Page 255 - Drilling Technology in Nontechnical Language

246 Drilling Technology in Nontechnical Language Second Edition

Electrical potential tools

Electrical potential tools, also called spontaneous potential tools,
measure the voltage arising between a formation down hole and the

surface. This was the first kind of log run, as mentioned above.

Temperature log

Temperature logs measure the temperature of the well, which varies
with depth. Temperature has a large effect on the setting time of cement,
and temperature must be accurately known when designing and testing
cement slurries.
The geologists and reservoir engineers will specify what logs they want
to run in each hole section, so that they can further identify interesting
formation characteristics. The reservoir will have a lot of logs run through
it, so that as much as possible can be known about the reservoir and the
fluids it contains.

Also the drilling engineers should add their own logging requirements
to the program, to ensure that they get the information they need to drill
the next wells with greater cost-effectiveness.

Conventional wireline logging

A standard logging cable is a wound wire rope with a diameter of
9/16". Instead of a rope core in the center of the wire rope, it contains a set
of electrical conductors that transmit power to the logging tools and data
back to the surface.
On the rig, a logging unit consists of a cabin that may be mounted on
skids for sending by boat to offshore rigs, or it may be installed on a truck
(see fig. 3–20). On a standard unit, the wireline winch contains 25,000 ft

to 30,000 ft of cable. Within the logging unit are controls for the winch (to
lower tools in and bring them out of the well) and a powerful computer
network that analyzes the signals from the tool, displaying the results on
screen and printing them out to continuous paper.

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