Measurement While Drilling

Measurement While Drilling tools are used by Drilling rigs to transmit information in real time from the tool, located near the drill bit, to the surface.

Directional Information

MWD tools are generally capable of taking directional surveys in real time. The tool uses accelerometers and magnetometers to measure the inclination and azimuth of the wellbore at that location, and they then transmit that information to the surface. With a series of surveys at appropriate intervals (anywhere from every 30 feet to every 500 feet), the location of the wellbore can be calculated.

By itself, this information allows operators to prove that their well does not cross into areas that they are not authorized to drill. However, due to the cost of MWD systems, they are not generally used on wells intended to be vertical. Instead, the wells are surveyed after drilling through the use of Multishot Surveying Tools lowered into the drillstring on slickline or wireline.

The primary use of real-time surveys in in Directional Drilling. For the Directional Driller to steer the well towards a target zone, he must know where the well is going, and what the effects of his steering efforts are.

MWD tools also generally provide toolface measurements to aid in directional drilling using downhole mud motors with bent subs or bent housings. For more information on the use of toolface measurements, see Directional Drilling.

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Drilling Mechanics Information

MWD tools can also provide information about the conditions at the drill bit. This may include:

Rotational speed of the drillstring

Smoothness of that rotation

Type and severity of any vibration downhole

Downhole temperature

Torque and Weight on Bit, measured near the drill bit

Mud flow volume

Use of this information can allow the operator to drill the well more efficiently, and to ensure that the MWD tool and any other downhole tools, such as Mud Motors, Rotary Steerable Systems, and Logging While Drilling tools, do not fail. This information can also give Geologists responsible for the well information about the formation which is being drilled.

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Formation Properties

Many MWD tools, either on their own, or in conjunction with separate Logging While Drilling tools, can take measurements of formation properties. At the surface, these measurements are assembled into a log, similar to one obtained by wireline.

The MWD tool allows these measurements to be taken and evaluated while the well is being drilled. This makes it possible to perform Geosteering, or Directional Drilling based on measured formation properties, rather then simply drilling into a preset target.

Most MWD tools contain an internal Gamma Ray sensor to measure

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