Mud pulse telemetry
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Mud Pulse Telemetry - The transmission of encoded data through a drilling rig's drilling mud system using rapid fluctuations in the pressure of a closed loop circulating system. There are three common methods of mud pulse telemetry: Continuous wave, Positive pulse, and negative pulse.
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[edit] Pulse Types
Continuous wave telemetry sends the sensory data accumulated by the downhole measurement tool, known as an MWD (measurement while drilling) or LWD (logging while drilling) tool, by phase variations in the rig standpipe in a specific analog signal sequence that can be converted to a digital signal by processors that can measure fluctuations in the medium's pressure. Positive pulse telemetry sends the sensory data by pressure increases. Negative pulse is the same transmission of encoded data using pressure decreases.
[edit] Pulse Determination
All digital data is formed by combining ones and zeros, known as the binary numeral system format. When the MWD (measurement while drilling)/LWD (logging while drilling) tool transmits data, it is in the form of an analog signal that sends ones and zeros. Combining the sequences of numbers into a word, (or symbol, or value or anything else a computer is programmed to look for), returns input for the specific variable the system was expecting at the time. Continued decoding of data will be achieved while the binary return values match the expected variable input data format.
[edit] Underbalanced Drilling
When underbalanced drilling is used, mud pulse telemetry can become unusable. This is because usually in order to reduce the equivalent density of the drilling mud a compressible gas is injected into the mud, drastically reducing its ability to transmit pulsed data. In this case it is necessary to use another method different than mud telemetry, such as electromagnetic waves to sensors located at the surface.
