An EM field is not the same as an EM wave. How does a field have a frequency? I feel like I am overlooking something fundamental here in regards to EM theory.
Lastly, a co-worker and I had a very long discussion about how this works. He stated that an EM wave actually isn't emitted at all, but a voltage gradient is created across the gap sub. He also stated that the drill string is essentially used as one leg of a transmission wire and the earth is used as the other. In other words, the drill string is used to transmit data up to the surface and the earth is used to receive data from the surface, or vice versa.
To me, this is just seems plain wrong, but perhaps I am the one mistaken. If this was the case, would not the two sides of the transmission wires the earth and drill string essentially short themselves out since they are in constant contact with each other?
Waveform at different polar distances when the hole depth is m. In order to study the influence of polar distance the distance between the drilling rig and the antenna on received signal, two polar distances are used in the experiment, 50 m and 70 m, at a depth of m, and the strength of the received signals is compared.
The experimental results indicate that the ground receiver of the developed EM-MWD system can receive strong signal, and the signal strength has a tendency to increase with depth increase within a certain depth. It is may be that the downhole instrument of the designed EM-MWD extends from the drill casing, with the transmission of the electromagnetic wave signal being affected by the shielding action of the drill casing. By analyzing the signal transmission results at the same hole depth but different polar distances, it is found that the strength of the received signal is high and unchanged when the dipolar distance is not more than 70 m, that is to say, the strength of the received signal is not affected by the dipolar distance within a certain dipolar distance.
The research work on the downhole instrument includes structural design, the selection of model sensors and the design of control and transmission circuits, etc. The research work on the ground instrument includes the overall plan of the signal processing, and the hardware and software design for the receiver.
In order to test the designed EM-MWD system, an indoor signal decoding experiment, a signal transmission experiment on the ground and an in-hole signal transmission experiment are performed. The research indicates that the developed EM-MWD system can monitor downhole drilling parameters effectively and send information to the ground via electromagnetic wave signals. After the ground instrument receives the signal, the signal will be amplified, filtered, trapped, AD converted and demodulated, and finally the desired signal will be extracted.
In addition, we perform some signal transmission experiments at different polar distances, and it is seen from the experimental results that the strength of the received signal is not affected by the dipolar distance within a certain dipolar distance. Because of the restrictions of drilling depths, the maximum depth of the downhole experiments is m, but we received very strong signal of mV. The paper was also funded by the China Scholarship Council. Google Scholar. Oxford University Press is a department of the University of Oxford.
It furthers the University's objective of excellence in research, scholarship, and education by publishing worldwide. Sign In or Create an Account. Sign In. Advanced Search. Search Menu. Article Navigation. Close mobile search navigation Article Navigation. Volume Article Contents Abstract. Overall scheme of electromagnetic MWD. Downhole instrument. Ground receiver.
Experimental study. The development of and experiments on electromagnetic measurement while a drilling system is used for deep exploration. Chunhua Lu , Chunhua Lu. Oxford Academic. Guosheng Jiang. Ziqi Wang. Jiahao Wang. Chenli Wang. Revision received:. Select Format Select format. Permissions Icon Permissions.
Abstract An electromagnetic measurement while drilling system EM-MWD can transfer well track state parameters to the ground in real time, which makes it an indispensable technology for deep-hole drilling. Figure 1. Open in new tab Download slide. Figure 2. You don't need a resonate antenna the length of the diameter of the earth to receive the signal.
EM telemetry can be understood in terms of voltage gradients and current conduction. That's all. There are various schemes for the transmission of ultra-low frequency electromagnetic waves while drilling information. The first is that the earth is used as a loop conductor, and the drill pipe is used as a loop conductor, transmitted to the ground, and then filtered and amplified by the ground receiving equipment to decode.
This method has disadvantages. It is greatly affected by formation resistivity. The second method is a direct electromagnetic wave transmission method. This method requires high-power ultra-low frequency transmitters and high-sensitivity receivers to transmit in true electromagnetic waves.
This method is not affected by formation resistivity. The working frequency of these two methods is generally selected between 2HzHz, the antenna structure is different. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. Asked 7 years ago. Active 1 year, 11 months ago. Viewed 4k times. Josh Josh 1 1 gold badge 5 5 silver badges 12 12 bronze badges.
You don't need the antenna to match the wavelength. It can be much shorter. Add a comment. Active Oldest Votes. Now, video is even available to help in the process.
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