Sensors & Transducers, Vol. 168, Issue 4, April 2014, pp. 155-161

Sensors & Transducers © 2014 by IFSA Publishing, S. L. http://www.sensorsportal.com

The Study of the Transducer Used in the Acoustic Telemetry Technology While Drilling 1 1

Haiming Xie, 1 Xiaoping Li, 2 Jing Zhou Xidian University, Shaanxi Province, 710065, China 1 Tel.: 86-029-88382636, fax: 86-029-88382636 E-mail: [email protected]

Received: 15 January 2014 /Accepted: 7 March 2014 /Published: 30 April 2014 Abstract: The technology of bi-directional data transmission between the well bottom and ground play an increasingly important role in modern drilling technology while drilling. The technology of acoustic data transmission while drilling can achieve higher band rate compared with the traditional. The transducer is one of the most imp-ortant components of it. This article has simulated the piezoelectric ceramic for the parameters, and verified by the measurement of material objects. It has obtained the channel characteristics of the 50 meters drilling string, with the help of the piezoelectric ceramic. Copyright © 2014 IFSA Publishing, S. L. Keywords: MWD, Acoustic, Piezoelectric ceramic, Finite element.

1. Introduction Communication between the ground and underground is one of the important components for the smart drilling system. Acoustic transmission in a drill string was originally proposed by Sun Oil Company in 1948, and completed the first wellsite acoustic attenuation measurement. In 1972, Barnes and Kirkowood established the frequency domain characteristics of the drill pipe model, proposes the passband and stopband alternate comb filter structure features, analysis the periodic structure of the drill string and supplement it by Drumheller, etc. in 1989. In 1998, the time-domain characteristics of drill pipe model was established by Niels. Drunheller and Poletto progress in acoustic telemetry theory, Studies have shown that long distance transmission of acoustic information can be achieved by the drill pipe in theory. In 1990, Halliburton began working on a wireless telemetry acoustic transport system (ATS) used in non-drilling. Commercialization in 2000 proved its value

Article number P_1973

in the non-drilling applications. In 2003 the acoustic telemetry system achieve the commercial application in the production environment [1-3]. In 2005, L. Gao established the transmission capacity theory of drill pipe transmission system. The theoretical value transmission rate of the drill string transmission system can reach 200 ~ 350 bit/s. In 2007 the United States Department of energy laboratory and Halliburton company jointly support, the use of the acoustic transfer of drilling information experiment-al prototype transmission rate can achieve 30 bit/s in while drilling environment. In the absence of relay case, the deepest test well depth is 2600 m. [4-5].

2. The Performance Analysis of Acoustic Transducers Sound wave as the transmission of information carrier, it’s the basic of acoustic remote transmission technology and come from the electric energy,

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Sensors & Transducers, Vol. 168, Issue 4, April 2014, pp. 155-161 transducer is the key component to realize this kind of electronic-to-sound transform. According to the different functional materials, the acoustic transducer can be roughly divided into two major categories: piezoelectric and magnetostrictive, which are the most used so far. Below, in combination with the application background of the logging while drilling and use restrictions, the essay respectively make a simple introduction on two types of transducer: 1) Piezoelectric Ceramic Transducer. Piezoelectric ceramic is a kind of functional materials, which can realize energy conversion between electric-mechanical (sound), high voltage low current incentives. In terms of piezoelectric ceramics, the vibration of the available forms such as model of 33 and 31 can be used. Considering the limited by the size of the drill pipe and the high efficient application of transducer, the model of 33 can be used. 2) Magnetostrictive Transducer. Magnetostriction can realize energy conversion between of electric- magnetic - machine, with the current incentives, the maximum current of resonance can reach several amperes, the energized coil is severe heated, the eddy current of the magnetostrictive materials make a large loss. There is no limit to the power and heat dissipation ideally, it has larger power capacity than piezoelectric ceramic. The main vibration of magnetostrictive transducer is mode 33, due to the existence of the electric coil, make this kind of transducer radial dimension is often greater than 50 mm, at the same time considering the drill pipe is a kind of magnetic material, this will affect the magnetic circuit and magnetic field of transducer. Combining the application background, after comprehensive comparison, piezoelectric ceramic materials was been selected and expect to design a transducer with the vibration mode of 33, which is suitable for the acoustic telemetry while drilling technology.

Fig. 2 is the 33 vibration pattern which the resonant frequency is 6.4 kHz, and signal vibrating along the axial direction of the tube. Fig. 3 is the transducer resonance mode of vibration, it shows the vibration of the design transducer is based on a first-order longitudinal vibration, the frequency f = 6.4 kHz. The dotted line in the figure is the outline before the transducer deformation.

