Definition
Measurement While Drilling — Measurement while drilling (MWD) is a downhole system that measures wellbore inclination, azimuth, and toolface in real time and transmits the data to surface, allowing directional drillers to steer the well as it is drilled.
Also known as: measurement while drilling, MWD, MWD tool
What MWD measures
Measurement while drilling places survey and directional sensors just above the bit in the bottomhole assembly. Accelerometers and magnetometers measure inclination, azimuth, and toolface, and many packages add drilling-dynamics data such as vibration, shock, and downhole weight. Because the sensors read the Earth’s magnetic field, they are housed in a non-magnetic drill collar to avoid interference from the steel string.
Getting data to surface
The most common telemetry is mud-pulse: a valve modulates pressure pulses in the circulating fluid that a surface transducer decodes. Electromagnetic and wired-pipe telemetry are also used. Real-time surveys let the directional driller set the mud motor or RSS toolface, verify the achieved dogleg severity, and keep the well on its planned path.
Why it matters for rentals
MWD is a sophisticated, service-intensive tool typically provided run-by-run, while the surrounding string and collars are rented to complete the BHA.
Pair MWD with our rental downhole tools and non-magnetic collars, or contact us to configure a directional BHA around your telemetry package.