Computation of cementation factor and saturation exponent for selected oil fields in southern Iraq

Abstract

This study aims to calculate cementation factor and water saturation exponent for four
different lithological formations from different oil fields in south of Iraq and compare the
results with typical values of these reservoir parameters. The formations that being selected
for this study are: Yamama Formation in West Quran (WQ-60 well), Zubair Formation in
south Rumaila (Ru-64 well), Nahr Umr Formation in Luhais oil field (Lu-5 well), and
Mishrif Formation in Tuba oil field (Tu-4 well). The cementation factor for clastic
formations (Zubair and Nuhr Umr) was calculated via Wyllie (1949) and He (2005)
empirical equations. It is found that the value of this parameter is estimated to be 1.1 and
1.90 m for the Zubair formation using Wyllie equation and is equal to 2.4 and 1.6 m for
Nahr Umr Formation according to the He equation. For the carbonate formations (Yamama
and Mishrif), the cementation factor was estimated using Borai (1987) and Focke and
Munn (1987) equations. This parameter was equal to 1.3 for both formations according to
Focke and Munn (1978) and estimated to be 1.95 and 1.98 for Yamama and Mishrif
formations according to equation developed by the Borai. The calculated saturation
exponent was 2.5, 2, 2.21 and 0.5 in Zubair, Nahr Umr, Mishrif, and Yamama formations,
respectively. The new calculated values were then applied in the Archi equation to estimate
water saturation. The obtained results were compared with that calculated in laboratory
(from core). Results showed that Wyille equation is better than the He equation. The final
result confirmed that Wyllie equation is more accurate than He equation for calculating
cementation factor in sandstone, while Borai equation was more accurate than Focke and
Munn equations for the cementation factor in limestone rocks.