Measurement while Drilling (MWD) Back to Articles

 
MWD Coach
 
Author: MWD Coach
 

MWD stands for Measurement While Drilling in the oil & gas industry. The simplest way to describe MWD is to relate it to the measurements a pilot takes. A pilot needs to know the direction they are flying (North, South, East, or West), the angle they are fly at (up, down, or horizontal), and what type of skies they will be flying through (rough, choppy, cloudy, rainy, etc). Like a pilot a directional driller needs to know these items about the ground formations that they are drilling through. MWD provides this information. Previous to MWD measurements were taken at various parts of the drilling process, but MWD has allowed these measurements to be sent to the surface continuously while the hole is being drilled. This allows for faster drilling, more accurate drilling, and safer drilling.

 

Beyond the basic concept MWD is a system developed to perform drilling related measurements down-hole that are transmitted to the surface while drilling a well. MWD tools are installed as part of the bottom-hole assembly (BHA) near the drill bit and are housed in a nonmagnetic drill collar or sometimes built directly into the collar.

MWD systems can take several measurements such as Gamma Ray, compass direction (shown as azimuth), tool-face (the direction that your bit is pointing), borehole pressure, temperature, vibration, shock, torque, etc. The MWD also provides the means of communication for operating rotary steering tools (RSTs).

The MWD measured results are transmitted digitally to the surface using mud pulse telemetry through the mud or other advanced technology such as electromagnetic (EM) frequency communications or wired drill pipe. MWD (Measurement While Drilling) is a system developed to perform drilling related measurements down-hole and then transmit that information to the surface while drilling a well with the least non-productive time (NPT) involved. The drilling process is stopped for only a few minutes as the readings are obtained and then sent to the surface software to be decoded. This process saves much more time compared to the wire-line method.

Before the introduction of MWD, all survey data were obtained by stopping the drilling process for wire-line logging or the use of single shot surveying. Wire-line logging required stopping the drilling process, putting the drill pipe in slips, breaking out the Kelly, and then lowering and retrieving the wire-line tool. The survey was read and a plan for further action was initiated. This process increased the non-productive time (NPT) while drilling the well.

Typically the MWD tool acquires three basic pieces of information that are critical for drilling a directional well, Inclination, Azimuth and Tool-face. These three parameters help the directional driller to position the well correctly according to the well plan set forth by the oil company. Additionally other measurements are transmitted including temperature and survey qualifiers that are used to confirm the validity of the down-hole information.

Later, standard MWD tool measurements would include a Gamma Ray sensor to detect the natural formation radioactivity. From there the LWD tool was developed and now a myriad of measurements are done while drilling including Density Neutron, Sonic, Rotary Steerable to mention a few.

 
 
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