INTRODUCTIONMeasurement While Drilling - MWD systems allow the driller to gather and transmit information from the bottom of the hole back to the surface without interrupting normal drilling operations.
This information can include directional deviation data, data related to the petrophysical properties of the formations and drilling data, such as WOB and torque.
The information is gathered and transmitted to surface by the relevant sensors and transmission equipment which is housed in a non-magnetic drill collar in the bottom hole assembly. This tool is known as a Measurement While Drilling Tool - MWD Tool. The data is transmitted through the mud
column in the drillstring, to surface. At surface the signal is decoded and presented to the driller in an appropriate format. The transmission system is known as mud pulse telemetry and does not involve any wireline operations.
To take a directional survey using conventional wireline methods may take 1-2 hours. Using an MWD system a survey takes less than 4 minutes. Although MWD operations are more expensive
than wireline surveying an operating company can save valuable rig time, which is usually more significant in terms of cost.
More recently MWD companies have developed more complicated tools which will provide not only directional information and drilling parameters (e.g. torque, WOB) but also geological data (e.g. gamma ray, resistivity logs). The latter tools are generally referred to as Logging While Drilling - LWD Tools.
As more sensors are added the transmission system must be improved and so MWD tools are becoming more sophisticated. Great improvements have been made over the past few years
and MWD tools are now becoming a standard tool for drilling operations.
We will talk here about the following subjects to get full picture about the MWD:
1- MWD Systems
2- MWD - DIRECTIONAL TOOLS
3- MWD - GAMMA RAY TOOLS
4- TRANSMISSION AND CONTROL SYSTEMS
5- SURFACE SYSTEM