STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

932 Drilling and Well Completions
These tools have been widely used in the past by the cost conscious operators.
The tool could be rented and operated by the rig floor personnel. However,
the inclination ranges are limited, only one tool, teledrift or teleorienter, can
be used during a trip, and only the tool-face angle is read by the teleorienter,
not the azimuth.
These tools are still available but tend to be replaced by the MWD systems.
Mud Pressure and EM Telemetry
Two methods are currently used to transmit data from downhole to surface:
mud pressure telemetry and electromagnetic earth transmission.
There are three principles for transmitting data by drilling mud pressure:
1. positive pulses obtained by a momentaneous partial restriction of the
downhole mud current;
2. negative pulses obtained by creating a partial and momentaneous communication
between the drill string internal mud stream and the annular
space at the level of the drill collars;
3. phase changes of a low-frequency oscillation of the drilling mud pressure
induced downhole in the drillstring.
Figure 4-243 shows sketches of the three systems.
Transmission by Positive Pulses. This system is used by Inteq/Teleco. It is
placed in a nonmagnetic drill collar containing sensors of the flux-gate type
Figure 4-243. Telemetry systems using mud pressure waves: (a) negative
pulse system; (b) positive pulse system; (c) continuous wave system.