Page 76 - Drilling Technology in Nontechnical Language

Chapter 3 – DRILLING A LAND EXPLORATION WELL 67

Fig. 3–17. Surface casing run, casinghead housing attached

The time to attach the CHH and attach and test the BOP on an average
operation would take around 10 to 15 hours, depending on the problems
encountered. While the BOP is nippled up, a survey tool is normally run
inside the casing on wireline. (Nipple up refers to a process of assembling
equipment. Conversely, nipple down refers to disassembling equipment.)
The survey tool will measure the direction (called the azimuth) and
inclination of the wellbore every few feet or meters. Knowing the azimuth
and inclination at various depths in the well allows the actual path of the
wellbore so far to be calculated. This is necessary to know exactly where
the bottom of the casing is located.

Drilling out the casing and testing the formation strength

The surface casing used in this example well has an outside diameter of
20" (508 mm) and an inside diameter of 19" (483 mm). The burst strength
(the internal pressure that the casing will hold without breaking) of this
particular casing is 2,410 psi (16.6 kPa).

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