Shale Volume Estimation (V sh )
In most reservoirs the lithologies are quite simple,
being cycles of sandstones and shales or carbonates
and shales. Once the main lithologies have been
identified, the gamma ray log values can be used to
calculate the shaliness or shale volume (V sh ) of the
rock. This is important, as a threshold value of shale
volume is often used to help discriminate between
reservoir and non-reservoir rocks. Shale volume is
calculated in the following way: First the gamma ray
index (I GR ) is calculated from the gamma ray log data
using the following relationship
I GR ¼ GR log À GR min
À
Á = GR max À GR min
ð
Þ
Â
Ã
(16.5)
Fig. 16.12 Gamma ray log responses for common lithologies. (Modified from Rider 2004)
398
N.H. Mondol
In most reservoirs the lithologies are quite simple,
being cycles of sandstones and shales or carbonates
and shales. Once the main lithologies have been
identified, the gamma ray log values can be used to
calculate the shaliness or shale volume (V sh ) of the
rock. This is important, as a threshold value of shale
volume is often used to help discriminate between
reservoir and non-reservoir rocks. Shale volume is
calculated in the following way: First the gamma ray
index (I GR ) is calculated from the gamma ray log data
using the following relationship
I GR ¼ GR log À GR min
À
Á = GR max À GR min
ð
Þ
Â
Ã
(16.5)
Fig. 16.12 Gamma ray log responses for common lithologies. (Modified from Rider 2004)
398
N.H. Mondol