Page 13 - Drilling a Straight Hole

DEVIATION-RECORDING INSTRUMENTS

Petroleum Extension-The University of Texas at Austin
Deviation-Recording

Instruments

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In this chapter:
• Measuring drift
• Measuring direction and angle

• How the go-devil works
• Running methods
• Types and usage of instruments

epending on the type of drilling contract between the contrac-
Dtor and the operating company, it might specify the maximum Go-devil = device
deviation a drilling contractor is allowed. The contract may also state in which the survey
instrument is run.
how often a deviation survey is to be run. This frequency can vary in
terms of footage (or metreage) drilled, from 15 to 500 feet (5 to 170
metres), depending on the area to be drilled (see fig. 8). Intervals of
100 to 250 feet (30 to 75 metres) are normal in areas where drilling
is slow and few deviation problems occur. If deviation problems are
expected, contractors might be required to run a survey more often
or, for their own protection, they might decide to run a survey more
often. Frequent surveys are desirable but they can also be risky, time-
consuming, and expensive. Many contractors own deviation-recording
instruments, but the cost in downtime required to lower and retrieve
the instruments can become excessive if too many surveys are run.
Furthermore, whenever a survey is run, there is a risk of sticking the
drill string or causing problems with the deviation tool.

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