Fig. 1. Assembly diagram.

Fig. 2. Transducer vibration modal results.

3. The Structure Design The appearance of the transducer is two semidocking circular tube structure, it can send along the axial acoustic energy and receive acoustic signal, using high voltage, low current incentives to reduce the loss. The transducer with the assembly structure of the drill collar parts must be in accordance with Fig. 1.

4. Simulation Result Finite element analysis for the design of transducer structure [6]. A. Modal Analysis. Obtain the transducer resonant frequency and model of vibration by modal analysis in ANSYS.

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Fig. 3. The transducer resonance mode of vibration.

Sensors & Transducers, Vol. 168, Issue 4, April 2014, pp. 155-161 When the transducer movement, both ends are always opposite, and radiate acoustic energy with the movement, which means when the transducer along the tube axis radiated sound the backend also radiated acoustic energy along an axis in the opposite direction, but the latter is negative for logging-while-drilling. In order to effectively control the forward radiation energy, there are two ways: 1) Increase the quality difference of the tube both ends, making the back-end quality far more weighted than front-end, so according to the principle of conservation of momentum, the front-end can obtain larger vibration velocity, so as to radiates energy forward; 2) Adding a sound insulation layer at the rear end of pipe, makes the backwards radiated acoustic energy consumed within the insulation layer, which prevent them passing drill collars. The sound insulation layer is double-deck, the first layer for special acoustic foam, the 2nd is air. It’s specific structure as shown in Fig. 3. Fig. 4 is the cloud diagram vibration type of the transducer, Fig. 5 is the vector diagram. The displacement of front the transducer is greater than back, front-end is almost 4 times more than back-end, and proved the effect of the modes (1) is effectively.

B. Harmonic Response Analysis. By harmonic response analysis, obtained various response curve of the transducer in the interest frequency band. Fig. 6 and Fig. 7 are conductance curve and suscept-ance curve respectively, According to these curves, the effect of the transducer resonance oscillation is remarkable, and the resonant frequency is 6.43 kHz, it is consistent with the results of modal analysis which analyzed above. In the resonance point, the conductance of the transducer is 7.5 ms, suggests that the transducer has a very good sound effect near the frequency.

Fig. 6. Conductance curve.

Fig. 4. Cloud diagram of vibration mode. Fig. 7. Susceptance curve.

Fig. 5. Cloud diagram of vector vibration mode.

C. The Simulation Results Summary. By the finite element analysis, the research circular tube structure transducer resonance oscillation frequency around 6.43 kHz. (This refers to the air, when the transducer is assembled to the drill collar, as a result of the action of the load leads to the resonance frequency of the transducer slightly skew), and the transducer is vibration along the axial of the circular tube, in accordance with 33 vibration mode. The simulation results show that the effect of resonance oscillation frequency of transducer is obvious, acoustic energy through the front-end sent occupies the main part. Transducer has transmitting

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Sensors & Transducers, Vol. 168, Issue 4, April 2014, pp. 155-161 and receiving function, the transmitted power capacity of active material used in design is more greater than 50 W.

5. Manufacture of the Transducer According to results of finite element analysis, produced a tube structure transducer. Considered the requirements of assembly, transducer is a two halves butt. The outer diameter of the transducer is 155 mm, the inner diameter of 117 mm and height of 97 mm. The front end of the transducer closely contact with the drill collar in Fig. 1, wrapped with active functional materials inside part 4, and the first floor of part 5 is the insulation materials, the air insulation layer back to it. It exists an 1 ~ 2 mm air insulation layer between the tube transducer and the inner surface of the drill collar. Each transducer has three evenly spaced bolts which impose appropriate prestressing from the rear.

Fig. 9. 2# admittance curve.

6. Physical Characteristics Test 6.1. Impedance Characteristic Test Measured the transducer admittance curve with a precision impedance analyzer the transducer. 1# shown in Fig. 8, Fig. 9 shows the transducer 2#. The resonant of the two transducers were respectively at 6.35 kHz and 6.32 kHz, which very close to the calculated 6.43 kHz results with the finite element. The conductance of the two transducers at the resonance point were 6.6 ms and 5.6 ms, the value slightly smaller than the finite element calculation 7.5 ms. The main reason is that the finite element model of the transducer cannot simulate various losses in the actual situation. The two transducers measuring the impedance curve of 4294A is shown in Fig. 10 and Fig. 11, according to the two graphs, the resistor values of two transducer at the resonant frequency are 148 Ω and 172 Ω.

Fig. 10. 1# impedance curve.

Fig. 11. 2# impedance curve.

