Page 84 - Basic Well Log Analysis for Geologist

RTE mime

POROSITY LOGS

Review - Chapter IV
|. The three types of porosity logs are: (1) sonic, (2) hydrogen ion concentration in a formation. In shale-free
density, and (3) neutron. formations where porosity is filled with water, the neutron
2. The sonic log is a porosity log that measures the log ean be related to water-filled porosity.
interval transit time (At) of a compressional sound wave 5. In gas reservoirs, the neutron log will record a lower
through one foot of formation. The unit of measure is porosity than the formation’s true porosity because gas has a
microseconds per foot (jsec/ft). Interval transit time ts lower hydrogen ion concentration than oil or water (gas
related to formation porosity. effect).
3. The density log is a porosity log that measures the 6. The Neutron-Density Log is a combination porosity
electron density of a formation. The formation’s clectron log. Porosity can be determined trom a Neutron-Density
density is related to a formation’s bulk density (p,) in Log either by a crossplot chart or by formula.
4. The neutron log ts a porosity log that measures the
ym/ce. Bulk density, in turn, can be related to formation 7. Additional uses of the combination Neutron-Density
Log are: (1) detection of gas bearing zones: and (2)
porosity. determination of lithology.

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