstone and carbonate formations in three wells
from different parts of the world. The predicted effective permeabilities to
oil are shown to be consistent with oil mobilities measured in the formations
by fluid-sampling tools.
© 2011. Society of Petroleum Engineers
View full textPDF
(
2,149 KB
)
History
- Original manuscript received:
21 December 2010
- Meeting paper published:
20 September 2010
- Revised manuscript received:
19 July 2011
- Manuscript approved:
30 August 2011
- Version of record:
28 December 2011
View Cart
