Page 127 - Principles of Applied Reservoir Simulation 2E

112 Principles of Applied Reservoir Simulation

Table 12-2
Well Log Response

Log Variable Response

Gamma ray Rock type Detects shale from in situ radioactivity.
4 High GR -» shales
+ Low GR =* clean sands or carbonates

Resistivity Fluid type Measures resistivity of formation water.
+ High resistivity =* hydrocarbons
4 Low resistivity =* brine

Density Porosity Measures electron density by detecting
Compton scattered gamma rays. Electron
density is related to formation density.
Good for detecting hydrocarbon gas with
low density compared to rock or liquid.
+ Low response ==» low HC gas content
^ Large response => high HC gas content

Acoustic Porosity Measures speed of sound in medium.
(sonic) Speed of sound is faster in rock than in
fluid.
4 Long travel time =* slow speed => large
pore space
4 Short travel time =* high speed =» small
pore space
Neutron Hydrogen Fast neutrons are slowed by collisions to
content thermal energies. Thermal neutrons are
captured by nuclei, which then emit
detectable gamma rays. Note: Hydrogen
has a large capture cross-section for
thermal neutrons. Good for detecting gas.
+ Large response =» high H content
+ Small response =* low H content

Spontaneous Permeable Measures electrical potential (voltage)
potential beds associated with movement of ions.
+ Low response =* impermeable shales
4 Large response => permeable beds