Design Strategies and Experimental Validation of High-Performance Logging-While-Drilling Piezocomposite Transducers

Open Access
Author:
Jiang, Runkun
Graduate Program:
Electrical Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
December 20, 2016
Committee Members:
  • Qiming Zhang, Dissertation Advisor
  • Qiming Zhang, Committee Chair
  • Sumeet Kumar Gupta, Committee Member
  • Zhiwen Liu, Committee Member
  • Bernhard R. Tittmann, Outside Member
Keywords:
  • LWD acoustic transducer
  • COMSOL design and optimization
  • extreme-environment fabrication
  • transducer testing protocol
Abstract:
In the oil and gas industry, logging-while-drilling (LWD) acoustic transducers have been found to provide valuable sonic information of the borehole rock formation such as compressional wave velocity and shear wave velocity. These acoustic transducers consist of transmitters and receivers. Transmitters send out acoustic waves through the borehole. Waves then get received by an array of receivers. Through the phase delay of the arriving signals, one can calculate the mechanical and acoustic properties of the borehole rock formation and this information can be used further to indicate lithology, determine porosity, detect over-pressured zones, check well-to-well correlation, etc. This dissertation covers exhaustively on original research work on LWD acoustic transmitters and receivers, including design and optimization, fabrication, and testing. Some necessary theoretical background was given in the Theories chapter. The fundamentals of elasticity, wave motion and wave equations were introduced. Wave theories on acoustic impedance matching (reflection and refraction), and attenuation were also covered briefly. Piezoelectricity constitutive equations and piezoelectrically stiffened wave equations were outlined. And theories on different piezoelectric vibration modes were presented in details, as well as the three-port network, equivalent circuit, and electrical impedance matching analysis of piezoelectric transducers. The compositing effect on piezocomposite transducers was explained and verified experimentally also in this chapter. These theories are central for understanding and optimizing LWD transducers. One of the research objectives is to design LWD transmitters that meet acoustic requirements such as transmitting power, transmitting voltage response (TVR), directivity, etc. In the Optimization chapter, focus was given to a detailed methodology for applying COMSOL Multiphysics® to achieve this goal. Material properties, meshing techniques, and physics coupling were presented in details. Displacement frequency responses of two piezocomposite transducer designs were compared and general design strategies were come up with. Targeted studies confirmed these design strategies. Two important strategies is disintegrating the height direction to reduce the height mode resonance around 8-10 kHz, and slanting the piezoelectric ceramic pieces to broaden response. A comparison of acoustic performance parameters including acoustic field spatial distribution, absolute acoustic pressure, TVR and directivity was made between the two designs. An extensive comparison between d33 and d31 configurations revealed the advantage and disadvantage of each. Usually LWD transducers work under extreme environment such as high temperature, high pressure, corrosive chemicals, and strong vibrations. This requires rigorous packaging for the piezocomposite transducers. In the Fabrication chapter, first some fabrication topics were discussed, including epoxy selection, solder selection, thermal expansion coefficient consideration, and in-vacuum bonding setup and method. These discussions are a summary of trial and error along the project progress. It might seem concise but it is equivalent to an immense amount of work. In-vacuum epoxy bonding and uniform thickness spacer are proven to achieve ultrahigh bonding strength in combination. Once the techniques were discussed, the fabrication of a successful high-performance piezocomposite transducer prototype was presented step-by-step. Typical steps were piezoelectric ceramic cutting, packaging material machining, epoxy bonding, and impedance analysis. Their performances matched the computation simulations. The preliminary prototypes leading to the final successful prototype were explained in the Appendix I. The first high-performance piezocomposite transducer featured slant-cut ceramics, resulting in broadband response at the expense of reduced resonance peaks. The second high-performance piezocomposite transducer featured non-slant-cut ceramics, bringing about strong resonance peaks but less broad response. One of the contributions of this dissertation work is to have successfully developed fabrication processes to use high-temperature polymer polyether ether ketone (PEEK) which is also corrosion resistant. The application of this polymer simplified the transducer design and fabrication significantly. Challenges conquered include ultrahigh bonding strength for large PEEK pieces, especially with in-vacuum bonding which leaves no trapped air bubbles suitable for high pressure applications. Extensive testing is needed before the transducers can be used in the field. In the Testing chapter, protocols for multiple tests were established. These tests are anticorrosion testing, to make sure transducers can withstand corrosive drilling fluids; thermal cycle testing, to make sure transducers can withstand high working temperature repeatedly without deteriorating in quality; high voltage testing, to make sure transducers can withstand high driving voltage without dielectric breakdown; high hydrostatic pressure testing, to make sure transducers can withstand high working pressure in the oil well; vibration testing, to make sure transducers can withstand strong vibration in the drilling practice; and acoustic testing, to make sure transmitters can transmit enough power at designated driving frequency for the logging application, and have desired TVR and directivity. The prototypes we fabricated passed all the tests. Receivers were discussed separately and presented in the Receiver Considerations chapter. Some receiver design strategies were looked into first. Structure-stress interaction studies by COMSOL Multiphysics® compared different piezoelectric ceramic configurations to find the receiver with the highest receiving sensitivity (RS) and signal-to-noise ratio (SNR). Different packaging materials were studied also aiming to improve receiver performance. In terms of fabrication and testing, there were more similarities between transmitters and receivers than differences. Therefore, this chapter focused on the deviations rather than repeating the same processes. Using the same fabrication techniques, receiver prototypes were manufactured and their impedance analysis was presented. They featured a flat response between 11 kHz and 15 kHz, which is a desired performance for LWD receivers so that the receiver is equally sensitive to all frequencies and less prone to excitation variations. Future work can be in four directions. The first one is to fabricate d33 mode transmitters, which will improve transmitting power and reduce material cost. The second one is to expand design and fabrication from the current monopole to dipole and quadrupole. Multipole transmitters will obtain certain data not available for monopole transmitters, especially shear data in slow rock formation. The third one is on 3D time-transient COMSOL Multiphysics® simulations of sonic well logging. It will enable transmitter and receiver design optimization in a virtual logging environment. Last but not least, guided wave simulations can be done on drill collar periodic groove design to create broader stopbands, which will then facilitate transmitter designs.