Formation Evaluation Through Casing - Cased-Hole Log Analysis and Reservoir Performance Monitoring - page 179

Fig. 11.37 Finding
ʣ ma and ʣ wf .

Fig. 11.38 Finding ʣ dc
and ʣ sb

ʣ hy can be found by conventional means. Thus, only the gamma ray response to
dry clay and response to the matrix remain to be found. It is assumed that neither
formation water nor hydrocarbon contribute to the gamma ray response, so it can be
written

= (

)

GR 1- f GR + V GR .

T ma dc dc

From which it follows that, in shales,

( )

GR = GR / 1 f - ,

dc T

and, in clean intervals,

( )

GR = GR / 1 f - .

ma T