The SureShot electromagnetic (EM) measurement-while-drilling (MWD) system from APS Technology transmits from a total vertical depth of 10,104 feet in oil-based mud. The system operates at up to 12 bits per second and 12 Hz. Maximum transmit power is 50 watts.
“One of the main advantages of EM is the time savings over mud pulse when taking surveys,” says Andy Roberts, EM project manager, APS Technology. “EM saves four to five minutes per survey over mud pulse. The game-changer is the high ROPs (rate of penetration) that are being achieved in today’s wells. At 20 surveys a day, EM can save 1 1/2 hours or more a day.”
Available in 4 3/4-, 6 1/2-, 6 3/4- and 8-inch sizes, the system communicates by transmitting electromagnetic waves through the formation instead of pressure pulses through fluid columns.
“For mud pulse telemetry, mud flow has to resume, be on long enough to detect flow, then take time while the survey is transmitted,” he says. “After the survey is received, the rig may have to wait a couple minutes while the directional driller evaluates the survey and decides the course of action. With EM, there is no need to wait until flow is established.”
Downhole components consist of an EM transmitter, a gap sub and a power source. The gap sub electrically isolates the drill string above the gap sub from that below. An electromagnetic field is created when a positive electrical charge is applied above the gap. A key feature of the system is two-way communication.
“The operator can use EM to talk down to the tool easily and quickly without disrupting the drilling process,” he says. “This has tremendous benefits. First, it allows the operator to adjust the tool for conditions on the fly. For example, if there is noise interference on a particular frequency, the tool can be commanded to transmit on a different frequency.”
The tool can be told to transmit at a high power to get through a difficult formation or at a low power setting to reduce battery draw
and expense.
“Downlinking allows the operator to select the optimum data and sequences for the drilling operation underway,” Roberts says. “For example, the tool can be instructed to send pressure more frequently upon drilling into an unknown formation.”
SureShot EM works with the entire family of APS directional and LWD sensors and offers a drop-in alternative to the APS mud pulse transmitter.
“The largest application is for directional drilling, providing directional measurements and gamma,” Roberts says. “The higher data rate of EM lends it to LWD work. Interest has also been expressed for use in coal mining.” 860/613-4450; www.aps-tech.com.
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