The electromagnetic wave transmission mode is to transmit the low-frequency electromagnetic wave signal reflecting the trajectory direction of the bottom hole and the formation characteristic parameters to the ground. During drilling, the drill pipe, the exposed shaft wall and the space between them and the surrounding strata form an electromagnetic wave transmission channel, and the electromagnetic wave radiates from the emission source to the surrounding infinite space and is received by the ground antenna fixed next to the drilling rig. It does not need mud as signal carrier, and has low requirements on drilling fluid quality and non-uniformity of drilling pump, so it has strong data transmission ability. Its advantage is that. Its disadvantage is that the background noise has a great influence on the signal, and the signal attenuates with the absorption of the signal by the rock stratum and the change of the earth resistance, which leads to the increase of the complexity of the transmission circuit. At present, these problems have been well solved. The advanced programmable filtering method completely suppresses the problem of large background noise. The automatic impedance adaptation system solves the problem of large signal attenuation. Electromagnetic wave method can be traced back to the early 1940s, and was first applied to coal mine safety and military affairs. Russia is one of the countries that developed the electromagnetic wave measurement while drilling system earlier, and they called MWD system as electromagnetic wave channel bottom hole telemetry system.
Abroad, electromagnetic wave MWD technology has been successfully used to transmit downhole measurement signals, and MWD instruments have been widely used. In China, a bold attempt was made to transmit the borehole deviation, azimuth, gravity sum, tool face angle, tool face angle, temperature, battery voltage and formation parameters measured by probe sensors to the ground in real time by electromagnetic waves. Breakthrough progress has been made in remote control, telemetry and two-way transmission. Due to the adoption of bidirectional electromagnetic wave wireless transmission technology, it greatly facilitates the control of underground instruments, remote control of underground equipment, convenient self-inspection of electromagnetic wave channels and remote management of power supply, and effectively improves the utilization rate of power supply. Second, the working principle of electromagnetic wave wireless drilling rig There are two working modes of electromagnetic wave wireless drilling rig, namely one-way working mode and two-way working mode. (1) One-way working mode, the data collected by sensors in the underground (bit part) are sent to the ground intermittently or continuously, and the instruments on the ground receive, decode and restore various dynamic data measured by sensors. Send it to the computer serial port for analysis, display and printing. The underground part consists of power supply system, wireless transmission system and antenna system, sensor data acquisition system and impedance automatic adaptation system. The power supply system consists of a hydroelectric generator and a rechargeable battery. The generator is driven by water pressure to generate electricity. When the motor works at 800~3000 rpm, it outputs a DC voltage of 36V ~ 48V. Generator requirements: the power is not less than 80W, and the discharge current of rechargeable battery is not less than 3A. There are three modulation modes for data transmission module: one is PWM pulse width modulation mode; The second is the narrow pulse modulation mode; This method has a good development prospect, and the biggest advantage of instantaneous super-energy transmission of electromagnetic energy is to save electric energy and generators. The third is the traditional sine wave transmission modulation mode. In this way, the receiving circuit is relatively simple and has good anti-interference ability. No matter which modulation method, as long as the transmission distance is long, the lowest bit error rate is the ultimate goal. The antenna is in dipole current mode. Communication distance is closely related to depth, working frequency and resistivity around antenna. The design of antenna mainly depends on its firmness, and the torque is required to reach more than 90% of the metal drill pipe. The insulation degree should be high, and the circuit value in air should be greater than 2mΩ. The theoretical design of AC impedance is greater than 50 Ω. (2) Bidirectional electromagnetic wave transmission is a half-duplex communication mode. There are electromagnetic wave transceiver circuits on the ground and underground. The transmitting part on the ground has the advantage that compared with the underground transmitting part, it is not limited by volume, and the power can be made very large. 3. Introduction of electromagnetic wave transceiver module: This module is mainly used for wireless inclinometer of electromagnetic wave in oil field, and carries out wireless bidirectional data communication between underground and ground to achieve the purpose of remote control and telemetry in deep wells. The circuit adopts the waveform synthesis method of single chip microcomputer for modulation and demodulation. In the extremely low frequency state, the transmission rate is fast, the error rate is low, the reliability is high and the transmission distance is long. Give full play to the power-saving advantages of optimized management technology. At the same time, the automatic impedance adaptation system is adopted, so that the transmission power can be kept in the best state at different depths and in different environments. In the aspect of temperature adaptation, high thermal conductivity radiator is used inside and temperature isolation is used outside to meet the needs of working environment at different temperatures underground. Main indicators: overall dimensions of the module: 32 mm in diameter and 520 mm in length. Working voltage: DC 36V. Maximum transmit power: 120W standby current: 10mA. The data interface is 232 serial port mode. Transmission rate: 5 16 hexadecimal characters per second. Transmission depth: (test depth) 5Km.