Short distance transmission system for wireless electromagnetic wave signals of downhole near bit and short distance transmission method

Abstract

The invention provides a short distance transmission system for wireless electromagnetic wave signals of a downhole near bit and a short distance transmission method, and belongs to the field of geosteering systems and measurement while drilling instruments in industries such as petroleum, mines and geological prospecting. The automatic gain control technology is adopted in the short distance transmission system for realizing the automatic adjustment of enlargement factors of downhole weak signals. The short distance transmission system comprises a short section receiving assembly and a short section transmitting assembly, wherein the short section receiving assembly and the short section transmitting assembly are respectively provided with a receiving antenna and a transmitting antenna. Due to the fact that radial coupled antennas are adopted, the short distance transmission system is relatively simple in structure. Meanwhile, the short distance transmission system is high in arithmetic speed and can meet demands for real-time transmission of a large number of signals. Moreover, a front end processing module special for the downhole weak signals is utilized for carrying out the automatic gain adjustment to the collected signals, maintaining stable output of the signals and lowering processing difficulty of subsequent signals, and therefore the signal transmission quality is greatly improved.

Description

technical field [0001] The invention belongs to the field of geosteering systems and measuring instruments while drilling in industries such as petroleum, mining, and geological exploration, and specifically relates to a short-distance transmission system and method for wireless electromagnetic wave signals near the drill bit in the well, which is used to realize the use of electromagnetic waves in the underground near the drill bit. Perform short-distance wireless data transmission. Background technique [0002] At present, the quality of my country's remaining oil resources is getting worse and worse, and the difficulty of oil exploration and development is increasing step by step. There are more and more thin oil layers, low-pressure, low-permeability, low-yield reservoirs, difficult-to-produce reservoirs, and heterogeneous reservoirs held by various oil fields. . The geological conditions of these oil reservoirs are complex, and the drilling construction is difficult. Du...

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Problems solved by technology

However, the antennas used in patents US 5160925 and CN200410004275.9, in order to match the size of the drill collar body during installation, often use buckle rings or split rings, cover the outside with an insulating protective layer, and protect them with a steel shell, so the structures are more complicated

[0009] The patent US6057784 first embeds a plurality of ferrite magnetic rods with outer winding coils radially into the central shaft, each magnetic rod has an insulating protective layer, and then the magnetic rod and the shaft are integrated with an insulating protective layer and a steel shell. Use this as an antenna for data transmission, and the structure of the antenna is also relatively complicated

US2009 / 0153355A1 proposed a near-drill wireless electromagnetic short transmission system specially used for electromagnetic MWD. ​​There is only one antenna above the screw drilling tool, which is used as the receiving antenna of the short transmission system and as the transmission of electromagnetic MWD data transmission to the ground. Antenna) simplifies the instrument structure to a certain extent, but this patent is only applicable to the electromagnetic MWD system

But the antenna of this patent is installed on the outer edge of the drill collar, and several cavities are opened in the drill collar wall, which are used to place the short-pass receiver and the integrated circuit used for electromagnetic MWD. ​​This will first reduce the drill collar wall thickness, and When drilling, the drill collar is subjected to relatively large torque and tension, which may easily cause damage to the drill collar. Secondly, once the integrated circuit is solidified in the cavity of the drill collar, it is difficult to replace it. In this patent, the short-pass receiver and electromagnetic MWD have been solidified in inside the cavity, causing the system to be only suitable for electromagnetic MW

[0010] To sum up, most of the antennas used in the current near-drill wireless electromagnetic short-transmission system are relatively complex in structure, which makes processing difficult and relatively high in cost. At the same time, complex parts are more likely to interfere with electromagnetic signals and reduce the accuracy of data transmission. sex

[0011] On the other hand, the electromagnetic signal received by the receiving antenna of the near-drill wireless electromagnetic short transmission system is relatively weak, generally at the milliampere level; and the harsh downhole environment and complex formation structure can easily interfere with the electromagnetic signal

Experiments have proved that when both the transmitting antenna and the receiving antenna are installed inside the drill collar and the mud is completely conductive, when the signal transmitting power is 0.3W, the signal-to-noise ratio at the receiving end is -60dB, and the receiving signal is affected by the conductivity of the formation around the wellbore. In this case, the signal processing technology used in the current near-drill wireless short transmission system cannot restore the received signal well, which may easily cause transmission errors

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