Measurement While Drilling (MWD)

Measurement While Drilling (MWD) is the collection of data during the drilling of a well. This information is collected from a tool that is placed above the drill bit. The measurements are made downhole, stored in memory and also transmitted to the surface. This information is sent to the surface continuously and in real time. This information is used to monitor and control drilling operations while drilling.

The primary use of this data is for directional drilling. The information collected from the MWD tool is used to steer the drill bit towards the target zone.

Type of Data Collected·

• Bit Position and Trajectory
• Formation Properties (Receptivity, Porosity, Density, Pressure, Etc.)
• Drilling Parameters (Rotational Speed of the Drill String, Torque, Weight of Bit, Vibration, Gamma Ray, and Drilling Fluid Flow)
  

The MWD tools that measure geological formation parameters are referred to as logging while drilling (LWD) tools.

Data Transition

Mud Pulse Telemetry

The most common method for transmitting the data collected by the MWD tool is by mud pulse telemetry. Data collected by the MWD tool is digitally encoded and transmitted to the surface as pressure pulses in the mud system. Depending on the type of MWD tool, these pulses may be positive, negative or continuous sine waves. The pulse valves are created by a valve located downhole which restricts the flow to create the pressure pulse wave. At the surface, pressure signals are received by pressure sensors and processed by computers.

Electromagnetic Telemety

In a electromagnetic telemetry system, data is transmitted via the drill string using low-frequency electromagnetic wave propagation. The electromagnetic waves are converted at the surface by computers into usable data.
Using the same method, information can be sent from the surface to the tool. Thus a two way communication can be established between the surface and the tool.

Wired Drill Pipe Telemetry

In this system, a data cable is installed in the drill pipe. This data cable carries electrical signals directly from the tool to the surface. This form of telemetry provides the fastest data transfer rates.

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