Well logging The Bore Hole

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Slide 12

The Density Log

The formation density log is a porosity log that measures electron density of a formation

Dense formations absorb many gamma rays, while low-density formations absorb fewer. Thus, high-count rates at the detectors indicate low-density formations, whereas low count rates at the detectors indicate high-density formations.

Therefore, scattered gamma rays reaching the detector is an indication of formation Density.

Scale and units:

The most frequently used scales are a range of 2.0 to 3.0 gm/cc or 1.95 to 2.95 gm/cc across two tracks.

A density derived porosity curve is sometimes present in tracks #2 and #3 along with the bulk density (rb) and correction (Dr) curves. Track #1 contains a gamma ray log and caliper.

Slide 13

Resistivity Log

Basics about the Resistivity:

Resistivity measures the electric properties of the formation,

Resistivity is measured as, R in W per m,

Resistivity is the inverse of conductivity,

The ability to conduct electric current depends upon:

The Volume of water,

The Temperature of the formation,

The Salinity of the formation

The Resistivity Log:

Resistivity logs measure the ability of rocks to

conduct electrical current and are scaled in units of ohm-

meters.

The Usage:

Resistivity logs are electric logs which are used to:

Determine Hydrocarbon versus Water-bearing zones,

Indicate Permeable zones,

Determine Resisitivity Porosity.

Slide 14

Acoustic Log

Shahbaz Younis (Pakistan)

Acoustic tools measure the speed of sound waves in subsurface formations. While the acoustic log can be used to determine porosity in consolidated formations, it is also valuable in other applications, such as:

Indicating lithology (using the ratio of compressional velocity over shear velocity),

Determining integrated travel time (an important tool for seismic/wellbore correlation),

Correlation with other wells

Detecting fractures and evaluating secondary porosity,

Evaluating cement bonds between casing, and formation,

Detecting over-pressure,

Determining mechanical properties (in combination with the density log), and

Determining acoustic impedance (in combination with the density log).