For centuries, drillers (whether drilling for oil or water) have been keeping keen notes of drilling activities. What started as a regular record of drilling depth versus cuttings observed (also known as mud logging) has transformed to encompass various technological well logging measurements, including electric logging, SP, induction and GR. Most recently, scientists and engineers have developed Logging-While-Drilling (LWD), a type of well logging that incorporates the logging tools into the drill string, administering, interpreting and transmitting real-time formation measurements to the surface.
Overcoming well logging challenges presented by directional drilling, LWD has revolutionized the well logging concept. By locating well logging tools near the drill bit on the end of the drilling apparatus, LWD enables drillers to log wells that exceed 60 degrees, which makes pushing the tool through the well impossible. Additionally, by providing real-time information, LWD helps drillers and engineers to make immediate decisions about the future of a well and the direction of drilling.
Providing information on porosity, resistivity, acoustic waveform, hole direction, and weight on bit, LWD transmits logging measurements at regular intervals while drilling is taking place. Data is transmitted to the surface through pulses through the mud column (also known as mud pulse of mud telemetry) in real time.
A type of LWD, Measurement-While-Drilling (MWD) specifically refers to information used to help in steering the drill, such as direction, orientation and drill bit information.
Drillers and engineers are able to use LWD information immediately to define well placement and predict drilling hazards. Known as "intelligent drilling," use of real-time logging information provided by LWD is enabling stronger, more successful wells both onshore and off.