The Applied Physics Systems Model AP250 Electromagnetic (EM) MWD system enables fast and accurate directional drilling by measuring and transmitting near bit data to the surface. Data is transmitted by electromagnetic signals from the drill bit up over two miles deep (1400 feet to the surface) at 1 to 5hz.
Read MoreData transmitted includes the inclination and azimuth angles of the borehole, the drilling system toolface (roll angle), the tool temperature, and raw accelerometer and magnetometer sensor values.
At the top of the system is a nonmagnetic drill collar with an electrically insulated gap sub. To generate electromagnetic signals that propagate to the surface, a low frequency phase modulated signal is applied across the insulating gap. An upper electrode and the bolt in dipole head are used to apply the signal across the gap.
The gap sub signal is generated by the power driver electronics unit mounted in a pressure barrel just below the dipole head. Typically, two 29 V, 29 amp-hour batteries encased in pressure barrels are used to power the electric dipole system, although use of three or more batteries is possible for situations where high power output for a long period is required.
The borehole angular orientation and drill string toolface are measured by a directional sensor mounted in a pressure barrel below the batteries. A gamma sensor is mounted directly below the system directional sensor.
The Electric Dipole Transmission System is approximately 222 inches long and uses 1.875” diameter pressure barrels for system electronics and batteries. The same basic system can be used with 4.75”, 6.5”, 8” and 9” drill collar sizes. Mounting spacers enable the use of drill collar sizes greater than 4.75”. To stabilize the tool string in the drill collars, rubber finned centralizers are used to connect the various system pressure barrels.
