NOV Wellbore Technologies introduced the BlackStar II electromagnetic (EM) measurement-while-drilling (MWD) tool, part of the InTerra family of sensors and systems. The BlackStar II EM MWD tool uses EM telemetry to transmit data measurements even while making a connection, enabling increases in survey speed and accuracy that drive performance gains. EM systems send information to the surface through the Earth’s crust using low-frequency EM waves. Information is received at a surface antenna, decoded and processed by a computer, and distributed to the driller’s readout display without the encumbrance of mud or wire transmission. EM tools have no moving parts, allowing for use in air-drilling conditions or high-lost-circulation-material environments where mud-pulse tools are rendered inoperable. The BlackStar II EM MWD tool transmits data measurements from the bottom of the hole back to the surface, allowing the driller to control and monitor the location and orientation of the drill bit. Surveys can be transmitted during connections, minimizing the nonproductive time associated with conventional mud-pulse tools. The flexibility of EM systems makes them the preferred strategy in a growing number of MWD applications, including underbalanced drilling, underpressured formations, vertical-control drilling, and coalbed methane.