Drill string · Drilling
MWD & LWD
Sensors in the bottomhole assembly that measure while drilling: trajectory, pressure and temperature (MWD) and formation properties (LWD).
What it does
Data is encoded and sent to surface as pressure pulses in the drilling mud, so the well can be steered in near real time. Data can also be stored in downhole memory.
Basics
| MWD | Trajectory, downhole pressure and temperature |
| LWD | Formation logs while drilling |
| Telemetry | Mud pulse, relatively low bandwidth |
| Backup | Downhole memory |
Common failures
- Loss of the mud pulse link to surface
Troubleshooting
- Symptom
- Data stops arriving at surface
- Likely cause
- Telemetry link lost
- What to check
- Keep drilling if safe and recover the full data from downhole memory when the tool is pulled