As drilling has become more complex, with horizontal and directional drills increasing in numbers, well logging has also had to adapt and improve. Measurement-While-Drilling (or MWD) is a type of well logging that incorporates the measurement tools into the drillstring and provides real-time information to help with steering the drill.
Once a well angle exceeds 60 degrees, the logging tools can no longer be pushed through the well to retrieve information, making conventional logging tools ineffective. Originally designed in the 1980s to overcome well logging challenges of wells being drilled at extreme angles, MWD is a type of Logging-While-Drilling (LWD) where tools are encompassed in a single module in the steering tool of the drillstring, at the end of the drilling apparatus (or the bottom hole assembly).
Providing wellbore position, drillbit information and directional data, as well as real-time drilling information, MWD uses gyroscopes, magnetometers and accelerometers to determine borehole inclination and azimuth during the actual drilling. The data is then transmitted to the surface through pulses through the mud column (mud pulse) and electromagnetic telemetry. Decoded at the surface, the data can also be transmitted to an offsite location immediately.
With such precise wells being drilled, MWD aids drilling engineers with real-time information so that they can make important decisions while drilling. Geosteering is a relatively new concept of positioning wells according to the geological features in the reservoir obtained through MWD. Now, video is even available to help in the process.