6.2. High-power Transmitting and Receiving Characteristics of High Sensitivity Test

Fig. 8. 1# admittance curve.

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The transducer is mounted on the drill collar as required above, the receiving transducer order sending again. Fig. 12 for 2# transducer emission characteristic of linear growth curve, Fig. 13 for 1# receivers linear

Sensors & Transducers, Vol. 168, Issue 4, April 2014, pp. 155-161 growth curve in experiment. Fig. 14 for the characteristics of 2# receivers linear growth curve in experiment, Fig. 15 for 2# transducer emission characteristic of linear growth curve. According to above cures, both 1# and 2# transducer are linear adjustable within 50 W power incentive. Actual experimental results show that 1#, 2# transducer resonance effect is clear in air, the resonant frequencies are 6.35 kHz and 6.32 kHz, Actual test curve consistent with finite element analysis results. After the transducer assembly to drill collar, the relevant characteristics of the transducer is changed

as a result of the action of drill collar load. Manifested in: 1) The resonant frequency shift, the assembled transducer resonant frequency around 6.7 ~ 6.9 kHz; 2) Transducers for electrical conductivity values decline. This change is caused by a boundary condition change of transducer. The design of acoustic transducers with transmitting and receiving function. Implements the acoustic power sending and high sensitivity receiving, maximum transmission electric power of more than 50 W, and linearly adjustable within 50 W.

Fig. 12. 1# transmitting curve.

Fig. 13. 2# receiving curve.

Fig. 14. 2# transmitting curve.

Fig. 15. 1# receiving curve.

7. Field Test Transmitting transducer emitting 1 kHz - 10 kHz linear frequency modulation (LFM) signal, receiving transducer and transmitter are separated by five single drill pipe, about 50 meters. LFM signal through the circuit into the transmitting transducer,

a total of five group test, receiving data fractional analysis as follows. When transmitting and receiving distance of 50 meters, the two group received data spectrum shown in Fig. 16 and Fig. 17. 2 kHz - 3 kHz frequency spectrum detail as shown in Fig. 18, and 5 kHz – 8 kHz as shown in Fig. 19.

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Sensors & Transducers, Vol. 168, Issue 4, April 2014, pp. 155-161 Frequency LFM

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Comparison of the two figures, under 2.2 kHz the two groups of band structure is different, but above 2.2 kHz both band structure basically remain unchanged. Fig. 19 comparison of the two band structure basically does not change, sub-center position and width of the pass band did not change significantly. Details of the plan that the drill pipe channel is a comb filter channel, test data also shows

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that the drilling system channel band width of less than 100 Hz.

8. Conclusions In view of the present LWD acoustic telemetry technology requirements, in accordance with the

Sensors & Transducers, Vol. 168, Issue 4, April 2014, pp. 155-161 corresponding size design corresponding transducer. First determine the parameters of the transducer by finite element simulation, through the physical measurements to verify the accuracy of the simulation, use of transducer in experiment, obtained the channel characteristics of the 50 meters drilling string.

Acknowledgment This paper was supported by the National 863 project "steerable rotary controllable eccentric engineering technology research" (2007AA090801-01), the oil in the "Twelfth Five Year Plan" special "while drilling exploration, intelligent drill pipe and acoustic information transmission technology research" (2011a-4206), National Science and Technology major projects "rotary steering drilling, logging and acidic gas testing technology and equipment" (2011ZX05021005).

References [1]. T. G. Barnes, B. R. Kirkwood, Passbands for Acoustic Transmission in an Idealized Drill String, J. Acoust. Soc. Am., 51, 5, 1972, pp. 1606-1608. [2]. D. S. Drumheller, Acoustic Properties of Drill Strings, J. Acoust. Soc. Am., 85, 3, 1989, pp. 1048-1064. [3]. J. M. Neff, Field-Test Results of an Acoustic MWD System, SPE/IADC105021 in Proceedings of the Drilling Conference Held in Amsterdam, The Netherlands, 20–22 February 2007. [4]. L. Gao, D. Finley, W. Gardner, Acoustic Telemetry Can Deliver More Real-Time Downhole Data in Underbalanced Drilling Operations, IADC/SPE 9894, in Proceedings of the Drilling Conference Held in Miami Florida, U.S.A., 21–23 February 2006. [5]. Li Zhigang, Wang Guan Zhichuan Law, LWD sonic telemetry and analysis of key issues, Oil Field Equipment, 9, 37, 2008, pp. 6-9 (in Chinese). [6]. Mo Kihei, ANSYS software simulation acoustic transducer in the application, Journal of Acoustics, 6, 26, 2007, pp. 1279-1290 (in Chinese).

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