The accurate determination of water saturation in shaly
sandstone
reservoirs has a significant impact on hydrocarbons in place estimation
and selection of possible hydrocarbon zones. The available numerical
equations for water saturation estimation are unreliable and depend
on laboratory core analysis. Therefore, this paper attempts to use
artificial intelligence methods in developing an artificial neural
network model (ANN) for water saturation (Sw) prediction. The ANN
model is developed and validated by using 2700 core measured points
from the fields located in the Gulf of Suez, Nile Delta, and Western
Desert of Egypt, with inputs including the formation depth, the caliper
size, the sonic time, gamma rays (GRs), shallow resistivity (Rxo),
neutron porosity (NPHI), the photoelectric effect (PEF), bulk density,
and deep resistivity (Rt). The study results show that the optimization
process for the ANN model is achieved by distributing the collected
data as follows: 80% for training and 20% for testing processes, with
an
R
2
of 0.973 and a mean square error
(MSE) of 0.048. In addition, a mathematical equation is extracted
out of the ANN model that is used to estimate the formation water
saturation in a simple and direct approach. The developed equation
can be used incorporating with the existing well logs commercial software
to increase the accuracy of water saturation prediction. A comparison
study is executed using published correlations (Waxman and Smits,
dual water, and effective models) to show the robustness of the presented
ANN model and the extracted equation. The results show that the proposed
correlation and the ANN model achieved outstanding performance and
better accuracy than the existing empirical models for calculating
the formation water saturation with a high correlation coefficient
(
R
2
) of 0.973, lowest mean-square error
(MSE) of 0.048, lowest average absolute percent relative error (AAPRE)
of 0.042, and standard deviation (SD) of 0.24. To the best of our
knowledge, the current study and the proposed ANN model establish
a novel base in the estimation of formation water saturation.