Although EM stands for electromagnetic, which may suggest radio frequency signals, the very low frequencies used in the drilling environment behave more like DC, or more or less static signals. These signals, as such, can be looked at and analyzed with the help of basic electrical theory. Electromagnetic technology has significant potential for use both in the petroleum industry and the mining industry.
EM Telemetry is a method of transmitting data from a measurement while drilling MWD kit assembly that resides just above an oil well drill bit. An electromagnetic telemetry system is used for transmitting data from a downhole assembly, which is operationally attached to a drill string, to a telemetry receiver system. Induced signal current is measured directly with the telemetry EM Frequency Interface receiver system. The signal current is modulated to represent the transmitted data.
The Compass Transmitter Module records pressure, receives data from the directional module, and transmits the data to an antenna rod that is connected to the Frequency Interface (FI) Receiver. The Compass Transmitter length is76.5” without the helix end. The tool gap on the Compass Transmitter Module should line up with the gap on the Isolation Sub within +/-6 inches. If the tool gap is too far from the sub gap, it will cause a weaker signal.
The sensor package contains 3-Axis Magnetic Sensor, 3-Axis Accelerometers and Temperature sensors capable of detecting the surrounding temperature, the Earth’s Magnetic and Gravitational Fields with high resolution. The data output is digitized and processed to determine the vector to the earth’s magnetic North Pole and the vector for the earth’s magnetic forces dipping down at the earth’s surface and below. This information and other measured parameters produce data such as Inclination, Azimuth, and magnetic and gravity toolface values that are transmitted to the surface via EM telemetry to assist in well deviation control. Numerous quality and tool environment data variables can also be transmitted via EM telemetry to quantify and qualify data values and tool health.
Compass is in the process of upgrading our EM system and will be available soon.
EM-MWD Gap Subs