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→Measurement techniques
==Measurement techniques==
==Measurement techniques==
[[file:rate-of-penetration_fig1.png|left|thumb|{{figure number|1}}Example of a geolograph chart.]]
Rate of penetration is calculated by measuring the length of time required to drill [[length::1 ft]] of depth. This is typically done by reading the chart on the geolograph.
Rate of penetration is calculated by measuring the length of time required to drill [[length::1 ft]] of depth. This is typically done by reading the chart on the geolograph.
The ''geolograph'', or drilling recorder, mechanically monitors depth and records drilling parameters in time. These parameters are recorded on a paper chart, graduated in minutes, that is wrapped around a drum. The drum rotates one revolution in 8, 12, or 24 hr. To record depth, a small cable is run from the geolograph to the top of the kelly via a pulley on the crown of the derrick (see “[[Land rigs]]”). Kelly height can then be measured and directly related to bit depth. As each foot is drilled, an ink pen on the geolograph places a small mark on the chart. Every [[length::5 ft]] the pen places a larger mark on the chart (Figure 1).
The ''geolograph'', or drilling recorder, mechanically monitors depth and records drilling parameters in time. These parameters are recorded on a paper chart, graduated in minutes, that is wrapped around a drum. The drum rotates one revolution in 8, 12, or 24 hr. To record depth, a small cable is run from the geolograph to the top of the kelly via a pulley on the crown of the derrick (see “[[Land rigs]]”). Kelly height can then be measured and directly related to bit depth. As each foot is drilled, an ink pen on the geolograph places a small mark on the chart. Every [[length::5 ft]] the pen places a larger mark on the chart ([[:file:rate-of-penetration_fig1.png|Figure 1]]).
[[file:rate-of-penetration_fig1.png|thumb|{{figure number|1}}Example of a geolograph chart.]]
Other more advanced monitoring techniques utilize computers and digital encoders to monitor depth. These systems are typically stand-alone. The digital encoder or transducer is attached to a part of the rig that moves in proportion to the movement of the drill string. Common attachment points are the drill line, drawworks drum, or crown sheaves.
Other more advanced monitoring techniques utilize computers and digital encoders to monitor depth. These systems are typically stand-alone. The digital encoder or transducer is attached to a part of the rig that moves in proportion to the movement of the drill string. Common attachment points are the drill line, drawworks drum, or crown sheaves.