The Investigation Of Giant Magnetostrictive Radiator Bases On LWD Acoustic Data Telemetry

The trend of the global oil drilling is transferring from land to sea in the twenty-firstcentury. And there will be more and more horizontal wells, highly-deviated wells andmultilateral wells. In this stage, the direction of the world’s drilling technology is developingtowards to automation and intelligent. Because of the complicated and harsh undergroundenvironment, the bidirectional data transmission system between the ground and undergroundhas become one of the restrictions. The LWD acoustic telemetry technology uses elastic waveas the carrier to upload the downhole measurement information and downlink the groundcontrol instruction. It compares with the other LWD data transmission modes, such as drillingfluid pressure pulse transmission, electromagnetic wave transmission and so on, which is notaffected by the formation characteristics and drilling fluid composition. And it is muchcheaper and easier to implement. Sonic transducer technology, which stimulates the elasticwave spreading along the pipe, is one of the cores of the acoustic telemetry transmissiontechnology. In this paper, we use giant magnetostrictive material(GMM) which has superiorperformance as the energy conversion devices. This kind of transducer is smaller, lighter andmore powerful than the traditional piezoelectric transducer. And it is much easier to meet therequirements of downhole environment. So the researching of the giant magnetostrictivetransducer which can meet the actual needs is pregnant for the development of LWD acoustictelemetry technology.We combined the finite element simulation method and experimental method to carry outthe research work of the giant magnetostrictive acoustic radiation in the paper. According tothe functional characteristics of the giant magnetostrictive material, the relationship betweenthe magnetic circuit structure and magnetic field homogeneity is analyzed by COMSOLMultiphysics software. The law between the magnetic structure, the size of GMM, thethickness of the soft iron and the magnetic field distribution in the GMM rod’s axial directionand radial direction. The results prove that we can reduce the length of the GMM rod, add softiron and overlay several rods to improve the homogeneity of GMM rod’s magnetic field. And the magnetic circuit structure is optimized. The relationship between the transducer’ resonantfrequency, impedance characteristic and structure size, excitation current is analyzed based onthe piezo-piezomagnetic method. The results show that the resonance frequency of thetransducer will be depressed if the length of the GMM rod and the thickness of the radiantpanel are shorter, the radius is smaller and the outer radius of the transducer is bigger. Thispart also gives the relation between the strength of the excitation signal and vibrationdisplacement of the radiant panel. According to the results of numerical calculation, wedesign and make the giant magnetostrictive acoustic radiation and text it’s resonant frequencyand admittance curves in the lab. The experimental result equals to the finite elementcalculation result nearly.In this chapter, we design the transducer which is appropriate for the LWD acoustictelemetry technology. Its structure is based on the optimized magnetic structure of the giantmagnetostrictive transducer. And its resonance frequency, impedance characteristic and timedomain transient are analyzed by COMSOL software. We also simulate the elastic waveexcitation in the dill collar. The related research results provide technical support for the LWDacoustic telemetry technology.