Design And Research On Down-hole Wireless Electromagnetic Short-transmission

The downhole fluid temperature and pressure parameters are the important data of production dynamic logging,we can know the production status of oil well, ,analyse the dynamic characteristic of down-hole oil and gas resources accurately and evaluate the exploitation effect of oil reservoir through them. The downhole fluid temperature and pressure rise as the exploitation depth of oil field increases, it needs the test system a higher reliability and accuracy.In this paper,we use the current transfer mode induced by electromagnetic to realize the production well temperature and pressure short-range wireless data transmission, to study a new data transmission technology used in production dynamic logging, which can do real-time monitoring of oil well temperature and pressure parameters, increase the continuous working hours, reduce the downhole working times and improve the operating efficiency. The technology can do a long span measurement through the wireless transmission mode, eliminate the impact of shut-in valves to the cable test, avoid test point fluid temperature and pressure perturbation by the cables, improve the measurement accuracy effectively, which has a significant technical and economic sense.This paper studies the basic theory of electromagnetic transmission, the downhole wireless transmission is based on the principle of electromagnetic induction current field, the time-varying magnetic field in the magnetic ring is produced by the time-varying current excitation, the time-varying magnetic field induces the current field which can spread in the semi-cost medium, in order to achieve the wireless transmission of data signals. Meanwhile, researching the media characteristics of electromagnetic field,understanding the relationship between the medium types and electromagnetic field frequency and the characteristics of themselves. Based on the determination of winding type and magnetic materials, we can do the overall structure design. In order to improve the efficiency of downhole power, we must ensure that the system communication is stable and reliable basis to minimized power supply current, and put the time cycle parameter as the basic computing elements.According to the available battery voltage, signal transmission frequencies and the specific size of downhole tools,we can design the structure parameters of magnetic core and calculate the coil turns.According to the calculated characteristic parameters of the coil, we can observe the magnetic flux density, magnetic field intensity and the distribution of magnetic field lines and gain the variation distribution between the signal output intensity and loading frequency. We did the structural design and processing of ground simulation equipment to do the wireless transmission system ground simulation experiment, validated the possibility of wireless electromagnetic short pass, gained the signal output voltage-Frequency variation, identified the signal frequency attenuation inflection point and gained the smallest attenuation frequency band for provide data t support of the design and selection of downhole power lines and electronic components.