Question 1

What is open hole logging?

Accepted Answer

Open hole logging refers to geophysical surveys run in a borehole after it has been drilled but before casing is installed. The borehole is open to the formation, allowing tools to measure the physical properties of the surrounding rock and sediment directly. This is when the most informative formation data can be collected.

Question 2

What does a Gamma-Ray (GR) log measure?

Accepted Answer

A Gamma-Ray (GR) log measures the natural radioactivity of formations. Clays and shales are typically high in radioactivity, while sands, gravels, and clean limestones are low. This makes the Gamma-Ray (GR) log one of the most reliable tools for identifying lithology and locating sand and gravel aquifer zones in water well applications.

Question 3

What is an electric log and what is it used for?

Accepted Answer

An electric log (Elog) measures the electrical resistivity and spontaneous potential of formations. Resistivity helps distinguish between fresh water, saline water, and non-water-bearing formations. In water well logging, electric logs are essential for identifying productive aquifer zones and estimating water quality.

Question 4

What is a caliper log?

Accepted Answer

A caliper log measures the diameter of the borehole as the tool is pulled upward through the well. It identifies zones of washout or enlargement where soft formations have caved in, as well as tight spots. Caliper data is important for calculating cement volumes, selecting screen and casing sizes, and understanding borehole conditions.

Question 5

When must open hole logging be done?

Accepted Answer

Open hole logging must be performed after drilling is complete but before casing is run. Once casing is set, most open hole tools can no longer access the formation. Timing with the drilling contractor is critical — SWS is available 24/7 to accommodate your drilling schedule.

Question 6

What is a deviation survey?

Accepted Answer

A deviation survey measures how far a well has drifted from vertical during drilling. Most water wells are intended to be straight, but drilling through variable formations can cause drift. Knowing the actual path of the borehole is important for pump installation, casing placement, and for wells with regulatory verticality requirements.

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